Synapses and brain injury
Synapse - junction between one neurone and another neurone or effector.
A neurone may have up to 10000 synapses with 1000 other cells.
Synaptic cleft - Gap between two cells.
Action potentials cannot cross a synapse.
Neurotransmitter - carries the transmission across the synaptic cleft.
Cholinergic synapses - those in which the neurotransmitter is acetylcholine (ACh)
(Note: Look in book for picture of cholinergic synapse)
Synapses consist of:
Synaptic bulb - where neurotransmitter are made. In the synaptic bulb are numerous mitochondria, together with large amounts of endoplasmic reticulum and synaptic vesicles containing the neurotransmitter.
Postsynaptic membrane - has receptors for binding the neurotransmitter.
Synaptic cleft - Bewteen the presynaptic and postsynaptic membranes.
Transmission across a cholinergic synapse
- An action potential arrives at the membrane of the synaptic bulb.
Action potential is where a stimulus above a certain intensity or threshold arrives at a receptor or nerve ending, its energy causes a temporary and rapid reversal of the polarity of the membrane of the neurone. This causes the voltage gated Na+ channel to open. Na+ diffuses rapidly into the neurone and the cell becomes positively charged inside compared with the outside. The cell is depolarised. The potential difference across the plasms membrane reaches -40mV. The sodium ion channels close and the voltage gated potassium ion channels open allowing potassium ions to diffuse out of the cell. The cell is repolarised. The potential difference overshoots slightly (-70 to -90mV) making the cell hyperpolarised. The resting membrane potential is restored by the…