Sight & Hearing

Sense of Hearing Outer (External) Ear The outer ear consists of three parts Auricle- An earlike structure; the portion of the heart that forms the wall of an atrium. External acoustic meatus- passageway that leads from the outside of the head to the tympanic membrane, or eardrum membrane, of each ear. Eardrum- A thin membrane that covers the auditory canal and separates the external ear from the middle ear.

Middle ear The middle ear is also known as the tympanic cavity, which is an air-filled space in the temporal bone. Contains three small bones: malleus, incus, and stapes. These bones bridge the eardrum and the inner ear, transmitting vibrations between these specific parts. Ligaments hold the stapes to an opening in the wall of the tympanic cavity called the Oval window, which leads into the inner ear.

Inner (Internal) Ear A complex system of communicating chambers and tubes are called Labyrinth. Each ear has two parts to the labyrinth the osseous labyrinth, and membranous labyrinth. The osseous is a bony canal, and the membranous labyrinth is a tube that lies within the osseous labyrinth and has a similar shape. The auditory tube helps maintain equal air pressure on both sides of the eardrum, which connects each middle ear to the throat.

Sense of sight Visual Accessory Organs Each eyelid has four layers- skin, muscle, connective tissue, and conjunctiva. The eyelids are moved by the orbicularis oculi muscle, which acts as a sphincter and closes the lids when it contracts, by the levator palpebrae superioris muscle, which raises the upper lid and helps open the eye. Conjunctiva is a mucous membrane that lines the inner surfaces of the eyelids and folds back to cover the anterior surface of the eyeball, except for its central proportion (cornea).

Cont.….. Extrinsic muscles arise from, the bones of the orbit and insert by broad tendons on the eyes outer surface. Six extrinsic muscles move the eye in various directions: Superior rectus, inferior rectus, medial rectus, lateral rectus, superior oblique, and inferior oblique.

Structure of the eye/Outer layer Cornea- the window of the eye and helps focus entering light rays. Sclera-the white portion of the eye. The eye has a total of three layers

Middle layer The middle layer includes the choroid coat, ciliary body, and iris. Choroid coat is loosely joined to the sclera and is honeycombed with blood vessels, which nourish surrounding tissues. The ciliary body, which is the thickest part of the middle later, extends forward from the choroid coat and forms an internal ring around the front of the eye. The iris is a thin diaphragm composed mostly of connective tissue and smooth muscle fibers.

Cont.….. From the outside, the iris is the colored portion of the eye. The iris divides the space (anterior cavity) separating these parts into an anterior chamber, and a posterior chamber containing the lens, between the iris and the vitreous body. The light-sensitive biochemical in rods are called rhodopsin, also known as visual purple. The pupil decreases in size when it encounters a bright light.

Meniere's disease Meniere's disease is an inner ear disorder that affects balance and hearing. Causes-It occurs with the result of the abnormal volume or composition of fluid in the inner ear. The disease isn't fully understood. Symptoms-Recurring episodes of vertigo, Hearing loss, Ringing in the ear, and the Feeling of fullness in the ear.