TOPIC 13 - nerve and muscle Flashcards
what are the two nervous systems?
central and peripheral
what is the central nervous system?
- brain and spinal cord
- recieves, processes, interprets and stores information and sends messages destined for muscles, glands and organs
what is the peripheral nervous system?
- peripheral nerves
- transmits information to and from the CNS by way of sensory and motor nerves
what parts of the brain are in the CNS?
- forebrain (cerebrum, thalamus and hypothalamus)
- midbrain
- hindbrain (pons, medulla oblongata and cerebellum)
how many segments of the spinal cord are in the CNS?
31
what are the two divisions of the PNS?
- somatic
- autonomic (ANS)
what is the role of the somatic nervous system?
carries sensory information from sensory organs to the CNS and relays motor (movement) commands to muscle; controls voluntary movements
what is the autonomic nervous system divided into?
- sympathetic
- parasympathetic
- enteric and cardiac peluxes (intimately connected with parasympathetic)
what is the roles of the parasympathetic and sympathetic nervous systems?
sympathetic - fight or flight (speeds things up)
parasympathetic - rest and digest (calms things down
what are the main characteristics of neurones?
- high metabolic rates
- main component of brains ‘grey matter’
- dendrites for signal inputs
- axon for signal conduction
- synaptic terminals for signal output
what is a motor neurone?
- carries signals from CNS to outer parts of body
- have dendrites connected to the cell body, then axon then axon terminal
what is a interneuron?
- relay neurone
- connect various neurones within the brain and spinal cord
- dendrite not coming out of cell body but connected, cell body connected to axon then axon to axon terminals
what is a sensory neurone?
- carries signals from the outer parts of the body into the CNS
- dendrites connected to axon, cell body coming off of side of axon, axon terminals off of axon
what is a multipolar neurone?
a single long axon and many dendrites emerging from cell body (motor neurones)
what is a unipolar neurone?
found in sensory ganglia
what is a bipolar neruone?
found in sensory structures - eg retina
what is white matter and how does it stain?
- consists of axons carrying information to and from the brain
- will stain dark as has most myelin as mostly axons
what is grey matter and how does it stain?
- consists of cell bodies in sensory and motor nuclei
- stains pale as mostly cell bodies
what stain is used for myelin?
weigert’s stain
what are ganglia?
nodular masses of neuronal cell bodies (ganglion cells) and supporting neuroglia (satellite cells)
what are sensory ganglia?
cell bodies of sensory (afferent) neurons
what are autonomic ganglia?
cell bodies of motor (efferent) neurons from the autonomic nervous system
what does the epineurium do?
connective tissue layer that covers the whole nerve
what does the perinurium do?
covers a fasicle
what does the endoneurium do?
covers individual nerve axons
what is a fasicle?
a bundle of nerve fibres
what are neuroglia?
supporting cells for neurones
- regulate neurone metabolism and function
- repair and recovery from injury
- regulate blood brain barrier
- destroy pathogens and remove dead neurones
what types of neuroglia are in the CNS?
- astrocytes (most common)
- oligodendrocytes (most common in white matter
- microglia (less common)
- ependyma
what do astrocytes do?
structural - supportive framework
metabolic - provide neurone with nutrients
growth - promote neurone growth and synapse formation
blood brain barrier - restrict movement of substances from blood stream
potassium clearance - absorb K+ released from neurone at synapse
what do oligodendrocytes do?
myelinate axons (1 does up to 50)
what do microglia do?
immune defence - become phagocytic
what do ependyma do?
lining cells for the ventricles and central spinal canal, produce cerebral spinal fluid, have cilia on luminal side
what neuroglia are in the PNS?
schwann cells and satellite cells
what do satellite cells do?
surround nerve cell body and may aid in controlling chemical environment of neurons
what do schwann cells do?
form myelin sheath around large nerve fibres in the PNS and is also phagocytic
what is myelination?
- wrapping of axon in spiral of concentric layers of fatty myelinated membrane
- provides insulation to aid impulse transmission
what are nodes of ranvier?
gaps between adjacent cells
what do non-myelinated nerves have?
a supporting schwann cell - the axon is imbedded in a channel called the mesaxon (invaginations of the plasma membrane of the schwann cell)
what is a demylelinating disease?
a condition that results in damage to the myelin sheath —> nerve impulses slow/stop causing neurological problems
damage to the sheath can eventually lead to axonal degeneration
what is primary demylenating disease called?
leukodystrophic - myelin is abnormal and degenerates (usually genetic, some causes not known)
what is secondary demyelinating disease called?
myelinoclastic - healthy myelin is destroyed by a toxn, infectious agent, chemical or autoimmune substance
what is multiple sclerosis?
- common autoimmune demyelinating disease of the CNS
- loss of tolerance to self proteins —> inflammation and injury to myelin sheath and nerve fibres
what causes the sclerosis and scarring in MS?
- blood brain barrier is disrupted, allowing T cell entry to the brain
- T cells recognise myelin as foreign and attack it
- T cells release cytokines - promote degradation of myelin and blood brain barrier - B cells and macrophages can enter the brain
- B cells make antibodies to myelin (further degeneration)
- macrophages degrade myelin
what is located in the CNS, PNS and target tissue of sensory (1) and motor neurones (2)?
CNS - 1. axon terminals 2. cellbody and dendrites
PNS - 1. cell body and ganglion 2. axon
Target tissue - 1. sensory nerve endings 2. axon terminals
which autonomic nervous system has long preganglionic fibres?
parasympathetic
which autonomic nervous system has long and very branched postganglionic fibres?
sympathetic
where are the ganglia located in the parasympathetic and sympathetic nervous system?
parasympathetic - near or in target tissue
sympathetic - close to spinal cord
do both autonomic nervous systems have the same preganglionic transmitter?
yes - acetylcholine
do both autonomic nervous systems have the same postganglionic transmitter?
no
parasympathetic - acetylcholine
sympathetic - noradrenaline
how does erlanger-gasser classification work?
given a letter A B or C
what classification of nerve has the slowest conduction velocity?
C/IV - non myelinated - hot, pain, itch
what classification of nerve has the fastest conduction velocity?
A⍺/I - thick and v myelinated - propiroreceptors of skeletal muscle
what classification of nerve is for touch and pressure?
Abeta/II
what classification of nerve is for pain (fast) and cold?
Adelta/III
Going from A-C/ I-IV, what is the trend in diameter and velocity?
diameter and velocity decrease
how do you measure nerve conduction velocity?
place two electrodes either end of the nerve, measure distance between them and time for impulse to travel
how are sensory receptors classified by location?
exteroreceptors - external surface
interoreceptors - internal organs
prprioceptors - internal (position of muscles, tendons and joints)
how are sensory receptors classified by stimulus?
mechanoreceptors - touch, pressure, vibration stretch
thermoreceptors - hot, cold, temperature change
photoreceptors - light
chemoreceptors - chemicals
nociceptors - pain (usually chemicals)
sensory receptor - muscle spindles
found in skeletal muscles
respond to stretch
sensory receptor - free, endings uncapsulated
found in connective tissue, joints and skin
respond to pain, touch, light and pressure
sensory receptor - pacinian corpuscles
found in deep dermin, tendons, joints and genitalia, respond to vibration and deep pressure
sensory receptor - meissner’s/ krause’s bulbs
found in oral mucosa, lips, genitalia and fingertips
respond to touch, vibration and light pressure
sensory receptor - ruffini organs
found in deep dermis, ligaments and joint capsules
respond to stretch and deep pressure
outline the spinal cord reflex pathway
- sensory receptor detects stimulus
- sensory neurone transmits info to CNS
- integration centre - one or dome synapses in CNS
- motor neurone conducts efferent impulses to effector
- effector - muscle or gland that responds to impulses
what is the effect of negatively charged intracellular proteins in the nerve cell?
- they are large
- too big- cannot cross the cell membrane
- leave the cell and contribute to its negativity with respect to extracellular fluid as trapped inside
what does the sodium potassium ion pump do?
moves 3 Na+ ions out for every 2 K+ ions in.
= Thus inside of the cell gets more negative
what direction is the potassium ion gradient and what are its effects?
- K+ tends to leak out of the cell though selective channels down gradient as more potassium in cell than out due to conc gradient
- but…. cells large(-) charge inside = pulls K+ back in down electrochemical gradient due to the negativity in the cell
- eventually influxes become balances = K+ distribution equilibrium = -70mV
how is the equilibrium potential for an ion determined?
Nernst equation
used to calculate electrical potential of an ion of a particular charge across a membrane
whats the process of chemical transmission
- action potential reaches the axon terminal of the presynaptic cell.
- AP triggers calcium entry causing release of neurotransmitter chemical from the storage vesicles, which fuse with the synaptic membrane.
- Vesicles are “docked” and “primed” before action potential arrives – kept close to the terminal plasma membrane, so that release is as rapid as possible upon increase in calcium concentration.
- Upon calcium influx and concentration, the vesicle and plasma membranes merge
- the contents of the vesicles are released in to the synaptic cleft
how can we increase the probability of vesicle being released?
- by increasing calcium concentration) or decreased (i.e. by blocking depolarisation of the membrane and preventing calcium influx).
what is the sodium ion gradient and what effect does it have?
- the net inward diffusion gradient of Na+ slightly adds positivity of the cell
- Na + move into the cell due to the conc gradient
- Na+ move out of the cell due to the electrochemical gradient
- sodium ions both the concentration and electrical gradients operate in the same direction to cause inward flow of ions
- membrane is only slightly permeable to Na+ = effects on resting potential are small
- net effect of this is to bring the resting potential back up to about -65 mV
what is the value for the resting potential and how is it maintained?
- -65 to -70 mV
- electrical and chemical gradients acting on ions
- sodium potassium pump
what time of neurons have a resting potential value out of the normal range?
retinal neurones it is only -40 mV, in cortical pyramidal cells it is -75 mV.
-variation is due to differing levels of expression of ion channels in the membrane
what is the basis for the generation of an AP?
Ion flow across the membrane is the basis for signalling in neurones during action potentials- movement of ions contributes to AP
what is an AP?
means by which a neurone sends information down its axon, away from the cell body.
-The action potential (aka “spike” or “impulse“) is an explosion of electrical activity that is created by a depolarising current
describe the curve on the AP graph (the massive spike and then comes down)
membrane potential decreases and moves towards 0
becomes more positive until we get to +30mV: depolarisation
then charge becomes more negative and we reach -65mV: repolarzation
-then overshoot: membrane potential increases and so charge becomes more negative than -65mV : hyperpolerisation
describe the phases of an AP: phase 1 depolarisation
phase 1:
- Na+ channels open
- Na+ enters/diffuses into nerve cell (inward current)
- membrane potential rises
- resting membrane potential moves closer to zero and the cell becomes depolarised
- If negatively charged ions (e.g. Cl-) diffuse into a nerve cell across the membrane (outward current) the resting membrane potential moves further away from zero and the cell becomes hyperpolarised
- When the flow of ions stops, the potential rapidly returns to the resting level as the ions redistribute along and across the membrane according to their concentration/potential differences and permeabilities (i.e. negative feedback effect to maintain the status quo).
how does Ca influx lead to release of transmitter in an electrical synapse
- Action potential arrives at synaptic terminal causing depolarization.
- Voltage-gated Ca2+ channels are opened by depolarization and Ca2+ ions rush into the terminal.
- With rise in [Ca2+]I vesicles move to active zone, undergo fusion with membrane and release contents.
- membrane of the synaptic vesicle fuses to the presynaptic membrane at the active zone (docking), allowing the contents of the vesicle to spill out into the synaptic cleft
- Ca2+ enters the axon terminal directly at the active zone, precisely where vesicles are primed and ready for exocytosis, ensuring a rapid release of neurotransmitter.
- Fused vesicle membrane is taken back into the cell by endocytosis.
describe the phases of an AP: phase 3 repolarisation
- Na+ channels close so less sodium into cell as electrochemical force driving their movement has diminished due to overshoot
- voltage gated K+ channels open as potential difference for K+ is now far from equilibrium and K+ ions flow out of cell -increased potassium conductance-causing a rapid repolarisation back towards the resting membrane potential.
- membrane potential reverses
describe the phases of an AP: phase 3 hyperpolarisation
- When the resting membrane potential is reached the K+ channels are still open K+ ions continue to flow out of cell while Na+ channels closed (so K+ movement not opposed by this)
- membrane potential overshoots past the normal resting level -falls below resting level-(hyperpolarisation) for a brief period before the normal resting potential is restored
- During this brief period (refractory period) another action potential cannot be generated, so APs cannot summate and can only travel one way along the axon
what is required for ion influx to occur?
the threshold has to be reached and so the Na+ and K+ channels open
what determines the activation and inactivation of gates?
groups of charged amino acid residues at critical points of the ion channel structure that form the ion pore
whats gates are open and closed during resting state?
all voltage gated Na+ and K+ channels closed
NB- K+ channels are different to the ones that allow K+ to pass through membrane at rest
what gates are open and closed during the depolarising phase?
- voltage gated Na+ channel fast activation gates open (at about -40mV)
- Na+ can now enter cell, so inside becomes more positive – it depolarises
- this opens more activation gates = accelerating the flow of ions
what gates are open and closed during the overshoot phase
- inactivation gates of Na+ channels start to close and activation gates of K+ channels begin to open and K+ ions begin to exit the cell
- electrostatic force attracting Na+ into the cell becomes neutralised Na+ no longer able to enter cell, so no further depolarisation occurs as anterior of the cell becomes more negative
what gates are open and closed during repolarisation phase
inactivation gates of Na+ (fully closed) channels closed and K+ channels open= k+ rapidly leave the cell so membrane returns towards resting potetial
-K+ can now leave cell, so inside becomes more negative – it repolarises
what gates open and close during undershoot pahse/after potential?
K+ channels still remain open, Na+ channels closed
-K+ continue to leave cell, so inside becomes even more negative than the resting potential – it hyperpolarises
what gate are open and closed during the resting state
all voltage gated Na+ and K+ channels closed
-No movement of ions across membrane, so resting potential restored
(-65mV)
Whats the all or nothing principle?
- A neurone either fires or it does not, regardless of signal size – “all-or-nothing”
- A stimulus (e.g. injection of current) insufficient to raise the membrane potential to the threshold potential will never induce an AP
what impact does a stimulus have its its above threshold?
Further increase above threshold -> higher AP frequency not larger AP amplitude
what is a threshold?
All excitable cells have a threshold membrane potential
-Membrane has to be depolarised beyond threshold for an AP to be generated
what is the absolute refractory period?
During the absolute refractory period no further action potentials can be elicited no matter how much you stimulate it
This refractory period means that an action potential can only travel along the axon from cell body to axon terminal, not in the opposite direction. It cannot reverberate (i.e. go backwards towards its point of origin – normally the point where the axon joins the nerve cell body- cant get depolariation upstream).
what happens during the relative refractory period?
a larger stimulus can result in action potential
explain the action of AP along a non-myelinated axon
- Na+ influx deplorises area in front of it and triggers voltage gated Na+ channels to open
- causes AP in the next membrane section
- membrane behind impulse is refractory
- impulse can only go forward along the axon
explain the action of AP along a myelinated axon
- nodes of Ranvier are the only areas where current can pass through membrane
- nodes are only areas where membrane can depolarise
- excess of positive charge causes impulse travels in ‘jumps’ from one node to another and from there out into the extracellular space, causing depolarisation and an AP at the next Node- not slow flow
- AP jumps along the axon from Node to Node (salutatory conduction) – a much quicker means of conduction than in the non-myelinated fibre.
what are at the end of sensory neurones?
sensory receptors
what are sensory receptors
tuned’ to specific signals or sensory modalities, i.e., different forms of energy (light, vibration, chemicals, etc.)
what is sensory transduction?
conversion of environmental or internal signals into electrochemical energy.
what does detection of stimulus by reeptor cause?
- receptor potential
what is a receptor potential
- Graded electronic response (not action potential)
- Causes action potential
- receptor potential can build up to from AP
- Specific signals – rate and pattern of action potential firing – decoded in CNS
what does the magnitude of a receptor potential depend on
strength of stimulus
- If the receptor potential is large enough and the neurone reaches threshold, an action potential occurs
- An even stronger stimulus results in an increased number of action potentials
what 2 sensory receptors in muscles respond to stretch
proprioceptors and mechanoreceptors
where is the muscle spindle located and how is it stimulated?
within the muscle and stimulated when the muscle is passively stretched.
where is the golgi tendon organ located and what does it respond to?
is located in the tendon and responds to tension (it is stimulated when associated muscle contracts or is stretched).
describe the muscle spindle and its role
bundle of modified skeletal muscle fibres (intrafusal fibres) enclosed in connective tissue capsule. Intrafusal fibres detect stretch and initiate reflex which causes the muscle to contract to reduce the danger of over stretching
describe the golgi tendon organ and its role
small bundles of tendon (collagen) fibres enclosed in a layered capsule with the terminal branches of a large diameter (mechanoreceptive Ib) , ib aafernt ,afferent fibre intertwined with collagen bundles. Stimulated when the associated muscle contracts or is stretched. Sets up reflex causing muscle to relax and removing stimulation. Senses changes in tension/force.
how does the muscle spindle work?
- When a muscle is stretched passively the spindle is activated
- increasing firing of AP and so initiates a reflex causing mulches to contract.
- When the muscle contracts and shortens it is switched off.
- Protects muscle being overstretched
what is the knee-jerk reflex pathway an example of and how does it work
muscle spindle pathway
- This is a monosynaptic stretch reflex:
- Stretching of the muscle stretches the spindle -Striking the patellar ligament with a reflex hammer just below the patella stretches the intrafusal fibres of the muscle spindle in the quadriceps muscle activates them resulting in increased discharge of the sensory nerves.
- the stimulus produces impulses in sensory afferent fibres (type Ia) This results in increased firing of the motor neurone and the muscle contracts.
- No spinal interneurone is involved in this case- only at the level of L4 in the spinal chord, independent of higher centers
- alpha-motoneurone conducts an efferent impulse back to the quadriceps muscle, triggering contraction. This contraction, coordinated with the relaxation of the antagonistic flexor hamstring muscle causes the leg to kick-involves inhibitory interneurone in relaxation of the antagonistic hamstring muscle
- The effect is to dampen the stretch of the muscle.
- Specific for the muscle stretched
in what state is GTO active?
passive stretch and active contraction
what is the main function of the GTO
tension detector that protects muscle against excess load
Function to protect the muscle and connective tissue from injury
how is the GTO stimulated?
excessive tension during muscle contraction or passive stretch
what does the GTO do?
Causes a reflex inhibition of the muscle ……relaxation before tendon tension becomes high enough to cause damage
Helps prevent excessive muscle contraction or passive muscle stretch
what are the steps to GTO effect
- Sends AP down sensory afferent fiber
- Activates inhibitory interneurone
- Inhibits alpha motor neurone that supplies muscle
- Reduces no AP in neurone
- Muscle relaxes
- Excessive tension relived
- Same time activate sensory efferent neurons activate effterent tendon neurone causing it to contract as activates antagonistic muscle
what are the 2 types of synaptic junctions
- electrical synapses: direct passage of current via ions flowing through gap junctions from one cell to another
- Chemical synapses: release of vesicles containing chemical transmitter which has an effect on receptors on a pro-synaptic target cell.
where are electrical synapses found?
More common in invertebrate nervous systems, but do occur in human brain and may be involved in epileptiform activity.
what are gap junctions made of
Formed by interlocking connexon channels of adjacent neurones. Connexons comprise connexin proteins.
where are gap junctions found
present at points of contact between neurones with no synaptic cleft, only a very narrow gap between their membranes – ions and therefore current flow can pass directly from one cell to the next – resulting in direct, very fast electrical transmission between neurones.
what direction do ions flow in gap junctions
Current flow is usually unidirectional in electrical (rectifying) synapses in the mammalian CNS, but can be bidirectional (non-rectifying) in invertebrates
what is a chemical synapse and what does it do
Interface for chemical communication between neurones.
Release of transmitter from synaptic vesicles on arrival of an action potential in the terminal ‘bouton’ of neuronal axon
whats the process of chemical transmission
- action potential reaches the axon terminal of the presynaptic cell.
- AP triggers calcium entry causing release of neurotransmitter chemical from the storage vesicles, which fuse with the synaptic membrane.
- Vesicles are “docked” and “primed” before action potential arrives – kept close to the terminal plasma membrane, so that release is as rapid as possible upon increase in calcium concentration.
- Upon calcium influx and concentration, the vesicle and plasma membranes merge
- the contents of the vesicles are released in to the synaptic cleft.
- Probability of release – a vesicle either will or won’t be released. The probability of release can be increased
what is a NT
A substance that is released at a synapse by one neurone that affects another cell, either neuron or effector organ, in a specific manner and have a physiological action on specific receptors on a target cell
what is neuromodulator
a substance that is released and modifies the action of a transmitter, but doesn’t have a direct action itself
what is neuroactive substance
– a neutral term if a substance is known to have an effect in the CNS but its precise action is not known
what is the most common NT
Acetylcholine
name some amine NT
Dopamine (DA) Noradrenaline (Norepinephrine)(NA) Adrenaline (Epinephrine) Histamine Serotonin (5-hydroxytryptamine 5-HT)
name some AA NTs
Gamma-aminobutyric acid (GABA-inhibitory)
Glutamate (Glu)-ecitory
Glycine (Gly)-inhibiotry
name some peptide NTs
Dynorphin Enkephalins Neuropeptide Y (NPY) Calcitonin gene-related peptide (CGRP) Somatostatin Galanin Substance P (SP) Thyrotropin-releasing hormone (TRH) Vasoactive intestinal polypeptide (VIP)
how does Ca influx lead to release of transmitter
- Action potential arrives at synaptic terminal causing depolarization.
- Voltage-gated Ca2+ channels are opened by depolarization and Ca2+ ions rush into the terminal.
- Entry calcium into terminal= vesicles move to active zone terminal= fuse with membrane and release contents into synapse
- Taken into via endocytosis
what are active zones?
specialised areas on presynaptic membrane that guide the vesicles towards the membrane
what does binding of a NT to the receptor cause?
conformational change in the receptor proteins, and the protein functions differently.
what are the 2 NT receptors?
- Ionotropic receptor
- Metabotropic receptors
what is a ionotropic receptor?
- cluster of similar subunits forming ion channels, that depolarise or hyper-polarise the postsynaptic cell (fast responses): depending on the kind of postsynaptic cell different affect
- when ligand binds: conformational change that briefly opens the pore and ions pass through to cause a rapid change in the resting potential of the underlying cytoplasm
- mostly 4 or 5 similar protein subunits arranged around a central pore that is normally closed to ion movements
what is a metaotropic receptor?
is a 7-transmembrane molecule coupled to intracellular proteins that transduce a signal to cell interior (slow responses)
- long protein molecules, mostly crossing the cell membrane 7 times
- no ion pore
- ligand binds: conformational change in the molecule that causes the intracellular part to interact with a G-protein that then sets off a chain of intracellular events
what happens when glutamate or acetlycholine binds to receptor?
- influx Na+ ions giving rise to an excitatory post-synaptic potential (EPSP)- can result in formation of AP in postsynaptic cell
- EPSPs depolarise cell brining it closer to threshold potential and may initiate an AP
what happens when inhibitory NT GABA and glycine binds to inhibitory transmitter receptors?
-associated with cl channels
efflux of K+ or influx of Cl- causing a net outward current. This results in an inhibitory postsynaptic potential (IPSP) bringing the postsynaptic cell further away from the threshold for firing action potentials – i.e. hyperpolarising it as it beings negative charge in - harder to fire AP
if more transmitter is released what effect does this cause?
more ion channels open (greater conductance), the greater the current flow and so the greater the EPSP or IPSP, i.e. summation of individual channel postsynaptic potentials. One action potential leading to release of transmitter results in only an EPSP or IPSP. Many action potentials (e.g. From multiple synapses on same postsynaptic neurone) cause the threshold for firing to be reached and so an action potential is initiated in the postsynaptic neurone
give 5 features of the excitory post synaptic potentials?
No threshold
Decrease resting membrane potential
i.e. closer to threshold for depolarization
Graded in magnitude
No refractory period
Can summate (ie. add up)inhibitory post synaptic potentials?
No threshold
Hyperpolarize post synaptic membrane
Increase membrane potential
i.e. moving it further from threshold for depolarization- harder to fire AP= silence cell
No refractory period
Can summatewhat is a motor unit?
-consists of the motor nerve and all the muscle fibres innervated by that nerve.
how do muscle fibers in a motor unit contract?
all the muscle fibers in a motor unit contract together when the motor nerve fires
what does the size of motor unit depend on?
function of muscle
what is 1:1 transmission?
A chemical transmission which is designed so that every presynaptic action potential results in a postsynaptic one
corresponding muscle AP for AP being transmitted down the nerve
does neuromuscular transmission have a time delay ?
yes
inherent delay 0.5-1ms
unidirectional
do drugs effect the neuromuscular transmission?
yes and other factors due to various steps in transmission
what is the neuromuscular junction and what are the specialised regions of prejunctional and postjunctional?
a specialised region prejunctional: large SA- for NT to be released lots of mitochondria lots of vesicles
postjunctional:
indentations= increase SA exposed to motor end plate
