Neuron: The building block of the Nervous System
A neuron is a specialized nerve cell that acts as the structural and functional unit of the nervous system.
31 pairs of nerves are originated from the spinal cord.
12 pairs of nerves are originated from the brain.
Nervous System
The nervous system is a collection of related organs and tissues that controls and coordinates the overall functions of the body with the help of nerves.
Central Nervous System
The central nervous system consists of the brain and spinal cord. It is made up of kind of cells, viz. neurons and glia. The brain and spinal cord consists of white matter and gray matter. The white matter contains bundles of axons, each coated with a myelin sheath, and the gray matter consists of masses of cell bodies and dendrites, each covered with synapses.
The Brain
The human brain is located inside the skull and is protected by the cerebrospinal fluid.
Cerebrospinal fluid is a colourless watery fluid present in the space between arachnoid and pia mater in the brain and spinal cord, as well. Its main function is to protect the brain and the spinal cord from mechanical injuries.
It is divided into five major parts, viz Cerebrum, Cerebellum, Mid-brain, Medulla Oblongata, and Pons Varolli.
Cerebrum
The cerebrum is the largest part of the brain, which occupies about 80% of the total weight of the brain. It is a dome shaped part, which is divided into right and left cerebral hemispheres by a deep median longitudinal groove called the corpus callosum. It transmits information from one hemisphere to another. The cerebral hemispheres are covered by a thin layer of gray, matter called cerebral cortex.
Functions:
- It governs mental abilities like thinking, learning, reasoning, memorizing and intelligence.
- It controls feelings of love, admiration and hatred.
- It enables us to observe things around us with the help of the sense organs.
Cerebellum
The cerebellum is the second largest part of the brain, which occupies about 10% of the total weight of the brain. It consists of two deeply convoluted hemispheres. A small injury to the cerebellum causes dizziness, which disturbs the body balance.
Functions:
- The cerebellum maintains equilibrium (body balance) and controls posture.
- It makes body movements smooth, steady and coordinated.
- It regulates and coordinates the contraction of voluntary muscles, i.e., muscular tone.
Mid-brain
The mid-brain is a thick-walled structure which constitutes a small middle portion of the brain. It is located between the cerebrum and pons varoli. It connects the anterior region of the brain to the posterior region.
Functions:
- It helps to coordinate and control the involuntary movement of the head, neck and body.
- It controls the pupil movement and size of the eye lens.
It helps to regulate feeling excitement and motivation.
Medulla Oblongata
The medulla oblongata is the lowermost part of the brain. It is located between the pons varoli and upper ed of the spinal cord. It encloses a cavity called the fourth ventricle. It contains vital reflex centers like the cardiac center and centers for the coughing, sneezing, swallowing, vomiting, etc. Damage to the medulla oblongata causes instant death.
Functions:
- It controls breathing, blood pressure and heart beat.
- It controls activities of the digestive tract, peristalsis, secretion of saliva, hormones and enzymes.
- It controls contraction and relaxation of blood vessels.
- It regulates blood pressure, breathing and heart function.
Pons Varolli
The pons varoli is a 2.5cm long organ of brain stem which is present between the mid brain and the medulla oblongata.
Functions:
- It helps to regulate breathing and respiration.
- It regulates chewing and swallowing.
- It acts as a relay station between the medulla and the other parts of the brain.
Spinal Cord
Spinal cord is a long, cylindrical structure that arises from the medulla oblongata of the brain and passes through the neural canal of the vertebral column.
It is located inside the bony cage of the vertebral column.
Major functions of spinal cord are:
- It governs reflex action.
- It connects a large part of the peripheral nervous system to the brain.
Reflex Action
Reflex action is the sudden and automatic response of the body to an unexpected event.
It is generally carried out by the spinal cord. In most cases, there is no involvement of brain in this task.
Example: watering of mouth at the sight of tasty food.
Peripheral Nervous System
A part of the nervous system that communicates between the brain and the other parts of the body with the help of nerves is called peripheral nervous system.
Following are the two types of PNS:
- Cranial nervous tissue
2. Spinal nervous tissue
Autonomous Nervous System
A part of human nervous system that controls the functions of muscles and glands without out prior intention is called autonomous nervous system. It is different than reflex action. For example: the process of breathing, digestion, excretion, etc. takes place in the body without our own wish and this is controlled by autonomic nervous system.
Following are two types of autonomous nervous system:
- Sympathetic nervous system:
- Parasympathetic nervous system:
Functions of the Nervous System
Following are the main functions of the nervous system:
- Input: To gather the impulses from the outer environment and inside the body and carry them to the brain or spinal cord for response.
- Process: To analyse the received impulses and process to determine the best result.
- Output: To execute the information determined by the brain or spinal cord as action.
- It controls reflex action of the human body.
Other Important Terms
Reflex Arc: A reflex arc is the pathway followed by the the sensory and motor nerves in a reflex action.
Ganglia: Ganglia are the groups of small nervous tissues located near the spinal cord.
Synapse: A synapse is the loose connection between the axon ending of one nerve cell and cell body of the next cell.