Human Nervous System: The nervous system in humans can be divided into three main parts
1. Central Nervous System: The central nervous system is composed of the brain and the spinal cord. The brain controls all the functions in the human body. The spinal cord works as the relay channel for signals between the brain and the peripheral nervous system.
2. Peripheral Nervous System: The peripheral nervous system is composed of the cranial nerves and spinal nerves. There are 12 pairs of cranial nerves. The cranial nerves come our of the brain and go to the organs in the head region. There are 31 pairs of spinal nerves. The spinal nerves come out of the spinal cord and go to the organs which are below the head region.
3. Autonomous Nervous System: The autonomous nervous system is composed of a chain of nerve ganglion which runs along the spinal cord. It controls all the involuntary actions in the human body. The autonomous nervous system can be divided into two parts :
Sympathetic nervous system.
Parasympathetic nervous system.
Sympathetic Nervous System: This part of the autonomous nervous system heightens the activity of an organ as per the need. For example, during running, there is an increased demand for oxygen by the body. This is fulfilled by an increased breathing rate and increased heart rate. The sympathetic nervous system works to increase the breathing rate the heart rate, in this case.
Parasympathetic Nervous System: This part of the autonomous nervous system slows the down the activity of an organ and thus has a calming effect. During sleep, the breathing rate slows down and so does the heart rate. This is facilitated by the parasympathetic nervous system. It can be said that the parasympathetic nervous system helps in the conservation of energy.
Functions of the nervous system
Nervous system receives information from the environment.
To receive the information from the various body.
To act according to through muscles and glands.
A neuron is the structural and functional unit of the nervous system.
Neuron is a highly specialized cell which is responsible for the transmission of nerve impulses. The neuron consists of the following parts
(i) Cyton or cell body: The cell body or cyton is somewhat star-shaped, with many hair like structures protruding out of the margin. These hair-like structures are called dendrites. Dendrites receive the nerve impulses.
(ii) Axon: This is the tail of the neuron. It ends in several hair-like structures, called axon terminals. The axon terminals relay nerve impulses.
(iii) Myelin sheath: There is an insulator cover around the axon. This is called myelin sheath. The myelin sheath insulates the axon against nerve impulse from the surroundings.
Types of Neuron
Sensory neuron: These neurons receive signals from a sense organ.
Motor neuron: These neurons send signals to a muscle or a gland.
Association or relay neuron: These neurons relay the signals between sensory neuron and motor neuron.
Synapse: The point contact between the terminal branches of axon of one neuron with the dendrite of another neuron is called synapse.
Neuromuscular Junction: It is the point where a muscle fibre comes in contact with a motor neuron carrying nerve impulse from the control nervous system.
Transmission of nerve impulse: Nerve impulses travel in the following manner from one neutron to the next: Dendrites → cell body → axon → nerve endings at the tip of axon → synapse → dendrite of next neuron.
Chemical released from axon tip of one neuron, cross the synapse or neuromuscular junction to reach the next cell.
Receptors: Receptors are the specialized tips of the nerve fibres that collect the information to be conducted by the nerves.
Receptors are in the sense organs of the animals.
These are classified as follows :
Phono-receptors: These are present in inner ear.
Functions: The main functions are hearing and balance of the body.
Photo-receptors: These are present in the eye.
Function: These are responsible for visual stimulus.
Thermo-receptors: These are present in skin.
Functions: These receptors are responsible for pain, touch and heat stimuli.
These receptors are also known as thermo-receptors.
Olfactory-receptors: These are present in nose.
Functions: These receptors receive smell.
Gustatory-receptors: These are present in the tongue.
Functions: These helps in taste detection.
Shaalaa.com | Control & Co-ordination part 11 (Nervous System: Introduction)
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