Flashcards in Nerves Deck (46)
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1
Examples of graded potentials
Generator potentials at sensory receptors
Postsynaptic potentials at synapses
Endplate potentials at neuromuscular junction
Pacemaker potentials in pace maker tissues
2
How are graded potentials decremental
loose signal therefore can only be used over short distances
3
How are graded potentials graded
as the intensity of stimuli effects signals amplitude
4
How can cells be hyperpolorised
Opening of Cl gates, letting Cl in- fast ISPS
Opening K gates letting K out the cell - slow ISPS
5
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
6
Why is potassium gates slower in producing a response
are G protein coupled - metabotrophic
7
How are post synaptic potentials produced
by a neurotransmitter opening or closing ion channels
= ligand-gated ion channels
8
What are the two different ways Graded potentials can summate
Temporal - same signal
spatial - different signals
9
Name two inhibitory PSP
GABA and Glycine
10
What must happen for an action potential to be fired
reach threshold potential > -55mV
11
What depolarises cells in AP quickly
Na channels open and move into cell rapidly then close again
12
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
13
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
14
How do action potentials self propagate
When a voltage gate opens it depolarises the next gate stimulating it to open as well
15
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
16
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
17
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
18
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
19
What are the gaps in-between myelin sheath called
Nodes of ranvier
20
What is the movement because the refractory period of cells called
saltatory conduction
21
What is myelin sheath produced by in the CNS and the PNS
CNS- oligodendrites
PNS- schwann cells
22
Where are the voltage gated Na channles located
In between myelinated axons = Node of raniver
23
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.
24
What is the effect of demyelination
Big local current delays quicker, therefore does not depolarise the next node e.g. multiple sclerosis
25
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
B
C (smallest)
26
What size of fibres are most sensitive to anaesthetics
small fibres - C
27
What type of fibres are most likely to go numb if you lie in them for to long e.g. anoxia
Large fibres
28
What fibre signal is the fastest and what
A alpha because it has the largest axon
29
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
30
