Receptor Potentials : trigger release of a neurotransmitter through exocytosis, diffuse across the synaptic cleft and produce a postsynaptic potential in the first-order neuron. PSPs may trigger one or more nerve impulses which propagate into the CNS.
Types of Sensory Receptors
1) Free Nerve Endings : bare dendrites that lack any structural specializations. Receptors for pain, thermal, tickle, itch, and some touch sensations are free nerve endings. 2) Encapsulated Nerve Endings : enclosed dendrites in a connective tissue capsule with a distinct structure. Receptors for other somatic and visceral sensations such as pressure, vibration, and some touch sensations. The different types of capsules enhance the sensory receptor. 3) Specialized Cells : synapse with sensory neurons. These receptors are for some special senses. Hair cells for hearing and equilibrium, gustatory receptor cells in taste buds, olfactory receptors in the nose, photoreceptors in the retina of the eye.
Location of Receptors
1) Exteroceptors : located at or near the surface of the body; sensitive to stimuli outside of the body providing information about the external environment. These include sensations of hearing, vision, smell, taste, touch, pressure, vibration, temperature, and pain. 2) Interoceptors or Visceroceptors : located in blood vessels, visceral organs, muscles, and the nervous system monitoring conditions of the internal environment. These impulses are not usually perceived. 3) Proprioceptors : located in muscles, tendons, joints, and the inner ear, and provide information about body position, muscle length and tension, and the position and movement of joints.
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