Synapses

• A synapse is the junction between a neuron and another neurone, or between a neurone and an effector cell.
• The tiny gap between the cells at the synapse is called the synaptic cleft.
• The presynaptic neurone has a swelling called a synaptic knob. This contains synaptic vesicles filled with chemicals called neurotransmitters.
• When an action potential reaches the end of a neurone it causes neurotransmitters to be released into the synaptic cleft. They diffuse across the postsynaptic membrane and bind to specific receptors.
• When neurotransmitters bind to receptors they might trigger an action potential, cause muscle contraction or cause a hormone to be secreted.
• Neurotransmitters are removed from the cleft so that the response doesn't keep happening (taken back to the presynaptic neurone or broken down by enzymes).
• There are many different neurotransmitters. Synapses that use acetyletylcholine are called cholinergic synapses. Their structure is the same. They bind to receptors called cholinergic receptors and are broken down by acetylcholinesterase.
• Synapses can be exitatory or inhibitory.