What is the difference between macula and cupula

Shearing of the hair cells opens potassium channels, as discussed at the beginning of the auditory section See Figure Then, press PLAY to watch the reaction to head movement. There are three pairs of semicircular ducts, which are oriented roughly 90 degrees to each other for maximum ability to detect angular rotation of the head.

Each slender duct has one ampulla. When the head turns, fluid in one or more semicircular ducts pushes against the cupula and bends the cilia of the hair cells.

Fluid in the corresponding semicircular duct on the opposite side of the head moves in the opposite direction. 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. Thus, with any position of the head, gravity will bend the cilia of one patch of hair cells, due to the weight of the otoconia to which they are attached by a gelatinous layer. This bending of the cilia produces afferent activity going through the VIIIth nerve to the brainstem. Activate Figure The utricle is most sensitive to tilt when the head is upright.

The saccule is most sensitive to tilt when the head is horizontal. Unlike the semicircular ducts, the kinocilia of hair cells in the maculae are NOT oriented in a consistent direction. The kinocilia point toward in the utricle or away from in the saccule a middle line called the striola. The striola is shown as a dashed line in Figure Because hair cells are oriented in different directions, tilts in any direction will activate some afferents.

Then press PLAY to watch the reactions to head movement. The vestibulo-occular reflex VOR controls eye movements to stabilize images during head movements. As the head moves in one direction, the eyes reflexively move in the other direction. The action of the VOR can be seen by moving your head from side to side.

The image you see is stable, despite the head movement. But as you increase the speed of oscillatory head movements, you can get to a rate of angular velocity where the VOR is no longer effective, and you will see the visual image start to shift. The VOR would occur in the dark, because the eyes move due to angular acceleration of the head. The inset in Figure This is a three-neuron circuit. One neuron is in Scarpa's the vestibular ganglion ; one neuron is in a vestibular nucleus; and one neuron is in an extraoccular motor nucleus.

Press PLAY to watch the reactions to caloric testing. A variant of the VOR, called caloric nystagmus , is used as a test of the vestibular system. If the ear is irrigated with a fluid having a temperature different than the body either warmer or cooler , a thermal gradient will be conduced across the small space of the middle ear.

Here, cold water is put in the right ear. About 20 ml is injected over about 30 s. The cold water cools the tympanic membrane, which cools the air in the middle ear, and finally the endolymph. This primarily affects the horizontal semicircular canal because it is close to the middle ear space. Cooling somehow hyperpolarizes the hair cells, causing the eyes to drift slowly to the right as if the head was moving to the left.

When the eyes have moved as far to the side as they can go, there is a quick resetting movement in the opposite direction. This cycle of slow and fast eye-movements is called a nystagmus. By comparing the relative movements of both the horizontal and vertical ampullae, the vestibular system can detect the direction of most head movements within three-dimensional 3-D space. Balance is coordinated through the vestibular system, the nerves of which are composed of axons from the vestibular ganglion that carries information from the utricle, saccule, and semicircular canals.

The system contributes to controlling head and neck movements in response to vestibular signals. An important function of the vestibular system is coordinating eye and head movements to maintain visual attention.

Most of the axons terminate in the vestibular nuclei of the medulla. Some axons project from the vestibular ganglion directly to the cerebellum, with no intervening synapse in the vestibular nuclei. The cerebellum is primarily responsible for initiating movements on the basis of equilibrium information. Neurons in the vestibular nuclei project their axons to targets in the brain stem. One target is the reticular formation, which influences respiratory and cardiovascular functions in relation to body movements.

A second target of the axons of neurons in the vestibular nuclei is the spinal cord, which initiates the spinal reflexes involved with posture and balance. To assist the visual system, fibers of the vestibular nuclei project to the oculomotor, trochlear, and abducens nuclei to influence signals sent along the cranial nerves. These connections constitute the pathway of the vestibulo-ocular reflex VOR , which compensates for head and body movement by stabilizing images on the retina Figure Finally, the vestibular nuclei project to the thalamus to join the proprioceptive pathway of the dorsal column system, allowing conscious perception of equilibrium.

Skip to content The Vestibular System Equilibrium Along with audition, the inner ear is responsible for encoding information about equilibrium , the sense of balance.

Figure The difference in inertia between the hair cell stereocilia and the otolithic membrane in which they are embedded leads to a shearing force that causes the stereocilia to bend in the direction of that linear acceleration. As one of the canals moves in an arc with the head, the internal fluid moves in the opposite direction, causing the cupula and stereocilia to bend. The movement of two canals within a plane results in information about the direction in which the head is moving, and activation of all six canals can give a very precise indication of head movement in three dimensions.

Central Processing of Vestibular Information Balance is coordinated through the vestibular system, the nerves of which are composed of axons from the vestibular ganglion that carries information from the utricle, saccule, and semicircular canals. During head movement, the eye muscles move the eyes in the opposite direction as the head movement, keeping the visual stimulus centered in the field of view.

Previous: