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1

sensation

conscious or subconscious awareness of changes in the external or internal environment

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perception

conscious awareness and interpretation of sensations; primarily a function of the cerebral cortex

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sensory modality

each unique type of sensation i.e. touch, pain, vision or hearing

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general senses

refers to both somatic and visceral senses

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somatic senses

includes tactile senses (touch, pressure, vibration, itch, tickle), thermal sensations (warm and cold), pain sensations and proprioceptive sensations (perception of static and moving positions of the body)

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visceral senses

provide info about conditions within internal organs (i.e. pressure, stretch, chemicals, nausea, hunger and temperature)

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special senses

include the sensory modalities of smell, taste, vision, hearing and equilibrium/balance

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process of sensation (4 steps)

1. Stimulation of a sensory receptor
2. Transduction of the stimulus (converts energy into a stimulus into a graded potential)
3. Generation of nerve impulses
4. Integration of sensory input

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3 ways to classify sensory receptors

1. microscopic structure
2. location of the receptors and origin of stimuli that activate them
3. type of stimulus detected

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3 classifications based on microscopic structure

1. free nerve endings of first order sensory neurons
2. encapsulated nerve endings of first order sensory neurons
3. separate cells that synapse with first order sensory neurons

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free nerve endings

bare dendrites; lack any structural specializations that can be seen under a microscope; i.e. pain, temperature, tickle, itch and some touch sensations

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encapsulated nerve endings

dendrites enclosed in connective tissue capsule ; a distinctive microscopic structure; i.e. somatic and visceral sensations (pressure, vibration and some touch sensations)

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separate cells

synapse with sensory neurons; i.e. hair cells for hearing and equilibrium in the inner ear; gustatory receptor cells in taste buds and photoreceptors in the retina in the eye for vision

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generator potential

a potential created by stimulation of dendrites of free nerve endings, encapsulated nerve endings and receptive part of olfactory receptors; if the potential is big enough to reach threshold, it triggers one or more nerve impulses in the axon of a first order sensory neuron

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receptor potential

produced by sensory receptors that are separate cells; the potential triggers release of NT through exocytosis of synaptic vesicles

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3 classifications based on location

Exteroceptors, Interoceptors and Proprioceptors

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Exteroceptors

located at or near the external surface of the body; sensitive to stimuli originating outside the body; provide info about external environment; i.e. hearing, vision, smell, taste, touch, pressure, pain etc.

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interoceptors/ visceroceptors

located in blood vessels, visceral organs, muscles and nervous system; monitor conditions of internal environment; nerve impulses produced by interoceptors are not consciously received unless strong stimuli (can be felt as pain or pressure)

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proprioceptors

located in muscles, tendons, joints and the inner ear; provide info about body position, muscle length and tension and the position and movement of joints

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6 classifications based on type of stimulus detected

Mechanoreceptors, thermoreceptors, nociceptors, photoreceptors, chemoreceptors and osmoreceptors

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mechanoreceptors

detect mechanical stimuli; provide sensations of touch, pressure, vibration and proprioception and hearing and equilibrium; monitor stretching of blood vessels and internal organs

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thermoreceptors

detect changes in temperature

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nociceptors

respond to painful stimuli resulting from physical or chemical damage to tissue; free nerve endings; found in every tissue of the body except the brain

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photoreceptors

detect light that strikes the retina of the eye

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chemoreceptors

detect chemicals in the mouth (taste), nose (smell) and body fluids

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osmoreceptors

sense osmotic pressure of body fluids

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rapidly adapting receptors/ phasic receptor

adapt very quickly; specialized for signaling changes in a stimulus; i.e. receptors associated with pressure, touch, and smell

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slowly adapting receptors/ tonic receptor

adapt slowly; continue to trigger nerve impulses as long as the stimulus persists; monitor stimuli associated with pain, body position and chemical composition of the blood

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tactile sensations

include touch, pressure, vibration, itch and tickle

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touch

result from stimulation of tactile receptors in the skin or subcutaneous layer