How Neves Work

Question 1

Ionic basis of the resting membrane potential

Answer 1

K+ is moved into the cell by the Na/K pump which gives approximately equal charge
Leaky K channels allow potassium to travel down the conc. gradient of the cell to establish ELECTROCHEMICAL EQUILIBRIUM
Also large -vely charged intracellular molecules

Question 2

Ionic basis of the action potential

Answer 2

All or none
Determined by frequency, not magnitude
At rest, Na permeability is very low
When the threshold is reached, voltage-gated Na channels open almost immediately
Na floods into and depolarises the cell
Positive feedback – massive increase in permeability and decrease in resistance
Only stay open for a short time
Voltage-gated K channels open and cause hyperpolarisation
Eventually these shut and cell returns to normal

Question 3

Refractory period

Answer 3

The period during which the cell is unable to fire another action potential while it recovers

Question 4

Myelin

Answer 4

Insulates axon and so is more efficient at passing on electrical charge - less curretn is wasted leaking out of the membrane

Question 5

Generator potentials

Answer 5

At sensory receptors

Question 6

Post-synaptic potentials

Answer 6

At synapses

Question 7

Endplate potentials

Answer 7

At neuromuscular junction

Question 8

Pace maker potentials

Answer 8

In pace maker tissues

Question 9

EPSPs

Answer 9

Excitatory post synaptic potentials
Transmitters tend to open types of channel permeable to Na and K but more Na than K gets out, so it depolarises
Or some leaky K channels are blocked

Question 10

IPSPs

Answer 10

Inhibitory post synaptic potentials

Cl channels or more K channels are opened which hyperpolarises the cell and takes them away from the threshold

Question 11

Neuromuscular transmission

Answer 11

An action potential opens Ca channels in the presynaptic terminal
Triggers the fusion of vesicles and ACh is released into the cleft
Diffuses across and binds to the receptors in the junctional folds
Ligand gated Na/K channels are opened
An end-plate potential is always produced, so an action potential is fired which opens up voltage-gated Na channels
ACh removed by acetylcholinesterase

Question 12

Tetrodotoxin

Answer 12

Blocks Na channels and so blocks the action potential

Question 13

Joro spider toxin

Answer 13

Blocks Ca channels and so blocks transmitter release

Question 14

Botulinum toxin

Answer 14

Disrupts the release machinery and so blocks transmitter release

Question 15

Curare

Answer 15

Blocks ACh receptors and so prevents the end-plate potential

Question 16

Anticholinesterases

Answer 16

Block ACh breakdown and so increase transmission at the NMJ

Question 17

Axo-somatic

Answer 17

Synapse attached to the soma

Question 18

Axo-dendritic

Answer 18

Axon attached to the dendrite

Question 19

Axo-axonal

Answer 19

Not on the axon itself, Attached to another synapse

Question 20

CNS more complex than NMJ

Answer 20

Range of neurotransmitters
Range of PSPs
Small potentials (and synaptic integration)

Question 21

Graded potentials

Answer 21

End-plate
EPSP
IPSP
Pacemaker potential
Generator potential