Topic 6B: Nervous Coordination Flashcards
What is meant by a resting potential?
- When inside the neurone is more negative than the outside
- membrane is polarised
What is the voltage at resting potential?
-70mV (millivolts)
How is resting potential maintained?
3 Na ions are actively pumped out of the neurone for every 2 K ions pumped inside the neurone through the sodium potassium pump
-the membrane of the neurone is more permeable to potassium than sodium
If stimulus is big enough…
it causes an action potential
Stages of the changes in potential difference during an action potential
1) Stimulus
2) Depolarisation
3) Repolarisation
4) Hyperpolarisation
5) Resting Potential
What happens in Stage 1-Stimulus
- excites the neurones cell membrane
- membrane increases in permeability to sodium
- sodium channels open
- sodium diffuses into the neurone
- down the electrochemical gradient
- inside of the neurone less negative
What happens at Depolarisation?
- potential difference reaches at -55mV
- more sodium channels open
- more sodium ions diffuse rapidly
What happens at Repolarisation?
- reaches +30mV
- sodium channels close
- potassium channels open
- membrane is more permeable to potassium
- potassium ions diffuse out
What is Hyperpolarisation?
- potassium ion channels are too slow to close so there is a slight overshoot where too many potassium ion diffuses out of the neurone
- potential difference becomes more negative than the resting potential
What is the refractory period?
- When ion channels are recovering and cant be opened
- acts as a time delay
The time delay in the refractory period mean…
- action potential doesnt overlap
- pass along discrete impulses
- action potential is unidirectional (travel in one direction)
What are the three factors affect the speed of conduction of action potential?
- myelination
- axon diameter
- temperature
Why is there in a time delay in the refractory period?
-so that the ion channels start to recover and so they cant be made open
When are the sodium and potassium ion in a refractory period?
- sodium ion channels closed during repolarisation
- potassium ion closed during hyperpolarisation
How does action potential move along the neurone?
-the sodium ions that enter the neurone sometimes diffuses sideways
-causes Na ions in the next region of the neurone to open
-Na ion diffuses in
-causes a wave of depolarisation that travel along the neurone
-
Once the threshold is reached, an action potential will always fire…
- at the same voltage
- maximal response
The bigger the stimulus….
the more times action potentials occur frequently
How does myelination increases the speed of conduction of action potential?
- myelin sheath is an electrical insulator
- It has a faster saltatory conduction
What is the saltatory conduction?
The neurones cytoplasm conducts enough electrical charge to depolarise the next node so the impluses jump from node to node.
What is myelin sheath made out of?
Schwann cells in the peripheral system
Between the Schwann cells there are tiny patches of bare membrane called…
Nodes of Ranvier
What are in the nodes of Ranvier?
Concentrated in the sodium ion channels
In myelinated neurone, depolaristion happens ONLY in the…
Nodes of Ranvier
How does impluses travel along a non myelinated neurone?
- Travels along the whole length of the axon membrane
- so depolarisation occurs along the whole length of the membrane
- therefore slower saltatory conduction
