Physiology: Skeletal Muscular Junction

Question 1

define motor unit

Answer 1

neurone and number of fibres that it innervates

Question 2

are motor neurones myelinated or unmyelinated near the muscle

Answer 2

unmyelinated (are myelinated further up)

Question 3

what is the terminal ending of the motor fibres called (where it forms a chemical synapse with muscle membrane at NMJ)

Answer 3

bouton

Question 4

schwann cell

Answer 4

cell in PNS that forms myelin sheath around neuronal axons

Question 5

what do synaptic vesicles contain

Answer 5

ACh

Question 6

what receptors are located at regions of the junctional folds opposite active zones

Answer 6

nicotinic ACh receptors

Question 7

describe the pre synaptic process

Answer 7

choline is transported into the terminal

Ach is synthesised from choline and acetyl coenzyme A by the enzyme choline acetyl transferase

Ach is concentrated in vesicles by vesicular ACh transporter

Question 8

what happens when AP arrives at terminal

Answer 8

depolarisation and opening of voltage activated Ca channel allowing Ca to enter terminal.

Ca allows Ach to diffuse into synaptic cleft to activate post synaptic nicotonic ACh receptors

Question 9

describe the post synaptic process

Answer 9

activated nicotinic ACh receptors allow Na influx into muscle cell and K efflux

Na influx > K efflux as driving force for Na is greater = end plate potential generated

Question 10

what is the miniature end plate potential

Answer 10

the electrical response to one quantum of transmitter due to activation of nicotinic ACH receptors

many mepps produce epp

Question 11

what does a epp that exceeds threshold trigger

Answer 11

all or none AP that initiates contraction