1. Somatic and special senses
Ch. 15

2. Introduction
Sensory receptors - make it possible for the body to respond to stimuli caused by changes occurring in the internal or external environment
Different types of receptors respond to different stimuli
General function—responds to stimuli by converting them to nerve impulses
Sensations
Sensory adaptation - receptor potential decreases over time in response to a continuous stimulus
Receptors for special senses of smell, taste, vision, hearing, and equilibrium are grouped into localized areas or into complex organs

3. Receptors and sensations
Types of receptors
Chemoreceptors activated by amount or changing concentration of certain chemicals; e.g., taste and smell
Pain receptors - Nociceptors—activated by intense stimuli that may damage tissue; the sensation produced is pain
Thermoreceptors — activated by changes in temperature
Mechanoreceptors activated when “deformed” to generate receptor potential
Proprioceptors -Location limited to skeletal muscle, joint capsules, and tendons
Provide information on body movement, orientation in space, and muscle stretch
Photoreceptor— found only in the eye; respond to light stimuli if the intensity is great enough to generate a receptor potential

4. Somatic senses Touch and pressure Free ends of dendrites
Called nociceptors
Receptors for pain
Meissner’s corpuscles
sense touch
large and superficial
Pacinian corpuscles
Respond to deep pressure/stretch
Deep dermis and joint capsules
Stretch receptors
Found in tendons and muscles
Once stretched, the muscle shortens

5. Temperature senses
Organs of Ruffini - also called Ruffini’s corpuscles
Deep in dermis
Sense heat degrees
Bulbs of Krause - sense cold

6. Sense of pain Free nerve endings Visceral pain
Referred pain
Pain nerve fibers - Chronic/acute
Regulation of pain impulse - awareness of pain - thalamus. Impulse conducted to cerebral cortex - judges intensity and location of pain.
Endorphins provide natural pain control.
Serotonin inhibits release of pain impulses in spinal cord.

7. Special senses - receptors are in specialized organs
Smell - olfactory sense
Taste - gustatory sense
Hearing - auditory sense
Static equilibrium - balance when stationary
Dynamic equilibrium - balance when moving
Sight - sense of vision

8. Sense of smell

9. Sense of smell Olfactory receptors
Cilia in nasal cavity
chemoreceptors
Olfactory organs - epithelial supporting tissue
Nerve pathways
Action potential to olfactory nerves in olfactory bulb
Thalamic and olfactory centers in brain

10. Sense of taste

11. Sense of taste Taste receptors - chemoreceptors Taste sensations
Taste hairs portrude from taste pores
Chemicals dissolved in saliva
Taste sensations
Sweet
Sour
Salt
Bitter
Nerve pathways
Facial, glossopharyngeal, vagus nerves to medulla oblongata to gustatory cortex in cerebrum.

12. Sense of hearing

13. Sense of hearing External ear Middle ear Inner ear -
Auricle or pinna - visible - collects sound
External auditory meatus - tube
Middle ear
in temporal bone- contains ossicles
Malleus - attached to tympanic membrane
Incus - attached to malleus and stapes
Stapes - attached to chochlea
Inner ear -
semicircular canals - equilibrium
Cochlea - hearing
Organ of corti - located in the cochlear duct. Contains supporting cells and hair cells

14. Sense of hearing Nerve pathways - sound waves move tympanic membrane
Movement of membrane moves ossicles which move oval window which create waves which bend hairs.
Hearing - stimulation of auditory area in cerebral cortex.
Range of hearing 20-20,000 decibels, whisper 40 db, rock concert 120 db, pain, 140 db

15. Causes and types of hearing loss

16. Sense of equilibrium - two types
Static equilibrium—ability to sense the position of the head relative to gravity or to sense acceleration or deceleration
Dynamic equilibrium—needed to maintain balance when head or body is rotated or suddenly moved; able to detect changes both in direction and rate at which movement occurs

17. Static Equilibrium Stability of head when body is motionless
Utricle and Saccule - location for static equilibrium sense
Macula - movement provides information about head position
Otoliths located in macula, gravity shifts them, bending hair cells.
Nerve fibers send message to brain
Body is restored to normal position.

18. Dynamic equilibrium Cristae ampullaris, located in semicircular canal
Cupula - gelatinous cap in which hairs are embedded, moves with flow of endolymph (fluid)
Semicircular canals placed at right angles - detect motion in all directions
When cupula moves, hair cells are bent, sending action potential to medulla oblongata and then other areas for interpretation.

19. Sense of balance and equilibrium

20. Visual accessory organs
Eyelid - palpebrae
voluntary muscle and skin, lined with mucous membrane called conjunctiva.
Eyelashes and eyebrows - give some protection agains foreign objects entering eye
Lacrimal gland -secret tears. Tears are drained from surface of eyeball.

21. Extrinsic muscles of the eye
Attach to outside of eyeball and bones of the orbit

22. Structure of the eye Outer tunic Middle tunic
Cornea - transparent portion that lies over the iris.
Sclera - tough outer coat
Middle tunic
Choroid coat - vascular and pigmented
Ciliary body - attaches to iris
Iris - colored part of the eye
Lens - held in place by suspensory ligaments and ciliary muscles. Has elasticity - shape is adjustable.

23. Inner tunic and cavities/chambers
Retina - innermost coat of eyeball
Contains receptors
Macula lutea
Fovea centralis
Optic disk
Cavities - anterior and posterior chamber
Anterior cavity contains anterior/posterior chambers
Filled with aqueous humor - watery fluid - involved in bending light
Posterior cavity - right behind lens.
Filed with Vitreous humor - semisolid, maintains intraocular pressure.

24. Overview of the eye

25. Light refraction and the process of seeing
Refraction - Light waves bent
Accomplished by cornea, lens, aqueous humor
Accomodation of the lens - increase in curvature for near vision.
Pupil constricts controlling the entering of light

26. Visual receptors - undergo changes that generate nerve impulses
Rods - black and white vision
Rhodopsin - photo pigment
Breaks down into opsin and retinal
Energy is required to reform rhodopsin
Cones - color vision
Three types

27. Visual Pigments Rhodopsin Isodopsin Opsin, retinal Erythrolabe - red
Chlorolabe - green
Cyanolabe - blue

28. Visual nerve pathways Optic nerves Optic chiasma cross over Thalamus
Visual cortex of occipital lobe