Nervous tissue is the main tissue component of the nervous system. The nervous system regulates and controls bodily functions and activity. It consists of two parts: the central nervous system (CNS) comprising the brain and spinal cord, and the peripheral nervous system (PNS) comprising the branching peripheral nerves.
Nervous tissue is composed of neurons and neuroglial cells. Four types of neuroglia found in the CNS are astrocytes, microglial cells, ependymal cells, and oligodendrocytes.
Two types of neuroglia found in the PNS are satellite cells and Schwann cells. In the central nervous system (CNS), the tissue types found are grey matter and white matter. The tissue is categorized by its neuronal and neuroglial components.
Classification of tissue:
In the central nervous system:
- Grey matter is composed of cell bodies, dendrites, unmyelinated axons, protoplasmic astrocytes (astrocyte subtype), satellite oligodendrocytes (non-myelinating oligodendrocyte subtype), microglia, and very few myelinated axons.
- White matter is composed of myelinated axons, fibrous astrocytes, myelinating oligodendrocytes, and microglia.
In the peripheral nervous system:
- Ganglion tissue is composed of cell bodies, dendrites, and satellite glial cells.
- Nerves are composed of myelinated and unmyelinated axons, Schwann cells surrounded by connective tissue.
The three layers of connective tissue surrounding each nerve are:
- Endoneurium. Each nerve axon, or fiber is surrounded by the endoneurium, which is also called the endoneurial tube, channel or sheath. This is a thin, delicate, protective layer of connective tissue.
- Perineurium. Each nerve fascicle containing one or more axons, is enclosed by the perineurium, a connective tissue having a lamellar arrangement in seven or eight concentric layers. This plays a very important role in the protection and support of the nerve fibers and also serves to prevent the passage of large molecules from the epineurium into a fascicle.
- Epineurium. The epineurium is the outermost layer of dense connective tissue enclosing the (peripheral) nerve.
The function of nervous tissue is to form the communication network of the nervous system by conducting electric signals across tissue.
In the CNS, grey matter, which contains the synapses, is important for information processing.
White matter, containing myelinated axons, connects and facilitates nerve impulse between grey matter areas in the CNS.
In the PNS, the ganglion tissue, containing the cell bodies and dendrites, contain relay points for nerve tissue impulses. The nerve tissue, containing myelinated axons bundles, carry action potential nerve impulses.