6.2.1: Nerve impulses Flashcards
What are the structures of a myelinated motor neurone? (8)
1) Nucleus
2) Dendrites
3) Cell body
4) Axon
5) Myelin sheath
6) Schwann cell
7) Terminal end
8) Nodes of Ranvier
Function of dendrites
Thin extensions that carry nerve impulses towards the cell body. Receive impulses from surrounding cells
Function of cell body
Contains nucleus and ribosomes which forms neurotransmitters (proteins)
Function of axon
Conductive, long fibre that carries nerve impulses along motor neurone
Function of schwann cells
Wrap around the axon to form myelin sheath which is a lipid sp doesn’t allow ions to pass through.
Function of nodes of ranvier
Intervals along myelin sheath which speed nerve impulse transmission
Functions of terminal end
Ending of axon, divides into branches
What is a resting potential?
The difference in electrical charge between the inside and outside of a neurone
What is the resting potential and why?
- 70mV
There is more positive Na+ and K+ outside compared to the inside of the neurone which is more negative
How to establish and maintain resting potential?
- The sodium-potassium pump pumps 2 K+ ions in and 3 Na+ ions out
- This creates an electrochemical gradient and results in K+ diffusing out and Na+ diffusing in
- Membrane is more permeable to K+ ions
What is an action potential?
Neurones voltage increases beyond a set point from the resting potential which generates a nerve impulse
What is depolarisation?
Increase in voltage due to neurone membrane becoming more permeable to Na+
What is repolarisation?
Once potential difference reaches +40mV the Na+ voltage gated channel proteins close and the K+ voltage gated channel proteins opens
- More K+ inside axon then out so K+ diffuse out down the concentration gradient
What is hyper polarisation?
The K+ ion channel protein remain open longer than needed to reach resting potential, making the inside of the cell even more negative
What is the all or nothing principle?
- Any stimulus that triggers depolarisation will always peak at the same maximum voltage. Bigger stumble will increase the frequency of action potentials
- If depolarisation doesn’t exceed -55mV then action potential is not produced
Why is the all or nothing principle important for animals?
So animals only respond to large enough stimuli rather than every slight change in the environment, which would overwhelm them
What is the refractory period?
The time taken to restore the resting material
Why is the refractory period important (3)
1) Produces discrete impulses so another action potential can’t be formed until the period is over to separate each one
2) Ensure action potential travels in one direction. If not would prevent aa repose
3) Limits number of impulses which would overwhelm senses
What are the three factoring affecting speed of conduction?
1) Myelin sheath and saltatory conduction
2) Temperature
3) Axon diameter
How does saltatory conduction affect the speed of transmission?
- Impulses jumps between the nodes of ranvier
- Myelin sheath provides electrical insulation along the axon
- Electrical impulses depolarises each node of ranvier in turn
- Increasing transmission as less of the axon needs to be depolarised
How does temperature affect speed of conduction?
Higher temperature, increases kinetic energy, increases rate of diffusion of ions, increasing rate of diffusion
How does axon diameter affect speed of conduction?
Larger the diameter, greater the speed of conductance, larger membrane surface area, increased number of channel proteins
