Outer Ear Diagram

Outer Ear

The outer ear leads to the external auditory canal, which is part of the structure of the outer ear. This canal is skin lined and ends at the eardrum or the tympanic membrane. Its exterior surface is skin lined. The eardrum has a mid-part that is a fibrous tissue and an inner layer that is a mucous membrane.

The ear resides in the temporal bone. This bone comprises an outer bony structure which is a part of the skull and skull base. It meets with different other bones which form part of the skull and its base.

The human ear has three main sections – the outer ear, the middle ear and the inner ear.

Hearing

Our sense of hearing relies on sensitive and complex structures that function with great efficiency over a range of tones and volumes. A healthy and young human ear can hear frequencies in the range of 20 to 20,000 cycles every second or Hertz (Hz). It transforms vibrations in the environment into meaningful signals which inform us, allowing the development of the language spoken.

Diagram of Outer Ear

The outer or the external ear comprises –

• Auricle or pinna – outer part of the ear
• External auditory canal or tube – tube connecting the outer ear to the middle ear or the inside

The Tympanic membrane (eardrum) is a connective tissue, it separates the outer ear from that of the middle ear.

Structure of the Outer Ear

Pinna and Ear Canal

The auricle or pinna forms a part of the outer ear and the most visible part. Its main function is to catch and direct sound waves into the ear canal. Further, it aids in localizing the direction of sounds. The most evident mark of the auricle is the bowl-shaped part called the concha. The auricle is made up of skin-covered cartilage and is not vital to humans, though it serves as a sound funnel in many animals.

It channels the sound waves to the external auditory canal (ear canal). This S-shaped canal is called the external auditory meatus and is about 0.5 to 1 inch in length (1 to 2.5 cm).

The outer third of the ear canal is surrounded by cartilage, while the internal two-thirds by the skull’s temporal bone. The skin slinging the cartilage shows hair follicles and glands, which produce wax that is jointly sebaceous and ceruminous glands. The bony section is usually touch-sensitive, as there is some cushion between the bone and the skin.

External ear canal

The ear canal serves as a tunnel to the middle ear and the temporal bone. The eardrum extends across the end of the ear canal, producing vibrations when struck by sound waves. The vibrations are passed to the three auditory bones called malleus, incus and stapes. The stapes (last bone), pass vibrations to the oval window via the inner ear.

In the external ear canal, the skin migrates from the eardrum towards the entrance. Any pile in the external ear canal, like the debris, dead skin cells, dust, wax or shed hair, migrates naturally out into the conchal bowl.

Since the glands are present in the outer third of the external ear canal only, this is the only place in the canal where the wax is seen. Wax is somewhat acidic, protecting the external ear canal from fungal and bacterial infection. The ear canal moves downwards and somewhat forward into the skull, with a minute bend and narrowing at the intersection of the cartilage and skull’s bone.

Eardrum

The eardrum is at the end of the external ear canal which is located at a slant, keeping a tilt towards the anterior wall of the ear canal. The tympanic membrane separates the external from the middle ear. It is somewhat oval in shape and around 9 to 10 mm, and it’s the widest diameter.

Pars tensa

The pars tensa constitutes most of the membrane and is located at the lower part of the eardrum. It is made of three layers –

• The epithelium that is continuous with the external ear canal
• Fibrous middle layer
• Mucosal layer which lines the complete middle ear and the upper respiratory tract

Above the pars tensa is the pars flaccida – a triangular section lacking a fibrous layer.

The tympanic membrane, at its exterior rim, is thick and is called the annulus. The first of the three bones of the middle ear – the malleus is linked at its tip to the centre of the membrane referred to as the umbo.

The handle of the malleus, which is the most distinguishing mark on the eardrum, is located between the fibrous layer and mucosal layer of the pars tensa and is linked both at the lateral process and the umbo.

Structure of External ear or Outer ear

Auricle 

Auricle or pinna is the visible portion of the ear and comprises a fine plate of yellow elastic cartilage connected with the surrounding section by muscles and ligaments and covered with integument. It is connected to start of the ear canal by fibrous tissue.

Ear canal

Sound waves from the pinna advance towards the ear canal, a simple tube which runs through the middle ear. The tube opens interiorly from the base of the auricula and brings vibrations to the tympanic cavity, amplifying frequencies.

Muscles of Outer ear

• Intrinsic muscles
• Extrinsic muscles

Intrinsic muscles 

• Helicis minor – It is an oblique fasciculus
• Helicis major – Narrow vertical band located on the anterior edge of the helix. It emerges from the spina helicis and leads to the anterior part of the helix
• Antitragicus – Emerges from the exterior part and leading to the antihelix and cauda helicis
• Traficus – flat, short vertical band on the lateral side of the tragus
• Transverse muscle – found on the cranial side of the pinna consisting of scattered fibres which stretches from the eminentia conchae to the prominence relative to the scapha
• Oblique muscle – comprises few fibres stretching from back and upper section of the concha to the convexity over it

Extrinsic muscles

There are three extrinsic muscles which surround the outer ear, they are –

• Posterior auricular muscle
• Superior auricular muscle
• Anterior auricular muscle

How Do We Hear?

The middle ear is involved in converting air vibrations that are directed down the external ear canal to the eardrum, into fluid vibrations in the cochlea. The three bones (the malleus, incus and stapes) seen in the middle ear together form the ossicles and are vital to hearing.

Found superior in the middle ear and suspended by a ligament, the head of the malleus articulates with the body of the incus by a synovial joint. The incus communicates with the stapes, and the footplate of the stapes resides in the oval window at the cochlea’s base.

The stapes attach to the oval window by a ligament. The sound waves pass along the external ear canal causing the vibration of the eardrum. The implanted lateral process of the malleus induces vibrations to persist across the ossicles to the footplate of the stapes. The middle ear partially decreases the loudness of the sound by passing the medium of the sound from air to fluid from the ossicles to the cochlea by the function of the ligaments also.

The sound waves which transmit to the ossicles disturb the endolymph in the cochlea and induce movement of the hair-like projections on the basilar membrane. The movement of the hair produces neural impulses that are relayed to the brain through the cochlear nerve.

The muscles attached to the malleus and stapes contract to protect against loud sounds, reducing vibrations and protecting the cochlea. This acoustic reflex takes approximately 40 milliseconds for occurrence.

Function of Outer ear

The arrangement of the outer ear particularly is to boost the pressure of the sound. Auricle catches and directs sound waves into the ear canal. The amplification makes humans sensitive to a range of frequency. Apart from collecting and funeling sound to the eardrum, it also provides cues about the position of the wideband sources of the sound in the vertical plane.

Outer Ear – Highlights

In humans, the outer ear is the only visible part. It comprises –

• Pinna – flesh coloured cartilage which is linked to the side of the head that catches sound waves
• Ear canal – carries sound waves to the tympanic membrane
• Tympanic membrane – most superficial part of the eardrum; it vibrates the moment it receives a sound wave

This was a brief on the outer ear and its structure. For related articles, visit BYJU’S.

More here:

• The Human Ear
• Explain how the human ear works