Nervensystems

Nervous systems are complex networks that coordinate perception, behavior, and homeostasis in animals. They are built from neurons and glial cells organized into circuits that transmit information as electrical impulses and chemical signals.

Most animals have a centralized nervous system, divided into a central nervous system (CNS) and a peripheral nervous system (PNS). The CNS, consisting of the brain and spinal cord in vertebrates, integrates sensory input and generates motor commands. The PNS comprises nerves and ganglia that carry signals to and from the CNS and connect to muscles, glands, and organs. Some simple animals rely on nerve nets rather than a true CNS.

Neurons are the primary signaling units. They communicate through synapses, releasing neurotransmitters that influence the activity of downstream neurons, muscles, or glands. Glial cells provide support, insulation, and metabolic help; oligodendrocytes and Schwann cells form myelin sheaths that increase conduction speed.

Functions include sensation, perception, movement, and autonomic regulation of internal states such as heart rate, digestion, and respiration. Neural circuits exhibit plasticity, enabling learning and memory through changes in synaptic strength and network structure.

Developmentally, nervous tissue arises from the ectoderm; in vertebrates, the CNS is encased in protective bone and meninges. Evolutionarily, nervous systems vary from diffuse nerve nets in some invertebrates to highly centralized brains in vertebrates, often accompanied by cephalization.

Damage or disease can disrupt signaling, leading to conditions such as neuropathies, stroke, epilepsy, or neurodegenerative diseases. Understanding nervous systems underpins neuroscience, medicine, and related technologies.