neurones

Question 1

what is a neurone made up of?

Answer 1

• cell body
• dendrites
• nucleus
• axon
—> myelin sheath, schwann cells, nodes of ranvier
• axon terminal

Question 2

what do schwann cells do

Answer 2

• surround the axon
• protect it and provide electrical stimulation
• carry out phagocytosis
• play a part in nerve generation
• wrap themselves around axon many times so that layers of their membrane build up around it

Question 3

what is an axon?

Answer 3

a single long fibre that carries nerve impulses away from the cell body

Question 4

what 3 factors affect the speed at which an action potential travels?

Answer 4

• the myelin sheath
• the diameter of the axon
• temperature

Question 5

why does myelin sheath increase the speed at which an action potential?

Answer 5

• acts as an electrical insulator
• prevents an action potential forming in the part of the axon covered in myelin
• it jumps from one node of ranvier to another (saltatory conduction)

Question 6

why does the diameter of the axon affect the speed an action potential travels?

Answer 6

• the greater the diameter of the axon, the faster the speed of conduction
• due to less leakage of ions from a large axon

Question 7

why does temperature affect the speed at which an action potential travels?

Answer 7

• affects rate of diffusion of ions
• higher the temp higher the faster the nerve impulse
• energy for active transport comes from respiration which is controlled by enzymes

Question 8

what is the resting potential of an axon?

Answer 8

-70 mV

Question 9

what is the threshold potential?

Answer 9

-40 mV

Question 10

what is the refractory period?

Answer 10

• period of time where a neurone cell membrane can’t be stimulated to produce another action potential
• sodium channels are in recovery from activation

Question 11

why do more sodium channels open during an action potential?

Answer 11

• some sodium ions diffuse sideways
• causes a depolarisation in the next region of the neurone
• more sodium channels open
• if threshold is reached the all or nothing principle occurs and another action potential is produced

Question 12

why does wave of depolarisation only occur in one direction?

Answer 12

• the refractory period in intimacy region prevents a further action potential to be fired

Question 13

what is a pacinian corpuscle?

Answer 13

• receptor

Question 14

what type of sodium channels do pacinian corpuscles have?

Answer 14

stretch-mediated

permeability changes when shape changes

Question 15

explain how the pacinian receptor generates an action potential?

Answer 15

• resting = SM sodium channels are too narrow to allow sodium to pass along, has a resting potential of -70mV
• when pressure applied, it’s deformed and membrane around its neurone is stretched
• this widens the Na channels and sodium ions diffuse into neurone (F diffusion)
• influx of Na ions makes more positive, goes past -40mV reaches threshold so generator potential is produced
• in turn creates an action potential that passes along the neurone and to the CNS

Question 16

how will greater pressure affect the pacinian corpuscle?

Answer 16

• more sodium channels will open

* more ions move in, make more positive

Question 17

process of an axon becoming more positive?

Answer 17

depolarisation

Question 18

process of an axon becoming more negative?

Answer 18

repolarisation

Question 19

what channels are open during depolarisation?

Answer 19

sodium

Question 20

what channels are open during repolarisation?

Answer 20

potassium

Question 21

what channels are open in a resting axon?

Answer 21

none

Question 22

what is the process of an axon becoming too negative?

Answer 22

hyperpolarised

Question 23

what happens when an axon is hyperpolarised?

Answer 23

the channels go into the refractory period