Neuromuscular junctions

Question 1

Label the image

Answer 1

Question 2

What happens at neuromuscular junctions (ACh)

Answer 2

ACh is chemical intermediary in transfer of excitation from nerve to muscle

Released in synaptic vesicles

ACh released into synaptic cleft where it combines with ACh receptors

Causes depolarisation of muscle cell

Then broken down by acetylcholinesterase

Question 3

What are T tubules

Answer 3

Conduct action potentials from cell surface to core of fibre

In direct contact with sarcoplasmic reticulum surrounding myofibrils

Question 4

Explain excitation contractile coupling

Answer 4

1. Action potential in T tubule
2. Opens Ca2+ channels in SR
3. Ca2+ released – causes more channels to open
4. Ca2+ pumped back into SR

Question 5

What is a motor unit

Answer 5

Single α-motor neuron & all corresponding muscle fibres it innervates

Size varies

Muscle to nerve ratio also varies

In contraction, smallest motor units are used first

Question 6

What are the receptors in muscles fibres

Answer 6

Muscle spindle:
Sensitive to stretch
Provide information on muscle length
Modified muscle fibres

Golgi tendon organ (GTO):
Monitor tension developed in muscle
Prevents damage during excessive force generation