The Synapse

The gap between two nerves or between a nerve and a muscle cell is called the synapse or synaptic gap (20 nm). The axon bringing the action potential signal is on the presynaptic neuron. The axon terminals of the presynaptic neuron contain vesicles with neurotransmitter chemicals. The action potential causes the neurotransmitter chemicals to be released in the synaptic gap by exocytosis. The neurotransmitters diffuse through the extra-cellular fluid and bind to specific neurotransmitter receptors on the membranes of the post-synaptic neurons dendrites.

There are over 60 neurotransmitters including acetylcholine, serotonin, dopamine and norepinephrine. The neurotransmitters can be:
1. Excitatory – cause Na+ channels to open in the postsynaptic neuron, increasing the possibility of initiating an action potential.
2. Inhibitory – cause K+ channels to open in the post-synpatic neuron, causing the dendrites to be hyperpolarized (-100 mV) and decreases the possibility of generating an action potential.

1. Pre-synaptic neuron generating action potential
2. Post-synaptic neuron receiving action potential signal
3. Axon terminal vesicles containing neurotransmitters
4. Mitochondria providing energy
5. The synapse or space between the pre-synaptic and post-synaptic neurons
6. Neurotransmitters diffuse through synapse
7. Dendrite of post-synaptic neuron with protein receptors for neurotransmitters
8. Enzymes are released from post-synaptic dendrite that break down neurotransmitters.

The Synapse

The gap between two nerves or between a nerve and a muscle cell is called the ________ _____________________________________________. The axon bringing the action potential signal is on the __________________________________ neuron. The ____________________ of the presynaptic neuron __________________________________________________. The ____________________________________________________________________ in the synaptic gap by _________________________. The neurotransmitters _______________ through the extra-cellular fluid and