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| Parts of the Nervous System - Central Nervous System |
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| The human nervous system can be divided into three main parts: |
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 Central nervous system |
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Peripheral nervous system |
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Autonomic nervous system |
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| It is made up of the brain and the spinal cord which is the continuation of the brain. Brain and spinal cord are surrounded by membranes called the meninges. There are three layers - outermost dura mater, middle arachnoid and the inner pia mater. The space between the arachnoid and pia mater is filled with the cerebrospinal fluid (CSF). It acts as a shock absorber. An infection of the meninges is called meningitis. |
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| It is the part of the central nervous system that is present in the head and protected by the skull, dorsally and laterally. The box that houses the brain within the skull is called the cranium. It has three main regions - the fore brain, the mid brain and the hind brain. The three regions have different parts that have specific functions. |
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| The Human Brain |
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| Fore Brain |
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| It is made up of cerebrum, hypothalamus and thalamus. |
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| Cerebrum |
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| It is the largest part of the brain and is made up of two hemispheres called the cerebral hemispheres. The two hemispheres are joined together by a thick band of fibres called the corpus callosum. The cerebrum is made up of four distinct lobes - frontal, parietal, temporal and occipetal. |
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| The outer portion of the cerebrum is called the cortex and the inner part is called the medulla. The cortex consists of the cells of the neurons and appears grey in colour. It is also called the grey matter. The medulla consists of the fibres of the neurons and is white. The cortex is highly convoluted which increase the surface area. It is believed that higher the number of convolutions, higher is the intelligence. The cerebrum has sensory areas, association areas and motor areas. |
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| The sensory areas receive the messages, the association areas associate this information with the previous and other sensory informations and the motor areas are responsible of the action of the voluntary muscles. Cerebrum is responsible for the intelligence, thinking, memory, consciousness and will power. There are also other important functions associated with the cerebrum. They are diagrammatically represented as follows- |
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| The Cerebral Cortex |
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| Thalamus |
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| It is an area which coordinates the sensory impulses from the various sense organs - eyes, ears and skin and then relays it to the cerebrum. |
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| Hypothalamus |
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| Hypothalamus, though a small region situated below the thalamus, is an important region of the brain. It receives the taste and smell impulses, coordinates messages from the autonomous nervous system, controls the heart rate, blood pressure, body temperature and peristalsis. It also forms an axis with the pituitary which is the main link between the nervous and the endocrine systems. It also has centres that control mood and emotions. |
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| Mid Brain |
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| It is a small portion of the brain that serves as a relay centre for sensory information from the ears to the cerebrum. It also controls the reflex movements of the head, neck and eye muscles. It provides a passage for the different neurons going in and coming out of the cerebrum. |
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| Hind Brain |
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| It consists of cerebellum, pons and medulla oblongata. |
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| Cerebellum |
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| Cerebellum is like cerebrum. It consists of outer grey cortex and inner white medulla. It is responsible for maintaining the balance while walking, swimming, riding, etc. It is also responsible for precision and fine control of the voluntary movements. For example, we can do actions like eating while talking or listening. One has to concentrate for talking sensibly. However the action of eating, while talking is done automatically. This is controlled by the cerebellum. |
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| Pons |
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| Pons literally means bridge. It serves as a relay station between the lower cerebellum and spinal cord and higher parts of the brain like the cerebrum and mid brain. |
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| Medulla Oblongata |
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| It is a small region of the brain. It is hidden as it is well protected because of its importance. It has the cardiovascular centre and the breathing centre. It also controls activites such as sneezing, coughing, swallowing, salivation and vomiting. |
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| It is a collection of nervous tissue running along the back bone. It is, in fact, protected by the vertebral column. It is a continuation of the brain. |
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| Spinal Cord |
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| It consists of a central canal that has cerebrospinal fluid that is continuous with the fluid in the brain. The canal is surrounded by an |
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| H-shaped grey area that is made up of nerve cells, dendrites and synapses. Outer to this is the white area that is made up of the axons. This arrangement is reverse of what is seen in the brain - outer grey and inner white portions. |
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| The four ends of the H-shape appear like horns extending into the white matter. The upper (dorsal) horn contains the sensory or afferent neurons entering the grey matter and the lower (ventral) horn contains the motor or efferent neurons leaving the grey matter. |
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| The white matter consists of ascending and descending tracts of neurons connecting the different parts of the body with the brain. |
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| The functions of the spinal cord are: |
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Coordinating simple spinal reflexes |
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Coordinating autonomic reflexes like the contraction of the bladder |
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Conducting messages from muscles and skin to the brain |
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Conducting messages from brain to the trunk and limbs |
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