Unit 4 Special Senses Flashcards
general senses
Temperature Pressure Fine touch Pain (nociceptors) Proprioceptors of muscles and joints
special senses
Smell Sight Equilibrium Taste Hearing
vision
dominant sense
70% of body’s sensory receptors are in the eye
Half of cerebral cortex is involved in visual processing
eye structure
- wall with 3 layers
- internal cavities
- lens
fibrous layer (wall)
outermost layer; dense avascular connective tissue
sclera
cornea
sclera
- opaque posterior region
- Protects and shapes eyeball
- Anchors extrinsic eye muscles
- Posteriorly, continuous with dura mater (where optic nerve exits)
cornea
- Transparent anterior 1/6th of fibrous layer
- Forms clear window that lets light enter and bends light as it enters
- Epithelium covers both surfaces
a. Outer layer protects from abrasions
b. Inner layer, corneal endothelium, contains sodium pumps that help maintain clarity of cornea - Numerous pain receptors contribute to blinking and tearing reflexes
vascular layer
middle pigmented layer, aka uvea
- choroid region
- ciliary body
- iris
choroid region
- Posterior portion of uvea
- Supplies blood to all layers
- Brown pigment absorbs light to prevent light scattering (causes visual confusion)
ciliary body
- Anteriorly, choroid becomes ciliary body
- Thickened ring of tissue surrounding lens
- Consists of smooth muscle bundles, ciliary muscles, that contort shape of lens
- Capillaries of ciliary processes secrete fluid for anterior segment
- Ciliary zone (suspensory ligament) extends from ciliary processes to lens (holds position)
iris
- Colored part of eye, lies between cornea and lens, continuous with ciliary body
- Pupil: central opening that regulates amount of light entering eye
- Changes in emotional state: pupils dilate when subject matter is appealing or requires problem solving skills
pupil
- Close vision, bright light, cause sphincter papillae (circular muscles) to contact and pupils to constrict; parasympathetic control
- Distant vision, dim light cause dilator papillae (radial muscles) to contract and pupils to dilate; sympathetic control
retina (inner layer)
originates as an out pocketing of brain contains: Millions of photoreceptor cells that transduce light energy Neurons Glial cells
outer pigmented layer of retina
- single-cell-thick lining next to choroid, extends anteriorly, covering ciliary body and iris
- Absorbs light and prevents its scattering
- Phagocytes photoreceptor cell fragments
- Stores vitamin A
inner neural layer
- transparent layer that runs anteriorly to margin of ciliary body; anterior end has serrated edges called ora serrata
- composed of neurons: photoreceptors, bipolar cells, ganglion cells
a. Signals spread from photoreceptors to bipolar cells to ganglion cells
b. Ganglion cell axons exit eye as optic nerve - Optic disc
- Has quarter-billion photoreceptors called rods and cones
optic disc
where optic nerve leaves eye, lacks photo receptors (blind spot)
rods
- Dim light, peripheral vision receptor
- More numerous and more sensitive to light than cone
- No color vision or sharp images
- Numbers greatest at periphery
cones
- Vision receptor for bright light
- High-resolution color vision
- Macula lutea at posterior pole lateral to blind spot (mostly cones)
- Fovea centralis
fovea centralis
tiny pit in center of lacuna luted that contains all cones, best visual acuity; eye movement allows us to focus in on object so fovea can pick it up
aqueous humor
clear fluid around lens
vitreous humor
gelatinous mass of transparent connective tissue
lens
separates internal cavity into anterior and posterior segments
focuses light
external ear
auricle (pinna) external acoustic meatus (auditory canal) tympanic membrane (ear drum)
auricle
shell-shaped structure surrounding ear canal that functions to funnel sound waves into auditory canal
a. Helix: cartilaginous rim
b. lobule: fleshy earlobe
external acoustic meatus
- Short curved tube lines with skin bearing hairs, ceruminous glands (ear wax)
- Transmits sound waves to eardrum
tympanic membrane
- Boundary between external and middle ears
- Thin, translucent connective tissue membrane
- Vibrates in response to sound
- Transfers sound energy to bones of middle ear
middle ear
small air filled cavity
- pharyngotympanic (auditory) tube
- auditory ossicles
pharyngotympanic tube
- connects middle ear to nasopharynx
- Formally called eustachian tube
- Usually flattened tube, but can be opened. By yawning or swallowing to equalize pressure in middle ear cavity with external air pressure
a. Tympanic membrane cannot vibrate efficiently if pressures on both sides are not equal
b. Sounds distorted
auditory ossicles
A. smallest bones in tympanic cavity, named for their shape
1. Malleus: the hammer is secured to eardrum
2. Incus: anvil
3. Stapes: stirrup base fits into oval window
B. Synovial joints allow malleus to articulate with incus, which articulates with stapes
C. Suspended by ligaments; transmit vibratory motion of eardrum to oval window
D. Tensor tympani and stapedius muscles contract reflexively in response to loud sounds to prevent damage to hearing receptors
internal ear
aka labyrinth, located in temporal bone behind eye socket
- Bony labyrinth
- membranous labyrinth
bony labryrinth
system of tortuous channels and cavities through bone, filled with perilymph fluid similar to CSF
- vestibule
- semicircular canals
- cochlea
vestibule
- Central egg-shaped cavity of bony labyrinth
- Sacs house equilibrium receptor regions (maculae) that respond to gravity and changes in position of head
a. Saccule is continuous with cochlear duct
b. Utricle is continuous with semicircular canals
semicircular canals
- Three canals oriented in 3 planes: anterior, lateral, posterior. Anterior/posterior at right angles to each other, lateral is horizontal
- Membranous semicircular ducts line each canal and communicate with utricle
- Ampulla
ampulla
enlarged area of ducts of each canal that houses equilibrium receptor region called crista ampullaris; receptors respond to angular (rotational) movement of the head
cochlea
1,. small, spiral, conical, bony chamber, size of split pea
- Extends from vestibule
- Coils around bony pillar (modiolus)
- Contains cochlear duct, which houses spiral organ (organ of Corti) and ends at cochlear apex
cochlea cavity chambers
- Scala vestibule: above oval window, contains perilymph
- Scala media (cochlear duct): contains endolymph
- Scala tympani: terminates at round window; contains perilymph
- Scalae tympani and vestibule are continuous with each other at helicotrema (apex)
Vestibular membrane
‘roof’ of cochlear duct that separates scala media from scala vestibule
Spiral organ
- contains cochlear hair cells functionally arranged in one row of inner hair cells and 3 rows of outer hair cells; hair cells are sandwiched between tectorial and basilar membranes
- Cochlear branch of cranial nerve VIII runs from spiral organ to brain
membranous labyrinth
series of membranous sacs and ducts contained in bony labyrinth; filled with potassium rich endolymph
