nervous coordination

Question 1

describe resting potential

Answer 1

inside of axon has negative charge relative to outside
as more positive ions outside vs inside

Question 2

explain how. a resting potential is established across axon membrane in a neurone

Answer 2

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

Question 3

stimulus

Answer 3

na channels open so membrane permeability to na increases
na diffuse into axon down electrochemical gradient
causing depolarisation

Question 4

depolarisation

Answer 4

if threshold potential reached AP generated
as more voltage gated na channels open
so more na diffuse in rapidly

Question 5

repolarisation

Answer 5

voltage gated na channels close
voltage gated k channels open
k diffuse out axon

Question 6

hyperpolirisation

Answer 6

k channels slow to close so slight overshoot to many diffuse out

Question 7

all or nothing principle

Answer 7

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

Question 8

non myelinated axon

Answer 8

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

Question 9

myelinated axon

Answer 9

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

Question 10

how can damage to myelin sheath lead to slow response and jerky movement

Answer 10

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

Question 11

nature of refectory period

Answer 11

time take to restore axon to resting potential when no further action potentials can be generated
as na channels are closed or inactive

Question 12

Importance of refractory period

Answer 12

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

Question 13

factors affecting speed of conductance

Answer 13

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