Sense Organs (Eyes) Flashcards by Neil Noga

(the organ for vision) develops as a neuroectodermal outgrowth of the embryonic prosencephalon that contacts surface ectoderm and is enveloped by induced mesodermal and neural crest mesenchyme.

Eyes

How well did you know this?

Not at all

Perfectly

The definitive eye and its adnexa are contained within an orbit that is only partly bony

Eyes

How well did you know this?

Not at all

Perfectly

Associated with the bulb of the eye are extraocular muscles that move it; periorbital fascia and fat that surround and cushion it; eyelids and conjunctiva that protect it; and a lacrimal apparatus that keeps its surface moist, provides the first barrier to infection, and helps to nourish the
cornea.

Eyes

How well did you know this?

Not at all

Perfectly

As a consequence of its dual origin, the eye has both central and peripheral neural elements.
The optic nerve is a central nervous system structure with myelin formed by oligodendroglial cells, whereas the nerves of the extraocular muscles and iris are peripheral nervous system structures with lemmocyte (Schwann cell) sheaths for myelin.
The vascular and fibrous tunics surrounding the optic nerve are homologous to the meninges surrounding the brain and spinal cord.
The intervaginal space of the optic nerve is continuous with the subarachnoid space of the brain and contains cerebrospinal fluid.

Eyes

How well did you know this?

Not at all

Perfectly

Structures of the Eye

Orbit
The eyeball or Globe
– Fibrous tunic (outer)
– Vascular tunic (middle)
– Nervous tunic (inner)
Adnexa
– Eyelids and Conjunctiva
– Nictitating membrane
– Lacrimal Apparatus
– Extraocular muscles
– Vessels and nerves within the orbit

How well did you know this?

Not at all

Perfectly

Structures of the Eye– The eyeball or Globe

– Fibrous tunic (outer)
– Vascular tunic (middle)
– Nervous tunic (inner

How well did you know this?

Not at all

Perfectly

Structures of the Eyes– Adnexa

– Eyelids and Conjunctiva
– Nictitating membrane
– Lacrimal Apparatus
– Extraocular muscles
– Vessels and nerves within the orbit

How well did you know this?

Not at all

Perfectly

*deep bony cavity in the rostral surface of the skull
*it houses the globe and adnexa

The Orbit

How well did you know this?

Not at all

Perfectly

Composed of very dense collagenous and elastic tissue and fibrocytes

Fibrous Tunic

How well did you know this?

Not at all

Perfectly

Functions:
– gives the eyes its shape and stiffness by resisting pressure of internal fluid
– protects internal vascular and light sensitive portions of the eye from environment
– refracts (bends) the light and conducts light to retina
– provide site for attachment of extraocular muscles

FIbrous Tunic

How well did you know this?

Not at all

Perfectly

TWO PARTS OF FIBROUS TUNIC

Sclera and Cornea

How well did you know this?

Not at all

Perfectly

Opaque/white portion of the eye, approximately 75 % of the globes surface
– consists of a dense network of collagen and elastic fibers and their fibrocytes

Sclera

How well did you know this?

Not at all

Perfectly

– Transparent/clear portion of the eye, approximately 25% of anterior segment of fibrous tunic
– avascular, nutrients arrive thru the capillary loops at the limbus
– innervation: long ciliary nerves enters the cornea at the limbus

Cornea

How well did you know this?

Not at all

Perfectly

border where sclera and cornea meets

Limbus Corneae

How well did you know this?

Not at all

Perfectly

Referred to as “uvea” (latin: grape)
Lies internal to fibrous tunic
Extremely vascular and heavily pigmented

Vascular Tunic

How well did you know this?

Not at all

Perfectly

The three regions of Vasular Tunic

Choroid
Ciliary body
iris

How well did you know this?

Not at all

Perfectly

Posterior part, consists of dense meshwork of blood vessels

Choroid

How well did you know this?

Not at all

Perfectly

Functions:
– provide nutrient and oxygen to retina
– limits light scatter
– improves vision in low-light situations

Choroid

How well did you know this?

Not at all

Perfectly

– structure adapted to increase light intensity under low-lighting situations
– avascular region of choroid
– contains rod shaped crystals that refract incoming light
– Present in all domestic mammals except the pigs
– exquisitely sensitive to the toxic effects of a beta adrenergic blocking agent but no toxic effects to Beagles since it inherit an aplasia of the tapetum

Tapetum Lucidum

How well did you know this?

Not at all

Perfectly

forms from thickening of choroid that is raised inward into posterior chamber of the eye
suspends the lens within the eyes
acts to change the thickness of the lens
(accommodation)
muscles are smooth muscle bundles that originate on the sclera and attach to the base of the ciliary body

Ciliary Body

How well did you know this?

Not at all

Perfectly

Most anterior, smallest segment of vascular tunic
Thin, flat circular structure attached to ciliary body

Iris

How well did you know this?

Not at all

Perfectly

responsible for eye coloration

Melanin Granules

How well did you know this?

Not at all

Perfectly

is the only pigment present in the iris

Melanin

How well did you know this?

Not at all

Perfectly

central opening in the iris; round in dogs; has set of smooth muscles

Pupil

How well did you know this?

Not at all

Perfectly

radially arranged; draws pupil open and admits more light; sympathetic

pupillary dilator

circumferentially arranged; draws the pupil closed; parasympathetic

pupillary constrictor (sphincter)

the innermost layer of the eye that contains the retina

Nervous Tunic

inner most layer; having 3 parts and a divisionary zone

Retina

Retina --visual

Optic

Retina-- Non-visual

Ciliary and Iridial

3 Parts of the Retina

-optic part (pars optica retinae) -ciliary part (pars ciliaris retinae) -iridial part (pars iridica retinae)

boundary between visual (optical) and non-visual (ciliary and iridial) parts of retina

Ora Serrata

– has the photoreceptor layer, in which are found the specialized neural receptor cells of the visual system, the rods and cones – largest part, relatively thick with 10 layers of cells; has pigment that gives the pupil black color – presence of light sensitive cells that are layer 9 out of 10 – optic disc, a “blind” spot because no photoreceptors are present, leaves the globe to become optic nerve – central area is the area of particularly acute vision

Optic Part (pars optica retinae)

– produces aqueous humor via active secretion

Ciliary part (pars ciliaris retinae)

– bilayered epithelial layer – covering posterior surface of iris

Iridial part (pars iridica retinae)

* solid yet soft, transparent, deformable structure situated in hyaloid fossa: a depression in the anterior surface of vitreous body * composed of elongate epithelial cells (lens fibers); fixed in position by a delicate suspensory apparatus, the zonula ciliaris * enveloped by elastic capsule; avascular in adult dogs

Lens

* Functions: – Brings images into focus in the retina

Lens

– process by which ciliary processes zonules and ciliary muscles alter the shape of the lens to change the distance at which objects are focused

Lens accommodation

Chambers of the Eye (interior)

-Anterior -Posterior -Vitreous Chamber

– the space bounded by the cornea anteriorly and the iris and anterior lens surface posteriorly

Anterior Chamber

– bounded anteriorly by the iris, posteriorly by the lens capsule and anterior face of the vitreous, and peripherally by the zonule and ciliary epithelium

Posterior Chamber

these two chambers has direct communication thru the pupil and filled with aqueous humor: produced by ciliary part of the retina

Anterior Chamber and Posterior Chamber

– approximately 80% of the volume of the globe (a chamber of the Eye)

Vitreous Chamber

– a clear gel that fills the vitreous chamber – almost 98% water, other components are solid (eg. Protein) and fine fibers – normally acellular – tightly adheres to lens capsule, ciliary part of retina, and optic disc

Vitreous Body

mucous membrane that covers certain regions of the eye

Conjunctiva

lines inner surface of upper, lower and third eyelid

Palpebral conjunctiva

Covers the Sclera

Bulbar conjunctiva

point of reflection of palpebral ang bulbar conjunctiva

Conjunctival fornix

* mobile skin folds, upper and lower * closes over the corneal surface to protect the cornea, exclude light and spread essential tear film * upper eyelid more mobile and larger; in dog only the superior eyelid has eyelashes (cilia) *medial and lateral commisures *medial and lateral angles (canthi) *lacrimal caruncle

Eyelids (Palpebrae)

Glands of the eyelids:

Sebaceous glands Tarsal Glands

Found in the follicles of the cilia

Sebaceous glands

Present in the free edges of of both eyelids

Tarsal glands

Ligaments of the eyelids:

Lateral palpebral ligament Medial palpebral ligament

poorly developed, anchors the lateral commisure to zygomatic arch

Lateral palpebral ligament

anchors medial commisure to frontal bone, serves as origin and insertion of orbicularis oculi muscle

Medial palpebral ligament

* fold of tissue on ventromedial region of medial canthus * large and very mobile, capable of covering the entire cornea * when eye is open, it is withdrawn completely into the medial canthus

Third eyelid ( Semilunar Fold) / Nictitating Membrane

– mixed seromucous gland that surrounds the base of the cartilage plate – tear film

Superficial gland of the 3rd eyelid

responsible for production, dispersion and disposal of tears

Lacrimal Apparatus

Tear Producing Structures:

– lacrimal gland – tarsal gland – conjunctival goblet cells – superficial gland of the 3rd eyelid

Tear Disposing Structures:

– lacrimal puncta – lacrimal canaliculi – lacrimal sac – nasolacrimal duct

Composition of Tear Film

-superficial oily layer -middle aqueous layer -deep mucous layer

Produced by tarsal glans

Superficial oily layer

produced by lacrimal gland and gland of the 3rd eyelid

Middle aqueous layer

produced by the goblet cells of the conjunctiva

Deep mucous layer

Functions: – plays an absolute essential role in maintaining health of the eyes and normal transparency of the cornea – keep cells of cornea moist – washes foreign body away from the eyes – facilitates diffusion of respiratory gases and nutrients to and from the avascular cornea – contains antimicrobial substance and dissolves antibodies that help protect against infection.

Tear Film

Musculature of the Eye

* intraocular muscles (intrinsic) * extraocular muscles (extrinsic) * muscles of the eyelids (palpebral muscles)

all smooth muscles lies entirely with-in the globe – ciliary muscles – pupillary dilator – pupillary constrictor

Intraocular Muscles

all skeletal muscles, 7 extra orbital muscles: 4 rectus muscles, 2 oblique muscles, 1 retractor muscle

Extraocular muscles

rotate the globe upward

Dorsal rectus

rotate the globe downward

Ventral rectus

rotate the globe medially

Medial rectus

rotate the globe laterally

Lateral rectus

*all are innervated by oculomotor nerve except lateral rectus which is innervated by abducent nerve

- dorsal rectus – ventral rectus – medial rectus – lateral rectus

rotate the dorsal surface of the globe medially, innervated by TROCHLEAR NERVE

dorsal oblique

rotate the dorsal surface of the globe laterally, innervated by OCULOMOTOR NERVE

Ventral oblique

withdraws the globe deeper into the orbit, innervated by ABDUCENT NERVE

Retractor bulbi / oculi

– move the eyelid to open or close the eye – adjust eyelid position in response to positional changes of the globe

Palpebral muscles

Muscles of the Eyelids

-Palpebral Muscles 1) Orbicularis oculi – facial nerve 2) Levator palpebrae superioris – oculomotor nerve 3) Retractor anguli oculi superioris – facial nerve 4) Palpebral part of the deep sphincter of the neck 5) Superior and Inferior tarsal muscles

– orbital part surrounds the bony orbit – palpebral part within the upper and lower eyelid

Orbicularis oculi – facial nerve

– primary muscle that act to raise the upper eyelid – ptosis ( drooping upper eyelid)

Levator palpebrae superioris – oculomotor nerve

– draws the lateral canthus caudally – assists in closure of the eye

Retractor anguli oculi superioris – facial nerve

– depresses the lower lid assists in opening the eye – Innervated by buchal branches of facial nerve

Palpebral part of the deep sphincter of the neck

– assists in holding the eyelids open – innervated by sympathetic fibers

Superior and inferior tarsal muscles

Sense Organs (Eyes) Flashcards

(83 cards)