Action Potentials

Question 1

What is the potential difference that exists across the membrane of all cells

Answer 1

The resting membrane potential

Question 2

What is the range for the resting membrane potential

Answer 2

in the range of 20-90 mV

Question 3

Which is negative - ICF or ECF

Answer 3

ICF

Question 4

How is the charge distributed across the membrane

Answer 4

There is equal numbers of positive and negative charges in the ECF and ICF but ion/charge distribution is ‘polarized’

Question 5

What ions are in high concentration in the ECF

Answer 5

Na+ and Cl-

Question 6

What ions are in high concentrations in the ICF

Answer 6

K+

Question 7

What is the resting membrane impermeable to

Answer 7

Sodium

Question 8

What is the resting membrane permeable to

Answer 8

Potassium

Question 9

What does the diffusion of potassium leave excess of inside the cell

Answer 9

a negative charge

Question 10

What does the RMP arise from

Answer 10

the separation of charges on either side of the membrane

Question 11

What is the RMP due to

Answer 11

diffusion of potassium from cell interior through potassium channels

Question 12

What is the small amount of sodium that leaks into the cell expelled by

Answer 12

sodium potassium pump

Question 13

Although the RMP is due mainly to the diffusion of potassium from cell interior what else contributes

Answer 13

Na/K pump exchanging unequal numbers of sodium and potassium

Question 14

What is the rising phase in an AP due to

Answer 14

na influx from voltage gated channels

Question 15

What is the falling phase in an AP due to

Answer 15

K efflux through voltage gated channels

Question 16

What are the ion channels

Answer 16

they are membrane proteins

they are aqueous channels through the membrane

Question 17

What are the different types of gated opening channels

Answer 17

ligand

voltage

Question 18

What are the ion specific channels

Answer 18

sodium
potassium
calcium 2+

Question 19

What are the 2 gates on the voltage gated sodium channel

Answer 19

m gate

h gate

Question 20

When the channel is closed what gate is open and which is closed

Answer 20

The m gate is closed

The h gate is open

Question 21

When the channel is open which gate is open and which is closed

Answer 21

The m gate is open

The h gate is open

Question 22

When the channel is closed during the refractory period which gate is open and which is closed

Answer 22

The m gate is open

The h gate is closed

Question 23

Describe the stages of an AP

Answer 23

1. stimulus applied results in depolarization meaning that the MP moves towards the treshold
2. threshold is reached causing sodium channels to open and a sodium influx causing more depolarization while the potassium channels remain closed
3. When MP reaches the peak the sodium channels shut with inactivation of the h gate closes. potassium channels are open and efflux begins
4. Sodium channels are inactivated resulting in the refractory period while K efflux continues

Question 24

What does the refractory period mean

Answer 24

It is a period of inexcitability

After an AP is initiated, the neuron cannot generate another AP until the first one has ended

Question 25

What is the refractory period due to

Answer 25

``` inactivation of voltage gated sodium channels The inactivation ('h) gates are shut so sodium cannot diffuse into the neuron ```

Question 26

What are the consequences of the refractory period

Answer 26

it limits maximum firing frequency of AP in axons it ensures unidirectional propagation of action potentials It prevents summation of contractions in cardiac muscle - the cardiac AP lasts as long as the ventricular contraction

Question 27

Describe AP propagation

Answer 27

AP in one section of axon sets up longitudinal current flow This depolarizes adjacent resting parts of the axon AP is regenerated further along the axon More current flows and the next region of the axon is activated AP travel as a wave

Question 28

How does axon diameter effect the speed of AP propagation

Answer 28

it increases as the axon diameter increases

Question 29

What does myelin do

Answer 29

speeds up AP propagation

Question 30

Why are not all axons myelinated

Answer 30

Shwann cells make up the myelinated axon and these cells require nutrients to survive This means an increased number of cells meaning they require more energy so isn't efficient if speedy AP is not required

Question 31

How does myelin speed up conduction

Answer 31

It forms an insulating layer, reducing leakage of current from axon

Question 32

What are nodes of ranvier

Answer 32

Where the myelin sheet is interrupted | Here the axon membrane is exposed to the ECF and ion flow can occur

Question 33

What is saltatory conduction

Answer 33

Saltatory conduction (from the Latin saltare, to hop or leap) is the propagation of action potentials along myelinated axons from one node of Ranvier to the next node, increasing the conduction velocity of action potentials.

Question 34

What is the endoneurium

Answer 34

a layer of connective tissue around the myelin sheath of each nerve fiber in the peripheral nervous system

Question 35

What is the perineurium

Answer 35

the sheath of connective tissue surrounding a bundle (fascicle) of nerve fibres within a nerve

Question 36

What is the epineurium

Answer 36

The epineurium is the outermost layer of dense irregular connective tissue surrounding a peripheral nerve

Question 37

What is the end, peri and epineurium made up of

Answer 37

lipid

Question 38

What respects are the axons in peripheral nerves different

Answer 38

``` in their size (axon diameter and conduction velocity function (sensory, motor) ```

Question 39

What are the axon types present in cutaneous nerves

Answer 39

Abeta Adelta C

Question 40

What is the structure of Abeta nerves in cutaneous nerves

Answer 40

myelinated

Question 41

What is the structure of Adelta nerves in cutaneous nerves

Answer 41

myelinated

Question 42

What is the structure of C nerves in cutaneous nerves

Answer 42

unmyelianted

Question 43

What is the function of Abeta nerves

Answer 43

mechanoreceptors

Question 44

What is the function of Adelta nerves

Answer 44

mechanoreceptors thermoreceptors (cold) nociceptors chemoreceptors (taste)

Question 45

What is the function of C nerves

Answer 45

mechanoreceptors thermoreceptors (hot and hot) nociceptors

Question 46

Is there a lot of myelinated axons in the coronal tooth pulp

Answer 46

In the pulp there will be a larger number of unmyelinated fibers