nervous coordination Flashcards
describe resting potential
inside of axon has negative charge relative to outside
as more positive ions outside vs inside
explain how. a resting potential is established across axon membrane in a neurone
na and k pump AT
3 na out of axon
and 2 k into axon
creating an electrochemical gradient
as higher k+ conc inside and higher na+ conc outside
differential membrane permeability as the membrane is more permeable to k+ so they move out by FD
and less permeable to na+ as closed channels
stimulus
na channels open so membrane permeability to na increases
na diffuse into axon down electrochemical gradient
causing depolarisation
depolarisation
if threshold potential reached AP generated
as more voltage gated na channels open
so more na diffuse in rapidly
repolarisation
voltage gated na channels close
voltage gated k channels open
k diffuse out axon
hyperpolirisation
k channels slow to close so slight overshoot to many diffuse out
all or nothing principle
for action potential to be produced
depolarisation must exceed threshold potential
action potentials produced always the same magnitude
bigger stimuli instead increase frequency of action potentials
non myelinated axon
action potentials pass as wave of depolarisation
influx of na in one region increase permeability of adjoining regions to na
by causing voltage gated na channels to open so adjoining regions depolarise
myelinated axon
myelination provides electrical insulation
depolarisation of axon at nodes of ranvier only
resulting in saltatory conduction
so there is no need for depolarisation along the whole length of the axon
how can damage to myelin sheath lead to slow response and jerky movement
less to no saltatory conduction
so depolarisation along the whole length of the axon
so nerve impulses may take longer to reach NMJ
delaying muscle contraction
depolarisation may leak to other neurones
causing wrong muscle fibres to contract
nature of refectory period
time take to restore axon to resting potential when no further action potentials can be generated
as na channels are closed or inactive
Importance of refractory period
ensures discrete impulses are produced
limits frequency of impulse transmission at a certain intensity to prevent over reaction to stimulus
ensures action potentials travel in one direction - cant be propagated In a refectory period
factors affecting speed of conductance
myelination - depolarisation at nodes of ranvier only so saltatory conduction so impulse doest depolarise whole length of axon
axon diamater - bigger less resistance to flow of ions in cytoplasm
temp - increases rate of diffusion of na and k as more ke
but protiens enzymes could denature at certain temp
