special senses

chapter 8 of Essentials of Human Anatomy and Physiology 12e

Accessory Structures (Eye)

Include: Extrinsic eye muscles, Eyelids, Conjunctiva, Lacrimal apparatus

Eyelids

Meet at the medial and lateral commissure,

Canthus (medial and Lateral commissure)

Corners of the eye, either lateral or medial

Eyelashes

A protective measure, keeping airborne irritants out of your eye; tarsal glands are located within and ciliary glands are located between

Tarsal glands

produces oily secretion that lubricates the eye

Conjunctiva

the thin, protective mucous membrane lining the eyelids and covering the anterior surface of the eyeball; connects with the edge of the transparent cornea

Conjunctivitis (Pink eye)

inflammation of the conjunctiva, results in redness and irritated eyes; pink eye is its infectious form, via bacteria and viruses, is highly infectious

Lacrimal apparatus

consists of the lacrimal glands and multiple ducts that drain into the nasal cavity

Lacrimal gland

located laterally and superior to the eye; continuously release a dilute salt solution (tears) onto the anterior surface of the eye through several small ducts

Lacrimal canaliculi

tears flush across the eyeball medially, and end up here

Lacrimal sac

from the lacrimal canaliculi, tears move here

Nasolacrimal duct

tears end up here after passage through the lacrimal sac; which empties out into the inferior meatus of the nasal cavity

Lysozyme

an enzyme that destroys bacteria; part of the dilute solution of salt that makes up tears, along with mucus and antibodies

Eye muscles

there are six of these, that hold the eyeball in its socket; attach to the outer surface of the eye; produce gross motor movement

Fibrous layer (Sclera)

firm white fibrous outer layer of eyeball'; protects and maintains eyeball shape

Cornea

transparent anterior portion of the eyeball

Vascular Layer

middle layer; has three distinguishable regions: the **choroid**, the **ciliary body**, and the **iris**

Choroid

highly vascularized (blood and nutrient-rich) and pigmented layer that absorbs and prevents the scattering of light

Ciliary Body

moving anteriorly, the choroid is modified to form two smooth muscle structures, the iris, and ciliary zonule; the choroid thickens anteriorly as the pigmented and fibromuscular surrounds the lens; held by the ciliary zonule

Ciliary Zonule

suspensory ligament that attaches the lens to the ciliary body in the anterior eye

Iris

on the anterior aspect of the ciliary body; a thin, epithelial, and fibromuscular layer circumscribes the pupil in front of the lens; controlled by cranial nerve III (oculomotor); acts as the diaphragm of a camera;

Pupil

an opening at the center of the iris through which light enters the eye

Sensory Layer (retina)

the deepest layer of the eye; most light sensitive; contains rods and cones, or photoreceptors; consists of two layers

Pigmented layer of the retina

the layer of the retina closest to the choroid; consists of pigmented cells that absorb light and prevents scattering; also acts as phagocytes that remove dead and damaged receptor cells and store vitamin A

Neural Layer of the retina

transparent inner layer of retina; contains that contains millions of rods and cones (photoreceptors)

Photoreceptors

specialized neurons/receptors that respond to light energy, converts it into electrical signals

Rods

only register a gray scale of black and white; responsible for peripheral vision; up to a hundred of them attach to one ganglion cell; give information about general shape or light or darkness

Cones

detects fine detail and color; red, green, and blue varieties; only hit activation threshold in bright conditions; each cone has one ganglion cell

Bipolar and ganglion cells

two-neuron chain that works together to create a pathway for light; light goes from photoreceptor to bipolar cell to ganglion cell which creates the optic nerve

Optic nerve

the second cranial nerve; leaves through the optic disc at the posterior of eyeball and connects those impulses up to the thalamus then to the visual cortex of the brain

Optic disc / Blind spot

where the optic nerve leaves the eyeball; devoid of cones and rods; making a blind spot

Night blindness

makes driving at night extremely dangerous; most common cause is prolonged vitamin A deficiency, which eventually causes the neural retina to deteriorate;

Fovea centralis

lateral to each blind spot; a tiny pit that contains only cones; spot of greatest visual acuity

Visual acuity

the ability of the eye to distinguish detail; greatest spot for this is the fovea centralis

Color blindness

condition where the lack of one type of cone leads to partial; most common is red-green _____ ; is considered a sex-linked condition as genes regarding color vision are on the X chromosome, resulting in the condition appearing almost exclusively in males

Lens

light enters the eye through this; focuses the image on the retina; a flexible biconvex crystal-like structure; held up by the ciliary zonule attached to the ciliary body; divides the eye into two sections

Cataracts

is the loss of lens transparency; causes vision to become hazy and distorted; can eventually leads to blindness;

Aqueous humor

fluid found between the cornea and the lens; similar to blood plasma and is continually secreted by a special of the choroid; it helps maintain intraocular pressure

Vitreous humor

jelly-like fluid found behind the lens in the posterior cavity of the eye that maintains its round-ish shape; also keeps intraocular pressure stable

Sclera venous sinus or canal of Schlemm

absorbs aqueous humor into the venous blood through this; which is located at the junction of the sclera and cornea;

Glaucoma

an abnormal increase of intraocular pressure

Fundus

posterior wall of eye

Ophthalmoscope

illuminates the interior of the eyeball; allowing the retina, optic disc, and internal blood vessels at the fundus to be examined; examination using this device can allow for detection of diabetes, arteriosclerosis, and degeneration of the optic nerve and retina

Refracted light

bending of light

Accommodation

the ability of the eye to focus specifically on close objects; the adjustment of the eye for seeing objects at close range

Real image

image formed on the retina that is reversed left to right and inverted upside down (and smaller) due to the refraction of light by the lens

Optic chiasma

the partial crossover of fibers of the optic nerves from the medial side of each eye crosses over to the opposite side of the brain to form optic tracts

Optic Tracts

each contains fibers of the lateral side of the on the same side, and the medial side of the opposite eye; synapse into the neurons of the thalamus, whose axons form the optic radiation

Optic radiation

the axons of the thalamus from this, which runs to the visual cortex in the occipital lobe of the brain for processing

Hemianopia

is the loss of sight in one side of the visual field due to **neurological issues** rather than a problem with your eyes; partial blindness

Convergence

the reflexive movement of the eyes medially when looking at closer objects

Photopupillary reflex

occurs when the eyes are suddenly exposed to bright light, the pupils immediately constrict; prevents excessively bright light from damaging delicate photoreceptors

Accommodation pupillary reflex

pupils also constricts reflexively when viewing close objects; provides acute vision

Mechanoreceptors

receptors sensitive to mechanical pressures such as sound, touch or contractions

Outer ear

external or outer ear; composed of the auricle/ pinna and the external acoustic meatus

Auricle / pinna

the visible portion of the ear;shell shaped structure surrounding the external acoustic meatus opening; acts as funnel for sound waves

External acoustic meatus

aka the auditory canal; short, narrow chamber carved into the temporal bone of the skull; the skin within is lined with ceruminous glands which secrete yellow cerumen, or earwax

Tympanic membrane (ear drum)

sound waves hit this after traveling through the auditory canal, vibrating it; this is the end of the external ear and the beginning of the middle ear

Middle ear / tympanic cavity

**small, air-filled, mucus-lined cavity** within the temporal bone of the skull; within this cavity, **three of the body’s smallest bones sit**, the hammer (malleus), the anvil (incus), and the stirrup (stapes); **has two openings,** the oval window and the inferior membrane covered round window

Oval window

membrane-covered opening in the middle ear wall, that sits superior to the round window; sound is conveyed through this opening via the stirrup (stapes)

Round window

mucus-covered opening within the middle ear wall between the vestibule and cochlea; inferior to the oval window

Pharyngotympanic tube / Auditory tube

tube that connects the pharynx and the middle ear; allows pressure to be equalized on both ends of the eardrum; mucus-lined

Otitis media

inflammation of the middle ear, most often due to a sore throat; most common in children; if fluid and pus builds up with in the tympanic cavity, an emergency myringotomy is performed

Ossicles

the three bones of the middle ear; hammer, anvil, and stirrup; transmits the vibratory motion of the eardrum to the fluid filled inner ear

Hammer / malleus

the first of the ossicles; vibrations from the eardrum move this and in turn moves the anvil (incus)

Anvil / incus

the second of the ossicles; vibrations from the hammer (malleus) move this which in turn vibrates the stirrup (stapes)

Stirrup / stapes

the third of the ossicles (most medial of the three); vibrations from the anvil (stapes) moves the stirrup (stapes) which then presses upon the oval window of the inner ear

Internal ear

this is a maze of boney chambers called the boney (or osseous) labyrinth, located deep within the temporal bone, behind the eye socket

Bony / osseous labyrinth

made up of three parts: the cochlea (a coiled tunnel), the vestibule, and the semicircular canals (semicircular tunnels) located deep within the temporal bone, behind the eye socket

Cochlea

snail shell shaped; houses the hearing receptors

Vestibule

in between the cochlea and semicircular canals; houses the static equilibrium receptors: maculae

Semicircular canals

the canals for each one of the 3 planes; houses the dynamic equilibrium receptors

Perilymph

plasma like fluid that fills the osseous labyrinth

Membraneous labyrinth

a series of membrane sacs that more or less follows the shape of the osseous labyrinth; contains endolymph

Vestibular apparatus

a collective name for all the equilibrium receptors of the inner ear; divides into static and dynamic equilibrium systems

Maculae

static equilibrium receptors located in the vestibule of the inner ear

Static equilibrium

sense concerned with changes in the placement of the head

Otolithic membrane

gelatinous membrane in a macula with receptor hairs embedded in it and otoliths studded on it

Otiliths

small calcified masses located on the otolithic membrane of the maculae; like weights on a rube goldberg machine;

Vestibular nerve

a division of cranial nerve VIII

Dynamic equilibrium

sense that reports on angular and rotary movements of the head; uses multiple crista ampullaris to sense

Crista ampullaris

receptors in the ampullae of the semicircular canals that reports dynamic equilibrium; consists of tuft of hair cells covered in a gelatinous cap, the cupula

Cupula

a dome like structure within the cristae; a gel-like cap covering the “hairs” of the receptor cells;

Cochlear duct

location of the spiral organ of corti in the cochlea; filled with endolymph

Spiral organ of corti

location of the hearing receptors in the cochlea

Hair cells

mechanoreceptor cells

Basilar membrane

membrane in the cochlear duct that vibrates to transmit soundwaves; houses the base of the receptor cells for hearing

Tectorial membrane

gel like membrane within the cochlear duct in which the “hairs” of the receptor cells are embedded

Cochlear nerve

division of cranial nerve VIII (vestibulocochlear nerve)

Deafness

hearing loss of any degree

Conduction deafness

hearing loss due to interference in transmitting sound waves to the inner ear (effects the external and middle ear only)

Otosclerosis

fusion of the ossicles (bones) in the middle ear; results in conduction deafness

Sensorineural deafness

hearing loss due to degeneration or damage to the inner ear: receptor cells in spiral organ of corti, to the cochlear nerve, to the neurons of the auditory cortex

Meniere’s syndrome

progressive deafness occurs; individuals become nauseated, have howling or ringing sounds in their ears and vertigo so severe that they cannot stand up

Vertigo

a sensation of whirling or spinning even when stationary and loss of balance

Chemoreceptors

receptors sensitive to various chemicals in solution; gustatorial (smell) receptors and olfactory (taste) receptors

Olfactory receptors

neurons equipped with olfactory hairs that detect chemicals

Olfactory receptor cells

modified peripheral (axon) processes of bipolar sensory neurons buried in the olfactory mucosa at roof for nasal cavity

Olfactory hairs

long cilla that protrude from the olfactory receptor cells into the olfactory mucosa

Olfactory filaments

bundled axons of olfactory neurons that collectively make up the olfactory cranial nerve (CN I)