Nervous System

The system of organs and cells that make organism able to detect changes within themselves and their environment is called nervous system. Changes in the external environment include those of light, temperature, sound, motion, taste and odour, while changes in the internal environment include those in the position of the head and limbs as well as in the internal organs. Once detected, these internal and external changes must be analyzed and acted upon in order to survive. Human nervoous system is divided to three major parts, they are,

1. Central nervous system
2. Peripheral nervous system
3. Autonomic nervous system

1. Central nervous system consists of brain and spinal chord.

Brain: Brain is the largest part of central nervous system situated safe inside skull. Brain is covered by three layered membrane called meninges that help protect the brain. The three layers are called duramater, piamater and arachnoid. Duramater is attached to inner skull, piamater is attached to brain and space between arachnoid and piamater is filled with a fluid called cerebrospinal fluid. This fluid protects brain from shocks. Brain is divided into three major parts

a. Cerebrum: cerebrum occupies about 80% of brain volume. It is spread from frontal, parietal to occipital zone. It is divided to left and right hemisphere lobes. The left and right hemispheres are divided from top side by deep fissure. Outer part of cerebrum is made up of grey matter and inner part from white matter. Major function of cerebrum are

• To detect odor
• To control speech
• Record memory and events
• Hearing control
• Detect sensation like touch, pain, pressure, temperature etc
• Thought control
• Analysis
• Emotions
• Anger control
• Future telling

Shock or wound on cerebrum causes person to coma.

b. Cerebellum: Cerebellum also called small brain is situated behind cerebrum and above medulla oblongata. It is divided to two hemispheres on the size of lemon each. It is also formed by grey matter and white matter. The major functions of cerebellum are

• Plays the role of body balance
• Decides the tone of muscle
• Controls voluntary movements

c. Medulla oblongata: it is situated below cerebellum and at the top of spinal cord. It is smallest part of

brain. It is cylindrical in shape. Shock or wound on this may cause death of person. It is also made by gray matter and white matter. The major functions of medulla oblongata are

• Control of sneezing, swallow of food
• Control of vomiting and to cough
• Control of breathing
• Control contraction and relaxation of blood vessels
• Contraction and relaxation of digestive canal
• secretion of digestive juice, secretion of hormones etc

Spinal cord: spinal cord is a long nervous tissue which starts from lower part of medulla oblongata to the end of lumbar vertebrae.  Its outer part is made up of white matter and inner part from grey matter. It is covered by meninges. If spinal cord gets shock or injured the lower part below wound remain paralyzed which is called spinal injury or spinal paralysis. Main functions of spinal cord are

• It is the centre of reflex action. It shows instant reaction to change in outer environment
• Establishes relationship between different parts of body and brain

Next: Peripheral Norvous System and autonomic nervous system