How Nerves Work 5 Flashcards

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1
Q

What are most synapses?

A

Chemical

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2
Q

What is the basis of a chemical synapse?

A

An electrical signal (AP) is turned into a chemical signal that is squirted onto the post synaptic cell to evoke a new electrical signal

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3
Q

Where is muscle contraction triggered?

A

Triggered by AP in sacrolemma

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4
Q

What occurs in the presynaptic cell at a NMJ?

A
  • AP in motor neurone
  • Opens voltage gated Ca channels in presynaptic terminal
  • Triggers fusion of vesicles
  • Acetylcholine released
  • Diffuses across synaptic cleft
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5
Q

What happens after the ACh diffuses across the cleft?

A
  • 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
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6
Q

What does tetrodotoxin do?

A

Blocks Na channels and so blocks the AP

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7
Q

What does joro spider toxin do?

A

Blocks Ca channels and so stops transmitter release

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8
Q

What does botulinum toxin do?

A

Disrupts the release machinery and so blocks transmitter release

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9
Q

What does curare do?

A

Blocks ACh receptors and so prevents the end plate potential

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10
Q

What does anticholinesterase do?

A

Blocks ACh breakdown and so increases transmission at the NMJ

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11
Q

How many neurotransmitters can be used at CNS synapses?

A

A range each with several receptors

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12
Q

What postsynaptic potentials are therefor CNS synapses?

A
  • Fast EPSPs (ionotropic)
  • Slow EPSPs (metabotropic)
  • Fast IPSPs
  • Slow IPSPs
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13
Q

How does the anatomical arrangement of synapses vary?

A
  • NMJ does not change

- CNS synapses can be axo-somatic, ax-dendritic or axo-axonal

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14
Q

What is the synaptic connectivity of NMJ?

A

Always motor neurone to muscle cell

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15
Q

What is the synaptic connectivity of CNS synapses?

A
  • Convergence
  • Divergence
  • Feedback inhibition
  • Monosynaptic vs polysynaptic pathways
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16
Q

Why are CNS synapses more complex than NMJ?

A
  • Range of neurotransmitters
  • Range of postsynaptic potentials
  • Small potentials
  • Variations on anatomical arrangement
  • Variations on connectivity of neurones