Somehow every living organism becomes aware of what is going around it and appropriately take actions for its survival. These actions are not only taking place in the external environment but also take place so many activities inside our body of which we are unconcerned. Proper timing and coordination are required for such actions. With the help of the nervous system and the hormonal systems, such coordination takes place inside our body.
Human Nervous System
The nervous system is required in our body is for the following major activities
- It extracts information from the outside world through the sense organs and keeps us informed
- It facilitates us to recognize, to think and to find a solution. It sends signals to the central nervous system, processes the information to determine an appropriate response and send signals to muscles or glands to start a response.
- It regulates and co ordinates all voluntary muscular activities.
- It controls involuntary functions such as beating of the heart, blinking, growing of nails and hair, digestion etc.
The unit of the human nervous system is neuron which is also known as the nerve cell.
Structure of a Neuron
The common compositions of a neuron are the cell body, dendrites, and axon. Conducting impulse is the main feature of the neuron. A neuron is an electrically excitable cell that processes and transmits information through electrical and chemical signals. The following is the general composition of the neuron.
1. The cell body
- It involves a well-defined nucleus and circled by granular cytoplasm.\
- It contains all the cell organelles like other cells, the only centrosome is absent due to the inability of nerve cells to divide.
- Dendrites are a thin structure that arises from the cell body. They reach the finest part of the body, giving rise to a complex “dendritic tree” and conduct nerve impulses to the cyton.
- It is a long cellular extension from the cell body.
- It sizes from few millimeters to more than one meter in length.
- It is circled by a white insulating sheath called neurolemma.
- The gaps shown by the myelin sheath at full length are known as nodes of ranvier.
- Collaterals are known as the side branches of axons.
- The end parts of the axons have waollen ends that store some chemicals called neurotransmitters.
- Axons are closely located near the dendrites of other neurons but are not linked. Such gaps in between are called synaptic clefts.
Polarization And Depolarization
The outer portion of the nerve fiber bears positive charge in resting condition. This is known as polarized state. This is due to more Na+ ions outside the axon membrane. During stimulation, the axon membrane outside becomes more accessible to Na+ ions which move inwards and lead to depolarization. The state of depolarization becomes a catalyst for the near by membrane which in turn become depolarized. Meanwhile, the previous part becomes repolarized due to active transport of Na+ ions again to the outside.
Brain possesses 2 percentage of our body weight, but it uses 20 percentage of the oxygen we consume and 20 percentage of the energy we consume. The brain is like the CPU of a computer, it is important for our existence.