In the human beings as well as other higher animals the nervous system and the endocrine system have evolved for regulating the function of different organs of the body and for maintaining synchronization between their activities. The nervous system receives information from different sensory organs which are called receptors and integrates them to determine the response to be made by day organs of the body. Regulation of the activities of different organs according to the need of the body is done by it. So, the nervous system keeps the body aware of the changes occurring in its internal or external environment and helps the body to react properly so that it can deal with different situation. The nervous system acts very rapidly but its actions are relatively short lusting, on the other hand the endocrine system acts slowly for a prolonged period.
Organisation of nervous system: –
By two types of cells the nervous system is made up, those are neurons and neuroglia. The highly specialised cells neurons carry out the functions of nervous system by transmitting information in the form of nerve impulses from one part of the body to another through the complex path involving synapses. There are more than 10,000 million of neurons in the nervous system of the human beings which are formed during the foetal life. New neurons are never formed during their lifespan as after birth the neurons do not divide. However the neurons increase in length and new synapses are formed with the growth and development of the body after birth. The neuroglia cells support and nourish the neurons. They continue to multiply after birth and increase in number.
Anatomically the nervous system is divided into two parts; those are central nervous system (CNS) and peripheral nervous system (PNS). The CNS comprises of brain and spinal cord which lie in the axial part of the body. The part expended part of CNS is the brain lying within the cranial cavity. The weight of a adult human brain is about 1.36 kilogram in males and 1.25 kilograms in females. From above downward, the human brain is divisible into three primary regions; those are (i) forebrain, (ii) midbrain, and (iii) hindbrain.
The largest part of human brain is forebrain and further divided into two parts namely the cerebrum and the diencephalon. The diencephalon comprises of thalamus and hypothalamus.
The midbrain remains undivided but the hindbrain is further divided into two parts: met-encephalon and myelencephalon. The metencephalon comprises of pons and cerebellum. The brainstem he’s formed by midbrain, pons and medulla together. The spinal cord is the long, tubular lower part of the CNS lying within the cavity of vertebral column.
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The peripheral nervous system includes all the nerve pathways of the body outside the brain and spinal cord. Contact with the CNS is made by these pathways in various part of the body. By 43 pairs of nerves the PNS is comprises of. Among them, 12 pairs of peripheral nerves are connected with brain and are called cranial nerves. The remaining 31 pairs of peripheral nerves are connected to spinal cord, which are called spinal nerves.
The total central nervous system is histologically divisible into two distinct zones – grey matter and white matter. The grey matter is composed of cell bodies of neurons; hence, synapses are formed in the region of the CNS. On the other hand the white matter consists of nerve fibres called Axons. Due to the presence of myelin sheath on the actions it appears as white. In cerebrum and cerebellum, the grey matter is present on the outer side which is also called cortex and the white matter on the inner side. The remaining parts of CNS are called nerve tracts whereas in the PNS, they are called peripheral nerves. There are two types of peripheral nerve fibres – sensory or afferent fibres and motor or efferenr fibres.
Sensory fibres carry the information received by the receptors, from different part of the body to the central nervous system to make CNS aware to the change happening within the body or in the external environment. Motor fibres carry the commands of the CNS to different organs for necessary modification in their activities. Peripheral nerves may be of three types depending on the types of nerve fibres, those are – sensory, motor and mixed.
The nervous system can also be divided functionally into two parts, such as, somatic nervous system and automatic nervous system. The somatic nervous system is concerned with conscious sensations arising from the sense organ, muscles, tendons and joints and movement control of skeletal muscles. On the other hand the automatic nervous system is concerned with the control of involuntary organs.