Exercise 24: Special Senses

Created by poorlilrich 

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Palpabrae

eyelids

Conjunctiva

the thin, protective mucous membrane that covers the anterior eye and folds to cover the inner eyelid

Palpebral conjunctiva

covers the interior of the eyelid

Bulbar conjunctival

covers the anterior part of the white of the eye, but not the cornea

Lacrimal apparatus

is a group of structures involved in producing and draining tears

Lacrimal gland

produces and secreates tears onto the eye surface

Lacrimal canals

drain tears from teh eyes into the enlarged lacrimal sac

Lacrimal sac

the lacrimal canals drain tears from the eyes into this sac

Nasolacrimal duct

receives tears from the lacrimal sac and drains the tears into the nasal cavity

Extrinsic eye muscles

aare six skeletal muscles that insert on teh exterior of the eyeball to move the eyeball in all directions: the superior, inferior, medial, and lateral rectus muscles are parallel to the long axis of the eyeball; the superior and inferior oblique muscles attach to the eye ball at an angle

Inferior oblique

moves eye superiorly and laterally

Inferior rectus

moves eye inferiorly

Lateral rectus

moves eye laterally

Medial rectus

moves eye medially

Superior oblique

moves eye inferiorly and laterally

Superior rectus

moves eye superiorly

Wall of the eyeball

has three layers: the outer fibrous tunic, the middle vascular tunic, and the inner retina

Fibrous tunic

is composed of teh cornea and sclera

Cornea

the transparent anterior portion that covers the iris and pupil

Sclera

the touch, white part of the eye that forms the majority of the eyeball

Scleral venous sinus

is an opening found at the junctino of the cornea and sclera; drains aqueous humor back into the bloodstream

Vascular tunic

is composed of the iris, ciliary body, and choroid

Iris

the most anterior portion of the vascular tunic and contains pigmented cells; it is made of circular smoth muscle and controls the pupil size

Pupil

is the opening in teh middle of the iris that allows light to enter the eyeball and changes size in response to teh intensity of light

Ciliary body

begins posterior to teh iris at the junction of the cornea and sclera and consists of the ciliary muscle and ciliary processes

Ciliary muscle

is a circular smooth muscel that ocntracts to control the sape of the lens

Ciliary processes

are folds that protrude from teh ciliary body toward the lens; they contain capillaries that secrete aqueous humor, the fluid in the anterior chamber of the eyeball

Suspensory ligaments

are thin fibers that attach the lens to the ciliary processes

Choroid

is the most posterior part of the vascular tunic that lines most of the interior of the sclera; it contains many blood vessels that nourish teh retina

Retina

is the inner coat that begins at teh ora serrata; the retina continues posteriorly, lining the interior of the choroid; teh pigmented layer of the retina is the outer portion, and the neural layer is the inner portion that contains photoreceptors and associated neurons

Ora serrata

the serrated boundary between the ciliary muscle and the retina

Interior of the eyeball

contains the lens, anterior cavity, and vitreous chamber

Lens

divides the interior of the eyeball into an anterior cavity and a vitreous chamber (posterior cavity)

Anterior cavity

is a space between teh cornea and the lens that is filled with watery aqueous humor; this cavity is subdivided into an anterior chamber and a posterior chamber

Anterior chamber

part of the anterior cavity; between the cornea and the iris

Posterior chamber

part of the anterior cavity; betwen teh iris and the lens

Vitreous chamber

is the larger, posterior cavity located between teh lens and the retina; is filled with a gel-like substance called teh vitreous body (humor) that holds the retina flat agains the choroid

Neural portion of the retina

an outgrowth of the brain and contains three layers of neurons: the photoreceptor layer (deepest cell layer), the bipolar cell layer (middle layer), and the ganglion cell layer (the superficial cell layer)

Photoreceptor cell layer

contains the rods and cones, which synapse with the bipolar neurons in teh bipolar cell layer

Rods

are used in night vision and respond to low levels of light, allowing us to perceive shades of gray, black, and white; visual acuity with rods is low

Cones

require brighter light for stimulation, but allow us to see color and provide high visual acuity

Bipolar cell layer

cells here synapse on the ganglion cells in teh ganglion cell layer

Ganglion cell layer

axions from the ganglion cells extend through the optic disc and leave the eyeball as the optic nerve

Optic disc

does not contain photoreceptors and forms the blind spot of the retina; it is also teh site where the central retinal artery and vein center enter and leave the retina, and the only place where the retina is secured to teh otehr layers of the eyeball

Macula lutea

the site of macular degeneration, is in the center of the neural portion of the retina

Central fovea

in the middle of the macula lutea is this; this area of the retina has the highest density of cones of any area of the retina and is not covered by ganglion and bipolar cell layers; therefore , this area ahs the highest visual acuity of any area of the retina; when we look at an object, the light rays reflected from teh object are focused onto teh central fovea

Ophtalmoscope

the retina can be viewed with this; it illuminates teh interior of the eye

Regions of the ear

the external ear, the middle ear, the internal ear

External ear

consists of the auricle, external auditory canal, and tympanic membrane; extends fromt eh auricle to teh tympanic membrane

Auricle

teh flexible external structure that is commonly called the ear, collects sound waves and directs them toward the external auditory canal

Helix

the rim of the auricle

Lobule

the flesy, inferior portion of the auricle

External auditory canal

conducts sound waves from the auricle to the tympanic membrane

Tympanic membrane

(eardrum) converts sound waves to vibrations that are transferred to middle ear structures

Middle ear

is an air-filled cavity within the temporal bone that extends from teh tympanic membrane to teh oval window; structures include the auditory ossicles, oval window, roudn windown and auditory tube

Auditory ossicles

are small bones within teh cavity that are connected by synovial joints; they transfer vibrations from the tympanic membrane to teh oval window; include the malleus, incus, and stapes

Malleus

the outermost auditory ossicle and is attached to the tympanic membrane

Incus

the middle auditory ossicle and connects to the stapes

Stapes

the innermost auditory ossicle; connects to the incus and teh oval window

Oval window

the membrane-covered opening that separates teh mdidle and inner ear and transfers vibrations to the inner ear

Round window

is a membrane-covered opening between teh middle ear and cohlea

Auditory tube

conects the middle ear to the nasopharynx, and equalizes the air pressure of the ear with atmospheric air

Internal ear

is housed within the temporal bone; it consists of cavities within teh bone called the bony labyrinth that encloses a series of connected membranous sacs, the membranous labyrinth

Bony labyrinth

contains a fluid called perilymph that surrounds the membranous labyrinth; endolymph is the fluid within teh membranous labyrinth; the bony labyrinth has 3 main regions: the vestibule, the semicircular canals, and the cochlea

Vestibule

is the middle area of the bony labyrinth that encircles 2 sections of membranous labyrinth, the utricle and the saccule

Utricle

is the posterior section of the membranous labyrinth within the vesttibule, and is houses equilibrium receptors

Saccule

is the anterior section of the membranous labyrinth within the vestibule; the saccule is continuous with the utircle and also houses equilibrium receptors

Semicircular canals

are 3 bony canals posterior to the vestibule that project posteriorly, laterally, and superiorly from teh vestibule; each canal is at right angles to the other two

Semicircular ducts

are sections of membranous labyrinth within the semicircular canals which contain equilibrium receptors and connects with the utricle

Ampulla

is the widened end of each semicircular canal and duct

Cochlea

the spiral area of teh bony labyrinth anterior to the vestibule; makes 3 turns around a bony cone; a section through this shows 3 channels: the scala vestibuli, teh cochlear duct, and teh scala tympani

Cochlear duct

is teh section of membranous labyrinth within the cochlea; contains the hearing receptors and is connected to teh saccule

Vestibulocochlear nerve

hearing and equilibruim receptors initiate nerve impulses which are carried by this nerve to the brain; has 2 branches: the vestibular branch and the cochlear branch

Vestibular branch

part of the vestibulocochlear nerve; carries nerve nerve impulses generated by equilibrium receptors

Cochlear branch

carries nerve impulses generated by the hearing receptors

Scala vestibuli

is part of the cochlea and is superior to teh cochlear duct; it is separated frmo the cochlear duct by the vestibular membrane; it is continuous with the scala tympani and is filled with perilymph

Scala tympani

is also part of the cochlea and is posterior to cochlear duct; it is separated from teh cochlear duct by the basilar membrane; it is continuous with the scala vestibuli and is filled with perilympth

Cochlear duct

is part of the membranous labyrinth, houses the spiral organ of corti and is filled with endolymph

Spiral organ of Corti

sits on teh basilar membrane; it contains hair cells (receptors for hearing) and supporting cells

Hair cells

have a hair bundle composed of stereocillia at their apical end; superior and in contact with teh stereocilia is the tectorial membrane; the basal end of teh hair cells synapse with sensory and motor neurons from the cochlear branch of the vestibulocochlear nerve

Types of equilibrium receptors

there are 2 types: the maculae and the cristae

Maculae

located in teh utricle and saccule; provide information on head position (static equilibrium), as well as linear acceleration and deceleration, a type of dynamic equilibrium; consists of hair cells with hair bundles and supporting cells

Otolithic membrane

is in contact with teh hair bundles of the maculae; contains calcium carbonate crystals called otoliths

Otoliths

movemtn of the head causes movemetn of the otoliths and otolithic membrane, which bends the hair bundles; the dirrection of movement will determine if the hair cells release more or less neurotransmitter to the associated sensory neurons

Crista

located in teh membranous semicircular ducts within the ampullae; detects rotational accelaeration and deceleration, a type of dynamic equilibrium; each consists of hari cells and supporting cells; the hair bundles of the hair cells are covered by a gelatinous structure called the cupula

Cupula

a gelatinous structure that covers the hair bundles of the hair cells in teh crista; when the head moves, movement of the endolympth pushes the cupula causing the hair cells to bend; bending of the hair bundles results in generation of nerve impulses in the vestibular branch of the vestibulocochlear nerve

Olfactory epithelium

covers teh inferior surface of the cribriform plate, the superior nasal concha, and the upper part of the middle nasal concha; contains olfactory receptors cells, basal stem cells, and ducts of olfactory glands

Olfactory receptor cells

are bipolar neurons whose dentritic end is embedded in the mucus layer covering the surface of the olfactory epithelium and whose axons form the olfactory nerves; they are located on olfactory haris that project from the dentrites of the olfactory receptor cells

Olfactory nerves

pass through the olfactory foramina in the cribriform plate and synapse on neurons in the olfactory bulb; nerve impulses then travel along the olfactory tract to the lateral olfactory area of teh cerebral cortex; olfactory receptors adapt to odors very quickly

Taste buds

are found on the tongue, soft palate, pharynx (throat) and larynx; are microscopic, onion shaped structures that contain gustatory cells, gustatory hairs, and supporting cells

Gustatory cell

each has one gustatory hair that projects through an opening, the taste pore, on the apical end of the taste bud

Gustatory receptors

are located on the gustatory hairs; the basal end of gustatory cells synapse onto the dendritic end of sensory neurons; axons from the sensory neurons contribute fibers to the facial nerve (cranial nerve VII), glossopharyngeal nerve (IX), or vagus nerve (X), depending on the location of the taste bud

Papillae

taste buds on teh tongue are located here; elevated structures that give the tongue its rough appearance; there are 4 types: vallate, fungiform, foliate, and filiform

Vallate papillae

are the largest papillae and form an inverted V at the posterior of the tongue

Fungiform papillae

are mushroom shaped and are scattered over the surface of the tongue

Filiform papillae

are slender, pointed, projections that cover teh surface of the tongue and give the tongue a rough texture; these papillae have tactile receptors but not taste buds; taste buds are found in vallate, fungiform, and foliate papillae

Foliate papillae

are present mostly in children and are lcoated in lateral margins of the tongue

Taste sensations

there are four primary: sweet, bitter, salty, and sour; and a possible fifth, MSG (monosodium glutamate); gustatory receptors most senstive to sweet and salty sensations are found on the tip of the tongue, while bitter sensation are in teh back and sour sensations are on teh sides of the tongue; other taste sensations are a mixture of these four; smell, temperature, and texture (tactile sensation) contribute to our sense of taste

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