How Nerves Work 5 Flashcards
What are most synapses?
Chemical
What is the basis of a chemical synapse?
An electrical signal (AP) is turned into a chemical signal that is squirted onto the post synaptic cell to evoke a new electrical signal
Where is muscle contraction triggered?
Triggered by AP in sacrolemma
What occurs in the presynaptic cell at a NMJ?
- AP in motor neurone
- Opens voltage gated Ca channels in presynaptic terminal
- Triggers fusion of vesicles
- Acetylcholine released
- Diffuses across synaptic cleft
What happens after the ACh diffuses across the cleft?
- It binds to ACh (nicotinic) receptors
- Opens ligand gated Na/K channels
- Evokes graded (local) potential (end plate potential)
- Always depolarises adjacent membrane to threshold
- Opens voltage gated Na channels which evokes a new AP
- ACh removed by acetylcholinesterase
What does tetrodotoxin do?
Blocks Na channels and so blocks the AP
What does joro spider toxin do?
Blocks Ca channels and so stops transmitter release
What does botulinum toxin do?
Disrupts the release machinery and so blocks transmitter release
What does curare do?
Blocks ACh receptors and so prevents the end plate potential
What does anticholinesterase do?
Blocks ACh breakdown and so increases transmission at the NMJ
How many neurotransmitters can be used at CNS synapses?
A range each with several receptors
What postsynaptic potentials are therefor CNS synapses?
- Fast EPSPs (ionotropic)
- Slow EPSPs (metabotropic)
- Fast IPSPs
- Slow IPSPs
How does the anatomical arrangement of synapses vary?
- NMJ does not change
- CNS synapses can be axo-somatic, ax-dendritic or axo-axonal
What is the synaptic connectivity of NMJ?
Always motor neurone to muscle cell
What is the synaptic connectivity of CNS synapses?
- Convergence
- Divergence
- Feedback inhibition
- Monosynaptic vs polysynaptic pathways
