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Front Cover: Human Anatomy and Physiology, Eleventh Edition by Marieb and Hoehn.

PowerPoint® Lectures Slides prepared  by Karen Dunbar Kareiva, Ivy Tech Community College 

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Understanding the anatomy and  physiology of the eye helps  to identify diseases such as glaucoma 

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The sense of touch is one of the general senses,  mediated by general receptors (covered in Chapter 13) Special senses of body include: Vision Taste Smell Hearing Equilibrium 

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70% of body's sensory receptors are in eye Half of cerebral cortex is involved in visual processing 

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Small sphere; only one-sixth of surface visible Most of eye enclosed and protected by fat cushion and  bony orbit Consists of accessory structures and the eyeball 

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Part (a) is a photo of an eye with leader lines identifying following structures:  eyebrow, upper eyelid, eyelashes, site where conjunctiva merges with cornea, palpebral fissure, lateral commissure, iris, lower eyelid, pupil, sclera (covered by conjunctiva), lacrimal caruncle and medial commissure.

THE EYE AND ACCESSORY STRUCTURES (1 OF 2) 

Figure 15.1a The eye and accessory structures. 

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ACCESSORY STRUCTURES OF THE EYE (1 OF 8) 

Accessory structures protect  the eye and aid eye function Structures include: Eyebrows Eyelids Conjunctiva Lacrimal apparatus Extrinsic eye muscles 

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ACCESSORY STRUCTURES OF THE EYE (2 OF 8) 

Eyebrows Overlie supraorbital margins Function Shade eye from sunlight Prevent perspiration from reaching eye 

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ACCESSORY STRUCTURES OF THE EYE (3 OF 8) 

Eyelids Also called palpebrae; thin,  skin-covered folds that protect eye anteriorly Separated at palpebral fissure (slit) Meet in corners at medial and lateral commissures Lacrimal caruncle located  at medial commissure contains oil and sweat glands Tarsal plates: supporting connective tissue for folds,  as well as anchor orbicularis oculi and  levator palpebrae superioris muscles 

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ACCESSORY STRUCTURES OF THE EYE (4 OF 8) 

Eyelids (cont.) Eyelids blink reflexively every 3–7 seconds Offers protection from foreign objects and  spreads secretions to moisten eye Eyelashes have follicles that are innervated Nerve endings initiate reflex blinking Lubricating glands associated with eyelids Tarsal (Meibomian) glands Modified sebaceous glands produce  oily secretion that lubricates lid and eye Ciliary glands between hair follicles are Modified sweat glands 

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Part (b) is an illustration of a lateral view of eye with some structures shown in sagittal sections.  Labels include levator palpebrae superioris muscle, orbicularis oculi muscle, eyebrow, tarsal plate, palpebral conjunctiva, tarsal glands, cornea, palpebral fissure, eyelashes, bulbar conjunctiva, conjunctival sac, and orbicularis oculi muscle.

THE EYE AND ACCESSORY STRUCTURES (2 OF 2) 

Figure 15.1b The eye and accessory structures. 

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ACCESSORY STRUCTURES OF THE EYE (5 OF 8) 

Conjunctiva Transparent mucous membrane that produces  a lubricating mucous secretion Palpebral conjunctiva: membrane that lines  underside of eyelids Bulbar conjunctiva: membrane that covers  white of eyes (not cornea) Small blood vessels found in this membrane;  seen  easily in "bloodshot" eyes Conjunctival sac: space between palpebral and  bulbar conjunctiva Area where contact lens rests 

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ACCESSORY STRUCTURES OF THE EYE (6 OF 8) 

Lacrimal apparatus Consists of lacrimal gland and  ducts that drain into nasal cavity Lacrimal gland is located  in orbit above lateral end of eye and  secretes lacrimal secretion (tears),  a dilute saline solution containing  mucus, antibodies, and antibacterial lysozyme Blinking spreads tears toward medial commissure,  where they enter paired  lacrimal canaliculi via lacrimal puncta 

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ACCESSORY STRUCTURES OF THE EYE (7 OF 8) 

Lacrimal apparatus (cont.) Tears then drain into lacrimal sac and  nasolacrimal duct, which empties into nasal cavity 

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Figure is an illustration of the eye and nose showing position of lacrimal apparatus, including lacrimal punctum, lacrimal canaliculus, inferior meatus of nasal cavity and nostril.  Figure also shows arrows to indicate flow of lacrimal fluid (tears) from lacrimal gland to nasal cavity.
- Step (1):  The lacrimal gland produces and secretes tears (lacrimal secretions).
- Step (2):  Tears enter the conjunctival sac via the excretory ducts of the lacrimal gland.
- Step (3):  Tears flow down and across the eyeball.
- Step (4):  Tears enter the lacrimal canaliculi at openings called lacrimal puncta.
- Step (5):  Tears drain into the lacrimal sac.
- Step (6):  From the lacrimal sac, tears empty via the nasolacrimal duct into the inferior meatus  of the nasal cavity.

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ACCESSORY STRUCTURES OF THE EYE (8 OF 8) 

Extrinsic eye muscles Six straplike extrinsic eye muscles Originate from bony orbit and insert on eyeball Enable eye to follow moving  objects, maintain shape of eyeball, and hold it in orbit Four rectus muscles originate  from common tendinous ring; names indicate movements Superior, inferior, lateral, and medial rectus Two oblique muscles move eye in vertical plane and  rotate eyeball Superior and inferior oblique muscles 

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This four-part figure illustrates the extrinsic eye muscles in the lateral, superior, and frontal view, plus a table that summarizes each muscle’s action and controlling cranial nerve.

- Part (a) is an illustration of a lateral view of the right eye showing the following ocular structures:  superior oblique tendon, superior oblique muscle, superior rectus muscle and lateral rectus muscle.

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- Part (b) is an illustration of the superior view of the right eye, showing the following ocular structures:  trochlea, superior oblique tendon, superior oblique muscle, superior rectus muscle, axis of rotation of eye, inferior rectus muscle, medial rectus muscle, lateral rectus muscle and common tendinous ring.

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- Part (c) is an illustration of an anterior view of the right eye, showing the following ocular structures:  trochlea, superior oblique, medial rectus, inferior rectus, inferior oblique, lateral rectus and superior rectus.  Arrows also indicate direction of eye movement controlled by each muscle.

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- Part (d) is a chart listing the muscle along with its action, as well as cranial nerve that innervate it.  Chart lists:
 - Lateral rectus muscle – moves eye laterally – controlled by cranial nerve VI (abducens)
 - Medial rectus muscle – moves eye medially – controlled by cranial nerve III (oculomotor)
 -  Superior rectus muscle – elevates eye and turns it medially – controlled by cranial nerve    III (oculomotor)
 - Inferior rectus muscle – depresses eye and turns it medially – controlled by cranial nerve    III (oculomotor)
 - Inferior oblique muscle – elevates eye and turns it laterally – controlled by cranial nerve III   (oculomotor)
 - Superior oblique muscle – depresses eye and turns it laterally – controlled by cranial nerve    IV (trochlear)

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Chalazion:  obstructed tarsal glands that may result  in a firm, usually painless bump Sty: painful inflammation of any of the sebaceous glands at the base of an eyelash 

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Conjunctivitis: inflammation of the conjunctiva resulting  in reddened, irritated eyes Pinkeye: conjunctival infection caused  by bacteria or viruses Highly contagious 

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Nasal cavity mucosa is continuous with mucosa of lacrimal duct system,  so a cold or nasal inflammation often causes  lacrimal mucosa to swell Swelling constricts the ducts and  prevents tears from draining, causing "watery" eyes 

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CLINICAL – HOMEOSTATIC IMBALANCE 15.4 (1 OF 2) 

Diplopia (double vision):  occurs when movements of external muscles of two eyes are  not perfectly coordinated Person cannot properly focus  images of same area of the visual field from each eye,  so sees two images instead of one Can result from paralysis, extrinsic muscle weakness,  or neurological disorders 

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CLINICAL – HOMEOSTATIC IMBALANCE 15.4 (2 OF 2) 

Strabismus ("cross-eye" ): congenital weakness of external eye muscles Eye rotates medially or laterally Eyes may alternate focusing  on objects, or only controllable eye is used Brain begins to disregard inputs from deviant eye,  which can become functionally blind if not treated  early 

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Wall of eyeball contains three layers Fibrous layer Vascular layer Inner layer Internal cavity filled with fluids called humors Lens separates internal cavity into anterior and  posterior segments 

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Part (a) is a diagrammatic view of a sagittal section of eyeball showing the following structures:  ora serrata, ciliary body, ciliary zonule (suspensory ligament), cornea, iris, pupil, anterior segment (contains aqueous humor), lens, sclera venous sinus, posterior segment (contains vitreous humor), sclera, choroid, retina, macula lutea, fovea centralis, optic nerve, central artery and vein of retina and the optic disc.

INTERNAL STRUCTURE OF THE EYE (SAGITTAL SECTION) 

Figure 15.4a Internal structure of the eye (sagittal section). 

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Fibrous layer Outermost layer; dense avascular connective tissue Two regions: sclera and cornea Sclera Opaque posterior region Protects and shapes eyeball Anchors extrinsic eye muscles Posteriorly, where optic nerve exits,  sclera is continuous with dura mater of brain 

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Cornea  Transparent anterior one-sixth of fibrous layer Forms clear window that lets  light enter and bends light as it enters eye Epithelium covers both surfaces Outer surface protects from abrasions Inner layer, corneal endothelium,  contains sodium pumps that help  maintain clarity of cornea Numerous pain receptors contribute  to blinking and tearing reflexes 

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Vascular layer Middle pigmented layer of eye, also called uvea Three regions: choroid, ciliary body, and iris Choroid region Posterior portion of uvea Supplies blood to all layers of eyeball Brown pigment absorbs light to prevent  scattering of light, which would cause  visual confusion 

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Ciliary body Anteriorly, choroid becomes ciliary body Thickened ring of tissue surrounding lens Consists of smooth muscle bundles,  ciliary muscles, that control shape of lens Capillaries of ciliary processes secrete  fluid for anterior segment of eyeball Ciliary zonule (suspensory ligament) extends  from ciliary processes to lens Holds lens in position 

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Iris Colored part of eye that lies between cornea and lens,  continuous with ciliary body Pupil: central opening that regulates  amount of light entering eye  Close vision and bright light cause sphincter pupillae (circular muscles) to contract  and pupils to constrict; parasympathetic control  Distant vision and dim light cause dilator pupillae (radial muscles) to contract  and pupils to dilate; sympathetic control Changes in emotional state— pupils dilate when subject matter is  appealing or requires problem-solving skills 

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INTERNAL STRUCTURE OF THE EYE (SAGITTAL SECTION) (1 OF 2) 

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Part (b) is a photograph of a sagittal section of a human eye.

INTERNAL STRUCTURE OF THE EYE (SAGITTAL SECTION) (2 OF 2) 

Figure 15.4b Internal structure of the eye (sagittal section). 

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Figure is illustration of the muscles of the pupil shown in three sections:
 - Middle section shows the two muscles:  sphincter pupillae and dilator pupillae
 - Left section shows how parasympathetic nerves can cause sphincter pupillaeto contract    which constricts pupil (size decreases). 
 - Right section shows how sympathetic nerves can cause dilator papillae muscles to contract    which causes pupil to dilate (size increases).

Figure 15.5 Pupil constriction and dilation. 

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Inner layer (retina) Retina originates as an outpocketing of brain Contains: Millions of photoreceptor cells that transduce  light energy Neurons Glial cells Delicate two-layered membrane Outer pigmented layer Inner neural layer 

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Part (a) is an illustration of the posterior aspect of the eyeball, showing the location of the retina, neural layer, pigmented layer, choroid, sclera, optic nerve, optic disc and central artery and vein of the retina.  The axons of the ganglion cells form the optic nerve which leaves the back of the eyeball at the optic disc.

Figure 15.6a Microscopic anatomy of the retina. 

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Inner layer (retina) (cont.) Pigmented layer of the retina Single-cell-thick lining next to choroid Extends anteriorly, covering ciliary body and iris Functions: Absorbs light and prevents its scattering Phagocytizes photoreceptor cell fragments Stores vitamin A 

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Inner layer (retina) (cont.) Neural layer of the retina Transparent layer that runs  anteriorly to margin of ciliary body Anterior end has serrated edges called ora serrata Composed of three main types of neurons Photoreceptors, bipolar cells, ganglion cells Signals spread from photoreceptors to bipolar cells to ganglion cells Ganglion cell axons exit eye as optic nerve 

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Inner layer (retina) (cont.) Neural layer of the retina (cont.) Optic disc Site where optic nerve leaves eye Lacks photoreceptors, so referred to as blind spot Retina has quarter-billion photoreceptors that are  one of two types: Rods Cones 

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MICROSCOPIC ANATOMY OF THE RETINA (1 OF 3) 

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Inner layer (retina) (cont.) Rods Dim light, peripheral vision receptors More numerous and more sensitive to light than cones No color vision or sharp images Numbers greatest at periphery 

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Inner layer (retina) (cont.) Cones Vision receptors for bright light High-resolution color vision Macula lutea area at posterior pole lateral to blind spot Contains mostly cones  Fovea centralis: tiny pit in center of macula lutea that contains  all cones, so is region with best visual acuity Eye movement allows us to focus  in on object so that fovea can pick it up 

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Part (b) is a close-up of a section of Part (a) diagram showing cells of the neural layer of the retina in more detail.  Arrows are drawn to indicate the pathway of light, and in the opposite direction, the pathway of signal output.  Light (arrow points from anterior to posterior of eyeball)passes through the retina to excite the photoreceptor cells (rods and cones).  Information flows in opposite direction of light pathway (output signal shown as arrow passing from posterior to anterior of eyeball) via bipolar and ganglion cells.  Labels include amacrine cells, horizontal cell, pigmented layer of retina, photoreceptors (rods and cones), bipolar cells, ganglion cells and axons of ganglion cells.

MICROSCOPIC ANATOMY OF THE RETINA (2 OF 3) 

Figure 15.6b Microscopic anatomy of the retina. 

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Part (c) is a photomicrograph of retina showing pigmented layer of retina, nuclei or rods and cones, nuclei of bipolar cells, axons of ganglion cells, nuclei of ganglion cells, outer segments of rods and cones and choroid.

MICROSCOPIC ANATOMY OF THE RETINA (3 OF 3) 

Figure 15.6c Microscopic anatomy of the retina. 

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Inner layer (retina) (cont.) Two sources of blood supply to retina Choroid supplies outer third (photoreceptors) Central artery and vein of retina supply  inner two-thirds Enter/exit eye in center of optic nerve Vessels are visible in living person 

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Figure is a photo of part of the posterior wall (fundus) of the right eye as seen with an opthalmascope.  It shows the fundus as a circular image. The retina, colored red, fills the circle. Near the center of the circle is a pale oval area which is the optic disc. Branching away from it are red lines which indicate the central artery and vein emerging from the optic disc. To the left of the optic disc, approximately halfway between it and the edge of the circular image, is a slightly darker oval region which is the macula lutea.

PART OF THE POSTERIOR WALL (FUNDUS) OF THE RIGHT EYE AS SEEN  WITH AN OPHTHALMOSCOPE 

Figure 15.7 Part of the posterior wall (fundus) of the right eye as seen  with an ophthalmoscope. 

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CLINICAL – HOMEOSTATIC IMBALANCE 15.5 (1 OF 2) 

Retinal detachment: condition where pigmented and  neural layers separate  (detach), allowing jellylike vitreous humor to seep  between them Can lead to permanent blindness Usually happens when retina is  torn during traumatic blow to head  or sudden stopping of head during movement (example:  bungee jumping) 

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CLINICAL – HOMEOSTATIC IMBALANCE 15.5 (2 OF 2) 

Symptom described by victims as " curtain being drawn across the eye"  and/or sootlike spots or light flashes Treatment: reattachment of retina with laser surgery 

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Internal chambers and fluids The lens and ciliary zonule separate eye into two segments Posterior segment Anterior segment 

Human Anatomy and Physiology

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