What type of substances are released by nerves to affect target cells?

Nerves release neurotransmitters to communicate with target cells effectively. Neurotransmitters are chemical messengers that transmit signals across synapses from one neuron to another or to non-neuronal cells such as muscle or gland cells. This precise mechanism allows for rapid communication within the nervous system, facilitating essential functions such as muscle contraction, glandular secretion, and various central nervous system activities like mood regulation and cognition.

Neurotransmitters operate at synaptic junctions, where they bind to specific receptors on target cells, triggering a response that can be excitatory or inhibitory depending on the type of neurotransmitter and receptor involved. Examples of well-known neurotransmitters include dopamine, serotonin, acetylcholine, and norepinephrine, each playing a critical role in various physiological processes.

Other substances listed, such as hormones, cytokines, and antibodies, function in different biological systems. Hormones are released into the bloodstream by endocrine glands to affect distant target cells and regulate various physiological activities over longer durations. Cytokines are signaling proteins typically involved in immune responses, helping to modulate the immune system. Antibodies are proteins produced by B-cells in response to antigens, playing a role in the immune response by identifying and neutralizing pathogens.