Synaptic Transmission

Question 1

What does synaptic transmission involve?

Answer 1

Signal transmission from nerve terminals to a
post-synaptic cell (e.g. another nerve, skeletal & smooth muscle, glandular tissue)

Question 2

What are the 2 types of synapses?

Answer 2

• chemical (cholinergic)
• electrical

Question 3

What happens at chemical synapses?

Answer 3

• signal transfer from pre-synaptic cell to post-synaptic cell
• release of a neurotransmitter which activates and binds to a receptor on the surface of the post-synaptic cell

Question 4

What happens at electrical synapses?

Answer 4

• direct transfer of electrical signals through gap junctions (pores in membrane between cells), which allow the passage of ions
• therefore charge some areas of the brain, eye, cardiac muscle, smooth muscle

Question 5

What happens at cholinergic synapses?

Answer 5

release acetylcholine (ACh) as the neurotransmitter

Question 6

Where are cholinergic synapses located?

Answer 6

very common type of synapse located at:
- skeletal muscle (NMJ)
- many synapses in the CNS
- all nerve-nerve synapses in the ANS
- all neuro-effector synapses in the parasympathetic NS

Question 7

What are the 4 events at a cholinergic synapse?

Answer 7

1) arrival of AP in presynaptic neurone
2) ACh diffuses across synaptic cleft
3) ACh binds to receptors at postsynaptic neurone
4) removal of ACh

Question 8

What happens in step 1 at a cholinergic synapse?

Answer 8

• arrival of AP at synaptic terminal
• opening of voltage gated Ca channels

Question 9

What happens in step 2 at a cholinergic synapse?

Answer 9

• entry of extracellular Ca2+ which
• stimulates exocytosis of ACh from synaptic vesicles
• ACh diffuses across synaptic cleft

Question 10

What happens in step 3 at a cholinergic synapse?

Answer 10

• binding of ACh to receptors on post-synaptic membrane, which
• opens Na+ channels causing
• depolarisation of post-synaptic membrane (GP)

Question 11

What happens in step 4 at a cholinergic synapse?

Answer 11

• removal of ACh within synapse by AChE which
• hydrolyses ACh to choline and acetate
• recycling of choline and new ACh formed with acetyl CoA

Question 12

What toxins are associated with blocking cholinergic synapses?

Answer 12

• botulinum toxin (clostridium botulinum)
• curare (plant toxin)
• alpha-bungarotoxin (snake venom)

Question 13

What drug is associated with blocking cholinergic synapses?

Answer 13

Neostigmine (acetylcholinesterase inhibitor)

Question 14

What disease is associated with blocking cholinergic synapses?

Answer 14

Myasthenia Gravis (MG) (autoimmune disease)