The outer ear, or the external part of the ear, functions to collect sound waves. It is responsible for the sound transfer from the external environment into the ear canal. This has a range of 10-15 dB gain from 2500-5000 Hz, which is the range of sounds of the environment and speech sounds.

The external parts of the ear are mainly divided into three – the pinna or auricle, external auditory canal or ear canal, and the tympanic membrane or eardrum (although the EAM is on the boundary between the outer and middle ear). The basic concept of the transmission of sounds in the ear, particularly the outer ear, is that the pinna receives the sound from the external environment and passes it to the external auditory meatus, which then transmits it into the tympanic membrane.

Alberti (2006) expressed that the pinna is angled in such a manner because of its role to catch sounds that come from the front more than the sounds behind. He added that this positioning is helpful in localizing sound, especially those of higher frequencies. The pinna also aids in the protection of the external auditory meatus from various foreign objects and trauma.

Wageih Felfela (2017) stated that the pinna or auricle is the visible part of the outer ear. The researcher added that excluding the depression between the tragus and anterior crus of the helix and the ear lobule, the pinna is a single piece of yellow elastic cartilage. The researcher also added that the skin of the pinna is more prone to frostbite because of its thinness and its location which is closely attached to the perichondrium at the lateral surface.

He further stated that fine hair is present at the concha and scaphoid fossa, while thick hair, if applicable, is present over the tragus and intertragic notch. Moreover, there are three extrinsic muscles present at the pinna: the auricularis anterior (Attrahens aureum); auricularis posterior, which holds the outer part of the ear in place; and the auricularis superior. He also stated that there are six intrinsic muscles, but those muscles do not have useful functions in humans.

The pinna or auricle is based off auricular cartilages and several muscles, which include the helix, lobule, antihelix, tragus, intertragic notch, cymba concha (depressions), and the concha cavum. These parts will be thoroughly discussed in the succeeding paragraphs.

Helix

The helix or the curvature refers to the outer curve that forms the shape of the pinna. This part curves to form the ear’s cup shape. It is based off auricular cartilages and several muscles. The helix also has landmark called the “Darwin’s Tubercle” which is a cartilaginous protuberance that looks like the thickening of the helix. The Darwin’s Tubercle is believed to be a trait inherited from the previous species that existed before humans and greatly represents the evolution of humans.

Lobule

The helix terminates to the lobule, which is the one of the most well-known parts of the ear since this is the common site for piercings. This is the sole portion that has no cartilage which is why it is considered as the fleshy part. This part is composed of connective tissues which do not have the elasticity and firmness of other parts of the auricle. In cold climates, the lobule serves as a warming mechanism because of its large blood supply.

Tragus

Meanwhile, the tragus is a flap of cartilage on the anterior wall of the external auditory meatus. Also, the earphones commonly rest on the tragus.

Intertragic Notch

The intertragic notch is a funnel-like structure that drains cerumen (ear wax) as it comes out of the external auditory meatus.

Concha

The concha refers to the depressions in the auricle that leads to the external auditory meatus. The helix’s anterior extension in the anterior entrance of the concha is known as the “cymba concha,” while the one that is more superior to the concha is known as the “concha cavum.”

The concha primarily functions for the amplification of sound and has a resonant frequency of 5000 Hz.

Wageih Felfela (2017) described the external auditory meatus (EAM) as an S-shaped pathway towards the tympanic membrane. Its dimensions are 9 mm high X 6.5 mm wide and is roughly 2.5 cm long. The posterior wall of the EAM is shorter than the anterior wall by 6 mm.

Moreover, the EAM is two-thirds cartilaginous and one-third bony. The two-thirds cartilaginous part is filled with a lining with oil glands. These oil glands produce ear wax, which is scientifically or medically known as cerumen, to keep the ear canal clean and to protect it against insects and other foreign objects. The cilia, or the hair follicles, aid the cerumen in protecting the ear. The cilia also helps in reducing the dust and wax build-up.

The EAM is also the external ear’s narrowest part. Its shape is slightly curved downward since it aids the cerumen slide down and go external from the external auditory meatus.

Furthermore, the EAM is the most sensitive portion to sounds. Noises in this range are also the most hazardous to hearing.

Wageigh Felfela (2017) considers the tympanic membrane or ear canal as a part of both the outer ear and middle ear for it serves as the boundary between the outer and middle ear. The tympanic membrane is thin, semitransparent, round-like and has a concave shape that bulges inwards or medially towards the middle ear. Further details on the tympanic membrane will be discussed in the next chapter (the middle ear).

References

Alberti, P. (2006). 2 THE ANATOMY AND PHYSIOLOGY OF THE EAR AND HEARING.

Wageih Felfela, G. M. (2017). Ear Anatomy. Global Journal of Otolaryngology, 4(1). https://doi.org/10.19080/gjo.2017.04.555630