Brain and Spinal cord together constitute the Nervous System. The nervous system receives information in the form of impulses from all parts of the body and integrates this information. The messages or impulses that come from receptors are of two types –
- Those which require quick response, and
- Those which require analysis which needs a thought process to go on.
The impulses of the first category are first dealt by the spinal cord while the impulses of the second category are sent to the brain. In reflex actions, messages that come from sensory organs require quick responses and so they are tackled by the spinal cord though the information is also sent to the brain about these impulses.
- Structure of Human Brain
Human Brain is the principal coordinating centre of the body. It has control over all the activities and actions and coordinates them.
It is a complex but most delicate structure which is protected inside a hard covering called as Cranium. Like a mushroom, it is oval on the upper side but narrow in the lower side.
It is covered by three membranes that are called as meninges. A specific shock absorbing fluid called as cerebro-spinal fluid remains filled between these membranes.
There are three parts of Human Brain –
(1).Cerebrum,
(2) Cerebellum, and
(1). Fore Brain: It is the upper and the largest part of the human brain. It mainly consists of cerebrum. It occupies two third volume of the brain. It is divided in left and right hemispheres. These are called as Cerebral Hemispheres. These two hemispheres are connected with a bundle of axons called as Corpus callosum.
The inner part of the cerebrum is covered by an outer part made of numerous neurons. This is called as Cerebral Cortex. This portion contains centres of hearing, vision, smell, touch, speech etc. Twelve pairs of cranial nerves emerge out from this part of the brain.
Forebrain or the cerebrum is the main thinking part of the brain. It is the site of major faculties like learning, reasoning, intelligence, personality, and memory. Thoughts, actions, movements and sensations are controlled by this part of the brain.
There are different areas in the cerebrum for the performance of different functions. The associated areas of cerebrum control thinking and memory. These areas also store information and experiences. This part of the brain has sensory areas where information is received through sensory neurons from sense organs or receptors like eyes, ears, nose, tongue and skin.
The associated areas of cerebrum also enable us to feel sensation. It also has motor areas from where signals for responses are sent to respective muscles of the concerned organs through motor neurons.
(2). Midbrain: It is also called as the Mesencephalon. It is the region of the developing vertebrate brain which is composed of tectum and tegmentum.
It is located within the brainstem and between the two other developmental regions of the brain, the forebrain and the hindbrain; compared with those regions, the midbrain is relatively small.
Midbrain is the centre of control for reflex movements of the head, neck and trunk in response to visual and auditory stimuli. This area of brain is also concerned with the control of reflex movements of the eye muscles, changes in pupil size and shape of the eye lens.
(3). Hindbrain: This comprises Pons, Cerebellum, and Medulla oblongata. Pons is concerned with regulation of respiratory activities.
Cerebellum helps maintain posture and balance of body. It also helps in making precise and accurate movements. Smooth body movements like walking, dancing and picking up a pencil are also coordinated by cerebellum.
Various involuntary actions of body are controlled by medulla. These involuntary actions include heart beat, blood circulation, breathing, blood pressure and peristaltic movement of the muscles of intestine. It is the controlling centre of reflexes like swallowing, coughing, sneezing, salivation and vomiting.
Functions of the Human Brain
The overall functions of the Human Brain in brief are mentioned below –
(i).It receives impulses from all the sensory organs and analyses the impulses so received.
(ii).It sends the impulses it receives to muscles and glands to result into responses.
(iii). It establishes coordination between the impulses received from sensory organs and physical activities.
(iv). It collects and stores all the information pertaining to knowledge and sensibility and causes changes in the human behaviour accordingly.
(v).It controls all the voluntary and involuntary actions of the body.
(B) Spinal Cord
A delicate rope like structure comes out from the base of the lower end of medulla oblongata and passes through the hollow cavity formed through the vertebral column to the lowermost end of the back is called as the Spinal Cord.
Through the study of the micro- structure of the Spinal Cord it is found that a hollow tubular passes exists in the middle of the spinal cord which is filled with the Cerebrospinal fluid. Grey matter is found filled around this hollow line which is spread in the area forming H like structure.
Innumerable cytons of neurons are found in it. White matter is filled in the external area which shows ends of neuron fibres. These are filled in the vertical position in the spinal cord. About 31 pairs of spinal nerves emerge out of the spinal cord.
Functions of the Spinal Cord
(i). It helps in the conduction of impulses to and from the brain, and
(ii). It acts as centres of the reflex actions.
Peripheral Nervous System
The part of the nervous system which consists of nerves and ganglia outside of the brain and spinal cord is called as Peripheral Nervous System (PNS).
This nervous system connects the central nervous system to the limbs and organs. It serves as communication relay going back and forth between the brain and the extremities.
The nerves of this system remain unprotected due to which they remain exposed to toxins and mechanical injuries. This nervous system is divided into two parts-
- Somatic Nervous System and
- Autonomic Nervous System.
The Somatic Nervous System (SNS) is the part of the peripheral nervous system that handles voluntary control of body movements. It contains all the neurons connected with skeletal muscles and skin.
The Autonomic Nervous System (ANS) is the part of the peripheral nervous system that acts as an involuntary control system (below the level of consciousness), and controls visceral functions.
The ANS controls the connections between the brain, spinal cord and organs/glands, whereas the SNS connects external sensory organs through the brain to the muscles.
In fact, the Autonomic nervous system remains outside but parallel to the Central Nervous System. It helps in the control and coordination of digestive system, respiratory system, urinary tract, reproductive tract, muscles of blood vessels, muscles of eyes, muscles of the heart, and endocrine glands.
In brief, the Autonomic Nervous System has following important functions –
(i).Control of contraction and relaxation of involuntary muscles,
(ii). Control of heart beat and pressure,
(iii). Control of secretion of glands of the alimentary canal, and
(iv). Control of contraction and relaxation of the muscle of pupil.
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