Chapter 8 Special Senses Essentials of Human Anatomy & Physiology Seventh Edition Elaine N. Marieb Chapter 8 Special Senses Slides 8.1 – 8.19 Lecture Slides in PowerPoint by Jerry L. Cook Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

The Senses General senses of touch Special senses Temperature Pressure Pain Special senses Smell Taste Sight Hearing Equilibrium Slide 8.1 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Accessory Structures of the Eye Eyelids-protects Eyelashes- modified sebaceous glands-protect Sebaceous glands-empty oil into hair follicle Figure 8.1b Slide 8.3a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Accessory Structures of the Eye Meibomian glands –a a modified sebaceous gland that produces an oily secretion to seal the eye and trap tears preventing evaporation. Dry eyes are a meibomian gland dysfunction Figure 8.1b Slide 8.3b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Accessory Structures of the Eye Conjunctiva Membrane that lines the eyelids Connects to the surface of the eye Secretes mucus to lubricate the eye Conjunctivitis: inflammation of the conjunctiva Pinkeye caused by bacteria or virus; very contagious Slide 8.4a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Accessory Structures of the Eye Lacrimal apparatus Lacrimal gland – produces lacrimal fluid(tears) Releases a diluted salt solution that flushes across the eyeball canal. It enters the lacrimal sac and then into the nasolacrimal duct and then into the nasal cavity Figure 8.1a Slide 8.4b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Properties of lacrimal fluid Contains antibodies and lysozyme Protects, moistens, and lubricates the eye Colds can cause lacrimal musosa to become inflamed and swell causing watery eyes. When tears spill over the eyelid and fill the nasal cavit it can cause congestion Slide 8.5 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Extrinsic Eye Muscles Muscles attach to the outer surface of the eye Produce eye movements Figure 8.2 Slide 8.6 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

3 Parts of the Eye 1. Tunics-sclera & cornea Humors Aqueous-watery Vitreous-jelly like 3. Lens- focusing apparatus Divides eye into 2 cavities

Tunics The wall is composed of three tunics Fibrous tunic – outside layer Choroid – middle layer Sensory tunic – inside layer Figure 8.3a Slide 8.7 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

The Fibrous Tunic- outermost layer Sclera White connective tissue layer Seen anteriorly as the “white of the eye” Cornea Transparent, central anterior portion Supplies with many pain fibers Allows for light to pass through Repairs itself easily The only human tissue that can be transplanted without fear of rejection Slide 8.8 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Choroid Layer- Middle Tunic Blood-rich nutritive tunic Pigment prevents light from scattering Slide 8.9 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Sensory Tunic (Retina)-Intermost Contains millions of receptor cells (photoreceptors) Rods Cones Photoreceptors respond to light Optic nerve sends impulses from the retina to the brain. Optic disc/blind spot – place on the retina that does not contain photreceptors(rods & cones) Slide 8.10 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Neurons of the Retina Figure 8.4 Slide 8.11 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Neurons of the Retina and Vision Rods Most are found towards the edges of the retina Allow dim light vision and peripheral vision Perception is all in gray tones Night Blindness- anything that interferes with rod function; can be caused from a Vitamin A deficiency. Slide 8.12a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Neurons of the Retina and Vision Cones Allow for detailed color vision in bright light Densest in the center of the retina Fovea centralis – area of the retina with only cones; found on eithr side of the blind spot; point of sharpest vision Slide 8.12b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Cone Sensitivity There are three types of cones Different cones are sensitive to different wavelengths Color blindness is the result of lack of one cone type Slide 8.13 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.6

Images Formed on the Retina Figure 8.10 Slide 8.17 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Visual Pathway Photoreceptors of the retina Optic nerve Optic nerve crosses at the optic chiasma Figure 8.11 Slide 8.18a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Internal Eye Chamber Fluids Aqueous humor Watery fluid found in chamber between the lens and cornea Similar to blood plasma Helps maintain intraocular pressure Provides nutrients for the lens and cornea Slide 8.15a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Internal Eye Chamber Fluids Vitreous humor Gel-like substance behind the lens Keeps the eye from collapsing Lasts a lifetime and is not replaced Slide 8.15b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Lens Biconvex crystal-like structure Held in place by a suspensory ligament attached to the ciliary body Figure 8.3a Slide 8.14 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Lens Accommodation Light must be focused to a point on the retina for optimal vision The eye is set for distance vision (over 20 ft away) The lens must change shape to focus for closer objects Slide 8.16 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.9

Structures around the lens Cilliary body – smooth muscle Suspensory ligament- hold lens Iris-regulates the amount of light entering eye. Pigmented layer that gives eye color Pupil – rounded opening in the iris

Lens Problems Emmetropia- perfect vision; light focused exactly on retina Myopia-nearsightedness; lens & cornea bend light too much; curved out too much Hyperopia-farsightedness; lens & cornea are flatter than need; babies are born slighlty hyperopic

Eye Conditions Cataracts-cloudiness of lens; can lead to blindness Night Blindness- rod lack a pigment Rhodopsin; sometimes caused by lack of vitamin A Astigmatisms- misshaped cornea causing problems focusing image onto the retina; blurred vision; near and farsightedness; cornea is football shaped and should be baseball shaped

Colorblindness Color blindness occurs when there is a problem with the color-sensing granules (pigments) in certain nerve cells of the eye. These cells are called cones. They are found in the retina, the light- sensitive layer of tissue that lines the back of the eye.

Glaucoma Glaucoma is a disease of the optic nerve. Glaucoma is characterized by a particular pattern of progressive damage to the optic nerve that generally begins with a subtle loss of side vision (peripheral vision). If glaucoma is not diagnosed and treated, it can progress to loss of central vision and blindness.