Chapter 15: The Special Senses Flashcards
The Eye and Vision
vision is dominant sense with 70% of all sensory receptors in the eyes
Eyebrows
shade eyes from sun; helps keep perspiration (sweat) out of the eye
Corrugator Supercili
draws the eyebrows medially
Orbicularis Oculi
depresses eyebrows
Frontal Belly
elevates eyebrows
Eyelids
aka palpebrae; skin covered folds supported by tarsal plates; eyelashes project from free margin of each eyelid; blink every 3-7 secs (helps spread accessory structure secretions, keeping eye moist)
Levator Palpebrae Superioris
raises eyelid to open eye
Lacrimal Caruncle
fleshy elevation in medial corner of eye; produces sandmans eye sand (the crusties)
Tarsal Glands
located within tarsal plates; produces oily secreation (lubricates eye; prevents lids from sticking together)
Sebaceous glands of eyelash follicles…
keeps eyelashes flexibile
What is a chalazion?
inflammed tarsal galnd and is PAINLESS
What is a sty?
inflammation of sebaceous gland of eyelash; PAINFUL
Conjunctiva
transparent mucous membrane; produces a lubricating mucus (keeps eyelids from drying out)
Palpebral Conjunctiva
lines eyelids
Bulbar Conjunctiva
covers surface of eyeball with exception of cornea
What is pink eye?
inflammation of conjunctiva bc of bacteria or virus
What is conjunctivitis?
inflammation of conjunctiva
Lacrimal Apparatus
consists of lacrimal gland (produces tears) and ducts draining tears into nasal cavity
Tears
contain mucus, antibodies and lysozyme (bacterial killing enzyme)
Flow of Tears
lacrimal gland to eyeball to lacrimal puncta (tear holes) to lacrimal canaliculi to lacrimal sac to nsaolacrimal duct to nasal cavity
Extrinsic Eye Muscles
attach to surface of the eye; skeletal muscles that control movement of the eyeball; lateral rectus, medial rectus, superior rectus, inferior rectus, inferior oblique, superior oblique
Lateral Rectus
moves eye laterally; controlled by cranial nerve VI (abducens)
Medial Rectus
moves eye medially; controlled by cranial nerve III (oculomotor)
Superior Rectus
elevates eye and turns it medially; controlled by cranial nerve III (oculomotor)
Inferior Rectus
depresses eye and turns it medially; controlled by cranial nerve III (oculomotor)
Inferior Oblique
elevates eye and turns it laterally; controlled by cranial nerve III (oculomotor)
Superior Oblique
depresses eye and turns it laterally; controlled by cranial nerve IV (trochlear)
What is Diplopia?
double vision; left and right eye not coordinating properly
What is strabismus?
congenital; weakness in 1 or more extrinsic eye muscles; treated by therapy or putting an eyepatch over the good eye
Fibrous Layer of the Eye
outermost layer; consists of dense avascular connective tissue
Sclera
white of eye; protects and shapes eye ; anchors extrinsic eye muscle
Cornea
transparent, anterior most region; contains nociceptors; only tissue in body that can be transplanted with little risk of rejection
Vascular Layer
aka uvea; pigmented layer consisting of choroid, ciliary body and iris
Choroid
vascular, dark brown membrane; nourishes alll eye layers; absorbs light preventing it from scattering
Ciliary Body
thickened ring of tissue around iris; ciliary muscle: controls lens shape; Ciliary Process: folds that secrete aqueous humor; Suspensory Ligaments: (ciliary zonule) thin fibers connecting lens to ciliary process
Iris
colored portion of the eye anterior to lens; contains muscles (sphinctor and dilator pupillae) that alter size of pupil to regulated amount of light entering the eye
Sphincter Pupillae
constricts pupil; bright light and close vision
Dilator Pupillae
pupil dilates; dim light and far vision
Retina
innermost layer; delicate; extends anteriorly to ora serrata; consists of two layers: pigmented and neural layer
Pigmented Layer
single layer of cells adjacent to choroid; absorbs light preventing it from scattering
Neural Layer
contains 3 main types of neurons: photorecptors (rods and cones; more rods than cones), bipolar cells, and ganglion cells
What is a detached retina?
photoreceptors detach from pigmented layer; pigmented layer nourishes photoreceptors
Optic Disc
blind spot; region of eye where optic nerve and blood vessels enter the eye; lacks photoreceptors
The choroid nourishes….
the upper part of the photoreceptors; central artery nourishes remaining cells of the retina
Macula Lutea
lateral to optic disc; region of mostly cones
Fovea Centralis
cones only; region of greatest visual activity
Cone Density and Rod Density
cone density decreases and rod density increases as you move away from macula lutea
Suspensory Ligaments Divides the Eye into 2 Main Compartments…
posterior segment and anterior segment
Posterior Segment
contains gel-like vitreous humor which functions to transmit light, support lens, hold neural layer of retina against pigmented layer
Vitreous humor is…
formed in the embryo and retained for life; does not regenerate
Anterior Segment
contains watery aqueous humor which transmits light, supplies nutrients and O2 to lens and cornea, carries metabolic wastes away; it forms and drains CONTINUOUSLY (unlike vitreous humor)
Anterior Segment subdivided…
by iris into 2 chambers: anterior chamber (in front of lens) and posterior chamber (kinda where suspensory ligaments are)
What is Glaucoma
to much aqueous humor and puts pressure on lens which pressures the vitreous humor which in turn pressures the photoreceptors which can cause damage
ADD CIRCULATION OF AQUEOUS HUMOR
Lens
transparent, biconvex, flexible structure; avascular; held in place by suspensory ligaments; enlarges throughout life; becomes denser and less elastic as we age
What are Cataracts?
clouding of lens (NOT the cornea); smoking and sun exposure increases risk
Photoreceptors detect…
wavelengths of visible light (400-700 nm) which is a small portion of the electromagnetic spectrum; gama, xray, and UV is damaging; infrared, micro, and radio waves are harmless
Properties of Light
consists of photons (packets of energy); when photons strike an object they can be reflected, absorbed or transmitted; reflected wavelengths give objects their color; white objects reflect all wavelengths of light; black absorbs all wavelengths of light; light travels in a straight line at a constant speed, however speed changes as it passes through transparent media that have different densities; it speeds up when it passes into a less dense medium and slows down when it passes into a denser medium; because of difference in speed light is refracted
Lens of our Eye is….
convex; light is bent as it passes through, converging behind the lens at a focal point
The more convex the lens is…
the shorter the focal distance
The less convex the lens is…
the longer the focal distance
What is the image formed by the lens called?
real image; it is upside down and reverse
Pathway of Light
cornea to aqueous humor to pupil to lens to vitreous humor to ganglion cells to bipolar cells to photoreceptors
Light Refracts when it
enters the cornea, enter the lens and exists the lens; light refracts in the eye a total of three times
What changes shape to focus images onto the retina?
lens
What changes the shape of the lens?
ciliary muscle and ciliary zonule (suspensory ligament)
Relaxation of ciliary muscle…
tightens suspensory ligaments allowing lens to flatten
Contraction of ciliary muscle…
loosens suspensory ligaments and allows lens to bulge
Focusing on Distant Objects
> 20 ft away; the lens flattens for distance vision; sympathetic input relaxes the ciliary muscles; “far point of vision” (lens completely flattened) aout 20 ft away; eyes are best adapted for distance vision because it is less work (muscles do not need to contract)
Focusing on Nearby Objects
< 20 ft away; lens bulges for close vision, parasympathetic input contracts the ciliary muscles; involves 3 simultaneous events: accommodation- increasing the refractory power of the lens by contracting the ciliary muscle; 2) pupillary constriction- (accommodation pupillary reflex) prevents the most divergent light rays from entering the eye which would cause blurred vision; 3) convergence of eyeballs- medial rectus muscles of both eyes contracted; “near point vision” (lens completely rounded) about 4 inches (but less in children)
Why is viewing close objects more tiring than viewing distant objects?
requires a lot of muscle work
Myopic Eye
eye too long; the images are focused in front of retina; concave lenses needed to move focal point further back; nearsighted (can see near things)
Hyperopic Eye
eye is too short; focal point behind retina; convex lens needed to move focal point forward; farsighted (can see far things)
What is an astigmatism?
the lens or cornea is not shaped properly
Rods
more numerous; non color vision; dim light (high sensitivity); low accuracy; mostly in peripheral retina
Cones
color vision; low sensitivity (function in bright light); high acuity (clear vision); less numerous; mostly in central retina
Visual Pigment
formed when retinal (light absorbing pigment made from vitamin A) combines with different types of opsins (proteins)
Visual Pigments in Rods
retinal + rodopsin = phodopsin
Visual Pigments in Cones
retinal + S coneopsin = blues cones; retinal + M coneopsin = green cones; retinal + L coneopsin = red cones
What is colorblindness?
genetic x linked recessive disorder; ren/green most common
Light Adaptation
occurs when you move from dark into bright light; flood of white light bc retina is “set” for dim light; rod system shuts down; cones activated rapidly (5-10 mins)
Dark Adaptation
occurs when we move from well lit area to darkness; complete blackness; cones stop functioning due to low light; rods need more time to regenrate rhodopsin (20-30)mins
Retinitis Pigmentosa
disease that destryos rods; main cause of night blindness in US
What is the Visual Pathway?
photoreceptors to bipolar cells to ganglion cells to optic nerve (made of ganglion axons) to optic chiasma to optic tracts to thalamus to primary visual cortex
Each primary visual cortex receives input from…
both eyes
Right Visual Cortex receives…
input from left visual field (temporal photorecptors) of right eye and medial from left)
Left Visual Cortex recieves…
input from right visual field (temporal photoreceptors of left eye and medial photoreceptors of right eye)
Olfactory Receptors
are chemorecptors; respond to odorants (volatile chemicals) dissolved in fluids of the nasal cavity
Olfactory Epithelium
covers the superior nasal conchae; consists of olfactory neurons (ciliated bipolar neurons; life span of 30-60 days); support cells (produce mucus); olfactory stem cells (differentiate to replace olfactory neurons)
What is the olfactory pathway?
olfactory neurons to olfactory nerves (pass through cribriform plate of ethmoid) to olfactory bulb to olfactory tract to primary olfactory cortex (in uncus of temporal lobe); olfactory info also routed to limbic system where emotional responses to odors are elicited
Anosmia
inability to smell; typically results from head injuries that tear olfactory nerves or nasal cavity infection
Gustation Receptors
chemoreceptors; respond to food chemicals dissolved in saliva
Taste Bud Structure
most located on papillae (raised areas) on tongue ; consists of gustatory epithelial cells (receptor cells with gustatory cells and have a life span of 7-10 days); basal epithelial cells (differentiate to replace gustatory epithelial cells)
Basic Tastes
sweet, sour, umami, salts, bitter; taste is 80% smell
Gustatory Pathway
taste buds to crnaial nerves VII, IX and X to medulla oblongata to thalamus to gustatory cortex (insular lobe); gustatory info also routed to limbic system where we gain an appreciation of what we are tasting
External (outer) Ear
consists of auricle and external acoustic meatus
Auricle
consists of elastic cartilage; funnels sound waves itno the external acoustic meatus
External Acoustic Meatus
channel extending from aurcile to tympanic membrane (eardrum); lined with sebaceous glands and ceruminous glands which secrete cerumen (earwax) (which traps forein materials and repels insects)
The tympanic membrane…
separates external ear and middle ear and is therefore not part of either
What are the three regions of the ear?
external ear, middles ear, and internal ear
Auricle
consits of elastic cartilage; funnels sound waves into the external acoustic meatus; part of external ear
External Acoustic Meatus
channel extending from auricle to tympanic membrane (eardrum); lined with sebaceous glands and ceruminous glands which secrete cerumen (earwax); which protects against foreign materials and repels insects
Middle Ear
tympanic cavity; air filled cavity in temporal bone; medial wall has 2 openings: oval window (superior) and round window (inferior); cavity connected to nasophaynx by pharynotympanic tube (equalizes air pressure in cavity with external ear pressure)
What is otitis media?
middle ear infection; typically caused from something that caused a sore throat and it traveled up the pharyngotympanic tube
The middle ear contains…
auditiory ossicles: malleus, incus, and stapes; function to amplify sound and transmit vibrations to oval window
Tensor Tympani and Strapedius Muscles
contract reflexivley in response to loud sounds (limits vibrations to protect auditory receptors)
Internal Ear
aka labyrinth; consits of a bony labyrinth and membranous labrynth
Bony Labyrinth
cavities within temporal. bone that contain perilymph
Membranous Labyrinth
interconnected membranous sacs within bony labyrinth containing endolymph
What are the three regions of the bony labyrinth?
vestibule, semicircular canals and cochlea
Vestibule
central oval cavity; contains 2 connected membranes sacs suspended in perilymph, the utricle and saccule which house maculae (static equilibrium receptors; respond to head position relative to gravity and linear acceleration)
Semicircular Canals
anterior, posterior, and lateral; contain membranous semicircular ducts that form ampullae (bulges) at junction with utricle; each ampulla houses a crista ampullaris (dynamic equilibrium receptor; responds to rotations/angular acceleration of head)
Cochlea
spiral, bony cavity; extends from vestibule and coils about 2 1/2 turns around bone modiolus; running through center of cavity is the membranous cochlear duct
What three chambers is the cochlea divided into?
scala vestibuli; cochlear duct, and scala tympani
Scala Vestibuli
part of bony labyrinth; begins at oval window; contains perilymph
Cochlear Duct
scala media; middle chamber; part of membranous labyrinth; houses spiral organ (receptor for hearing); contains endolymph
Scala Tympani
part of bony labyrinth; ends at round window; contains perilymph
Vestibular Membrane
separates scala vestivuli from cochlear duct
Basilar Membrane
separates cochlear duct from scala tympani
Scala vestibuli is continous…
with scala tympanu at apex of cochlea
Sound
pressure disturbances that travel through a medium; speed of sound is slower than light; sound must travel through a medium (fastest in solids; slowest in air)
Frequency
quality of sound; number of waves per second (hertz, Hz); human range is 20-20000 hz; greatest sensibility is 1500-4000 hz; frequency is perceived by the brain as pitch
Amplitude
loudness of sound; height of waves measured in decibels (dB); human range is 0dB (barely audible) to > 120 dB (threshold of pain); perceived by the brain as intensity ; severe hearing loss occurs at frequent or prolonged intensities (>90dB)
Order of Sound through the Ear
auricle to external acoustic meatus to tympanic membrane to malleus to incus to stapes to oval window to scala vestibuli thru the cochlear duct to basilar membrane which vibrates
Different sound frequencies cross basilar membrane at different locations
low frequency sounds cross near apex; medium frequency sounds cross near middle; high frequency sounds cross near base
Transduction of Sound
occurs within spiral organ as basilar membrane deflects (bends) stereocilia of inner hair cells
Hairs pivoting TOWARDS tallest hair results in…
increase hair cell depolarization which leads to increase neurotransmitter release which increases action potential in cochlear nerve
Hair pivoting AWAY from tallest hair results in…
hair cell hyperpolarization which leads to decrease in neurotransmitter release which decreases action potential in cochlear nerve
Outer hair cells act on…
basilar membrane; amplifies motion of basilar membrae which increases responsiveness of inner hair cells; helps prevent loud sounds from damaging inner hair cells by dampering motion of basilar membrane
The Auditory Pathway
inner hair cells to bipolar neurons of cochlear branch of vestibulocochlear nerve to medulla oblongata to thalamus to primary auditory cortex (in temporal lobe); each auditory cortex receives info from both ears
What two regions are involved with equilibrium?
vestibule (receptors are macula) and semicircular canals (receptors are cristae ampullaris)
Maculae
located within utricle and saccule; each consists of supporting cells; ahir cells with protruding stereocilia (hairs) and 1 kinocilium embedded in an overlying gel-like membrane studded with otoliths (ear stones)
Static Equilibrium Receptors
maculae; monitor linear (straight line) acceleration and position of head with respect to gravity; macula in utricle is horizontal–> hairs are vertical and detect straight line movemet in the horizontal plane; macula in saccule is vertical–> hairs are horizontal and detect straight line movement in vertical plane
Cristae Ampullaris
1 located witin ampulla of each semicircular canal; each consists of hair cells with protruding hair bundles embedded in an overlying gel-like cupula; supporting cells
Dynamic Equilibrium Receptors
monitor changes in rotational (angular) movement of head; crista ampullaris
The Equilibrium Pathway
LOOK AT CHART
Conduction Deafness
occurs when something hampers sound info from reaching internal ear
Sensorineural Deafness
results from damage to hearing neural structures (hair cells, nerves, auditory cortex)
