Chapter 15-General and Special Senses

External Auditory Canal

2.5 centimeter long passage in the temporal bone from the auricle to the tympanic membrane.

Lens

Flexible crystalline structure that focuses light onto the retina.

Sclera

The posterior part of the fibrous tunic that makes up the white part of the eyeball.

Retina

Thin, delicate structure in the sensory tunic containing photoreceptors.

Auditory ossicles

Tiny bones of the middle ear that transmit vibrations from the tympanic membrane to the inner ear.

The six extrinsic eye muscles move the eyeball.

True

Iris

Visible pigmented portion of the eye, most anterior portion of the vascular tunic.

The disease macular degeneration is characterized by a gradual loss of vision as a result of degeneration of the macula lutea. Considering the type of cells located in the macula lutea, which type of vision do you think a sufferer of macular degeneration would lose? Why?

Cones are located in the macula lutea and are responsible for color and high-acuity vision. Patients with this condition lose color vision and are unable to see objects clearly.

The fluid in the anterior cavity is known as ________________________, whereas the fluid in the posterior cavity is known as _______________________.

1) Aqueous humor 2) Vitreous humor

The rods are responsible for _______________, where as the cones are responsible for _____________________.

1) Peripheral and dim light vision 2) high-acuity color vision

The structures of the cochlea are responsible for ___________, whereas the structures of the saccule and utricle are responsible for _____________ equilibrium, and semicircular ducts and ampulla are responsible for _________________ equilibrium.

1) hearing 2) static 3) dynamic

The pharyngotympanic tube connects the _____________ to the ______________.

1) middle ear 2) pharynx

Which type of papillae of the tongue does not house taste buds?

Filiform papillae

Lacrimal Gland

Gland located in the superolateral orbit that produces tears.

Choroid

Highly vascularized layer in the posterior part of the fibrous tunic.

Kevin presents to your office after a mountain biking accident last weekend during which he fell on his left elbow. He says that since the accident, his forearm alternates between periods of numbness and feeling "like he has hit his funny bone." You test the two-point discrimination on Kevin's left fifth digit and find that it is 6 mm. On his right fifth digit, however, it is less than 1 mm. You also find that his forearm muscles that flex his hand on the left side are very weak, as are most of the intrinsic muscles of his left hand. What has likely happened? How does this explain the results of the two-point discrimination test? (Hint: You may want to refer to Unit 14, pp. 359-388 for help.)

Kevin likely damaged his ulnar nerve, which supplies the skin on his fifth digit. The damage has decreased the sensitivity in this location, making the two-point discrimination on his left side greater than on his right side.

The most common cause of hearing loss is exposure to loud noise such as music, which can permanently damage the hair cells of the cochlea. Would you expect this to result in conductive or in sensorineural hearing loss? What results would you expect from the Rinne and Weber tests in an individual with noise-induced hearing loss?

Noise-induced hearing loss results in sensorineural deafness, as the hair cells can no longer transmit action potentials along the cochlear nerve. The results from the Rinne test should show lateralization to the good (non-deaf) ear, assuming the deafness is not bilateral. The results from the Weber test should show that air-conducted sound is heard longer than bone-conducted sound, although both are likely to be very diminished in the deaf ear.

Pupil

Opening in the center of the iris that controls the amount of light entering the eye.

Pharyngotympanic Tube

Passage that connects the middle ear to the pharynx.

Auricle

Shell-shaped portion of the outer ear made of elastic cartilage.

Olfactory epithelium

Small patch of tissue in the roof of the nasal cavity containing olfactory receptor cells.

Cochlea

Spiral bony canal in the inner ear that houses the organ of Corti, responsible for transmitting sound impulses.

Ciliary Body

Structure composed of smooth muscle that controls the shape of the lens.

Cornea

The anterior, clear part of the fibrous tunic that refracts light coming into the eye.

LASIK, or laser-assisted in situ keratomileusis, is a surgical procedure on the eye that millions of people have undergone to improve visual acuity. It involves the use of a laser to reshape the cornea in individuals suffering from astigmatism, near-sightedness (myopia), or far-sightedness (hyperopia). How could changing the shape of the cornea affect one's visual acuity?

The cornea is the eye's main refractive medium, especially when viewing distant objects. Changing its shape will change the amount that it is able to bend light, which alters where it focuses the light.

Your patient is in a car accident and several days later complains of a loss of smell. An X-ray reveals a fracture of the cribriform plate. What structures specifically have been damaged? How has this interfered with your patient's sense of smell?

The fracture of the cribriform plate likely damaged cranial nerve I, as the axons of the olfactory neurons pass through the cribriform plate on their way from the olfactory epithelium to their synapses on the olfactory bulb. With damage to these neurons, they are unable to transmit olfactory stimuli to the central nervous system, and so the patient is unable to detect odors.

Chemosenses

The senses of smell and taste (chemical).

Explain why infectious otitis media (inflammation of the middle ear) may result in a simultaneous pharyngitis (inflammation of the throat).

The two structures are connected by the pharyngotympanic tube, and pathogens can easily travel between the two locations.

Tympanic Membrane

Thin membrane between the external and middle ear that vibrates when struck by sound waves.

Conjunctiva

Thin mucous membrane covering much of the anterior eyeball and internal surface of the eyelids.

Astigmatism refers to irregularities in the surface of the lens or cornea.

True

Sensorineural hearing loss results from damage to the inner ear or the vestibulocochlear nerve.

True

Smell and taste are considered chemosenses (chemical senses).

True

The auditory ossicles transmit vibration through the oval window.

True

Accommodation is the adjustment of the lens necessary for near vision.

True.

You would expect the error of localization and the two-point discrimination threshold to be highest on the ______________.

back.

The axons of the olfactory nerve synapse on neurons located in the ______________.

olfactory bulb

A standard hearing aid functions by amplifying the sound conducted through the external auditory canal. Explain why this type of hearing aid is effective for conductive hearing loss, but not sensorineural hearing loss.

Amplifying the sound waves will increase the transmission of the vibrations through the outer ear, middle ear, and temporal bone to the inner ear, which helps individuals with conduction deafness. However, sensorineural deafness makes one unable to detect the vibrations, so amplifying them will not help these individuals. (Note: Standard hearing aids can be effective in certain kinds of sensorineural hearing loss in which the loss isn't complete.)

Semicircular canals

Bony cavities in the inner ear that house the semicircular ducts and the ampulla and function with other organs of the inner ear to maintain equilibrium.

Vesitbule

Bony cavity of the inner ear that houses the structures responsible for equilibrium.

A person who visits the eye doctor is often given eye drops containing the drug atropine to dilate the pupils. A side effect of this drug is paralysis of the ciliary muscle, an effect called cycloplegia. Will a person with cycloplegia have difficulty with near vision or distance vision? Explain.

Cycloplegia causes difficulty with near vision. A paralyzed ciliary body cannot contract, which prevents the lens from "rounding up" in order to accommodate for viewing near objects.

Cones

Photoreceptors responsible for color and high-acuity vision in bright light.

Rods

Photoreceptors responsible for vision in dim light and for peripheral vision.

Tongue papillae

Projections from the tongue housing taste buds.