Action Potential

Question 1

What does the potential in skeletal muscle change from and to?

Answer 1

-90mV -> +40mV

Question 2

What does the potential at the SAN change from and to?

Answer 2

-60mV -> +30mV

Question 3

What does the potential in a cardiac ventricle change from and to?

Answer 3

-90mV -> +30mV

Question 4

Describe the ARP

Answer 4

Most Na+ channels are inactivated

Cannot fire another AP no matter how strong the stimulus

Question 5

Describe the RRP

Answer 5

Na+ channels are recovering therefore many in the closed state ready to be opened again
AP may be fired with a strong enough stimulus

Question 6

What does accommodation mean?

Answer 6

The longer the stimulus lasts, the more sodium channels will be in the inactivated state. This means a larger depolarisation is necessary to initiate AP and the amplitude of the AP will be reduced.

Question 7

Describe the Na+ channels

Answer 7

1 polypeptide
4 sets of repeated sequence
Each sequence has 6 TMDs 
Pore at the H5 region 
Voltage sensor is the 4th domain 
Has an inactivation particle that blocks the pore

Question 8

Describe the K+ channels

Answer 8

4 individual polypeptides
4 alpha subunits
6 TMDs per polypeptide
4th TMD is the voltage sensor

Question 9

How do many local anaesthetics work?

Answer 9

Block Na+ channels

Question 10

Give the order in which local anaesthetics block particular axons

Answer 10

1. Small, myelinated
2. Unmyelinated
3. Large, myelinated

Question 11

Name 2 diseases that attack the myelin sheath of the CNS

Answer 11

Multiple sclerosis

Devic’s disease

Question 12

Name 2 diseases that attack the myelin sheath of the PNS

Answer 12

Landry-Guillain-Barre Syndrome

Charcot-Marie-Tooth Disease

Question 13

What are the 4 classes of peripheral axons?

Answer 13

A alpha
A delta
B
C

Question 14

Which axons will be A alpha and are they fast or slow?

Answer 14

Fast
Sensory fibres from muscle spindle
Motor neurones to skeletal muscle

Question 15

Which axons will be A delta?

Answer 15

Sensory fibres from pain and temperature receptors (sharp, localised pain)

Question 16

Which axons will be B?

Answer 16

Preganglionic neurones of ANS

Question 17

Which axons will be C?

Answer 17

Sensory fibres from pain, temperature and itch receptors (diffuse pain)

Question 18

Which class of peripheral axon has the slowest conduction?

Answer 18

C

Question 19

Define capacitance

Answer 19

Ability to store charge

Question 20

What does the spread of local current depend on?

Answer 20

Resistance

Capacitance

Question 21

Does a larger diamter cause faster or slower conduction?

Answer 21

Faster

Question 22

What is the approximate distance between the nodes of Ranvier?

Answer 22

1mm

Question 23

How does a myelin sheath change resistance and capacitance?

Answer 23

Increases resistance

Reduces capacitance

Question 24

In myelinated axons, how do conduction velocity and diameter relate?

Answer 24

Conduction velocity is proportional to diameter

Question 25

In unmyelinated axons, how do conduction velocity and diameter relate?

Answer 25

Conduction velocity is proportional to the square root of the diameter

Question 26

When are unmyelinated axons faster than myelinated?

Answer 26

When the diameter is less than 1 micrometer

Question 27

What does the potential in an axon change from and to?

Answer 27

-70mV -> +30mV