Nerve Fibres

On the basis of structure, the nerve fibers are of two types:

1. Medullated (myelinated) nerve fibers: These are found in the brain, spinal cord, and cranial and spinal nerves. They have myelin sheath and nodes of Ranvier and Schwann cells. In the central neural system, these fibers form white matter. Saltatory conduction occurs in medullated nerve fibers.
2. Non-medullated (nonmyelinated) nerve fibers: These are found in the autonomic neural system. In the central neural system, these fibers create grey matter.

Functionally, the nerve fibers are again of two types:

1. Afferent or sensory fibers
2. Efferent or motor fibers

Nerve impulses pass between neurons through the synapse with the help of chemicals which are called neurotransmitters such as acetylcholine.

A nerve is a bundle of numerous nerve fibers which are separated into several small bundles, termed fasciculi. The latter are bound together by vascular connective tissue, the epineurium. The epineurium also creates a sheath around the nerve itself. Each fascicule is surrounded by another connective tissue called the perineurium. Inside the fascicule, its fibers are bound together by another connective tissue called the endoneurium.

All living organisms are made of cells. A unicellular organism has a single cell in its body, i.e., a single cell performs all basic life activities. However, in multicellular organisms, there are millions of cells. Most of these cells are specialized to carry out only a few functions efficiently. These functions are taken up by a distinct group of cells. Thus, it can be said that there is a division of labor in multicellular organisms.

A tissue is a group of cells that are similar in structure, origin, and function. The term ’tissue’ was given by Bichat. The branch of science dealing with the tissues is called ‘histology’. Mayer introduced the term histology. Malpighi is considered the “founder of histology. Broadly animal tissues are classified into four types: epithelial, connective, muscular, and neural.