The inner ear, the transfert of vibrations

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Cette page est également disponible en français.

Perhaps we must accept that the division, the war, the violence, the diseases, benefit some who will do nothing to change that. Not everyone wishes, consciously or unconsciously, to live in Peace on Earth. But they are not “Life”. Life is Life. We are Humanity. We carry out at the individual level through our daily acts, at the citizen level with petitions, associations, fraternal actions. We can achieve it on a global scale with movements of movements, for Peace, for Justice, for the Joy of Living, for Freedom: a Movement of Movement For.

Man is born barbarous.
He is ransomed from the condition of Beasts, only by being cultivated.
 » The courtiers manual oracle – To cultivate and embellish »
by Baltasar Garcián, 1601-1658

The inner ear, the movement of a fixed point that becomes mobile and changes the encoding of data to make systems that everything separate:

The wave that propagates

Waves of sound arrive in the outer ear and cause vibrations in the tympanic membrane.

  • These vibrations in turn generate the movements of the ossicles responsible for the vibrations of the stapes in the vestibular window (oval),
  • leading to mobilize in waves the liquid (perilymph) located in the vestibular ramp and the tympanic ramp of the cochlea,
  • which eventually causes the tiny hair cells of the organ of Corti to tilt and depolarize.
  • Action potentials ensue in the afferent axons of the spiral ganglion cells, which are then transported centrally to the cochlear nucleus of the elongated cord.

From this nucleus, information is transferred to overlying centers in the brain and ends in the auditory cortex of the temporal lobe.

Complementarity at the service of action

While half of the nerve fiber contingent in the vestibulo-cochlear nerve (Cranial Nerve VIII) carries auditory information, the other half carries sensory information in maintaining a specialized sense of balance.

Receivers intended for balance are specific in two functional aspects:

  • Static: a special receptor called an acoustic macule resides in each utricle or saccule and helps analyze head position, linear accelerations, as well as gravity and low frequency vibrations (saccule only);
  • Dynamic: special receptors called the ampullary crest sit in the bulb of each semicircular canal (anterior bulb, lateral bulb, posterior bulb) and are affected by the angular (rotational) movements of the head

Vertigo is a sensation of spinning motion with loss of balance (dizziness).

It can occur by excessive stimulation of the vestibular system as in seasickness, motion sickness (car), carousel rides.

Viral infections, certain medications, and tumors can cause dizziness.

From oscillations to nerve impulses

The important step in the auditory transduction pathway is the transformation of mechanical vibrations leading to neural action potentials which are then transported to the brain.

This step occurs in the organ of Corti in the cochlea:

  • Cochlear hair cells (internal or external) sit on a basilar membrane and are functionally organized.
  • Pressure waves in the vestibular ramp are transmitted to the endolymph that occupies the cochlear duct through the vestibular membrane.
  • These pressure waves mobilize the basilar membrane (the loudest sounds induce more movements) but also the tectorial membrane.
  • Hair cells resting on the basilar membrane have the end of their cilia attached to the tectorial membrane and the divergent movements of these two membranes result in a shearing motion.
  • This effect leads to tilting of the cilia, depolarization of hair cells, release of neurotransmitters and initiates the action potential in the afferent axons of spiral ganglion cells.

The acoustic macule (of the vestibular apparatus of equilibrium) also carries hair cells (like the organ of Corti above) and a simple kinocilium (the longest eyelash) is present and covers the end of each bundle of stereocilia (very long microvilli).

  • During linear acceleration, the cilia move and this movement results in an increased release of neurotransmitters to the sensory axons of the cells of the vestibular ganglion.
  • This occurs when the cilia move to and from the kinocilium, causing depolarization of the hair cells.
  • The movements of the cilia away from the kinocilium causing hyperpolarization of hair cells, reducing the release of neurotransmitters.
  • Finally, the macules of the utricle feel the accelerations in a horizontal plane,
  • while the macules of the saccule perceive vertical accelerations, the sensation perceived when taking the elevator.

The ampulla crest of semicircular canals also possess hair cells and a kinocilium like a macule.

Let’s use our body’s feeling and its ability to transform it into analyzable data to amplify our sensitivity to Living:

If we consider any movement (of people, animals, nature)
as a displacement of space generating a vibration,
and our skin as a vibratory sensor;

Developing our senses can give us the opportunity to know the world;

Let’s decide to tame our feelings,
we will find how to live together.

Bibliographic references:
– The information on the auditory and vestibular system and the picture of hair cells, are taken from the book « The Netter’s Anatomy Coloring Book », John T. HANSE, Elsevier Masson SAS, 2017 (the french version),
– The other three pictures are taken from the book « Atlas of Human Anatomy », Seventh edition, Franck H. NETTER, Elsevier Masson SAS, eBook.

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