What is the pinna? The pinna is the only visible part of the ear (the auricle) with its special helical shape. It is the first part of the outer ear’s anatomy that reacts to sound. The pinna’s function is to act as a kind of funnel which assists in directing the sound further into the ear. Without this funnel the sound waves would take a more direct route into the auditory canal. This would be both difficult and wasteful, as much of the sound would be lost, making it harder to hear and understand the sounds.
The pinna is essential due to the difference in pressure inside and outside the ear. The resistance of the air is higher inside the ear than outside because the air inside the ear is compressed and thus under greater pressure.
In order for the sound waves to enter the ear in the best possible way the resistance must not be too high. This is where the pinna helps by overcoming the difference in pressure inside and outside the ear. The pinna functions as a kind of intermediate link which makes the transition smoother and less brutal allowing more sound to pass into the auditory canal (meatus).
The ear canal – the auditory canal
Once the sound waves have passed the pinna, they move two to three centimetres into the auditory canal before hitting the eardrum, also known as the tympanic membrane. The external auditory canal’s function is to transmit sound from the pinna to the eardrum.
What is the eardrum? The eardrum (tympanic membrane) is another important part of the outer ear. It is a membrane at the end of the auditory canal and marks the beginning of the middle ear. The eardrum is an extremely sensitive part of the outer ear anatomy. Pressure from sound waves makes the eardrum vibrate. In order to protect the eardrum, the auditory canal is slightly curved making it more difficult for insects, for example, to reach the eardrum. At the same time, earwax (cerumen) in the external auditory canal functions as a barrier to help keeping unwanted materials like dirt, dust, and insects out of the human ear.
In addition to protecting the eardrum, the external auditory canal also functions as a natural hearing aid which automatically amplifies low and less penetrating sounds of the human voice. In this way the ear compensates for some of the weaknesses of the human voice, and makes it easier to hear and understand ordinary conversation.