Sensory Organs
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113 Terms
Q: What are the special senses and their organs?
A: Vision (eye), hearing & balance (ear), smell (nose), taste (tongue)
Q: What makes up the eye?
A: Globe (eyeball) + appendages (eyelids, conjunctiva, lacrimal glands)
Q: What are the 3 tunics of the eye?
A: Fibrous, vascular (uvea), retina
What structures form the fibrous tunic?
Cornea + sclera
Q: What structures form the vascular tunic (uvea)?
A: Iris, ciliary body, choroid
Q: What are the layers of the retina?
A: Neural layer + pigmented layer
Q: Key features of the cornea?
A: Avascular, highly innervated, transparent (light refraction)
Q: Type of epithelium in cornea?
A: Nonkeratinized stratified squamous epithelium
Q: What is the corneal stroma?
A: ~90% thickness; collagen layers + keratocytes
Q: What is Descemet’s membrane?
A: Thick basement membrane of corneal endothelium
Q: Function of corneal endothelium?
Q: Function of corneal endothelium?
Q: Structure of corneal endothelium?
A: Single layer of squamous to low cuboidal cells
Q: Function of sclera?
A: Protection + attachment for extrinsic eye muscles
Q: Composition of sclera?
A: Dense CT (type I collagen, fibroblasts, elastic fibers) + melanocytes
Q: What is the limbus?
A: Junction between cornea and sclera
Q: Location of choroid?
A: Between sclera and retina
Q: Function of choroid?
Nourishes retina
Q: Structure of choroid?
A: Loose, vascular CT + melanocytes (light absorption)
Q: What is the tapetum lucidum?
A: Reflective structure in choroid that enhances night vision
Q: Function of tapetum lucidum?
Q: Function of tapetum lucidum?
Q: Where is the tapetum located?
A: Dorsal fundus (lower visual field)
Q: Which animals have a tapetum lucidum?
A: Most domestic mammals (not pigs), carnivores, horses, ruminants
Q: Tapetum in carnivores vs herbivores?
A:
Carnivores: cellular
Horses/ruminants: fibrous (collagen layers)
Q: Special case: marine mammals?
A: Entire fundus tapetalized (dim 3D environment)
Q: Where is the ciliary body located?
A: Between choroid and iris; posterior to limbus, resting on sclera
Q: What are the main components of the ciliary body?
A: Ciliary muscle + ciliary processes + stroma
Q: Function of ciliary muscle?
A: Changes lens shape (accommodation)
Q: What are ciliary processes?
A: Radial ridges from inner ciliary body
Q: Epithelium of ciliary processes?
A: Pigmented basal layer + nonpigmented surface layer
Q: Function of ciliary processes?
A: Produce aqueous humor (low protein, plasma-like ions)
Q: What is the ciliary zonule?
A: Fibers connecting ciliary body to lens (suspends lens)
Q: Location of iris?
A: Most anterior part of uvea; continuous with ciliary body
Q: What is the iris?
A: Contractile diaphragm controlling pupil size
Q: What shapes can the pupil have?
A: Round (dog), oval (horse/cow), vertical slit (cat)
Q: What is in the iris stroma?
A: Loose CT + melanocytes + sphincter muscle
Q: Function of sphincter muscle?
A: Constricts pupil
Q: What covers the posterior surface of the iris?
A: Two epithelial layers
Q: Layers of posterior iris epithelium
A:
Pigmented layer
Myoepithelial layer → forms dilator muscle
Q: Function of iris dilator muscle?
Dilates pupil
Is the anterior iris surface epithelialized?
No
Q: What are corpora nigra?
A: Pigmented projections on iris (horses, ruminants, pigs)
Q: What is the retina?
A: Innermost layer of the eye
Q: Extent of photosensitive retina?
A: Ora ciliaris retinae → optic disc
Q: What are the two parts of the retina?
A: Retinal pigment epithelium + neural retina
Q: What is the RPE?
A: Single layer of cuboidal cells between neural retina and choroid
Q: Pigmentation difference in tapetal vs nontapetal regions?
A:
Tapetal: little/no pigment
Nontapetal: high melanin (absorbs light)
Q: Main function of RPE?
A: Support + nourish photoreceptors
Q: Role of RPE in photoreceptor maintenance?
A: Phagocytoses old rod/cone outer segments
Q: RPE role in vision cycle?
A: Involved in vitamin A–rhodopsin cycle
Q: RPE and barriers?
A: Forms part of blood-retina barrier
Q: What is the neural retina?
A: Multilayered photosensitive membrane between vitreous humor and RPE
Q: What cells are in the neural retina?
A: Neurons + Müller (glial) cells
Q: How many layers does the neural retina have?
9 layers.
Q: Rod and cone layer?
A: Outer segments of photoreceptors
Q: Outer limiting membrane?
Junctions between photoreceptors and Muller cells
Q: Outer nuclear layer?
A: Cell bodies of rods and cones
Q: Outer plexiform layer?
A: Synapses between photoreceptors and bipolar cells
Q: Inner nuclear layer?
A: Cell bodies of bipolar neurons
Q: Inner plexiform layer?
A: Synapses between bipolar and ganglion cells
Q: Ganglion cell layer?
A: Cell bodies of ganglion cells
Q: Nerve fiber layer?
A: Axons of ganglion cells → optic nerve
Q: Inner limiting membrane?
A: Basement membrane (inner retinal boundary)
Q: Function of rods?
A: Detect light intensity (dim light)
Q: Function of cones?
A: Detect color (wavelengths)
Q: Which are more numerous?
Rods
Q: What is the optic disc?
A: Point where nerve fibers exit → optic nerve
Q: Why is optic disc the “blind spot”?
A: No photoreceptors present
Q: What is the lamina cribrosa?
A: Sieve-like scleral region where nerve fibers pass
Q: Why is the retina highly metabolic?
A: High energy demand for phototransduction
Q: What is the retina’s blood supply?
Dual supply
Q: Supply to outer retina (photoreceptors)?
Choroidal vessels
Supply to inner retina?
Retinal vessels (visible on ophthalmoscopy)
What is the lens?
A: Transparent, avascular, biconvex structure that refracts light
Q: Where is the lens located?
A: Between iris (anterior) and vitreous (posterior)
Q: What holds the lens in place?
Zonular fibers (ciliary zonule)
What is the lens capsule?
Basement membrane secreted by lens epithelial cells
What are lens fibers?
Modified cells lacking nucleus and organelles, filled with crystallins
Q: Why is the lens transparent?
Orderly structure + no organelles +no vessels + dehydration
Q: How does structure contribute to transparency?
A: Hexagonal fibers align → minimal light scattering
Q: Role of crystallins?
Create uniform refractive index
Q: Why does lack of organelles help?
Reduces light scattering
Q: How is the lens nourished?
A: Aqueous humor (no blood vessels)
Q: Why is dehydration important?
A: Maintains clarity (~65% water)
Q: What maintains lens dehydration?
A: Na⁺/K⁺ pump in anterior epithelium
Q: How do lens cells produce energy?
A: Anaerobic glycolysis
Q: Why anaerobic metabolism?
A: No mitochondria or organelles
Q: What is the conjunctiva?
A: Transparent mucous membrane covering eye and eyelids
Q: What is the palpebral conjunctiva?
A: Lines inner eyelids
Q: What is the bulbar conjunctiva?
A: Covers anterior sclera
Q: What is the conjunctival fornix?
A: Junction between palpebral and bulbar conjunctiva
Q: What is the conjunctiva of the third eyelid?
A: Continuous with other conjunctiva regions
Q: Epithelium of conjunctiva?
A: Nonkeratinized stratified squamous → columnar + goblet cells
Q: Function of goblet cells?
A: Secrete mucus (tear film stability)
Q: What is in the lamina propria of conjunctiva?
A: Connective tissue + lymphoid tissue
Q: What is the main function of eyelids?
Protects the eye
What layers make up the eyelid?
Skin + muscle + tarsal plate + palpebral conjunctiva
Q: What type of skin is in the eyelid?
A: Thin epidermis + dermis
Q: What type of muscle is in the eyelid?
A: Skeletal muscle (opening/closing)
Q: What is the tarsal plate?
A: Dense fibrous CT providing structural support
Q: What lines the inner eyelid?
A: Palpebral conjunctiva
