Nervous System of Humans

The nervous system consists of two parts:

  1. Central nervous system
  2. Peripheral nervous system

The central nervous system of humans includes a highly developed brain and spinal cord. Peripheral Nervous system is made of nerves.

Brain

The brain is a very delicate organ lodged inside the cranium of the skull. It is protected by three coverings, the meninges: an outer tough duramater, a thin delicate web-like middle arachnoid, and the innermost highly vascular piamater richly supplied with blood vessels.

The space between the membranes is filled with a fluid called cerebrospinal fluid. There are cavities inside the brain, which are also filled with the same fluid. The brain consists of three main regions:

  1. forebrain consisting of cerebrum and diencephalon
  2. midbrain a small tubular part between the fore and the hindbrain
  3. hindbrain consists of cerebellum, pons, and medulla oblongata

Cerebrum

This is the largest part of the brain, divided into two (the right and the left) parts called cerebral hemispheres. Their outer surface is highly convoluted with ridges and grooves. Each hemisphere is hollow internally and the walls have two (an inner and an outer) regions. The outer region (cerebral cortex) contains cell bodies of the nerve cells and being grayish in colour it is called gray matter. The inner region is composed of whitish axon fibres and is called the white matter. Corpus callosum is a sheet of cris-cross nerve fibres connecting the two cerebral hemispheres. Left side of the cerebrum controls the right side of the body and vice-versa.

The cerebral cortex has three main functions:

  1. It controls and initiates voluntary muscle contractions.
  2. It receives and processes information form the sense organs, like eyes, ear, nose, etc.
  3. It carries out mental activities of thinking, reasoning, planning, memorizing, etc.

Diencephalon

This is the part of the forebrain lying below the cerebrum. It consists of the following two parts:

1. Thalamus

This is an egg shaped mass of gray matter, located in the centre below the cerebrum. It is the relay centre for sensory impulses (e.g. pain and pleasure) going to the cerebrum.

2. Hypothalamus

This is a region of the brain located below thalamus. It controls motivated behavior such as eating, drinking and sex. It controls the secretions of pituitary gland hanging below it. It also serves as the regulation centre of body temperature and body fluids.

Cerebellum

The cerebellum is a smaller region of the brain located at the base and under the cerebrum. It has numerous furrows. It also has a cortex of gray matter. Its two main functions are:

  1. to maintain the balance of the body
  2. to coordinate muscular activities

Medulla Oblongata

This is the last part of the brain, which is connected to the spinal cord. Its functions are as follows:

  1. It is the cente for breathing, coughing, swallowing, etc.
  2. It controls heartbeat, the movement of alimentary canal and many other involuntary actions.

In all, 12 pairs of nerves (cranial nerves) come out of the brain, some of these are sensory, some motor and some are of mixed type.

Spinal Cord

The spinal cord extends form the medulla of the brain downward almost the whole length of the backbone. It is also wrapped in the same three meninges as the brain and the space between them contains the same cerebrospinal fluid. The arrangement of the white and gray mater is reversed in it i.e. white matter is outside and the gray matter inside.

Functions of Spinal Cord

  1. Carry out reflexes below the neck
  2. Conducts sensory impulses from the skin and muscles to the brain
  3. Conducts motor responses from the brain to the trunk and limbs