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Flashcards in Action Potential Deck (34)
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What is the resting membrane potential



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

ICF is negative
ECF is positive


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

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


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

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


Describe the diffusion potential of a cell at resting membrane potential

Impermeable to Na
Very permeable to K


Describe the diffusion gradients of a cell

Na diffuses into the cell
K diffuses out of the cell


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


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

It is expelled by the Na/K pump


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


What causes an action potential to form

A stimulus


What is the threshold in an action potential

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


What causes the falling phase in an action potential

Voltage gated K channels open allowing K efflux


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


Describe a voltage gated sodium channel at resting membrane potential

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


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


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


Describe a voltage gated potassium channel

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


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


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


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


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


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


What increases the speed of action potential propagation

Increasing axon diameter
Myelin sheaths


What is a myelin sheath

Many layers of cell membranes wrapped around the axon


What cells lay down myelin sheaths

CNS - oligodendrocytes
PNS - Schwann cells


What is the function of myelin sheaths

Forms an insulating layer, reducing leakage of current from axons


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


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


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


What are the function of Ab axons



What are the functions of As axons

Thermoreceptors (cold)
Chemoreceptors (taste)


What are the functions of C axons

Thermoreceptors (hot and cold)


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


Which type of axon forms the majority of the pulp

C fibres