Structure and function of Ear-1

The Ear

The hearing organ is the ear. But it also serves as the body's balance and equilibrium sense organ.

Structure

There are three main sections of the ear:

• The external ear
• The middle ear
• The inner ear

The External Ear

The auricle, external auditory meatus, and tympanic membrane are the three components of the external ear. It is the portion of the ear that is visible.

The Auricle

The auricle (L. auris ear) is made up of a plate of elastic cartilage that has an amorphous shape and is covered in thin skin. There are many elevations and depressions on the auricle. The deepest depression is in the concha of the auricle. The helix is the raised auricular border. The lobe's non-cartilaginous lobule is made up of blood vessels, fat, and fibrous tissue. For inserting earrings and obtaining tiny blood samples, it is readily pierced. A tongue-like projection called the tragus covers the external acoustic meatus' opening. Its form aids in gathering sound waves and directing them in the direction of the external auditory meatus.

• Blood Supply of the Auricle
  • The superficial temporal and posterior auricular arteries make up the majority of the auricle's arterial supply.
• Nerve Supply of the Auricle
  • The major auricular and auriculotemporal nerves are the primary nerves that supply the skin of the auricle. the medial (cranial) surface Helix, antihelix, and lobule of the lateral surface, which are together referred to as the "back of the ear," and ("front"). The epidermis of the auricle anterior to the external acoustic meatus is supplied by the auriculo temporal nerve, a branch of CN V3.

The External Auditory Meatus

The external auditory meatus is an adult's 24-mm-long, s-shaped, curving tube that runs from the auricle to the eardrum. It is composed of an inner 16mm cartilaginous portion and an outside 1/3 (8mm) bony portion. The outer portion faces forward, upward, and medially. The inner portion faces forward, below, and medially. So, by drawing the auricle upward, backward, and somewhat laterally, the meatus is probed. Hairs and ceruminous glands, which create cerumin or earwax, line its inside. In the exterior of the ear canal, hairs develop. Lysozyme and immune globulins, which act as a disinfectant, are found in earwax. The delicate eardrum is protected from foreign objects by the ear wax, hairs, and meatus's curvature.

• Blood Supply of the External Auditory Meatus
  • The superficial temporal artery and posterior auricular artery, which are branches of the external carotid artery, supply the canal's outer portion with blood, while the deep auricular branch of the maxillary artery supplies the canal's inner portion. The external tubular and maxillary veins are responsible for carrying out venous drainage.
• Nerve Supply of the External Auditory Meatus
  • Auriculotemporal nerve and the facial nerve's auricular branch provide nerve supply.

The Tympanic Membrane (Eardrum)

At the medial end of the external acoustic meatus, the tympanic membrane—a thin, oval, semitransparent membrane with a diameter of about 10 mm—is located. This membrane creates a barrier between the middle ear's tympanic chamber and external acoustic meatus. The mucous membrane of the middle ear covers the tympanic membrane internally and externally, respectively, and there is a fibrous layer sandwiched between the two layers.

When viewed through an otoscope, the tympanic membrane has a concavity that slopes down toward the external acoustic meatus and a shallow depression in the center that resembles a cone, the umbo being its apex. The tympanic membrane's central axis runs anteriorly and inferiorly as it goes laterally through the umbo like the handle of an umbrella. The membrane is thin and is known as the pars flaccid. It is located superior to the lateral process of the malleus, one of the middle ear's small ear bones or auditory ossicles. It lacks the pars tensa, a fibrous layer that is found in the rest of the membrane (tense part). The flaccid portion creates the lateral wall of the tympanic cavity's superior recess. Air vibrations that reach the tympanic membrane through the external acoustic meatus cause it to move. The auditory ossicles send membrane movements to the internal ear through the middle ear.

The primary nerve that supplies the auriculotemporal glossopharyngeal nerve, a branch of CN V3, supplies the exterior of the tympanic membrane. A tiny vagus branch called the auricular branch provides some innervations (CN X). The glossopharyngeal nerve supplies the tympanic membrane's interior surface (CN IX).

Functions of the External Ear

• The external ear gathers the sound waves and directs them through the external auditory canal in the direction of the middle ear.
• The middle ear is shielded from bacteria and other hazardous substances by the earwax.
• The external ear's anatomical design helps keep debris from damaging the sensitive eardrum.