What chemicals are released when a nerve impulse arrives at the synapse?

When an electrical nerve impulse reaches the end of an axon, it triggers a sequence of events that lead to the release of neurotransmitters, which are specialized chemical messengers that transmit the signal to the neighboring neuron. The specific neurotransmitters released depend on the type of synapse.

In general, there are two main types of synapses:

1. Chemical synapses: In these synapses, neurotransmitters are released into the synaptic cleft, which is the gap between the pre- and post-synaptic neurons. The neurotransmitters bind to receptors on the post-synaptic neuron, causing an electrical signal to be generated in that neuron.

2. Electrical synapses: In electrical synapses, the pre- and post-synaptic neurons are directly connected by gap junctions, which allow ions to flow between the neurons. This results in a direct electrical connection, rather than a chemical signal being released.

Here are some common neurotransmitters that are released at chemical synapses:

1. Acetylcholine (ACh): ACh is a neurotransmitter that is involved in many functions, including muscle contractions, memory, and arousal. It is found in both the central and peripheral nervous systems.

2. Dopamine (DA): DA is involved in reward, motivation, and movement. It is produced in the brain and is associated with feelings of pleasure, as well as with drug addiction and Parkinson's disease.

3. Serotonin (5-HT): Serotonin plays a role in mood regulation, sleep, and appetite. It is produced in the brain and gut, and is associated with feelings of well-being and happiness.

4. Noradrenaline (norepinephrine): Noradrenaline is released by the sympathetic nervous system and is important for the body's response to stress. It increases heart rate, blood pressure, and breathing.

5. Glutamate: Glutamate is the primary excitatory neurotransmitter in the central nervous system. It plays a crucial role in learning, memory, and cognition.

6. GABA (gamma-aminobutyric acid): GABA is the primary inhibitory neurotransmitter in the central nervous system. It helps to reduce neuronal excitability and has calming effects.

The release of these neurotransmitters is essential for the transmission of signals between neurons and for the proper functioning of the nervous system. Dysregulation of neurotransmitter levels or signaling can lead to various neurological and psychiatric disorders.