EYES AND EARS

By Malerie Vega

BIO:120 Medical Terminology

Presentation Chapter: 13

The Eye

The Eyeball

The Anatomy of the Eyeball

• Anterior Chamber: The space in the eye that is behind the cornea and in front of the iris.

• Upper & lower lid: a thin fold of skin that covers and protects the eye.

• Conjunctiva: a clear mucuse membrane consisting of cells and underlying basement membrane that covers the sclera (white part of the eye) and lines the inside part of the eyelid.

• Pupil: a hole located in the center of the iris of the eye that allows light to enter the eye

• Cornea: a transparent front part of the eye that covers the iris and the pupil.

• Aqueous humor: The liquid between the lens and the cornea.

• Posterior chamber: A narrow crack behind the perpherial part of the iris

• Fovea centralis: The part of the eye located in the center of the Macula region of the retina, this

part is responsible for the sharp central vision.• Optic nerve: Transmits visual information from the

retina to the Brain.• Central retinal artery: It pierces the optic nerve close to

the eyeball, sending branches over the internal surface of the retina, and these terminal

branches are the only blood supply to the larger part of the eye

• Sclera: fibrous, protective, outer layer of the eye containing collagen and elastic fiber.

• Choroid: The vascular layer containing connective tissue, of the eye lying between the retina

and the sclera. In humans its thickness is about 0.5 mm. The choroid provides oxygen and nourishment to the outer layers of the retina

• Retina: A light-sensitive tissue lining the inner surface of the eye

Muscles of the eye

The extraocular muscles are the six muscles that control the movements of the (human) eye. The actions of the extraocular muscles depend on the position of the eye at the time of muscle contraction.

Lacriminal apparatuseThe lacrimal apparatus is the physiologic system containing the orbital structures for tear production and drainage[1].It consists of

(a) the lacrimal gland, which secretes the tears, and its excretory ducts, which convey the fluid to the surface of the eye

(b) the lacrimal canaliculi, the lacrimal sac, and the nasolacrimal duct, by which the fluid is conveyed into the cavity of the nose, emptying anterioinferiorly to the inferior nasal conchae at the nasolacrimal duct.

(c) the nerve supply of lacrimal apparatus done by carotid plexuse of nerves along artery internal and external sympathetically but parasympathetic from lacrimal nucleus of the facial nerve

• Vision begins when light rays are reflected off an object and enter the eyes through the cornea, the transparent outer covering of the eye. The cornea bends or refracts the rays that pass through a round hole called the pupil. The iris, or colored portion of the eye that surrounds the pupil, opens and closes (making the pupil bigger or smaller) to regulate the amount of light passing through. The light rays then pass through the lens, which actually changes shape so it can further bend the rays and focus them on the retina at the back of the eye. The retina is a thin layer of tissue at the back of the eye that contains millions of tiny light-sensing nerve cells called rods and cones, which are named for their distinct shapes. Cones are concentrated in the center of the retina, in an area called the macula. In bright light conditions, cones provide clear, sharp central vision and detect colors and fine details. Rods are located outside the macula and extend all the way to the outer edge of the retina. They provide peripheral or side vision. Rods also allow the eyes to detect motion and help us see in dim light and at night. These cells in the retina convert the light into electrical impulses. The optic nerve sends these impulses to the brain where an image is produced.

How we see

The Ear

External ear

The outer ear has no bones. It is the external portion of the ear, which consists of the pinna, concha, and auditory meatus. It gathers sound energy and focuses it on the eardrum (tympanic membrane).

Middle ear

The middle ear is the portion of the ear internal to the eardrum, and external to the oval window of the cochlea. The mammalian middle ear contains three ossicles, which couple vibration of the eardrum into waves in the fluid and membranes of the inner ear. The hollow space of the middle ear has also been called the tympanic cavity, or cavum tympani. The eustachian tube joins the tympanic cavity with the nasal cavity (nasopharynx), allowing pressure to equalize between the middle ear and throat.

Inner ear

The inner ear is the innermost part of the vertebrate ear. It consists of the bony labyrinth, a system of passages comprising two main functional parts:The cochlea is dedicated to hearingThe vestibular system is dedicated to balanceThe inner ear is found in all vertebrates, with substantial variations in form and function. The inner ear is innervated by the eight cranial nerve in all vertebrates.

How we hear

When something makes a noise, it sends vibrations, or sound waves, through the air. The human eardrum is a stretched membrane, like the skin of a drum. When the sound waves hit your eardrum, it vibrates and the brain interprets these vibrations as. After the vibrations hit your eardrum, a chain reaction is set off. Your eardrum, which is smaller and thinner than the nail on your pinky finger, sends the vibrations to the three smallest bones in your body. First the hammer, then the anvil, and finally, the stirrup. The stirrup passes those vibrations along a coiled tub in the inner ear called the cochlea. Inside the cochlea there are thousands of hair-like nerve endings, cilia. When the Cochlea vibrates, the cilia move. Your brain is sent these messages (translated from vibrations by the cilia) through the auditory nerve. Your brain then translates all that and tells you what you are hearing. Neurologists don't yet fully understand how we process raw sound data once it enters the cerebral cortex in the brain.