A&P chapter 15

What two things does the ciliary body do?

1. Constriction of the ciliary muscle that is attached to the lens via the ciliary zonule causes the lens to change shape. 2. The epithelium of the ciliary body secretes aqueous humor.

Ling, a 75-year-old grandmother, complained that her vision was becoming obscured. Upon examination by an ophthalmologist she was told she had cataracts. What are they, how do they occur, and how are they treated?

A cataract is a clouding of the lens that causes the world to appear distorted, as if looking through frosted glass. Some cataracts are congenital, but most are due to age-related hardening and thickening of the lens, or are a possible consequence of diabetes mellitus. The direct cause is probably inadequate delivery of nutrients to the deeper lens fibers. The metabolic changes that result are thought to promote unfolding of the lens proteins. Unprotected exposure to the UV rays of sunlight over time is also associated with cataract formation. The lens can be removed and replaced with an artificial lens.

Trace the pathway of sound as it enters the external ear until it is perceived in the brain.

A sound wave passing through the external acoustic meatus causes the eardrum to vibrate at the same frequency as the wave. The auditory ossicles amplify and deliver vibrations to the oval window. Pressure waves in the cochlear fluids cause basilar membrane resonance that stimulates the hair cells of the spiral organ (of Corti). Impulses are then generated along the cochlear nerve that travel to the cochlear nuclei of the medulla and, from there, through several brain stem nuclei to the auditory cortex of the brain.

After head trauma from an automobile accident, a man has anosmia. Define anosmia. Why is this condition fairly common after such injuries and in cases of severe nasal cavity inflammation?

Anosmia means the loss of chemical sense of smell due to some olfactory disorder. Most anosmia results from head injuries or nasal cavity inflammations, allergies, smoking, and aging. The olfactory pathways are very sensitive to irritations or to damage, especially if the ethmoid bones have been damaged due to trauma.

A nurse is administering Pilocarpine eye drops. The nurse instructs the patient to press on the nasolacrimal duct for 30 seconds because the medication can have some systemic side effects, such as affecting the heart rate. Explain the rationale for pressing on the nasolacrimal duct.

Applying gentle pressure to the nasolacrimal duct prevents the delivery of the drug to the nasal mucosa and general circulation, where it may affect heart rate.

Roger went for his yearly eye examination and was informed that his intraocular pressure was slightly elevated (at 22 mm Hg). The physician expressed concern over this condition and noted that if the condition got worse, eye drops would be merited. What is wrong with Roger's eyes, and what are the possible consequences of this condition? Explain the function of eye drops used for therapy.

If the drainage of the aqueous humor is blocked, pressure within the eye can increase, causing compression of the retina and optic nerve, resulting in a condition called glaucoma. The resulting destruction of the neural structures causes blindness unless the condition is detected early. Early glaucoma can be treated with eye drops that increase the rate of aqueous humor drainage or decrease its production.

Distinguish between the maculae and cristae ampullaris in terms of their sensory reception.

Maculae are sensory receptors for static equilibrium. They monitor the position of the head in space by responding to linear acceleration forces. Cristae ampullaris respond to rotary (angular) movements.

Explain why prolonged periods of reading tire the eye muscles and result in eye strain.

Reading or other close work requires almost continuous accommodation, pupillary constriction, and convergence, which lead to tiredness of the eye muscles.

What is the chemical composition of the rod pigment, rhodopsin, and how does it appear to act in the reception of light?

Rhodopsin is a combination of retinal and opsin. Retinal is chemically related to vitamin A and is synthesized from it. Retinal can form a variety of three-dimensional forms called isomers. The opsin protein combines with the 11-cis retinal to form rhodopsin. The light-triggered changes in retinal cause hyperpolarization of the rods. This happens because the light turns off sodium entry, which then inhibits the release of neurotransmitter, thus turning off electrical signals.

Describe the process of light and dark adaptation and include the role of the rods and cones.

Rods respond to low-intensity light that provides night and peripheral vision, while cones are bright-light, high-discrimination receptors that provide color vision. During light adaptation, rods are inactivated and as cones respond to the high-intensity light, high visual acuity results. In dark adaptation, cones do not function (visual acuity decreases) and rod function resumes when sufficient rhodopsin accumulates.

A 60-year-old woman is experiencing vertigo. She ignores the symptoms initially, but now her attacks are accompanied by severe nausea and vomiting. Following an attack, she hears a roaring in her ears that causes temporary deafness for some time after. What do you think her problem is, and what is its suspected cause?

She most likely has a condition known as Ménière's syndrome. It affects both the semicircular canals and the cochlea. The cause of the syndrome is uncertain, but it may result from distortion of the membranous labyrinth by excessive endolymph accumulation. Less severe cases can usually be managed by antimotion drugs. For more debilitating attacks, salt restriction and diuretics are used to decrease overall extracellular fluid volumes.

Baby Susie's pediatrician notices that one of her eyes rotates outward and that she does not appear to be using it for vision. What is her condition and what does the pediatrician recommend?

Susie has strabismus, caused by congenital weakness of the external eye muscles in her affected eye. To prevent this eye from becoming functionally blind, the doctor will recommend either eye exercises or putting a patch on the unaffected eye to force her to use the affected eye. If her case is deemed severe, surgery on the eye muscles will be recommended.

Explain why a bad cold can result in food not tasting the same as it normally does.

Taste is 80% smell. When the ability to smell is blocked due to nasal congestion, taste is primarily via the taste receptors which account for only about 20% of the taste sensation. This results in a distinct difference in the "taste" of food.

Explain the role of the endolymph of the semicircular canals in activating the receptors during angular motion.

The crista ampullaris responds to changes in the velocity of head movement (angular acceleration). The crista consists of a tuft of hair cells whose microvilli are embedded in the gelatinous cupula. Rotational movement causes the endolymph to flow in the opposite direction, thus bending the cupula and exciting the hair cells.

What is the pharyngotympanic tube and what is its purpose?

The pharyngotympanic tube links the middle ear cavity with the nasopharynx. Normally it is flattened and closed, but swallowing or yawning opens it briefly to equalize pressure in the middle ear cavity with external air pressure.

Explain why your nose runs during and immediately after a good cry.

The tears flow into the lacrimal canaliculi and then into the nasolacrimal sac. As the sac fills, the tears begin to run down the nasolacrimal duct and out your nose.

When you go to the fair and ride the roller coaster, where do those wild sensations come from?

The wild sensations occur when the receptor for dynamic equilibrium, the crista ampularis, is excited by endolymph moving in the semicircular canals. This movement is the result of rotational acceleration or deceleration. Many times these wild rides spin us around enough that our eyes tell us we are going one way but the vestibule and semicircular canal tell us something different. Conflicts like that can often cause us to get quite dizzy or even sick.