CH 15. THE SPECIAL SENSES

olfaction:

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\: interaction of chemicals with sensory receptors 

\: **sense of smell =** in the response to odorants entering the nasal cavity 

olfactory epithelium:

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lines the small superior part of the nasal cavity, contains 10 million olfactory neurons 

olfactory neurons:

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\: bipolar neurons with dendrites extending to the epithelial surface of the nasal cavity

\: distal ends are olfactory hairs (cilia) 

\: ^^replaced often, every two months^^

\: %%most exposed nerve endings%% 

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olfactory hairs:

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\: bulbous enlargements with long, specialized cilia

\: lie in a thin mucous film on the epithelial surface 

(keeps it moist, traps, dissolves, and removes from epithelium) 

airborne odorants can stimulate an action potential in olfactory nerves:

are dissolved in the mucous and bind to olfactory receptors on olfactory hairs

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olfactory receptors:

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\: odorants must be dissolved in fluid to reach the olfactory receptors 

\: receptors activate G proteins opening the ion channels, depolarization, and production of action potentials in olfactory neurons 

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what cranial nerve is involved in transmission of olfactory info:

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olfactory nerve (CN 1) 

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olfaction - neuronal pathway:

\: axons form olfactory nerves which pass through olfactory foramina into the olfactory bulb where they synapse with interneurons 

\: interneurons send AP to brain via olfactory tracts 

(bypass the thalamus = rare)

areas of the brain where olfaction is processed:

\: each olfactory tract terminates in the olfactory cortex

\- olfactory cortex = located in the temporal and frontal lobes

list the primary odors:

\- camphor (e.g. moth balls) \n - musk \n - floral \n - peppermint \n - ethereal (e.g. fresh pears) \n - pungent \n - putrid

list types of papillae:

\- filiform papillae

\- vallate papillae

\- fungiform papillae

\- foliate papillae 

filiform papillae:

filament-shaped, most numerous, no taste buds, gives tongue its rough surface

\- enables tongue to manipulate food

vallate papillae:

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largest, least numerous, 8-12 in V along border between anterior & posterior parts of tongue

\- contains taste buds

fungiform papillae:

mushroom-shaped, scattered irregularly over the superior surface of tongue, look like small red dots interspersed among filiform

\- contains taste buds

foliate papillae:

leaf-shaped, in folds on sides of tongue, decrease in number w/age

\- contain **most sensitive taste buds**

taste buds:

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\: supporting structures that surround taste (gustatory cells) 

\: oval structures embedded in the epithelium of the papillae (small raised areas on the surface tongue) 

\: contain **taste cells** 

taste cells:

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\: sensory cells, detects taste stimuli 

\: %%microvilli = taste hairs which extend into tiny openings in the epithelium called taste pores%% 

\: ^^contain basilar cells & supporting cells^^ 

(replaced every ten days) 

taste cells located:

tongue, palate, lips, & throat

five major tastants:

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salty, sour, sweet, bitter, umami

salty:

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\: stimulated by **Na+** 

\: **most sensitive receptors on tip of tongue** 

\: shares low sensitivity with sweet 

\: craved by humans 

sour:

\: stimulated by **acids** 

\: most sensitive receptors on lateral aspects of tongue 

sweet:

\
\
\: stimulated by sugars, some carbs, some proteins 

\: sensitive receptors on tip of tongue 

\: l**owest sensitivity** with salty 

\: craved by humans 

bitter:

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\: stimulated by alkaloids 

\: sensitive receptors on posterior aspect 

\: **highest sensitivity** 

umami (savory):

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\: stimulated by the **amino acid glutamate** 

\: scattered sensitivity 

\: craved by humans 

action potential formed in taste cell:

\: tastings dissolve in saliva and enter taste pores causing depolarization of taste cells which release neurotransmitters that diffuse to sensory neurons

\: neurotransmitters stimulate action potentials in sensory neuron and are conducted to brain where taste is perceived

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cranial nerves involved in transmission of gustatory information:

^^facial nerve (VII): carries taste sensation from anterior 2/3 of tongue^^ 

%%glossopharyngeal nerve (IX): carries taste sensations from the posterior 1/3 of tongue%% 

@@vagus nerve (X): carries taste sensations from the epiglottis@@ 

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neural pathways for taste:

extend from **medulla oblongata** -- to the **thalamus** -- to the **taste area of the cerebral cortex**

external ear:

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\: extends from the outside of the head to the tympanic membrane 

\: involved in hearing 

contains:

\- auricle (pinna)

\- external acoustic meatus

\- tympanic membrane (eardrum)

external ear

auricle (pinna):

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fleshy part that collects sound waves and directs them to the external acoustic meatus 

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external ear

external acoustic meatus:

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\: passageway that transmits sound waves to tympanic membrane 

\: lined with hairs and ceruminous glands (produce cerumen = earwax) 

(prevent foreign objects from enter the ear) 

middle ear:

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\: small, air filled space mucosa-lined cavity 

\: flanked laterally by the eardrum 

\: flanked medially by the oval and round windows 

\: ^^contains 3 small bones = malleus, incus and stapes^^ 

(transmit vibratory motion of eardrum to oval window) 

\: dampened (vibrations from loud noises) by the tensor tympani and stapedius muscles 

contains:

\- auditory tube:

middle ear

auditory tube:

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\: connects middle ear to pharynx 

\: equalizes pressure in the middle ear cavity with external air pressure

inner ear:

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set of fluid-filled chambers medial to middle ear

contains: 

**-** bony labyrinth

\- membranous labyrinth

\- lymphs 

inner ear

bony labyrinth:

**:** chambers in temporal bone 

contains:

\- cochlea = hearing

\- vestibule = balance

\- semicircular canals = balance

inner ear

membranous labyrinth:

\: tunnels and channels within the bony labyrinth 

inner ear

endolymph:

\: located within membranous labyrinth

inner ear

perilymph:

\: located within space between membranous labyrinth and periosteum of bony labyrinth

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functions of fluids in inner ear:

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\: the movement of the fluid in the inner ear causes the hair cells in the cochlea to bend 

\: the hair cells change the movement into electrical impulses 

\: these electrical impulses are transmitted to the hearing (auditory) nerve and up to the brain, where they are interpreted as sound 

cochlea:

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\
\: spiral-shaped canal in the temporal bone 

\: divided by vestibular and basilar membranes 

\- scala vestibuli and scala tympani contain perilymph 

\- cochlear duct contains endolymph and spiral organ 

(spiral organ consists of inner and outer hair cells that attach to the tectorial membrane) 

(these hair cells contain very long projections called microvilli or sterocillia)

properties of sound:

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\: vibrations of matter create sound, vibrations consist of bands of compressed air followed by bands of less compressed air 

characteristics of sound:

**pitch, volume, and timbre** 

sound

pitch:

determined by the frequency of the sound wave

sound

volume:

determined by the amplitude of a sound wave

sound

timbre:

resonant quality (overtones) of sound

sound wave passing through the **external, middle and inner parts** of the ear to the **cochlea**:

(1) sound waves are funneled by the **AURICLE** down the **EXTERNAL AUDITORY CANAL** and @@cause the tympanic membrane to vibrate@@ 

(2) **TYMPANIC MEMBRANE** vibrations cause vibrations of the **AUDITORY OSSICLES** @@which are transferred to the oval window of the inner ear@@ 

(3) movement of stapes in the **OVAL WINDOW** @@causes the perilymph, vestibular membrane and endolymph to vibrate and produce movement of the basilar membrane@@

(4) movement of the basilar membrane causes the bending of stereo cilia of the inner hair cells in the **SPIRAL ORGAN**

the process where an action potential is generated within the cochlea in response to sound (stereocilia):

(5) the bending of the **STEREO CILIA** pulls on gating springs and @@opens K+ channels@@ 

(6) K+ ions enter the hair cell and result in @@depolarization@@ of the cell 

(7) depolarization causes the @@release of glutamate, generating action potentials in the sensory neurons associated with hair cells@@ 

(8) the round window @@dampens sound waves@@ and @@protects the inner ear from pressure build up@@ 

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what cranial nerve is involved in transmission of auditory information? 

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vestibulocochlear nerve 

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what areas in the brain is auditory information processed? 

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\: the temporal lobe contains the primary auditory cortex, which receives auditory information from the ears and processes the information so we understand what we're hearing 

static balance:

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associated with the vestibule and **evaluates the position of the head relative** and detects linear acceleration and deceleration 

dynamic balance:

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associated with the semicircular canals; **evaluates movements of the head**

what cranial nerve is involved in transmission of info related to balance to parts of the CNS & eyes?

oculomotor, trochlear, and abducens

accessory structures of the eye:

\- eyebrows

\- eyelids

\- conjunctiva

\- lacrimal apparatus

\- extrinsic eye muscles

eyebrows:

\: prevent sweat/perspiration from entering the eyes

\: help shade the eyes

eyelashes:

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\: project from the free margin of each eyelid

\: initiate reflex blinking

\: l__ubrication glands:__ meibomian glands & ciliary glands

eyelids (palpebrae):

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\: protect eyes from objects

\: lubricate eyes by spreading tears over their surface

\- __canthi:__ lateral & medial eyelids meet

conjunctiva (pink eye):

\: **mucous membrane**

\: covers the inner eyelid & anterior part of the eye

extrinsic eye muscles:

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\: six strap-like muscles that enable the eye to follow moving objects maintain shape of eyeball 

\: rectus muscles (4) = originate from annular ring 

\: oblique muscles (2) = move eye in vertical plane 

pathway of a tear from production to drainage:

(1) tears are produced in **LACRIMAL GLAND** and exit gland through several **LACRIMAL DUCTS** 

(2) the tears pass over the **SURFACE OF THE EYE**

(3) tears enter the **LACRIMAL CANALICULI** 

(4) tears are carried through the **NASOLACRIMAL DUCT** 

(5) tears enter **NASAL CAVITY** from the nasolacrimal duct

chambers of the eye:

\- anterior chamber

\- posterior chamber

\- vitreous chamber

anterior chamber of the eye:

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\: located between the cornea and the iris

\: contains aqueous humor

posterior chamber of the eye:

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\: located between the iris and the lens

\: contains aqueous humor

vitreous chamber of the eye:

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\: much larger than other two

\: located posterior to the lens 

\: contain vitreous humor 

three layers of the eye:

%%fibrous layer:%%

\- sclera

\- cornea

%%vascular layer:%%

\- choroid

\- ciliary body

\- iris

%%nervous layer:%%

\- retina

\- macula

\- optic disc

FIBROUS LAYER

sclera:

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white connective tissue that maintains shape of eyeball (posterior 4/5ths of the eye), site for muscle attachment 

FIBROUS LAYER

cornea:

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transparent and refracts light that enters the eye (anterior 1/5ths of the eye) 

VASCULAR LAYER

choroid:

prevents the reflection of light inside the eye, melanin contain pigment cells (appear black) 

VASCULAR LAYER

ciliary ring:

thickening ring of tissue surrounding the lens composed of smooth muscle bundles controls shape of lens 

VASCULAR LAYER

ciliary process:

attached to the suspensory ligament that holds the lens in place produces aqueous humor 

VASCULAR LAYER

iris:

a smooth muscle regulated by the automatic nervous system controls the amount of light entering the pupil 

NERVOUS LAYER

retina:

inner layer of eyeball

NERVOUS LAYER

macula:

\: area of ^^**greatest sensitivity to light**^^

\: highest concentration of photoreceptor cells

NERVOUS LAYER

optic disc:

\: location in which nerves exit, blood vessels enter the eye

\: ^^**no photoreceptor cells**^^

\: the “blind spot” of the eye

EYE CHAMBERS

aqueous humor:

\: fills anterior & posterior chambers

\: supports, nourishes, & removes wastes for cornea

EYE CHAMBERS:

vitreous humor:

\: fills vitreous chamber

\: contributes to intraocular pressure

\: helps maintain shape of eyeball

\: holds lens & retina in place

\: functions in refraction of light in the eye

what are the conditions where the pupil would be dilated or constricted?

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\: **sphincter pupillae and dilator pupillae** 

\: pupils also dilate when the subject matter is appealing or requires problem-solving skills 

CONDITIONS PUPILS DILATED/CONTSTRICTED

sphincter pupillae

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close vision and bright light, **pupils constrict**

CONDITIONS PUPILS DILATED/CONTSTRICTED

dilator pupillae:

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distant vision and dim light, **pupils dilate**

what are the structures responsible for focusing the eye?

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\- refracts light

\- cornea

\- aqueous humor

\- lens

\- vitreous humor

FOCUSING SYSTEMS OF EYE

refracts light:

light is passing through the focusing system is refracted to strike the retina

FOCUSING SYSTEMS OF EYE

cornea:

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responsible for most of the gross refraction of light 

FOCUSING SYSTEMS OF EYE

lens:

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fine adjustments to refraction are accomplished by changing the shape of the lens 

shape of lens:

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\: biconvex 

\: transparent 

\: flexible 

\: made of epithelium and lens fibers 

\: becomes more compact and dense and loses elasticity with age 

distant vision vs near vision

distant vision:

the lens is flattened and the image is focused on the retina

distant vison vs near vision

near vision:

the lens is more rounded and the image is focused on the retina

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what is the process that allows for an object to be brought into focus? 

\: accommodation by the lens:

* contraction of the ciliary muscles causes the lens to become more spherical, change in the lens shape enables the eye to focus on objects that are less than 20 feet away

\: constriction of the pupil = increases the depth of focus 

\: convergence of the eye = medial rotation of the eyes 

rods vs cones

rods:

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photoreceptors the responsible for **NON-COLOR vision**, vision in low illumination (night vision) 

rods vs cones

cones:

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photoreceptors that are responsible for %%**COLOR vision**%%, visual activity 

retina structure:

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**fovea centralis, remaining macula, periphery of retina bipolar and ganglion cells, and interneurons** 

optic disc vs macula/fovea centralis

optic disc:

\: “blind spot”

optic disc vs macula/fovea centralis

macula/fovea centralis:

\: area of greatest sensitivity to light

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what cranial nerve is involved in transmission of visual info?

optic nerve

what area of the brain is where vision is processed?

visual cortex in the occipital lobe

pathway action potential travels from rods & cones to visual cortex:

retina > optic chiasm > thalamus > visual cortex > each side of the brain

arrangement of visual field to binocular vision & depth perception:

\: @@left and right@@ **visual fields overlap** to produce binocular vision (depth perception) \n \n : %%monocular vision%% is where the **fields** **do not overlap**

list eye disorders:

\- myopia (nearsightedness)

\- hyperopia (farsightedness)

\- presbyopia

\- astigmatism

\- retinal detachment

\- color blindness

\- glaucoma

myopia (nearsightedness):

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\: ability to see **CLOSE** objects **CLEARLY** but **DISTANT** objects appear **BLURRY** 

\: defect of the eye's cornea being too optically too powerful or eyeball being too long 

\: can be fixed by lasik 

hyperopia (farsightedness):

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\: ability to see **DISTANT** objects **CLEARLY** but **CLOSE** objects appear **BLURRY**

\: defect of the eye's cornea being too optically weak or eyeball being too short 

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presbyopia:

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\: normal result of aging

\: result of lens becoming hard and less flexible 

\: corrected by reading glasses 

astigmatism:

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\: defect of eye in which the cornea or lens is not uniformly curved and the image is not sharply focused 

\: eyeball can become misshapen 

retinal detachment:

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\: common problem that can result in complete blindness 

\: defect of the eye due to a hole or tear occurring in the retina 

\: caused by severe blow to head, weight training, or shrinking of the vitreous humor