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Nerve cell
The neuron is the structural and functional unit of the nervous system. It consists of three parts-
1. Dendrites: Dendrites are branched cytoplasmic projections from the cell body. The dendritic tip of the nerve cells receive impulses and sets off a chemical reaction that creates an electrical impulse which is further transmitted to the cell body.
2. The cell body: The cell body contains a well-defined nucleus, surrounded by cytoplasm. It has cell organelles like any other cells. The cell body further transmits the impulse to the axon.
3. Axon: One branch arising out of the cell body is very long in comparison to others. This branch is called axon or nerve fibre.
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Types of synapse
A synapse is a junction between the pre-synaptic neuron and a post-synaptic neuron, which may or may not be separated by a gap called the synaptic cleft.
There are two types of synapses on the basis of the nature of the transfer of information.
Chemical synapses
1. They transfer/relay the information through the chemicals
2. These chemicals are neurotransmitter molecules.
3. Each synaptic vesicle contains neurotransmitter chemical molecules such as Acetylcholine.
4. The neurotransmitters thus released bind to their specific chemoreceptors present on the post-synaptic membrane of the dendron.
5. This binding opens sodium ion channels that allow the entry of ions to generate a new potential in the post-synaptic neuron.
6. Chemical synapses are slow and sturdy
7. They can transmit a signal only in one direction (post-synaptic to pre-synaptic )
Electrical synapses
1. An electrical synapse is a junction in which the two neurons are connected by channel proteins
2. They transfer/relay information through electrical signals
3. They are faster as they do not receptors
4. The signal can be transmitted in both directions.
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Cerebrum
1. The cerebrum is the principal and most anterior part of the brain in vertebrates, located in the front area of the skull and consisting of two hemispheres, left and right, separated by a fissure.
2. It is responsible for the integration of complex sensory and neural functions and the initiation and coordination of voluntary activity in the body.
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Cerebellum
It lies below the cerebrum and at the back of the brain and coordinates the motor functions.
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Medulla oblongata
1. Forms the brain stem; along with the pons (It is the portion of the brain stem, located above the medulla oblongata and below the midbrain and connects upper and lower parts of the brain).
2. Controls various involuntary functions; like a heartbeat, respiration.
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Structure of reflex arc
The path taken by the nerve impulses in a reflex is called a reflex arc.
Components of a reflex arc:
1. Receptor- Protein molecule usually found embedded within the plasma membrane surface of a cell that receives chemical signals from outside the cell.
2. Sensory nerve- Carries the message from the sensory neuron to the spinal cord.
3. Relay centre- Intermediate neuron of the spinal cord which transmits the impulse from sensory to the motor neuron.
4. Motor nerve- Carries the message from the spinal cord to the effector organ muscle or gland.
5. Effector organ- The organ receives the signal from the motor nerve and acts according to it.
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Eye
1. Our eyes contain orbits, eyelids, tear glands (lacrimal glands) and conjunctiva.
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Ear – Structure and function
Structure of ear
1. The ear has major three divisions.
2. Outer ear consisting of the pinna, the auditory canal and the eardrum.
3. The middle ear consists of ear ossicles (malleus, incus, stapes), oval window, round window and inner opening of the Eustachian tube.
4. The inner ear consists of semicircular canals, utriculus, sacculus and cochlea.
Functions of the ear
1. The internal ear is involved in two sensory functions: hearing and body balance.
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