Special Senses (VISUAL) Flashcards
- Each eyeball is positioned in a bony depression in the skull called orbit
- Only the anterior one-sixth of the eye’s surface can normally be seen
- Made up of the eyeball specialized for its ability to react to light
Visual Sense/Apparatus
- the stimuli for sense of vision, the light rays must pass through the different parts of the refractive media before reaching the retina.
- These are the following:
o cornea
o aqueous humor
o lens
o vitreous humor
Eyeball
protects, lubricate, move the eye
Accessory structures of the eye
Accessory structures of the eye :
- Extrinsic Eye Muscles
- Eyelids
- Conjunctiva
- Lacrimal apparatus
- controlled by orbicularis oculi
Eyelids
o Modified sebaceous glands associated with the eyelid edges
o Produce an oily secretion that lubricates the eyes
Meibomian Glands
- transparent covering of the eyeball
Conjunctiva
o Modified sweat glands between the eyelashes
Ciliary Glands
- Anteriorly the eyes are protected by the __________ which meet at the medial and lateral corners of the eye, the medial and lateral canthus respectively
Eyelids
____________ occur 20 times per minute.
____________ Projecting from the border of each eyelid.
- Blinking
- Eyelashes
o Lines the eyelids and covers part of the white eye (sclera) infront
o Secretes the mucus which helps to lubricate the eyeball and keep it moist
Conjunctiva
o Located above the lateral ends of each eye
o Continually release a dilute salt solution (tears= “ lacrimal fluid) that drain into the nasal cavity through the inferior meatus
o Lacrimal fluid not only moistens and lubricates conjunctival sac but also reduces eye infections because it contains bactericidal enzyme (lysozyme
Lacrimal Glands
CONTROL MOVEMENT OF EYEBALL
- lateral rectus moves eye
- medial rectus moves eye
- superior rectus moves eye
- inferior rectus moves eye
- inferior oblique moves eye
- superior oblique move eye
what are the action of those?
- laterally
- medially
- upwards medially
- downward and medially
- upwards and laterally
- downwards and laterally
➢ the outermost coat
➢ also called the fibrous tunic seen anteriorly as the “white of the eye”
➢ covered in the anterior part by the transparent conjunctiva
➢ densely packed collagenous fibers (type I collagen fibrils) – where tendons of extraocular muscles are attached
➢ pierced by optic nerve, ciliary nerves and blood vessels
Sclera
o Protects the delicate inner structure of the eye and with the intraocular pressure maintain the shape and turgor of the eyeball
o Sclera - posterior 5/6 - opaque, white of the eye
o Cornea - Anterior 1/6 – Transparent
Fibrous Coat
➢ The central transparent anterior portion of the eye covering the colored part of the eye which is the iris
➢ One of the few organs that can be successfully transplanted from one person to another without the worry of rejection because it has no blood vessels thus it is beyond the reach of the immune system
➢ Avascular and the central part depends on diffusion from aqueous humor for its nourishment.
➢ Thicker than sclera with refractive power 2x as high as the lens
Cornea
- Increase in light ?
- decrease in light ?
- Constrict
- Relax
o Concerned with nutrition of retina and production of aqueous humor
o Provides mechanisms for accommodation of the eyes for near vision and control of amount of light entering the eye
o Choroid – most of the blood vessels are located on choroid
o Ciliary body – secretes aqueous humor
o Iris
Vascular and Muscular coat or UVEA
➢ A thickened part of the vascular layer (tunic) of the eye.
➢ Links the choroid to the circumference of the iris.
➢ Contains the ciliary muscle, which aids in accommodation—the ability of the eye to focus on close objects.
➢ When the ciliary muscle contracts, the lens becomes more convex, enhancing focus for nearby objects.
➢ Eye strain occurs with focus less than 20 feet; beyond 20 feet, the eye muscles relax.
➢ Produce aqueous humor, which nourishes the eye and maintains intraocular pressure.
➢ secretes aqueous humor
Ciliary Body
➢ Middle coat of the eye
➢ Blood-rich nutritive tunic that contains a dark pigment that prevents light from the scattering inside the eye
➢ most of the blood vessels are located on this
Choroid
eye disease can cause vision loss if you are diabetic
Glaucoma
➢ Heavy pigmented colored part of the eye which is membranous extension of the choroid
➢ Partially covers the lens, leaving around opening at the center called pupil
➢ With sphincter and dilator pupillae (constrict and dilate pupils)
➢ Like the diaphragm of the camera; it can increase or decrease the diameter of its aperture (the pupil) to admit more or less light
➢ Constriction of the pupils is produced by contraction of the circularly arranged fibers within the iris supplied by parasympathetic, dilation is produced by contraction of the radially arranged fibers supplied by sympathetic
Iris
2 smooth muscles:
- Sphincter pupillae
- Dilator pupillae
➢ Circumferentially oriented fibers
➢ Constriction of pupil (parasympathetic)
➢ Constriction - miosis
Sphincter pupillae
Nerve Coat :
Retina
➢ Radially oriented fibers
➢ Dilation of pupil (sympathetic)
➢ Dilation - mydriasis
Dilator pupillae
➢ Innermost layer where receptors for sense of sight are found
➢ The nervous coat of the eyeball containing the photoreceptor cells
Retina
Photoreceptor :
- Rods
- Cones
➢ stimulated by low intensity light
➢ For night vision (scotopic vision)
➢ Contains reddish pigment
➢ Rhodopsin
➢ Night blindness – vitamin a deficiency
Rods
– very sensitive and produces detachable signal on absorption of a single photon of light
Rhodopsin
➢ stimulated by high intensity light
➢ For day vision/ color vision (photopic vision) sensitive to blue, green, and red lights – 3 kinds provide basis for color vision
Cones
➢ Transparent structures traversed by the light rays on the way to the photoreceptors of the retina
➢ These structures can bend or refract the light rays so the images can be focused on the retina.
o Cornea
o Aqueous humor (water) (in anterior and posterior chamber)
o Lens
o Vitreous humor
Refractive Media of the Eyes
➢ transparent biconvex body situated immediately behind the pupil.
➢ shape changes during accommodation
➢ covered by a homogenous highly refractile capsule which is essentially an exceedingly thick basal lamina
Lens
➢ photosensitive area
➢ with a circular depressed white area, optic disk or optic papilla where optic nerve exits and retinal vessels enter and leave
Pars Optica
➢ colorless, structureless. gelatinous mass with a glasslike transparency filling up the vitreous cavity between lens and retina.
➢ nearly 99% is water
➢ with liquid and solid phase.
Vitreous humor
➢ contains nerve fibers but no photoreceptors and is insensitive to light. Called physiologic blind spot.
➢ 2.5 cm lateral to optic disk is a small oval yellow area Macula Lutea with central depressed area Fovea Centralis. This is the area of most acute vision.
➢ Characterized by presence of cones and neural element greater than elsewhere. This is a rod free area
Optic Disk
lies on the superior bank of the calcarine cortex, receives the medial fibers of the visual radiations.
Cuneus gyri
farsightedness; corrects with convex
Hyperopia
lies on the inferior bank of the calcarine cortex, the medial fibers coursing in the visual radiations, which carry input from the upper
retina (i.e. the lower contralateral visual field), pass from the lateral geniculate body directly through the parietal lobe to reach the cuneus gyrus.
Lingual gyrus
nearsightedness; corrects with concave
Myopia
- Optic nerve has nasal fibers ( from the medial side) and temporal fibers (from the lateral side)
- Nasal fibers receive impulse from the temporal visual field and the temporal fibers receive impulse from the nasal visual field
- Nasal fibers decussate at the level of the optic chiasm while temporal fibers leave the optic chiasm without decussating
- Fibers from the optic chiasm going to the lateral geniculate bodies are called optic tract
- Lateral geniculate bodies are the last relay station of the visual pathway
- Cells from the lateral geniculate bodies project fibers to the primary visual area and are called optic radiation or geniculocalcarine tract
- Termination of the visual pathway is at the calcarine area, the primary visual area
Visual Pathway
Functions of the eye
* Functions like a camera.
* Pupil allows light into the eyes, which focused by the cornea
* The light striking the photoreceptors of the retina produces action potentials within the visual pathway
* The optic nerve conveys these action potentials to the brain where perception occurs
WHAT BROARDMANN’S ARE IS THE EYE?
(Brodmann’s area 17)
