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COMPONENTS OF THE EAR

Category: Medical

Topic: Nervous System A&P

Level: Paramedic

Next Unit: The Physiology of Hearing

8 minute read

The components of the ear include the outer, middle, and the inner ear. 
Each with their own individual sub-components and functions.

 

Outer Ear

The outer ear is made up of the pinna and the ear canal. The eardrum separates the outer and middle ear.

PINNA: The externally visible cartilage and skin, also known as the "auricle." This structure is both aesthetic and serves to concentrate sound waves, increasing both the volume of sounds and the number of sounds we perceive in the environment.

EAR CANAL: The passage from the visible section of the ear to the tympanic membrane ("eardrum"). This canal is lined with glands (cerumen glands) that produce oily secretions that moisturize the skin, prevent infection, and keep external debris away from the tympanic membrane.

 

Middle Ear

The middle ear is composed of the eardrum (tympanic membrane), malleus, incus, stapes, the oval window, and the eustachian tube. It consists of the space between the tympanic membrane and the bony walls that surround the cochlea.

TYMPANIC MEMBRANE: Also known as the eardrum, this thin layer of tissue vibrates when impacted by sound waves and stimulates the three bones of the inner ear:

  1. Malleus,
  2. Incus, and
  3. Stapes.

These 3 bones connect the tympanic membrane to the oval window of the cochlea. This allows for vibrations of be transmitted through the air filled middle ear.

  • The malleus connects to the tympanic membrane. and
  • the stapes connects to the oval window, and
  • the incus links these two bones.

OVAL WINDOW: The oval window is a small window through the bone that separates the middle and inner ear; it allows for the transmission of vibrations.

EUSTACHIAN TUBE: This smooth muscle tube connects the middle ear cavity with the nasopharynx, to balance the pressure in the middle ear, drain the middle ear to prevent infection, and help prevent damage from loud sounds.

 

Inner Ear

The inner ear is composed of the bony labyrinth, membranous labyrinth, and the cochlea.

BONY LABYRINTH: made up of the walls of the temporal bone, this structure is the cavity in which the semicircular canals, cochlea, and other structures of the membranous labyrinth reside.

MEMBRANOUS LABYRINTH: This structure forms the functional components of the inner ear.

It is a series of fluid-filled tubes and chambers that allow for the sensations of balance and hearing.

The

  • semicircular canals,
  • utricle, and
  • saccule

use the movement of fluid within the labyrinth over small hair cells to tell the body how it is moving in 3D space. The cochlea uses this same fluid in a different area to create the sensation of sound.

COCHLEA: Technically a component of the membranous labyrinth, this structure uses fluid (endolymph) to conduct sound from the oval window of the middle ear to small receptors ("hair cells") that vibrate when sound waves hit them. The spiral shape of the cochlea is what allows certain frequencies of sound to only stimulate certain hair cells, resulting in our ability to discriminate between certain frequencies.

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