What substances are released by nerves to affect cells?

Neurotransmitters are chemical messengers that are released by nerve cells (neurons) to communicate with other cells, including other neurons, muscle cells, or gland cells. When an electrical impulse travels down a neuron to its terminal, neurotransmitters are released into the synaptic cleft, the space between neurons. These substances bind to specific receptors on the target cell, leading to a response that can include muscle contraction, stimulation of another neuron, or secretion of hormones.

This mechanism of neurotransmitter action is fundamental to the functioning of the nervous system, as it allows for rapid and precise communication between cells, enabling everything from reflexes to complex behaviors. The nature and type of neurotransmitters (such as dopamine, serotonin, and acetylcholine) affect various physiological processes and are crucial for maintaining homeostasis in the body.

In contrast, hormones are released into the bloodstream by endocrine glands and have effects on distant target cells, enzymes facilitate biochemical reactions but do not serve as communicators between nerve cells, and cytokines are involved in immune responses and signaling between cells in the immune system rather than in direct nerve-to-cell communication.