Anatomy and Functioning of the Ear.
A) The outer or external ear
It includes three parts:
- Pinna (cartilage covered by skin placed on opposite sides of the head)
- Ear canal
- Ear drum outer layer (also called the Tympanic Membrane)
What is the Tympanic Membrane made up of?
The ear drum (also known as the Tympanic Membrane) is composed of three layers. The outer layer consists of a thin layer of skin, the middle layer is made of fibrous tissue and the inner layer is mucosa (similar to the tissue in the mouth and nose). The Tympanic Membrane is secured to the sidewalls of the end of the outer ear canal by a thick band of tissue called the Tympanic ring or annulus. This ring helps in the overall structural integrity and stability of the ear drum. The integrity of the Tympanic Membrane and associated structures is important for proper sound conduction.
How big is your ear drum?
The ear drum is an oval shaped pearly white membrane, with an average size of 8 x 10 mm.
B) The middle ear includes:
- Ear Drum
- Middle Ear Cavity (also called the Tympanic Cavity)
- Ossicles (3 tiny hearing bones connected like a chain; Malleus (or hammer) – long handle attached to the ear drum; Incus (or anvil) – the bridge bone between the malleus and the stapes; Stapes (or stirrup) – the footplate; the smallest bone in the body
C) Inner Ear
Inner Ear is the part of the ear that contains organs of the special sense of hearing and sense of equilibrium.The bony labyrinth in the temporal bone is divided into three parts the vestibule, the semicircular canals and the cochlea. Within the bony labyrinth is a membranous labyrinth, which is divided into three parts
- The semicircular ducts
- Two saclike structures, the saccule and utricle, located in the vestibule
- The cochlear duct, which is the only part of the inner ear involved in hearing. The entire inner ear is bathed in a cushioning fluid called the endolymph and the perilymph.
Mechanism of hearing: How sound vibrations transmitted in the Ear
The outer part of the ear collects sound and the sound travels through the pinna and the auditory canal, a short tube that ends at the ear drum. Ear drum function is to transmit the sound from the air to the ossicles (hearing bones) inside the middle ear and then to the inner ear through a window. Sound entering the outer ear travels through the middle ear and causes the ear drum and ossicles in the middle ear to vibrate and as it travels, sound amplifies (becomes louder) and changes from vibration in air to vibration in fluid. The sound vibrations then converted into electroneural signal and then reach the hearing centre in the brain, thus we perceive the sound as hearing sensation or as an understandable sound.
Mechanism of Balance or Equilibrium:
Motions of the head cause stimulation of another auditory nerve branch, the vestibular nerve, which signals the position of the head with respect to the rest of the body.
The three semi-circular canals are arranged at right angles to each other, so that they measure motions in all three planes and they transmit signals indicating changes of position through the vestibular nerve.