Chapter 15 Vocab

Wavelength

Forms of electromagnetic radiation like radio waves, light waves or infrared (heat) waves make characteristic patterns as they travel through space. Each wave has a certain shape and length. The distance between peaks (high points) is called wavelength. The difference in wavelength is the way we tell different kinds of electromagnetic energy apart.

Sphincter pupillae

In close vision and bright light, the sphincter pupillae (circular muscles) contract and the pupil constricts.

Incus

The incus lays at the middle of the ossicles, connecting the malleus to the stapes. It is shaped like an anvil, which is why "the anvil" is a widely used alternative name for the bone. One of its surfaces, called the head, forms a joint with the malleus ossicle. The incus also has two extensions known as the long and short crus. At the end of the long crus is the lenticular process, a hooked-shaped part of the incus that forms a joint with the head of the stapes. The short crus attaches to the back wall of the middle ear cavity, which houses the ossicles. The center of the incus is also known as the body

Retina

The innermost layer of the eyeball is the delicate, two-layered retina. Its outer pigmented layer, a single-cell thick lining, abuts the choroid, and extends anteriorly to cover the ciliary body and the posterior face of the iris. These pigmented epithelial cells, like those of the choroid, absorb light and prevent it from scattering in the eye. They also act as phagocytes to remove dead or damaged photoreceptor cells, and store vitamin A needed by the photoreceptor cells.

pupil

The iris's round central opening, the pupil, allows light to enter the eye. The iris is made up of two smooth muscles layers with bunches of sticky elastic fibers that congeal into a random pattern before birth. Its muscle fibers allow it to act as a reflexively activated diaphragm to vary pupil size.

Tinnitus

Tinnitus is noise or ringing or buzzing in the ears. A common problem, tinnitus affects about 1 in 5 people. Tinnitus isn't a condition itself rather it's a symptom of an underlying condition, such as age-related hearing loss or ear injury

Stapes

Vibrations travel through the stapes. The stapes looks like a horseshoe. The two branches, the inferior and superior crus, convey sound vibrations to the bone's flat base. From there, the vibrations enter the inner ear, where it is processed into neural data to be transmitted to the brain via the cochlear and the auditory nerve. If the stapes becomes damaged a person may lose some or all of his or her ability to hear.

Frequency

the rate at which a vibration occurs that constitutes a wave, either in a material, or in an electromagnetic field, usually measured per second

Conjunctiva

thin, protective mucous membrane lining the eyelids and covering the anterior surface of the eyelids itself.

cornea

tranparent anterior portion of the eyeball and it is part of the fibrous layer

Color blindness

Color blindness is the inability or decreased ability to see color or perceive color differences. Color blindness affects a significant amount of the population. There is no actual blindness though.

Cataract

The clouding of the eye's lens that often occurs due to old age or congenital.

Lacrimal apparatus

The lacrimal apparatus works to produce tears that are needed to wet the front of the eye and flush debris from the ocular surface. The lacrimal apparatus consists of the lacrimal gland, which secretes tears, and the series of drainage channels that carry the tears into the nose.

Lens

The lens is a biconvex, transparent, flexible structure that can change shape

Rods

The quarter billion photoreceptors found in the neural retinas are of two types: rods and cones. The more numerous rods are our dim-light and peripheral vision receptors. They are far more sensitive to light than cones are, but they do not provide either sharp images or color vision. This is why colors are indistinct and edges of objects appear fuzzy in dim light and at the edges of our visual field.

iris

The vascular layer, or middle coat of the eyeball, is also called the uvea. The pigmented uvea has three regions: the choroid, the ciliary body and iris. The iris, the visible colored part of the eye, is the most anterior portion of the uvea. Shaped like a flattened doughnut, it lies between the cornea and the lens and is continuous with the ciliary body posteriorly. Although, irises come in different colors (iris=rainbow), they contain only brown pigment. When they have a lot of pigment, the eyes appear brown or black. If the amount of pigment is the small and restricted to the posterior surface of the iris, the shorter wavelengths of light are scattered from the un-pigmented parts, and the eyes appear blue, green or gray. Most newborn babies' eyes are slate gray or blue because their iris pigment is not yet developed.

Malleus

There are three bones located in the middle ear: the incus, the malleus and the stapes. All three bones comprise the ossicles. The malleus is the outermost of the three.

Glaucoma

This is a condition in which intraocular pressure increases to levels that cause compression of the retina and optic nerve; results in blindness unless detected early

Hyperopia

a condition in which distant objects are usually seen clearly, but close ones do not come into proper focus; farsightedness

Astigmatism

a condition in which unequal curvatures in different parts of the cornea or lens of the eye leading to blurred vision.

Myopia

a condition in which visual images are focused in front of rather then on the retina; nearsightedness.

Tympanic membrane

it is the eardrum. The eardrum vibrates in response to sound waves.

Cochlea

snail-shaped chamber of the bony labyrinth that houses receptor for hearing.

Refraction

the bending of a light ray when it meets a different surface at an oblique rather than a right angle.

Amplitude

the maximum extent of a vibration or oscillation, measured from the position of equilibrium.

Optic disc

the optic disc is the point of exit for ganglion cell axons leaving the eye. Because there are no rods or cones overlying the optic disc, it corresponds to a small physiological blind spot in each eye. The ganglion cell axons form the optic nerve after they leave the eye.

Sound

vibrations that travel through the air or another medium and can be heard when they reach a person's or animal's ear.

Sensorineural deafness

A permanent sensorineural hearing loss is the result of damage to the hair cells within the cochlea or the hearing nerve (or both). Damage to the cochlea occurs naturally as part of the ageing process. Sensorineural hearing loss not only changes our ability to hear quiet sounds, but it also reduces the quality of the sound that is heard, meaning that individuals with this type of hearing loss will often struggle to understand speech. Once the cochlea hair cells become damaged, they will remain damaged for the rest of a person's life. Therefore sensorineural hearing loss is irreversible and cannot be cured.

Conduction deafness

Conductive hearing loss is the result of sounds not being able to pass freely to the inner ear. This usually results from a blockage in the outer or middle ear, such as a build-up of excess ear wax or fluid from an ear infection (especially common in children). It can also happen as a result of some abnormality in the structure of the outer ear, ear canal or middle ear - or be due to a ruptured eardrum.

Cones

Cones, by contrast to rods, operate in bright light and provide high-acuity color vision.

Dilator pupillae

In distant vision and dim light, the dilator pupillae (radial muscles) contract and the pupil dilates, allowing more light to enter the eye. Pupillary dilation and constriction are controlled by sympathetic and parasympathetic fibers, respectively. Changes in pupil size may also reflect our interests and emotional reactions to what we are seeing. Pupil dilation often occurs when the subject matter is appealing, in response to fear, and during problem solving.

Reflection

the return of light or sound waves from a surface