6b nervous coordination Flashcards
(52 cards)
describe neurones resting state
outside of membrane positicely charged
more positive ions on outside of membranes than inside
its polarised
what is the voltage across a memebrane at resting state
-70mv
what creates and maintains resting potentials
sodium potassium pumps
and potassium ion channels
describe how resting potential is made
- sodium potassium pump pumps sodium ions out of neurone and as membrane isnt permeable to sodium ions they cannot diffuse back in
- electrochemical gradient created
- sodium potassium pump moves potassium ions into the neurone but membrane is permeable to potassium ions so they diffuse out of the neurone via potassium channels
- creates positive charge outside of cell
how does sodium potassium pumps work
active transport to move 3 sodium ions out of neurone for every two potassium ions moved in
ATP required
describe stages of action potential
STIMULUS- excites nuerone membrane causing sodium channels to open
-membrane becomes more permeable to sodium so sodium ions diffuse into neurone down gradient making inside of neurone less negative
DEPOLARISATION- if the potential difference reaches threshold near -55mv more sodium ions open so more sodium ions diffuse into neurone
REPOLARISATION- at potnetial difference of +30 sodium ion channels close
- potassium ion channels open
- membrane more permeable to potassium so they diffuse out of neurone getting membrane back to resting potential
HYPERPOLARISATION-potassium ion channels slow to close so slight overshoot so potential difference becomes more negative than resting potential
RESTING POTENTIAL-ion channels reset -sodium potassium pump returns membrane to resting potential
what is the refractory period
after action potential neurone membrane cannot be excited again straight away as channels closed
explain wave of depolarisation
during action potential some sodium ions diffuse sideways causing sodium channels to open in next region of neurone causing wave of depolarisation
what happens due to refractory period
- action potentials dont overlap they pass on discrete impulses
- limit to frequency at which impulses can be transmitted
- action potentials are unidirectional
describe all or nothing principle
bigger stimulus doesnt mean bigger action potential it means more frequent action potentials
if threshold isnt reached action potential will not fire
what three factors affect the speed of conduction of action potentials
myelination
axon diameter
temperature
what is a myelin sheath
electrical insulator
what cells make up myelinated sheath
schwann cells
what are between schwann cells
nodes of ranvier where sodium ions are concentrated
why does myelinated sheath increase speed of conduction to action potential
in myelinated neurone depolarisation only happens at the nodes of ranvier
cytoplasm conducts enough electrical charge to depolarise next node so impulse jumps from node to node
this is saltatory conduction
why is speed of conduction slower in non myelinated sheath
as impulses have to travel along the whole length of axon membrane
how does the diameter of axon effect speed of conduction
bigger axon means action potential conducted quicker as less resistance to flow of ions so depolarisation reaches other parts of neurone cell membrane quicker
how does temperature effect speed of conduction of action potential
speeds up diffuseion but after 40 degrees proteins begin to denature
what is a synapse
junction between two neurones 12
how does synapse work
- presynaptic neurone has synaptic knob which contains synaptic vesicles filled with neurotransmittors
- when action potential reaches end of neurone ig causes neurotransmitters to be releases to synaptic cleft and diffuse across tpo the postsynaptic membrane and bind to specific receptors
- when they bind with receptors they can trigger action potential
explain how synapses are unidirection
as receptors are only on postsynaptic membrane
how are neurotransmitters removed
removed from cleft to stop response from happening
taken back into presynaptic neurone and broken down by enzymes
describe nerve impulse across a cholingeric synapse
1-action potential arrives at synaptic knob of presynaptic neurone
2-action potential causes stimulates calcium ion channels to open
3- calcium ions diffuse into the synaptic knob
4-influx of calcium causes synaptic vesicle to move to presynaptic membrane
5-vesicle releases acetylcholine into synaptic cleft |(exocytosis)
6-ACH diffuses across cleft and binds to spefic cholinergic receptor on post synaptic membrane
7-causes sodium ion channels to open in postsynaptic neurone
8-influx of sodium ions causes depolarisation
9- action potenital generated if threshold reached
10-acetylecholineesterase breaks down ACH and products go to presynaptic neurone
what do excitatory neurotransmitters do
depolarise postsynaptic membrane making it fire action potential if threshold
