(a) Mechanism of synaptic transmission:
When an impulse reaches at the axon terminal, it stimulates the movement of the synaptic vesicles towards the synaptic cleft and releases their neurotransmitters. The neurotransmitter binds with the receptors found on the post synaptic membrane. This binding opens ion channels allowing the entry of ions which can generate an action potential on the post synaptic neuron.
(b) Mechanism of vision:
The rays in visible wavelength focussed on the retina through the cornea and lens generate potentials (impulse) in rods and cones. The photo- sensitive compounds (photo pigments) in the human eyes is composed of opsin and retinal. Light induces dissociation of the retinal from opsin resulting in changes in the structure of the opsin. This causes membrane permeability to change.
As a result, potential differences are generated in the photoreceptor cells. This produces a signal that generates action potentials in the ganglion cells through the bipolar cells. These action potentials are transmitted by the optic nerves to the visual cortex area of the brain, where the neural impulses are analysed and the image formed on the retina is recognised based on earlier memory and experience.
