Ch 44.docx - 44.1 Sensory Receptors Overview Exteroreceptors sense stimuli from external ex Vision hearing taste smell touch Interoreceptors sense

Ch 44.docx - 44.1 Sensory Receptors Overview...

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TA: Victor Vinh ([email protected]) 44.1 Sensory Receptors Overview Exteroreceptors: sense stimuli from external, ex. Vision, hearing, taste, smell, touch Interoreceptors: sense stimuli that arise from within the body, ex. Muscle length, tension, pain, pressure, temperature 3 types of receptors: Mechanoreceptors: stimulated by mechanical forces (pressure) Chemoreceptors: detect chemicals/changes; smell & taste Electromagnetic receptors: react to light & heat energy; sight Sensory info conveyed in 4 steps: 1. Stimulation 2. Transduction: stimulus energy transformed into graded potentials in dendrites 3. Transmission: action potentials develop in axon & conducted to CNS by afferent nerves (sensory) 4. Interpretation brain interprets senses/stimulus Sensory cells respond to stimuli b/c of stimulus-gated ion channels Stimulus creates depolarization of receptor cell, called a receptor potential Receptor potentials are graded potentials Receptor potentials decrease in size with distance from the source the greater the stimulus, the greater the depolarization of the receptor potential, and the higher the frequency of the action potentials Mechanoreceptors cutaneous receptors: skin, interoreceptors o respond to stimuli at border between internal & external, ex. Pain, heat, cold, pressure Pain: tissue damage o Nociceptors: sensitive to pain & noxious stuff, free nerve endings o Transient receptor potential ion channels:found in nociceptors, stimulated by temp. to produce influx of Na + and Ca 2+ Depolarizing causes neuron to fire, releasing glutamate(EPSP) Thermoreceptors: naked dendritic endings of sensory (afferent) neurons, sensitive to temp. o TRP ion channels that respond to hot/cold o Cold receptors: stimulated by fall in temp. / inhibited by rise in temp., located immediately below epidermis o Hot receptors: stimulated by rise in temp. / inhibited by rise in temp., located deeper in dermis o Also found in hypothalamus Touch o Phasic type receptors : intermittently activated; hair follicle, Meissner corpuscles, pascinians, which are located on surfaces w/o hair o Tonic type receptors : continuously activated; Merkel’s disks, Ruffini’s corpuscles, located near surface; activated as long as stimulus is maintained o Merkel cells : Tonic receptors located near surface, sensitive to touch, pressure, duration (TEXTURE) o Meissner corpuscles: phasic receptors sensitive to fine touch, concentrated in hairless skin (DETAIL) o Ruffini corpuscles: tonic receptors located near surface of skin, sensitive to touch, pressure o Pascinian corpuscles: phasic; pressure-sensitive, located deep; capsulated end of afferent axons & monitor pressure Proprioceptors : monitor muscle length & tension & position/movement of body parts o Knee jerk reflex is a product of muscle spindle stimulation Baroreceptors: blood pressure monitoring; detect tension in blood vessel walls o Located in the carotid sinus and aortic arch walls of blood vessels o When BP decreases , frequency of impulses by baroreceptors decreases ; CNS responds to this by
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