M&R 4.2 - Conduction of the Nerve Impulse Flashcards Preview

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Flashcards in M&R 4.2 - Conduction of the Nerve Impulse Deck (14):

Describe the process of propagation of the nerve impulse

- Depolarisation causes transmembrane currents (positive areas in membrane promotes a positive charge in adjacent regions of the membrane)

- Further current spreads = faster velocity current


What are the factors that affect membrane conduction? (3)

- High membrane resistance

- Large axon diameter

- Low membrane capacitance


What is the effect of a high membrane resistance on conduction? Why?

- Increased resistance = Increased potential difference across membrane

- Increased voltage = Increase Na+ channels open

- Easier to reach threshold = Easier to generate an AP

- Increases conduction velocity


What is the effect of a large axon diameter on membrane conduction? Why?

- Results in a lower cytoplasmic resistance = Increased current

- Action potential travels further = Increased conduction velocity


What is membrane capacitance?

The ability of a membrane to store charge


What is the effect of a low membrane capacitance on membrane conduction? Why?

- Low capacitance = less time taken to charge

- Increases the conduction velocity


What is the effect of myelination on conduction velocity? Why?

- Increases conduction velocity

- Reduces capacitance
- Increases membrane resistance


What is saltatory conduction? Why does it happen?

- Action potential 'jumps' between Nodes of Ranvier

- Myelin sheath is a good insulator = depolarises local circuit currents at next node

- Reach threshold = action potential


How do myelinated axons differ to unmyelinated axons?

- Nodes of Ranvier are dense in Na+ Vg Channels

- Unmyelinated have an equal distribution


What forms myelin? How?

- Schwann Cells in PNS

- Oligodendrocytes in CNS

- Wrap around axons to in plasmalemma until it becomes myelin


What is Multiple Sclerosis caused by?

- Autoimmune

- Myelin is destroyed in certain areas of the CNS


What are the effects of Multiple Sclerosis?

- Can't conduct action potentials properly

- Decreases conduction velocity (completely or only some can be transmitted)


Describe the action of Procaine (a local anaesthetic)

- Binds and blocks Na+ channels when open

- Have a higher affinity to inactivated Na+ channels

- Prevents generation of action potentials


What is the order of nerves in which local anaesthetics block conduction?

- Small myelinated axons

- Non-myelinated axons

- Large myelinated axons

(affect sensory before motor)

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