What does synaptic transmission involve?
Signal transmission from nerve terminals to a
post-synaptic cell (e.g. another nerve, skeletal & smooth muscle, glandular tissue)
What are the 2 types of synapses?
- chemical (cholinergic)
- electrical
What happens at chemical synapses?
- 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
What happens at electrical synapses?
- 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
What happens at cholinergic synapses?
release acetylcholine (ACh) as the neurotransmitter
Where are cholinergic synapses located?
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
What are the 4 events at a cholinergic synapse?
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
What happens in step 1 at a cholinergic synapse?
- arrival of AP at synaptic terminal
- opening of voltage gated Ca channels
What happens in step 2 at a cholinergic synapse?
- entry of extracellular Ca2+ which
- stimulates exocytosis of ACh from synaptic vesicles
- ACh diffuses across synaptic cleft
What happens in step 3 at a cholinergic synapse?
- binding of ACh to receptors on post-synaptic membrane, which
- opens Na+ channels causing
- depolarisation of post-synaptic membrane (GP)
What happens in step 4 at a cholinergic synapse?
- removal of ACh within synapse by AChE which
- hydrolyses ACh to choline and acetate
- recycling of choline and new ACh formed with acetyl CoA
What toxins are associated with blocking cholinergic synapses?
- botulinum toxin (clostridium botulinum)
- curare (plant toxin)
- alpha-bungarotoxin (snake venom)
What drug is associated with blocking cholinergic synapses?
Neostigmine (acetylcholinesterase inhibitor)
What disease is associated with blocking cholinergic synapses?
Myasthenia Gravis (MG) (autoimmune disease)
