Human body is composed of cells, tissues and organs. The cell is the basic unit of the human body. Cells make up tissues and a group of tissues makes up an organ;whereas a group of organs forms the human body system (organ system). The organ systems work together in fine-tuned balance for the well-being of an individual. Thus, we need to learn about the composition and functions of organ systems. We are going to study about nervous system, endocrine system. and reproductive system in this unit.
Nervous System
The nervous system is made up of neurons. The basic unit of the nervous system is a nerve cell or neuron. The neuron contains an axon, dendrites and nucleus. The special extensions are axons and dendrites. The axons are tail-like structures and the dendrites are fibrous roots. The axons are longer than the dendrites. There is a nucleus in the middle of the nerve cell which is enclosed by protoplasm.
The nervous system controls and coordinates the internal and external activities of the human body. It also gives the necessary command to other organ systems. Therefore, it is also known as 'Master Syste1n or Coilllnand Centre'. It has three main parts: Central Nervous System, Peripheral Nervous System and Automatic Nervous System.
A. Central Nervous System
The central nervous system (CNS) consists of the brain and spinal cord. The brain controls how we think, learn, move, and feel, whereas the spinal cord carries messages back and forth between the brain and the nerves that run throughout the body.It is known as the centre because it combines information from the entire body and coordinates the activities across the whole organis1n.
a. Brain
The brain is housed inside the skull. The average weight of the brain of an adult is 1.5 kg. It is made of soft tissue.It is protected by the thin layer of the membrane which is known as the meninges.
Cerebrum, cerebellum, midbrain, pons varolii and medulla oblongata are the main parts ofthe brain. Cerebrum is the largest part of the brain which is located at the top of the head. It is divided into two halves; the right hemisphere and the left hemisphere. It enables us to think, remember, and use logic. It also enables us to interpret the situation or events and take the right decision. It manages the functions of senses such as sight, sound, smell, taste and touch. Overall, it commands and coordinates the functions of other organs of the body including the brain.
Cerebellum (little brain) is located under the cerebrum and at the back of the pons varolii. Its main function is to control and coordinate muscle inovements such as walking, running, eye movement, and other physical activities. It helps to maintain the balance and posture of the body.It sends information and signals it has received to the cerebrum.
Midbrain is located between the cerebrum and pons varolii. It consists of a nu1nber of nerve cells and fibres. It works as a bridge for transmitting information between the cerebrum and the spinal cord. It receives information from the spinal cord and sends it to the cerebrum. Likewise, it passes com111and from the cerebrum to the spinal cord.
Pons varolii works as a bridge between the midbrain and medulla oblongata. Infonnation and command transmit through pons varolii from the cerebrum to the medulla oblongata. The medulla oblongata is the bottom-most part of the brain. It connects the brain to the spinal cord. It regulates and controls circulation and respiration. It also regulates the reflex actions such as quick withdrawal of hands from a hot item, and sudden blinking when an insect comes very close to the eyes.
b. Spinal Cord
Spinal cord is an extension of the central nervous system. It begins at the bottom of the brain stem and ends in the lower back. It is surrounded by the back bones (vertebrae). It is about 45 cm in length and cylindrical in shape. There are 31 pairs of spinal nerves and roots. These spinal nerves cord emerge from different segments of the spinal cords. It carries nerves signals from the brain and vice versa. It also regulates the reflex action. The damage of spinal cord is called spinal injury. The spinal injury is caused by direct injury to the spinal cord itself or from damage to the tissues and bones that surround it. This injury affects other organs of the body and severe injury can cause disability.
B. Peripheral Nervous System
Peripheral nervous system is composed of 12 pairs of cranial nerves and 31 pairs of spinal nerves that branch out from brain and spinal cord respectively. It establishes communication network between central nervous system and body parts.
C. Automatic Nervous System
Some activities are continuously happening in our body, but we are not conscious about them. The auto1natic nervous system is an auto- running system. It is divided into the sympathetic nervous system and the parasympathetic nervous system. The sympathetic system speeds up the respiration rate and heartbeat. It also enlarges the pupils, and slows down the rate of digestion. The parasympathetic systen1, on the other hand, lowers the heartbeat, increases the rate of digestion, contracts the pupils, etc.
Functions of Nervous System
The essential functions of our body are coordinated and controlled by the nervous system. As a result, the balance among the systems of the body is maintained. Major functions of the nervous system are listed below.
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It receivesinternal and external information of the body.
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It sends information to the brain and spinal cord for essential tasks.
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It implements the received information into action.
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It comn1ands and controls organs and glands to react properly.
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It enables us to think, remember and analyze the situation or events.
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As a whole, it coordinates and controls the activities of the body.