8.1

Question 1

where do relay neurones travel from and to?

Answer 1

CNS -> CNS (interneurones)

Question 1

where do sensory neurones travel from and to?

Answer 1

receptors -> CNS

Question 2

where do motor neurones travel from and to?

Answer 2

CNS -> effectors

Question 3

what is the role of Schwann cells?

Answer 3

to produce myelin sheath

Question 4

what is the role of the myelin sheath?

Answer 4

provides fatty insulating layer

Question 5

where is the cell body in a sensory neurone?

Answer 5

away from axon

Question 6

where is the cell body in a relay neurone?

Answer 6

middle of axon

Question 7

where is the cell body in a motor neurone?

Answer 7

at dendrites end of axon

Question 8

which way does an action potential travel down a neurone?

Answer 8

dendrites -> axon terminal

Question 9

what is a bundle of neurones called?

Answer 9

a nerve

Question 10

what does the CNS consist of?

Answer 10

brain + spinal cord / relay neurones

Question 11

what does the PNS (peripheral) consist of?

Answer 11

motor and sensory neurones

Question 12

in bright light which muscles contract/ relax in the eye and does the pupil dilate or constrict?

Answer 12

• circular muscles contract
• radial muscles relax (lines don’t pull pupil out)
  => pupil constricts

Question 13

in dim light which muscles contract/ relax in the eye and does the pupil dilate or constrict?

Answer 13

• circular muscles relax
• radial muscles constrict (lines pull pupil out)
  => pupil dilates

Question 14

what are reflex arcs responsible for?

Answer 14

the rapid, involuntary response to stimuli

Question 15

what controls pupil size?

Answer 15

photoreceptors in retina

Question 16

what is the resting potential?

Answer 16

-70mV (inside axon is 70mV less than outside)

Question 17

what does the sodium-potassium pump, pump in and out of the axon and what gradients are formed?

Answer 17

• 2 potassium into axon
• 3 sodium out of axon
  => creates electrical gradient + concentration gradient

Question 18

how is an action potential stimulated?

Answer 18

• stimulus arrives at axon
• causes Na+ channels to open: Na+ diffuses into axon down conc. gradient
  => depolarisation
• if -55mV reached, voltage-gated Na+ channels open, more Na+ can diffuse into axon (positive feedback) (membrane becomes more permeable to Na+
• at +40mV voltage-gated Na+ channels close and voltage-gated K+ channels open
• K+ diffuses out of cell, down conc. gradient
  => repolarisation
• voltage-gated K+ channels are very slow to close again: causes hyperpolarisation (to -90mV)
  -> creates refractory period so there’s a delay between action potentials (allows for only one way movement down. neurone
• action potential restored

Question 19

what’s the all or nothing response?

Answer 19

-55mV must be reached for an action potential to occur