Session 5: Action Potential and Synaptic Transmission Flashcards
Describe the properties of voltage-gated ion channels
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Describe the general features of electrically excitable membranes
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Describe the permeability changes associated with the action potential
Permeability to Na increases as sodium channels open when the membrane depolarises
What factors can affect conduction velocity in nerves?
The axon diameter
Myelination
Resistance
Capacitance
How do ligand-gated ion channels work?
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What steps are involved in the neurotransmission at the mammalian neuromuscular junction?
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Why is the control of intracellular Ca2+ concentration so important?
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What is saltatory conduction?
The propagation of action potentials along myelinated axons from one Node of Ranvier to the next node. This increases the conduction velocity of action potentials
How does conduction work in unmyelinated nerves?
The local current theory:
The first action potential occurs at the stimulus and propagates along the neuron by altering the membrane potential around the channels, when it reaches threshold the nearby channels will open and the action potential propagation continues
How does conduction work in myelinated nerves?
It works by jumping between nodes of Ranvier, where the action potential occurs and allowing the conduction to occur with greater conduction velocity, skipping the internodal region
How do the ionic movements through ion channels occur in myelinated nerve fibres?
They occur through Na+ channels at the Nodes of Ranvier where there is a high density of Na+ channels
How does myelination occur?
It is formed by cells:
Schwann cells in peripheral axons
Oligodendrocytes in CNS axons
When during development does myelination occur?
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What conditions cause demyelination to occur?
Multiple Sclerosis (all CNA nerves) Devic's disease (optic and spinal cord nerves)
What are the consequences of demyelination?
Poorer transition of the local circuit which therefore fails to reach threshold and the signal is not propagated along the axon
Density of the action current is reduced because of resistive and capacitive shunting
Some myelinated nerve fibres are able to regenerate from the central end if cut. Does this occur in the PNS or the CNS? What is the rate of such regeneration?
This regeneration occurs in the PNS, not in the CNS
What is known of the distribution of ion channels in the myelinated nerve fibres?
The ion channels are found at the nodes of Ranvier in high densities and very few are found in the internodal region
Describe the properties of the action potential
- Change in voltage across the membrane
- Depends on ionic gradients and relative permeability
- Only occurs if threshold is reached
- It is all or nothing
- It is propagation without loss of amplitude
Describe the ionic basis of the action potential and the associated changes in membrane ionic permeability
It is generated by an increase in permeability to Na+, bringing the membrane close to the Na+ equilibrium potential which re
What is the basis of the all-or-nothing law?
That the depolarisation of the membrane needs to reach a threshold level in order to generate an action potential, once over the threshold the same action potential is generated despite the strength of the signal
What is refractoriness?
The idea that behind the action potential, the sodium channels are still recovering and are inactive, yet the K+ channels are activated. There is a refractory period where no action potential can be generated in the area that has just been activated
What are the key molecular properties of ion channels?
q
Outline the action of local anasthetics
Work by blocking Na+ channels and thereofore blocking action potentials
What is the basis of extracellular recording
Voltage-clamp
Electrical stimulation under a cathode (-), excitability can be reduced under an anode (+). Which can be used to stimulate an axon or group of axons to threshold, thus initiating an action potential
