Unit 6: Nervous coordination

Question 1

What is the value of the resting potential inside the axon?

Answer 1

-70mV

Question 2

What is the resting potential

Answer 2

the potential difference across the membrane of an axon when an impulse isn’t being transmitted

Question 3

Which ions are in a polarised neurone?

Answer 3

more sodium ions outside the axon and more potassium ions inside the axon

Question 4

How is the resting potential maintain

Answer 4

• membrane is differentially permeable
  more permeable to the loss of K+ than intake of Na+
• Na/K pump actively transports 3 Na+ out and 2 K+ in against their diffusion gradients ensuring that an electrochemical gradient is maintained

Question 5

What is a respiratory inhibitor

Answer 5

prevents production of ATP so Na/K pump cant function and conc of these ions will eventually reach equilibrium and the potential difference will be 0

Question 6

What causes an action potential

Answer 6

when a receptor is stimulates above its threshold

Question 7

What happens during delolarisation

Answer 7

increase in permeability of the axon to Na+
Na voltage gated channels open and Na+ diffuses down a conc gradient into axon and value increases to +40mV

Question 8

What happens during repolarisation

Answer 8

Na channels close
K voltage gated channels open and K+ diffuse out of axon making it less + e

Question 9

How does the Na/K pump restore the resting potential?

Answer 9

actively removes Na+ which have entered and returns K+ back into axon

Question 10

What happens during hyper polarisation

Answer 10

membrane pitential becomes more negative bc K+ diffuses out slowly

Question 11

What is the refractory period?

Answer 11

period after the formation of an action potential when a neurone cant generate another action potential

resulting in discrete impulses

ensures that impulse travels in one direction

Question 12

What is the all or nothing principle

Answer 12

a stimulus must be above a certain threshold level for an impulse to be generated

a strong stimulus above threshold will result in a greater frequency of impulses than a weak stimulus

amplitide of impulses always remain the same

Question 13

How does temperature affect the speed of conductance?

Answer 13

increase in temperature will increase speed of transmission up to a particular temperature

provides more KE for the diffusion of ions inside and out the axon

Question 14

How does a temperature above optimum affect speed of concordance

Answer 14

denaturation of enzymes and proteins in the plasma membrane would stop the transmission

Question 15

How does axon diameter affect speed of conductance

Answer 15

greater the diameter the faster less resistance

Question 16

How does myelination affect speed of conductance?

Answer 16

myelinated neurones increase speed as action potential jumps from one gap (node of ranvier) to another to the next

depolarisation only occurs at the nodes > saltatory conduction

in non myelinated neurones depolarisation occurs along the whole membrane of the axon slowing down transmission

Question 17

Why does the synaptic knob contain many mitochondria

Answer 17

to provide ATP for the synthesis of the neurotransmitter

Question 18

What happens during synaptic transmission

Answer 18

• action potential reaches synaptic knob causing depolatisation of PreSM
• stimulated Ca2+ to open in PreSM and diffuse into synaptic knob
• cause vesicles to fuse with preSM and break open
• neurotransmitter acetylcholine is released and diffuses across synaptic cleft
• acetylcholine attatches to specific receptor on postSM
• stimulates entry of Na+ leading to depolarisation of postSM and transmission of an impulse

Question 19

How is acetylcholine broken down then resynthesised

Answer 19

• broken down in postSM by enzyme acetylcholinesterase making acetyl and choline
• acetyl and choline is taken up into the synaptic knob by active transport and is resynthesised

Question 20

What is spatial summation?

Answer 20

two or more impulses from different synaptic knobs arrive simultaneously at different regions on the same neurone

mores likely to reach threshold as there are more knobs

Question 21

What is temporal summation?

Answer 21

two or more impulses arrive at the same place on the axon within a short period of time

more likely to reach threshold than if one impulse arrived

Question 22

how do synapse give an inhibitory effect on the postSM?

Answer 22

by stimulating influx of negative Cl- ions and by stimulating removal of K+ causing a more -ve charge in the axon

its more difficult to reach threshold than

Question 23

What is the neuromuscular junction?

Answer 23

The synaptic connection between a neuron and muscle fibre

Many drugs act on the neuromuscular junctions

Question 24

How do drugs work by mimicking?

Answer 24

drugs have a similar structure to a normal transmitter and have the same effect they bind to receptors and transmission is faster

Question 25

How do drugs work by blocking?

Answer 25

drugs have a **similar structure** in a normal transmitter, but **do not produce the same effect** They fit into the receptors and **prevent the normal transmitter** from entering this stop the transmitter from having its effect so **transmission is stopped**

Question 26

How do drugs work by preventing?

Answer 26

**prevent the release of the transmitter** substance from the preSM so that **transmission is stopped**

Question 27

How do drugs work by inhibiting?

Answer 27

The **inhibit the action of enzymes which hydrolyse neurotransmitters** therefore more transmitter is present so **transmission is enhanced**

Question 28

What are cholinergic neurones

Answer 28

neurones possessing acetylcholine