11 Muscle (Neuromuscular Junctions & Signalling)

Question 1

What is a neuromuscular junction?

Answer 1

a chemical synapse between the pre-synaptic terminal of a motor neuron and the post-synaptic membrane of a muscle fibre

Question 2

What is a motor unit?

Answer 2

a motor neuron and all of the muscle fibres that it innervates

Question 3

Which factors impact the strength of a muscle contraction?

Answer 3

The amount of motor units / muscle fibres recruited

the stimulus frequency (wave summation)

Question 4

what is the size principle of muscle fibre recruitment?

Answer 4

small muscle fibres contract first. as motor units with larger fibres are recruited, muscle contraction increases in strength

Question 5

what happens at a neuromuscular junction to initiate muscle contraction?

Answer 5

AP reaches axon terminal of pre-synaptic neuron

axon terminal releases neurotransmitter (AcH) into the synaptic cleft

AcH attaches to receptors in the muscle cell sarcolemma

chemical / ligand gated ion channels on the sarcolemma open

calcium diffuses into cell and cell depolarizes, generating an end plate potential

end plate potential generates an AP

AP travels along sarcolemma and into T tubules

terminal cisternae release calcium ions into sarcomere of myofibrils, initiating contraction