Week 29.10 – 04.11

Lecture 29.10

The topic of this week lecture was the human auditory system and the vestibular system. The systems have different functions, one is to hear the sounds surrounding and the other is to be able to keep balance. Their respective functions are not the same but yet some similarities can be found in their mechanism.

First, we explored the structure of the human’s ear. It is composed of three parts: the outer ear, the middle ear and the inner ear. Each part has some unique features and characteristics. The pinna and the auditory canal form the outer ear, their task is to collect the sounds from the surrounding environment and lead them into the ear so that they can be analyzed. We learned later on that the structure of the pinna plays an important role in the evaluation of the location of a sound in the vertical plane. The shape allows the ear to receive two different sounds, a direct and a reflected one.

Then the middle ear, composed of the ossicles and the tympanic membrane, was studied. It is quiet impressive to think that these very little bones can totally change the way we hear and that they are a necessity in the human ear.  They have two major roles to play. The first is to amplify the sound force up to 20-fold amplification. The second is the attenuation reflex; it is a system that includes the contraction of muscles attached to the ossicles in case of a loud noise. This provides the human ear with a good protection against loud sounds that could damage the inner ear. The two roles combine to provide a great capability to the human’s ear.

Finally the inner ear, the cochlea, was inspected. It is a very important step in the auditory pathway. In the cochlea, the sounds signals are analyzed with the help of the hair cells. A quiet complex system of potassium pumps allows determining the movement of the basilar membrane, which characterize the sounds. The informations collected are then send to neurons to be translated.

The experiment described in the lecture shows that there is a relation between the nature of the sounds and the location they are processed in the brain. It is interesting because it shows that we already have an idea of the sounds before actually analyzing it. It allows the neurons to be more specific and therefore to ear better.

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