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nerve and muscle Flashcards

1
Q

what does the CNS consist of?

A 
the brain (forebrain, midbrain and hindbrain)
spinal cord (31 segments)
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2
Q

what are the subunits of the PNS?

A

autnomic nervous system

somatic nervous system

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3
Q

what does the ANS do?

A

involunatry nervous system split into symapthetic and parasympathetic nervous system

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4
Q

what does the somatic nervous system do?

A

voluntaery nervous system,
has somatic, efferent motor neurones
innervates and contols voluntary, striated msucles and has sensory afferent neurones

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5
Q

what does the sympathetic nervous system do?

A

fight or flight response

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6
Q

what does the parasympathetic nervous system do>

A

rest and digest response

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7
Q

what are glial cells?

A

support cells of neurones

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8
Q

what do gial cells do?

A

regulate neurone metabolism and function
repari and recover them from njury
regulate blood - brain barriers
destroy pathogens and remove dead neurones

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9
Q

give examples of glial cells in the PNS?

A

satellite cells and schwann cells

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10
Q

give examples of glial cells in the CNS

A

epideymal cells
oligodendrocytes
ostrocytes
microglia

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11
Q

describe the myelination of axons

A

olgiodendrocytes in the CNS
schwann cells in the PNS
wrap around the axon in spiral of concentric layers of fatty myelinated membrane
insulation for axons to aid impulse transmission
the gaps between the adjacent cells are called the nodes of ranvier

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12
Q

how are nerve fibres classified?

A

based on their diameter and conduction velocity

one classifcation system refers to motor fibres and non-msucle sensory neurones, A, B, C

another refers to sensory fibres from muscles - I,II,III,IV

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13
Q

describe the pathway of sensory info from the PNS to the CNS

A

through somatic sensory neurones to dorsal root

to interneurons

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14
Q

describe the pathway of sensory info from the CNS to PNS

A

from CNS to ventral root to somatic motor neurone

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15
Q

what are some differences between somatic and autonomic pathways?

A

somatic has sensory and motor pathways, autonomic only has motor pathways

somatic controls msucles and movement, autonomic controls internal organs and glands

somatic has no subdiivisons where as autonomic is split into symapthetic and parasympathetic

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16
Q

how are sensory receptors classified?

A

classified based on location and stimulus

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17
Q

where are muscle spindles found, what stimulates them?

A

found in skeletal muscle.

stimulated by stretch

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18
Q

where are pancian corpuscles found and what stimulates them?

A

deep in dermis, tendons, joints and genetalia

vinbrations, deep pressure

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19
Q

where are meissners orkrauses bulbs found and what stimulates them?

A

oral muscus, lips, genetalia, fingertips

touch, light vibration

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20
Q

what are refuni organs foudn and what stimulates them?

A

deep in dermis, ligaments, joint capsule

stretch and deep pressure

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21
Q

state the order in the spinal reflex pathway

A 
sensory receptor
sensory neurone
integration centre 
motor neurone 
effect
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22
Q

how is action potential generated?

A

Na+ channels open and Na+ enters the cell. this causes the membrane potential to rise towards zero

if the threshold potential is reached, voltage gated Na+ channels open and more Na+ flows into cell action potential spike

Na+ channels close when Na+ equilibrium potential is reahced. voltage gated K+ channels open and K+ flows out of the cell = membrane potential reverses

K+ ions continue to flow out of cell while Na+ channels close and hyperpolrisation results

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23
Q

how is impulse conducted along a myelinated neurone?

A

nodes of ranvier are the only area where current can pass through the membrane, so the only area where the membrane can depolarise

the impulse travels in jumps not in slow flow

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24
Q

describe the spinal reflex pathway from muscles

A

stretching of the muscle stretches muscle spindle = increased discharge of the sensory enrves

this results in increased firing of motorneurone and the muscle contracts

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25
Q

what are the 2 types of synapses?

A

electrical and chemical

26
Q

how does an electrical synapse work?

A

direct passage of current via ions through gap junctions

formed by interlocking connexon channels of adjacent neurones

27
Q

how do chemical synapses work?

A

release of vesicles contraining chemical transmitter which has an effect on receptors on a target cell

28
Q

describe chemical transmission across a synapse

A

action potential arrives at the synaptic terminal causing depolarisation

voltage gated Ca2+ chennels are opened by depolarisation and Ca2+ ions rush into the terminal

rise in Ca2+ causes vesicles to move to active zone and undergo fusion with the membrane and release contents by exocytosis

transmitter bidns to post synaptic receptors and ion channels open - excitation (EPSP) or inhibition (IPSP) occurs

29
Q

what are the 2 types of receptor in synapses?

A

ionotropic receptors

metabotropic receptors

30
Q

what are ionotropic receptors

A

a cluster of similar subunits forming ion channels that depolarise or hyperpolarise the presynaptic cell (fast response)

31
Q

what are metabotropic receptors?

A

7-transmembrane molecule coupled to intracellular proteins that transduce a signal to cell interior (slow responses)

32
Q

how does postsynaptic excitation occur?

A

binding of released transmitter to a ligand gated ion channel receptor cyases opening of channel pore

bidning of glutamate or acetylcholine to receptors causes influx of Na+ = EPSP, depolarising cell towards threshold potential = AP

33
Q

how does postsynaptic inhibition work?

A

binding of GABA or glycine to their receptors causes influx of Cl- ions giving rise to an inhibitory post synaptic potential (IPSP) in post synaptic cell.

yperpolarise cell and make reaching AP less likely

34
Q

mechanism of skeletal muscle contraction

A

Ca released by sarcoplasmic reticulum in response to depolarisation

Ca binds to TnC region on troponin

troponin changes shape, moving tropomyosin, exposing binding site on actin filament

attachment - myosin head with ATP binds actin

power stroke - mysoin head bends, ulling along the actin filament, ADP and Pi are released

35
Q

What is the crossbridge theory?

A

myosin head is attached to actin, forming a cross bridge
inorganic phosphate generated in previous contraction cycle is released intitiating the power stroke - the mysoin head pivots and pulls actin along and ADP is released

as new ATP binds to myosin head, the crossbridge weakenns and detaches

as ATP splits to ADP and Pi, the mysoin head is energised

36
Q

what are 3 factors that affect the force of muscle contraction

A

number of action potentials per second

amount of overlap between thick and thin filaments

number of motor units recruited

37
Q

give a genetic muscle disorder

A

muscular dystrophy

38
Q

give 2 inflammation muscle disorder

A

myositis

polymyalgia rheumatica

39
Q

give 3 neurological msucle disorders

A

multiple sclerosis
myasthenia gravis
parkinsons disease

40
Q

what does the motor unit consist of?

A

motor nerve and all muscle fibres innervated by that nerve

41
Q

describe the release and reception of ACh at the NMJ

A
  1. AP arrives and depolarises terminal bouton
  2. opening of voltage gated Ca2+ channels
  3. influx of Ca2+ in synaptic bouton
  4. fusion of vesicles and release by exocytosis
  5. binding of ACh to nicotinic receptors on muscle cell membrane
  6. receptor activation = Na+ enters#
  7. membrane depolarisation
42
Q

how are nicotinic receptors activated?

A

when 2 ACh molecules bind to it - one on each bidning site on the 2 alpha subunits

43
Q

describe the breakdown of ACh

A

ACh is hydrolysed to choline and acetate by acetylcholinesterase - bound mainly to basal lamina

choline is taken up by nerve terminal by cotransport with Na+

vesicles become part of membrane - endocytosis, clathri coated and internalised, fuses with endosome - new vesicles formed by budding new cycle

acitic acid excreted as waste and broken down into water and carbon dioxide

44
Q

state 3 types of drugs used on NMJ?

A

non-depolarising competitive nAChR antagonist
choline esterase inhibitors
depolarising nAChR agonist

45
Q

give an example of a nondepolarising competitive nAChR antagonist drug?

A

tubocurarine

46
Q

give 2 examples of choline esterase inhibitor drug

A

neostigimine and endophosim

47
Q

how does tubocurarine work?

A

competes with ACh for nictotinic receptor sites

reversed by AChE inhibitors and hydrolysed by circulating esterases

48
Q

what is neostigimine used for ?

A

treatment of myothenia gravis

49
Q

what is endophosism used for?

A

diagnosis of myithenia gravis

50
Q

how does succinylcholine work?

A

persistant depolarisation of neuromuscular junction

51
Q

what is lambert eaton syndrome?`

A

rare autoimmune response which inhibits Ca2+ channels and thereby reducing ACh release

52
Q

describe the structure of cardiac muscle

A 
striated
branched
interconnected
cells are smaller than skeletal cells
rich in glycogen, myoglobin and mitochondria
53
Q

describe the ultrastructure of cardiac muscle

A

each cell contains 1-2 centrally located nuclei
mitchondria comprise 30% of cell volume
intercalated discs are specialised cell-cell contacts with desmosomes acting as mechanical coupling and gap junctions allowing the spread of action potential

54
Q

describe ventral action potential

A

depolarisation - greatly increased membrane permeability to Na
partial repolarisation - loss of Na and K conductance
plateau - slow inward flow of Ca2+ and some movement of Na
repolarisation - fall in Ca conductance and rise in K conductance - becomes negative again and NA/K pump re-establishes distribution
interva between AP when ventricular muscles are at their stable resting membrane potential

55
Q

describe cardiac excitation

A

Action potential invades T tubules

voltage gated L-type Ca2+ channels opne in T tubule membrane

Ca2+ enters through L-type Ca channels and triggers further Ca release from sarcoplasmic reticulum

Ca binds to troponin-C and contraction proceeds in same way as muscles

56
Q

what 2 hormones control autonomic regulation of heart rate

A

acetylcholine and noradrenaline

57
Q

how does acetycholine control autonomic regulation of heart rate

A

via parasympathetic nerves

  1. stimulates vagus nerve
  2. decreases SA node rate
  3. decreases heart rate
58
Q

how does noradrenaline control autonomic regulation of heart rate?

A

via sympathetic nerves

  1. increases rate of depolarisation of pacemaker cells of SA node
  2. develop AP at an increased rate
  3. increases heart rate
59
Q

describe the structure of smooth muscle

A 
2 sheets of closely opposed fibres
smaller fibres than skeletal muscles 
spindle sahped with single central nucleus
no sarcomere or t tubules
more actin than myosin
caveosae
actin attached to dense bodies
60
Q

describe the contraction of smooth muscle

A
  1. Ca binds to calmodulin (not troponin) and interacts with myosin kinase to phosphorylate myosin
  2. phosphorylation gives tension
  3. when Ca falls then Ca-calmodulin complex dissociates = inactivates myosin kinase
  4. cross bridgs are dephosphorylated by myosin phophatase

IMS (14 decks)

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