Anatomy II Lesson 2

What are the 5 special senses?
olfaction, gustation, vision, equilibrium, and hearing
olfactory epithelium
layer of olfactory organs that contains olfactory receptor cells, supprting cells, basal (stem) cells
lamina propria
layer of olfactory organs that contains areolar connective tissue, blood vessels, nerves, olfactory glands
olfactory glands
produce secretions that coat surfaces of olfactory organs
olfactory reception
involves detecting dissolved chemicals as they interact with odorant-binding proteins
olfactory pathways
axons leaving olfactory epithelium: penetrate cribriform plate of ethmoid and reach olfactory bulbs of cerebrum where first synapse occurs; axons leaving olfactory bulb: travel along olfactory tract to reach olfactory cortex, hypothalamus, and portions of limbic system
dissolved chemicals that stimulate olfactory receptors
provides info about the foods and liquids consumed
taste/gustatory receptors
distributed on tongue and portions of the pharynx and larynx; clustered into taste buds
filiform papillae
lingual papillae that do NOT contain taste buds; provide friction
fungiform papillae
lingual papillae that contain about five taste buds each
vallate papillae
lingual papillae that contain 100 taste buds each
What are the four types of lingual papillae?
filiform, fungiform, vallate, and foliate
gustatory receptor cells
extend taste hairs through taste pore; survive 10 days before replacement
taste buds
are monitored by cranial nerves that synapse within solitary nucleus of medulla oblongata then on to thalamus and primary sensory cortex
4 primary taste sensations
sweet, salty, sour, bitter
additional taste sensation with receptors sensitive to amino acids, small peptides, and nucleotides
water receptors
additional taste sensation located in the pharynx which detects the taste of water
salt and sour receptors
receptors that use chemically gated ion channels (Na+ or H+); stimulation produces depolarization of cell
sweet, bitter, and umami receptors
receptors activate G proteins called gustducins
taste sensitivity

1000x more sensitive to acids (sour) than sweet/salty

100x more sensitive to bitter than acids

What percentage of caucasians cannot taste phenylthiocarbamide (PTC)?
protein complexes that use second messengers to produce their effects
How do salt and sour channels work?
diffusion of sodium ions from salt solutions or hydrogen ions from acids/sour solutions into the receptor cell leads to depolarization of the membrane which stimulates the release of chemical neurotransmitters
How do sweet, bitter, and umami channels work?
receptors that produce these taste sensations are linked to G proteins that activate second messengers to stimulate the release of chemical neurotransmitters
tarsal glands
accessory structure of the eye that secretes lipid-rich product that helps keep eyelids from sticking together
lacrimal caruncle
mass of soft tissue containing glands producing thick secretions; contributes to gritty deposits after good night’s sleep
epithelium covering inner surfaces of eyelids (palpebral) and outer surface of eye (ocular)
inflammation/redness in eye caused by allergy, chemical irritation
lacrimal apparatus
produces, distributes, and removes tears
lacrimal gland
secrets lysozyme, an antibacterial enzyme
Tears pass through:
lacrimal punta, lacrimal canaliculi, lacrimal sac, nasolacrimal duct (to reach inferior meatus of nose)
large posterior cavity (eye)
filled with vitreous humor
smaller anterior cavity (eye)
filled with aqueous humor; consists of anterior chamber (anterior to iris) and posterior chamber (posterior to iris)
outer fibrous layer (eye)
sclera, cornea, corneal limbus
white of the eye
transparent anterior region of the eye
corneal limbus
border b/w cornea and sclera of the eye
vascular layer (uvea) functions
provides route for blood vessels, regulates amount of light entering eye, secretes/reabsorbs aqueous humor, controls shape of lens
vascular layer (eye)
iris, ciliary body, choroid
contains papillary muscles; changes diameter of pupil
ciliary body
contains ciliary processes and ciliary muscle that attaches to suspensory ligaments of lens; controls lens position and shape
delivers oxygen and nutrients to retina
retina (inner layer)
innermost layer of eye; consists of a thin outer layer called the “pigmented part” which absorbs light that passes through the “neural part” preventing light from bouncing back through neural part and producing visual “echoes”
photoreceptor that does not discriminate among colors of light; highly sensitive to light (allow us to see in dimly lit rooms, twilight, pale moonlight, etc)
photoreceptor that provides color vision; densely clustered in fovea, at center of macula
bipolar cells
act as signal couriers between photoreceptors (rods/cones) and the ganglion cells that carry these signals out of the eye and into the cortex
horizontal cells
extend across outer portion of retina
amacrine cells
where bipolar cells synapse with ganglion cells
optic disc
circular region just medial to fovea; origin of optic nerve; blind spot located here
abnormal blind spots (located in other areas than optic disc)
anterior chamber (of smaller anterior cavity of eye)
extends from cornea to iris
posterior chamber (of smaller anterior cavity of eye)
located b/w iris, ciliary body, and lens
aqueous humor
fluid circulates within eye; diffuses through walls of anterior chamber into scleral venous sinus before re-entering circulation
intraocular pressure
fluid pressure in aqueous humor; helps retain eye shape
decreased aqueous humor drainage causes increase in pressure; compresses optic nerve affecting peripheral vision first
large posterior cavity (vitreous chamber)
vitreous body/humor; helps stablize eye shape and supports retina
diabetic retinopathy
visual acuity decreases as photoreceptors die; caused by blockage of normal blood vessels, growth of abnormal blood vessels in retina, or blood leakage into cavity
lens fibers
cells in interior of lens; no nuclei or organelles; filled with crystallins
provide clarity and focusing power to lens
condition in which lens has lost its transparency
light refraction
bending of light by cornea and lens
condition where light passing through cornea and lens is not refracted properly; visual image is distorted
normal vision
hyperopia in older people as lenses lose elasticity
retinitis pigmentosa
most common inherited visual problem caused by mutation in visual pigment; results in photoreceptor cell death and blindness
color vision
integration of information from red, green, and blue cones
night blindness; can result from deficiency of vitamin A
visual pathways
photoreceptors to bipolar cell to ganglion cell and ends at visual cortex of cerebral hemispheres
optic radiation
bundle of projection fibers linking lateral geniculates with visual cortex
depth perception
ability to judge distance by comparing relative positions of objects b/w left and right-eye images
circadium rhythm
some fibers from lateral geniculate nucleus goes to hypothalamus; affects day-night cycle and other metabolic processes
external portion of ear; surrounds entrance to external acoustic meatus; protects opening of canal; provides directional sensitivity
external acoustic meatus
ear canal which ends at tympanic membrane (eardrum)
tympanic membrane
eardrum; separates external ear from middle ear
ceruminous glands
glands that secrete waxy material along external acoustic meatus
middle ear (tympanic cavity)
communicates with nasopharynx via auditory tube; permits equalization of pressure on either side of tympanic membrane; encloses 3 auditory ossicles (malleus, incus, stapes)
tensor tympani muscle
stiffens tympanic membrane (to protect ossicles and tympanum from loud noises)
stapedius muscle
reduces movement of stapes at oval window (to protect ossicles and tympanum from loud noises)
internal ear
contains fluid called endolymph; bony labrynth surrounds and protects membranous labrynth (subdivided into vestibule, semicircular canals, cochlea)
encloses saccule and utricle; hair cells provide sense of gravity and acceleration
semicircular canals
contain semicircular ducts; receptors stimulated by rotation of head
contains cochlear duct (elongated portion of membranous labrynth); receptors provide sense of hearing
hair cells
basic receptors of inner ear; provide info about direction and strength of mechanical stimuli
utricle and saccule
provide equilibrium sensations; detects vertical and horizontal acceleration
oval structures where hair cells of the utricle and saccule cluster
densely packed calcium carbonate crystals on surface of gelatinous mass
otolith (ear stone)
gelatinous matrix and statoconia
vestibular receptors (pathway for equilibrium sensations)
activate sensory neurons of vestibular ganglia; axons form vestibular branch of vestibulocochlear nerve (VIII); synapse within vestibular nuclei
functions of vestibular nuclei
integrate sensory info about balance and equilibrium from both sides of head; relay info from vestibular complex to cerebellum and cerebral cortex (provide conscious sense of head position and movement); send commands to motor nuclei in brain stem + spinal cord
superior colliculi
directs sensations of motion; attempt to keep focus on specific point
trouble controlling eye movements or keeping eyes focused on a single point; caused by damage to brain stem or inner ear
round window of cochlea
thin, membranous partition; separates perilymph from air spaces of middle ear
oval window of cochlea
formed of collagen fibers; connected to base of stapes
frequency of sound
determined by which part of cochlear duct is stimulated
intensity (volume) of sound
determined by the number of hair cells stimulated
pressure waves
consist of regions where air molecules are crowded together
distance between two adjacent wave troughs
number of soundwaves that pass fixed reference point at given time
number of cycles per second
our sensory response to frequency
intensity of sound wave
basilar membrane
separates cochlear duct (scala media) from tympanic duct (scala tympani); hair cells on membrane lack kinocilia; stereocilia of hair cells are in contact w/ overlying tectorial membrane
sound transductions steps
1. sound waves arrive at tympanic membrane
2. movement of tympanic membrane causes vibration of auditory ossicles
3. stapes vibrates and taps on oval window, establishing pressure waves in the perilymph of the scala vestibuli
4. pressure of waves distort basilar membrane on their way to the round window of scala tympani
5. vibration of basilar membrane causes hair cells to vibrate against tectorial membrane
6. info about region and intensity of stimulation is relayed to CNS over the cochlear branch of cranial nerve VIII
cochlear branch
formed by afferent fibers of spiral ganglion neurons
auditory pathways
enters medulla oblongata; synapses at dorsal and ventral cochlear nuclei; info crosses to opposite side of brain + ascends to inferior colliculus of midbrain; synapse in medial geniculate nucleus of thalamus; projection fibers deliver info to auditory cortex of temporal lobe of BOTH hemispheres
damage to auditory cortex
person will have normal auditory reflexes but will be unable to interpret sounds/patterns
buzzing, whistling, ringing sound absence of external stimulus

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