1. Somatic and Special Senses

2. Senses constantly provide us with information about our surroundings
Grouped into two major categories:
- general senses
- special senses

3. Sensory Pathway Includes: - receptors - sensory neurons
- sensory tracts
- sensory area

4. Receptors Sensory Neurons 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)

5. Sensory Tracts Sensory Areas 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

6. 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

7. Special Senses Somatic: - visual - sight - auditory - hearing
- equilibrium - static and dynamic equilibrium
Visceral:
- olfactory - smell
- gustatory - taste

8. Skin Receptors

9. Tactile Sensations Touch receptors: - root hair plexuses
- tactile discs
- type II cutaneous mechanoreceptors
- corpuscles of touch - (Meissner’s corpuscles)

10. Root Hair Plexuses dendrites arranged around hair follicles
receptors that rapidly adapt to detect movements when hair is disturbed

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

12. 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

13. 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

14. Corpuscles of Touch (cont.)
rapidly adapting receptors that respond to low frequency vibrations
also respond to pressure and touch stimuli

15. Tactile Sensations Pressure and vibration receptors:
- corpuscles of touch (Meissner’s)
- lamellated corpuscles (Pacinian)

16. 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

17. Tactile Sensations (itch and tickle receptors)
free nerve endings are receptors for both tickle and itch sensations

18. 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)

19. Thermal Sensations (cont.)
intermediate temperature sensory input from combination of cold and heat receptors
both heat and cold receptors rapidly adapt to continuous stimulation

20. Pain Sensations (Nociceptors)
free, naked nerve endings
located between cells of epidermis
respond to all types of stimuli

21. 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