L17: Neurons Flashcards
What is the function of Purkinje cells (found in the cerebellum, heart)?
Conduct nerve impulse for contraction
What is a spinal interneuron?
- Important for reflexes;
- Form motor responses without the cortex.
What is a sensory neuron?
Receive nerve impulses
What is a motor neuron?
Relay nerve outputs
Describe resting membrane potential (RMP)
A potential charge difference across the membrane of all cells
What is RMP in nerve cells?
-70mV
At RMP, what is the difference in charges across the membrane?
Inside (ICF) is NEGATIVE to outside (ECF) i.e. polarised
How is RMP maintained?
Na-K pump contributes by moving 3 Na+ OUT and 2 K+ IN
What does a hyperpolarising current do?
Moves the membrane potential further from 0
What does a depolarising current do?
Moves the membrane potential closer to 0, i.e. leads to depolarisation of neuron
What is the intensity of the output dependent on?
Action potential frequency
What is the threshold potential?
-55mV
What happens at threshold potential?
- Opening of voltage-gated sodium channels;
- Influx of sodium.
What does an influx of sodium cause?
Depolarisation
When do voltage-gated sodium channels close?
+35mV
What happens at +35mV?
- Voltage-gated sodium channels close;
- Voltage-gated potassium channels open;
- K+ leave, taking positive charge with it;
- Start of repolarisation (ICF becomes more negative).
What is repolarisation?
Rebalance of ions back to -70mV MP
What is the refractory period?
When a membrane repolarises, no action potentials can be generated in this period (inactivation of Na+ channels)
Why can nerve impulses only move in one direction?
Refractory period
How do local anaesthetics work?
By blocking the Na+ channels, so no action potentials can be generated
How does the speed of action potentials differ with the diameter and width of an axon?
Longer or wider axons conducti
How does myelination effect the conduction speed?
Increases
How do nodes of Ranvier (intervals within the myelin sheath) speed up electrical impulses?
- Axon is exposed to ECF;
- NOR are rich in ion channels where quick exchange can happen;
- Action potentials ‘jump’ (conduct) between NOR rather than along entire length of axon.
