HAPIA: Cells & Communication

Nervous system + function

a bodily communication system responsible for taking in external or internal informatio, processing it and enacting a responce if required

Functions include meaintain homeostaia by

• receiving sensory inputs

• Process and interpretting information

• Instructing and eliciting responces by controling muclse galnds or mainatain mental activity

Basci process of NS communication + response

Sensry Neurons: takin in information from snesory organs and sends it back to the barin afer process \ing (afferent)

Intregration of information at which it is processed and inter[reted and decded if a response is required (occurs in brain)

Motor neurons then take signalls from the barin and sen them to effector organs to enact what ever respose is required (efferent)

Central nervous system

Composed of the brain and spinal cord and is used to process infomation received from senroy input and tell the motor neurons to enact a responce that is appropriate to the situation

• protceted by bone and muscle as they are essential to life

Peripheral nervous system

Inclues the cranial nerves, spinal nerves and peripherla nerves which have both snesory and motor neurons and is used to take into senory information and enact the commands given by the central nervous sytem.

• contain 2 didvsion and multiple subdidvions

Peripheral nervous system: Sensory divisom

the division responsible for taking it sensory information that is split into two different divisions

• Somatic sensory divdion rescive sensation that we are consious of souch as the 5 sense, and from nerves in skin facia, joints and muslces

• Visceral snesory division recives information from thing we aren’t concious of like the nerves in blood vessels, glands and organs ( we can’t feel our intestines move by it still happens)

Motor division: Somatic Motor

te divsison of the motor diviosn that is responsibel for telling organs to enact responses that we are conscious of and can controll like standing up and sitting down

• the nerves are usually found in skeletal muslce

Motor division: Autonomic motor

a divison of the motor division responsible for telling effectors to enact responses that we aren’t conscious of like the contraction of smoothe muclse in veien aor cardoac mucles in he haert

Autonomic Motor subdivisions

Enteric: Involutary mtoro controll of the digestive systm

Sympathetic: controls flight or flight responces in reponce to dangerous situations to prepare to fight or run away that often causes discomfort, stress or anxiety

Parasympathetic: the recalibration of the body after the sympathetic division has riled us up that retursn us to normal

Cells in the nervous system

ther are two types of cells in the body

• glial or support cells

• Neurons or functional cells

Glial cells ( characteristics + types)

acts asthe CT of the NS and makes up 90% of the cells in the NS that are able to repproduce unlike neurons and provide support, nuorishment and protection

• CNS: Microglia, Astrocytes,ependymal, oligodendrocytes

• PNS: Schwann cells, statellite cells

Microglia - functions

the immune cells of the CNS found that flaot around and acts as Phagocytic cells to clean up debri and waste or pathogens

• the blood bian barrier doesn’t allow in other immune cells

• acts as the first responder to injury and can enact inflammatory responces using pro/antinflammatory cytokines

Microglia - Structures

Resting: small inner body with longer extension used to serch for any possibel threats or unwanted substances ( ramified appearnce- branches like a tree)

Active: Larger inner body with no extension that becomes very mobile as to catch as foregn body objects (amoeboid state)

• activated by injury/infection

Astrocyte - structure

Star shaoed cells with ote of processors that are the most sbundent in the barin and larger than microglia

Astrocyte Function: structural support

form the final outer layer of the blood barin barrier by acting as a wall surrounding the vessel using their extensions/feet

• also help in forming glial scars after injury

Astrocyte function: Homestasis

• reguate ion. nutrinet, and dissovled gas concentration in the interstitial fluid of the barin

• - absorbs / recycle any unused nuerotransimitter hence prventing them from exicte the wrong neurons and causing damage

Ependymal cells - strcture

specilised cells used to produced cerebrospinal fluid that appear as simple, columnar, epithelial cells with cilia and microvili

• cillia help circulate fluid and microvili help rebaosorb it for recycling

Ependymal cells functions

form the lining of cavities/ventricles in the brian that hold CSF called the ependyma and produces the CSF found in these cavities trkough the filtration of blood plsma

• CSF: cushions the barin and provides nutirents (proteins, sugars and electrolytes), removes watse

Oligodendrocytes- structure

Myelin producng cell in the CNS made of 1 cell contain 20-60 processors that extend and grab onto nurons to myelinate them

• cell body is not in contcat with neuron

Oligodendrocytes- fucntion

Produces myelin which is a protein-lipid complex and ensures that neurons and their signals are protected

• is able to meylinate multiple neurons at once by wrapping arounf then using their processors

Schwann cells

Myelin producing cells of the PNS the entirely wrapp themselves around the neurous axon and can only myelinate 1 neuorn at a time

• forms like a cinamon roll by the cinamon in meylin and the dough is the cell

• is able to regenrate to some degree if damaged

Myelin

a protein lipid complex that is deposited on cell membrane to increase their condution spedd / insulate them

• not all neurons are mylinated

• contribute to the white matter in the ND

• Node of ranvier are the gaps beteen the myelin

Satellite cells

the astrocytes of the PNS that look like small flatt cell surrounding the cell body of neurons

• support and protect

• controll extracellular environment

• supllies nutrients

Nueron featirs

make up 10% of the cells in our CNS ( about 80-100 billion)

• cna’t replicate

• communicate using electrical signals that become cehmical at te synapse

Neuron function

• reception of stimuli

• Integration or processing of stimuli

• Conduction of action potential

• Transimission of signal to the next cell or effetor organs)

Neuron structures

• soma

• dendrites

• Axon

• myeline sheath

• node of ranveir

• axon terminal

Neuron: Soma + dendrites

Soma: the cell body that n=houses the nucleus and organeele to ensure tehir survival

• can very is size by about 20 microns

• where all information processing occurs

Dendrites: Brahes off od the cell bod that recives and process signals from the axon terminal of another neuron

Neuron: Axon

the pathways at which the electrocal signal follows that is made up of a cytoplasmic extension

• can differ is size with some going all the way doen the spinal cord

• Transfers info between the soma and the axon terminal

• the axon hilock is the first part of the axon that the forms the axon proper and is where the action protential forms

Neuron: Myelin sheath

Insulates the action potential flowing through the axon and propragate it to ensure it isn’t lost in tersm of intesity

• made of myelin secreted by oligodendricytes or schwann cells

• Gaps between them ae called node od ranveir that regulate the speed of the signal down the axon

Neuron: Axon terminal

a terminal that braches off of the axon and is were bueron connect to one another or too effector ogans

• the electrocal signal is converted to a chemical one

the synapse

where an axon terminal meets a densrite of effecyor cell and transmits a cehmical signal

• a synaptic celf is left betwee them where neurtransmitter travel acroos to transfer the message

Strctural classification of neurons

Determied by the number of brances off of the cell body with 1 extension = a Neurite ( does chnage the flow of information across a nueron)

• Psuedounipolar: contain 1 brnch that extend into processors both dircetions off of the cell body and is found in the CNS and PNS

• bipolar: two extentions either side of the cell body with one having dendricytes and the other the axon terminal ( more rare)

• Multipolar Multiple extentsions coming out of a cell bod and only one axon ( the most common)

Functional classification of neurons

relats the the kinds of info passed throuhg the neuron and wher in the body it is found

Sensory (afferent) neurons: carry nfo from sensory organs usch as the skin from the PNS to the CNS ( can be pseudo or unipolar)

Internuerons: stors and processors info for the CNS and makes up 90% of nuerons ( multipolar only)

Motor (effernt) neurons: execute the responce given by the inetrnuerons from the CNS to the PNS ( multipolar only)

nerves structure

a bundle of neuron axons +CT in facicle surrounded by more CT

• 1 fascicle = axons surrdounded by endoneurium

• Multiple Fascicles make up a nerve and are surounded by Perneurium which is lined with epinneurium

cellular communication

cells communicate by electricla signals controlled through the movement of soecifc ions across he memebrane of a cells via pumps and channels

signals in Neural communication

the first signal is electrical and is caised by an accumulation of positive ions called the action potentail

• this electrical signal then ercahes the terminal where it becomes cehmical and is recived by another neuron and becomes lectrcal again

Cell membrane( structure/function)

made up of a phospholipid bilayr with the hydrophillic head lining the outside and the hydrophobic tails lining the inside

• isolates the cytoplasm from theextracelluar fluid

• controlls solute movement into and out of the cell

• miantains electrical insulation

Passive transportation

the movement of solutes across the cell memebran using simple or facilitated diffusion that requires no energy as the solutes move withe their concentration gradient

simple: movementof small uncharged molecules throuhg the membrane

facilitated: movement of solutes using memebrane porteins such as pums and chaneels as seen in neura communication

Active transportation

the movement of solutes aganst their concentration gradinet that requires energy

• Ion pumps: uses ATP to transport solutes ( maintains membarne potentila using Na+ /K+ ATPase

• endocytosis and exocytosis

Membrane transport in Neurons

Nuerons utilises passive facilitatded diffusion to comminucate and allowing in postive ions such as sodium and potassium

• leakey cahnnels allow in ions readily but gated cahnnels like the ones used in neural commincation need to be triggered by stimuli to open

Ion channels in Nuerons

in facilitated diffudsion there are 4 kinds of Ion channels

• Leaky (not very reliant and have little control oevr what enters (not used in nerural commincation)

• Ligand-gated ( required cehmical signal/nuertransmitter to open)

• Volatge gated ( requires a certain memebrane potential to open)

• Mechanical gated ( open due to mehanical force like pressure or tension)

Ion pumps in neural communiation

usinf in active transportation ot push molecule from areas fo low to high concentration

• the sodium/potasssium pump is used in active transport to regulate memebrane potential

• passage of ions across the emebrane allows for the creation of action potential

Fluid ( use and composition)

the water tha surroudning the memebrane( both in and out) can be used to regulate emebrane potential as it is comprise of dissolved ions and water

Membrane potential in neural communication

the differnec in charges between the extracellular and intercellualar fluid due to the precemce of ions

• inside the cell is negative at rest

Resting membrane potentai

the memebrane potential/ concentration of ions when the neuron is not active communicating

• is maintain by the used of ion pumps (Na/K) that pump 3 Na out for every 2 K in

Action potential

a wave of positive ions that moves through a neuron from the axon hilock to the terminal

• requires and change in emembrane potential to occur and become more positive

• cahnge in MP in detected by teh dendrie befire being feed to the body to be assesed for importance

stages of action potential

1. thereshold (MP reaches the threshold of charge and is deemed important)

2. Depolarisation

3. Repolarisation

4. hyperpolarisation

Action potential: Phase 0

The membrane potential sites at rest at -70 millivolts whilst being maintained by the Na+/K- pump

• not active recieving stimuli but is searching

Action potential: threshold

the dendrites recive info which is processed in the soma (is significant eneough then the MP will recah -55mv)

• the MP increase as nuerotransmitter are bound to ligand gated Na+ channe;s allows then to flood in ( if influx causes MP to recah -55mv then significant)

Action potential: Depolarisation

the buold of memebrane potential to reach Action potenial at 40mV

• change to -55mV causes the voltage gated ion cahnnel to pe allowing for a greater from of sodium ions

Action potential: Repolarisation

a lowering of memebrane potential after the cahrge has moved down the axon resulsting in a MP of -90mV

• recah 40mV casuses the voltage gated Na+ channels to close and the K+ one to open allowing for an efflux in K out of the cell

Action potential: Hyperpolarisation

since the MP has recahed bellow the resting -70mV and instead goes in -90 the K+ voltage channel is triggered to close

• makes it hard for action potential to reoccur so it allows for recalibration

Action potential: Phase 0 return

the Na+/K+ pumps does its magic and returns the membrane potential to -70mV

action potential along axon

as AP moves along the axon it is conatntly depolarising as it move forewrads while the section behind it repolarises

• the MP in front and behind are both at rest

types of Action potenial conduction

• continous conduction is a slower form of cinduction that occurs in unmeylinated axons where the depolarisation occurs in the immediate segment

• Saltatory conduction uses myelinated axon allow for quicker movement as the AP moves throuh the myelinated regions quickly before repolarising at the nodes of ravneir ( myelin insulates the charged area)

Synaptic transmission (+ location)

the commincaton that occurs between the axon terminal or one neuron and other cells

• can be neuron to neuron, motor Neuron to muscle (meuromuscular jucntion), Motor neuron to gland (neuroglandular junstion)

synapse conversion from action potential

the electrical action potential is converted to chemical signalling through the use of neurotransmitter which travel the length of the synapase to the other cell

• electrical synapses are possibel but less common

• neuritransmitter release is triggered by emebrane potential

How does the synpase send chemical messages

Neurotransmitter are created by ye cell body as they are proteins and are packaged in vesicle that ndergo exocytosis at the synapse

• will wit at terminal until signalled

Process of synapse transmission

1. action potential arrives at terminal causing chnage in MP that opens the Ca²⁺ voltage gated channels ( influx into the cell)

2. caclium ion icrease signals the vesicles to dock and realease neurotransmitters

3. Neurottransmitters bind to ligand gated channels of the postsynaptic cell casuing them to open/close

4. the ions eneter the postsynaptic cell and a responce is generated

Neurotranmitter

chemical proteins that enebale nerural communication by binding to cahnnels\ over 760 different types

• strcturally classified: AA’s, amines, neuropeptides

• Functionally classified: exictatory, inhibitory or both

Excitatory (EPSP) Neurotransmitters

Excitatory posynaptic pootential is the tranference of excitatory neurotransmitter onto the Na+ gated channel

• increases memebrane potential and chance of action potential threshold being achived

• causes depolarisation

Inhibitory (IPSP) Neurotransmitters

Inhibitory postsynaptic potential is atransferance of inhibitory neurtransmitter onto Cl- gated channels

• leads to deacrese in memebrane potential and less chance of action potential

• causes hyperpolarisation

examples of specfic Nuerotransmitters

Excitatory: Glutamate used in memory,learning and cognitive function

Inhibitory: GABA used in brian function and sleep

Multitransmitters: epinephrine,(fight/flight) Dopamine(movement/cognition/reward), Setotonin(mood + sleep), Acetylcholine

Graded potential

a local small change in MP done in stages that can determine whether action potential is recahed

what determines if action potentail

• type/naturea of signal (excites or inhibits)

• strength of signal ( number and timing)

Summation

Neurons will recive multiple excitatory and inhibitory signal which will lead to an influs of Na + Ca or Cl

• as a result the action taken will be hem sum of all the signal recieved and all the gradded potential chnages

spatial summation

a summation of how many cells are relasing the neurotransmitters for that postsynaptic cell

• the net effect of all incoming signals

• if more excitatory signal then action potential will be generated

Temporal summation

a summation of how many cells are tratgeting that cell and the speed at which their signals travel

• sum of all signal plus how many times they are repeated by one cell to indicate importance

Synapse outcomes

No net charge= nothing happens

Net inhibition = more no messages that prvent cell from reaching threshold

Net excitatory = more yes messages that allow the cell to reach threshold