Topic 5 Part 3: Action Potentials ⚡️

what two changes result in changes to the resting membrane potential?

alterations ion concentration, change in membrane permeability to any ion

define action potential

a neural impulse; a brief electrical charge that travels down an axon

describe the action potential threshold

specific level that the potential of the membrane initiate an action potential

what makes it easier for an AP to be generated?

resting membrane at zero

what makes it harder for action potential to happen?

making resting membrane more negative

what surface do electrical signals move across?

muscle tissue

what is the term used to describe an electrical signal that moves across the surface of muscle tissue?

excitable

define depolarisation

The change from a negative resting potential to a positive action potential (caused by opening of sodium channels)

define repolarisation

The change from a positive action potential back to a negative resting potential (caused by opening of potassium channels)

define hyperpolarisation

Hyperpolarisation is a change in a cell's membrane potential that makes it more negative

Is the resting membrane potential polarised or non-polarised?

polarised

Which side of the membrane is positive?

outside

what side of the membrane is negative?

inside

how do neurons generate and transmit an electrical signal?

by generating action potentials that propagate along axons

what are the two types of potentials?

graded and action

How are graded potentials generated?

By the opening of mechanically or ligand-gated ion channels that allow sodium to move into the cell (small quantities)

how do graded potentials lose their strength?

leakage of charge across the membrane

are graded potentials proportional or not proportional to the strength of the triggering event?

proportional

what do graded potentials need to overcome in order to stimulate an action potential?

Action potential threshold

Do graded potentials travel a long distance or a short distance?

short

do action potential travel long or short distances?

long

What are graded potential activated by?

mechanical or chemical gated channels

what are action potentials generated by?

voltage-gated channels

describe what is meant by graded potentials

changes to the membrane potential in response to weak stimuli that allow sodium to enter but insufficient amount

what direction do action potential travel?

forward

describe the 'all or nothing rule' for action potentials

Na floods into membrane, generates enough charge to open adjacent Na channels, AP moves along the axon

define depolarising in relation to the ions

more positively charged membrane as Na is more permeable

define repolarising in relation to ions

more potassium ions enter the membrane making it more negative

wha tis the normal resting membrane potential?

-70mV

Which ion starts the action potential?

Sodium (Na+)

how many voltage gates does sodium have?

2

how many voltage gates does potassium have?

1

which of sodium and potassium channels respond more rapidly to the change in voltage at the membrane?

sodium

Describe voltage gated sodium channels

sodium channels open = influx of sodium along electrochemical gradient, activation and inactivation gates stimulated at same time

how many states does the voltage gated sodium channel have?

3

how many states does the voltage gated potassium channel have?

2

TRUE OR FALSE

Sodium channels are still open when potassium ions fold out of the cell along the chemical gradient

False

what value in mV is the membrane potential at hyperpolarisation?

-90mV

What is the RMP of a neuron?

-70 mV

what is the voltage when an action potential is released?

+30mV

describe the absolute refractory period

Time in which the cells cannot respond to a stimulus

what is the purpose of the absolute refractory period?

assures one way travelling of action potential from trigger point

when can activation only occur and relies on a stronger than normal stimulus to reach threshold levels?

relative refractory period

does the amplitude of action potential change? what changes?

no, frequency

what does an increase in frequency do in relation to action potentials?

shortens the time between each action potential

what chemical blocks the voltage gated sodium channel?

tetrodotoxin (TTX)

What is tetrodotoxin?

made in ovaries and liver of Japanese puffer fish (fugu)

where does the action potential propagate?

from cell body down to the axon terminal

what is the rate of propagation dependant on?

axon diameter, degree of myelination

why does the voltage of graded potential decay over distances in the dendrites?

no myelin

describe continuous conduction

When one segment of the membrane depolarizes the flood of Na+ causes gated channels in the next section to open, etc.

Describe saltatory conduction

jumping of an action potential from node to node (node of ranvier)

how much faster is saltatory conduction compared to continuous conduction?

30 times

What might people with multiple sclerosis experience as a result of damage of myelin on axons?

muscle weakness fatigue, difficulty walking, can lose vision

what does lidocaine do to extend the effects of anaesthesia?

block voltage gated sodium channels