Nervous coordination-Nerve impulses Flashcards
how is a resting potential maintained?
The membrane is more permeable to K+ ions than Na+ ions
Na+ gated ion channels are closed
There is a higher concentration of Na+ outside the neurone than outside, so Na+ diffuse into the neurone
Higher concentration of K+ inside than outside, K+ diffuse out of the neurone
Na+/K+ pump will actively move 3Na+ ions out for every 2K+ inside
The inside is more negative than the outside
What are dendrons?
carry nerve impulses towards the cell body
what is the axon?
single long fibre that carries nerve impulses away from the cell body
describe the function of Schwann cells
surround the axon by wrapping around many times, protecting and providing electrical insulation
what is the myelin sheath
forms covering of axon made up of the membranes of Schwann cells
nodes of Ranvier
gaps between adjacent Schwann cells where there is no myelin sheath
gaps are 2-3 micrometers and occur every 1-3 mm
action potential jumps from node to node, this is called saltatory conduction
How is an action potential generated? (includes resting potential, generating at AP and what occurs afterwards)
- resting potential is maintained at -65/-70
- a stimuli causes some of the Na+ ion channels to open; some Na+ ions diffuse in
- depolarisation occurs, membrane voltage around -55
- if stimuli is strong enough, depolarisation reaches the threshold (0), causes MORE Na+ ion channels to open
- causes influx of Na+, inside becomes more positive than outside
- AP generated when membrane potential reaches +40
- after AP is established, the membrane enters the refractory period
- Na+ voltage-gated ion channels close; causes the K+ channels to open
- K+ ions diffuse out of membrane; inside becomes more negative
- As some K+ ions diffuse out, causes more K+ ion channels to open
- ‘Overshoot’- more K+ diffuse out than needed; inside membrane is more negative than it should be
- causes K+ ion channels to close, RP is restored by the Na+/K+ pump using ATP
- axon is repolarised
Non- myelinated neurones have a slower rate of conduction than myelinated neurones. explain why
- waves of depolarisation travel across the entire length of the axon
- depolarisation only occurs at the nodes of Ranvier in myelinated neurones
- the impulse jumps from node to node (saltatory conduction)
how do waves of depolarisation propagate an action potential along the axon?
Some of the Na+ that diffuse into the neurone causes Na+ channels to open in the next region of the axon
depolarisation occurs
what are the factors affecting the speed of an action potential?
- myelination
- temperature
- axon diameter
explain how mylination affects the speed of an action potential
- waves of depolarisation occur along the whole length of the axon
- depolarisation only occur at the nodes of ranvier
- impulses jump from node to node
how does temperature affect the speed of an action potential
- speed of an action potential increases as temperarure increases
- ions diffuse faster
- he speed only increases until 40C, as the protein channles denature
describe the ‘refreactatory period’
hint: 2 points
the time where a second action potential cannot be initiated
result of temporary closer of Na+ channels while resting potential is restored
what is the importance of the refractory period?
hint: 4 points
- allows APs to be propagated in only one direction
- ensures new APs cannot be generated immediately behind another
- allows seperation of APs
- limits the number of APs that can apss along the axon at any one time
describe the effect of axon diamater on the speed of an action potential
- APs are condicted quicker along the axon with larger diameters
- less resistance to the flow of ions
- so depolarisation reaches the other arts of the neurone faster
