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Chapter 17
The Special Senses
144
Anatomy
Undergraduate 2
12/06/2017

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Term
What are the layers of the olfactory organs called?
Definition
Olfactory epithelium and lamina propria
Term
What does the olfactory epithelium contain?
Definition
Olfactory receptor cells, supporting cells, and regenerative basal cells.
Term
What does the lamina propria contain?
Definition
Areolar tissue, numerous blood vessels, nerves and olfactory glands.
Term
Odorant
Definition
Dissolved compounds that stimulate olfactory receptors
Term
Steps involved in smelling
Definition
1. The binding of an odorant to its receptor protein (G-protein receptors) leads to the activation of adenylyl cyclase, the enzyme that converts ATP to cAMP.

2. The cAMP opens sodium ion channels in the plasma membrane, which then begins to depolarize.

3. If sufficient depolarization occurs, an action potential is triggered in the axon, and the information is relayed to the CNS.
Term
taste buds
Definition
Taste receptors and specialized epithelial cells on the tongue, pharynx, and larynx.
Term
Lingual papillae
Definition
Variously shaped epithelial projections on the tongue
Term
4 types of lingual papillae
Definition
1. Filiform papillae: provide friction, do not contain taste buds.

2. Fungiform papillae: small, contain about 5 taste buds

3. vallate papillae: large, contain as many as 100 taste buds

4. Foliate papillae: folds found on the lateral margins of the posterior tongue
Term
Taste buds are innervated by which cranial nerves?
Definition
CN VII (facial), CN IX (glossopharyngeal), and CN X (vagus).
Term
Where do the sensory afferent fibers carried by the cranial nerves synapse?
Definition
In the solitary nucleus of the medulla oblongata.
Term
Where does information about the texture of food, along with taste related sensations such as "peppery" or "burning hot" come from?
Definition
It comes from sensory afferents in the trigeminal cranial nerve (V).
Term
Umami
Definition
A pleasant savory taste due to the presence of free glutamates in food
Term
Olfactory glands (Bowman's glands)
Definition
Secretions coat surfaces of olfactory organs (mucus)
Term
gustatation
Definition
Taste-provides information about the foods we eat and drink
Term
Taste buds contain _______.
Definition
Basal (stem) cells which divide, differentiate, and mature

Gustatory receptor cells (mature cells)
Term
Gustatory cell
Definition
Extends microvilli (taste hairs) through a taste pore.

Survives for about 10 days before being replaced.
Term
How is the taste of water detected?
Definition
By the water receptors in the pharynx
Term
Gustducins
Definition
Protein complexes that use second messengers to produce their effects.

Respond to sweet, bitter, and umami receptors
Term
Accessory structures of the eye
Definition
Palpebrae (eyelids)

Superficial epithelium

The lacrimal apparatus
Term
Palpebral fissure
Definition
The gap that separates the free margins of the upper and lower eyelids
Term
Medial and lateral canthus
Definition
Where the two eyelids are connected
Term
Tarsal glands (Meibomian glands)
Definition
Secrete lipid-rich product that helps keep eyelids from sticking together
Term
Lacrimal caruncle
Definition
Mass of soft tissue, contains glands producing thick secretions, contributes to gritty deposits after good night’s sleep
Term
Chalazion
Definition
A cyst that results from an infection of a tarsal gland
Term
Orbicularis oculi
Definition
Muscle that closes the eyelids
Term
Levator palpebrae superioris muscle
Definition
Muscle that raises the upper eyelid
Term
Conjunctiva
Definition
Epithelium covering inner surfaces of eyelids (palpebral conjunctiva) and outer surface of eye (ocular conjunctiva)
Term
Cornea
Definition
A transparent part of the outer fibrous layer of the eye
Term
Conjunctivitis
Definition
An inflammation of the conjunctiva
Term
Functions of tears
Definition
Keeps conjunctival surfaces moist and clean
Reduce friction
Remove debris
Prevent bacterial infection
Provide nutrients and oxygen to conjunctival epithelium
Term
Lacrimal apparatus consists of
Definition
A lacrimal gland with associated ducts

Paired lacrimal canaliculi

A lacrimal sac

A nasolacrimal duct
Term
Functions of the lacrimal apparatus
Definition
Produces, distributes, and removes tears
Term
Fornix
Definition
A pocket created where the palpebral conjunctiva joins the ocular conjunctiva
Term
Lacrimal gland
Definition
Secretions contain lysozyme, antibacterial enzyme & antibodies

Its secretions provide nutrients and oxygen to the corneal cells by diffusion.
Term
Lacrimal lake
Definition
Where the tears accumulate in the medial canthus
Term
Lacrimal puncta
Definition
Two small pores that drain the lacrimal lake
Term
Lacrimal canaliculi
Definition
Small canals that the lacrimal punta empty into.
Term
Lacrimal sac
Definition
Leads from the lacrimal canaliculi, tears flow into the nasolacrimal duct
Term
Nasolacrimal duct
Definition
Delivers tears to the nasal cavity-runny nose when a person cries
Term
Eyeball is hollow- divided into two cavities:
Definition
Large posterior cavity
Smaller anterior cavity- anterior & posterior chambers
Term
Aqueous humor
Definition
A clear watery fluid that fills the anterior cavity of the eye
Term
Vitreous humor
Definition
A gelatinous substance that fills the posterior cavity of the eye and helps to stabilize the shape of the eye
Term
3 layers of the eye
Definition
1. Outer fibrous tunic

2. Middle vascular tunic

3. Inner layer (retina)
Term
Fibrous tunic consists of:
Definition
The sclera and the cornea.
Term
Functions of the Fibrous layer
Definition
1. Supports and protects

2. Serves as an attachment site for the extrinsic eye muscles

3. Contains structures that assist in focusing
Term
Sclera (white of the eye)
Definition
Dense, fibrous connective tissue containing both collagen and elastic fibers.

Covers most of the ocular surface

The 6 extrinsic eye muscles insert on the sclera
Term
Cornea
Definition
Transparent, avascular

Cornea very sensitive, limited ability to repair itself
Term
Vascular layer (uvea) functions
Definition
Provides route for blood vessels and lymphatics that supply tissues of eye

Regulates amount of light entering eye

Secretes and reabsorbs aqueous humor that circulates within chambers of eye

Controls shape of lens, which is essential to focusing
Term
The vascular layer (uvea) contains:
Definition
The iris, ciliary body, and choroid

Numerous blood vessels, lymphatic vessels, and the intrinsic (smooth) muscles of the eye
Term
Ciliary body
Definition
Extends posteriorly to level of ora serrata:

Serrated anterior edge of thick, inner portion of neural tunic

Contains ciliary muscle, covered by ciliary processes (folds of epithelium) that attach to suspensory ligaments of lens
Term
Iris
Definition
Contains blood vessels, pigment cells, pupillary muscles

Pupillary constrictor muscles- forms series of concentric circles around pupil, contract pupil decreases

Pupillary dilator muscles- extend radially away from edge of pupil, contract pupil enlarges
Term
The choroid
Definition
Vascular layer that separates fibrous and neural tunics posterior to ora serrata

Delivers oxygen and nutrients to retina

Also contains melanocytes
Term
Inner layer (retina) consists of:
Definition
Pigmented part: a thin, outer layer

Neural part: a thick, inner layer
Term
Pigmented part of retina
Definition
absorbs light that passes through neural part, preventing light from bouncing back through neural part
Term
Neural part of retina
Definition
Contains visual receptors and associated neurons preliminary processing & integration of visual information
Term
Retina organization
Definition
Outermost layer of cells closest to pigmented layer contains photoreceptors- cells that detect light

Rods and cones are types of photoreceptors:
Rods: allow you to see in dim light
Do not discriminate among colors of light
Highly sensitive to light

Cones: allow you to see color
3 types of cones
Sharper, clearer image than rods, require more light
Densely clustered in fovea, at center of macula lutea

Macula lutea- area where visual image arrives after passing through cornea & lens
Term
Macula
Definition
The area where a visual image arrives after it passes through the cornea and lens

It has no rods
Term
Fovea centralis
Definition
the center of the macula, where the hightest concentration of cones is

The site of sharpest vision

Establishes visual axis
Term
Optic disc
Definition
A circular region just medial to the fovea.

Has no photoreceptors, light striking here goes unnoticed

Blind spot

The origin of the optic nerve.
Term
Bipolar cells
Definition
Neurons that rods and cones synapse with

Bipolar cells then synapse with another layer of neurons- ganglion cells
Term
Horizontal cells
Definition
Extend across the neural part of the retina at the level of the synapses between photoreceptors and bipolar cells
Term
Amacrine cells
Definition
A layer of cells that occur where bipolar cells synapse with ganglion cells.
Term
Where does the aqueous humor go?
Definition
It circulates within the anterior cavity. It passes from the posterior chamber to the anterior chamber through the pupil. It also freely diffuses through the posterior cavity and across the surface of the retina.
Term
Aqueous humor
Definition
Fluid circulates within eye, resembles composition of CSF

Important route for nutrient & waste transport

Fluid cushion

Diffuses through walls of anterior chamber into canal of Schlemm (scleral venous sinus)

Intraocular pressure- fluid pressure in aqueous humor, helps retain eye shape
Term
Vitreous body
Definition
In the posterior cavity of the eye.

Gelatinous mass

Helps stabilize eye shape and supports retina

Formed during development of the eye- not replaced
Term
The lens
Definition
Posterior to cornea, held in place by suspensory ligaments

Primary function- focus the visual image on photoreceptors by changing its shape

Consists of concentric layers of cells, covered by fibrous capsule (elastic)

Cells in interior of lens- lens fibers, no nuclei or organelles

Filled with crystallins, provide clarity & focusing power to lens
Term
Cataract
Definition
A condition in which the lens has lost its transparency
Term
Chrystallins
Definition
Transparent proteins that give the lens its clarity and focusing power.

They remain intact and functional for a lifetime.
Term
Light refraction
Definition
The light is bent when it passes from one medium to another medium with different density.

The greatest amount of refraction occurs when light passes from the air into the corneal tissues.

Additional refraction occurs when the light passes from the aqueous humor into the lens
Term
focal distance
Definition
The distance between the center of the lens and its focal point.

Focal distance determined by 2 factors:
1. the distance of the object from the lens- closer an object is to the lens the greater the focal distance

2. The shape of the lens- the rounder the lens, the shorter the focal distance.
Term
Accomodation
Definition
The automatic adjustment of the eye to give us clear vision. The lens becomes rounder to focus the image of a nearby object. The lens becomes flatter to focus the image of a distant object on the retina.
Term
Visual acuity
Definition
Clarity of vision
Term
Photons
Definition
Basic unit of visible light
Term
Visual pigments
Definition
Special organic compounds located in each photoreceptor's outer segment in flattened membranous plates called discs.
Term
Light energy
Definition
Light energy travels in waves with characteristic wavelength

Human eyes can detect visible light 400-700 nm

700 nm (violet) high energy, 400 nm (red) low energy

Rods- provide CNS with info about presence/absence of photons, regardless of wavelength

Cones- provide info about the arriving photons, color perception
Term
Anatomy of rods and cones
Definition
Outer segment- contains hundreds of membranous discs
Rod- separate and elongated cylinder shape
Cone- infoldings of plasma membrane, cone shape

Inner segment- contains cellular organelles
Narrow stalk connects outer segment to inner segment
Inner segment releases neurotransmitters
Term
Photoreception
Definition
the detection of light
Term
Visual pigments
Definition
derivatives of the compound rhodopsion, which consists of a protein, opsin, bound to the pigment retinal
Term
First step in photoreception
Definition
The absorption of photons by visual pigments
Term
3 types of cones
Definition
Blue cones
Green cones
Red cones

Each type has a different form of opsin and is sensitive to a different range of wavelengths.
Term
Emmetropia
Definition
normal vision
Term
Myopia
Definition
nearsightedness

The eyeball is too deep or the resting curvature of the lens is too great
Term
Hyperopia
Definition
Farsightedness

The eyeball is too shallow or the lens is too flat
Term
Dark current
Definition
movement of Na+ into outer segment, on to inner segment, out of cell
Term
Step one of photoreception
Definition
Normally, the molecule is in the 11-cis form; on absorbing light it changes to the more linear 11-trans form. This change activates the opsin molecule.
Term
Step two of photoreception
Definition
Opsin activates transducin, which in turn activates PDE. (Transducin is a G protein, a membrane-bound enzyme complex)
Term
Step three of photoreception
Definition
Cyclic GMP levels decline and gated sodium channels close.
The removal of cGMP from the gated sodium channels results in their inactivation. The rate of Na+ entry into the cytoplasm then decreases.
Term
Step four in photoreception
Definition
Dark current is reduced and rate of neurotransmitter release declines.

Active transport continues to export Na+ from the cytoplasm. When the sodium channels close, the membrane potential drops toward -70mV. As the plasma membrane hyperpolarizes, the rate of neurotransmitter decreases, which signals the adjacent bipolar cell that the photoreceptor has absorbed a photon.
Term
Bleaching
Definition
Rhodopsin molecule breaks down into retinal and opsin

Before retinal can combine with opsin, must be enzymatically converted to 11-cis

Requires ATP and time
Term
Visual pathways
Definition
Begin at photoreceptors, end at visual cortex of cerebral hemispheres
Message crosses two synapses before it heads toward brain
Photoreceptor to bipolar cell
Bipolar cell to ganglion cell
Term
Ganglion cells
Definition
monitor a specific portion of a field of vision
Term
M cells
Definition
Ganglion cells that monitor rods, provide information about the general form of an object, motion, and shadows in dim lighting.

Relatively large
Term
P cells
Definition
Ganglion cells that monitor the cones

Smaller and more numerous than M cells

Active in bright light, provide information about edges, fine detail, and color
Term
Dark-adapted state
Definition
When almost all visual pigments have recovered from photobleaching, and the visual system is extremely sensitive.
Term
Light-adapted state
Definition
When the lights come on, the sensitivity decreases as bleaching occurs. Eventually, the rate of bleaching is balanced by the rate at which the visual pigments reassemble.
Term
On-center neurons
Definition
Excited by light arriving in center of their sensory field

Are inhibited when light strikes edges of their receptive field
Term
Off-center neurons
Definition
Inhibited by light in central zone
Stimulated by illumination at edges
Term
Central processing of visual information
Definition
Axons from ganglion cells converge on optic disc

Penetrate wall of eye

Proceed toward diencephalon as optic nerve (II)
Two optic nerves (one for each eye) reach diencephalon at optic chiasm
½ fibers stay same side
½ fibers cross to lateral geniculate nucleus on other side

From each lateral geniculate nucleus, visual information travels to the occiptal cortex

Optic radiation- bundle of projection fibers link lateral geniculate with visual cortex
Term
Depth perception
Definition
The ability to judge depth or distance by interpreting the 3 dimensional relationships among objects in view
Term
Equilibrium sensations
Definition
Position of the head in space
by monitoring gravity, linear acceleration, and rotation.
Term
Hearing
Definition
Enables us to detect and interpret sound waves
Term
Equilibrium and hearing
Definition
Both use mechanoreceptors- hair cells
Ear divided into external, middle, internal ear

External- collects, directs sound waves toward middle ear

Middle- collect sound waves, directs to inner ear

Inner ear- sensory organs for hearing & equilibrium
Term
External acoustic meatus
Definition
A passageway (auditory canal)
Term
Pinna (auricle)
Definition
Protects the opening of the auditory canal and provides directional sensitivity
Term
Tympanic membrane
Definition
A thin, semi-transparent sheet that separates the external ear from the middle ear

The eardrum
Term
Ceruminous glands
Definition
Integumentary glands along the external acoustic meatus that secrete a waxy material that helps keep out foreign objects or small insects.
Term
Cerumen
Definition
The slightly waxy secretion of the ceruminous glands, slows the growth of microorganisms and reduces the chance of infection
Term
Middle ear (tympanic cavity)
Definition
An air-filled chamber separated from the external acoustic meatus by the tympanic membrane.

Communicates with:
Nasopharynx through the auditory tube
Mastoid air cells through a number of small connections
Term
Pharyngotympanic tube (Eustachian tube), auditory tube
Definition
Consists of 2 portions:
First, near the connection to the middle ear, is narrow and supported by elastic cartilage.
Second, near the opening to the nasopharynx, is broad and funnel shaped

Equalizes pressure on either side of the tympanic membrane
Term
Middle ear has 3 auditory ossicles
Definition
These connect the tympanic membrane with one of the receptor complexes of the inner ear.

These are called the malleus, the incus, and the stapes.
Term
Malleus (hammer)
Definition
attaches at 3 points to the interior surface of the tympanic membrane.
Term
Incus (anvil)
Definition
Attaches the malleus to the stapes
Term
Stapes
Definition
The edges of the base of the stapes are bound to the edges of the oval window
Term
Oval window
Definition
An opening in the temporal bone that surrounds the internal ear.
Term
What does vibration of the tympanic membrane do?
Definition
Converts arriving sound waves into mechanical movements.
Term
What do the auditory ossicles do?
Definition
Conduct vibrations to the inner ear.
Term
Tensor tympani muscle
Definition
Stiffens the tympanic membrane to reduce the amount of movement possible.

Innervated by motor fivers of the mandibular branch of the trigeminal nerve (V)
Term
Stapedium muscle
Definition
Pulls the stapes reducing movement of the stapes at the oval window.

Innervated by the facial nerve (VII)
Term
Internal ear
Definition
Provides us with the sense of equilibrium and hearing
Term
Bony labyrinth
Definition
A layer of dense bone which forms the superficial contours of the internal ear.

Continuous with the surrounding temporal bone.
Term
Membranous labyrinth
Definition
A delicate, interconnected network of fluid-filled tubes where the receptors are found
Term
Perilymph
Definition
Between the bony and membranous labyrinths, a liquid that closely resembles CSF
Term
Endolymph
Definition
Inside the membranous labyrinth, a fluid with electrolyte concentrations that differ from those of typical body fluids.
Term
Subdivisions of the bony labyrinth
Definition
Vestibule
The semicircular canals
cochlea
Term
Vestibule
Definition
Consists of a pair of membranous sacs:
Saccule
Utricle

Receptors in these sacs provide sensations of gravity and linear acceleration.
Term
Semicircular canals
Definition
Contain semicircular ducts

Receptors stimulated by rotation of head

Vestibule + semicircular canals = vestibular complex
Term
Cochlea
Definition
A spiral-shaped bony chamber that contains the cochlear duct of the membranous labyrinth.

Receptors within the cochlear duct provide the sense of hearing.

The duct is sandwiched between a pair of perilymph-filled chambers
Term
Round window
Definition
A thin, membranous partition that separates the perilymph of the cochlear chambers from the air-filled middle ear
Term
Oval window
Definition
Formed of collagen fibers
Connected to base of stapes
Term
Equilibrium
Definition
Equilibrium sensations provided by receptors of vestibular complex

Semicircular canals- info about rotational movement of head


Saccule & utricle- info about position with respect to gravity & acceleration
Term
Semicircular ducts
Definition
Hair cells (sensory receptors) respond to rotational movements of the head

Ducts are continuous with utricle

Each duct contains
Ampulla- expanded region that contains receptors
Region in ampulla with hair cells- crista

Crista is bound to cupula- gelantinous structure extends full width of ampulla

Free surface of each hair cells has stereocilia (80-100)– resemble long microvilli:

Each hair cell has kinocilium – single, large cilium
Term
The Utricle and Saccule
Definition
Provide equilibrium sensations
Are connected with the endolymphatic duct, which ends in endolymphatic sac
Term
Maculae
Definition
Provide equilibrium sensations

Are connected with the endolymphatic duct, which ends in endolymphatic sac
Term
Statoconia
Definition
Densely packed calcium carbonate crystals
Whole complex- Otolith (ear stone) = gel and statoconia
Term
Vestibular nuclei
Definition
Found at the boundary between the pons and the medulla oblongata
Term
Functions of the vestibular nuclei
Definition
1. Integrating sensory information about balance and equilibrium that arrives from both sides of the head.

2. Relaying information from the vestibular complex to the cerebellum.

3. Relaying information from the vestibular complex to the cerebral cortex, providing a conscious sense of head position and movement.

4. Sending commands to motor nuclei in the brain stem and spinal cord.
Term
Superior caliculi
Definition
Directs the automatic movements of the eyes in response to sensations of motion
Term
Cochlear duct
Definition
Located between vestibular duct & tympanic duct
Hair cells located in organ of Corti, sits on basilar membrane
Term
Basilar membrane
Definition
Separates cochlear duct from tympanic duct

Hair cells arranged in longitudinal rows, lack kinocilia

Stereocilia in contact with overlying tectorial membrane

Tectorial membrane is attached to inner wall of cochlear duct
Term
Sound
Definition
Waves of pressure conducted through a medium such as air or water.

In air, each pressure wave consists of a region where the air molecules are crowded together and an adjacent zone where they are further apart.
Term
The hearing process
Definition
1. Sound waves arrive at the tympanic membrane.
2. Movement of the tympanic membrane causes displacement of the auditory ossicles.
3. Movement of the stapes at the oval window establishes pressure waves in the perilymph of the scala vestibuli.
4. The pressure waves distort the basilar membrane on their way to the round window of the scala tympani.
5. Vibration of the basilar membrane causes hair cells to vibrate against the tectorial membrane.
6. Information about the region and the intensity of stimulation is relayed to the CNS over the cochlear branch of CN VIII.
Term
Sine waves
Definition
S-shaped curves, repeat in a regular pattern
Travel air ~768 mph
Term
Wave length
Definition
inversely related to frequency- number of waves (cycles) that pass a fixed reference point in a given time
Frequency of sound measured in terms of number of cycles per second (cps)- hertz (Hz)
Term
Amplitude
Definition
intensity of sound wave
More energy- more amplitude
Sound energy is reported in decibels
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