rnedicalimaging - Tumblr blog

[rnedicalimaging]

21st May 2024

CC: A&P - Central Nervous System Terminology

Central Nervous System - Integrating sensory information and deciding how to respond to it are the primary functions of this part of the body.

Spinal Cord - This part of the central nervous system conducts signals between your brain and the rest of the body, and governs many reflexes and muscle patterns while walking.

Cerebral Cortex - The outer layer of gray matter of the cerebrum with all of the folds and grooves.

Neural Tube - In a developing embryo, the first structure that will go on to form the central nervous system.

Corpus Cullosum - The "large body" that connects the left and right cerebral hemispheres.

Mesencephalon - The middle of the three primary brain vesicles during brain development.

After about five weeks of development, when the primary brain vesicles divide into secondary vesicles, the prosencephalon divides into the diencephalon and... telencephalon.

After about five weeks of development, when the primary brain vesicles divide into secondary vesicles, the rhombencephalon divides into the myelencephalon and... metencephalon

Cerebellum - The metencephalon develops into the pons and this part of the adult brain responsible for coordinating muscle activity by comparing sensory and motor information.

Rhombencephalon - The most posterior or caudal of the three primary brain vesicles during brain development.

Gyri - On the cerebral cortex, the ridges that result from an embryological increase in surface area and folding of the cortex.

Sulci - On the cerebral cortex, the grooves or valleys that result from an embryological increase in surface area and folding

Cerebrum - The embryological telencephalon develops into this largest part of the brain, that is so big it covers most of the rest of the brain.

Cerebrospinal Fluid - The fluid in your central nervous system that cushions the brain and spinal cord and provides some nourishment.

Midbrain - The general region of the brain responsible for quickly processing sensory information and responding with visual and auditory reflexes.

Diencephalon - The thalamus, hypothalamus, epithalamus and mamillary bodies, which regulate homeostasis, make up this region of the brain.

Cerebrum - The part of the brain responsible for voluntary movement, conscious thought, thinking learning and recognising emotions.

Cerebellum - The metencephalon develops into the pons and this part of the adult brain reesponsible for coordinating muscle activity by comparing sensory and motor information.

Frontal Lobe - This region of the cerebrum, responsible for controlling voluntary muscle movement, and higher cognitive functions like planning and social inhibitions.

Parietal Lobe - The superior posterior regin of the cerebrum processes sensory information from the body like touch, pressure and pain.

Occipital Lobe - The most posterior part of the cerebrum, this processes visual information.

Temporal Lobe - This lateral region of the cerebrum processes auditory information like language and helps with balance

Temporal Lobe - This marked region of the cerebrum processes auditory information like language and helps with balance.

Brain Stem - The midbrain, pons, and medulla oblongata make up this general region of the brain, which regulates basic, vital, involuntary body functions.

Hippocampus - This part of the brain is the center of short term memory.

Frontal Lobe - The most anterior part of the cerebrum, this controls voluntary muscle movement, and higher cognitive functions like planning and social inhibitions.

Parietal Lobe - The region of the cerebrum processes sensory information for the body like touch, pressure and pain.

Amygdala - This part of the brain is a center of emotions, like fear, and controls sexual and social behaviours.

[rnedicalimaging]

21st May 2024

Crash Course: Anatomy & Physiology - Central Nervous System

Summary:

Central Nervous System: Locating and Brain Function

Brain Development

Neural Tube

Three Primary Vesicles

Five Secondary Vesicles

Four Adult Structures And Their Functions

Broca's Aphasia

Broca's Area

area in left hemisphere for the brain

partly responsible for ability to produce and process language

Broca's Aphasia

some ability to understand speech, but an inability to produce intelligible words

Broca's aphasia can sometimes be treated by teaching patients to sing, because singing uses a different region of the brain on the right side - analogous to Broca's area on the left.

A lot of knowledge about the brain ahs arisen from studying injuries.

The brain is made up of super-specific areas that have super-specific functions.

Central Nervous System Structure & Function

Central Nervous System

Brain

Spinal Cord

integrating sensory information (collected from peripheral nervous system)

coordinating both conscious and unconscious activity

Brain

Carries out most complex functions:

thinking

feeling

remembering

sorts out sensory information and gives orders

Spinal Cord

conducts two-way signals between brain and rest of body

governs basic muscle reflexes and patterns that don't need brains permission

The brain and spinal cord are made of fragile, jelly-like nervous tissue that is extremely suscepitble to injury.

The nervous tissue is protected by the bones of the vertebrae and cranium, as well as membrane layers, or meninges, before being bathed in clear cerebrospinal fluid.

Cerbrospinal fluid allows the brain to float somewhat in the skull, reducing its weight

"Your brain is divided into specialised regions that may, or may not, interact with each other to produce a given action."

Brain Development: Neural Tube

Inside a developing embryo, the central nervous system starts as a neural tube.

The caudal, or lower, end of the tube stretches to form the spinal cord, while the cranial end expands, divides and enlarges into three primary brain vesicles, or interconnected chambers.

Prosencephalon (Forebrain)

Mesencephalon (Midbrain)

Rhombencephalon (Hindbrain)

Brain Development: 3 Primary Vesicles

By an embryo's fifth week of development, these vesicles morph into five secondary vesicles that form the roots of your mature brain structures.

Brain Development: 5 Secondary Vesicles

Prosencephalon

The prosencephalon divides into two sections:

Telencephalon

Diencephalon

Rombencephalon

The rombencephalon forms into another pair:

Metencephalon

Myelencephalon

Mesencephalon

The mesencephalon remains undivided.

The five secondary vesicles develop into the major adult brain regions. Each vesicle grows in different ways, some developing more than others.

Brain Development: Major Adult Brain Regions

Brainstem

Cerebellum

Diencephalon (Interbrain)

Cerebral Hemispheres

Brain Development: Cerebellum & Brain Stem

Cerebellum

helps coordinate muscular activity

Brain Stem

Midbrain

vital role in relaying information between the body and higher regions of the brain

carries out higher-level functions

receives and processes sensory information and sends out reflexive motor signals

passes data to cerebral cortex

Pons

Medulla Oblongata

Together, they regulate many basic, vital, involuntary functions. E.g. keeping heart on pace, keeping lungs working, controlling sleep, appetite, pain sensitivity and awareness.

Brain Development: Reptillian Brain

Diencephalon:

Thalamus

Hypothalamus

Epithalamus

Mamillary Bodies

= Homeostasis, alertness, reproductive activity.

Part of The Limbic System

Strong emotions - fear

Reptillian Brain

eat

drink

sleep

mate

stay safe

Brain Development: Cerebral Hemispheres

The telencephalon develops into the two classic walnut-looking hemispheres - the cerebrum.

Cerebrum

largest region of brain

performs highest functions

rules voluntary movements

thinking

learning

regulating and recognising emotions

experiencing consciousness

Grey Matter = wrinkly outer layer

White Matter = inner squishy layer

Higher processing requires lots of synapses, which requires lots of nervous tissue.

In order to squeeze the cerebrum into the skull, the brain forms creases:

Gyri - little creases

Sulci - larger grooves

The Brain's Lobes

Although a big fissure seperates the left and right hemispheres, the two halves communicate, through a series of myelinated axon fibers called the corpus callosum.

Each hemisphere has other, smaller fissures that divide it into lobes - each with a different set of major functions.

Frontal Lobe

governs muscle control

cognitive functions. E.g. planning for the future, concentration, preventing socially unacceptable behaviours.

In most people, the frontal lobe doesn't finish developing until after teenage years.

The Broca's area lives in this lobe in the left hemisphere, it's also important in language comprehension and speech.

Occipital Lobe

processing bright visual cues

Parietal Lobe

processes sensations of touch, pain and pleasure

Temporal Lobe

sorts auditory information, including language

It contains Wernicke's area - an important region of the brain associate with production of written and spoken language.

Part of the Limbic System

Hippocampus

short-term memory keeper

Amygdala

emotional, controls sexual and social behaviour

[rnedicalimaging]

20th May 2024

CC: A&P - NT, Synapses - Terminology

Axon Terminal - The structure at the end of a neuron's axon at a chemical synapse that contains and releases neurotransmitter.

Presynaptic Neuron - The cell that is sending a signal releasing the neurotransmitter in a chemical synapse.

Postsynaptic Neuron - The cell in a chemical synapse that is receiving the neurotransmitter.

Voltage-Gated Calcium Channels - The channels that are opened by an action potential reaching an axon terminal, sending the final trigger to release neurotransmitters.

Synapse - The general term for a structure where one cell can directly communicate with another cell.

Synaptic Cleft - The name for a very narrow gap between the two cells in a synapse.

Synaptic Vesicle - The structure within the presynaptic neuron's axon terminal that contains neurotransmitter waiting to be released.

Chemical Synapse - A structure that requires the use of a neurotransmitter to allow one cell to communicate directly with another cell.

Electrical Synapse - A structure including gap junctions that allows an ion current to pass from one cell directly into another cell.

Reuptake - The term for the reabsorption from a synaptic cleft of neurotransmitters by the pre-synaptic neuron that released it.

Neurotransmitter - A chemical released by neurons into a synapse to send a signal to another cell.

Excitatory Neurotransmitters - Neurotransmitters that lead to depolarisation of the postsynaptic neuron.

Inhibitory Neurotransmitters - Neurotransmitters that lead to hyperpolarisation of the postsynaptic neuron.

Serotonin - A typically inhibitory neurotransmitter, associated with regulating mood, appetite, circadian rhythm and sleep.

Dopamine - A typically excitatory neurotransmitter that influences emotion and attention, and is active in reward centers in the brain.

Norepinephrine - An excitatory neurotransmitter important in the fight or flight response to increase heart rate, alertness and mobilise energy reserves.

[rnedicalimaging]

20th May 2024

Crash Course: Anatomy & Physiology - Nervous System, Synapses

Summary:

Electrical Synapses Use Ion Currents Over Gap Junctions To Transmit Neurological Signals

Chemical Synapses Turn Electrical Signals Into Chemical Ones

Chemical Synapses Use Neurotransmitters

Effects of Cocaine in the Electrochemical System

What are Synapses?

Synapse

the meeting point between two neurons

Greek - "to clasp or join"

If neurons form the structure of the nervous system, then synapses, the communication links between them, make it an actual system

"Neurons strength and purpose lies in their connection."

When an action potential sends an electrical message to the end of an axon, that messages hits a synapse that then translates, or converts it, into a different type of signal and flings it to another neuron. The human brain alone has 100 billion neurons, with each neuron having 1000 - 10,000 synapses.

100 - 1,000 trillion synapses in the brain.

"Synapses are able to change and adapt in response to neuron firing patterns" - either strengthening or weakening over time, depending how much they're used.

Synapses allow you to learn and remember.

Synapses are the root of many psychiatric disorders.

Synapses are why illicit drugs, and addictions to them, exist.

Electrical vs Chemical Synapses

Nerve cells have two main different communication settings, depending on how fast news needs to travel.

Electrical Synapses

the immediate group texts

Chemical Synapses

controlled, slower and more personal texts

How Electrical Synapses Work: Gap Junctions

"Electrical synapses are much more abundant in embryonic tissue where they help guide neural development, as the nervous system matures, many electrical synapses are replaced by chemical ones."

Electrical synapses send an ion current directly from the cytoplasm of one nerve cell to another through gap junctions.

The signal isn't converted from it's pure electrical state to another singla, like chemical synapses.

Instead, one cell and one synapse can trigger thousands of cell that act in synchrony.

Why Aren't All Synapses Electrical?

Control

With such a direct connection between cells, "An action potential in one neuron will generate an action potential in other cells across the synapse."

E.g The heart.

If every synapse in the body activated the neurons around it, the nervous system would be in "group text reply all" mode.

How Chemical Synapses Work: Neurotransmitters

Chemical Synapses

much more abundant

slower

more precise

more selective

Chemical synapses use neurotransmitter, or chemical signals, that diffuse across a synaptic gap to deliver a message.

effectively convert signal in steps: electrical > chemical > electrical

allows for different ways to control impulse.

"This sort of long term translation could be the result of:

Potentiation - the strengthening of a synapse through classical conditioning.

Habituation - when a synapse decreases its response to a common stimulus.

Sensitization - when a reaction to one stimulus causes other synapses to be more sensitive to reactions."

At the synapse, signal can be modified, amplified, inhibited or split, either immediately or over longer time periods.

Set-up - 2 Principal Parts:

Presynaptic Neuron Presynaptic Terminal

axon terminal

The cell that sends the signal is presynaptic neuron and it transmits through a knoblike structure called the presynaptic terminal, usually the axon terminal.

Synaptic Vesicles

The axon terminal holds a whole bunch of tiny synaptic vesicle sacs, each loaded with thousands of molecules of a given neurotransmitter.

Postsynaptic Neuron

Receptor Region

The receiving cell is the postsynaptic neuron, which accepts the neurotransmitters in its receptor region, which is usually on the dendrite or the cell body itself.

Synaptic Cleft

The neurons communicate, despite never touching, through a tiny gap called the synaptic cleft.

< five millionths of a cm apart

Messages that travel via chemical synapses are technically not transmitted directly between neurons, like in electrical synapses.

Instead, a chemical event that involves the release, diffusion and reception of neurotransmitters in order to transmit signals.

How Neurotransmitters Work

When an action potential travels along the axon of a neuron, activating sodium and potassium channels, it eventually comes down to the presynaptic terminal, and activates the voltage-gated calcium (Ca2+) channels to open and release calcium into the neuron's cytoplasm.

Voltage Gated Calcium Channels

-Ca2+

The flow of positively-charged calcium ions causes the tiny synaptic vesicles to fuse with the cell membrane and pure their chemical messengers.

It's these neurotransmitters that act like couriers diffusing across the synaptic gap and binding to receptor sites on the postsynaptic neuron.

The first neuron converts the electrical signal into a chemical signal.

In order for it to become an action potential again in the receiving neuron, it has to be converted back to an electrical signal.

This happens once a neurotransmitter binds to the receptor, causing the ion channels to open

"Depending on which particular neurotransmitter binds to which receptor, the neuron might either get excited or inhibited."

Excitatory Neurotransmitters

Excitatory Post-Synaptic Potentials (EPSPs): graded potentials that push the neuron closer to threshold, and make an action potential more likely.

Excitatory neurotransmitters depolarise the postsynaptic neuron by making the inside more positive and bringing it closer to its action potential threshold, making it more likely to fire the messageon to the next neuron.

Inhibitory Neurotransmitter

Inhibitory Post-Synaptic Potentials (IPSPs): graded potentials that push the neuron further from threshold, make an action potential harder to achieve.

Inhibitory neurotransmitters hyperpolarises the postsynaptic neuron by making the inside more negative, driving its charge down - away from the message. The message not only doesn't get passed down, it's harder to excite that portion of the neuron.

Any region of a single neuron may have hundreds of synapses, each with different inhibitory or excitatory neurotransmitters.

"The likelihood of that post-synaptic neuron developing an action potential depends on the sum of all of the excitations and inhibitions in that area."

100 Different Types of Naturally-Occurring Neurotransmitters

move around

keep vital organs humming along

amp us up

calm us down

make us hungry, sleepy or more alert

simply make us feel good

Neurotransmitters don't stay bonded to their receptors for more than a few milliseconds.

After delivering message, they pop back out and either degrade or recycled.

Some kinds diffuse back across the synapse are immediately re-absorbed by the sending neuron in a process called reuptake.

Others are broken down by enzymes in the synaptic cleft, or sent away from the synapse by diffusion.

How Cocaine Works

Illicit drugs either excite or inhibit the production, releasse and reuptake of neurotransmitters.

They can simply mimic neurotransmitters, tricking a neuron into thinking its receiving a natural chemical signal, when it's anything but.

Cocaine

Once in bloodstream, it targets 3 major neurotransmitters:

Serotonin

mainly inhibitory

role in regulating, mood, appetite, circadian, rhythm and sleep

Antidepressants can stabilise moods by stabilising serotonin levels.

Dopamine

influences emotion and attention

makes you feel awesome

E.g. hugging a loved one, sex, donuts

Norepinephrine

triggers fight or flight response

increases heart rate

primes muscle

Undersupply can depress mood.

In a sober state, once these neurotransmitters deliver their chemical payloads, they're usually diffused back out across the synapse to be absorbed by the neuron that sent them.

Cocaine blocks the reuptake, especially of dopamine, allowing these chemicals to float around and accumulate - causing euphoria, paranoia and "jitters".

As the body has a limited supply of these neurotransmitters, the body needs time to brew more.

Flooding synapses like this eventually depletes your supply, making you feel terrible in a number of ways.

Cocaine, and other drugs, that target neurotransmitters trick the brain, and after prolonged use may eventually cause it to adapt, as those synapses remember how great the extra chemicals feel.

As a result, you lose receptors, so it takes more cocaine, and finally cocaine, to function normally.

In a natural state, synapses know when to excite, when to inhibit, when to use electricity and when to dispatch chemical messengers.

[rnedicalimaging]

19th May 2024

Crash Course: Anatomy & Physiology - Nervous System, Action Potential

Summary:

Ion Channels Regulate Electrochemistry To Create Action Potential

Resting State

Depolarisation

Repolarisation

Hyperpolarisation

What are Neurons?

When a neuron is stimulated enough, it fires an electrical impulse down its axon to neighbouring neurons.

"They've only got one signal they can send and it only transmits at one uniform strength and speed."

Frequency varies.

Action Potential

buzz, nerve impulse

Your Body is a Sack of Batteries

Electricity

Electrically Neural

The body has equal amounts of positive and negative charge, with certain areas more positively or negatively charged than others.

Membranes, acting as barriers, separate the opposite-attracting positive and negative charges until ready to use the energy.

"We keep em separated to build potential."

Voltage

the measure of potential energy generated by separated charges

membrane potential

measured in millivolts

The bigger the difference between positive and negative areas, the higher the voltage, the large the potential.

Current

the flow of electricity from one point to another

The amount of charge in a current is related to both its voltage and resistance.

Resistance

whatever's getting in the way of the current

"Currents indicate the flow of positively or negatively charged ions across the resistance of cells' membranes."

Membranes separate the charges, so provide potential to convert electricity for use.

How Electricity Works Inside The Nervous System

Resting Neuron

more negative inside, relative to extracellular space around it

Resting Membrane Potential

The difference between the inside and outside charges.

-70 mV

Outside Cell

positive sodium ions

Inside Cell

positive potassium ions

bigger negative proteins

As there're more positive sodium outside than positive potassium ions inside, the cell's interior has an overall negative charge.

negative membrane potential = polarised

Sodium-Potassium Pump

Protein straddles the membrane of the neuron.

Tons all along the axon.

For every two potassium ions it pumps into the cell, it pumps three sodium ions out.

Electrochemical Gradient

This creates a difference in the concentration of sodium and potassium, and a difference in charges, making it more positive outside the neuron.

Types of Ion Channels: Voltage-Gated, Ligand-Gated and Mechanically-Gated

Ion Channels

Ion channels are large protein, riddle among the membrane, that provide passages across the membrane when their respective gates are open.

The gate open and close for different reasons, depending on structure and purpose.

Voltage-Gated Channels

most abundant

open and close in response to changes in membrane potential

E.g. Sodium channels in neurons open at -55 mV.

Ligand-Gated Channels

open when a neurotransmitter latches onto its receptor.

E.g serotonin, a hormone.

Mechanically-Gated Channels

open in response to the physical stretching of the membrane

When gates open, ions diffuse across that membrane down their electrochemical gradient, even out the concentrations and moving away from other positively charged ions.

"The movement of ions is the key to all electrical events in neurons."

Graded Potential vs. Action Potential

Graded Potential

E.g. If only a few channels open, and only a bit of sodium enters the cell, that causes just a little change in the membrane potential in a localised part of the cell.

Action Potential

E.g. In order to send long-distance signals all the way along an axon, you need a bigger change, one big enough to trigger those voltage-gated channels.

Depolarisation

Start:

neurons sitting at resting state

ion channels closed

inner voltage resting = -70 mV

An environmental stimulus occurs, E.g. like a spider brushing against your knee, triggering the sodium channels to open and increasing the charge inside the membrane.

The stimulus, and resulting change, have to be strong enough to cross a threshold for the true action potential to kick in.

-55 mV

all or nothing phenomenon

If the stimulus is too weak, and the change doesn't hit -55 mV, the neuron returns to its resting state.

At -55 mV, the many voltage-gated sodium channels open, so the positive sodium ions rush in, making the cell massively deporalised - so much so that it becomes positive, up to +40 mV.

"A brief depolarisation caused by changes in currents."

Unlike graded potentials, small and localised, an action potential kicks off a biological chain reaction, which sends the electrical signal down the axon.

Repolarisation

As each neuron has many voltage-gated sodium channels, so when a few in one area open, the local current is strong enough to change the voltage around them.

This striggers the neighbours, which triggers the volttage around them and so on.

Once underway, the process of repolarisation occurs.

The voltage-gated potassium ion channels open up, letting the potassium ions flow out in an attempt to rebalance the charges.

Hyperpolarisation

The voltage drops to -75 mV beofere the gates close and the sodium-potassium pump take over and bring things back to resting level.

Refractory Period

An axon during this process, with its ion channels open, can't respond to any other stimulus.

It prevents signals from travelling in both directions down the axon at once.

"The first phase of this period, from depolarisation to repolarisation, is called the absolute refractory peirod. It makes sure that each action potentials is its own unique all-or-nothing event. The phase immediately following the period, the one that spans from repolarisation through hyperpolisation and back to resting potential is the relative refractory period."

Voltage

Initial Threshold = -55 mV

Peak of Depolarisation = +40 mV

"A weak stimulus tends to trigger less frequent action potentials.

E.g.

Low Frequency - delicate action, picking up an egg

High Frequency - intense signal, crushing a can

Conduction Velocity

Action potentials can vary by speed.

The factor that affects a neuron's transmission speed most is whether there's a myelin sheath on its axon.

Axons coated in insulating myelin conduct impulses faster than non-myelin axons.

Instead of triggering one channel at a time in a chain reaction, a current can leap from one gap in the myelin to the next.

Nodes of Ranvier - little gaps

salatory conduction - propogation

Latin - "leaping"

"Axons with a larger diameter conduct signals faster because they offer less resistance, so allow action potentials to happen quicker."

[rnedicalimaging]

19th May 2024

CC: A&P - NS, Into to Nervous System Terminology

Central Nervous System - The part of the nervous system consisting of the brain and spinal cord.

Soma - Neuron's cell body that contains nucleus, DNA, mitochondria, etc.

Axon - Long extension or fiber that transmits electrical impulses away from the cell body to other cells.

Dendrites - Branch-like processes that pick up messages from other cells.

Astrocytes - Most abundant and versatile glial cells. They govern the exchange of materials between neurons and capillaries.

Neurons - In nervous tissue, the type of cell that can transmit signals from one cell to another.

Unipolar Neurons - A neuron with a single extension from the soma that leads to an axon with dendrites at one and and axon terminals at the other, peripheral sensory neurons are this type.

Bipolar Neuron - A neuron with one axon and a single dendrite extending from its soma, found in limited places like the retina of the eye.

Multipolar Neuron - A neuron with one axon and many dendrites extending directly from the soma, this is the most common type of neuron in the body.

Afferent Neurons - In the peripheral nervous system, these pick up messages from sensory receptors and transmit impulses toward the central nervous system.

Efferent Neurons - In the peripheral nervous system, these receive messages from the central nervous system and transmit impulses out to peripheral effector organs, like muscles and glands.

Interneurons - In the central nervous system, these transmit impulses between other neurons.

Schwann Cells - Produce insulating barrier called myelin sheath in the peripheral nervous system.

Satellite Cells - Surround and support cell bodies.

Microglial Cells - Main source of immune defense against invading microorganisms.

Ependymal Cells - Create, secrete and circulate cerebrospinal fluid.

Oligodendrocyte - Produce insulating barrier called myelin sheath in the central nervous system.

Schwann Cells - Produce insulating barrier called myelin sheath in the peripheral nervous system.

Integration - When the central nervous system processes an input and decides what should be done with it.

Somatic (Voluntary) Nervous System -The part of the nervous system that carries signals from your central nervous system to only your skeletal muscles.

Peripheral Nervous System - All the nerves that branch off from your brain and spine and allow your central nervous system to communicate with the rest of your body.

Autonomic Nervous System - Part of the nervous system that carries signal from your central nervous system to regulate things like your heart beating, lungs breathing, and stomach churning.

Motor (Efferent) Division - The part of the peripheral nervous system that carries signals from your central nervous system to your muscles and glands.

Sympathetic Division - The part of the autonomic nervous system that mobilises energy and gets the body ready to fight or flee.

Parasympathetic Division - The part of the autonomic nervous system that encourages digestion, relaxes the body, and stores excess energy.

Sensory Division (Afferent) - The part of the peripheral nervous system that picks up sensory stimuli and transmits these signals to the central nervous system.

Sensory Input - The first function of the nervous system, describes the reception of stimuli by our senses and transmission of the signal to to central nervous system.

Motor Output - The signal that the central nervous system sends out to activate certain parts of the body.

[rnedicalimaging]

19th May 2024

Crash Course: Anatomy & Physiology - Nervous System, Intro to the Nervous System

Summary:

Sensory Input, Integration and Motor Output

Organisation of Central and Peripheral Systems

Glial Cells

Role, Anatomy and Function of Neuron Types

Structure and Function of Neurons

Nervous System Fundamentals

"Its anatomy and organisation, how it communicates and what happens when it gets damaged."

Nervous System Functions: Sensory Input, Integration and Motor Output

Sensory Input, Integration & Motor Output

Sensory Input

E.g. Sensory receptors detect a spider on your knee.

Integration

"From there your nervous system processes that input and decides what should be done about it."

E.g. "Should I let it walk over me?" "Should I freak out and scream?"

Motor Output

"The response that occurs when the nervous system activates certain parts of your body."

E.g. Swatting the spider away.

Organisation of Central and Peripheral Nervous Systems

Central Nervous System (CNS)

brain

spinal cord

main control center

E.g It decided to remove the spider and gave the order to your hand.

Peripheral Nervous System (PNS)

nerves that branch off from brain and spine that allow your CNS to communicate with rest of body

It's job is communication, so is set up to work in both directions.

Sensory Division (Afferent)

picks up sensory stimuli

E.g. "There's a spider on you."

Motor Division (Efferent)

sends directions from your brain to muscles and glands

E.g. "Hand, how bout you do something about the spider?"

Somatic Nervous System (Voluntary)

rules skeletal muscle movement

Autonomic Nervous System (Involuntary)

keeps heart beating, lungs breathing, stomach churning

Autonomous Nervous System - Sympathetic & Parasympathetic Division

Sympathetic Division

mobilises body into action

E.g. "Gah! Spider!"

Parasympathetic Division

relaxes the body

E.g. "It's not a white tail. Breathe."

Neurons & Glial Cells

Neurons, or nerve cells, respond to stimuli and transmit signals.

Glial Cell Types

provide support, nutrition, insulation, and help with signal transmission in the nervous system

Central Nervous System

Astrocytes

support, regulate ions

Microglia Cells

defend

Ependymal Cells

line cavities

Oligodendrocytes

wrap and insulate, form myelin sheath

Peripheral Nervous System

Satellite Cells

surround neuron cell bodies

Schwann Cells

insulate, help form myelin sheath

Glial cell types serve many functions and make up about half of the brain's mass.

Central Nervous System Glial Cells: Astrocytes, Microglial, Ependymal and Oligodendrocytes

Astrocytes

exchange of materials between neurons and capillaries

Star-shaped astrocytes are found in the central nervous system.

most abundant and versatile glial cell

anchor neurons to their blood supply

govern the exchange of materials between neurons and capillaries

Microglial Cells

immune defense against invading microganisms

thorny-looking

Main source of immune defense against invading microorganisms in brain and spinal cord.

Ependymal Cells

create, secrete and circulate cerebrospinal fluid

line cavities in brain and spinal cord

Oligodendrocytes

produce an insulating barrier called the myelin sheath

Peripheral Nervous System Glial Cells: Satellite and Schwann

Satellite Cells

surround and support neuron cell bodies

Schwann Cells

produce an insulating barrier called the myelin sheath

Neuron Fun Facts

Neurons are some of the longest-lived cells in the body.

Neurons are irreplaceable.

Most neurons are amitotic, so once they take on given roles in the nervous system, they lose the ability to divide.

3. Neurons have huge appetites.

Neurons have a high metabolic rate, requiring a steady and abundant supply of glucose and oxygen.

"About 25% of the calories that you take in every day are consumed by your brain's activity."

Neuron Structure

Soma (Cell Body)

Neuron's life support.

nucleus

DNA

mitochondria

ribosomes

cytoplasm

Dendrites

listeners

Axon

talker

"The axons transmit electrical impulses away from the cell body to other cells.

Classifying Neuron Structures: Multipolar, Bipolar and Unipolar

"how many processes extend out from the cell body".

Process - a projecting part of an organic structure.

Multipolar

multiple processes

99% of neurons are multipolar neurons, with 3 or more processes sticking out of the soma.

E.g axon, multiple dendrites.

Bipolar

2 processes

E.g. axon, dendrite - extending from opposite ends of the cell body.

Bipolar neurons are rare, found only in special sensory places - like eye retina.

Unipolar Neurons

1 process

E.g. sensory receptors

Classifying Neuron Functionality: Sensory (Afferent), Motor (Efferent), Interneurons (Association)

"Which way an impulse travels through a neuron in relation to the brain and spine."

Sensory Neurons (Afferent Neurons)

transmit impulses from sensory receptors toward the CNS

mostly unipolar

E.g. neurons pick up messages and transmit impulses from sensory receptors, like skin or internal organs, and send them through the CNS.

Motor Neurons (Efferent Neurons)

impulse moves from the CNS to the rest of the body

mostly unipolar

Interneurons (Association Neurons)

impulse moves between sensory and motory neurons

mostly multipolar

most abundant neurons

[rnedicalimaging]

18th May 2024

CC: A&P - Skin Deeper Terminology

Skin - This organ functions as an immune barrier, blood storage unit, temperature regulator, vitamin producer, waste extractor, environment sensor, and odor producer.

Tactile Corpuscle - A type of receptor in the epidermis that is sensitive to light touch.

Lamellar Corpuscle - A type of receptor in the dermis that is sensitive to vibration and wide pressure.

Cutaneous Sensory Receptors - The collective name for all the parts of the nervous system that sense touch and pressure in the skin.

Sebaceous Glands - The type of skin glad that produces oil in hair follicles.

Ceruminous Glands - The type of modificed apocrine sweat gland that produces ear wax.

Mammory Glands - The type of modified apocrine sweat gland that produces milk in lactating women.

Sudoriferous Glands - A technical name for sweat glands, and located all over the body, these skin glands may produce either watery or sticky sweat.

Eccrine Sweat Glands -The type of sudoriferous glands located all over the body but concentrated on the palms of the hands and soles of the feet, these produce salty watery sweat.

Apocrine Sweat Glands - The type of sudoriferous glands located in the axillary and inguinal regions of the body, these produce viscous sweat, containing lipids and proteins that contributes to body odor.

Insensible Perspiration - A constant level of low level sweat produced constantly by the skin, at about 0.5 liters per day, to regulate temperature.

Sensible Perspiration - A variable and potentially high - up to 12 liters per day - amount of sweat produced as needed to cool the body.

Hair Root - The center of a hair in a follicle, where keratinisation is still active.

Hair Follicle - The part of every hair embedded in the skin.

Hair Shaft - The part of every hair that extends beyond the surface of the skin.

Hair Cuticle - The outermost layer of a hair, made of overlapping dead keratinocytes.

Vasodilate - Dermal blood vessels do this to dump excess body heat.

Vasoconstrict - Dermal blood vessels do this to reduce heat loss and send blood deeper to keep vital organs warm.

Jaundice - A yellow of skin, usually indicating liver dysfunction and a buildup of bile in the blood.

Cyanosis - Meaning "blue appearance", this term describes the colour of skin - usually the lips - when blood oxygen levels are low.

Erythema - Reddened skin caused by increased blood flow due to high body temperature, fever, inflammation, or embarrassment.

Vitamin D - The only vitamin that can be made in the body, its synthesis starts when sun hits the skin.

Melanin - The primary human skin pigment that mostly protects deeper layers of the skin from damage from UV light from the sun.

[rnedicalimaging]

18th May 2024

Crash Course: Anatomy & Physiology - The Integumentary System, Skin Deeper

Summary:

Integumentary System Protects Your Body

Senses The Outside World

Helps Excrete Waste

Stores Blood

Regulates Temperature

Makes Vitamin D

Indicates Signs of Poor Health

Integumentary System

Functions

Protection

Sensation

Blood Storage

Temperature Regulation

Vitamin D Synthesis

Excretion

"The first and most vital purpose of the integumentary system is to act as a protective barrier."

Protective & Sensory Functions of the Integumentary System

Skin, hair, nails, sweat and oil glands work to shield us from threats: excessive sunlight, infections, abrasions etc.

"The integumentary system is also vital to how you sense the world around you."

Cutaneous Sensory Receptors

Structures, part of the nervous system, that receive stimuli from outside environment and send them to the brain.

Corpuscles (Receptors)

register different sensations associated with touch

Tactile Corpuscles

transmits sensations of light touch and low frequency vibrations from periphery > central nervous system

E.g. Makes you aware of a tag scratching the back of your neck.

Lamellar Corpuscles

register the sense of pressure

E.g. Someone puts their hand on your shoulder.

Hair Follicle Receptors

feeling the breeze on skin/through your hair

More Functions: Removing Waste, Storing Blood & Regulating Body Temperature

"The integumentary system also plays a role in the excretion of waste."

Waste Removal

The integumentary system excretes small amounts of waste elimanted through the skin via sweat.

Urea, uric acid and ammonia, nitrogen-containing waste, are disposed via urine.

There's no evidence that heavy sweating rids the body of extra toxins, just water loss.

Blood Storage Unit

"About 5 percent of the entire blood volume is retained in your skin at any given time."

When more bloody supply is needed, like exercising, the nervous syste constricts dermal blood vessels to squeeze extra blood into circulation.

Body Temperature Regulation

During exertion, both blood and sweat glands regulate body temperature.

Insensible Perspiration

unnoticable sweat

The body excretes about 1.5L of sweat daily to maintain a comfortable body temperature.

Sensible Perspiration

noticeable sweat

Heavy exertion can cause 12L of sweat per day.

Vasoconstriction

To regulate heat loss, dermal blood vessels constrict, causing causing blood to head deeper into tissues to keep vital organs warm

Vasodilation

Once heat returns, blood vessels relax, allowing blood to return to the surface.

Skin Dyscolouration: Cyanosis, Jaundice or Erythema

Skin colour can indicate homeostatic imbalances.

As human skin colour spans, some conditions are easier to diagnose by discolouration of other tissues - mucous membranes, finger and toenail beds.

Cyanosis (Blue Skin)

In Caucasian people:

may indicate heart failure

poor circulation

severe respiratory issues

Blood depleted of oxygen turns darker in colour, which seen through the tissue of lips or skin, can look blue-ish.

Jaundice (Yellow Skin)

may indicate liver disorder

Yellow bile accumulates in the blood stream.

Erythema (Red Skin)

may indicate fever, inflammation, allergy

Fever, inflammation and allergy cause blood vessels expand and cause more blood flow to the skin's surface.

Melanin, Vitamin D & Skin Tone

Melanocyte

synthesizes melanin

Melanin is a pigment produced by melanocyte cells in the epidermis.

Melanin

produces reddish yellow pigments

produces brownish black pigments

It's main job is to protect against sun's ultraviolet rays.

Vitamin D

Bones require Vitamin D to produce new bone cells, which is the only vitamin the body can produce on its own.

Skill cells contain a molecule that converts to Vitamin D when in contact with UV light.

Vitamin D Path:

Skin > Bloodstream > Liver & Kidneys

In the liver and kidneys, Vitamin D becomes Activated D (Calcitriol).

Calcitriol circulated to all bones of the body.

How Does Hair Conditioner Work?

Skin Appendages

Hair

Nails

Sweat

Sebaceous Glands

Oil Glands

Hair

Hair, or pili, are flexible strands of dead keratin protein - like fingernails.

The outermost layer of the dead cells, the cuticle, look like overlapping roof shingles.

Shaft

keratinisation is complete

Root

keratinisation is still happening

Each follicle is a tube of epidermal cells.

Like the epidermis, cells at the bottom of each follicle are young, continually dividing and pushing older cells up through the skin's surface.

Finger & Toe Nails

root of nail

nail body

nail bed

At the back of the nail bed, new cells divide at the root and are pushed forward, creating scaly-hard keratin.

Types of Sweat Glands: Eccrine, Apocrine, Mammary and Ceruminious

Sweat & Oil Glands

"There are up to three million toiny sudoriferous, or sweat glands, distributed throughout the body."

secrete salty, watery sweat

Eccrine & Apocrine Glands

Eccrine Glands

palms

forehead

soles of feet

Eccrine glands are abundant.

They're simple coiled tubes that start in the dermis, extend through a duct and open into a pore on the skin's surface.

Apocrine Glands

armpit hair follicles

groin hair follicles

"deluxe" sweat - with fats and proteins

viscous

yellow-ish colour

odor

"You only have about 2000 of these, and they start cookin' around puberty, emptying into the hair follicles around the armpits and groin."

When the bacteria on the skin gets a hold of this sweat, it gets odorific, creating body odor.

Deodorants don't affect how much you sweat, but they reduce the smell by attacking odor-making bacteria.

Antiperspirants, using aluminum, block the sweat glands and prevent perspiration.

Modified Apocrine Sweat Glands

Mammary Glands

secrete milk

Ceruminious Glands

cerumen (earwax)

Sebaceous (Oil) Glands

Sebaceous Glands

oil glands

Sebaceous glands are everywhere but in thick skin on palms and foot soles.

Ducts are smaller on limbs but bigger on face, neck and upper chest.

Most sebaceous glands secrete sebum, an oily substance, into hair follicles that can travel to the skin's surface.

Although they cause pimples, their primary function is to soften and lubricate skin and hair, and slow skin's water loss in dry environments.

[rnedicalimaging]

18th May 2024

CC: A&P - Skin Deep Terminology

Integumentary System - The organ system that includes your skin, hair, nails, sweat glands and oil glands.

Friction Ridges - Structures supported by dermal papilae, also known as fingerprints.

Keratinocytes - The main type of cells in the epidermis, these make a lot of the protein keratin which makes the skin durable.

Melanocytes - The spider shaped cells in the epidermis that are responsible for producing the brown pigment melanin.

Tactile Cells (Merkel Cells) - Epidermal cells that work with neurons to provide sensation for light touch.

Dendritic Cells (Langerhans Cells) - Epidermal cells that are part of the immune system, and try to gobble up invading bacteria before they can break into the deeper layers of the skin.

Statified Squamous Epithelium - The tissue type found in the epidermis.

Thin Skin - The type of epidermis with just four named layers, and found everywhere on the body other than the palms of the hands and soles of the feet.

Thick Skin - The type of epidermis with five named layers, and only found on the palms of the hands, and the sole of the feet.

Epidermis - The most superficial of the three main layers of the skin.

Stratum Corneum - The most superficial layer of the epidermis, made of 20 - 30 layers of dead keratinocytes that eventually slough off, its name means "horny layer".

Stratum Lucidum - The so called "clear layer" of the epidermis, these 2 - 3 layers of keratinocytes are only found in thick skin on the palms of the hands and soles of the feet.

Stratum Granulosum - This layer of epidermal cells looks grainy because the cells are producing large amounts of keratin before they die.

Stratum Spinosum - This layer of epidermal cells is held together by protein fibers, and is the layer just superficial to the layer where active cell division is occuring.

Stratum Basale - This is the deepest layer of the epidermis, is made of just one layer of cells that are actively diving to produce cells that get pushed out to the other layers.

Dermis - The middle of the three main layers of the skin, where you find blood vessels, sweat glands, and most touch receptors.

Dermis - The layer of the skin just deep to the epidermis, containing blood vessels, and making skin elastic.

Papilary Layer - Made of loose areolar connective tissue, this is the layer of the dermis just deep to the epidermis.

Reticular Layer - The dermal layer just deep to the papilary layer, made of dense irregular connective tissue.

Hypodermis - The deepest of the three main layers of the skin, made mostly of adipose tissue.

[rnedicalimaging]

18th May 2024

Crash Course: Anatomy & Physiology - The Integumentary System, Skin Deep

Summary:

All About Skin

Epidermis, Dermis and Hypodermis

Melanin and Keratin Cells

Ensure You Get A Good Tattoo

Skin

Skin protects your body against infection and extreme temperatures, maintains your balance of fluids, and even synthesizes Vitamin D for personal use.

The nerve endings allow you to sense the outside world.

Sweat glands and blood vessels help maintain proper temperature and communicate - from health to emotions - through things like blushing, flushing and sweating

Integumentary System

Hair

Nails

Sweat

Oil Glands

Skin

Skin Layers: Epidermis, Dermis & Hypodermis

Epidermis

stratified squamous epithelial tissue

Dermis

sweating, blood circulation, feeling

Hypodermis (Subcutis)

adipose tissue

Types of Epidermal Cells: Keratinocytes, Melanocytes, Langerhan Cells and Merkel Cells

Keratinocytes

building blocks of the tough, fibrous protein keratin

make up the bulk of the epidermis

Provide structure, durability and waterproofing to hair, nails and outer skin.

Kertatinocytes are constantly dying and being replaced, losing milling of them daily, enough to completely replace the epidermis every 4 - 6 weeks.

Melanocyte

spider-shaped cell that synthesizes melanin

Skin colour isn't about the number of melanocytes but instead about the breath of their spidery cellular extensions, which in turn affect the amount of melanin that they contain.

Langherhan Cells (Denritic)

star-shaped

originate in bone marrow

defend the epidermis

Merkel Cells (Tactile)

combine with nerve endings to create a sensory receptor for touch

Found deep down at the boundary between the epidermis and dermis.

Thick Skin

Thick skin, found on the palms of hands and sole of feet, consists of five epidermal layers.

Thin Skin

Thin skin, found everywhere else, contains four epidermal layers.

Layers of Skin: Stratum Corneum, Stratum Lucidum, Straum Granulosum, Stratum Spinosum, and Stratum Basale

The deeper the epidermal layer, the younger the cells are.

Regeneration happens in the lower layers, with new cells moving up, maturing along the way, until they die on the surface.

This is because the epidermal is epithelial, so it's avascular, with all oxygen and nutrients coming from the dermis, so as they mature and move towards the surface, they lose their oxygen and nutrient supply and die.

Stratum Corneum

"horny layer"

Outermost, roughest layer.

20 - 30 sheets of dead keratinocyte cells.

Stratum Lucidum

"clear layer"

2 - 3 rows of clear, flat, dead keratinocytes that are only found in the thick skin of palms and soles.

Thin skin is only missing the stratum lucidum.

Stratum Granulosum

"granular layer"

Layer contains living keratinocytes that form keratin like "crazy".

Looks grainy as cells are compressed and flattened as they move up through the epidermal layers, maturing as they go.

Stratum Spinosum

"spiny layer"

Prickly appearance under a microscope.

Closer to the point where regeneration, or mitosis, is active.

Stratum Basale

"basal layer"

A single layer of columnar cells.

Cell factory - where most cell production happens.

It connects the epidermis to the layer of skin below it, the dermis.

Pneumonic - Come, Let's Get Sun Burned!

C - Stratum Corneum

L - Stratum Lucidum

G - Stratum Granulosum

S - Stratum Spinosum

B - Stratum Basale

Sunburn

The ultraviolet radiation in sunlight can damage the epidermis, cause elastic fibers to clump up to form a leathery appearance.

Sunburn temporarily depresses the immune system, with immune cells in the epidermis - and radiation can alter skin cell's DNA, leading to skin cancer.

Layers of the Dermis: Papillary, Reticular and Hypodermis

Dermis

collagen fibers, elastin fibers

capillaries

blood vessels

nerve fibers

parts of hair follicles, oil glands/sweat glands with ducts that lead to the skin's surface

Papillary Layer

areolar connective tissues

dermal pippilae

In thick skin, papillae are tiny protrusions that form unique friction ridges that press up through the epidermis to help grip - fingerprints.

Reticular Layer

dense irregular connective tissue

The reticular layer, deeper and thicker, make up 80% of the dermis.

All the dynamic parts contained within the dermis, like nerve fibers and capillaries, are distributed between both its layers.

Any time you're cut deep enough to bleed or feel pain, you've broken through the epidermis layer and lacerated the dermis.

Tattoos must reach the dermis for permanency.

Hypodermis (Subcutis)

adipose connective tissue

Basically a seam of fat, it provides insulation, energy storage, shock absorption and anchors the skin.

[rnedicalimaging]

17th May 2024

CC: A&P - Types of Connective Tissues Terminology

Loose & Dense - The two subclasses of connective tissue proper.

Loose Connective Tissue - The subclass of connective tissue proper with relatively fewer protein fibers but more ground substance and cells.

Dense Elastic - The type of stretchy connective tissue proper found in the walls of many of our large arteries.

Fibrocartilage - The connective tissue with thick bundles of collagen fibers that is found in the menisci in our knees, and in our intervertebral discs.

Dense Regular - The type of connective tissue proper dominated by thick collections of collagen fibers all running in different directions.

Dense Regular - The type of connective tissue proper found in ligaments and tendons.

Dense Irregular - The type of connective tissue proper with thick bundles of collagen fibers running in lots of different directions; it is good at resisting forces in lots of different directions.

Elastic Cartilage - The connective tissue with extra elastic protein fibers, it provides the structure for our ear pinnae.

Hyaline Cartilage - The glassy connective tissue found in our nose, between the ribs and sternum, covering the ends of bones in joints.

Areolar - The most common type of loose connective tissue, found just under the epidermis and wrapped around every organ.

Areolar - The type of loose connective tissue defined by a random arrangement of fivers, few fibroblast cells, and lots of space of watery ground substance.

Reticular Tissue - The type of loose connective tissue proper that is dominated by reticular fibers instead of elastic or collagen.

Reticular Tissue - The type of loose connective tissue proper that provides the structure and space in the liver, spleen, lymph nodes and bone marrow.

Compact Bone - The type of connective tissue that uses calcium and other minerals to form very hard and durable structures.

Osseous Tissue - The type of connective tissue that uses calcium and other minerals to form very hard and durable structures.

Osseous Tissue - Very dense osseous tissue that acts as a shell over every bone, provides the strength of the shafts of long bones, and stores calcium for the body.

Spongy Bone - Porous but strong osseous tissue that provides space for bone marrow and is found inside the ends of long bones and throughout flat bones.

Fibrocartilage - The connective tissue with thick bundles of collagen fibers that is found in the menisci in our knees, and in our intervertebral discs.

Adipose - The type of loose connective tissue that functions as insulation and a storage for energy and in the form of fat.

Adipocytes - The name of the cells that take up most of the space in adipose tissue.

Blood - Type of connective tissue that transports materials to all parts of the body, in which the ground substances is called plasma, and the extracellular fibers are usually invisible.

Erythrocytes - The name of red blood cells, the dominant cell type in blood.

[rnedicalimaging]

17th May 2024

Crash Course: Anatomy & Physiology - Types of Connective Tissues

Summary:

Loose and Dense Connective Tissue

Areolar, Adipose, Reticular, Tendons, Ligaments, Dense Irregular and Dense Elastic Tissue

Three Cartilage Types: Spongy and Compact Bone Connective Tissue

Blood is Connective Tissue Type

"No matter how different a tendon, bone or hunk of fat may appear, they are indeed very closely related."

All spring from the same embryonic cells, and their structures are dominated, not by cells, but by an extracurricular matrix full of fibers.

Connective Tissues

Proper

Cartilage

Bone

Blood

Loose vs Dense Connective Tissue Proper

Connective Tissue Proper

based on how many fibers it has in its ground substance

Loose

areolar

reticular

adipose

Loose connective tissue have fewer fibers, more cells and more ground substance.

Dense

regular

irregular

elastic

Tendons are an example of dense connective tissue.

Types of Loose Tissue Proper: Areolar, Adipose and Reticular

Areolar Tissue

fibroblast cells

elastic fibers

collagen fibers

Areolar tissue is the most common loose connective tissue, found all of your body, just under the epithelial tissue, and wrapped around organs.

It has a loose and random arrangement of fibers, with a few fibroblast cells that make the fibers.

Latin term - "a small open space"

E.g. If you slam your shin on a coffee table and inflame the area, the areolar tissue soaks up extra fluids like a sponge, and resulting swelling and puffiness is called edema.

Areolar tissue is a kind of sponge for watery ground substance.

Adipose Tissue (Fat Tissue)

adipocytes

nucleus

lipid vacuole

Adipose tissue is mostly cells, adipocytes, which store lipids for later use, insulate the body against heat loss and grow pot bellies/love handles.

The average person's weight is 18% adipose tissue.

Reticular Tissue

reticular fibers

developing blood cells

Reticular tissue is similar to areolar tissue, but with a woven mass of reticular fibers, instead of collagen and elastin fibers.

It provides the soft internal framework, or stroma, of the spleen, lymph nodes, and bone marrow, and supports lots of developing bloody cells.

While areolar tissue is a kind of sponge for watery ground substance, reticular tissue is what holds your blood in place in many of your organs.

Loose connective tissue proper types share an airy dispersal of fibers.

Types of Dense Tissue Proper: Regular, Irregular and Elastic

Dense Regular Tissue

fibroblast nucleus

collagen fibers

Dense regular tissue is full of tight bundles of collagen fibers all running parallel.

Found in tendons, muscle to bone, and ligaments, which bind bones together anywhere there's a joint

Dense Irregular Tissue

collagen fibers

fibroblasts

Dense irregular tissue, whose fibers are thicker and arranged erratically, are found wherever tension may be exerted in lots of different directions. E.g. the leathery dermis underlying skin

Dense Elastic Tissue

elastic fibers

stretchy, elastic tissue

Found in vertebrae, so spine can curve and twist.

Found in large artery walls, provides support and flexibility.

Connective tissue proper is the most diverse group in this tissue family.

Types of Cartilage: Hyaline, Elastic and Fibro

Cartilage

Cartilage doesn't have any blood or nerves and stands up against both tension and compression pretty well.

Hyaline

chondrocytes

lacunae

Hyaline cartilage is the most common type.

glassing-looking, provides pliable support

It connects ribs to the sternum and keeps the tip of the nose perky.

Its ground substance is rich with sticky, starchy proteoglycans.

Although it has collagen fibers, you can't really see them under a microscope, instead the tissue looks glass.

"Hyal" = glassy, transparent.

Elastic Cartilage

chondrocytes

elastic fibers

Elastic cartilage is similar to hyaline cartilage, but with more elastic fibers that are easier to see.

Found in places where strength and stretchability are needed.

Fibro Cartilage

chondrocyte

collagen fibers

Fibro cartilage acts as a shock absorber. It's dominated by thick fibers of collagen and is good at withstanding pressure, so it makes up the discs between vertebrae, and knee joints where it keeps bones from grinding together.

Types of Osseous (Bone) Tissue: Spongy and Compact

Fun Fact: Each bone is considered a separate organ

"Bone" can refer to an entire organ, like femur or scapula, or just bone tissue.

Bone, or osseous tissue, is calcified connective tissue, perfect for supporting and layering the body's various structures.

Spongy Bone Tissue

Spongy bone tissue is typically found in the heads of long bones and in the inner layer of flat bones. E.g. sternum.

It's strong, but porous, even to the naked eye, and uses the extra room to make and store bone marrow.

Compact Bone Tissue

osteocyte (within lacuna)

Compact bone tissue is quite dense, with no visible spaces. It forms the external layer of the bones and stores calcium for bone cells to use to make more tissue

Blood is a Connective Tissue

connects distant parts of your body

provides rigidity to other parts

Blood develops from mesenchyme, is made up of cells surrounded by an extracellular nonliving matrix.

The ground substance is the blood plasma, which has protein fibers floating around it.

The blood's main job is delivery - transports cells, nutrients, hormones wastes etc., keeping all the parts of the body connected in the process.

Blood

Red Blood Cells

Erythrocytes

Zoom around, carrying oxygen and carbon dioxide through the body.

White Blood Cells

Leukocytes

larger

infection-fighting

Platelets

The small cell fragments needed for blood cutting.

Unlike other connective tissues, it doesn't have typical fibers, but instead has protein dissolved in the plasma, and the protein molecules form fiber-like structures when blood needs to clot.

[rnedicalimaging]

16th May 2024

CC: A&P - NT, Connective Tissues Terminology

Fibers - These, together with the ground substance, makes up the extracellular matrix that surrounds cells in connectibe tissue.

Elastin - Long, thin, and stretchy protein fibers found in the extracellular matrix of some connective tissues, like those in arterial walls.

Reticular - Short brancing protein fibers found in the extracellular matrix of some connective tissues, form a delicate sponge like strucutre, and make up the structure of the spleen.

Collagen - The toughest and most abundant protein fiber found in the extracellular matrix of many connective tissues.

Ground Tissue - The watery and sometimes gelatinous component of the extracellular matrix in connective tissue.

Blood, Proper, Bone, Cartilage - The four major categories of connective tissue.

Connective Tissue - The major tissue varies, but all types develop from mesenchyme, most are vascularised, and are mostly described based on the extracellular matrix instead of the actual cells.

Connective Tissue - Marfan syndrome affects mostly this tissue, causing extra growth and weakness in joints, long bones and arterial walls.

Adipose (Fat) - This proper connective tissue serves as energy storage, thermal insulation, and cushioning for delicate organs like eyeballs and kidneys.

Chondroblasts - The "immature" type of cell that helps build the cartilage in your joints, nose and ears.

Osteoblasts - The "immature" type of cell that helps build your bones.

Osteocyte - The name of the mature cell type in bone that helps maintain bone structure. It developed from an osteoblast.

Macrophages - Large, hungry immune cells found roaming the extracellular matrix in connective tissue in search of invaders and dead cells.

[rnedicalimaging]

16th May 2024

Crash Course: Anatomy & Physiology - Tissues, Connective Tissues

Summary:

Four Types of Connective Tissue

Different Degrees of Blood Flow

Extracellular Matrix Full of Ground Substance and Fibers

Blast, Cyte and Immune Cell Types

Marfan Syndrome Affects Connective Tissue

Connective Tissue

keeps you looking young

makes up your skeleton

delivers oxygen and nutrients throughout your body

What is Connective Tissue?

Connective tissue is pretty much everywhere in your body, although how much of it shows up where, varies from organ to organ.

E.g. Skin is mostly connective tissue. Brain has very little connective tissue, as it's almost all nervous tissue.

Proper

connective tissue

found in ligaments, supporting your skin

Cartilage

connective tissue

Bone

connective tissue

Blood

connective tissue

Connective tissues do more than just connect muscles to bones:

binding and supporting

protecting

insulating

storing reserve fluid and energy

transporting substances within the body

movement

Fat

a type of proper connective tissue which provides insulation and fuel storage

also serves structural purposes like holding kidneys in place, keeping eyeballs from popping out of skull.

Bones, tendons and cartilage bind, support and protect organs and give you a skeleton so you can move with purpose.

Blood transports hormones, nutrients and other material amongst the body.

What Makes Connective Tissue Different From Other Tissue Types?

All connective tissues have three factors in common that set them apart from other tissue types:

Mesenchyme

Connective tissues have different degrees of vascularity or blood flow

All connective tissues are mostly composed of non-living material

Mesenchyme

Connective tissue develop from mesenchyme, a loose and fluid type of embryonic issue.

Mesenchymal cells can be situated any-which-way and can move from place to place.

Connective tissues have different degrees of vascularity or blood flow.

Most cartilage is avascular, meaning it has no blood vessels, while the dense irregular tissue in skin is vascular - brimming with blood vessels.

All connective tissues are mostly composed of non-living material - the extracellular matrix.

The Extracurricular Matrix

The inert matrix between connective tissue cells is more important than what's inside the cells.

The jello that gives jelly it's structure is like the extracellular matrrix in connective tissue.

The actual cells are just intermittent goodies floating around inside the matrix, like marshmallows.

The extracellular matrix is mostly made of two components.

Ground Substance

a watery, rubbery, unstructured material that fills in the spaces between cells and protects the delicate cells from their surroundings.

flexible, mostly made of starch and protein molecules mixed with water

Proteoglycans

protein anchors of the framework each sprouts lots and lots of long, starchy strands called glycosaminoglycans (GAGs) radiating out from the proteins like brush bristles

these molecules then clump together to form big tangles that trap water

Types of Fibers

Fibers provide support and structure to the otherwise shapeless ground substance.

Collagen

strongest and most abundant type of fiber

part of what makes skin look young/plump

tough, flexible

It's essentially a strand of protein, and stress tests show that it's actually stronger than a steel fiber of the same size.

Elastic Fibers

form a branching framework

stretch and recoil like rubber bands

longer, thinner

found in skin, lungs, blood vessel walls

Reticular Fibers

short, finer, collagen fibers

sponge-like network - cradle and support organs like fuzzy nets

extra coating of glycoprotein

Connective Tissue Cells

Immature & Mature

Immature = -blast suffix

"Blast" means forming.

Immature stem cells are still in the process of dividing to replicate themselves.

Each kind of blast cell has a specialised function - secrete the ground substances and fiber that form its unique matrix.

Chondroblast Cells

blast cells of cartilage

When chondroblast cells build their matrix around them, they're making the spongy tissue that forms the nose, ears and cushions the joints.

Osteoblasts

blast cells of bone tissue

The matrix they lay down is the nexus calcium carbonate that forms your bone.

Once formed, osteoblasts transition into a less active, mature phase.

At that point, they trade in the -blast suffix for the -cyte suffix.

An osteoblast in your bone becomes an osteocyte.

Ditto for chondroblasts becoming chondrocytes.

Cyte cells maintain the health of the matrix built by blast cells, but can sometimes revert back to their blast state if needed to repair or generate a new matrix.

The matrices that these cells create are what build you - assemble your bone, cartilage, tendons and everything that holds the rest together.

How Marfan Syndome Affects Connective Tissue

Marfan Syndome targets the elastic fibers, causing weakness in the matrix that's the root of many of the condition's most serious symptoms.

[rnedicalimaging]

16th May 2024

CC: A&P - T, Epithelial Tissue Terminology

Epithelial Tissue - The kind of tissue that forms coverings and linings in the body, and also forms glands that secrete hormones.

Connective Tissue - The kind of tissue deep to all epithelial membranes, and that provides support and a blood supply to those membranes.

Cell Shape & The Number of Layers of Cells - We classify epithelial tissues based on these two characteristics.

Squamous - Short, wide epithelial cells, in which even the nucleus appears flattemed.

Squamous - The shape of epithelial cells good for forming thin permeable membranes or for making multi-layered abrasion resistant surfaces where each cell is inexpensive to replace.

Columnar - Tall, narrow epithelial cells, sometimes with a vertically stretched nucleus.

Columnar - The shape of epithelial cells found in the stomach and intestinal linings, where they must secrete mucus and form an active and thick membrane.

Cuboidal - Epithelial cells that are aboust as tall as they are wide with a circular nucleus.

Cuboidal - The shape of epithelial cells found in sweat glands and kidney tubules, where materials are being secreted or actively transported across a membrane, respectively.

Stratified - The type of epithelial tissue made up of two or more layers of cells.

Simple - The type of epithelial tissue made up of a single layer of cells - where every cell reaches from the tissue's apical surface to its basal surface.

Pseudostratified - The type of epithelial tissue where some cells reach from the apical or basal surface in a single layer but other cells are stratified or multilayered.

Simple Squamous - The name for a single layer of flattened cells in an epithelial membrane, like the lining of the lungs

Stratified Cuboidal - The name for a tissue with multiple layers of square-like cells in an epithelial membrane, like the linings of ducts to our salivary glands.

Selectively Permeable - Many epithelial membranes, because they allow some level of absorption, filtration or excretion of specific types of molecules, are described as this.

Apical - The exposed surface of an epithelial membrane that is not attached to the connective tissue.

Polar - A word that describes something, like epithelial tissue, the Earth and water molecules, as having two distinct sides or ends.

Basal - The side of an epithelial membrane that is attached to the underlying connective tissue and basement membrane, opposite the exposed surface.

Exocrine Glands - The type of glands that secrete chemicals destined for the outside of the body, or for the inside of your digestive and respiratory tubes that connect to the outside of the body.

Endocrine Glands - The type of glands, made of epithelial tissue, that secrete chemicals into the bloodstream.

All epithelial tissues are avascular, meaning that those tissue... don't have their own blood vessels.

When naming epithelial tissues, the first word describes... number of cell layers.

When naming epithelial tissues, the second word describes... shape of the cells.

[rnedicalimaging]

16th May 2024

Crash Course: Anatomy & Physiology - Tissues, Epithelial Tissue

Summary:

Epithelial Tissues Creates Inner and Outer Boundaries

Layering: Simple or Stratified

Shape: Squamous, Cuboidal or Columnar

Epithelial Cells are Polar

Epithelial Tissue

Epithelial tissue lines, covers, and generally organises the body - creating order from what would be chaos. Without epithelial tissue, we'd essentially be a mushy pile of unarticulated goo.

Proper Epithelium & Glandular Epithelium

Proper Epithelium

covers and lines your outer and inner body

Glandular Epithelium

forms glands and secrete hormones and other substances

Primary Epithelium

protects your whole body, inside and out.

Primary epithilium is a great organiser, portioning everything into separate but connected units.

It covers the surface of your body when it combines with connective tissue to create skin. E.g. epidermis

...but it also line your body cavities, and coats the internal and external walls of many of your organs. E.g. Cranial cavity, thoracic cavity, pericardial cavity, vertebral cavity, abdominal cavity, pelvic cavity.

We're All Just Tubes

Epithelial tissue covers both the inside and outside of our tubes.

Invagination

the action or process of being turned inside out of folded back on itself to form a cavity or pouch

E.g. the membranes covering your lungs are actually invaginations of your epithelium, where the tissue that makes up your you-tube folds to form a cavity.

The epithelium does all this to protect your deeper layer of tissue from injury or infection.

E.g. lining your stomach with epithelial cells that produce mucus, so that you don't digest yourself along with your lunch.

Epithelial tissues are avascular - meaning they don't have a blood supply.

Instead they rely on the blood supply in the supporting connective tissues around them.

Epithelial tissues come in different varieties that serve different purposes. A lot of what classifies the different types of epithelium boils down to their shape and layering - that is, the shape of the individual cells, and the number of layers that they form in.

Cell Shapes: Squamous, Cuboidal or Columnar

Squamous Cells

fast absorption and diffusion, making thin membranes

Squamous cells are flat. Their name means "scale", and they look kind of squished, like fish scales. Even the cell's nucleus, which gets darkly stained and is usually easy to see, is flattened.

Cuboidal Cells

absorb nutrients

Cuboidal cells are cube-ish shaped, about as tall as they are wide. They absorb nutrients and produce secretions, like sweat. Their nucleus is pretty circular.

Columnar Cells

absorb nutrients

Columnar cells are tall and thick and look like columns, and they cushion underlying tissues. As if they were cuboidal cells that got stretched tall, their nuclei also are stretched into an ellipse.

How Form Relates To Function

The shape of each kind of epithelial cell correlates with its function.

E.g. Squamous cells are flat, which make its easy for materials like oxygen to move across them to the other side.

We see squamous cells where absorption or transportation is most important. E.g. sacs of lungs, blood vessels.

If the cells make up a tissue that need to brew up hormones or mucus, they'll need the internal machinery it takes to make that stuff, and that takes up a lot of space. The cells can't be flat - they've got to be cuboidal or columnar to accommodate more room for taking care of business.

The stomach lining is made up of big columnar cells, because they have to make and secrete mucus.

Cells, biologically speaking, are expensive. They take a lot of time, energy and raw materials to make.

E.g. In places where you lose a lot of cells, like your outer skin or mouth, you have more squamous cells - as they're smaller, flatter, and therefore cheaper, practically disposable - rather than big, expensive cuboidal or columnar cells.

Layering: Simple or Stratified

Simple Epithelium

one layer of cells

Stratified

multiple layers set on top of each other, like bricks

Pseudostratified

mostly just one layer

cells with different shapes and sizes

The nuclei can be at lots of different levels, so it can look messy/multilayered, even though it really isn't.

In a lab setting, the epithelial tissue is cited by both its shape and layer.

First Name = Number of Layers

Last Name = Shape of Cells

The tissue's first name as it's number of layers, and it's last name as the shape of its cells.

E.g.

Simple Squamous Epithelium

single layer

flat, scale-like cells

E.g. lining of the air sacs deep in the lungs

Stratified Cuboidal Tissue

layers of cube-shaped cells

E.g. linings of the ducts that leak sweat and spit

Squamous Cells

As they're thin, like scales, it takes many layers to form a tissue that's thick enough to offer protection.

A really dense stack of cells that, on an individual basis, are small and cheap to make.

E.g. When we scratch our hand or hit the inside of the mouth with a toothbrush, we can lose a couple of squamous cell layers.

Epithelial tissue regenerates really quickly.

Epithelial Cells: Apical & Basal Sides

Epithelial cells are polar, meaning they have distinct sides.

Apical Side

epithelial cells

The apical side is exposed to either the outside of the body or whatever internal cavity it's lining.

Basal Side

selectively permeable

allowing for some level of absorption, filtration, and excretion of substances

The basal side, or inner surface, is tightly attached to the membrane, a thin layer of mostly collagen fibers that helps hold the epithelium together, and anchors it to the next deeper layer - connective tissue.

Many of the boundaries that the cells form aren't absolute - instead, they're selectively permeable, allowing for some level of absorption, filtration, and excretion of substances.

E.g.

The tissue lining the small intestines is what allows you to absorb nutrients through diffusion and active transport.

All urinary waste gets filtered through a different epithelial lining in the kidneys.

Glandular Epithelial Tissue Forms Endocrine & Exocrine Glands

Glands are made up largely of epithelial tissue, so it plays a big role in facilitating all secretions - from sweat to mucus, hormones and enzymes.

The glandular epithelium forms the endocrine glands and the exocrine glands.

Endocrine Glands

secrete hormones right into your bloodstream or to nearby cells

E.g. The hormone thyroxin is secreted by an endocrine gland, the thyroid, and needs to be distributed throughout the entire body so it can stimulate the metabolism in all cells.

Exocrine Glands

secrete their juices into tubes or ducts that lead to the outside of the body (or the inside of your tube, rather than right into the blood)

E.g. sweat, saliva, mucus, stomach acid and milk.

All these secretions go right into ducts where they're ferried to an epithelial surface, which could be the outer layer of skin, in the case of sweat, or to the edge of stomach lining if it's stomach acid.