Nervous impulses Flashcards
Name all the parts of a myelinated motor neurone:
Nodes of Ranvier, Schwann cells, Axon, Cell body, Dendrites, Myelin sheath.
What do the axon and dendrites do?
The axon is the single long fiber that carries away nerve impulses, whilst the dendrites carry action potentials towards the cell body.
What is the myelin sheath?
Made up of Schwann cells which are lipids that cover the axon. They are made up of lipids and therefore do not let charged ions or the impulse pass through.
What is the voltage across the membrane at resting potential?
-70mV
How is the resting potential maintained?
Sodium potassium pump actively transports 3 sodium ions out of the neurone for every 2 potassium ions that are transported in. The membrane is more permeable to potassium ions so potassium ions will diffuse through back out when there is a diffusion gradient.
What does a cell body do?
Contains all usual cell organelles. Produces proteins and neurotransmitters so has large amounts of rough endoplasmic reticulum (more ribosomes).
Explain the all or nothing principle:
If the depolarisation does not exceed -55mV (threshold potential) no action potential and therefore no impulse is formed (nothing). If -55mV is reached then action potential is produced and all will peak at 40mV. Bigger stimuli increase frequency, not size.
Describe the repolarisation and hyperpolarisation of action potential taking place in a Pacinian corpuscle:
When a potential of 40mV is reached sodium ion channels will close and potassium ion channels are opened. Potassium ions then diffuse out rapidly decreasing polarisation causing hyperpolarisation where the potential is less than -70mV. This is the refractory period. Resting potential is then established back at -70mV.
What is the refractory period?
The period of time after an action potential when the neurone can’t be excited.
Why is the all-or-nothing principle important?
Makes sure animals only respond to big enough stimuli, rather than responding to every single change in the environment which might overwhelm them.
Name three reasons why the refractory period is important:
- Ensures discrete impulses are produced
- Ensures action potential only goes forward in one direction
- It limits the number of impulse transmissions (no overreaction and no overwhelm).
Name three reasons why the refractory period is important:
- Ensures discrete impulses are produced.
- Ensures action potential only goes forward in one direction.
- It limits the number of impulse transmissions (no overreaction and no overwhelm).
Why does myelination speed up the action potential conductance?
Action potential jumps from node of Ranvier to node of Ranvier (saltatory conduction. It travels along the axon faster because it doesn’t have to generate an action potential along the full length, only at the nodes of Ranvier.
How does axon diameter affect the speed of conductance along the axon?
With a wider diameter, the speed of conductance increases because there is less leakage of ions and therefore action potentials travel faster.
How does temperature affect the speed of conductance along the axon?
Higher temperature speeds up conductance because the ions will diffuse faster and enzymes involved in respiration will work faster so more ATP for the sodium-potassium pump.
