What causes multiple sclerosis (MS) ?
Axonal neurotransmission failure
Degeneration of myelin and development of scar tissue disrupts and eventually blocks neurotransmission along myelinated axons
What is temporal summation?
From a single neurone
When one presynaptic neurone releases neurotransmitter many times over a period of time to achieve the threshold on the postsynaptic neurone.
What is spatial summation?
From multiple neurones
When multiple presynaptic neurones together release enough neurotransmitter to exceed the threshold of the postsynaptic neurone
What do excitatory neurotransmitters do?
- Depolarise the cell membrane
- Increase probability of an action potential being elicited
- Causing an Excitatory Post Synaptic Potential (EPSP)
What do inhibitory neurotransmitters do?
- Hyperpolarise the cell membrane
- Decrease probability of an action potential being elicited
- Causing an Inhibitory Post Synaptic Potential (IPSP)
What is the threshold of excitation?
-60mv
How does Ouabain work?
Dart poison for hunting
Selectively blocks the Sodium/Potassium Pump so that the neurones cannot restore resting potential following an action potential
What is lidocaine and how does it work?
Local anaesthetics
Blocks voltage gate sodium ion channels which stops action potentials from being generated
What is the role of the myelin sheath?
Insulates sections of the axon leading to faster and more accurate transmission
What is saltatory conduction?
Decremental conduction between nodes of ranvier increasing velocity of action potential
Describe synaptic transmission
- Calcium ion channels open when action potential reaches pre-synaptic terminal
- Ca+ ions cause vesicles to move to release sites, fuse with the cell membrane and discharge their contents through exocytosis
- Neurotransmitter diffuses across synaptic cleft
- Attach to receptor sites on dendrites of post-synaptic membrane
What are the 3 ways that excess neurotransmitter is removed from the synaptic cleft?
- Diffuses out and is destroyed by surrounding tissues
- Transmitter re-uptake into the pre or postsynaptic terminal for reuse
- Enzymatic Degradation
