South College AVL Clinical Anatomy 1: Special Senses - Lecture 18

vision, smell, taste, hearing, equilibrium

what are the special senses?

eyebrows, eyelids, conjunctiva, lacrimal apparatus, extrinsic eye muscles

What are the accessory structures of the eye?

Eyelashes, tarsal plate, sebaceous glands

What are three important aspects of the eyelid?

eyelashes

Richly innervated by nerve endings

Reflexive blinking

tarsal plate

Connective tissue

Supports eyelids internally

Anchor eyelid muscles

sebaceous glands

Produce oily secretions - lubricate eye (tarsal glands, and other small glands)

Protect the eyes, keep the eye moist

Function of the eyelids?

chalazion

Painless nodule caused by obstruction of the eyelid gland

hordeolum (stye)

Acute eyelid inflammation that presents with localized pain, erythema, edema

conjunctiva

Transparent mucous membrane

Two types: (palpebral and bulbar)

Function: produced lubricating mucus that prevent prevents dry eye

palpebral conjunctiva

Lines the inner eyelid

bulbar conjunctiva

Covers the sclera on the anterior eye

viral conjuctivitis

most common etiology

Presents as injection, watery, or mucous discharge and burning, sandy, gritty feeling in one eye

lacrimal apparatus

Contains lacrimal glands - produced tears

Ducts - tears empty into the nasal cavity

Function: moisten/lubricate eye, cleanse/protect eye

Mucus, antibodies, and lysozymes

What does lacrimal fluid contain?

extrinsic eye muscles

Six muscles

Origin - walls of orbit

Insertion - outer surface of eyeball (sclera)

Function: control movement of eyeball (follow moving object), maintain shape, hold eye in orbit (it doesn't pop out of eye socket)

Strabismus (misaligned eyes)

Vision disorder in which both eyes do not look at the same point in the visual field

Congenital weakness of the external eye muscles

Three layers (fibers, vascular, inner layer), internal chambers, lens

What are the components of the eyeball?

fibrous layer of eye

Avascular - outermost layer

Sclera: white of eye, tough and tendon-like

Cornea: transparent, outer covering, many nerve endings, regenerate/repair repairs quickly

Function: protection, cornea bends light

corneal abrasion

scratch on the cornea, painful and photophobia

linear corneal abrasion

Commonly caused by a foreign body

vascular layer of eye

contains the choroid, ciliary body, and iris

choroid

Highly vascular, dark brown membrane - melanocytes

Function: nourish all layers, absorb light - prevent scattering

ciliary body

Ciliary muscles and ciliary processes

Function: control, lens shape, secrete fluid - fills anterior eyeball

Iris

"Colored part of the eye"

Two smooth muscles

Sphincter pupillae - constricts (parasympathetic)

Dilator pupillae - dilates (sympathetic)

Function: adjust to control the amount of light entering eye

Rentina

Contains pigmented and neural layer, optic disc (where optic nerve exits eye - "blind spot"), central artery and vein

Function: vision

pigmented layer of retina

Pigmented cells

Function: absorbs light - prevent light from scattering, store, vitamin A, act as phagocytes (photo receptor cell renewal)

neural layer of retina

Signals are produced in response to lay and spread from:

Photoreceptors - bipolar cells - ganglion cells - optic nerve - visual pathway

Photoreceptors

Rods and cones

rods, cones

1) Receptors for dim light, peripheral vision receptors

2) receptors for bright light, provide high-res color vision

macula lutea

Yellowish oval region of the retina

Contains mostly cones (sharp vision)

Located lateral to the optic disc

Function: provides detailed, central colored vision

macular degeneration

Common age related eye condition

Degeneration of the macular lutea

Loss of central vision -certain spots look blurry, especially in the center

Papilladema

Optic disc swelling due to raise cranial pressure

Many causes

early papilledema (no clear borders, not circular)

What does this show?

Fully developed papilledema

What does this show?

retinal detachment

separation of the retina from the underlying epithelium, disrupting vision and resulting in blindness if not repaired surgically

"Curtain vision"

Ocular emergency

Retinal detachment - retina is floating in the vitreous (tethering at the optic nerve -yellow arrows)

What does this ultrasound show?

Anterior and posterior segments

What are the segments of the internal chambers that are divided by the lens and ciliary zonule?

Anterior and posterior chamber (aqueous humor)

What does the anterior segment contain?

Everything from lens - retina (vitreous humor)

What does the posterior segment contain?

aqueous humor

Fills the anterior segment

Continuously forms and drains

Maintains a constant intraocular pressure of about 16 mmHg

Eyeball support internally, supplies nutrients/oxygen to lens and cornea, carries away metabolic waste

What is the function of acqueous humor?

vitreous humor

Fills the posterior segment

Forms in the embryo and lasts for a lifetime

Transmit light, support posterior surface of lens + holds neural layer of retina against pigmented layer, contributes to intraocular pressure (counteracts pulling force of extrinsic eye muscles)

What are the functions of vitreous humor?

acqueous humor - formed by ciliary processes - flow from posterior chamber through pupil to anterior chamber - aqueous humor is reabsorbed into venous blood by scleral venous sinus

What is the process of how aqueous humor is formed and how it flows?

Glaucoma

Drainage of aqueous humor is blocked

Pressure within the eye may increase to dangerous level

Compressed retina and optic nerve

Blindness

lens

Transparent, flexible, biconcave disc

Function: changes shape to focus light on retina

(Ciliary muscle and the ciliary zonule focus on an image by changing the shape of this)

Cataracts

Hardening, thickening, clouding of the lens

Causes vision to be distorted, as of seeing it through frosted glass

Cornea (outer layer, light is bent) - aqueous humor (front part of eye) - lens (refracts light - see close or far) - vitreous humor - retina: neural layer - photoreceptors (rods and cones)

What is the direction of light (from the sun) throughout the eye up to photoreceptors?

lens

Bends or refracts light rays so they converge to a point (inversion of an image)

Lens flattens, ciliary muscles completely relax, low refractory power (not bending a lot of light)

What happens during distant vision?

Lens bulges, ciliary muscles contract, high refractory power

(Constriction of pupils - accommodation, convergence of eyeballs - medial rotation of the eye to focus on an object)

What happens during close vision?

Myopia (nearsightedness)

"Short vision"

Can see up close objects

Distant objects are blurry

Hyperopia (farsightedness)

"far vision"

Can see distant objects

Close-up objects are blurry

astigmatism

Unequal curvatures in different parts of the cornea or lens of the eye - leads to blurry vision

Cornea - aqueous humor - lens (refracts light - see close or far) - vitreous humor - retina: neural layer - photoreceptors (rods and cones) - optic nerve (partial crossing over at the optic chasm) optic tracts - lateral geniculate nuclei (thalamus - "gatekeeper") - primary visual cortex

(The optic tract can veer off to other stops in the mid brain)

What is the direction of light (from the sun) throughout the eye all the way until primary visual cortex?

Vision, optic nerve, optic chasm, optic tract, primary visual cortex

What are the components of the visual fields?

vision

Lateral visual field - medial retina

Medial visual field - lateral retina

optic nerve

Carries info from right or left eye

optic chiasm

Medial optic nerve fibers crossover

optic tract

Carries all information from the same half of the visual field (example: left optic tract carries a complete representation of the right half of the visual field)

Contains fibers from the lateral (temporal) aspect of eye on same side and medial (nasal) aspect of the opposite eye

primary visual cortex

Left visual cortex receives input from the right visual field

Optic chiasm (both lateral visual fields lost)

A 42-year-old female patient presents to the primary care office with progressive loss of vision. She feels like she has "tunnel vision" . On physical examination, she has lost the lateral visual field in the right eye and loss of lateral visual field in the left eye. Which of the following anatomical locations is likely affected?

Left optic nerve

Left optic tract

Optic chiasm

Right optic nerve

Right optic tract

vitreous humor

Which of the following both supports the posterior surface of the lens and hold the retina against the back of the eye?

Lacrimal apparatus

Vitreous humor

Conjunctiva

Ciliary body

Sclera

Which of the following is visible on the exposed anterior surface of the eyeball?

Pigmented layer

Choroid

Sclera

Fovea

Chemoreceptors (smell and taste), smell receptors (excited by airborne chemicals - dissolve in fluid coating nasal membrane), taste receptors (excited by food chemicals dissolved in saliva)

What are the three things involved in smell and taste?

Tell us whether things are to be savored or avoided

What is the function of smell and taste?

CN I Olfactory Nerve

smell

olfactory receptors

Superior nasal cavity, poorly positioned for smell, olfactory epithelium

olfactory epithelium

Mucus -captures and dissolves airborne odorants

Olfactory sensory neurons:

- bipolar neurons

- olfactory cilia - extend from the dendrite (increase surface area)

Collectively, the axons form the CN 1

Stimulus (a.k.a. the smell of pizza) - travel to superior nasal cavity (mucus captures/dissolves airborne odorant) - olfactory sensory cells detect odor (AP to glomeruli in olfactory bulb for synapse) - mitral cells in olfactory bulbs (via olfactory tract) - primary olfactory cortex -

Frontal lobe (assist with conscious interpretation and identification)

Hypothalamus, amygdaloid body, limbic system (emotional response to odors)

What is the olfactory pathway?

sweet, sour, salty, bitter, umami

What are the basic taste sensations?

taste buds

Found in papillae

Gustatory epithelial cells (receptors for taste)

Basal epithelial cells (stem cells - differentiate into new gustatory epithelial cells)

Every 7 to 10 days

How often are taste buds replaced?

facial nerve (CN VII), glossopharyngeal nerve (CN IX), vagus nerve (CN X)

Which nerves receive impulses from taste receptors?

Facial Nerve (VII)

Anterior 2/3 of the tongue

Glossopharyngeal nerve (IX)

Posterior 1/3 of the tongue and pharynx

Vagus nerve (X)

Few taste buds in the epiglottis and the lower pharynx

Facial, glossopharyngeal, vagus nerve - solitary nucleus in medulla oblongata - Pons - thalamic nucleus (ventral posteromedial nucleus) — gustatory cortex (in insula)

What is the gustatory pathway?

hearing apparatus

Allows us to hear extraordinary range of sounds

Equilibrium (balance) receptors

Continually informed the nervous system of head movements and position

internal ear

Controls both hearing apparatus and equilibrium independently

External, middle, internal ear

What are the three parts of the ear?

Auricle (pinna), external acoustic meatus, tympanic membrane

What is the external ear composed of?

auricle (pinna)

Elastic cartilage

Function: funnels sound waves

external acoustic meatus

Gland secrete cerumen

tympanic membrane

Thin, translucent

Boundary of outer and middle ear

Function: transfer sound waves to the bones of the middle ear

middle ear

The small air-filled space between the auditory canal and the cochlea that contains the ossicles

Mastoid antrum, auditory ossicles, oval window, round window, pharyngotympanic tube (eustachian tube)

What are some of the components of the middle ear?

mastoid antrum

Communicates with mastoid air cells

Entrance - where air cells get infected

oval window

Stapes creates pressure waves in the fluid of the inner ear - transfer signal

Round window

Absorbs pressure wave vibrations from inner ear

pharyngotympanic tube (eustachian tube)

Links the middle ear with the posterior oropharynx

Opens with yawning or swallowing

(equalize pressure in the middle ear with external pressure)

(TM only vibrates normally with equal pressure)

malleus (hammer - secured to TM), incus (anvil), stapes (stirrup - base fits into oval window)

What are the auditory ossicles?

Transmit vibrations from TM to oval window

What is the function of the auditory ossicles?

otitis media (ear infection)

Inflammation of the middle ear

Eustachian tube often not working properly

Fluid not draining (bacteria/viruses can grow in the fluid, pressure buildup behind the TM)

Common among children

Bony labyrinth, membranous labyrinth, perilymph/endolymph

What are the four main components of the internal ear?

bony labyrinth

System of torturous channels worming through temporal bone

Contains perilymph - similar to CSF

(Vestibule, semicircular canal, cochlea)

membranous labyrinth

Continuous series of membranous and ducts contained within the bony labyrinth

Contains endolymph

perilymph and endolymph

Conduct sound vibrations

Shipped with body position and acceleration