nerve impulse Flashcards
what is a resting potential
refers to the situation in an axon when it’s not conducting an impulse / action potential
resting potential
Na+ / K+ pump in the axon membrane that pumps 3Na+ out for every 2K+ in
this active transport, using ATP contributes to the inside being negative
the pumping results in a reservoir of Na+ outside and K+ inside and concentration gradients for both ions
as a result:
Na+ diffuse in through dedicated Na+ channels
K+ diffuse out through dedicated K+ channels
in resting state - there are more open K+ channels than Na+ channels
- more K+ diffusing out than Na+ in
why is the membrane more permeable to potassium
in resting state - there are more open K+ channels than Na+ channels
- more K+ diffusing out than Na+ in
this contributes to the inside being negative
polarised
in the resting state, with the inside at -70 mV
we say the axon is polarised
depolarised
if we open Na+ channels, increasing the permeability of the membrane to Na+
more Na+ will rush in
the inside will become more negative = depolarisation
repolarisation , hyperpolarised
if we open k+ channels, increasing the permeability of the membrane to K+
more K+ will rush out
the inside will become more negative
what is an action potential
nerve impulse
self-propagating wave of depolarisation
- voltage gated Na+ channels open
- Na+ rush in, causing a local depolarisation ( +40 mV)
- causes voltage gated Na+ channels in the neighbouring areas to open
recovery
after the action potential has passed by, the areas left behind must return back to being negative so that another action potential can be transmitted
- after the action potential has passed by:
Na+ channels close
Na+ stops rushing in - K+ channels open
K+ rush out and the inside becomes more negative (repolarisation)
theres a brief period when the inside becomes extra negative = hyperpolarised
the K+ channels close and back to resting potential
restoring the ion balance
in the passage of the action potential, a lot of Na+ has rushed in and K+ rushed out
SO
in the aftermath of the action potential, the Na+ / K+ pump has to work harder to restore the ion balance using more ATP
why is higher conduction speed beneficial
allows the organism to react more rapidly to external or internal stimuli
larger diameter axon - invertebrates
- more Na+ and K+ channels
- more rapid depolarisation and repolarisation
- more rapid conduction
(takes up a lot of space)
myelination - vertebrates
schwann cell - contains fat called myelin
node of ranvier
ion exchange can only happen at the nodes of ranvier
depolarisation at one node will (due to the insulating effect of the myelin sheath) cause Na+ inrush at the next node
SALTATORY conduction - where depolarisation jumps from node to node
describe the general structure of a motor neuron
cell body - contains organelles and high proportion of RER
dendrons - branches into dendrites which carry impulses towards cell body
axon - long, unbranched fibre carries nerve impulses away from cell body
describe the additional features of a myelinated motor neuron
schwann cells - wrap around axon many tims
myelin sheath - made from myelin-rich membranes of schwann cells
nodes of ranvier - very short gaps between neighbouring schwann cells where there is no myelin sheath
(electrical insulation, phagocytosis, nerve regeneration)
refractory period
no stimulus is large enough to raise membrane potential to threshold
- no action potential can be generated in hyperpolarised sections of membrane
ensures unidirectional impulse, discrete impulses, limits frequency of impulse transmission
