Nervous tissue has two main functions: sensing stimuli and sending impulses to different parts of the body as a response. This tissue is what makes up the body’s nervous system, which is split into the central nervous system and the peripheral nervous system. Tissue in the central nervous system can be found in the brain and spinal chord. The peripheral nervous system is made up of all nerves and related tissue outside of these areas, and it gathers signals from all parts of the body and sends them to the central nervous system. Nervous tissue is responsible for many of the body’s activities and processes, including memory, reasoning and emotions. Signals from this tissue also cause muscle contractions.
Neurons and glial cells make up nervous tissue. Humans have billions of neurons, in varying size, in their bodies. Neurons can be broken down into the cell body, which contains each neuron’s nucleus and mitochondria, and nerve processes. Nerve processes are made of cytoplasm and resemble thin fingers. They extend outward from the neuron and are responsible for transmitting signals both to the neuron and away from it. There are two types of nerve processes: axons and dendrites. Axons carry messages away from the neuron and dendrites transmit signals to the neuron. Together, axons and dendrites form nerves.
Glial cells — called neuroglia when located in the central nervous system — are often found in bunches around neurons in both the central and peripheral nervous systems and are smaller than neurons. Glial cells have a special function when surrounding axons, though they do not transmit neurological signals. Called Schwann cells, these special glial cells provide the neurons of the nervous tissue with support, nutrition, and protection against bacteria. They hold the neurons together. Other types of glial cells include microglia and oligodendrocytes. Microglia help repair damage to the neurons, while oligodendrocytes support the axons.