How does information from external environment reach the dendritic tip of the receptor neuron?
The sense organs are highly specialized structures that receive information from the environment. These organs contain special sense receptors ranging from complex structures, such as eyes and ears, to small localized clusters of receptors, such as taste buds and olfactory epithelium (receptors for smell).
Smell and taste are chemical senses, which contain chemoreceptors that respond to chemicals in solution. Food chemicals dissolved in saliva stimulate taste receptors in taste buds. The nasal membranes produce fluids that dissolve chemicals in air. These chemicals stimulate smell receptors in olfactory epithelium. The chemical senses complement each other and respond to many of the same stimuli.
Photoreceptors, which include rods and cones, in back of the eye respond to light energy. Rods provide , black-and-white vision whereas cones operate in bright light and provide color vision. Information from the rods and cones travels via the optic nerve into the brain for interpretation. Sound waves enter the outer ear through the external auditory canal and strike the tympanic membrane. Vibration of the eardrum moves three ossicles ) inside the middle ear, which in turn stimulate the organ of Corti (hearing receptor in the inner ear). The ear also contains equilibrium (sense of balance) receptors. The vestibular apparatus, a group of equilibrium receptors in the inner ear, sense movement in space.
Mechanoreceptors respond to mechanical energy forces: touch, pressure, stretching, and movement. Ranging in complexity from free nerve endings beneath the skin to more complex tactile receptors at the bases of hair, mechanoreceptors change shape when pushed or pulled.
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