NEURO- Nerve cell potentials

Question 1

describe the ionic basis of the RMP

Answer 1

ATPase - sodium/ potassium pump = 3 Na out 2K in

potassium leak channel - potassium leaks out of the cell - leaning towards resting membrane potential of -95

sodium can leak through which leaves the RMP at -60/-70 mv

Question 2

Describe the permeability changes and ion fluxes underlying electrotonic potentials

Answer 2

gated channels only open when a neurotransmitter is bound

VGNC- allows sodium into cell causing depolarisation

electrotonic potential - graded potential - a stronger signal = stronger depolarisation / holding channel open for longer = longer depolarisation

generates an electric current which spreads depolarisation along the membrane
almost instantaneous - further away from generation = smaller depolarisation

only works over short distances

Question 3

what are the limitations of electrotonic condcution

Answer 3

small
slow depolarisation
slow decay
graded

Question 4

what are the benefits of action potentials

Answer 4

large
rapid depolarisation
rapid repolarisation
all or nothing

Question 5

describe the role of VGNC in the generation of a response

Answer 5

at rest - positive charge on the loop is repelled from the outside into the inside of the cell keeping the gate closed - activation gate

as electrotonic charge is applied - depolarises the membrane - if weak = gate remains closed, if strong = gate opens allowing sodium into the cell

positive feedback - depolarisation causes channel opening allows sodium influx

depolarisation causes the cancellation of the negative charge on the cell - reducing membrane potential

gate now closed

Question 6

describe the role of VGKC on a response

Answer 6

rapid repolarisation of the cell is dependent on VGKC
overall negative charge on the outside of the cell pulls the gate open allows potassium ions to influx into the cell - rapidly bringing membrane potential back to resting stage

Question 7

what is the absolute refractory period

Answer 7

after sodium channels have opened they cannot open again

each action potential is separate and individual event

Question 8

what is the relative refractory period

Answer 8

period during which the cell is hyperpolarised
delay in closing the VGKC
requires a stronger stimulus to produce effect to overcome hyperpolarisation

Question 9

why are refractory periods important

Answer 9

cannot fire another action potential once it has fired meaning signals move in one direction throughout the axon

Question 10

how are action potentials propagated through myelinated axons vs unmyelinated axons

Answer 10

action potential fires and produces electrotonic currents that spread through the neuron

electrotonic currents set up the next axon for action potential which fires, producing another electrotonic current etc…

unmyelinated axons - potassium leaks out of the neuron dragging the potential back to red
a larger diameter = faster

myelinated neurons - insulated thick fatty layer
prevents leakage of ions out of the membrane
electrotonic currents spread further
nodes of Ranvier - between the myelinated sheath - contain lots of VGC
saltatory / leaping conduction