UNIT 5-6

Describe the anatomical location and histological structure of the olfactory epithelium and its role in odor detection.

• Specialized area on roof of nasal cavity, superior nasal concha and adjacent septum.

  • Contains olfactory receptor neurons

  • Surrounded by supporting (sustentacular) and basal regenerative cells

• Composed of pseudostratified, immotile ciliated columnar epithelium

  • On top of lamina propria

  • Olfactory glands (Bowmans) that secrete serous fluid to enable interaction with olfactory receptors

• Detects airborne odorants dissolved by Bowman glands in the mucus layer.

Explain the pathway of olfactory signal transmission from receptor neurons to the primary olfactory cortex.

1. Axons of olfactory neurons form small fascicles → CN I

2. Unmyelinated axons pass through cribriform plate

   • Entering anterior cranial fossa

3. Synapse in olfactory bulb (superior to cribriform plate)

4. Signal is relayed posteriorly via olfactory tract

5. Nerves impulses travel to primary olfactory cortex (temporal lobe)

Recognize the unique aspects of the olfactory pathway, including its bypass of the thalamus.

Only sensory system that bypasses the thalamus, directly connecting to the limbic system, which links smell to emotion and memory.

Identify four types of lingual papillae and their locations on the tongue.

• Elevated structures of mucosa (epithelium + connective tissue)

  • Vallate (circumvallate) – V-shaped row anterior to terminal sulcus

  • Fungiform – Scattered across anterior 2/3

  • Foliate – Posterolateral tongue margins

  • Filiform – Most numerous; across tongue surface

Vallate papillae

• Largest and least numerous (8-12)

• V-shaped row anterior to terminal sulcus of tongue

  • Surrounded by deep trench and houses numerous taste buds on lateral walls

• Innervated by glossopharyngeal N = sensory of posterior 1/3 of tongue

Fungiform papillae

• Mushroom-shaped papillae that are scattered among filiform papillae

  • Apex and lateral margins of anterior 2/3 of tongue

  • Visible to naked eye

• Modest number of taste buds

• Innervated by facial N via chorda tympani branch

Foliate papillae

• Posterolateral margins of tongue

  • Parallel folds/ridges

• Taste buds primarily in early childhood

  • Decrease in age

• Prominent and functional in other mammals

• Innervated by glossopharyngeal N

  • Some anterior fibers may = facial N

Filiform papillae

• Most numerous

• Conical/thread-like

• Keratinized

• Serve mechanical function

  • NO TASTE BUDS = primarily aids in manipulating food and providing texture to tongue surface

• Dysfunction = nutritional deficiencies (iron amenia, B12) → smooth, red tongue (glossitis)

Compare the structure and function of papillae that contain taste buds with those that serve mechanical roles.

• Vallate, fungiform, foliate = contain taste buds

• Filiform = no taste buds, serve mechanical role (texture, food manipulation)

Describe the cellular composition and structure of a taste bud.

• Ovoid collection of 50–100 cells

  • Within epithelium of tongue, soft palate, pharynx, or epiglottis

• Primary cell types: gustatory receptor cells, supporting (sustentacular) cells, basal stem cells.

• Microvilli (taste hairs) project into a taste pore

  • Interacts with tastants = binding triggers receptors potentials → neurotransmitter release and activation of afferent cranial nerve fibers

• Found in vallate, fungiform, and foliate papillae

Trace the gustatory neural pathway from peripheral receptors to the primary gustatory cortex.

• Three-neuron chain transmits taste from periphery to cortex

  • First-order neurons

  • Second-order neurons

  • Third-order neurons

1. Receptor → CN VII, IX, X

2. Solitary nucleus (medulla)

3. Central tegmental tract → thalamus

4. Thalamus → primary gustatory cortex (insular cortex)

First-order neurons

• Gustatory receptor cells synapse with sensory fibers of cranial NN

  • Anterior 2/3 of tongue → via chorda tympani branch facial N

    • Damage to chorda tympani = distorted taste or loss of taste in anterior tongue

  • Posterior 1/3 of tongue → via glossopharyngeal N

  • Vagus N contributes to taste from epiglottis and pharynx

Second-order neurons

• In solitary nucleus of medulla oblongata

  • Axons ascend in central tegmental tract

• Goes to thalamus

Third-order neurons

• Project from thalamus → primary gustatory cortex

  • In insular cortex

Explain the functional integration of taste with olfaction.

• Taste perception is deeply integrated with olfactory input, as smell contributes significantly to flavor identification and complexity

  • Olfaction enhances flavor perception

    • Most of what we perceive as "taste" is actually smell

List the five primary taste modalities and the chemical stimuli that activate each.

• Sweet: sugars, alcohols found in fruits

• Salty: metal ions (Na⁺, K⁺)

• Sour: H⁺ ions from acidic substances

• Bitter: alkaloids can acts as protective mechanism against the ingestion of toxic substances

• Umami: glutamate (amino acids) especially in protein-rich foods

Differentiate between the roles of taste and smell in overall flavor perception.

• Taste detects basic modalities

  • Chemical interaction tastants and taste receptors

  • Specific classes of chemical compounds

    • Role in dietary preferences and protective mechanisms

• Smell provides complexity and identification → loss of smell = decreased flavor perception

  • Flavor = combined activation of gustatory and olfactory receptors

Identify the cranial nerves responsible for motor and sensory innervation of the tongue.

• Motor: CN XII (hypoglossal) for most & palatoglossus (vagus CN X)

• Sensory:

  • CN V3 (lingual): general sensation, anterior 2/3 (NO TASTE)

  • CN VII (chorda tympani branch): taste, anterior 2/3

  • CN IX: general sensation + taste, posterior 1/3

  • CN X: taste to root and epiglottis

Differentiate between general and special sensory (taste) innervation of the different parts of the tongue.

• General:

  • Anterior 2/3: CN V3 (lingual N of trigeminal N)

  • Posterior 1/3: CN IX (glossopharyngeal N)

• Special (taste):

  • Anterior 2/3: CN VII (facial N)

  • Posterior 1/3: CN IX (glossopharyngeal N)

  • Root/epiglottis: CN X (vagus N)

Infer the functional consequences of cranial nerve injury based on altered motor or sensory (both special and general sensation) function of the tongue.

• CN XII injury → tongue deviation, articulation issues

  • Damage to hypoglossal N = ipsilateral tongue deviation and atrophy affecting swallowing and articulation

• CN VII/IX/X injury → loss or alteration of taste; swallowing or speech difficulties

Describe the structure and function of the conjunctiva and lacrimal apparatus.

• Conjunctiva: stratified columnar epithelium with goblet cells; lubricates, protects

• Lacrimal apparatus: produces and drains tears for hydration, defense

Conjunctiva

• Transparent mucuous membrane lines inner eyelids (palpebral conjunctiva)

  • Reflects on anterior surface of sclera (bulbar conjunctiva)

    • Forms conjunctival sac and terminates at corenal marigin

    • Corneal margin = transition zone between transparent cornea and opaque sclera of eye

• Stratified columnar epithelium containing goblet cells = produce mucus to lubricate the eye

• Vascularized and innervated

  • Immune surveillance and maintains ocular hydration

• Infections disrupt surface → discomfort and blurred vision

Lacrimal apparatus

• Lacrimal gland = produce tears (lacrimal fluid/water, electrolytes, and lyzomes for antibacterial defense)

  • Orbital part

  • Palpebral part

• Tears provide lubrication and protection to anterior surface of eye

• Blockage (nasolacrimal duct) can cause excessive tearing (epiphora) or recurrente infections (dacryocystis)

Trace the flow of tears through the lacrimal drainage system.

1. Tears are produced in lacrimal gland

2. Swept across the eye surface

3. Enter the lacrimal puncta

4. Drain into lacrimal canaliculi

5. Lacrimal sac

6. Nasolacrimal duct

7. Inferior nasal meatus

Explain the role of accessory eye structures in maintaining ocular surface health and visual function.

• Maintain hydration, remove debris, prevent infection, and ensure smooth optical surface

• Protective, lubricative, and supportive

  • Ensuring proper function of eyeball and contribute to visual acuity by maintaining surface integrity and alignment

    • Conjuncitva

    • Lacrimal appartus

    • Eyelids

    • Extraocular muscles

    • Oribtal fat

Identify the origin, insertion, action, and innervation of each extraocular muscle.

Muscle	Action	Nerve
Superior rectus	Elevates/adducts/intorts	CN III
Inferior rectus	Depresses/adducts/extorts	CN III
Medial rectus	Adducts	CN III
Lateral rectus	Abducts	CN VI
Superior oblique	Depresses/abducts/intorts	CN IV
Inferior oblique	Elevates/abducts/extorts	CN III
Levator palpebrae superioris	Elevates eyelid	CN III (with sympathetics)

Infer the functional impact of cranial nerve damage on extraocular muscle function.

• CN III: ptosis, down-and-out eye, diplopia

• CN IV: vertical diplopia, trouble descending stairs

• CN VI: medial strabismus, horizontal diplopia

Recognize patterns of muscle dysfunction that suggest specific cranial nerve lesions (CN III, IV, VI).

• CN III palsy: eye down & out, ptosis (drooping eyelid)

• CN IV palsy: vertical diplopia, eye up

• CN VI palsy: inability to abduct eye

List the major branches of the ophthalmic artery and the anatomical structures they supply.

• First intracranial branch of internal carotid A

  • Through orbit and optic canal

• Supratrochlear: skin and muscles of medial forehead/scalp

  • Terminal branch

  • Ascends to forhead medial to supraorbital A

• Supraorbital: upper eyelid, forehead, and anterior scalp

  • Travels through supraorbital foramen with supraorbital N

• Anterior/posterior ethmoidal: nasal cavity, meninges

  • Arises medially in orbit

  • Enter anterior/posterior ethmoidal formania

  • Part of Kiesselbach’s triangle but posterior ethmoidal A is less consistently involved

• Central retinal artery: inner retina

  • Critical that pierce the optic N sheath and enters retina at opic disc

  • End artery without significant collateral circulation

  • Occlusion = painless monocular blindness

Describe the course of the central retinal artery and its functional significance.

• Pierces optic nerve sheath→ enters retina at optic disc → supplies inner retina

Infer the consequences of vascular occlusion of the central retinal artery.

• Sudden, painless monocular blindness → ophthalmic emergency & immediate intervention

Differentiate between the anterior chamber, posterior chamber, and vitreous chamber based on location and contents.

• Contribute to

  • Intraocular pressure

  • Optical function

  • Structural integrity

• Anterior: cornea ↔ iris

• Posterior: iris ↔ lens

  • Aqueous humor = anterior & posterior

• Vitreous: lens ↔ retina

  • Vitreous humor = vitreous chamber

    • Aqueous and virtuous humor fill spaces and support the cornea/retina facilitating nutrient and waste transport

Anterior chamber

• Between cornea and iris/pupil

• Filled with aqueous humor produced continously by ciliary processes

  • Fluid flows through pupil and drains through trabecular network and scleral venous sinus (canal of Schlemm)

• Impaired aqueous humor drainage (trabeculae network) = elevated intraocular pressure

  • Open-angle glaucoma = compress CN II

Posterior chamber

• Narrow space between posterior surface of iris and anterior surface of lens

  • Filled with aqueous humor produced by ciliary processes

• Fluid moves to pupil into anterior chamber

Vitreous chamber

• Posterior to lens

  • Filled with transparent gelatinous = virteous humor

    • Helps maintain shape of eye

    • Holds the retina in place against choroid

    • Supports lens posteriorly

  • Not replenished throughout life

    • Liquefaction with aging

• Detachment is common in older adults → floaters or flashes of light

  • Retinal detachment (vision-threat)

Describe the flow of aqueous humor and its role in intraocular pressure regulation.

Produced by ciliary processes → Posterior chamber → Pupil → Anterior chamber → Trabecular meshwork → Scleral venous sinus (Canal of Schlemm)

• Blockage = ↑ pressure = glaucoma

Explain the significance of vitreous humor in retinal support and its clinical relevance in aging.

• Supports retina & lens

• Not replenished → liquefies with age, may cause retinal detachment

Identify the three main layers of the eyeball and the components of each layer.

• Fibrous: sclera, cornea

• Vascular (uvea): choroid, ciliary body, iris

• Retinal: neural retina (photoreceptors: rods/cones), pigmented epithelium

Fibrous layer

• Outermost layer

  • Sclera = posterior 5/6 that provides protection and structure

  • Cornea = anterior 1/6 refracting light

    • Avascular and receives nourishment via diffusion from aqueous humor and tear film

    • Damage to cornea epithelium (non-stratified squamous epithlium) = photophobia and impair visual acuity

      • Abrasions and ulcers monitored to prevent scarring

Vascular layer

• Uvea (middle layer) ophthalmic A supplies

  • Choroid = pigmented/vascularized that nourishes outer retina

  • Ciliary body

    • Ciliary muscle = alter lens shape during accommodation

      • Smooth muscle that attaches to suspensory ligmaents that attaches to lens

      • Lens fatten = focus nearby

      • Less stretches = relaxes to see far ways (less as we age)

      • CN III = parasympathetic

    • Ciliary processes = secrete aqueous humor

  • Iris = regulates pupil diameter via dilator and sphincter pupillae muscles

    • Dilator = sympathetic

    • Sphincter = parasympathetic CN III

• Uveitis = infection autoimmune disease or trauma → pain, photophobia, and decreased vision

Inner layer

• Retinal layer (innermost)

  • Neural layer = photoreceptors (rods and cones)

  • Outer pigmented layer = reduces light scatter and supports photoreceptors metabolically

• Optic part of retina ends at ora serrata anteriorly

• Macula lutea and fovea centralis posteriorly

  • Specialized for high-acuity vision

• Retinal detachment = separation of neural retina from underlying pigmented epithelium → permanent vision loss if not treated

Explain the functional roles of the fibrous, vascular, and retinal layers in vision.

• Fibrous: protection, structure, light refraction

• Vascular: nourishment, lens accommodation, pupil control

• Retinal: light detection → neural signals

Sclera

• Dense, fibrous, opaque, protective

  • White portion of eye covering 85% of eye

    • Continous anteriorly with cornea and posteriotly with optic nerve sheath

  • Maintains shape of globe

  • Anchor point for six extraocular muscles

    • Avascular and made of dense collagen fibers

  • Osteogenis imperfecta = scleral thing → bluidh hue (underlying choroid showing through transluscent sclera)

Cornea

• Transparent, avascular anterior of fibrous tunic

  • Refraction of light (2/3 of eye’s total refractive power)

  • Densely innervated and highly sensitive

    • Sensory innervation supplies long cilary nerves, branches of nasociliary N (CN V1)

    • Corneal abrasions = significant discomfort due to dense innervation and may predispose the eye infection if the epithelial barrie is disrupted

Explain how the cornea contributes to the refractive power of the eye.

• Provides ~2/3 of total refraction power

  • Curvature bends light onto retina

Recognize how nerve supply to the cornea contributes to its protective sensitivity.

• Highly innervated (CN V1); detects irritation → triggers blinking/tears

  • Oxygen and nutrients supplied through diffusion from tear film (externally) and aqueous humor (internally)

• Integrity of corneal epithelium = maintains transparency and protecting against infection

Identify and describe the structure and function of the uvea’s components: choroid, ciliary body, and iris.

• Middle layer of eyeball (vascular tunic or uvea)

  • Highly vascularized and provides essential nourishment

  • Supports internal ocular structures

  • Aqueous humor production

  • Regulation of light entry through pupil

• Choroid: vascular, nourishes retina

• Ciliary body: secretes aqueous humor, accommodation

• Iris: controls pupil size/light entry

Choroid

• Between sclera and retina

  • Made of dense capillary bed and pigmented cells that minimize light scatter

• Primary vascular suply to outer retina & ends anteriorly at ciliary body

  • RECEIVES BLOOD FROM BRANCHES OF OPHTHLAMIC A

• Posterior uveitis/choroiditis = impair visual function

  • Floaters or blurred vision

  • Secondary to autoimmune or infectious processes

Ciliary body

• Ring of tissue that connects the choroid to iris

  • Cilary muscle

  • Cilary processes = secrete aqueous humor into posterior chamber, nourishing avascular cornea and lens

Ciliary muscle

• Smooth muscle control lens accomodation for near and far vision

  • Altering the tension on suspensory ligaments (zonular fibers) attached to lens

• Parasympathetic innervation from CN III

  • Rounds the lens for near focus

  • Relaxation flattens the lens for distant vision

Iris and pupil control

• Most anterior of uvea

  • Smooth muscles

    • Sphincter pupillae

    • Dilator pupillae

• Disruption of sympathetic innervation (Horner syndrome)

  • Miosis (pupillary constriction)

  • Ptosis

  • Anhidrosis

    • Pathology involving symmpathetic chain or upper thoracic spinal cord

Explain the role of the ciliary muscle in accommodation and how it changes with age.

• Contraction → lens rounds (near vision)

• Age → decreased elasticity = presbyopia

  • Lens loses elasticity

  • Ciliary muscle loses ability to induce accommodation is reduced

    • Lead to difficulty focusing on close objects

Describe the autonomic control of pupil size via sphincter and dilator pupillae muscles.

• Sphincter pupillae: parasympathetic (CN III) → constricts pupil

• Dilator pupillae: sympathetic → dilates pupil

  • Opposing actions regulate the amount of light entering the eye

Describe the dual-layered structure of the retina, including photoreceptors and pigmented epithelium.

• Inner layer of eye (photosensitive layer) that captures light and converts into neural components

  • Inner neural layer: light receptive and houses photoreceptor cells (rods & cones)

  • Pigmented epithelium: absorbs scattered light, maintain integrity of photoreceptors

    • Terminates anteriorly at ora serrata = junction between retina and ciliary body

Compare the function of rods and cones and their distribution in the retina.

• Rods = more numerous and highly sensitive to light

  • Essential for night vision

  • Function well in low light

  • No color information

• Cones = concentrated in macula lutea (fovea centralis)

  • Color vision

  • Visual acuity in bright conditions

Macula lutea

• Central region of retina

• Rich in cones

• Adaptated for detailed central vision

Fovea centralis

• Small depression in macula (back of retina)

• Contains only cones

• Highest visual acuity

  • Light entering eye is refracted by cornea and lens focused on retina

    • Where photoreceptors convert to electrochemical signals that are transmitted to the brain

Optic disc (blind spot)

• Optic nerve (CN II) exits the eyeball

• Lacks photoreceptors

  • Insensitive to light forming physiological blind spot

Identify key retinal landmarks and describe their significance in sight.

• Macula lutea: central vision

• Fovea centralis: sharpest vision

• Optic disc: blind spot (no receptors)

Trace the flow of visual information from the retina to the primary visual cortex.

Retina → Optic nerve → Optic chiasm → Optic tract → LGN (thalamus) → Optic radiations → Primary visual cortex (occipital lobe)

1. Photoreceptor cells in retina (rods and cones) initiate signal transduction

2. Ganglion cell axons form the optic N

3. At optic chiasm, nasal fibers decussate

4. Fibers continue as optic tract to lateral geniculate nucleus of thalamus

5. Optic radiations project to the primary visual cortex in the occipital lobe

Explain how visual field information is processed across the optic chiasm and projected to the appropriate hemisphere.

Nasal fibers cross. Temporal does not.

• Right visual field (both sides)→ left cortex

• Left visual field (both sides) → right cortex

  • Lateral (temporal) field of vision from medial (nasal) retina

  • Medial (nasal) field of vision from lateral (temporal) retina

• At the optic chiasm =

  • Lateral retina remain ipsilateral

  • Medial reina cross over to opposite side