Nerves

Question 1

How is the stretch reflex tested clinically?

Answer 1

A sharp tap to the inelastic tendon e.g. patellar tendon

Question 2

How many pairs of cervical spinal nerves are there?

Answer 2

Eight

Question 3

How many pairs of cranial nerves are there?

Answer 3

Twelve

Question 4

How many pairs of thoracic spinal nerves are there?

Answer 4

Twelve

Question 5

How many pairs of lumbar spinal nerves are there?

Answer 5

Five

Question 6

How many pairs of sacral spinal nerves are there?

Answer 6

Five

Question 7

How many pairs of coccygeal spinal nerves are there?

Answer 7

One

Question 8

How many pairs of spinal nerves are there altogether (not including cranial)?

Answer 8

Thirty one

Question 9

What is another term for the axon hillock?

Answer 9

Initial segment

Question 10

Which synaptic terminals release the neurotransmitter - presynaptic or postsynaptic?

Answer 10

Presynaptic

Question 11

Which cells form myelin sheaths in the CNS?

Answer 11

Oligodendrocytes

Question 12

What is the definition of the cell’s membrane potential? (Hint: think about how it’s measured)

Answer 12

The potential difference between the outside of the cell and the inside

Question 13

What would would happen to a person’s heart if someone intravenously administered 100mmol K+ to them, and why?

Answer 13

The rise in [K+] outside the cell would reduce the concentration gradient, as most of the K+ is inside. If the concentration is reduced then, according to Nernst, the electrical gradient will be reduced too. The cell will therefore depolarise - and the patient will exhibit ventricular fibrillation, and cardiac arrest.

Question 14

What would would happen to a person’s brain if someone intravenously administered 100mmol K+ to them, and why?

Answer 14

The brain is protected from changes in plasma [K+] thanks to tight capillaries, astrocytes and tight junctions between cells.

Question 15

When the Nernst equation is used to calculate the resting membrane potential, the answer is around -90mV. What is the main reason that the actual value is closer to -70mV?

Answer 15

The actual value is calculated using the Goldman equation (lots of Nernst equations added together), which takes into account other ions such as sodium and chloride, as well as potassium.

Question 16

Will the cell depolarise or hyperpolarise if you open

(more) K+ channels?

Answer 16

Hyperpolarise

Question 17

Will the cell depolarise or hyperpolarise if you open

Na+ channels?

Answer 17

Depolarise

Question 18

Will the cell depolarise or hyperpolarise if you open

Cl- channels?

Answer 18

Hyperpolarise

Question 19

Will the cell depolarise or hyperpolarise if you open

Ca2+ channels?

Answer 19

Depolarise

Question 20

Can you have high intensity and low intensity graded potentials?

Answer 20

Yes - it’s only action potentials that are ‘all or nothing’

Question 21

Are graded potentials depolarising or hyperpolarising?

Answer 21

Graded potentials can be depolarising OR hyperpolarising

Question 22

How are fast IPSPs (inhibitory postsynaptic potentials) achieved?

Answer 22

Certain neurotransmitters activate chloride ion channels, generating a fast IPSP by causing an influx of chloride ions into the cell, making the inside even more negative.

Question 23

How are slow IPSPs (inhibitory postsynaptic potentials) achieved?

Answer 23

Some neurotransmitters target G protein-coupled receptors, which in turn open (more) potassium channels. Potassium flows out following its concentration gradient, making the outside of the cell more positive and leaving the inside more negative. This happens slowly as potassium is already closer to its equilibrium at resting state, so there isn’t as much of a ‘pull’.

Question 24

How are fast EPSPs (excitatory postsynaptic potentials) achieved?

Answer 24

Ligands binding to sodium channels allow sodium to follow its concentration gradient into the cell. The net effect is a sharp rise in the positivity of the inside of the cell, and thus closer to the threshold, where it will eventually trigger an action potential.

Question 25

How are slow EPSPs (excitatory postsynaptic potentials) achieved?

Answer 25

Some ligands can bind to G protein-coupled receptors and induce the closure of potassium channels. This creates a slow build up of positive charge within the cell, leading to depolarisation.

Question 26

Which ion is responsible for the time taken to reach peak membrane potential during an action potential - Na+ or K+?

Answer 26

Na+

Question 27

Which ion is responsible for the time taken to return to normal membrane potential after an action potential - Na+ or K+?

Answer 27

K+

Question 28

Which cells deposit myelin sheaths in the PNS?

Answer 28

Schwann cells

Question 29

What is the name for the type of conduction that occurs in myelinated nerves, where the propagation of the action potential occurs by ‘leaping’ from one node to the next?

Answer 29

Saltatory conduction

Question 30

What is the mechanism of action of tetrodotoxin?

Answer 30

Blocks sodium channels and so blocks the action potential

Question 31

What is the mechanism of action of the joro spider toxin?

Answer 31

Blocks voltage gated calcium channels and so stops transmitter release

Question 32

What is the mechanism of action of botulinum toxin (botox)?

Answer 32

Disrupts the release machinery and so blocks transmitter release - stops proteins responding to calcium channels

Question 33

What is the mechanism of action of curare?

Answer 33

Blocks acetylcholine receptors and so prevents the endplate potential

Question 34

What is the mechanism of action of anticholinesterase?

Answer 34

Blocks acetylcholine breakdown and so increases transmission at the neuromuscular junction