What is Neurology ? Gross Anatomy

Written by Anjani Mishra

Nervous System

One should be cognizant of the fact that the nervous system, for the convenience sake, has been divided into a number of segments or portions which at times are not distinct either anatomically or physiologically. However, for ease of description and discussion the following definitions are given.

The nervous system is a complex mechanism by which the organism is brought into functional relation with its environment, and its various parts are coordinated.

The central nervous system (CNS) can be defined as consisting of the brain and spinal cord.

The peripheral nervous system (PNS) includes those nerves that are connected to the central nervous system (CNS). The peripheral nervous system is made up of the cranial and spinal nerves and the so called autonomic nervous system, which is a component part of both cranial and spinal nerves.

The term “autonomic nervous system” refers to the parts of the nervous system that regulate visceral structures that are involuntary and autonomic in nature, and thus includes the regulation of cardiac muscle, smooth muscle and glands. In general autonomic nervous system is largely concerned with those processes of secretion, digestion, excretion, contraction of smooth muscle and reproduction.

Ganglia

Ganglia are gray masses found on the dorsal root of the spinal nerves and on the course of many nerves.

They are commonly ovoid in form, but are irregular in shape.

They vary greatly in size; some are microscopic, while others are macroscopic. (several inches long).

They are enclosed in a fibrous capsule. They are composed largely of the cell bodies of neurons and are located outside or peripheral part of the central nervous system.

In origin and function the spinal ganglia belong properly to the central nervous system, but it is customary to include them with the peripheral part in gross anatomical description.

The neuron- The neuron is composed of a cell body together with its processes, the dendrites and axons. The processes of neurons that conduct impulses away from the cell body are termed axons or axocylinders. The neuron usually has a single axon, which emerges from the cell body on the side opposite to that from which the main dendrites enter. The dendrites are processes that conduct impulses towards the cell body. Most neurons have many dendrites and thus are classified as multipolar cells.

The neurons of the brain, spinal cord and autonomic ganglia are multipolar. The neurons of the spinal ganglia and the ganglia of certain cranial nerves are unipolar, that is they have only one process. This process divides into two branches, one which conduct impulses from sensory endings towards the cell body and another which conveys these impulses to the brain or spinal cord. The ganglia of the inner ear, retina of the eye and the olfactory mucous membrane have neurons which have two processes and are classified as bipolar. One process conduct towards and other away from the cell body.

The cell body of a neuron is variable in shape, usually containing a pale nucleus and a central nucleolus with cytoplasm characterized by stainable granules, Nissl bodies.

The term “neurofiber” is often used to include an axon and its various sheaths.

A myelinated nerve fiber presents a myelin sheath, where as non-myelinated fiber lacks a myelin sheath.

The gray matter of the central nervous system (CNS) contains cell bodies and fibers that, for the most part, are not myelinated. However, the white matter contains a large number of myelinated fibers and a few nerve cells. White matter is white because of its higher content of myelin sheath.