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Examples of graded potentials

Generator potentials at sensory receptors
Postsynaptic potentials at synapses
Endplate potentials at neuromuscular junction
Pacemaker potentials in pace maker tissues


How are graded potentials decremental

loose signal therefore can only be used over short distances


How are graded potentials graded

as the intensity of stimuli effects signals amplitude


How can cells be hyperpolorised

Opening of Cl gates, letting Cl in- fast ISPS
Opening K gates letting K out the cell - slow ISPS


How can cells be depolarised

Opening Na gate letting Na into the cell - fast ESPS
closing K gate, so K remains in the cell - slow EPSP


Why is potassium gates slower in producing a response

are G protein coupled - metabotrophic


How are post synaptic potentials produced

by a neurotransmitter opening or closing ion channels
= ligand-gated ion channels


What are the two different ways Graded potentials can summate

Temporal - same signal
spatial - different signals


Name two inhibitory PSP

GABA and Glycine


What must happen for an action potential to be fired

reach threshold potential > -55mV


What depolarises cells in AP quickly

Na channels open and move into cell rapidly then close again


What are the two different threshold stimulus

Sub threshold -sits above threshold but decreases as travels, therefore no AP fired
Suprathreshold - remains above threshold, fired AP


How does the refractory period occur

Threshold is reached and opens Na channels they only stay open for a short time though.
K+ permeability slowly rises as more K+ channels (this time the voltage dependent ones) open and leave the cell this causes repolarisation, and we eventually return to RMP


How do action potentials self propagate

When a voltage gate opens it depolarises the next gate stimulating it to open as well


How can signle only move forward

As the neighbouring gate thats just stimulated the other gate is now in refractory period therefore can not be stimulated to open again so signal can only be passed forward


How is the speed of AP increased

Larger axons - conducts quicker as resistance decreased, passive current spreads quicker
Myelination - increase the membrane resistance, preventing current leaking out, so passive current spreads quicker


What are properties of AP

mediated by voltage-gated channels
have a threshold
are all-or-none
can only encoded stimulus intensity in their firing frequency, not amplitude
are self-propagating
have a refractory period
travel slowly


Why is the frequency of the signals encoded

As AP fired are all the same size due to all or non phenomenon, therefore its how stimulus intensity is measured


What are the gaps in-between myelin sheath called

Nodes of ranvier


What is the movement because the refractory period of cells called

saltatory conduction


What is myelin sheath produced by in the CNS and the PNS

CNS- oligodendrites
PNS- schwann cells


Where are the voltage gated Na channles located

In between myelinated axons = Node of raniver


How does myelin sheath do to our AP conduction

The depolarisation evoked by voltage-gated Na channels at one node of Ranvier by spreads as a local circuit While this is decremental it travels further because less current is wasted leaking out of the membrane or charging up the capacitance, therefore big enough to reach the next node and trigger another AP.


What is the effect of demyelination

Big local current delays quicker, therefore does not depolarise the next node e.g. multiple sclerosis


What is the order of action potential fibres in most sensitivity to pressure and least sensitive to anaesthetics

A alpha (biggest)
A beta
A gamma
A delta
C (smallest)


What size of fibres are most sensitive to anaesthetics

small fibres - C


What type of fibres are most likely to go numb if you lie in them for to long e.g. anoxia

Large fibres


What fibre signal is the fastest and what

A alpha because it has the largest axon


List what happens at NMJ?

Action potential in motor neurone
Opens voltage-gated Ca2+ channels in presynaptic terminal
Triggers fusion of vesicles
Acetylcholine (ACh) released
Diffuses across synaptic cleft
Binds to ACh (nicotinic) receptors
Opens ligand-gated Na+/K+ channels
Evokes graded (local) potential (end plate potential)
Always depolarises adjacent membrane to threshold
Opens voltage-gated Na+ channels - evokes new AP
ACh removed by acetylcholinesterase


How does tetoduoxin work

Blocks Na+ channel

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