Physiology: skeletal neuromuscular junctions

Question 1

what is skeletal muscle innervated by

Answer 1

fast conducting alpha-motor neurones with myelinated axons in the spinal cord/brain stem

Question 2

describe what the terminal bouton is

Answer 2

it is where the multiple fine branches of the neurones that innervate skeletal muscle end

Question 3

what type of synapse and where does the terminal bouton synapse

Answer 3

forms a chemical synapse with the muscle membrane at the neuromuscular junction, in end plate region of skeletal muscle

Question 4

what does action potential reaching the terminal bouton cause

Answer 4

opening of voltage-gated Ca2+ channels and release of transmitter, acetylcholine(ACh)

Question 5

what are the key features of the neuromuscular junction

Answer 5

terminal bouton, synaptic vesicles, synaptic cleft and the end plate region

Question 6

what type of cell surrounds the terminal bouton

Answer 6

schwann cell

Question 7

describe the function of synaptic vesicles

Answer 7

concentration and storage of ACh

Question 8

describe how ACh is released into the synaptic cleft

Answer 8

Ca2+ dependant release by exocytosis

Question 9

where is ACh synthesised

Answer 9

in cytoplasm of terminal bouton

Question 10

describe the action of acetycholinesterase(AChE)

Answer 10

rapid termination of transmitter action, within synaptic cleft

Question 11

by what and what is ACh synthesised from

Answer 11

from choline and acetyl coenzyme A(acetyl CoA)

by choline acetyltransferase

Question 12

what is ACh concentrated by

Answer 12

vesicular ACh transporter, in vesicles

Question 13

how many ACh molecules activate each nicotinic ACh receptor

Answer 13

2

Question 14

describe the structure of nicotinic ACh receptors

Answer 14

pentamers of glycoprotein subunits, surrounding a central cation selective pore

Question 15

what is an (depolarising)end plate potential generated by

Answer 15

simultaneous opening of many nicotinic ACh receptors

Question 16

describe what happens to a nicotinic ACh receptor when ACh binds

Answer 16

the gate, contained in the pore, is opened

Question 17

describe what a miniature end plate potential is

Answer 17

the electrical response to one quantum of transmitter

Question 18

what is the result of many miniature end plate potentials

Answer 18

summate to produce end plate potential, a graded(electrotonic) response

Question 19

what does an end plate potential that reaches threshold trigger

Answer 19

voltage gated Na+ channels to open and an ‘all or none’ propagated action potential that initiates contraction
(this always occurs normally)

Question 20

how does the muscle action potential cause contraction

Answer 20

by release of Ca2+ from intracelullar stores