What do receptors in the vestibular sense

Skip to main content. Module 5: Sensation and Perception. Search for:. The Vestibular Sense Learning Objectives Describe the basic functions of the vestibular, proprioceptive, and kinesthetic sensory systems. Watch It Review the things you learned about the senses in the following CrashCourse video. Try It. Licenses and Attributions. In fact, gaze stabilization in humans has been shown to be completely compensatory essentially perfect for most natural behaviors.

The anterior and posterior semicircular canals along with the saccule control vertical and torsional turning of the eye around the line of sight eye movements, while the horizontal canals and the utricle control horizontal eye movements. The basic pathway consists of horizontal semicircular canal afferents that project to specific neurons in the vestibular nuclei. These nuclei cells, in turn, send an excitatory signal to the contralateral abducens nucleus , which projects through the sixth cranial nerve to innervate the lateral rectus muscle Figure 5.

Some abducens neurons send an excitatory projection back across the midline to a subdivision of cells in the ipsilateral oculomotor nucleus , which, in turn, projects through the third cranial nerve to innervate the right ipsilateral medial rectus muscle.

When a leftward head turn is made, the left horizontal canal vestibular afferents will increase their firing rate and consequently increase the activity of vestibular nuclei neurons projecting to the opposite contralateral right abducens nucleus. 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. The basic transduction mechanism is the same in the auditory and vestibular systems See Figure A mechanical stimulus bends the cilia of the hair cells. Fine thread-like tip links connect to trap doors in the adjacent cilium. Hair cells in the vestibular system are slightly different from those in the auditory system, in that vestibular hair cells have one tallest cilium, termed the kinocilium.

Bending the stereocilia toward the kinocilium depolarizes the cell and results in increased afferent activity. Bending the stereocilia away from the kinocilium hyperpolarizes the cell and results in a decrease in afferent activity. The semicircular ducts work in pairs to detect head movements angular acceleration. A turn of the head excites the receptors in one ampulla and inhibits receptors in the ampulla on the other side.

Then press PLAY to watch the reaction to head movement. Begin by pressing "expand" to show details from the horizontal semicircular ducts on both sides of the head. Beneath the ampullae are new details, which highlight the orientation of the stereocilia in both cristae and their outputs. The kinocilia are oriented in the direction of the ampullae ampullo fugal within the ducts on both sides.

The two sides are mirror images. There is a constant low level of ionic influx into the body of the hair cells, so there is a steady-state receptor potential and a spontaneous low-level discharge of afferent activity. These neutral neurophysiological properties are shown in graphs below each ampulla. By pressing the "play" button you will see an animation of this. A constant low level of spontaneous activity keeps all the muscles slightly and equally contracted, causing the eyes to look straight ahead.

When the head turns, inertia causes the fluid to move more slowly than the head, generating relative fluid motion in the semicircular duct in the opposite direction of the head turn. This moving fluid, shown by arrows in the lumens of the semicircular duct, bends the hair cells on both sides of the head.

Because the two sides are mirror images, the stereocilia are bent toward their kinocilium on one side and away from their kinocilium on the other side.

Shearing of the stereocilia toward the kinocilium causes a depolarization of the receptor potential and an increase in afferent action potentials. There is an opposite effect on the other side — a decrease in afferent activity. These counteracting bilateral changes in afferent activity affect the vestibular and occulomotor nuclei.

The ampullo fugal movement of fluid on the patient's right reader's left causes an increase in afferent activity shown in green for "go" in the inset. This has a positive effect on the right medial and superior vestibular nuclei, which in turn stimulate the ipsilateral occulomotor and contralateral abducens nuclei.

There are exactly opposite effects on the other side shown in red for "stop" in the inset. The result of these combined counteracting effects is a smooth movement of the eyes toward the left, keeping the visual field stable as the head turns.

Press "expand" to see the utricle at the top of Figure These two similar organs lie against the walls of the inner ear between the semicircular ducts and the cochlea.

The receptors, called maculae meaning "spot" , are patches of hair cells topped by small, calcium carbonate crystals called otoconia. The saccule and utricle lie at 90 degrees to each other.

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