Where is information from the vestibular system processed

Within the ampulla is a sensory organ called the crista ampullaris that contains hair cells , the sensory receptors of the vestibular system. Hair cells get their name because there is a collection of small "hairs" called stereocilia extending from the top of each cell.

Hair cell stereocilia have fine fibers, known as tip links, that run between their tips; tip links are also attached to ion channels. When the stereocilia of hair cells are moved, the tip links pull associated ion channels open for a fraction of a millisecond.

This is long enough to allow ions to rush through the ion channels to cause depolarization of the hair cells. Depolarization of hair cells leads to a release of neurotransmitters and the stimulation of the vestibulocochlear nerve.

The hair cells associated with the semicircular canals extend out of the crista ampullaris into a gelatinous substance called the cupula , which separates hair cells from the endolymph.

When the endolymph flows into the ampulla, however, it causes the distortion of the cupula, which leads to movement of hair cells. This prompts stimulation of the vestibulocochlear nerve, which transmits the information about head movement to the vestibular nuclei in the brainstem as well as to the cerebellum. The vestibular system uses two other organs, known as the otolith organs, to detect linear acceleration, gravitational forces, and tilting movements.

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Search Search. Deep inside the ear, positioned just under the brain, is the inner ear. It also coordinates the timing and force of muscle movements initiated by other parts of the brain. The abducens neurons produce contraction of the right lateral rectus and, through a separate cell projection to the left oculomotor nucleus, excite the left medial rectus muscles.

In addition, matching bilateral inhibitory connections relax the left lateral rectus and right medial rectus eye muscles. The resulting rightward eye movement for both eyes stabilizes the object of interest upon the retina for greatest visual acuity. For example, sideways motion to the left results in a horizontal rightward eye movement to maintain visual stability on an object of interest.

For these reflexes, the amplitude of the translational VOR depends on viewing distance. This is due to the fact that the vergence angle i. Visual objects that are far away 2 meters or more require no vergence angle, but as the visual objects get closer e. During translational motion, the eyes will change their vergence angle as the visual object moves from close to farther away or vice versa.

These responses are a result of activation of the otolith receptors, with connections to the oculomotor nuclei similar to those described above for the rotational vestibuloocular reflex.

With tilts of the head, the resulting eye movement is termed torsion , and consists of a rotational eye movement around the line of sight that is in the direction opposite to the head tilt.

As mentioned above, there are major reciprocal connections between the vestibular nuclei and the cerebellum. There are two vestibular descending pathways that regulate body muscle responses to motion and gravity, consisting of the lateral vestibulo-spinal tract LVST and the medial vestibulo-spinal tract MVST.

Reflexive control of head and neck muscles arises through the neurons in the medial vestibulospinal tract MVST. The MVST neurons receive input from vestibular receptors and the cerebellum, and somatosensory information from the spinal cord.

MVST neurons carry both excitatory and inhibitory signals to innervate neck flexor and extensor motor neurons in the spinal cord. For example, if one trips over a crack in the pavement while walking, MVST neurons will receive downward and forward linear acceleration signals from the otolith receptors and forward rotation acceleration signals from the vertical semicircular canals. The VCR will compensate by providing excitatory signals to the dorsal neck flexor muscles and inhibitory signals to the ventral neck extensor muscles, which moves the head upward and opposite to the falling motion to protect it from impact.

The LVST comprises a topographic organization of vestibular nuclei cells that receive substantial input from the cerebellum, proprioceptive inputs from the spinal cord, and convergent afferent signals from vestibular receptors. LVST neurons contain either acetylcholine or glutamate as a neurotransmitter and exert an excitatory influence upon extensor muscle motor neurons.

For example, LVST fibers produce extension of the contralateral axial and limb musculature when the body is tilted sideways. Some vestibular nucleus neurons send projections to the reticular formation, dorsal pontine nuclei, and nucleus of the solitary tract.

These connections regulate breathing and circulation through compensatory vestibular autonomic responses that stabilize respiration and blood pressure during body motion and changes relative to gravity. They may also be important for induction of motion sickness and emesis.

The cognitive perception of motion, spatial orientation, and navigation through space arises through multisensory information from vestibular, visual, and somatosensory signals in the thalamus and cortex Figure 6A. Vestibular nuclei neurons project bilaterally to the several thalamic regions.

The posterior nuclear group PO , near the medial geniculate body, receives both vestibular and auditory signals as well as inputs from the superior colliculus and spinal cord, indicating an integration of multiple sensory signals.