1. Somatic Nervous System & Special Senses
Chapter 12

2. Special Senses
Part B

3. Sciences of Special Senses
Ophthalmology – is the science that deals with the eye and its disorders
Otorhinolaryngology – deals with all the other senses.

4. Olfaction: Smell Sense of smell
Requires 10 million to 100 million receptors

5. Structures Olfactory epithelium
Located in the upper portion of the nasal cavity
Consists of three types of cells
Olfactory receptors
Supporting cells
Basal stem cells

6. Olfactory Receptors
Are the stimulated by olfactory hairs, which project from knob-shaped tip of the olfactory receptor
Odorants (chemicals in the air) stimulate the olfactory hairs
Short life span – only about 1 month
See nose hairs are good

7. Supporting Cells
Columnar epithelial cells of the mucous membrane lining of the nose
Provide physical support, nutrients, and electrical insulation for the olfactory receptors

8. Basal Cells
Cells that are responsible for producing new olfactory receptors

9. Olfactory glands
Responsible for the production of mucus that moistens the surface the surface of the olfactory epithelium and serves as a solvent for inhaled odorants.

11. Stimulation of Olfactory Receptors
Unique because adaptation to a chemical is very rapid
You may smell something bad but over time if you remain in that environment you won’t smell it anymore.

12. Hyposmia
Reduced ability to smell, affects over half of those over the age of 65 and 75% over 80.
Caused by head injury, Alzheimer’s disease or Parkinson’s disease
Also by certain drugs, such as antihistamines, or steriods

13. Gustation: Taste
Five primary tastes
Sour
Sweet
Bitter
Salty
Umani

14. Umami
Describe as a “savory” taste

15. Taste Buds Taste buds – are the location of receptors for taste
Taste buds are found on the papillae, which are the bumps on the tough
Number of tastes bud decrease with age
Location
Mostly on the tongue
Some on the roof of mouth, throat and epiglottis

17. Tastants
Chemicals that activate the gustatory receptors

18. Stimulation
Tastants are dissolved in saliva which then allows them to enter the pores and come into contact with the gustatory hairs.
Stimulation of hairs causes an electrical impulse to be sent to the brain

19. Vision
More than half the sensory receptors in the human body are found in the eye
The largest part of the cerebral cortex is devoted to vision

20. Careers Associated with vision
Ophthalmologist – physician who specializes in the diagnosis and treatment of eye disorders with drugs, surgery and corrective lenses
Optometrist – has a doctorate of optometry and is licensed to test the eyes and treat visual defects b y prescribing corrective lenses
Optician – technician who fits, adjusts and dispenses corrective lenses using the prescription supplied by an ophthalmologist or optometrist

21. Accessory structures of the eye
Accessory structures – are eyebrows, eyelashes, eyelids, muscles the move eyeballs and lacrimal (tear) apparatus

22. Eyelashes and Eyebrows
Protect the eyeballs from foreign objects, perspiration, and direct rays from sun

23. Eyelids Upper and lower Shade the eye during rest
Protect eyes from excessive light
Protect eyes from foreign objects
Spread lubricating secretions over the eyeballs by blinking

24. Eye Muscles Six muscles control the movement of the eyeball
Right, left, up, down and diagonally

25. Lacrimal apparatus
Group of glands, ducts, sacs that produce and drain lacrimal fluid as tears
Lacrimal glands (one for each eye)
About the size and shape of an almond and are responsible for secreting lacrimal through the lacrimal ducts to the eyeballs
Tears can also pass through the nasolacrimal duct, which allows lacrimal to drain into your nasal cavity

27. Lacrimal
Is a watery solution containing salts, some mucus, and a bacteria killing enzyme called lysozyme

28. Layers of the eyeball Adult eyeball measures about 2.5 cm across
Three layers
Fibrous Tunic
Vascular Tunic
Retina

29. Fibrous Tunic Outer coat of the eyeball Consists of
Cornea – transparent fibrous coating that colors the iris (colored portion of your eye)
Also helps focus light
Sclera – is the “white” of the eye, dense connective cove
Gives the shape of the eye, makes it more rigid and protects inside of eyeball
Conjunctiva – epithelial layer, covers the anterior surface of eyeball and lines inner surface of eyelid

30. Corneal Transplant
If your cornea is damaged it can be replaced with a donor cornea

31. Vascular Tunic Middle Layer of the eye Composed of:
Choroid – thin membrane that lines most of the internal surfaces of the sclera
Contains many blood vessels that nourish the retina
Ciliary body – consists of
ciliary processes, which are folds on the inner surface of the ciliary body whose capillaries secrete a fluid called aqueous humor and the
ciliary muscles, a smooth muscle that alters the shape of the lens for viewing objects up close or at a distance
Lens – transparent structure that focuses light rays onto the retina
Constructed of many layers of elastic protein fibers
Attached to ciliary muscles by zonular fibers

32. Iris and pupil Part of the vascular tunic Iris Pupil
Colored portion of the eye
Muscle that regulates the amount of light let into the eye
Pupil
Hole in the center of the eye through which light enters

33. Retina Portion that lines posterior of the eye about ¾ of the eyeball
Consists of two layers
Neural layer
Pigmented layer

34. Neural Layer Consists of three distinct layers Photoreceptor layer
Bipolar cell layer
Ganglion cell layer

35. Photoreceptor layer Two types of cells
Rods – allow us to see shades of gray in dim light (6 million)
Cones – allow us to see color (120 million)
Found in central fovea in the center of the macula lutea

37. Pigmented Layer
A sheet of melanin is located between the choroid and the neural part of the retina
Melanin absorbs stray light, helping to keep the image sharp and clear

38. Pathway Photoreceptor layer to Bipolar cell layer to
Ganglion cell layer to
Optic nerve

39. Interior of Eyeball Two cavities divided by the lens Anterior cavity
Vitreous cavity

40. Anterior cavity
Contains aqueous humor that helps maintain the shape of the eye and supplies oxygen and nutrients to the lens and cornea.

41. Vitreous Chamber
Contains the vitreous body, which helps maintain the shape of the eyeball and keeps the retina attached to the choroid
Vitreous body – develops in embryonic life and is not replaced
Choroid – provides blood supply and absorbs scattered light

42. Intraocular pressure Pressure in the eye
Maintains the shape of the eye
Keeps the retina pressed against choroid
Normal pressure is 16mm of Hg