A&P 15: The Special Senses Flashcards
Special senses
vision, taste, smell, hearing, and equilibrium
Special sensory receptors
distinct receptor cells confined to the head region and are highly localized, either housed within complex sensory organs or in distinct epithelial structures (taste buds and olfactory epithelium)
Eye
in adults, a sphere with a diameter of about 2.5cm; only the anterior 1/6 of the surface is visible; rest is enclosed and protected by a cushion of fate and the walls of the bony orbit
Accessory structures of the eye
eyebrows, eyelids, conjunctiva, lacrimal apparatus, & extrinsic eye muscles
Eyebrows
short, coarse hairs that overlie the supraorbital margins of the skull; help shade the eyes from sunlight and prevent perspiration trickling down the forehead from reaching the eyes
Eyelids
anteriorly, the eyes are protected by these mobile structures; AKA palpebrae
Palpebral fissure
the eyelids are separated by this slit and meet at the medial and lateral angles of the eye
Medial and lateral commissures
the medial and lateral angles of the eye
Lacrimal caruncle
the medial commissure supports this fleshy eleveation; contains sebaceous and sweat glands and produces the whitish oily secretion (eye sand) that collects, especially during sleep
Tarsal plates
the eyelids are thin, skin-colored folds supported internally by these connective tissue sheets; support the orbicularis oculi and levator palpebrae superioris
Eyelashes
projecting from the free margin of each eyelid are these; the follicles of these are richly innervated by nerve endings so anything that touches them triggers reflex blinking
Tarsal glands
glands embedded in the tarsal plates; their ducts open at the eyelid edge just posterior to the eyelashes
Conjunctiva
transparent mucous membrane; major function is to produce a lubricating mucus that prevents the eyes from drying out
Palpebral conjunctiva
transparent mucous membrane that lines the eyelids
Bulbar conjunctiva
transparent mucous membrane that reflects (folds back) over the anterior surface of the eyeball; covers only the white of the eye, not the cornea; very thin; blood vessels are clearly visible beneath it
Conjunctival sac
when the eye is closed, a slitlike space occurs between the conjunctiva-covered eyeball and eyelids; where a contact lens lies; eye medications are often administered into its inferior recess
Lacrimal apparatus
consists of the lacrimal gland and the ducts that drain lacrimal secretions into the nasal cavity
Lacrimal gland
lies in the orbit above the lateral end of the eye and is visible through the conjunctiva when the lid is everted
Lacrimal secretion
the lacrimal gland continually releases this dilute saline solution (tears) into the superior part of the conjunctival sac through several small excretory ducts
Lacrimal canaliculi
blinking spreads the tears downward and across the eyeball to the medial commissure, where they enter these paired structures
Lacrimal puncta
“prick points;” tears enter the paired lacrimal canaliculi through these 2 tiny openings on the medial margin of each eyelid
Lacrimal sac
from the lacrimal canaliculi, tears drain into here
Nasolacrimal duct
from the lacrimal sac, tears drain into here, which empties into the nasal cavity at the inferior nasal meatus
Lysozyme
tears contain mucus, antibodies, and this enzyme that destroys bacteria
Extrinsic eye muscles
6 straplike muscles that control the movement of each eyeball; originate from the walls of the orbit and insert into the outer surface of the eyeball
Common tendinous ring
the 4 rectus muscles of the eye originate from this annular ring at the back of the orbit and run straight to their insertion on the eyeball
Superior, inferior, lateral and medial rectus muscles
4 of the 6 extrinsic eye muscles named after the locations and the movements they promote
Superior oblique muscle
originates in common with the rectus muscles, runs along the medial wall of the orbit, and then makes a right-angle turn and passes through the fibrocartilaginous loop called the trochlea suspended from the frontal bone before inserting on the superolateral aspect of the eyeball
Trochlea
fibrocartilaginous loop suspended from the frontal bone that the superior oblique muscle of the eye passes through
Inferior oblique muscle
originates from the medial orbit surface and runs laterally and obliquely to insert on the inferolateral eye surface; rotates the eye up and laterally
Diplopia
condition in which a person cannot properly focus the images of the same area of the visual field from each eye and so sees 2 images instead of one; AKA double vision; can result from paralysis or weakness of certain extrinsic muscles, neurological disorders, or it may be a temporary consequence of acute alcohol intoxication
Strabismus
“cross-eyed;” congenital weakness of the external eye muscles may cause this condition in which the affected eye rotates medially or laterally; to compensate, the eyes may alternate in focusing on objects
Eyeball
the eye itself; a slightly irregular hollow sphere; has poles
Anterior pole
most anterior point of the eye
Posterior pole
most posterior point of the eye
Fibrous layer
the outermost coat of the eyeball; composed of dense avascular connective tissue; has 2 obviously different regions - sclera and cornea
Sclera
forms the posterior portion and the bulk of the fibrous layer; glistening white and opaque; seen anteriorly as the “white of the eye;” tough, tendon-like structure protects and shapes the eyeball and provides a sturdy anchoring site for the extrinsic eye muscles; posteriorly, where it is pierced by the optic nerve, it is continuous with the dura mater of the brain
Cornea
the anterior 6th of the fibrous layer is modified to form this transparent structure, which bulges anteriorly from its junction with the sclera; forms a window that lets light enter the eye; major part of the light-bending apparatus of the eye
Vascular layer
pigmented middle coat of the eyeball; also called the uvea (“grape”); 3 regions - choroid, ciliary body, iris
Choroid
blood vessel-rich, dark brown membrane that forms the posterior 5/6 of the vascular layer; nourishes all eye layers; pigment produced by melanocytes - helps absorb light, preventing it from scattering and reflecting within the eye (which would cause visual confusion); incomplete posteriorly where the optic nerve leaves the eye
Ciliary body
anteriorly, the choroid becomes this thickened ring of tissue that encircles the lens; consists chiefly of interlacing smooth muscle bundles (ciliary muscles) which act to control lens shape
Ciliary muscles
chiefly forms the smooth muscle bundles of the ciliary body; act to control lens shape
Ciliary processes
near the lens, the posterior surface of the ciliary body is thrown into these radiating folds which secrete the fluid that fills the cavity of the anterior segment of the eyeball
Ciliary zonule (suspensory ligament)
extends from the ciliary processes to the lens; this halo of fine fibers encircles and helps hold the lens in its upright position
Iris
visible colored part of the eye; most anterior portion of the vascular layer; shaped like a flattened doughnut, it lies between the cornea and the lens and is continuous with the ciliary body posteriorly;
Pupil
round central opening of the iris; allows light to enter the eye
Retina
the innermost layer of the eyeball which originates as an outpocketing of the brain; contains millions of photoreceptors that transduce (convert) light energy, other neurons involved in processing light responses, and glia; 2 layers - outer pigmented layer & inner neural layer
Pigmented layer
outer layer of the retina; a single-cell-thick lining; abuts the choroid, and extends anteriorly to cover the ciliary body and the posterior face of the iris; pigmented cells absorb light and prevent it from scattering in the eye; pigmented cells also act as phagocytes participating in photoreceptor cell renewal and store vitamin A needed by photoreceptor cells
Neural layer
transparent inner layer of the retina; extends anteriorly to the posterior margin of the ciliary body
Ora serrata
“saw-toothed margin” where the neural layer of the retina meets the posterior margin of the ciliary body
Photoreceptors
most posterior type of neuron in the neural layer of the retina; signals are produced in response to light and spread from these
Bipolar cells
middle type of neuron in the neural layer of the retina; signals spread from photoreceptors to these
Ganglion cells
innermost type of neuron in the neural layer of the retina; signals spread from bipolar cells to these, where action potentials are generated
Optic disc
where the optic nerve exits the eye; blind spot
Fundus
posterior wall of the eye; optic disc is a weak spot because it is not reinforced by sclera
Blind spot
optic disc; lacks photoreceptors, so light focused on it cannot be seen
Rods
dim-light and peripheral vision receptors; more numerous and far more sensitive to light than cones, but do not provide sharp images or color vision
Cones
vision receptors for bright light; provide high-resolution color vision
Macula lutea
lateral to the blind spot of each eye, and located precisely at the eye’s posterior pole is this oval region with a minute pit; contains mostly cones
Fovea centralis
the minute pit in the macula lutea; contains only cones
Central artery & central vein of the retina
the inner 2/3 of the eye is served by these vessels, which enter and leave the eye through the center of the optic nerve
Posterior segment of the eye
larger segment of the eye; filled with vitreous humor
Vitreous humor
clear gel in the posterior segment of the eye that binds tremendous amounts of water, transmits light, supports the posterior surface of the lens, holds the neural layer of the retina firmly against the pigmented layer, contributes to intraocular pressure, helping to counteract the pulling force of the extrinsic eye muscles
Anterior segment of the eye
smaller front segment of the eye; the iris divides it into the anterior and posterior chambers
Anterior chamber
area of the eye between the cornea and the iris
Posterior chamber
area of the eye between the iris and the lens
Aqueous humor
the entire anterior segment of the eye is filled with this clear fluid similar in composition to blood plasma; forms and drains continuously and is in constant motion
Scleral venous sinus
aqueous humor drains into the venous blood via this unusual venous channel that encircles the eye in the angle at the corneoscleral junction
Glaucoma
condition in which the pressure within the eye increases to dangerous levels; compresses the retina and optic nerve; eventually results in blindness unless it is detected early
Lens
biconvex, transparent, flexible structure that can change shape to precisely focus light on the retina; enclosed in a thin, elastic capsule and held in place just posterior to the iris by the ciliary zonule; avascular (blood vessels interfere with transparency)
Lens epithelium
region of the lens confined to the anterior lens surface; consists of cuboidal cells that eventually differentiate into lens fibers
Lens fibers
fibers that form the bulk of the lens; packed tightly together; contain no nuclei and few organelles; contain transparent, precisely folded proteins (crystallins) that form the body of the lens
Crystallins
transparent, precisely folded proteins that form the body of the lens
Cataract
“waterfall;” clouding of the lens that causes the world to appear distorted, as if seen through frosted glass; some are congenital, but most result from age-related hardening and thickening of the lens or are a secondary consequence of diabetes mellitus; heavy smoking and frequent exposure to intense sunlight increase the risk
Electromagnetic radiation
includes all energy waves, from long radio waves to very short gamma waves and X rays
Visible light
our eyes respond to this part of the spectrum, with a wavelength of 400-700nm
Photons, quanta
light can be envisioned as these small particles or packets of energy
Visible spectrum
band of colors
Refraction
bending of a light ray; occurs when it meets the surface of a different medium at an oblique angle rather than at a right angle
Focal point
if the lens surface is convex (thickest at its center like a camera lens), the light rays bend so they converge/intersect at this single point
Real image
the image formed by a convex lens; inverted (upside down and reversed from left to right)
Far point of vision
distance beyond which no change in lens shape (accommodation) is needed for focusing
Emmetropic
an eye with normal vision
Accommodation
process that increases the refractory power of the lens
Near point of vision
the closest point on which we can focus clearly; represents the maximum bulge the lens can achieve
Presbyopia
in many people over 50, the lens is nonaccommodating; “old people’s vision”
Accommodation pupillary reflex
the sphincter pupillae muscles of the iris enhance the effect of accommodation by reducing the size of the pupil toward 2mm; mediated by parasympathetic fibers of the oculomotor nerves
Convergence
controlled by somatic motor fibers of the oculomotor nerves; medial rotation of the eyeballs by the medial rectus muscle so that each is directed toward the object being viewed; the closer the object, the greater the degree of this required
Myopia
“short vision;” occurs when distant objects focus in front of the retina rather than on it; can see close objects without problems because they can focus them on the retina, but distant objects are blurred; AKA nearsightedness
Hyperopia
AKA farsightedness; occurs when the parallel light rays from distant objects focus behind the retina; can see distant objects perfectly well because their ciliary muscles contract almost continuously to increase the light-bending power of the lens, which moves the focal point forward onto the retina; diverging light rays from nearby objects focus so far behind the retina that the lens cannot bring the focal point onto the retina even at its full refractory power
Astigmatism
refractory problem in which unequal curvatures in different parts of the cornea or lens also lead to blurry images
Phototransduction
process by which light energy is converted into a graded receptor potential
Outer segments
photoreceptors are modified neurons, but structurally they resemble tall epithelial cells turned upside down with their tips immersed in the pigmented layer of the retina; the tips are the receptive regions of rods and cones and are called this
Inner segment
a connecting cilium joins the outer segment of a rod or cone to this
Visual pigments (photopigments)
the outer segments contain an elaborate array of these that change shape as they absorb light; embedded in areas of the plasma membrane that form discs
Retinal
light-absorbing molecule; combines with proteins (opsins) to form 4 types of visual pigments; chemically related to vitamin A
Opsins
proteins that combine with retinal to form 4 types of visual pigments
Color blindness
due to a congenital lack of 1 or more cone pigments; X-linked; far more common in males than females; 8-10% of males have
11-cis-retinal
when bound to opsin, retinal has a bent/kinked shape called this
All-trans-retinal
when the pigment is struck by light and absorbs a photon, retinal twists and snaps into this new configuration
Rhodopsin
the visual pigment of rods is this deep purple pigment; its molecules are arranged in a single layer in the membranes of each of the 1000’s of discs in the rods’ outer segments
Bleaching of the pigment
the breakdown of rhodopsin to retinal and opsin
Transducin
G protein activated by rhodopsin; activates PDE (phosphodiesterase)
Cyclic GMP (cGMP)
broken down by PDE; in the dark, it binds to cation channels in the outer segments of photoreceptor cells, holding them open; this allows NA+ and Ca2+ to enter, depolarizing the cell to its dark potential (-40mV); in the light, it breaks down, the cation channels close, NA+ and Ca2+ stop entering the cell, and the cell hyperpolarizes to about -70mV
Light adaptation
occurs when we move from darkness into bright light
Dark adaptation
occurs when we go from a well-lit area into a dark one
Optic nerves
the axons of the retinal ganglion cells exit the eye here
Optic chiasma
a this X-shaped place, fibers from the medial aspect of each eye cross over to the opposite side and then continue on
Optic tracts
past the optic chiasma, fibers from the medial aspect of each eye cross over to the opposite side and then continue on via these
Lateral geniculate nuclei
the paired optic tracts sweep posteriorly around the hypothalamus and send most of their axons to synapse with neurons in this part of the thalamus; they maintain the fiber separation established at the chiasma, but they balance and combine the retinal input for delivery to the visual cortex
Optic radiation
axons of the thalamic neurons project through the internal capsule to form this of fibers in cerebral white matter
Primary visual cortex
the fibers in cerebral white matter project to this in the occipital lobes, where conscious perception of visual images occurs
Superior colliculi
some nerve fibers in the optic tracts send branches to the midbrain; one set of these fibers ends in these visual reflex centers controlling the extrinsic muscles of the eyes
Pretectal nuclei
ganglion cells in the retina respond directly to light stimuli and their fibers project to these nuclei, which mediate pupillary light reflexes
Suprachiasmatic nucleus
ganglion cells in the retina respond directly to light stimuli and their fibers project to this nucleus of the hypothalamus, which functions as the time to set our daily biorhythms
Depth perception
AKA 3D vision; the visual cortex fuses slightly different images delivered by the 2 eyes; an accurate means of locating objects in space
Striate cortex
AKA the primary visual cortex; receives the thick bundles of fibers coming in from the lateral geniculate nucleus; contains an accurate topographical map of the retina
Prestriate cortices
the striate cortex provides form, color, and motion inputs to visual association areas collectively called this
Chemoreceptors
respond to chemicals in an aqueous solution; the receptors for smell and taste are of this type
Olfactory epithelium
yellow-tinged patch (5cm^2) of pseudostratified epithelium, located in the roof of the nasal cavity
Olfactory sensory neurons
bowling pin-shaped receptor cells that aid in smell
Supporting cells
columnar cells which make up the bulk of the penny-thin epithelial membrane; contain a yellow-brown pigment similar to lipofuscin, which gives the olfactory epithelium its yellow hue
Olfactory stem cells
at the base of the olfactory epithelium lie these short cells
Olfactory cilia
substantially increase the receptive surface area; typically lie flat on the nasal epithelium and are covered by a coat of thin mucus produced by the supporting cells and by olfactory glands in the underlying connective tissue
Filaments of the olfactory nerve
the slender, nonmyelinated axons of the olfactory sensory neurons are gathered into small fascicles that collectively form this; they project superiorly through the openings in the cribiform plate of the ethmoid bone, where they synapse in the overlying olfactory bulbs
Olfactory bulbs
axons of the olfactory sensory neurons form the olfactory nerves that synapse in these overlying distal ends of the olfactory tracts
Mitral cells
the filaments of the olfactory nerves synapse with these second-order sensory neurons in complex structures called glomeruli
Glomeruli
“little balls”; axons from neurons bearing the same kind of receptor converge on a given type of these
Olfactory tracts
when mitral cells are activated, impulses flow from the olfactory bulbs via these, which are composed mainly of mitral cell axons, to the piriform lobe of the olfactory cortex
Taste buds
10,000 sensory organs for taste located on the tongue
Papillae
most taste buds are found on these peglike projections of the tongue mucosa that make the tongue surface slightly abrasive
Fungiform papillae
taste buds are located mainly on the tops of these mushroom-shaped projections scattered over the entire tongue surface
Foliate papillae
taste buds are located mainly in fungiform papillae and in the epithelium of the side walls of these projections & of the large round vallate papillate
Vallate papillae
large round projections where taste buds are found; least numerous papillae, 7-12 of them form an inverted V at the back of the tongue
Gustatory epithelial cells
receptor cells for taste; AKA taste cells
Gustatory hairs
long microvilli project from the tips of all gustatory epithelial cells; sensitive portions (receptor membranes) of the gustatory epithelial cells
Taste pore
gustatory hairs extend through this opening to the surface of the epithelium, where they are bathed by saliva
Basal epithelial cells
act as stem cells, dividing and differentiating into new gustatory epithelial cells
Facial nerve (VII)
a branch of this nerve (the chorda tympani) transmits impulses from taste receptors in the anterior 2/3 of the tongue
Glossopharyngeal nerve (IX)
the lingual branch of this nerve services the posterior 1/3 of the tongue and the pharynx just behind it
Vagus nerve (X)
taste impulses from the few taste buds in the epiglottis and the lower pharynx are conducted primarily by this nerve
Solitary nucleus
afferent fibers synapse in this nucleus of the medulla; from there impulses stream to the thalamus and ultimately to the gustatory cortex in the insula
External (outer) ear
consists of the auricle and the external acoustic meatus
Auricle
AKA pinna; what most people call the ear; the shell-shaped projection surrounding the opening of the external acoustic meatus; composed of elastic cartilage covered with thin skin and an occasional hair; function = funnel sound waves into the external acoustic meatus
Helix
rim of the auricle; somewhat thicker
Lobule
fleshy, dangling part of the helix of the auricle; lacks supporting cartilage; AKA earlobe
External acoustic meatus
auditory canal; short, curved tube that extends from the auricle to the eardrum
Ceruminous glands
modified apocrine sweat glands that secrete cerumen
Cerumen
earwax; provides a sticky trap for foreign bodies, repels insects
Tympanic membrane
eardrum; boundary between the outer and middle ears; thin, translucent, connective tissue membrane, covered by skin on its external face and by mucosa internally; shaped like a flattened cone; its apex protrudes medially into the middle ear
Middle ear
tympanic cavity; small, air-filled mucosa-lined cavity in the petrous portion of the temporal bone; flanked laterally by the eardrum and medially by the bony wall with 2 openings (the superior oval window and the inferior round window)
Oval window
superior opening in the petrous portion of the temporal bone
Round window
inferior opening in the petrous portion of the temporal bone
Epitympanic recess
superiorly, the tympanic cavity arches upward as this roof of the middle ear cavity
Mastoid antrum
canal in the posterior wall of the tympanic cavity; allows it to communicate with mastoid air cells housed in the mastoid process
Pharyngotympanic (auditory) tube
formerly called the eustacian tube; runs obliquely downward to link the middle ear cavity with the nasopharynx (superiormost part of the throat); the mucosa of the middle ear is continuous with that lining of the pharynx (throat)
Otitis media
middle ear inflammation; fairly common result of a sore throat, especially in children, whose pharyngotympanic tubes are shorter and run more horizontally; most frequent cause of hearing loss in children
Auditory ossicles
3 smallest bones in the body that span the tympanic cavity
Malleus
auditory ossicle AKA the hammer
Incus
auditory ossicle AKA the anvil
Stapes
auditory ossicle AKA the stirrup
Tensor tympani
tiny skeletal muscle arising from the wall of the pharyngotympanic tube, inserts on the malleus
Stapedius
tiny skeletal muscle running from the posterior wall of the middle ear to the stapes
Internal ear
the labyrinth; lies deep in the temporal bone behind the eye socket and provides a secure site for all of the delicate receptor machinery
Bony labyrinth
system of tortuous channels worming through the bone;
Membranous labyrinth
continuous series of membranous sacs and ducts contained within the bony labyrinth and following its contours
Perilymph
the bony labyrinth is filled with this fluid, which is similar to CSF and continuous with it
Endolymph
the membranous labyrinth is suspended in the surrounding perilymph and its interior contains this fluid, chemically similar to K+ rich intracellular fluid
Vestibule
central egg-shaped cavity of the bony labyrinth; posterior to the cochlea, anterior to the semicircular canals, flanks the middle ear medially; in its lateral wall is the oval window
Saccule
membranous labyrinth sac; small; continuous with the membranous labyrinth extending anteriorly into the cochlea; house equilibrium receptor regions (maculae) that respond to the pull of gravity and report on changes of head position
Utricle
membranous labyrinth sac, continuous with the semicircular ducts extending into the semicircular canals posteriorly; house equilibrium receptor regions (maculae) that respond to the pull of gravity and report on changes of head position
Semicircular canals
lie posterior and lateral to the vestibule; each defines about 2/3 of a circle; anterior, posterior, and lateral in each internal ear
Semicircular duct
snaking through each semicircular canal is this corresponding membranous duct, which communicates with the utricle anteriorly; each has an enlarged swelling at one end (ampulla)
Ampulla
enlarged swelling of a semicircular duct which houses an equilibrium receptor region called a crista ampullaris (“crest of the ___”); respond to angular (rotational) movements of the head
Cochlea
spiral, conical, bony chamber extending from the anterior part of the vestibule; coils for about 2 1/2 turns around a bony pillar (modiolus)
Modiolus
bony pillar that the cochlea coils around (2 1/2 turns)
Cochlear duct
running through the center of the modiolus like a wedge-shaped worm is this membranous duct, which ends blindly at the cochlear apex; houses the receptor organs of hearing
Spiral organ
organ of Corti; receptor organs of hearing, housed in the cochlear duct
Osseous spiral lamina
thin, shelflike extension of bone that spirals up the modiolus; with the cochlear duct, divides the cavity of the bony cochlea into 3 chambers
Scalae
chambers of the cochlea
Scala vestibuli
lies superior to the cochlear duct; continuous with the vestibule and abuts the oval window
Scala media
middle chamber of the cochlea; the cochlear duct itself
Scala tympani
chamber of the cochlea which terminates at the membrane-covered round window; inferior to the cochlear duct
Helicotrema
“hole in the spiral”; region where the perilymph chambers are continuous with each other at the cochlear apex
Vestibular membrane
the roof of the cochlear duct, separating the scala media from the scala vestibuli
Stria vascularis
the cochlear duct’s external wall; composed of an unusual, richly vascularized mucosa that secretes endolymph
Basilar membrane
plays a critical role in sound reception; narrow and thick near the oval window; gradually widens and thins as it approaches the cochlear apex
Sound
a pressure disturbance (alternating areas of high and low pressure) produced by a vibrating object and propagated by the molecules of the medium
Frequency
number of waves that pass a given point in a given time
Wavelength
the distance between 2 consecutive crests or troughs of a wave; constant for a particular tone; the shorter this is, the higher the frequency of the sound
Pitch
we perceive different sound frequencies as differences in this; the higher the frequency, the higher this is
Quality
characteristic of sound that enables us to distinguish between the same musical note played on different instruments (or sung); also provides the richness and complexity of sounds (and music) we hear
Amplitude
height of the sine wave crests; reveals a sound’s intensity, which is related to its energy, or the pressure differences between its compressed and rarefied areas
Loudness
refers to our subjective interpretation of sound intensity
Decibels (dB)
sound intensity and loudness are measured in these logarithmic units
Cochlear hair cells
one row of inner hair cells and 3 rows of outer hair cells; arranged functionally, sandwiched between the tectorial and basilar membranes
Cochlear nerve
division of the vestibulocochlear nerve (VIII); coil about the bases of the hair cells
Tectorial membrane
the longest stereocilia are enmeshed in this overlying, stiff, gel-like membrane
Spiral ganglion
impulses generated in the cochlea pass through this cluster, where the auditory bipolar cells reside, and along the afferent fibers of the cochlear nerve to the cochlear nuclei of the medulla
Cochlear nuclei
impulses generated in the cochlea pass through the spiral ganglion and to these nuclei of the medulla
Superior olivary nucleus
neurons project to this nucleus, which lies at the junction of the medulla and pons
Lateral lemniscus
axons ascend in this fiber tract to the inferior colliculus
Inferior colliculus
auditory reflex center in the midbrain
Medial geniculate nucleus
nucleus of the thalamus
Primary auditory cortex
provides conscious awareness of sound
Vestibular apparatus
the equilibrium receptors in the semicircular canals and vestibule are collectively called this; under normal conditions, they send signals to the brain that initiate reflexes needed to make the simplest changes in position as well as more complex moves
Maculae
“spots” in each saccule wall and one in each utricle wall; sensory receptor organs that monitor the position of the head in space; play a key role in controlling posture; respond to linear acceleration, but not rotation
Hair cells
each macula is a flat epithelial patch containing these cells having stereocilia plus one kinocilium that project into a gel-like mass
Supporting cells
these cells surround the macula’s scattered hair cells
Otolith membrane
the “hairs” of the hair cells are embedded in this overlying jelly-like mass studded with tiny stones (calcium carbonate crystals)
Otoliths
“ear stones”; calcium carbonate crystals that stud the otolith membrane; increase the membrane’s weight and its inertia
Vestibular nerve
the hair cells synapse with fibers of this nerve, whose endings coil around their bases; division of CN VIII
Superior & Inferior Vestibular Ganglia
the cell bodies of the sensory neurons are located in these clusters
Crista ampullaris
receptor for rotational acceleration; a minute elevation in the ampulla of each semicircular canal; excited by head movement (acceleration and deceleration)
Ampullary cupula
delicate, loosely organized network of gelatinous strands that radiate outward to contact the “hairs” of each hair cell
Vestibular nystagmus
complex of rather strange eye movements that occurs during and immediately after rotation; often accompanied by vertigo
Vestibular nuclei
major integrative center for balance
Cerebellum
integrates inputs from the eyes and somatic receptors (as well as from the cerebrum); coordinates skeletal muscle activity and regulates muscle tone to maintain head position, posture, and balance; its specialty = fine control of delicate postural movements and timing
Motion sickness
appears to be due to sensory input mismatches; visual inputs indicate your body is fixed, but vestibular apparatus detects movement (like when you are in a ship’s cabin)
Deafness
any hearing loss; conduction or sensorineural deafness
Conduction deafness
occurs when something hampers sound conduction to the fluids of the internal ear; most common causes are otitis media and otosclerosis
Otosclerosis
hardening of the ear; occurs when overgrowth of bony tissues fuses the base of the stapes to the oval window or welds the ossicles to one another
Sensorineural deafness
results from damage to neural structures at any point from the cochlear hair cells to and including the auditory cortical cells; typically results from the gradual loss of hair cells throughout life
Tinnitus
ringing or clicking sound in the ears in the absence of auditory stimuli; usually a symptom rather than a disease
Meniere’s Syndrome
a labyrinth disorder that seems to affect all 3 parts of the internal ear; the afflicted person has repeated attacks of vertigo, nausea, and vomiting; balance is so disturbed that standing erect is nearly impossible; may result from excessive endolymph that distorts the membranous labyrinth or a membrane rupture that allows the perilymph and endolymph to mix
Optic vesicles
by the 4th week of development, the eyes begin forming as these that protrude from the diencephalon
Optic cups
hollow optic vesicles indent to form these double-layered structures; their stalks form the optic nerves and provide a pathway for blood vessels to reach the eye interior
Lens vesicle
once an optic vesicle reaches the overlying surface ectoderm, it induces the ectoderm to thicken and then form this vesicle that pinches off into the cavity of the optic cup, where it becomes the lens
Otic placodes
the internal ears develop first, from thickenings of the surface ectoderm called this which lie lateral to the hindbrain on each side
Otic pit
the invagination of the otic placode
Otic vesicle
formed from the otic pit; detaches from the surface epithelium
Pharyngeal pouches
the middle ear cavity and pharyngotympanic tube of the middle ear develop from these lateral outpocketings of the endoderm lining the pharynx
Pharyngeal cleft
the external acoustic meatus and external face of the tympanic membrane of the external ear differentiates from this branchial groove, an indentation of the surface ectoderm
Presbycusis
type of sensorineural deafness; loss of the ability to hear high-pitched sounds; considered a disability of old age
