The Ear

Middle ear cont

Also in the tympanic cavity are the auditory ossicles. These are 3 small bones known as the malleus (hammer), incus (anvil) and stapes (stirrup) They are linked by synovial joints and form a flexible chain across the middle ear. The malleus is in contact with the tympanic membrane. The stapes is in contact with the oval windwn of the inner ear. The oval windown is the junction between the middle and inner ear. Just below the oval window is the round window which leads to the opening of the cochlea. The function of the ossicles is to transmit and amplify the vibrations caused by sound waves across the middle ear to the inner ear.

Inner ear

Consist of: Bony labyrinth (tunnels in the bone of the skull) Membranous labyrinth (membrane lining the tunnels) Consists of 3 areas: The cochlea- hearing- sound waves are channelled down to a receptor area called the oran of corti. The vestibule- balance when standing still- 2 sac like structures called saccule & utricle- detect gravity. The semilunar canals- balance when moving.

The pinna or ear flap

Funnel shaped, made of cartilage. Function is to guide sound waves, picked up from the external environment, down the external auditory meatus to the tympanic membrane. The ear pinae also play an important part in communication between animals. In breeds such as the poodle, hair grows inside the ear and predisposes to ear infections. The ear canal itself runs vertically down each side of the skull and then turns inwards to run horizontally. The ear canal itself runs vertically down each side of the skul and then turns inwards to run horizontally, they are lines with a thin layer of skin which contains ceruminous glands. These glands secrete wax to protect the ear canal from damage by foreign bodies.

Pereception of sound

Sound travels through the air as waves or vibrations, these are picked up by the funnel shaped pinna of the ear and they travel down the external auditory meatus to the tympanic membrane (ear drum). The sound waves cause the tympanic membrane to vibrate. This in turn causes the chain of auditory ossicles to vibrate. The third and last ossicle, the stapes, vibrates against the oval window leading into the inner ear.

Ear

The ear contains receptors cells that respond to sound waves and to the movement of the body. The ear can be divided into three parts: External ear Middle ear Inner ear

The external ear

The pinna or ear flap. The external auditory meatus- also called the external ear canal.

The middle ear

Tympanic membrane or eardrum. Bony timpanic cavity. Auditory ossicles. The divide betwee the external and middle ear is the tympanic membrane or eardrum, this is a thin oval sheet of tissue, which is concave when views from the outside. The function of the timpanic membrane is to convey the vibrations caused by sound waves from the external auditory meatus to the ossicles of the middle ear. Opening into the bony tympanic cavity is the auditory or Eustachian tube, this is a short canal which leads into the nasopharynx at the back of the nasal chambers. The function of this tube is to equalize air pressure on either side of the tympanic membrane.