Neurones

Question 1

What is myleination

Answer 1

• Shwann cells wrap around axon of neurone = myelin sheath
• acts as insulator = impermeable to Na+ and K+
• depolarisation cannot occur at myelinated sectors

Instead depolarisation happens in gaps ( nodes of ranvier) = impulse jumps between gaps = faster transmission

Question 2

What effects rate of transmission

Answer 2

Temp= higher kinetic energy = ions move across membrane faster/ faster diffusion = faster transmission

Axon diameter= large diameter = large surface area for movement of ions = faster transmission

Question 3

What is a synapse

Answer 3

Junction between 2 neurones or neurone and effector

Question 4

What does the synaptic knob contain a lot of

Answer 4

Mitochondria

Question 5

What are the 2 types of neurotransmitters

Answer 5

Excitatory= generate Action potential in postsynapic cell = when binds causes depolarisation

Inhibitory= prevents Action potential in postsynaptic cell = when binds to postsynaptic causes hyper-polarisation = membrane becomes more negative so harder for AP to form

Question 6

What are the 2 types of summation

Answer 6

Spatial= multiple presynaptics to 1 postsynaptic eg rod cells

Temporal= multiple impulses from the same presynapyic

Summation is for when 1 impulse may not be enough to reach threshold

Question 7

Transmission across synapse

Answer 7

1- Action potential cause’s depolarisation in synaptic knob = Ca2+ channels open
2- influx of Ca2+ ions causes synaptic vesicles to fuse with presynaptic membrane releasing neurotransmitter into synaptic cleft
3- neurotransmitter diffuses across cleft and bind to receptor on Na+ ion channel
4- channel open creating depolarisation in postsynaptic neurone

Question 8

What happens to neurotransmitter after it causes new action potential

Answer 8

• hydrolysed and diffuses back into presynaptic neurone
• ATP regenerates NT and stored in synaptic vescicle

Question 9

What are dendrites

Answer 9

• small branched fibres that carry nerve impulse to cell body

Question 10

What organelle does neurones have a lot of and why

Answer 10

Rough ER
- production of proteins = neurotransmitter

Question 11

What is it called in mylenitated neurones when action potential “jumps” from one node to the next

Answer 11

• saltory conduction

Question 12

What type of neurotransmitter is acetylcholine

Answer 12

• can be excitatory or inhibitory

Question 13

What is the refractory period

Answer 13

• time after depolarisation where no new AP can start
• time needed to restore voltage ion channels to original resting conditions
• Na+ channel cannot be opened = as it cannot be depolarised again

Question 14

What is the all or nothing theory

Answer 14

• AP only happens if stimulus reaches threshold value
• once it starts it travels to the synapse

Question 15

Features of size of Action potentials

Answer 15

• AP is always the same size
• AP same size along axon

Question 16

How do we detect size of stimulus

Answer 16

• number of impulses = larger the stimulus
• different threshold values tells brain how size

Question 17

Description of sodium potassium pump

Answer 17

1- pump binds 3 Na+ and a ATP
2- splitting of ATP = changes shape of channel
3- Na+ released to other side of membrane + new shape allows 2 K+ bind to channel
4- release of phosphate from channel changes channel back to original shape releasing K+ to other side

Question 18

What is the potential difference like at resting potential

Answer 18

• more negative in neurone than outside
• maintained by Na-K pump

Question 19

Depolarisation of neurone

Answer 19

1- Na+ ion channels open + Na flood into neurone = more positive in neurone
2- if reaches above threshold = depolarisation = more Na channels open
3- after depolarisation Na channels shut + K channels open
4- K+ transported out of neurone = more negative in neurone = Repolarisation
5- short period after repolarisation where becomes more negative than resting potential = hyperpolarisation
6- K+ channels close and returns to resting potential

Question 20

What does refractory period ensure

Answer 20

• AP can only go in one direction