Chapter 15 part 1) Special Senses

Question 1

The Eye and Vision

Answer 1

• 70% of the body’s sensory receptors are in the eye
  
  • nearly half of the cerebral cortex is involved in visual processs
• Small sphere; only about a 6th of eye shows
  
  • rest is protected by fat and orbit bones

Question 2

Acessory Structure of the Eye

Answer 2

• Eyebrows
  
  • Shade eyes, prevents perspiration (sweat) from entering eye
• Eyelids (Blink, Moisten eyeball, and protectins)
  
  • Palpebral Fissue) slit of eye
  • Corners) Medial and Lateral commusires
  • Lacrimal Carnucle) Locaded at medial commisure, contains oil and sweat glands.
• Eyelashes)
  
  • Have hair follicles that are innervated; initiate blink reflex
• Lubricating Glands
  
  • Tarsal Glands) Modified sebacous glands that lubricates eye
  • Ciliary glands) Between eyelash hair follicles, modified sweat glands
• Conjunctiva (mucous membrane that prevents eye from drying)
  
  • Palpebral conjuntica) Lines underside of eyelids
  • Bulbar Conjuntiva) covers white of eyes (not cornea)
  • Conjuntival sac) lies between the two conjuntiva
• Lacrimal Apparatus (Lacrimal gland and duct)
  
  • Lacrimal Secretion) made by lacrimal gland
  • Tears drain into lacrimal sac and nasolacrimal duct.

Question 3

Entrinsic Eye Muscles

Answer 3

• Six Straplike muscles
  
  • orginate from bony orbit and insert on eyeball
  • Enable eye to follow object, mantain shape, and hold it in place
• Rectus Muscles (move eyeball in direction name signifies)
  
  • Superior, inferior, lateral and medial
• Oblique Muscles (rotate eyeball)
  
  • Superior and Inferior

Question 4

Conjuntivitis/ Pinkeye

Answer 4

• Conjuctivitus) Inflmation of the conjuntiva resulting in redness
• Pinkeye) Infection caused by bacteria or virus
  
  • very contagiois
  • Nasal cavity inflamation causes tears to be trapped in the eye

Question 5

Diplopia

Answer 5

• Also known as double vision
  
  • occurs when movments of eye muscles are not perfectly cordinated.
  • eyes cannot focus on same image

Question 7

Strabismus

Answer 7

• Also known as cross-eye. Congenital weakess of external eye muscles
• One eye rotates medially or lateraly
  
  • may alternate focus on objects

Question 8

Structure of the Eyeball

Answer 8

• Eye is made of three layers
  
  • Fibrous
  • Vascular
  • Inner
• Internal cavity filled with humor
• Lens seprates internal cavity into anterior and posterior segments.

Question 9

Fibrous Layer

Answer 9

• Outermost layer of eye
  
  • Made of Dense avascular connective tissue.
  • Two regions.
• Sclara
  
  • Posterior region
  • Protects and shapes eyeball
  • Anchors extrensic eye muscles
  • Where the optic nerve exits the sclera is continuous with the dura mater of the brain.
• Cornea
  
  • Anterior 1/6th of fibrous layer
  • Forms a clear window that lets light enter as it bends
• Epithelium covers both surfaces.
  
  • Outer) protects cornea
  • Inner) Mantains clarity of cornea,.

Question 10

Vacsular Layer (Uvea)

Answer 10

• Middle Pigmented Layer of the Eye
  
  • Three regions
• Choroid Region (membrane)
  
  • Posterior part of Uvea
  • Supplies blood to all layers of eye
  • Brown pigment absorbs excess light
• Ciliary Body
  
  • Anterior Part of Uvea (Chorid turns into Ciliaru body)
  • Cilary muscles) smooth muscle that controls lens size
  • Ciliary processes) secrete fluid for anterior segment of the eye
  • Cilary Zonule) holds lens in position
• Iris (colored part of eye)
  
  • Between conrnea and lens
  • Pupil) Regulates ammount of light let into the eye
    
    • Sphincter Pupillae) Constricts pupils (parasympathetic control)
    • Dilator Pupillae) Dialates Pupils (Sympathetic Control)

Question 11

Inner Layer: The Retina

Answer 11

• The retina Contains millions of photoreceptor cells. It is a delicate two-layered membrane.
  
  • Outer) Pigmented Layer
  • Inner) Neural Layer
• Pigmented Layer of Retina)
  
  • Single cell thick lining next to chorid
  • Absorbs light and prevnets it from scatering, stores vitamin A
• Neural Layer of Retina
  
  • Tranparent layer of the eye that runs anteriorly to margin of cilary body
  • Composed of Photoreceptors, Bipolar Cells, and Ganglion Cells
  • Bipolar Cells) internuerons
  • Ganglion Cells) Axons exit eye as optic nerve
  • Optic Disc) site where optic nerve leaves eye, called our blind spot.

Question 12

Photoreceptors

Answer 12

• Rods
  
  • Dim light, prepherial vison receptors
  • More numerous than cones
  • do not provide color or sharp images
• Cones)
  
  • Bright Light Receptor
  • High-Resolution Images
• Macula Lutea (yellow spot)
  
  • At posterior pole lateral to blind spot.
  • Made of mostly cones
• Fovea Centralis
  
  • Center of Macula Lutea
  • Contains All cones

Question 13

Retinal detachment

Answer 13

• Pigmenteted and Nueral Layers of eye seperate.
  
  • allows jellylike humor to seep betwen them
  • can lead to blindness
  • Treatment is to reattach retina with laser surgery.

Question 14

Posterior Segment of Internal Eye Chamber

Answer 14

• Contains a Vitrous Humor fluid
  
  • transmits light
  • supports posterior surface of lens
  • holds layers of retina togehter
• Our Vitrous Humor forms in our embro and is not replaced our whole life

Question 15

Anterior Segment of Internal Chamber

Answer 15

• Iris Divides anterior segment into two chambers
  
  • Anterior Chamber) between cornea and Iris
  • Posteior Chamber) between iris and lens
• Entire Segment is filled with Aqueous Humor
  
  • Contnusolly formed throuought ones life.
  • Drains via Scleral Venous Sinus.

Question 16

Lens

Answer 16

• Biconvex, Transpararent and flexible structure that changes shape to focus light on the retina.
  
  • Is also avascular
• Two Lens Regions
• Lens Epithelium) Anterior Region of Cubodial cells
  
  • diffreientiate lens into fiber cells.
• Lens Fibers) Form Bulk of Lens
  
  • Filled with transparent protein crystallin
  • Fibers are continually added so lens becomes more dense and less elastic (less functional) with age.
• Cataract) Clouding of Lens.

Question 17

Visible Light

Answer 17

• Small portion of electromagnetic spectrum
  
  • wavlength of 400-700nm
• Light) packets of photons that travel in waves
  
  • Redlight) lowest frequency (long wavelength)
  • Violent) Hightst Frequency (short wavelength)
• Color That eye precives is reflection of that wavlength
  
  • Grass is green because it absorbs all colors except green
  • White reflects all colors, and black absorbs all colors

Question 18

Refraction and Lenses

Answer 18

• Refraction) bending of light rays
  
  • Lenses can refract light because they are curved on both sides
• Convex lenses bend light passing through them and focus them on focal point
  
  • Image is upside-down and reversed (left is on right) after focusing
  • brain takes information and corrects image

Question 19

Focusing Light on the Retina

Answer 19

• Light pathway in eye
  
  • cornea > aqueous humor > lens> vitreous humor> entire neural layer of retina> and finally photoreceptors
• Light is refracted three times along the path of the eye
  
  1. When entering the cornea
  2. When entering the lens
  3. When leaving the lens

Question 20

Focusing for Distant Vision

Answer 20

• Eyes are best adapted for distant vision
• Far point of vision) Distance beyond which no change of lens shape is needed for focusing
  
  • Distance is 20 feet for a normal eye
  • at 20 feet the lens is perciscly focused on the retina
• Cilary Muscles Relaxed = Tension in Cilary Zonule = Streatched Lens

Question 21

Focusing for Close Vision

Answer 21

Requires three adjustments

• Accomodation of the lenses
  
  • Changes lense shape to increase refraction
  • Near Point of vision) Closest Point on which the eye can focus
  • Presbyopia) loss of accomidation
• Constriction of Pupils
  
  • Prevent divergent rays from entering the eyes
  • managed by parasympathetic nervous system
• Convergence of the eyeball
  
  • Medial roation of eyeballs toward object being viewd

Question 22

Problems with Refraction

Answer 22

• Myopia (nearsightedness)
  
  • Eyeball is too long, so focal point is in front of retina
  • Corrected with a concave lens
• Hyperopia (farsightedness)
  
  • Eyeball is too short, so focal point is behind retina
  • Corrected with a convex lens
• Astigmatism
  
  • Unequal curvatures in different parts of cornea or lens
  • Corrected with cylindrically ground lenses or laser procedures