Nervous Coordination (Topic 6B) Flashcards
(93 cards)
what is the value for resting potential?
-70mV
how is resting potential established?
- 3 Na out 2 K in via Na/K pump
- more Na outside than K inside, creating chemical gradient
- Na try naturally diffuse in but most gates are closed so can’t and K diffuse out naturally
- generating further distance and charge & electro and chemical gradient
- equilibrium met between electric and chemical gradients
describe how the resting potential is established in an axon by the movement across the membrane
2 marks
pump of Na+ out the axon
diffusion of K+ out the axon
why can sodium and potassium ions can only cross the axon membrane through proteins?
2 marks
- cannot pass through phospholipid bilayer
- because the ions are water soluble
the membrane is depolarised at what value?
+ 40mV
what is a nerve impulse?
a self propagating wave of electrical disturbance
when the membrane is hyper polarised the value is?
below -70mV
how does the membrane go from depolarised to hyper polarised?
the voltage dependent Na channels close and voltage dependent K channels open and K+ leave axon repolarising membrane
how does the membrane go from hyper polarised to polarised?
voltage dependent K channels close and K+ diffuse back in
when a neurone transmits a series of impulses, why does its rate of oxygen consumption increase?
more respiration
more energy supplied
for active transport of ions
why does a myelinated axon conduct impulses faster than a non-myelinated axon?
3 marks
- in myelinated action potential only at nodes
- the sheath makes the impulse jump from node to node
- action potential doesn’t have to travel along the whole length
what factors affect the speed of nerve impulse conduction?
temperature
myelin sheath presence
axon diameter
pre synaptic neurones…
send messages
the post synaptic neurone…
recieves messages
cholinergic synapses use…
acetylcholine
the properties of an action potential are…
• have a threshold
• all or nothing
• all the same size
• have a refractory period
what is the refractory period?
where channels remain closed so no further depolarisation occurs which ensures they are separate and only go in one direction
describe what is meant by the all or nothing principle
once the threshold is reached an action potential will always fire with the same change in voltage no matter the size of the stimulus
how does action potential change for a bigger stimulus?
action potentials are fired more frequently
how does axon diameter affect speed of conduction? why?
the bigger the diameter the quicker they are conducted.
because there is less resistance to the flow of ions than in the cytoplasm of a smaller axon so reached other parts of the neurone quicker
how does temperature affect speed of conduction? why?
as temperature increases, speed of conduction increases
because ions diffuse faster
(until denaturing)
the synaptic knob contains….
synaptic vesicles filled with neurotransmitter
what are the 3 steps for a nerve impulse to travel across a synapse?
- arrival of an action potential
- fusion of the vesicles
- diffusion of acetylcholine
at cholinergic synapses,
when action potential arrives at the synaptic knob what happens?
stimulates voltage-gated calcium ion channels in the presynaptic neurone to open so Ca+ diffuse into the knob
