Physiology of neurons

Question 1

What are the properties of electrical synapses?

Answer 1

Faster than chemical
no plasticity so no learning
don’t release neurotransmitter so no amplification
signal always weakened as its transmitted
signal won’t transmit if post synaptic cell much bigger than pre synaptic
excitatory pre-synaptic signal can’t inhibit post-synaptic cell

Question 2

Define spatial summation

Answer 2

neuron fires based on converging signal from multiple neurons synapsing onto it. If many small depolarisations can reach threshold

Question 3

Define temporal summation

Answer 3

input neuron firing fast enough repeatedly so receiving neuron adds together many tiny signals to reach threshold

Question 4

What channels are open when membrane is at rest?

Answer 4

Inward rectifier K+ channels

Question 5

What channels open upon initial depolarisation

Answer 5

voltage gated Na channels

Question 6

what are the 2 delayed events that happen during repolarisation?

Answer 6

1. sodium channels close

2. delayed K+ rectifier channels open

Question 7

What is the after hyperpolarisation period?

Answer 7

at the end of the action potential where voltage goes more negative than at rest followed by return to resting membrane potential

Question 8

What channels open when membrane goes below -60mb during after hyperpolarisation?

Answer 8

Inward K+ rectifier channels

Question 9

What is the refractory period?

Answer 9

Period of time when neuron is incapable of regenerating new action potential. refractory period occurs during hyperpolarisation

Question 10

How is the intensity of neurons coded?

Answer 10

Increased threshold = decreased firing frequency

Increased excitatory synaptic activity = increased firing frequency

Question 11

Define excitability

Answer 11

how easy to start nervous signalling.

decreased threshold = decreased excitability

Question 12

What occurs when Na channels are open?

Answer 12

Na flows into the cell and membrane becomes more positive on the inside

Question 13

What occurs when K channels are open

Answer 13

K flows out of the cell and membrane becomes more negative on the inside

Question 14

What occurs when Ca channels are open

Answer 14

Ca flows into the cell and membrane becomes more positive on the inside

Question 15

What is lidocaine and how does it work?

Answer 15

local anaesthetic. blocks Na channels in pain neurons, raises threshold and decreases excitability to stop action potentials locally

Question 16

What is quinidine and how does it work?

Answer 16

antiarrythmic drug. decreases conduction velocity which extends the refractory period

Question 17

What is carbamazepine and how does it work?

Answer 17

Anticonvulsant. Inactivates Na channels, raises AP threshold so decreases excitability. Has a weak effect

Question 18

What is Tetrolotoxin?

Answer 18

Fugu fish poison. Blocks all Na channels.

Question 19

What is the chemical force acting on ions?

Answer 19

Also called the diffusional force. Is the mass of ion. Based upon difference in concentration across the membrane

Question 20

What is the electrical force acting on ions?

Answer 20

Depends on the Vm (membrane potential at rest) which varies. If positive charge separate from negative charge= powerful electrical field

Question 21

What are equilibrium potentials?

Answer 21

The more permeable the cell is to a certain ion, the more the membrane potential approaches its equilibrium

Question 22

What are the membrane potentials of the following?
ENa
EK
ECa
ECl

Answer 22

ENa: +60
EK: -90
ECa: +123
ECl: -40

Question 23

Properties of graded action potentials

Answer 23

decrease as they move along
electrically localised 
last long time 
much flatter in shape 
conducted almost instantly 
in receptor cells (rods and cones)

Question 24

Properties of Action potentials

Answer 24

stereotyped electrical signal
short duration
in most neurons, skeletal and cardiomyocytes
A spike
always the same ‘all or nothing’
require time to start due to conformational changes

Question 25

How do graded potentials transmit signals?

Answer 25

changes in membrane potential don’t propagate very far via passive electrical forces.
graded potentials transmit signals along length of axon
the action potential is a way for re-amplifying the signal

Question 26

Describe saltatory conduction

Answer 26

when action potential jumps from node to node. Net effect= faster conduction velocity. Electronic jumps between nodes are very fast.

Question 27

What is conduction velocity and what affects it?

Answer 27

Signal transmission along length of axon
faster when myelinated and large diameter
100 m/s for alpha motor fibres (myelin)
1 m/s for c nociceptive fibres (no myelin)