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Flashcards in Action Potential Deck (34)
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1

What is the resting membrane potential

-70mV

2

At the cell membrane, are the ICF and ECF positive or negative

ICF is negative
ECF is positive

3

What concentrations of Na, K and Cl are found in the ECF

Na - 145mM
K - 4mM
Cl - 110mM

4

What concentrations of Na, K and Cl are found in the ICF

Na - 15mM
K - 150mM
Cl - 10mM

5

Describe the diffusion potential of a cell at resting membrane potential

Impermeable to Na
Very permeable to K

6

Describe the diffusion gradients of a cell

Na diffuses into the cell
K diffuses out of the cell

7

What creates the resting membrane potential

Diffusion of K gives an excess negative charge inside of the cell membrane and an excess positive charge outside of the cell

8

What happens to small amounts of Na which leak into the cell at resting membrane potential

It is expelled by the Na/K pump

9

How does the N/K pump contribute to the resting membrane potential

It exchanges unequal numbers of Na and K ions
It moves 3Na outwards and 2K inwards

10

What causes an action potential to form

A stimulus

11

What is the threshold in an action potential

The voltage at which the voltage gated sodium channels open, allowing sodium influx
-55mV

12

What causes the falling phase in an action potential

Voltage gated K channels open allowing K efflux

13

What are the different types of ion channels

Ligand gated - activated by a ligand binding to a receptor
Voltage gated - when the RMP is moved to a threshold voltage which opens the channel

14

Describe a voltage gated sodium channel at resting membrane potential

M-gate is closed and h-gate is open so sodium cannot pass through

15

Describe voltage gated sodium channels when the threshold is reached

Both the m-gate and the h-gate are open so sodium can pass through

16

Describe a voltage gated sodium channel during the refractory stage

M-gate is open but the h-gate is closed so sodium cannot pass through

17

Describe a voltage gated potassium channel

Can either be open or closed
Potassium leaves the ICF when open

18

Describe an action potential when the threshold potential is met

Na channels start opening causing sodium influx which promotes depolarisation and sodium channels keep opening
Potassium channels remain closed

19

What happens after depolarisation

When MP reaches 35mV the Na channels shut as the h-gate closes
K channels open and K efflux begins, creating a recovery to the RMP

20

What is the refractory period

The period of inexcitability of an action potential due to the inactivation of voltage gated sodium channels
The h-gates are shut so NA can’t diffuse into the neurone

21

What are the effects of the refractory period

Limits maximum firing frequency of APs in axons
Ensures unidirectional propagation of APs
Prevents summation of APs
Prevents summation of contractions in the cardiac muscle - AP lasts as long as ventricular contraction

22

Describe action potential propagation

An AP sets up longitudinal current flow
This depolarises adjacent resting parts of the axon
The AP is regenerated further along the axon
More current flows and the next region of axon is activated
APS travel along the axon as waves of depolarisation

23

What increases the speed of action potential propagation

Increasing axon diameter
Myelin sheaths

24

What is a myelin sheath

Many layers of cell membranes wrapped around the axon

25

What cells lay down myelin sheaths

CNS - oligodendrocytes
PNS - Schwann cells

26

What is the function of myelin sheaths

Forms an insulating layer, reducing leakage of current from axons

27

What are nodes of Ranvier

Points along the axon where the myelin sheath is interrupted and the axon membrane is exposed to the ECF and ion flow can occur

28

Describe saltatory conduction

In myelinated nerves, the currents spread further along the axon, so there are fewer regeneration steps per unit length of axon
So the AP propagates more rapidly than in unmyelinated axons

29

Describe the different connective tissue layers that surround axons

Endoneurium - surrounds a single axon
Perineurium - surrounds a bunch of axons joined together
Epineurium - surrounds a number of different neurones joined together

30

What are the function of Ab axons

Mechanoreceptors

31

What are the functions of As axons

Mechanoreceptors
Thermoreceptors (cold)
Nociceptors
Chemoreceptors (taste)

32

What are the functions of C axons

Mechanoreceptors
Thermoreceptors (hot and cold)
Nociceptors

33

Describe how the average axon size compared from the mental nerve to the canine nerve

The mental nerve has more axons with a large diameter while the canine nerve has more thinner axons

34

Which type of axon forms the majority of the pulp

C fibres