signalling in the nervous system

Question 1

why is there a Resting membrane potential (RMP)

Answer 1

it Arises due to a difference in charge (due to
ions) between the inside and outside of the
neuron at rest
• More +ve ions outside cell / more –ve ions
inside cell
• Measured in relation to outside, therefore RMP
is a –ve value
• Typical RMP of neurons -60mV to -70mV

Question 2

voltage-gated

Answer 2

opened / closed depending on

membrane potential

Question 3

ligand-gated

Answer 3

opened in response to binding /

activation by neurotransmitter or drug

Question 4

Equilibrium potential:

Answer 4

membrane potential where No
ions entering cell =
No
ions leaving cell (no net gain or loss of ions)

Question 5

principal features of the action potential

Answer 5

an action potential is very brief but dramatic change in membrane potential.
depolarisation, repolarisation , hyperpolarisation

Question 6

what is depolarisation related to

Answer 6

increased permeability to Na+ ions . fast opening of voltage gated Na channels

Question 7

repolarisation and hyperpolarisation due to

Answer 7

increased permeability of potassium ions .

slow opening of voltage gated K channels

Question 8

voltage gated sodium channel drugs in medicine

Answer 8

lidocaine = sodium channel antagonist

Question 9

positive charge can travel where?

Answer 9

along axon

out of axon via membrane

Question 10

destination of current depends on

Answer 10

1. axon diameter 2. number of open pores /channels in membrane

Question 11

Saltatory conduction

Answer 11

Action potential ‘jumps’ from node to node in the myelinated axon. increasing the conduction velocity of action potentials

Question 12

Synaptic transmission

Answer 12

Chemical transmission between excitable cells.

1. Action potential enters presynaptic terminal
2. calcium ion entry through votage gated calcium channels
3. docking of synaptic vesicles containing neurotransmitters
4. neurotransmitters released -exocytosis
5. neurotransmitter bids to and activates receptorson post synaptic membrane
6. ions sodium and chloride ions enter the cell
7. causes depolarisation(excitation) or hyperpolarisation (inhibition)

Question 13

Excitatory postsynaptic

potential (EPSP)

Answer 13

An EPSP brings the post-synaptic membrane closer to threshold
(depolarisation), therefore increasing the probability of the postsynaptic
cell producing an action potential

Question 14

Inhibitory postsynaptic

potential (IPSP)

Answer 14

An IPSP moves the post-synaptic membrane further away from threshold
(hyperpolarisation), therefore reducing the probability of the postsynaptic
cell producing an action potential

Question 15

temporal summation

Answer 15

frequency of firing

Question 16

spatial summation

Answer 16

firing at multiple sites.

mechanism of eliciting an action potential in a neuron with input from multiple presynaptic cells

Question 17

what is botulism

Answer 17

it affects the neuromuscular junction .
clostridium bacteria produces botulinum toxin and it disrupts exocytosis preventing ACh release .
Causes skeletal muscle weakness and paralysis of the diaphragm

Question 18

how does myasthenia gravis affect the neuromuscular junction

Answer 18

it is an inflammatory disease
antibodies bind to ACh receptors in the post synaptic membrane at motor end plate.
Causes severe muscle weakness , particularly affects
- eyelids, eyes, face, throat , limb muscles