The Nervous System

The Nervous System

A complete understanding of the human nervous system remain s a challenge. Several billion cells remain associated with this system. The varying functions of these cells and the nervous system are responsible for human behaviour and activities. Hence, scientists from different fields collectively are interested in understanding the functioning of this system. Studies on brain and other related structures began several years ago. Even to-day thousands of scientists are involved in researches for knowing the structure and functioning of the brain. For a thorough knowledge of this system, further works in anatomy, physiology, molecular,biology, psychology, medicine and other related fields are needed. Basically the nervous system is formed of nerve cells or neurons. Neurons are responsible for transmission of impulses. They also help in realising, analysing and storing messages. They can stimulate muscles to work. The network of interconnected neurons in the nerves, brain and spinal cord have highly complicated  ethods of functioning. A neuron has a basic cell structure called the cyton. The projections of the cyton are the dendrites and the dendrons. The inter communicating long projection is the axon. There are variations in the shape of the cyton, number of dendrons and nature of axon. A neuron is interconnected with the dendrite of the neighbouring neuron through the endplate of the axon. Such specialized connections are called as synapses. In the terminal regions of the effector nerves the axon of the nerve cells are in contact with the muscle tissue. These joints are named as neuro - muscular junctions.

The structure of a peripheral nerve :
A nerve is made up of several nerve fibres. A nerve fibre contains axons with their coverings called schwann cells. The fibres are grouped into fasciculi. The number and pattern of fasciculi vary in different nerves. Thus a nerve trunk possesses many such fasciculi. Such a trunk is surrounded by an epineuruium. The individual fasciculi are enclosed by a multilayered perineurium. The perineurium surrounds the endoneurium or intra fascicular connective tissue. In a peripheral nerve the epineurium constitutes 30 -70 % of the total cross sectional area of the nerve bundle. The thickness is more when there are more fasciculi. A layer of fat in the epineurium provides a ‘cushion’ effect to the nerve. The perineurium contains alternating layers of flattened polygonal cells. The endoneurium remains condensed around axons. The components of the endoneurium remain bathed in endoneurial fluid. The fasciculi of the nerve are supplied blood by vasa nervosum. These minute blood vessels radiate upto the endoneurium.

Nervous System

The organs of the nervous system are continuous in nature. However,for study purposes it can be divided into systems and organs.

A. Central Nervous System (C N S)

This system includes the brain and the spinal cord or medulla spinalis. They are protected by surrounding bones. While the brain is located within the cranium, the spinal cord is placed within the vertebral canal of the vertebrae. Through an opening called foramen magnum, the spinal cord descends down from the brain.

B. Peripheral Nervous System.

It consists of nerves and ganglia. The nerves that are formed from the brain are called the cranial nerves. There are 12 pairs of cranial nerves and 31 pairs of spinal nerves.

C. Autonomous Nervous System.

The nerves in this system transmit impulses from the C N S to smooth muscles, cardiac muscles and glands. It is also called the involuntary nervous system. It is subdivided into sympathetic and parasympathetic divisions.