NMJ + Synapses

Question 1

What happens when the propagation of the action potential reaches the presynaptic terminal?

Answer 1

• Action potential opens voltage-gated Ca2+ channels at presynaptic terminal
• Ca2+ influx → vesicle exocytosis to release neurotransmitters

Question 2

What happens after neurotransmitters are released into the synaptic cleft?

Answer 2

• NT binds to receptors on post-synaptic membrane

- Receptors modulate post-synaptic activity

Question 3

What happens after the neurotransmitter is detected at the post synaptic terminal?

Answer 3

Neurotransmitter Reuptake - Neurotransmitter dissociates from receptor and can be:
→ Metabolised by enzymes in synaptic cleft
→ Recycled by transporter proteins

Question 4

What is autocrine signalling?

Answer 4

Cell secretes an autocrine agent (hormone) or chemical messenger that binds to autocrine receptors on the same cell

Question 5

What is paracrine signalling?

Answer 5

Cell produces a signal to cause changes to nearby cells

Question 6

What is a axodendritic synapse?

Answer 6

connection to neuronal dendrite

Question 7

What is a axosomatic synapse?

Answer 7

connection to neuronal soma

Question 8

What is a axoaxonic synapse?

Answer 8

connection to neuronal axon

Question 9

What is a neuromuscular junction?

Answer 9

specialised structure incorporating the axon terminal & muscle membrane allowing unidirectional chemical communication between peripheral nerve & muscle

Question 10

What kind of cell signalling happens at the NMJ?

Answer 10

Paracrine signalling

Question 11

What is the purpose of the NMJ?

Answer 11

Place of paracrine signalling from the nervous system, determines whether the muscle contracts or relaxes!

Question 12

What neurotransmitter is used at the NMJ?

Answer 12

Acetyl choline

Question 13

What receptors are at the post synaptic terminal of the NMJ?

Answer 13

nicotinic ACh receptors (nAChR) on the sarcolemma → changes the end-plate potential

Question 14

What happens after Ach binds to the receptors at the post synaptic terminal of the NMJ?

Answer 14

• Miniature end-plate potential causes release of ACh in vesicles into the post-synaptic cell
• This causes ion channels to open and allows sodium and other cations to flow across the membrane into the muscle cell
• The flow of sodium ions across the membrane into and potassium ions out of the muscle cell generates an action potential which travels to the myofibril and results in muscle contraction

Question 15

What is sarcoma?

Answer 15

• skeletal muscle membrane
• contains nACh receptors
• T-tubules are continuous with the sarcolemma + closely connected to the sarcoplasmic reticulum; action potential travels through these tubules

Question 16

What is the sarcoplasmic reticulum?

Answer 16

• surrounds myofibrils (contractile units of muscle)

- involved in Ca2+ storage + release following depolarisation of sarcolemma

Question 17

Name 3 disorders of the NMJ?

Answer 17

• Botulism
• Myasthenia Gravis (MG)
• Lambert-Eaton myastenic syndrome (LEMS)

Question 18

What is botulism?

Answer 18

• Botulinum toxin (BTx): causes irreversible disruption of stimulation-induced ACh release from the
  presynaptic nerve terminal

Question 19

What is myasthenia gravis?

Answer 19

• Autoimmune disorder where antibodies are directed against ACh receptor
• Causes fatiguing weakness (i.e. becomes more pronounced with repetitive use)

Question 20

What is lambert-eaton myastenic syndrome?

Answer 20

• Autoimmune disorder where antibodies are directed against voltage-gated Na+ channels