A&P CH 17

Other tastants, responsible for stimulating sweet, bitter, and umami tastes, do not themselves enter gustatory receptor cells. Rather, they bind to receptors on the plasma membrane that are linked to __ proteins. The ___ proteins then activate several different chemicals known as second messengers inside the gustatory receptor cell. Different second messengers cause ______ in different ways, but the result is the same— release of _______.

G, G, depolarization, neurotransmitter

The eyelids form from surface _____ and _____. The upper and lower eyelids meet and fuse at about eight weeks of development and remain closed until about 26 weeks of development.

ectoderm, mesenchyme

The cochlear duct or scala media is a continuation of the membranous labyrinth into the cochlea; it is filled with ____. The channel above the cochlear duct is the ___ ___, which ends at the oval window. The channel below is the ___ ___, which ends at the round window.

endolymph, scala vestibuli, scala tympani,

The anterior portion of the optic cup forms the _____ of the ciliary body, ___, and _____ and ____ muscles of the iris.

epithelium, iris, circular, radial

Once ___ ____ arise in the outer segments of rods and cones, they spread through the inner segments to the ___ ____. Neurotransmitter molecules released by rods and cones induce local graded potentials in both bipolar cells and horizontal cells. Between 6 and 600 rods synapse with a single _____ cell in the outer synaptic layer of the retina; a ____ more often synapses with a single ____ cell. The convergence of many ___ onto a single _____ cell increases the light sensitivity of ____ vision but slightly blurs the image that is perceived.

receptor potentials, synaptic terminals, bipolar, cone, bipolar, rods, bipolar, rod

The orbits help protect the eyes, stabilize them in three-dimensional space, and anchor them to the muscles that produce their essential movements. The extrinsic eye muscles extend from the walls of the bony orbit to the ____ of the eye and are surrounded in the orbit by a significant quantity of _____ fat. These muscles are capable of moving the eye in almost any direction.

sclera, periorbital,

There are two types of equilibrium (e ̄-kwi-LIB-re ̄-um) or balance. _____ equilibrium refers to the maintenance of the position of the body relative to the force of gravity. Body movements that stimulate the receptors for ____ equilibrium include tilting the head and linear acceleration or deceleration, such as when the body is being moved in an elevator or in a car that is speeding up or slowing down. _____ equilibrium is the maintenance of body position (mainly the head) in response to sudden movements such as rotational acceleration or deceleration. Collectively, the receptor organs for equilibrium are called the vestibular apparatus; these include the ___, ____, and ____ ducts.

Static, static, Dynamic, saccule, utricle, semicircular

The external ear consists of the _____, external ___ ___, and ____.

auricle, auditory canal, eardrum

The vestibular membrane separates the cochlear duct from the scala vestibuli, and the ____ membrane separates the cochlear duct from the scala tympani.

basilar

The first portion of the ear to develop is the ____ ear. It begins to form about 22 days after fertilization as a thickening of the surface ectoderm, called ___ ___, that appears on either side of the rhombencephalon (hindbrain). The otic placodes invaginate quickly to form the otic pits. Next, the otic pits pinch off from the surface ectoderm to form the otic vesicles within the mesenchyme of the head. During later development, the otic vesicles will form the structures associated with the membranous labyrinth of the internal ear. Mesenchyme around the otic vesicles produces cartilage that later ossifies to form the bone associated with the bony labyrinth of the internal ear.

internal, otic placodes

The pressure in the eye, called ____ ____, is produced mainly by the aqueous humor and partly by the vitreous body; normally it is about 16 mmHg (millimeters of mercury). This pressure maintains the shape of the eyeball and prevents it from collapsing. Puncture wounds to the eyeball may lead to the loss of aqueous humor and the vitreous body. This in turn causes a decrease in this pressure, a detached retina, and in some cases blindness.

intraocular pressure,

Images focused on the retina are _____. They also undergo right-to-left reversal; that is, light from the right side of an object strikes the left side of the retina, and vice versa.

inverted,

The anterior chamber develops from a cavity that forms in the mesenchyme between the ____ and ___; the posterior chamber develops from a cavity that forms in the mesenchyme between the ___ and ____.

iris, cornea, iris, lens

The cornea is a transparent coat that covers the colored ____. Because it is curved, the cornea helps focus light onto the ______. Its outer surface consists of ____ ____ ____ ____. The middle coat of the cornea consists of collagen fibers and fibroblasts, and the inner surface is _____ _____ ____.

iris, retina, nonkeratinized stratified squamous epithelium, simple squamous epithelium

When light strikes the retina and cis-retinal undergoes ______, enzymes are activated that break down cGMP. As a result, some cGMP-gated Na channels close, Na inflow decreases, and the membrane potential becomes more negative, approaching 70 mV. This sequence of events produces a ______ receptor potential that decreases the release of _____. Dim lights cause small and brief receptor potentials that partially turn off glutamate release; brighter lights elicit larger and longer receptor potentials that more completely shut down neurotransmitter release. Thus, light excites the bipolar cells that synapse with rods by turning off the release of an inhibitory neurotransmitter. The excited bipolar cells subsequently stimulate the ganglion cells to form action potentials in their axons.

isomerization, hyperpolarizing, glutamate

As mentioned previously, the absorption of light and ________ of retinal initiates chemical changes in the photoreceptor outer segment that lead to production of a ____ ____. To understand how this arises, however, we first need to examine the operation of photoreceptors in the absence of light. In darkness, sodium ions flow into photoreceptor ____ segments through ligand-gated Na channels. The ligand that holds these channels open is ____ ___ ____ . The inflow of Na, called the "dark current," partially ______ the photoreceptor. As a result, in darkness the membrane potential of a photoreceptor is about 30 mV. This is much closer to zero than a typical neuron's resting membrane potential of 70 mV. The partial depolarization during darkness triggers continual release of neurotransmitter at the ___ ___. The neurotransmitter in rods, and perhaps in cones, is the amino acid glutamate (glutamic acid). At synapses between rods and some bipolar cells, glutamate is an inhibitory neurotransmitter: It triggers inhibitory postsynaptic potentials (IPSPs) that hyperpolarize the bipolar cells and prevent them from transmitting signals to the ganglion cells.

isomerization, receptor potential, outer, cyclic guanosine monophosphate, depolarizes, synaptic terminals

In the medial commissure is a small, reddish elevation, the ____ ____, which contains sebaceous (____) glands and sudoriferous (____) glands. The whitish material that sometimes collects in the medial commissure comes from these glands

lacrimal caruncle, oil, sweat

The connective tissue of the ciliary body, ciliary muscle, and zonular fibers of the lens develop from _____ around the anterior portion of the optic cup.

mesenchyme

On each side of the nose, about 40 bundles of the slender, ______ axons of olfactory receptor cells extend through about 20 ____ ____ in the cribriform plate of the ______ bone. These 40 or so bundles of axons collectively form the right and left olfactory (I) nerves. The olfactory nerves terminate in the brain in paired masses of gray matter called the ___ ___, which are located below the frontal lobes of the cerebrum and lateral to the ___ ___ of the ethmoid bone. Within the olfactory bulbs, the axon terminals of olfactory receptor cells form synapses with the dendrites and cell bodies of ___ ___ neurons in the olfactory pathway.

unmyelinated, olfactory foramina, ethmoid, olfactory bulbs, crista galli, olfactory bulb

Complete adaptation to a specific taste can occur in _-_ minutes of continuous stimulation. Taste adaptation is due to changes that occur in the taste receptors, in olfactory receptors, and in neurons of the gustatory pathway in the CNS.

1-5,

To make this possible, the nose contains ____ million to ____ million receptors for the sense of smell or olfaction, contained within a region called the ____ ____.

10, 100, olfactory epithelium

It is estimated that humans can recognize about _______ different odors

10,000

Hearing is the ability to perceive sounds. The ear is an engineering marvel because its sensory receptors can transduce sound vibrations with amplitudes as small as the diameter of an atom of gold (0.3 nm) into electrical signals _____ times faster than photoreceptors can respond to light. The ear also contains receptors for equilibrium, the sense that helps you maintain your balance and be aware of your orientation in space.

1000,

The eyes are responsible for the detection of visible light, the part of the electromagnetic spectrum with wavelengths ranging from about ____ to ____ nm.

400, 700

With a total area of __ cm^2, the olfactory epithelium occupies the superior part of the ___ ___, covering the inferior surface of the ____ ___ and extending along the superior ____ ___. The olfactory epithelium consists of three kinds of cells: ___ ___ cells, ____ cells, and ____ cells

5, nasal cavity, cribriform plate, nasal concha, olfactory receptor, supporting, basal

Adaptation (decreasing sensitivity) to odors occurs rapidly. Olfactory receptors adapt by about ___% in the first second or so after stimulation but adapt very slowly thereafter. Still, complete insensitivity to certain strong odors occurs about a minute after exposure. Apparently, reduced sensitivity involves an adaptation process in the central nervous system as well.

50,

_____ papillae are located in small trenches on the lateral margins of the tongue, but most of their taste buds degenerate in early childhood.

Foliate

______ papillae are mushroom-shaped elevations scattered over the entire surface of the tongue that contain about five taste buds each.

Fungiform

____ is the light-absorbing part of all visual photopigments. In the human retina, there are four different opsins, _____ in the cones and _____ in the rods (rhodopsin). Small variations in the amino acid sequences of the different opsins permit the rods and cones to absorb different colors (wavelengths) of incoming light

Retinal, three, one

If the light level decreases abruptly, sensitivity increases rapidly at first and then more slowly. In complete darkness, full regeneration of cone photopigments occurs during the first 8 minutes of dark adaptation. During this time, a threshold light flash is seen as having color. _____ regenerates more slowly, and our visual sensitivity increases until even a single photon (the smallest unit of light) can be detected. In that situation, although much dimmer light can be detected, threshold flashes appear gray-white, regardless of their color. At very low light levels, such as starlight, objects appear as shades of gray because only the rods are functioning.

Rhodopsin

The eyelashes, which project from the border of each eyelid, and the eyebrows, which arch transversely above the upper eyelids, help protect the eyeballs from foreign objects, perspiration, and the direct rays of the sun. ________ glands at the base of the hair follicles of the eyelashes, called ____ ____ glands, release a lubricating fluid into the follicles. Infection of these glands, usually by bacteria, causes a painful, pus-filled swelling called a sty.

Sebaceous, sebaceous ciliary, sty

The walls of both the utricle and the saccule contain a small, thickened region called ______. The two _____ (plural), which are perpendicular to one another, are the receptors for static equilibrium. They provide sensory information on the position of the head in space and are essential for maintaining appropriate posture and balance. The _____ also detect linear acceleration and deceleration— for example, the sensations you feel while in an elevator or car that is speeding up or slowing down.

amacula, maculae, maculae

The lens divides the interior of the eyeball into two cavities: the _____ _____ and _____ ____.

anterior cavity, vitreous chamber

The fibrous tunic is the superficial layer of the eyeball and consists of the ____ ____ and ____ ____.

anterior cornea, posterior sclera

Branches of the central retinal artery fan out to nourish the ____ surface of the retina; the central retinal vein drains blood from the retina through the optic disc.

anterior,

The threshold for taste varies for each of the primary tastes. The threshold for _____ substances, such as quinine, is lowest. Because poisonous substances often are _____, the low threshold (or high sensitivity) may have a protective function. The threshold for ____ substances, as measured by using hydrochloric acid, is somewhat higher. The thresholds for ____ substances, and for _____ substances are similar, and are higher than those for _____ or ____ substances.

bitter, bitter, sour, salty, sweet, bitter, sour

Neural circuits in the ___ ___ and _____ coordinate and synchronize the movements of the eyes.

brain stem, cerebellum

Near the exterior opening, the external auditory canal contains a few hairs and specialized sweat glands called ______ glands that secrete earwax or cerumen. The combination of hairs and cerumen helps prevent dust and foreign objects from entering the ear. Cerumen also prevents damage to the delicate skin of the external ear canal by water and insects. Cerumen usually dries up and falls out of the ear canal. However, some people produce a large amount of cerumen, which can become impacted and can muffle incoming sounds. The treatment for impacted cerumen is usually periodic ear irrigation or removal of wax with a blunt instrument by trained medical personnel.

ceruminous

Some mesenchyme around the developing eye enters the optic cup through the ____ ___. This mesenchyme occupies the space between the lens and retina and differentiates into a delicate network of fibers. Later the spaces between the fibers fill with a jellylike substance, thus forming the vitreous body in the vitreous chamber.

choroid fissure

The pigmented layer is a sheet of melanin-containing epithelial cells located between the _____ and the ____ part of the retina.

choroid, neural,

The pupil appears black because, as you look through the lens, you see the heavily pigmented back of the eye (_____ and _____). However, if bright light is directed into the pupil, the reflected light is red because of the ___ ___ on the surface of the retina. It is for this reason that a person's eyes appear red in a photograph when the flash is directed into the pupil. Autonomic reflexes regulate pupil diameter in response to light levels. When bright light stimulates the eye, parasympathetic fibers of the ______ (III) nerve stimulate the circular muscles or ____ ____ of the iris to contract, causing a decrease in the size of the pupil (constriction). In dim light, sympathetic neurons stimulate the radial muscles or ___ ___ of the iris to contract, causing an increase in the pupil's size (dilation).

choroid, retina, blood vessels, oculomotor, sphincter pupillae, dilator pupillae

Mesenchyme surrounding the optic cup and optic stalk differentiates into an inner layer that gives rise to the _____ and an outer layer that develops into the _____ and part of the cornea. The remainder of the cornea is derived from surface _____.

choroid, sclera, ectoderm

The iris, the colored portion of the eyeball, is shaped like a flattened donut. It is suspended between the cornea and the lens and is attached at its outer margin to the ____ ___. It consists of melanocytes and circular and radial smooth muscle fibers. The amount of melanin in the iris determines the eye color. The eyes appear brown to black when the iris contains a large amount of melanin, blue when its melanin concentration is very low, and green when its melanin concentration is moderate.

ciliary processes,

Aqueous humor continually filters out of blood capillaries in the ____ ____ of the ciliary body and enters the ___ ___. It then flows forward between the iris and the lens, through the pupil, and into the anterior chamber. From the anterior chamber, aqueous humor drains into the scleral venous sinus and then into the blood. Normally, aqueous humor is completely replaced about every 90 minutes.

ciliary processes, posterior chamber

About 12 very large, ______ _____ papillae or _____ papillae form an inverted V-shaped row at the back of the tongue. Each of these papillae houses 100-300 taste buds.

circular vallate, circumvallate

Photopigments respond to light in the following cyclical process: 1. In darkness, retinal has a bent shape, called____ ___, which fits snugly into the opsin portion of the photopigment. When it absorbs a photon of light, it straightens out to a shape called ____ ____. This conversion is called _____ and is the first step in visual transduction. After retinal _____, several unstable chemical intermediates form and disappear. These chemical changes lead to production of a receptor potential

cis retinal, trans retinal, isomerization, isomerizes

Anterior to the vestibule is the _____, a bony spiral canal that resembles a snail's shell and makes almost three turns around a central bony core called the modiolus. Sections through the cochlea reveal that it is divided into three channels: ____ ____, ____ ____, and ___ ____

cochlea, cochlear duct, scala vestibuli, scala tympani

The sclera, the "white" of the eye, is a layer of dense connective tissue made up mostly of ____ ____ and _____. The sclera covers the entire eyeball except the _____; it gives shape to the eyeball, makes it more rigid, protects its inner parts, and serves as a site of attachment for the extrinsic eye muscles. At the junction of the sclera and cornea is an opening known as the ___ ___ ___.

collagen fibers, fibroblasts, cornea, scleral venous sinus

Supporting cells are _____ ____ cells of the mucous membrane lining the nose. They provide physical support, nourishment, and electrical insulation for the olfactory receptor cells and help detoxify chemicals that come in contact with the ____ ____.

columnar epithelial, olfactory epithelium

Normally, tears are cleared away as fast as they are produced, either by evaporation or by passing into the lacrimal canals and then into the nasal cavity. If an irritating substance makes contact with the _____, however, the lacrimal glands are stimulated to oversecrete, and tears accumulate (watery eyes). Lacrimation is a protective mechanism, as the tears dilute and wash away the irritating substance. Watery eyes also occur when an inflammation of the ___ ____, such as occurs with a cold, obstructs the ____ ___ and blocks drainage of tears. Only humans express emotions, both happiness and sadness, by crying. In response to parasympathetic stimulation, the lacrimal glands produce excessive lacrimal fluid that may spill over the edges of the eyelids and even fill the nasal cavity with fluid. This is how crying produces a runny nose.

conjunctiva, nasal mucosa, nasolacrimal ducts

The tarsal plate is a thick fold of ____ ____ that gives form and support to the eyelids. Embedded in each tarsal plate is a row of elongated modified sebaceous glands, known as tarsal glands or _______ glands, that secrete a fluid that helps keep the eyelids from adhering to each other. Infection of the tarsal glands produces a tumor or cyst on the eyelid called a _____.

connective tissue, Meibomian, chalazion

Horizontal cells transmit inhibitory signals to bipolar cells in the areas lateral to excited rods and cones. This lateral inhibition enhances _____ in the visual scene between areas of the retina that are strongly stimulated and adjacent areas that are more weakly stimulated. Horizontal cells also assist in the differentiation of various colors. _____ cells, which are excited by bipolar cells, synapse with ganglion cells and transmit information to them that signals a change in the level of illumination of the retina. When bipolar or amacrine cells transmit excitatory signals to ganglion cells, the ganglion cells become _____ and initiate nerve impulses

contrasts, Amacrine, depolarized

Binocular vision occurs when light rays from an object strike corresponding points on the two retinas. When we stare straight ahead at a distant object, the incoming light rays are aimed directly at both pupils and are refracted to comparable spots on the retinas of both eyes. As we move closer to an object, however, the eyes must rotate medially if the light rays from the object are to strike the same points on both retinas. The term _______ refers to this medial movement of the two eyeballs so that both are directed toward the object being viewed, for example, tracking a pencil moving toward your eyes. The nearer the object, the greater the degree of convergence needed to maintain binocular vision. The coordinated action of the extrinsic eye muscles brings about convergence.

convergence

Within the neural layer of the retina, certain features of visual input are enhanced while other features may be discarded. Input from several cells may either converge on a smaller number of postsynaptic neurons (convergence) or diverge to a large number (divergence). Overall, ______ predominates: There are only 1 million ganglion cells, but 126 million photoreceptors in the human eye.

convergence

When the surface of a lens is _____, that lens will refract incoming light rays toward each other, so that they eventually intersect. If the surface of a lens curves inward, like the inside of a hollow ball, the lens is said to be _____ and causes light rays to refract away from each other. The lens of the eye is _____ on both its anterior and posterior surfaces, and its focusing power increases as its curvature becomes greater. When the eye is focusing on a close object, the lens becomes more curved, causing greater refraction of the light rays. This increase in the curvature of the lens for near vision is called _____. The near point of vision is the minimum distance from the eye that an object can be clearly focused with maximum accommodation. This distance is about 10 cm (4 in.) in a young adult.

convex, concave, convex, accommodation

The anterior cavity—the space anterior to the lens—consists of two chambers. The anterior chamber lies between the _____ and the _____. The posterior chamber lies behind the ____ and in front of the _____ fibers and ____. Both chambers of the anterior cavity are filled with _____ ____, a transparent watery fluid that nourishes the lens and cornea.

cornea, iris, iris, zonular, lens, aqueous humor

About 75% of the total refraction of light occurs at the _____. The ____ provides the remaining 25% of focusing power and also changes the focus to view near or distant objects. When an object is 6 m (20 ft) or more away from the viewer, the light rays reflected from the object are nearly _____ to one another. The lens must bend these parallel rays just enough so that they fall exactly focused on the central fovea, where vision is sharpest. Because light rays that are reflected from objects closer than 6 m (20 ft) are divergent rather than parallel (Figure 17.12c), the rays must be refracted more if they are to be focused on the retina. This additional refraction is accomplished through a process called ______.

cornea, lens, parallel, accommodation

Within the cells of the lens, proteins called _____, arranged like the layers of an onion, make up the refractive media of the lens, which normally is perfectly transparent and lacks blood vessels. It is enclosed by a clear ____ ____ capsule and held in position by encircling _____ fibers, which attach to the ciliary processes. The lens helps focus images on the retina to facilitate clear vision.

crystallins, connective tissue, zonular

Each crista contains a group of hair cells and supporting cells. Covering the crista is a mass of gelatinous material called the _____. When you move your head, the attached semicircular ducts and hair cells move with it. The endolymph within the ____, however, is not attached and lags behind. As the moving hair cells drag along the stationary endolymph, the hair bundles bend. Bending of the hair bundles produces receptor potentials. In turn, the receptor potentials lead to nerve impulses that pass along the vestibular branch of the _______ (VIII) nerve.

cupula, ampulla, vestibulocochlear

The hair cells transduce mechanical vibrations into _____ signals. As the basilar membrane vibrates, the hair bundles at the apex of the hair cell bend back and forth and slide against one another. A tip link protein connects the tip of each stereocilium to a mechanically gated ion channel called the ______ channel in its taller stereocilium neighbor. As the stereocilia bend in the direction of the taller stereocilia, the tip links tug on the transduction channels and open them. These channels allow cations in the _____, primarily K, to enter the hair cell cytosol. As cations enter, they produce a depolarizing receptor potential. Depolarization quickly spreads along the plasma membrane and opens voltage- gated Ca2 channels in the base of the hair cell. The resulting inflow of Ca2 triggers exocytosis of synaptic vesicles containing a neurotransmitter, which is probably _____. As more neurotransmitter is released, the frequency of nerve impulses in the first-order sensory neurons that synapse with the base of the hair cell increases. Bending of the stereocilia in the opposite direction closes the transduction channels, allows _____ to occur, and reduces neurotransmitter release from the hair cells. This decreases the frequency of nerve impulses in the sensory neurons.

electrical, transduction, endolymph, glutamate, hyperpolarization

Electromagnetic radiation is energy in the form of waves that radiates from the sun. There are many types of electromagnetic radiation, including gamma rays, x-rays, UV rays, visible light, infrared radiation, microwaves, and radio waves. This range of electromagnetic radiation is known as the ____ ____. The distance between two consecutive peaks of an electromagnetic wave is the wavelength. Wavelengths range from short to long; for example, _____ rays have wavelengths smaller than a nanometer, and most radio waves have wavelengths greater than a meter.

electromagnetic spectrum, gamma

Resting on the basilar membrane is the spiral organ or organ of Corti. The spiral organ is a coiled sheet of _____ cells, including supporting cells and about 16,000 hair cells, which are the receptors for hearing. There are two groups of hair cells: The inner hair cells are arranged in a single row, whereas the outer hair cells are arranged in three rows. At the apical tip of each hair cell are 40-80 stereocilia and a kinocilium (cilium) that extend into the endolymph of the cochlear duct. Despite their name, stereocilia are actually long, hairlike microvilli arranged in several rows of graded height.

epithelial,

The middle ear is a small, air-filled cavity in the petrous portion of the temporal bone that is lined by ____. It is separated from the external ear by the tympanic membrane and from the internal ear by a thin bony partition that contains two small openings: the ___ ___ and the ___ _____. Extending across the middle ear and attached to it by ligaments are the three smallest bones in the body, the auditory ossicles which are connected by ___ ___. The bones, named for their shapes, are the ____, ____, and ____— commonly called the hammer, anvil, and stirrup, respectively.

epithelium, oval window, round window, synovial joints, malleus, incus, stapes

The anterior wall of the middle ear contains an opening that leads directly into the auditory tube, commonly known as the ___ ____. The auditory tube, which consists of both ____ and ___ ___, connects the middle ear with the _____. It is normally closed at its ____ end. During swallowing and yawning, it opens, allowing air to enter or leave the middle ear until the pressure in the middle ear equals the atmospheric pressure. Most of us have experienced our ears popping as the pressures equalize. When the pressures are balanced, the tympanic membrane vibrates freely as sound waves strike it. If the pressure is not equalized, intense pain, hearing impairment, ringing in the ears, and vertigo could develop. The auditory tube also is a route for pathogens to travel from the nose and throat to the middle ear, causing the most common type of ear infection (see otitis media in Disorders: Homeostatic Imbalances at the end of this chapter).

eustachian tube, bone, elastic cartilage, nasopharynx, medial

The accessory structures of the eye include the_____, _____, ______, the ___ ____, and _____ eye muscles.

eyelids, eyelashes, eyebrows, lacrimal apparatus, extrinsic

Three cranial nerves contain axons of the first-order gustatory neurons that innervate the taste buds. The _____ (VII) nerve serves taste buds in the anterior two-thirds of the tongue; the _______ (IX) nerve serves taste buds in the posterior one-third of the tongue; and the _____ (X) nerve serves taste buds in the throat and epiglottis. From the taste buds, nerve impulses propagate along these cranial nerves to the gustatory nucleus in the _____ _____. From there, some axons carrying taste signals project to the _____ system and the ______; others project to the _____. Taste signals that project from the ______ to the primary gustatory area in the parietal lobe of the cerebral cortex give rise to the conscious perception of taste.

facial, glossopharyngeal, vagus, Medulla Oblongata, limbic, hypothalamus, thalamus, thalamus

The adult eyeball measures about 2.5 cm in diameter. Of its total surface area, only the anterior one-sixth is exposed; the remainder is recessed and protected by the orbit, into which it fits. Anatomically, the wall of the eyeball consists of three layers: (1) _____ ____, (2) ____ ____, and (3) _____

fibrous tunic, vascular tunic, retina

In addition, the entire surface of the tongue has _____ papillae. These pointed, threadlike structures contain tactile receptors but no ____ ___. They increase friction between the tongue and food, making it easier for the tongue to move food in the oral cavity

filiform, taste buds

From the primary olfactory area, pathways also extend to the ____ ___. An important region for odor identification and discrimination is the ___ ___. People who suffer damage in this area have difficulty identifying different odors. Positron emission tomography (PET) studies suggest some degree of hemispheric lateralization: The orbitofrontal area of the ____ hemisphere exhibits greater activity during olfactory processing.

frontal lobe, orbitofrontal area, right

All photopigments associated with vision contain two parts: a ______ known as ____ and a derivative of vitamin A called _____. Vitamin A derivatives are formed from ____, the plant pigment that gives carrots their orange color. Good vision depends on adequate dietary intake of carotene-rich vegetables such as carrots, spinach, broccoli, and yellow squash, or foods that contain vitamin A, such as liver.

glycoprotein, opsin, retinal, carotene

Once a tastant is dissolved in saliva, it can make contact with the plasma membranes of the ____ ___, which are the sites of taste ____. The result is a receptor potential that stimulates exocytosis of synaptic vesicles from the ____ ____ cell. In turn, the liberated neurotransmitter molecules trigger nerve impulses in the first-order sensory neurons that synapse with ____ ___ cells.

gustatory microvilli, transduction, gustatory receptor, gustatory receptor

Each gustatory receptor cell has a life span of about 10 days. This is why it does not take taste receptors on the tongue too long to recover from being burned by that too hot cup of coffee or cocoa. At their base, the gustatory receptor cells synapse with dendrites of the first-order neurons that form the first part of the ____ ____. The dendrites of each first-order neuron branch profusely and contact many ___ ___ cells in several taste buds.

gustatory pathway, gustatory receptor

The maculae consist of two kinds of cells: ___ cells, which are the sensory receptors, and _____ cells. Hair cells have on their surface 40-80 _____ of graduated height, plus one ____, a conventional cilium anchored firmly to its basal body and extending beyond the longest ______. As in the cochlea, the _____ are connected by tip links. Collectively, the _____ and _____ are called a hair bundle.

hair, supporting, stereocilia, kinocilium, stereocilim, stereocilia, stereocilia, kinocilium

The auricle is a flap of elastic cartilage shaped like the flared end of a trumpet and covered by skin. The rim of the auricle is the ____; the inferior portion is the ____. Ligaments and muscles attach the auricle to the head. The external auditory canal is a curved tube about 2.5 cm (1 in.) long that lies in the _____ bone and leads to the ______.

helix, lobule, temporal, eardrum

Two other types of cells present in the bipolar cell layer of the retina are called ______ cells and ______ cells. These cells form laterally directed neural circuits that modify the signals being transmitted along the pathway from photoreceptors to bipolar cells to ganglion cells.

horizontal, amacrine

The lens placodes also invaginate and develop into lens vesicles that sit in the optic cups. The lens vesicles eventually develop into the lenses. Blood is supplied to the developing lenses (and retina) by the ___ ___. These arteries gain access to the developing eyes through a groove on the inferior surface of the optic cup and optic stalk called the ___ ___. As the lenses mature, part of the ___ ___ that pass through the vitreous chamber degenerate; the remaining portions of the these arteries become the ___ ___ ___.

hyaloid arteries, choroid fissure, hyaloid arteries, central retinal arteries

The lacrimal apparatus is a group of structures that produces and drains lacrimal fluid or tears in a process called _____. The lacrimal glands, each about the size and shape of an almond, secrete lacrimal fluid, which drains into 6-12 lacrimal ducts that empty tears onto the surface of the conjunctiva of the upper lid. From here the tears pass medially over the anterior surface of the eyeball to enter two small openings called ____ ____. Tears then pass into two ducts, the superior and inferior lacrimal canaliculi, which lead into the ____ ___ and then into the ___ ___. This duct carries the lacrimal fluid into the nasal cavity just inferior to the inferior nasal concha where it mixes with mucus. An infection of the lacrimal sacs is called _______. It is usually caused by a bacterial infection and results in blockage of the nasolacrimal ducts.

lacrimation, lacrimal puncta, lacrimal sac, nasolacrimal duct, dacryocystitis

Some motor neurons serve only two or three muscle fibers—fewer than in any other part of the body except the _____. Such small motor units permit smooth, precise, and rapid movement of the eyes. For example, looking to the right requires simultaneous contraction of the right _____ rectus and left ____ rectus muscles of the eyeball and relaxation of the left _____ rectus and right _____ rectus of the eyeball. The oblique muscles preserve rotational stability of the eyeball.

larynx, lateral, medial, lateral, medial,

Behind the pupil and iris, within the cavity of the eyeball, is the ____.

lens

The larger posterior cavity of the eyeball is the vitreous chamber, which lies between the ____ and the ____. Within the vitreous chamber is the ___ ____, a transparent jellylike substance that holds the retina flush against the choroid, giving the retina an even surface for the reception of clear images. It occupies about four-fifths of the eyeball. Unlike the aqueous humor, the ___ ____ does not undergo constant replacement. It is formed during embryonic life and consists of mostly water plus _____ ____ and ___ ___. It also contains _____ cells that remove debris, keeping this part of the eye clear for unobstructed vision. Occasionally, collections of debris may cast a shadow on the retina and create the appearance of specks that dart in and out of the field of vision. These vitreal floaters, which are more common in older individuals, are usually harm- less and do not require treatment.

lens, retina, vitreous body, vitreous body, collagen fibers, hyaluronic acid, phagocytic

Olfaction, like all the special senses, has a ___ threshold. Only a few molecules of certain substances need to be present in air to be perceived as an odor. A good example is the chemical __ ___, which smells like rotten cabbage and can be detected in concentrations as low as ____ billionth of a milligram per milliliter of air. Because the natural gas used for cooking and heating is odorless but lethal and potentially explosive if it accumulates, a small amount of __ ___ is added to natural gas to provide olfactory warning of gas leaks.

low, methyl mercaptan, 1/25, methyl mercaptan

The ____ ____ is in the exact center of the posterior portion of the retina, at the visual axis of the eye. The ____ ___, a small depression in the center of the ____ ___, contains only cones. In addition, the layers of bipolar and ganglion cells, which scatter light to some extent, do not cover the cones here; these layers are displaced to the periphery of the ___ ___. As a result, the ___ ____ is the area of highest visual acuity or resolution (sharpness of vision).

macula lutea, fovea centralis, macula lutea, fovea centralis, fovea centralis,

The supporting cells contain ____ and surround about 50 gustatory receptor cells in each taste bud. Gustatory ______ project from each gustatory receptor cell to the external surface through the taste pore, an opening in the taste bud. Basal cells, stem cells found at the periphery of the taste bud near the ___ ____ layer, produce supporting cells, which then develop into ___ ___ cells.

microvilli, microvilli, connective tissue, gustatory receptor

The tympanic membrane or eardrum is a thin, semitransparent partition between the external auditory canal and ___ ___. The tympanic membrane is covered by epidermis and lined by ___ ___ ___. Between the epithelial layers is connective tissue composed of ____, ___ ___, and _____.

middle ear, simple cuboidal epithelium, collagen, elastic fibers, fibroblasts

The vascular tunic is the _____ layer of the eyeball. It is composed of three parts: ____, ____ ____, and ___.

middle, choroid, ciliary body, iris

The normal eye, known as an emmetropic eye, can sufficiently refract light rays from an object 6 m (20 ft) away so that a clear image is focused on the retina. However, many people lack this ability because of refraction abnormalities. Among these abnormalities are ____, or nearsightedness, which occurs when the eyeball is too ____ relative to the focusing power of the cornea and lens, or when the lens is ____ than normal, so an image converges in front of the retina. Myopic individuals can see close objects clearly, but not distant objects. In _____ or far- sightedness the eyeball length is _____ relative to the focusing power of the cornea and lens, or the lens is _______ than normal, so an image converges behind the retina. Hyperopic individuals can see distant objects clearly, but not close ones. Another refraction abnormality is ______, in which either the cornea or the lens has an irregular curvature. As a result, parts of the image are out of focus, and thus vision is blurred or distorted

myopia, long, thicker, hyperopia, short, thinner, astigmatism

Photoreceptors are specialized cells in the photoreceptor layer that begin the process by which light rays are ultimately converted to ____ ____. There are two types of photoreceptors: ____ and _____. Each retina has about 6 million ____ and 120 million ____.

nerve impulses, rods, cones, cones, rods

The conjunctiva is a thin, protective mucous membrane composed of ____ ___ ____ ___ with numerous goblet cells that is supported by ____ ____ tissue.

nonkeratinized stratified squamous epithelium, areolar connective

The vestibular nuclei integrate information from vestibular, visual, and somatic receptors and then send commands to (1) the nuclei of cranial nerves- ____ (III), _____ (IV), and _____ (VI)—that control coupled movements of the eyes with those of the head to help maintain focus on the visual field; (2) nuclei of the ______ (XI) nerves to help control head and neck movements to assist in maintaining equilibrium; (3) the _______ tract, which conveys impulses down the spinal cord to maintain muscle tone in skeletal mus- cles to help maintain equilibrium; and (4) the ventral posterior nucleus in the ______ and then to the vestibular area in the parietal lobe of the cerebral cortex to provide us with the conscious awareness of the position and movements of the head and limbs

oculomotor, trochlear, abducens, accessory, vestibulospinal, thalamus

Olfactory receptor cells react to ____ molecules in the same way that most sensory receptors react to their specific stimuli: A ___ ____ (depolarization) develops and triggers one or more nerve impulses. This process, called ____ ____, occurs in the following way: Binding of an odorant to an olfactory receptor protein in an ___ ___ stimulates a membrane protein called a __ protein. The _ protein, in turn, activates the enzyme __ ___ to produce a substance called ___ ___ ___ (cAMP). The cAMP opens a sodium ion channel that allows to enter the cytosol, which causes a depolarizing generator potential to form in the membrane of the olfactory receptor cell. If the depolarization reaches threshold, an action potential is generated along the axon of the olfactory receptor cell.

odorant, generator potential, olfactory transduction, olfactory cilium, G, G, adenylate cyclase, cyclic adenosine monophosphate

Within the plasma membranes of the ____ ____ are olfactory receptors that detect inhaled chemicals. Chemicals that have an odor that bind to and stimulate the olfactory receptors in the olfactory cilia are called ____. Olfactory receptor cells respond to the chemical stimulation of an odorant molecule by producing a ___ ___, thus initiating the olfactory response.

olfactory cilia, odorants, generator potential

Within the connective tissue that supports the olfactory epithelium are ___ ____ or ___ ____, which produce mucus that is carried to the surface of the epithelium by ducts. The secretion moistens the surface of the olfactory epithelium and dissolves odorants so that _____ can occur. Both supporting cells of the nasal epithelium and olfactory glands are innervated by ____ neurons within branches of the _____ (VII) nerve, which can be stimulated by certain chemicals. Impulses in these nerves in turn stimulate the ____ ____ in the eyes and ___ ____ glands. The result is tears and a runny nose after inhaling substances such as pepper or the vapors of household ammonia.

olfactory glands, Bowman's glands, transduction, parasympathetic, facial, lacrimal glands, nasal mucous

Olfactory receptor cells are the first-order neurons of the _____ ____. Each olfactory receptor cell is a ____ neuron with an exposed knob-shaped ____ and an axon projecting through the ___ ____ that ends in the ____ ___. Extending from the dendrite of an olfactory receptor cell are several nonmotile olfactory cilia, which are the sites of olfactory transduction.

olfactory pathway, bipolar, dendrite, cribriform plate, olfactory bulb

Many attempts have been made to distinguish among and classify "primary" sensations of smell. Genetic evidence now suggests the existence of hundreds of primary odors. Our ability to recognize about 10,000 different odors probably depends on patterns of activity in the brain that arise from activation of many different combinations of__ ____ ___.

olfactory receptor cells

Basal cells are stem cells located between the bases of the supporting cells. They continually undergo cell division to produce new ____ ____ ____, which live for only a month or so before being replaced. This process is remarkable considering that olfactory receptor cells are neurons, and as you have already learned, mature neurons are generally not _____.

olfactory receptor cells, replaced

Photopigments respond to light in the following cyclical process: 2. In about a minute, trans-retinal completely separates from ____. The final products look colorless, so this part of the cycle is termed bleaching of photopigment.

opsin

Photopigments respond to light in the following cyclical process: 4. The cis-retinal then can bind to ____, reforming a functional _____. This part of the cycle—resynthesis of a photopigment—is called regeneration.

opsin, photopigment

The inner wall of the optic cup forms the neural layer of the retina, while the outer layer forms the pigmented layer of the retina. Axons from the neural layer grow through the optic stalk to the brain, converting the optic stalk to the ____ (II) nerve. Although myelination of the optic nerves begins late in fetal life, it is not completed until the tenth week after birth.

optic

The axons within the optic (II) nerve pass through the ___ ___, a crossing point of the optic nerves. Some axons cross to the opposite side, but others remain uncrossed.

optic chiasm,

After passing through the optic chiasm, the axons of the optic nerve, now part of the__ ___, enter the brain and most of them terminate in the lateral geniculate nucleus of the _____. Here they synapse with neurons whose axons form the optic radiations, which project to the primary visual areas in the occipital lobes of the cerebral cortex, and visual perception begins. Some of the fibers in the optic tracts terminate in the ___ ___, which control the extrinsic eye muscles, and the ___ ___, which control pupillary and accommodation reflexes.

optic tract, thalamus, superior colliculi, pretectal nuclei

The third and inner layer of the eyeball, the retina, lines the posterior three-quarters of the eyeball and is the beginning of the visual pathway. This layer's anatomy can be viewed with an ophthalmoscope, an instrument that shines light into the eye and allows an observer to peer through the pupil, providing a magnified image of the retina and its blood vessels as well as the ____ (II) nerve. The surface of the retina is the only place in the body where _____ ____ can be viewed directly and examined for pathological changes, such as those that occur with hypertension, diabetes mellitus, cataracts, and age-related macular disease. Several landmarks are visible through an ophthalmoscope. The ___ ___ is the site where the ____ (II) nerve exits the eyeball. Bundled together with the optic nerve are the ___ ___ artery, a branch of the ophthalmic artery, and the ___ ___ vein.

optic, blood vessels, optic disc, optic, central retinal, central retinal

In the anterior portion of the vascular tunic, the choroid becomes the ciliary body. It extends from the ____ ____, the jagged anterior margin of the retina, to a point just posterior to the junction of the sclera and cornea. Like the choroid, the ciliary body appears dark brown in color because it contains melanin-producing melanocytes. In addition, the ciliary body consists of ____ ____ and ___ ___.

ora serrata, ciliary processes, ciliary muscle

From superficial to deep, each eyelid consists of epidermis, dermis, subcutaneous tissue, fibers of the _____ ____ muscle, a _____ plate, _____ glands, and ______.

orbicularis oculi, tarsal, tarsal, conjunctiva

The eyes sit in the bony depressions of the skull called the _____.

orbits

Besides its role in detecting sounds, the cochlea has the surprising ability to produce sounds. These usually inaudible sounds, called _____ emissions, can be picked up by placing a sensitive microphone next to the eardrum. They are caused by vibrations of the outer hair cells that occur in response to sound waves and to signals from motor neurons. As they depolarize and repolarize, the outer hair cells rapidly shorten and lengthen. This vibratory behavior appears to change the stiffness of the tectorial membrane and is thought to enhance the movement of the basilar membrane, which amplifies the responses of the inner hair cells. At the same time, the outer hair cell vibrations set up a traveling wave that goes back toward the stapes and leaves the ear as an otoacoustic emission. Detection of these inner earroduced sounds is a fast, inexpensive, and noninvasive way to screen newborns for hearing defects. In deaf babies, otoacoustic emissions are not produced or are greatly reduced in size.

otoacoustic,

Scattered among the hair cells are columnar supporting cells that probably secrete the thick, gelatinous, glycoprotein layer, called the ___ membrane,that rests on the hair cells. A layer of dense calcium carbonate crystals, alled otoliths, extends over the entire surface of the otolithic membrane.

otolithic

From photoreceptors, information flows through the ____ ___ layer to _____ cells and then from _____ cells through the ___ ___ layer to ganglion cells. The axons of ganglion cells extend posteriorly to the optic disc and exit the eyeball as the optic (II) nerve. The optic disc is also called the ____ ___. Because it contains no rods or cones, we cannot see images that strike the blind spot.

outer synaptic, bipolar, bipolar, inner synaptic, blind spot

The upper and lower eyelids, or ______, shade the eyes during sleep, protect the eyes from excessive light and foreign objects, and spread lubricating secretions over the eyeballs. The upper eyelid is more movable than the lower and contains in its superior region the ___ ___ ___ muscle.

palpebrae, levator palpebrae superioris,

The space between the upper and lower eyelids that exposes the eyeball is the ____ ____. Its angles are known as the ___ ___, which is narrower and closer to the temporal bone, and the ____ ____, which is broader and nearer the nasal bone.

palpebral fissure, lateral commissure, medial commissure,

The _____ conjunctiva lines the inner aspect of the eyelids, and the _____ conjunctiva passes from the eyelids onto the surface of the eyeball, where it covers the ____ (the "white" of the eye) but not the _____, which is a transparent region that forms the outer anterior surface of the eyeball.

palpebral, bulbar, sclera, cornea

Taste buds are found in elevations on the tongue called ______, which increase the surface area and provide a rough texture to the upper surface of the tongue

papillae

The lacrimal glands are supplied by _____ fibers of the _____ (VII) nerves. The lacrimal fluid produced by these glands is a watery solution containing salts, some mucus, and ______, a protective bactericidal enzyme. The fluid protects, cleans, lubricates, and moistens the eyeball. After being secreted from the lacrimal gland, lacrimal fluid is spread medially over the surface of the eyeball by the blinking of the eyelids. Each gland produces about 1 mL of lacrimal fluid per day.

parasympathetic, facial, lysozyme,

Both the scala vestibuli and scala tympani are part of the bony labyrinth of the cochlea; therefore, these chambers are filled with ____. The scala vestibuli and scala tympani are completely separated by the cochlear duct, except for an opening at the apex of the cochlea, the _____. The cochlea adjoins the wall of the vestibule, into which the scala vestibuli opens. The perilymph in the vestibule is continuous with that of the scala vestibuli.

perilymph, helicotrema,

The middle ear develops from a structure called the first ____ ____, an endoderm-lined outgrowth of the primitive _____. The auditory ossicles develop from the first and second pharyngeal arches. The external ear develops from the first ____ ___, an endoderm-lined groove between the first and second pharyngeal arches

pharyngeal pouch, pharynx, pharyngeal cleft

As the light level increases, more and more ______ is bleached. While light is bleaching some photopigment molecules, however, others are being regenerated. In daylight, regeneration of rhodopsin cannot keep up with the bleaching process, so rods contribute little to daylight vision. In contrast, cone photopigments regenerate rapidly enough that some of the cis form is always present, even in very bright light.

photopigment,

The first step in visual transduction is absorption of light by a ______, a colored protein that undergoes structural changes when it absorbs light, in the outer segment of a photoreceptor. Light absorption initiates the events that lead to the production of a ___ ___. The single type of photopigment in rods is ____. Three different cone photopigments are present in the retina, one in each of the three types of cones. Color vision results from different colors of light selectively activating the different cone photopigments.

photopigment, receptor potential, rhodopsin

Rods and cones were named for the different appearance of the outer segment—the distal end next to the pigmented layer—of each of these types of -____. The outer segments of rods are cylindrical or rod-shaped; those of cones are tapered or cone-shaped. Transduction of light energy into a receptor potential occurs in the outer segment of both rods and cones. The photopigments are integral proteins in the plasma membrane of the outer segment. In cones the plasma membrane is _____ in a pleated fashion; in rods the pleats pinch off from the plasma membrane to form ____. The outer segment of each rod contains a stack of about 1000 discs, piled up like coins inside a wrapper.

photoreceptors, folded, discs

Photoreceptor outer segments are renewed at an astonishingly rapid pace. In rods, one to three new discs are added to the base of the outer segment every hour while old discs slough off at the tip and are phagocytized by ____ ___ cells. The inner segment contains the cell nucleus, ____ ____, and many _____. At its proximal end, the photoreceptor expands into bulblike synaptic terminals filled with synaptic vesicles.

pigment epithelial, Golgi complex, mitochondria

The pigmented layer of the retina adjacent to the photoreceptors stores a large quantity of vitamin A and contributes to the regeneration process in rods. The extent of rhodopsin regeneration decreases drastically if the retina detaches from the _____ layer. ____ photopigments regenerate much more quickly than the rhodopsin in ____ and are less dependent on the pigmented layer. After complete bleaching, regeneration of half of the rhodopsin takes 5 minutes; half of the cone photopigments regenerate in 90 seconds. Full regeneration of bleached rhodopsin takes 30 to 40 minutes.

pigmented, Cone, rods

The retina consists of a _____ layer and a neural layer.

pigmented, neural

Visual signals in the retina undergo considerable processing at synapses among the various types of neurons in the ____. Then, the axons of ___ ___ cells provide output from the retina to the brain, exiting the eyeball as the optic (II) nerve.

retina, retinal ganglion

Photopigments respond to light in the following cyclical process: 3. An enzyme called ____ _____ converts trans-retinal back to cis-retinal.

retinal isomerase

The highly vascularized choroid, which is the _____ portion of the ____ ____, lines most of the internal surface of the sclera. Its numerous blood vessels provide nutrients to the posterior surface of the retina. The choroid also contains ______ that produce the pigment melanin, which causes this layer to appear dark brown in color. Melanin in the choroid absorbs stray light rays, which prevents reflection and scattering of light within the eyeball. As a result, the image cast on the retina by the cornea and lens remains sharp and clear. Albinos lack melanin in all parts of the body, including the eye. They often need to wear sunglasses, even indoors, because even moderately bright light is perceived as bright glare due to light scattering.

posterior, vascular tunic, melanocytes,

Axons of olfactory bulb neurons extend ____ and form the ____ ____. Some of the axons of the olfactory tract project to the primary olfactory area of the ____ ___; located at the inferior and medial surface of the temporal lobe, the primary olfactory area is where conscious awareness of smell begins. Olfactory sensations are the only sensations that reach the cerebral cortex without first synapsing in the _____. Other axons of the olfactory tract project to the limbic system and _____; these connections account for our emotional and memory-evoked responses to odors. Examples include sexual excitement on smelling a certain perfume, nausea on smelling a food that once made you violently ill, or an odor-evoked memory of a childhood experience.

posteriorly, olfactory tract, cerebral cortex, thalamus, hypothalamus,

The eyes begin to develop about 22 days after fertilization when the ectoderm of the lateral walls of the ______ (forebrain) bulges out to form a pair of shallow grooves called the ____ ____. Within a few days, as the neural tube is closing, the ___ ___ enlarge and grow toward the surface ectoderm and become known as the optic vesicles. When the optic vesicles reach the surface ectoderm, the surface ectoderm thickens to form the ___ ____. In addition, the distal portions of the optic vesicles invaginate, forming the optic cups; they remain attached to the prosencephalon by narrow, hollow proximal structures called ___ ___

prosencephalon, optic grooves, optic grooves, lens placodes, optic stalks

A principal function of the iris is to regulate the amount of light entering the eyeball through the _____, the hole in the center of the iris.

pupil

The internal (inner) ear is also called the labyrinth because of its complicated series of canals. Structurally, it consists of two main divisions: an outer bony labyrinth that encloses an inner membranous labyrinth. It is like long balloons put inside a rigid tube. The bony labyrinth is a series of cavities in the petrous portion of the temporal bone divided into three areas: (1) the ___ ___, (2) the ____, and (3) the ____. The bony labyrinth is lined with _____ and contains perilymph. This fluid, which is chemically similar to _____ fluid, surrounds the membranous labyrinth, a series of epithelial sacs and tubes inside the bony labyrinth that have the same general form as the bony labyrinth and house the receptors for hearing and equilibrium. The epithelial membranous labyrinth contains ______. The level of potassium ions (K) in endolymph is unusually high for an extracellular fluid, and potassium ions play a role in the generation of auditory signals.

semicircular canals, vestibule, cochlea, periosteum, cerebrospinal, endolymph

Although we have just described the visual pathway as a single pathway, visual signals are thought to be processed by at least three separate systems in the cerebral cortex, each with its own function. One system processes information related to the ____ of objects, another system processes information regarding the ____ of objects, and a third system processes information about ____, ____, and ___ ____.

shape, color, movement, location, spatial organization

The receptor potential arises differently for different tastants. The _____ ions in a salty food enter gustatory receptor cells via ___ channels in the plasma membrane. The accumulation of ___ inside the cell causes ______, which leads to release of neurotransmitter.

sodium, Na, Na, depolarization,

The hydrogen ions (H) in ____ tastants may flow into gustatory receptor cells via H channels. They also influence opening and closing of other types of ion channels. Again, the result is _____ and the liberation of neurotransmitter.

sour, depolarization

Chemicals that stimulate gustatory receptor cells are known as ______.

tastants

The receptors for sensations of taste are located in the _____ ____.

taste buds

Taste or gustation, like olfaction, is a chemical sense. However, it is much simpler than olfaction in that only five primary tastes can be distinguished: ____, ____, _____, ____, and _____. The ____ taste, more recently discovered than the other tastes, was first reported by Japanese scientists and is described as "meaty" or "savory." Umami is believed to arise from taste receptors that are stimulated by l-glutamate and nucleotides, substances present in many foods. Monosodium glutamate, added to foods as a flavor enhancer, confers the umami taste to foods. All other flavors, such as chocolate, pepper, and coffee, are combinations of the five primary tastes, plus accompanying olfactory and tactile (touch) sensations. Odors from food can pass upward from the mouth into the nasal cavity, where they stimulate olfactory receptors. Because olfaction is much more sensitive than taste, a given concentration of a food substance may stimulate the olfactory system thousands of times more strongly than it stimulates the gustatory system. When you have a cold or are suffering from allergies and cannot taste your food, it is actually olfaction that is blocked, not taste.

sour, sweet, bitter, salty, umami, umami,

Bending of the stereocilia of the hair cells of the spiral organ causes the release of a neurotransmitter (probably glutamate), which generates nerve impulses in the sensory neurons that in- nervate the hair cells. The cell bodies of the sensory neurons are located in the ___ ____. Nerve impulses pass along the axons of these neurons, which form the cochlear branch of the ______ (VIII) nerve. These axons synapse with neurons in the cochlear nuclei in the ___ ____ on the same side. Some of the axons from the cochlear nuclei decussate (cross over) in the medulla, ascend in a tract called the ___ ___ on the opposite side, and terminate in the inferior colliculus in the _____. Other axons from the cochlear nuclei end in the superior olivary nucleus in the pons on each side. Slight differences in the timing of nerve impulses arriving from the two ears at the superior olivary nuclei allow us to locate the source of a sound. Axons from the superior olivary nuclei also ascend in the lateral lemniscus tracts on both sides and end in the inferior colliculi. From each inferior colliculus, nerve impulses are conveyed to the medial geniculate nucleus in the thalamus and finally to the primary auditory area of the cerebral cortex in the temporal lobe of the cerebrum. Because many auditory axons decussate in the medulla while others remain on the same side, the right and left primary auditory areas receive nerve impulses from both ears.

spiral ganglia, vestibulocochlear, medulla oblongata, lateral lemniscus, midbrain,

The melanin in the pigmented layer of the retina also helps to absorb ___ ___ ___. The neural layer of the retina is a multilayered outgrowth of the brain that processes visual data extensively before sending nerve impulses into axons that form the ___ ___. Three distinct layers of retinal neurons—the ______ layer, the ___ ___ layer, and the ___ ____ layer—are separated by two zones, the outer and inner synaptic layers, where synaptic contacts are made.

stray light rays, optic nerve, photoreceptor, bipolar cell, ganglion cell

Six extrinsic eye muscles move each eye: the _____ rectus, _____ rectus, _____ rectus, _____ rectus, _____ oblique, and ____ oblique. They are supplied by the _____ (III), _____ (IV), or ______ (VI) nerves. In general, the motor units in these muscles are small.

superior, inferior, lateral, medial, superior, inferior, oculomotor, trochlear, abducens

Each taste bud is an oval body consisting of three kinds of epithelial cells: ___ cells, ___ ___ cells, and ____ cells.

supporting, gustatory receptor, basal

Different tastes arise from activation of different groups of ____ ____. In addition, although each individual gustatory receptor cell responds to more than one of the five primary tastes, it may respond more strongly to some tastants than to others.

taste neurons

Besides the ligaments, two tiny skeletal muscles also attach to the ossicles. The ___ ___ muscle, which is supplied by the mandibular branch of the _____ (V) nerve, limits movement and increases tension on the eardrum to prevent damage to the inner ear from loud noises. The ____ muscle, which is supplied by the _____ (VII) nerve, is the smallest skeletal muscle in the human body. By dampening large vibrations of the stapes due to loud noises, it protects the oval window, but it also decreases the sensitivity of hearing. For this reason, paralysis of the stapedius muscle is associated with _____, which is abnormally sensitive hearing. Because it takes a fraction of a second for the tensor tympani and stapedius muscles to contract, they can protect the inner ear from prolonged loud noises but not from brief ones such as a gunshot.

tensor tympani, trigeminal, stapedius, facial, hyperacusia

Most of the nearly 10,000 taste buds of a young adult are on the ____, but some are found on the ___ ____ (posterior portion of the roof of the mouth), _____ (throat), and _____ (cartilage lid over voice box). The number of taste buds declines with age.

tongue, soft palate, pharynx, epiglottis

The vestibule is the oval central portion of the bony labyrinth. The membranous labyrinth in the vestibule consists of two sacs called the ____ and the ____, which are connected by a small duct. Projecting superiorly and posteriorly from the vestibule are the three bony semicircular canals, each of which lies at approximately right angles to the other two. Based on their positions, they are named the _____, ____, and ____ semicircular canals. The anterior and posterior semicircular canals are _____ oriented; the lateral one is _____ oriented. At one end of each canal is a swollen enlargement called the ____. The portions of the membranous labyrinth that lie inside the bony semicircular canals are called the semicircular ducts. These structures connect with the utricle of the vestibule.

utricle, saccule, anterior, posterior, lateral, vertically, horizontally, ampulla

Bending of hair bundles of the hair cells in the semicircular ducts, _____, or _____ causes the release of a neurotransmitter (probably glutamate), which generates nerve impulses in the sensory neurons that innervate the hair cells. The cell bodies of sensory neurons are located in the ____ ___. Nerve impulses pass along the axons of these neurons, which form the vestibular branch of the vestibulocochlear (VIII) nerve. Most of these axons synapse with sensory neurons in vestibular nuclei, the major integrating centers for equilibrium, in the ____ ____ and _____. The vestibular nuclei also receive input from the eyes and proprioceptors, especially proprioceptors in the neck and limb muscles that indicate the position of the head and limbs. The remaining axons enter the cerebellum through the ___ ___ ____. Bidirectional pathways connect the cerebel- lum and vestibular nuclei

utricle, saccule, vestibular ganglia, medulla oblongata, pons, inferior cerebellar peduncles

Over the sclera, the conjunctiva is _____. ______ and _____ of the blood vessels of the bulbar conjunctiva due to local irritation or infection are the cause of bloodshot eyes.

vascular, Dilation, congestion

The three semicircular ducts function in dynamic equilibrium. The ducts lie at right angles to one another in three planes: The two _____ ducts are the anterior and posterior semicircular ducts, and the _____ one is the lateral semicircular duct. This positioning permits detection of rotational acceleration or deceleration. In the ______, the dilated portion of each duct, is a small elevation called the _____.

vertical, horizontal, ampulla, crista

As the hair cells depolarize and repolarize, they release neurotransmitter at a faster or slower rate. The hair cells synapse with first-order sensory neurons in the vestibular branch of the ______ (VIII) nerve. These neurons fire impulses at a slow or rapid pace depending on the amount of neurotransmitter present. Motor neurons also synapse with the hair cells and sensory neurons. Evidently, the motor neurons regulate the sensitivity of the hair cells and sensory neurons.

vestibulocochlear

The vestibular branch of the ______ (VIII) nerve consists of ______, _____, and ____ nerves. These nerves contain both first-order sensory neurons and motor neurons that synapse with receptors for equilibrium. The first-order sensory neurons carry sensory information from the receptors, and the motor neurons carry feedback signals to the receptors, apparently to modify their sensitivity. Cell bodies of the sensory neurons are located in the ____ ____.

vestibulocochlear, ampullary, utricular, saccular, vestibular ganglia

At their basal ends, inner and outer hair cells synapse both with first-order sensory neurons and with motor neurons from the cochlear branch of the ______ (VIII) nerve. Cell bodies of the sensory neurons are located in the ___ ____. Although outer hair cells outnumber them by 3 to 1, the inner hair cells synapse with 90-95% of the first-order sensory neurons in the cochlear nerve that relay auditory information to the brain. By contrast, 90% of the motor neurons in the co- chlear nerve synapse with outer hair cells. The tectorial mem- brane, a flexible gelatinous membrane, covers the hair cells of the spiral organ. In fact, the ends of the stereocilia of the hair cells are embedded in the tectorial membrane while the bodies of the hair cells rest on the _____ membrane.

vestibulocochlear, spiral ganglion, basilar

Visible light exhibits colors: The color of visible light depends on its wavelength. For example, light that has a wavelength of 400 nm is ____, and light that has a wavelength of 700 nm is ____. An object can absorb certain wavelengths of visible light and reflect others; the object will appear the color of the wavelength that is reflected. For example, a green apple appears green because it reflects mostly green light and absorbs most other wavelengths of visible light. An object appears white because it reflects all wavelengths of visible light. An object appears black because it absorbs all wavelengths of visible light.

violet, red

The ciliary processes are protrusions or folds on the internal surface of the ciliary body. They contain blood capillaries that secrete aqueous humor. Extending from the ciliary process are _____ fibers or ____ ____ that attach to the lens. The fibers consist of thin, hollow fibrils that resemble elastic connective tissue fibers. The ciliary muscle is a circular band of smooth muscle. Contraction or relaxation of the ciliary muscle changes the tightness of the _____ fibers, which alters the shape of the lens, adapting it for near or far vision.

zonular, suspensory ligaments, zonular