Give abrief account of:
(a)Mechanism of synaptic transmission
(b)Mechanism of vision
(c) Mechanism of hearing
Give abrief account of:
(a)Mechanism of synaptic transmission
(b)Mechanism of vision
(c) Mechanism of hearing
(a)Mechanism of synaptic transmission
Synapse isa junction between two neurons. It is present between the axonterminal of one neuron and the dendrite of next neuron separated by acleft.
There aretwo ways of synaptic transmission.
(1) Chemical transmission
(2)Electrical transmission
1.Chemical transmission – When a nerve impulse reaches theend plate of axon, it releases a neurotransmitter (acetylcholine)across the synaptic cleft. This chemical is synthesized in cell bodyof the neuron and is transported to the axon terminal. Theacetylcholine diffuses across the cleft and binds to the receptorspresent on the membrane of next neuron. This causes depolarization ofmembrane and initiates an action potential.
2.Electrical transmission – In this type of transmission, anelectric current is formed in the neuron. This electric currentgenerates an action potential and leads to transmission of nerveimpulse across the nerve fibre. This represents a faster method ofnerve conduction than the chemical method of transmission.
(b)Mechanism of vision
Retina isthe innermost layer of eye. It contains three layers of cells –inner ganglion cells, middle bipolar cells, and outermostphotoreceptor cells. A photoreceptor cell is composed of a proteincalled opsin and an aldehyde of vitamin A called retinal. When lightrays are focused on the retina through cornea, it leads to thedissociation of retinal from opsin protein. This changes thestructure of opsin. As the structure of opsin changes, thepermeability of membrane changes, generating a potential differencein the cells. This generates an action potential in the ganglioniccells and is transmitted to the visual cortex of the brain via opticnerves. In the cortex region of brain, the impulses are analysed andimage is formed on the retina.
(c)Mechanism of hearing
The pinnaof the external region collects the sound waves and directs ittowards ear drum or external auditory canal. These waves strike thetympanic membrane and vibrations are created. Then, these vibrationsare transmitted to the oval window, fenestra ovalis, through threeear ossicles, named as malleus, incus, and stapes. These ear ossiclesact as lever and transmit the sound waves to internal ear. Thesevibrations from fenestra ovalis are transmitted into cochlear fluid.This generates sound waves in the lymph. The formation of wavesgenerates a ripple in the basilar membrane. This movement bends thesensory hair cells present on the organ of corti against tectorialmembrane. As a result of this, sound waves are converted into nerveimpulses. These impulses are then carried to auditory cortex of brainvia auditory nerves. In cerebral cortex of brain, the impulses areanalysed and sound is recognized.
(a)Mechanism of synaptic transmission
Synapse isa junction between two neurons. It is present between the axonterminal of one neuron and the dendrite of next neuron separated by acleft.
There aretwo ways of synaptic transmission.
(1) Chemical transmission
(2)Electrical transmission
1.Chemical transmission – When a nerve impulse reaches theend plate of axon, it releases a neurotransmitter (acetylcholine)across the synaptic cleft. This chemical is synthesized in cell bodyof the neuron and is transported to the axon terminal. Theacetylcholine diffuses across the cleft and binds to the receptorspresent on the membrane of next neuron. This causes depolarization ofmembrane and initiates an action potential.
2.Electrical transmission – In this type of transmission, anelectric current is formed in the neuron. This electric currentgenerates an action potential and leads to transmission of nerveimpulse across the nerve fibre. This represents a faster method ofnerve conduction than the chemical method of transmission.
(b)Mechanism of vision
Retina isthe innermost layer of eye. It contains three layers of cells –inner ganglion cells, middle bipolar cells, and outermostphotoreceptor cells. A photoreceptor cell is composed of a proteincalled opsin and an aldehyde of vitamin A called retinal. When lightrays are focused on the retina through cornea, it leads to thedissociation of retinal from opsin protein. This changes thestructure of opsin. As the structure of opsin changes, thepermeability of membrane changes, generating a potential differencein the cells. This generates an action potential in the ganglioniccells and is transmitted to the visual cortex of the brain via opticnerves. In the cortex region of brain, the impulses are analysed andimage is formed on the retina.
(c)Mechanism of hearing
The pinnaof the external region collects the sound waves and directs ittowards ear drum or external auditory canal. These waves strike thetympanic membrane and vibrations are created. Then, these vibrationsare transmitted to the oval window, fenestra ovalis, through threeear ossicles, named as malleus, incus, and stapes. These ear ossiclesact as lever and transmit the sound waves to internal ear. Thesevibrations from fenestra ovalis are transmitted into cochlear fluid.This generates sound waves in the lymph. The formation of wavesgenerates a ripple in the basilar membrane. This movement bends thesensory hair cells present on the organ of corti against tectorialmembrane. As a result of this, sound waves are converted into nerveimpulses. These impulses are then carried to auditory cortex of brainvia auditory nerves. In cerebral cortex of brain, the impulses areanalysed and sound is recognized.
