Anatomy Lecture Notes Chapter 16

Chapter 16 Lecture Outline

A. gustation - gustatory receptor cells are located in organs called buds

1. taste buds located in mucosa of mouth and most are on the sides of fungiform and circumvallate papillae

2. taste buds made of epithelial cells taste pores are openings in the surface of the

gustatory cells - receptor cells supporting cells - separate gustatory cells from each other basal cells - immature cells that replace the other cells

3. gustatory cells have microvilli on apical surface, just inside taste pore membrane covering microvilli contains receptors for sweet, salty, sour, bitter and (glutamate)

gustatory cells with sensory at base of taste bud

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Anatomy Lecture Notes Chapter 16

4. gustatory cells activated when molecules dissolved in saliva bind to membrane receptors on microvilli

gustatory cell releases neurotransmitter, which initiates action potential in sensory

5. afferent pathways:

VII - facial anterior 2/3 of IX - glossopharyngeal posterior 1/3 of tongue X - vagus and pharynx

sensory neurons terminate in in

B. olfaction - receptors located in olfactory epithelium 1. olfactory epithelium covers superior nasal conchae and superior nasal septum 2. olfactory epithelium contains olfactory cells receptors supporting cells columnar e. basal cells form new olfactory cells

3. olfactory cells

have apical that project to surface of mucosa olfactory cilia project from surface of olfactory epithelium the membrane of each olfactory cell covering the cilia contains one (out of about a possible 1000) type of olfactory receptor

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Anatomy Lecture Notes Chapter 16

the of the olfactory cells (cranial nerve I) project through the cribriform plate of the ethmoid bone into the olfactory bulb there they synapse with mitral cells in clusters called glomeruli

each glomerulus gathers all olfactory cells for the same olfactory receptor convergence amplifies the signal

4. each odorant molecule combines with a unique set of olfactory cell membrane receptors (signature)

5. afferent pathway for olfaction:

olfactory cells - axons form cranial nerve I; project to olfactory bulb mitral cells - axons form olfactory tract; project to: limbic system olfactory cortex

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Anatomy Lecture Notes Chapter 16

C. vision

1. eyelids / palpebrae = skin-covered folds

tarsal plates - c.t. attachment for orbicularis oculi

levator palpebrae superioris m. - roof of orbit to tarsal plate of upper eyelid

tarsal (Meibomian) glands - open onto margin of eyelid; secrete oil

ciliary glands - associated with eyelashes; sebaceous and sweat glands

palpebral fissure - space between eyelids

canthus (canthi) - medial and lateral corners of palpebral fissure

lacrimal caruncle - tissue in medial canthus

2. conjunctiva = mucous membrane lining eyelids and covering exposed sclera

palpebral conjunctiva - lines eyelids

ocular (bulbar) conjunctiva - covers sclera

conjunctival sac - space between eyelids and eyeball

3. lacrimal apparatus

a. lacrimal gland - in orbit superiorlateral to eyeblal secretes tears (water, mucus, antibodies, lysozyme) excretory ducts open under superior lateral eyelid

b. lacrimal puncta - 2 openings in lacrimal caruncle puncta open into lacrimal canals (canaliculi) canals open into lacrimal sac, drains by nasolacrimal duct into nasal cavity under inferior choncha

4. eyeball - spherical sac made of 3 layers and filled with fluid

a. fibrous tunic (outermost) made of dense c.t.

sclera posterior 5/6; white; opaque anterior 1/6; cornea clear, more curved, avascular corneal epithelium - covers surface of cornea corneal endothelium - lines inside of cornea; removes excess water from cornea

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scleral venous sinus - vein at junction of cornea and sclera

b. vascular tunic

i. choroid - posterior to ciliary body, vascular, pigmented membrane absorbs light

ii. ciliary body - posterior to iris, anterior to choroid

ciliary muscle – circular fibers, controls lens shape

ciliary processes - anchor suspensory ligaments (ciliary zonula)

iii. iris - anterior to ciliary body; between cornea and lens

opening in center = pupil iris contains muscle fibers that control pupil diameter sphincter inner circular fibers constrict pupil dilator outer radial fibers dilate pupil

color caused by brown melanin in pigmented epithelial cells blue or gray - melanin is in posterior epithelial layer of iris only green, hazel and brown - melanin is in the anterior muscular layer and the posterior epithelial layer

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Anatomy Lecture Notes Chapter 16

c. sensory tunic = retina

i. pigmented layer next to choroid. made of a single layer of melanocytes extends forward to cover the back of the ciliary body and the iris absorbs excess light; helps photoreceptors maintain photopigments

ii. nervous layer inside consists of 3 cell layers: photoreceptor cells (rods and cones) - tips embedded in pigmented layer, sensitive to light bipolar cells - superficial to photoreceptors, connect photoreceptors to ganglion cells ganglion cells - surface of nervous layer; axons form cranial nerve II (optic nerve)

anterior margin of nervous layer = ora serrata

macula lutea - spot in exact center of back of eyeball

fovea centralis - indentation in the macula lutea; contains only cones; maximal visual acuity

optic disc = where II leaves eyeball; medial to macula lutea; lack of photoreceptors causes blind spot

central artery and vein - enter/leave with optic nerve

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Anatomy Lecture Notes Chapter 16

d. lens = biconvex transparent elastic disc

changes shape to focus images on retina

outside is an elastic capsule

inside the capsule on the front of the lens is a layer of lens epithelium

behind the lens epithelium are lens fibers, which are made by the peripheral cells of the lens epithelium

the lens is avascular

its density increases with age and its elasticity decreases with age, preventing focusing on near objects (presbyopia)

cataracts are clouding of the lens and are correlated with smoking, exposure to UV radiation, and diarrhead. cavities and fluids

e. cavities and fluids

i. posterior segment posterior to lens filled with vitreous body (humor) made mostly of collagen and water holds retina in place helps maintain intraocular pressure

ii. anterior segment anterior to lens subdivided into: o anterior chamber - anterior to iris o posterior chamber - posterior to iris contains aqueous humor o formed at ciliary processes in posterior chamber o circulates through pupil to anterior chamber o drains into scleral venous sinus o maintains intraocular pressure glaucoma - caused by increased intraocular pressure

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Anatomy Lecture Notes Chapter 16

5. photoreceptors (rods and cones) = specialized neurons

outer segment = receptor region of cell embedded in pigmented layer plasma membrane contains visual pigment molecules that are sensitive to light plasma membrane folded inwards increases surface area folds form membrane-covered discs

rods cones 1 type 3 types: red, blue, green sensitive to entire visual spectrum each sensitive to part of the visual spectrum shades of gray color work in dim light only work in bright light only low acuity (convergence of rods onto high acuity (no convergence) bipolar cells) concentrated around periphery of concentrated in center of retina retina

6. afferent pathway

rods and cones

bipolar cells

ganglion cells

optic nerve

optic chiasma

optic tract

superior colliculus of midbrain

thalamus

primary visual cortex

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Anatomy Lecture Notes Chapter 16

D. hearing and equilibrium

1. outer ear

a. auricle/pinna - funnels sound into ear canal

b. external auditory canal goes through external acoustic meatus 2.5 cm long, angled anteriorly skin contains ceruminous glands, hair follicles, hair, sebaceous glands

c. tympanic membrane made of 2 layers of collagen and elastin fibers external surface covered by skin internal surface covered by simple squamous or cuboidal e.

2. middle ear - inside petrous temporal bone

a. ossicles amplify sound vibrations (they form a "bridge" between the tympanic membrane and the inner ear) malleus attached to tympanic membrane incus stapes fits into oval window of inner ear

b. muscles adjust sensitivity of middle ear:

tensor tympani (O) pharyngotympanic tube (I) tympanic membrane increases tension of tympanic membrane, decreases vibration

stapedius (O) posterior wall of middle ear cavity (I) stapes limits movement of stapes

c. openings into inner ear: oval window - where sound waves enter cochlea round window - where sound waves leave cochlea

d. pharyngotympanic (auditory or Eustachian) tube connects middle ear to nasopharynx equalizes air pressure across eardrum

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Anatomy Lecture Notes Chapter 16

3. inner ear

a. bony labyrinth = cavity inside temporal bone filled with perilymph 3 subdivisions: semicircular canals (posterior) vestibule cochlea (anterior)

b. membranous labyrinth = set of interconnected membrane tubes that are suspended in the perilymph filled with endolymph 3 subdivisions: semicircular ducts utricle and saccule cochlear duct

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4. cochlea - hearing

a. overall structure

modiolus - pillar of bone in center of cochlea

spiral lamina - shelf of bone coiling around modiolus

scala vestibuli - filled with perilymph, oval window located at basal end

vesibular membrane divides scala vestibuli from cochlar duct/scala media

scala media/cochlear duct - contains organ of Corti, filled with endolymph

basilar membrane - divides cochlar duct/scala media from scala vestibuli

scala tympani - filled with perilymph, round window located at basal end

scala vestibuli and scala tympani are continuous at the helicotrema

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b. organ of Corti sits on basilar membrane columnar supporting cells cochlear "hair" cells o on apical end they have microvilli (hairs) , also called stereocilia o on basal end they synapse with sensory neurons that form the cochlear branch of VIII tectorial membrane - jelly-like flap that sits on hair cells

c. afferent pathway

cochlear hair cells

afferent neurons (1st order)

dendrites synapse with hair cells

cell body located in spiral ganglion

central processes form cochlear branch of VIII

terminate in cochlear nuclei in medulla oblongata

second order neurons go from cochlear nucleus to superior olivary nucleus

third order neurons go from medulla oblongata to inferior colliculus of midbrain

fourth order neurons go from midbrain to thalamus

fifth order neurons go from thalamus to primary auditory cortex in temporal lobe

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5. vestibule - between semicircular canals and cochlea

a. general structure membranous labyrinth consists of utricle - continuous with semicircular ducts saccule - continuous with cochlear duct

b. each utricle and saccule contains a macula, a receptor organ for static body position and linear acceleration

supporting cells hair cells o apical microvilli o basal synapse with afferent neurons of the vestibular branch of VIII otolithic membrane - jelly-like disc covering hair cells otoliths - crystals of calcium carbonate embedded in surface of membrane; "gravity amplifiers"

6. semicircular canals - 3 in each ear in 3 different planes

a. general structure bony labyrinth located posterior and lateral to vestibule o anterior o posterior o lateral ampulla - enlargement at one end of each canal membranous labyrinth consists of 3 semicircular ducts located inside the canals (same names as bony labyrinth)

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b. at one end of each semicircular duct is a membranous ampulla containing one crista ampullaris, a receptor organ for angular acceleration

supporting cells hair cells o apical microvilli o basal synapse with afferent neurons of the vestibular branch of VIII cupula - jelly-like flap covering apical microvilli of hair cells and extending out into membranous ampulla *the maculae and cristae are sometimes collectively called the vestibular apparatus

c. afferent pathway for equilibrium

hair cells of maculae and cristae

first order neurons form vestibular branch of VIII and go from hair cells to vestibular ganglia in the medulla oblongata

other subsequent neurons project to the brainstem and cerebellum

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