Topic 5: Nervous Transmission Flashcards
(31 cards)
What are action potentials?
nerve impulses
What do nerve action potentials require?
- A membrane potential:
An electrical charge difference across cell membrane – like a battery
- And Ion Channels: allow ions to move by diffusion
If there is no action potential, the resting cell has a resting membrane potential of?
-70mv
What does actual resting membrane potential depend on?
the relative leakage channel numbers
What do leakage channels consist of and what is their function
- Cytosol high in K+ & interstitial fluid high in Na+ (sodium –potassium pumps)
- Leakage lets K+ through easily and Na+ poorly
- inside is negative relative to outside
Explain what action potential (AP) is
- Series of active events
- Channels actively open & close
- Some initial event is required to reach a voltage threshold (~ - 55 mv)
- Stimulus (Any event bringing membrane to threshold)
In action potential: What are the 2 phases that can occur after the arrival of a stimulus
Depolarizing phase
Repolarizing phase
What happens in the Depolarizing phase
- membrane potential rises and becomes positive
What happens in the Repolarizing phase
- potential restored to resting value
- may overshoot = hyperpolarizing phase
- then recovery to rest.
In Action potential events, What happens if Stimulus is strong enough to reach threshold?
- Na+ channels open
- K+ channels then open
- Sodium/potassium pump
In action potential events, What happens if the Na+ channels open
- Na+ ions enter the cell from extracellular fluid
- depolarization (positive membrane potential)
In action potential events, What happens when K+ channels open
- K+ leave the cell
- repolarization (negative membrane potential)
In action potential events what does the sodium/potassium pump restore?
restores original ion concentrations
Explain the all or none law
- This sequence is always the same
- If threshold is reached then the action potentials are always the same size.
- Stimulus must reach threshold to start
- After one AP there is a short period before next can be triggered = refractory period
- A strong stimulus changes the frequency of action potentials not the size of the peak
What effect does caffeine have on nervous transmission
Caffeine=a stimulant found in coffee, tea, cocoa, cola etc.
Acts by lowering the threshold level of the nerve
increases the possibility for a stimulus to result in a nerve potential
What effect does alcohol have on nervous transmission
Alcohol=acts as a depressant
increases the nerve threshold level
decreases the possibility of a stimulus to result in a nerve action potential
What effect does Local Anaesthetics have on nervous transmission
Local Anaesthetics = Generation of nerve action potentials can be prevented by local anaesthetics such as novocaine and xylocaine.
These drugs prevent the opening of sodium gated channels in the nerve cell membrane
pain messages are not carried from the site of injury back to the CNS.
Conduction of nerve impulses:
each section triggers the next by using what?
Local currents
Conduction of nerve impulses:
What is the function of the refractory period in conduction of nerve impulses
refractory period keeps it going the right direction
Conduction of nerve impulses:
Function of unmyelinated fibre in conduction of nerve impulses
Unmyelinated fibre = continuous conduction
Conduction of nerve impulses:
Function of fibre with myelin in conduction of nerve impulses
With myelin = saltatory conduction
- can only be triggered at Nodes of Ranvier
- Myelinated fibers faster & larger neurons faster
What is synaptic transmission and how is it triggered?
- Sequence of events at synapse
- Triggered by voltage change of the action potential
A sending neuron is described as:
Sending neuron = presynaptic
A receiving neuron is described as:
Receiving neuron = postsynaptic
