Physiology of neurones

Question 1

Electrical synapses

Answer 1

Faster

Bidirectional

Much smaller gap= 3.5nm

No plasticity

No amplification

Used for defensive reflexes

Question 2

No amplification in electrical synapse

Answer 2

Signal is always weakened as it is transmitted from pre-synaptic to post synaptic cell

Will not transmit if PostS cell much bigger than Pre

Excitatory PreS cannot inhibit the PostS cell

Question 3

Spatial summation

Answer 3

A neurone determines whether to fire based on the ‘add together’ all of the tiny signals it is receiving from several other neurones

Means small depolarisations can reach threshold

Question 4

Temporal summation

Answer 4

When input neurone is firing fast enough so that the receiving neurone can ‘add together’ the many tiny signals ultimately reaching threshold

Question 5

Stages of action potential

Answer 5

Threshold

Depolarisation

Repolarisation

Hyperpolarisation

Resting stage

Question 6

4 steps of action potential

Answer 6

1. Rest: K+ going out clamps MP at -70mV
2. External factor: slight depolarisation, threshold
3. Na+ conductance shoots up, Na+ current goes in so MP more positive
4. Time delay: Na+ conductance diminishes, K+ conductance increases, K+ leaves cell, RP

Question 7

Action potentials are all or none

Answer 7

Carry no information regarding size of the stimulus that elicited them

Question 8

Firing frequency

Answer 8

Increasing threshold lowers firing frequency

Increasing excitatory synaptic activity increases firing frequency

When lengthy synaptic currents are small, higher threshold potential than larger currents

Question 9

Excitability

Answer 9

How easy to start nervous signalling

Question 10

Inactivated channel

Answer 10

When membrane is positive channel tends to stop conducting

Question 11

Closed channel

Answer 11

When membrane is negative channel tends to stop conducting

Question 12

Ionic permeabilities control voltage

Answer 12

Increased permeability to K+ makes membrane more negative

Increased permeability to Na+ makes membrane more positive

Question 13

Lidocaine

Answer 13

Local anaesthetic

Apply topically

Raised the threshold so lowers excitability which stops AP

Specifically blocks Na+ channels in inactivated state

Question 14

Carbamezapine- anticonvulsant

Answer 14

Inactivates sodium channels

Raises AP threshold and lowers excitability

Used to treat seizure disorders and neuropathic pain

Question 15

The chemical force

Answer 15

Based on the difference in concentration across the membrane

Question 16

Electrical force

Answer 16

Based on Vm

Question 17

ENa

Answer 17

+60mV

Question 18

EK

Answer 18

-90mV

Question 19

ECa

Answer 19

+123mV

Question 20

ECl

Answer 20

-40mV

in neurones -65mV

Question 21

Action potentials

Answer 21

A stereotyped electrical signal

Short duration

In most neurones, skeletal and cardiomyocytes

A spike

All or none

Question 22

Graded potentials

Answer 22

Decrease as they move along

Electrically localised

Last a long time

Much flatter in shape

Are conducted almost instantly

(rods and cones)

Question 23

Saltatory conduction

Answer 23

When AP jumps from node to node

Faster conduction velocity

Initiating an AP at each node is slower

Question 24

Conduction velocity

Answer 24

Faster when

• myelinated
• large diameter

Question 25

Conduction velocity of alpha motor fibres

Answer 25

(myelinated)

100m/s

Question 26

Conduction velocity for C nociceptive fibres

Answer 26

(unmyelinated)

1m/s

Question 27

Clinical uses of conduction velocity

Answer 27

Nerve conduction studies used for evaluation of paraesthesias

Evaluation of weakness of arms and legs