neurones

Question 1

what are the types of neurones

Answer 1

1) sensory
2) motor
3) relay

Question 2

outline a sensory neurone

Answer 2

carries impulses from the sense receptors or organs to the CNS

Question 3

outline a relay neurone

Answer 3

receives impulses from sensory neurones and transmits them to motor

Question 4

outline motor neurones

Answer 4

carries impulses from the CNS to effector organs

Question 5

draw and label a motor neurone

Question 6

what is meant by the term resting potential

Answer 6

the potential difference across the membrane of the cell when no nervous impulses are being conducted

Question 7

how is a resting potential established

Answer 7

1) sodium potassium pumps actively transport 3 sodium ions out the cell and 2 potassium ions into the cell
2) the cell is impermeable to sodium ions so their conc increases on the outside
3) the outside of the cell is more positive than the inside so the resting potential is -70mv

Question 8

what is meant by the term action potential

Answer 8

the rapid rise and fall of electronic potential across a nerve cell membrane as a nervous impulse passes

Question 9

outline depolarisation

Answer 9

1) energy from a stimulus reaches threshold potential -55mv
2) sodium ion voltage gated channels are opened and sodium ions flood into the cell
3) as a result the inside of the cell becomes more positive and reaches around 40mv (action potential)
4) the sodium ions are self perpetuating so diffuse down the cell opening more sodium ion gated channels
5) once the cell reaches 40mv sodium ion voltage gated channels close preventing the influx of more sodium ions

Question 10

out line repolarisation

Answer 10

1) at +40mv the sodium ion gates shut and the potassium ion gated channels open
2) this causes the potassium ions inside the cell to flood out down their conc gradient
3) the outside of the cell is now more positive than the inside and the cell is repolarised

Question 11

outline hyperpolarisation

Answer 11

more potassium ions diffuse out than sodium ions diffused in, the PD across the membrane becomes even more negative than the resting potential,-90mv.

Question 12

how does the cell return to resting potential after hyperpolarisation

Answer 12

sodium potassium pumps pump potassium ions back in and sodium ions out restoring the ion balance

Question 13

define the absolute refractory period

Answer 13

the period of time which no new action potential may be initiated

Question 14

explain how only one action potential can occur at one time

Answer 14

the site of the initial action potential- the sodium channels are inactivated and cant open again until resting potential has been re-established so a new action potential cant be initiated there

Question 15

what is the importance of an absolute refractory period

Answer 15

ensures that the action potential cant be propagated back in the direction from which it came- therefore, the action potential only moves in one direction

Question 16

outline the all or nothing law

Answer 16

if the intensity of the stimulus is below a certain threshold no action potential will be initiated- but if intensity exceeds threshold value an action potential is initiated however, it will be initiated at the same size no matter the intensity

Question 17

what does the all or nothing law ensure

Answer 17

acts as a filter preventing minor stimuli from setting up nervous impulses so the brain isn’t overloaded with information

Question 18

what factors affect the speed of conduction

Answer 18

temp
diameter of axon
myelination

Question 19

how does temp affect speed of conduction

Answer 19

ions move faster at higher temps due to more kinetic energy

Question 20

how does the diameter of the axon affect speed of conduction

Answer 20

larger the diameter the greater its volume, so more sodium ions can flow through the axon so impulses travel faster

Question 21

how does myelination affect the speed of conduction

Answer 21

speeds up rate of transmition by insulating the axon - the myelination nerve fibres only depolarise where resistance is low at nodes of Ranvier therefore gated ion channels only occur here so action potentials jump across from node to node via saltatory conduction