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Somatic and Special Senses

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Senses constantly provide us with information

about our surroundings Grouped into two major categories:

- general senses

- special senses

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Sensory Pathway Includes:

- receptors

- sensory neurons

- sensory tracts

- sensory area

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Receptors detect stimuli specific with respect to changes to which

they respond

Sensory Neurons transmit impulses from receptors to central

nervous system found in both spinal and cranial nerves

(each carries only one type of receptor)

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Sensory Tracts white matter in spinal cord or brain transmit impulses to a specific part of brain

Sensory Areas most are in cerebral cortex feel and interpret sensations learning to interpret sensations begins in infancy

without awareness and continues throughout life

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General Senses Somatic:

- tactile - touch, pressure, vibration, itch, etc.

- thermal - hot and cold

- pain - acute and chronic

- proprioceptive - muscle, tendon, joint Visceral

- distension of viscera - internal organs

- chemical composition of extracellular fluid

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Special Senses Somatic:

- visual - sight

- auditory - hearing

- equilibrium - static and dynamic equilibrium Visceral:

- olfactory - smell

- gustatory - taste

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Skin Receptors

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Tactile Sensations Touch receptors:

- root hair plexuses

- tactile discs

- type II cutaneous mechanoreceptors

- corpuscles of touch - (Meissner’s corpuscles)

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Root Hair Plexuses dendrites arranged around hair follicles receptors that rapidly adapt to detect

movements when hair is disturbed

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Tactile Discs expanded (flattened) nerve endings slowly adapting touch receptors for

discriminative touch

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Type II Cutaneous Mechanorecptors also called end organ for Ruffini expanded nerve endings embedded in dermis receptors that adapt slowly to heavy

and continuous touch

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Corpuscles of Touch (Meissner’s Corpuscles)

small, oval, encapsulated nerve endings rapidly adapting touch receptors recognize exactly what point to which

body is touched abundant in hairless portions of skin

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Corpuscles of Touch (cont.)

rapidly adapting receptors that respond to low frequency vibrations

also respond to pressure and touch stimuli

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Tactile Sensations Pressure and vibration receptors:

- corpuscles of touch (Meissner’s)

- lamellated corpuscles (Pacinian)

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Lamellated Corpuscles(Pacinian)

oval structures composed of connective tissue layered like an onion enclose a dendrite rapidly adaptive receptors that respond

to pressure and high frequency vibrations

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Tactile Sensations(itch and tickle receptors)

free nerve endings are receptors for both tickle and itch sensations

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Thermal Sensations(thermoreceptors)

heat receptors most sensitive to temperatures above 25oC (77oF) and become unresponsive at temperatures above 45oC (113oF)

cold receptors most sensitive to temperatures between 10oC (50oF) and 20oC (68oF)

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Thermal Sensations (cont.)

intermediate temperature sensory input from combination of cold and heat receptors

both heat and cold receptors rapidly adapt to continuous stimulation

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Pain Sensations(Nociceptors)

free, naked nerve endings located between cells of epidermis respond to all types of stimuli

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Referred Pain pain that feels as if it originated from a

part other than site being stimulated Example:

- pain from heart attack (myocardial infarction) may be felt in left shoulder or inside of left arm

- pain from gallstones may be felt in right shoulder