Synapses

Synapse

- A synapse is the junction between a neurone and another neurone or between neurone and an effector cell e.g. a muscle or gland - The gap between the cells at a synapse is called the synaptic cleft. - The presynaptic neurone (the one before the synapse) has a swelling called the synaptic knob. - This contains synaptic vesicles filled with chemicals called neurotransmitters.

Explain the presynaptic process of neurotransmitter transmission

- An action potential arrives at the synaptic knob of the presynaptic neurone. - The action potential stimulates the voltage gated calcium ion channels in the presynaptic neurone to open. - Calcium ions diffuse into the synaptic knob (and they are pumped out afterwards by active transport) - The influx of calcium ions into the synaptic knob causes the synaptic vesicles to move to the presynaptic membrane. - They then fuse with the membrane and the vesicles release the neurotransmitter into the synaptic cleft through exocytosis.

Explain the postsynaptic process of neurotransmitter transmission

- The neurotransmitter diffuses across the synaptic cleft and binds to specific receptors on the postsynaptic membrane. - This causes sodium ion channels in the postsynaptic neurone to open. - The influx of sodium ions into the postsynaptic membrane causes depolarisation. - An action potential on the postsynaptic membrane is generated if the threshold is reached. - The neurotransmitter is removed from the synaptic cleft so the response doesn't keep happening

Outline how synapses work

- When an action potential reaches the end of a neurone it causes neurotransmitters to be released into the synaptic cleft. - They diffuse across to the postsynaptic membrane (the one after the synapse) and bind to specific receptors. - When neurotransmitters bind to receptors they might trigger an action potential (in a neurone), cause muscle contraction (in a muscle cell), or cause a hormone to be secreted (from a gland cell)

Synaptic convergence

- When many neurones connect to one neurone information can be amplified (made stronger).

Synaptic divergence

- When one neurone connects to many neurones information can be dispersed to different parts of the body.