{"id":21515,"date":"2023-08-12T17:11:33","date_gmt":"2023-08-12T11:41:33","guid":{"rendered":"https:\/\/anatomystudyguide.com\/?p=21515"},"modified":"2024-10-07T11:41:33","modified_gmt":"2024-10-07T06:11:33","slug":"vestibular-system-structure-and-function-notes","status":"publish","type":"post","link":"https:\/\/anatomystudyguide.com\/vestibular-system-structure-and-function-notes\/","title":{"rendered":"Vestibular System: Structure and Function Notes"},"content":{"rendered":"<h2><span class=\"ez-toc-section\" id=\"Vestibular_Apparatus_Introduction\"><\/span>Vestibular Apparatus Introduction<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>The vestibular apparatus is the part of the labyrinth or inner ear. It plays an important role in maintaining posture and equilibrium through statokinetic reflexes. The other part of the labyrinth is the cochlea, which is concerned with the sensation of hearing.<\/p><div id=\"ez-toc-container\" class=\"ez-toc-v2_0_69_1 counter-hierarchy ez-toc-counter ez-toc-grey ez-toc-container-direction\">\n<p class=\"ez-toc-title\">Table of Contents<\/p>\n<label for=\"ez-toc-cssicon-toggle-item-6751e6f1550fb\" class=\"ez-toc-cssicon-toggle-label\"><span class=\"ez-toc-cssicon\"><span class=\"eztoc-hide\" style=\"display:none;\">Toggle<\/span><span class=\"ez-toc-icon-toggle-span\"><svg style=\"fill: #999;color:#999\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" class=\"list-377408\" width=\"20px\" height=\"20px\" viewBox=\"0 0 24 24\" fill=\"none\"><path d=\"M6 6H4v2h2V6zm14 0H8v2h12V6zM4 11h2v2H4v-2zm16 0H8v2h12v-2zM4 16h2v2H4v-2zm16 0H8v2h12v-2z\" fill=\"currentColor\"><\/path><\/svg><svg style=\"fill: #999;color:#999\" class=\"arrow-unsorted-368013\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"10px\" height=\"10px\" viewBox=\"0 0 24 24\" version=\"1.2\" baseProfile=\"tiny\"><path d=\"M18.2 9.3l-6.2-6.3-6.2 6.3c-.2.2-.3.4-.3.7s.1.5.3.7c.2.2.4.3.7.3h11c.3 0 .5-.1.7-.3.2-.2.3-.5.3-.7s-.1-.5-.3-.7zM5.8 14.7l6.2 6.3 6.2-6.3c.2-.2.3-.5.3-.7s-.1-.5-.3-.7c-.2-.2-.4-.3-.7-.3h-11c-.3 0-.5.1-.7.3-.2.2-.3.5-.3.7s.1.5.3.7z\"\/><\/svg><\/span><\/span><\/label><input type=\"checkbox\"  id=\"ez-toc-cssicon-toggle-item-6751e6f1550fb\"  aria-label=\"Toggle\" \/><nav><ul class='ez-toc-list ez-toc-list-level-1 ' ><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/anatomystudyguide.com\/vestibular-system-structure-and-function-notes\/#Vestibular_Apparatus_Introduction\" title=\"Vestibular Apparatus Introduction\">Vestibular Apparatus Introduction<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/anatomystudyguide.com\/vestibular-system-structure-and-function-notes\/#Labyrinth\" title=\"Labyrinth\">Labyrinth<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/anatomystudyguide.com\/vestibular-system-structure-and-function-notes\/#Functional_Anatomy_Of_Vestibular_Apparatus\" title=\"Functional Anatomy Of Vestibular Apparatus\">Functional Anatomy Of Vestibular Apparatus<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-4\" href=\"https:\/\/anatomystudyguide.com\/vestibular-system-structure-and-function-notes\/#Receptor_Organ_In_Vestibular_Apparatus\" title=\"Receptor Organ In Vestibular Apparatus\">Receptor Organ In Vestibular Apparatus<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-5\" href=\"https:\/\/anatomystudyguide.com\/vestibular-system-structure-and-function-notes\/#Nerve_Supply_To_Vestibular_Apparatus\" title=\"Nerve Supply To Vestibular Apparatus\">Nerve Supply To Vestibular Apparatus<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-6\" href=\"https:\/\/anatomystudyguide.com\/vestibular-system-structure-and-function-notes\/#Functions_Of_Vestibular_Apparatus\" title=\"Functions Of Vestibular Apparatus\">Functions Of Vestibular Apparatus<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-7\" href=\"https:\/\/anatomystudyguide.com\/vestibular-system-structure-and-function-notes\/#Effects_Of_Stimulation_Of_Semicircular_Canals\" title=\"Effects Of Stimulation Of Semicircular Canals\">Effects Of Stimulation Of Semicircular Canals<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-8\" href=\"https:\/\/anatomystudyguide.com\/vestibular-system-structure-and-function-notes\/#Applied_Physiology_Effect_Of_Labyrinthectomy\" title=\"Applied Physiology Effect Of Labyrinthectomy\">Applied Physiology Effect Of Labyrinthectomy<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-9\" href=\"https:\/\/anatomystudyguide.com\/vestibular-system-structure-and-function-notes\/#Motion_Sickness\" title=\"Motion Sickness\">Motion Sickness<\/a><\/li><\/ul><\/nav><\/div>\n\n<p><strong>Read And Learn More:\u00a0<a href=\"https:\/\/anatomystudyguide.com\/medical-physiology-notes\/\">Medical Physiology Notes<\/a><\/strong><\/p>\n<h2><span class=\"ez-toc-section\" id=\"Labyrinth\"><\/span>Labyrinth<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>The labyrinth (inner ear) consists of two structures:<\/p>\n<ol>\n<li>\u00a0Bony labyrinth<\/li>\n<li>\u00a0Membranous labyrinth.<\/li>\n<\/ol>\n<p>1. <strong>Bony Labyrinth:<\/strong><\/p>\n<ul>\n<li>The bony labyrinth is a series of cavities or channels present in the petrous part of the temporal bone. The membranous labyrinth is situated inside the bony labyrinth.<\/li>\n<li>The space between a bony labyrinth and the membranous labyrinth is filled with a fluid called perilymph or periotic fluid. This fluid is similar to ECF in composition with a large amount of sodium ions. A bony labyrinth encloses a membranous labyrinth.<\/li>\n<\/ul>\n<p>2. <strong>Membranous Labyrinth: <\/strong>The membranous labyrinth is formed by membranous tubules and sacs. It consists of two portions:<\/p>\n<ol>\n<li>Cochlea which is concerned with the sensation of hearing<\/li>\n<li>Vestibular apparatus which is concerned with posture and equilibrium.<\/li>\n<\/ol>\n<p>The membranous labyrinth is filled with a fluid called endolymph or otic fluid. The endolymph is similar to ICF in composition. It has a large quantity of potassium ions.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-21555\" src=\"https:\/\/anatomystudyguide.com\/wp-content\/uploads\/2023\/08\/Vestibular-Apparatus-Labyrinth.png\" alt=\"Vestibular Apparatus Labyrinth\" width=\"429\" height=\"466\" srcset=\"https:\/\/anatomystudyguide.com\/wp-content\/uploads\/2023\/08\/Vestibular-Apparatus-Labyrinth.png 429w, https:\/\/anatomystudyguide.com\/wp-content\/uploads\/2023\/08\/Vestibular-Apparatus-Labyrinth-276x300.png 276w\" sizes=\"auto, (max-width: 429px) 100vw, 429px\" \/><\/p>\n<h2><span class=\"ez-toc-section\" id=\"Functional_Anatomy_Of_Vestibular_Apparatus\"><\/span>Functional Anatomy Of Vestibular Apparatus<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>The vestibular apparatus is formed by three semicircular canals and an otolith organ (vestibule).<\/p>\n<p>1. <strong>Semicircular Canals: <\/strong>The semicircular canals are the tubular structures placed at right angles to each other. Because of this type of arrangement, the semicircular canals represent the three axes of rotation: vertical, anteroposterior, and transverse axes. The semicircular canals are named according to the situation as follows:<\/p>\n<ol>\n<li style=\"list-style-type: none;\">\n<ol>\n<li>Anterior or superior canal<\/li>\n<li>Posterior canal<\/li>\n<li>Lateral or horizontal or external canal.<\/li>\n<\/ol>\n<\/li>\n<\/ol>\n<ul>\n<li>The anterior and posterior canals are situated vertically and the lateral canal is situated in the horizontal plane. When the head is tilted forward at an angle of 30\u00b0, the lateral canals of both sides are at a horizontal plane parallel to the earth with the convexities directed outward and a little backward.<\/li>\n<li>The anterior canals are at the vertical plane and directed forward and outward at 45\u00b0. The posterior canals are also at the vertical plane but directed backward and outward at 45\u00b0. Therefore, the plane of the position of the anterior canal of one side is parallel to the plane of the posterior canal of the opposite side.<\/li>\n<\/ul>\n<p><strong>Ampulla:<\/strong><\/p>\n<ul>\n<li>There are two ends for each semicircular canal. One end is narrow and the other end is enlarged. The enlarged end is called the ampulla. The ampulla contains the receptor organ of semicircular canals known as crista ampullaris.<\/li>\n<li>The ampulla of all three canals and the narrow end of the horizontal canal open directly into the utricle. The narrow ends of anterior and posterior canals open into the utricle jointly, by forming the common crus. Thus, all three semicircular canals open into the utricle by means of five openings. Utricle opens into saccule.<\/li>\n<\/ul>\n<p>2. <strong>Otolith Organ Or Vestibule:<\/strong><\/p>\n<ul>\n<li>Otolith organ or vestibule is formed by utricle and saccule. Often utricle and saccule are together called otoliths. Utricle communicates with the saccule through the utriculosaccular duct. Saccule communicates with the cochlear duct through ductus reuniens.<\/li>\n<li>Another duct called the endo-lymphatic duct arises from the utriculosaccular duct. It ends in a bag-like structure called an Endolymphatic sac, which lies on the cranial surface of the petrous bone.<\/li>\n<\/ul>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-21557\" src=\"https:\/\/anatomystudyguide.com\/wp-content\/uploads\/2023\/08\/Vestibular-Apparatus-Position-Of-Semicircular-canals-When-The-Head-Is-Tilted-At-30.png\" alt=\"Vestibular Apparatus Position Of Semicircular canals When The Head Is Tilted At 30\" width=\"621\" height=\"384\" srcset=\"https:\/\/anatomystudyguide.com\/wp-content\/uploads\/2023\/08\/Vestibular-Apparatus-Position-Of-Semicircular-canals-When-The-Head-Is-Tilted-At-30.png 621w, https:\/\/anatomystudyguide.com\/wp-content\/uploads\/2023\/08\/Vestibular-Apparatus-Position-Of-Semicircular-canals-When-The-Head-Is-Tilted-At-30-300x186.png 300w\" sizes=\"auto, (max-width: 621px) 100vw, 621px\" \/><\/p>\n<h2><span class=\"ez-toc-section\" id=\"Receptor_Organ_In_Vestibular_Apparatus\"><\/span>Receptor Organ In Vestibular Apparatus<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>The receptor organ in the semicircular canal is called the crista ampullar and that in the otolith organ is called the macula. These receptor organs contain the proprioceptors.<\/p>\n<p>1. <strong>Receptor Organ In Semicircular Canal &#8211; Crista Ampullaris: <\/strong>Crista ampullaris is a crest-like structure situated inside the ampulla of semicircular canals. The crest is formed by a receptor epithelium (neuroepithelium) which consists of hair cells, supporting cells, and secreting epithelial cells. The secreting epithelial cells secrete the ground substance, proteoglycan. These cells are arranged in planum semilunar (a group of epithelial cells) around hair cells.<\/p>\n<ul>\n<li><strong>Hair Cells:<\/strong> Hair cells are the receptor cells of crista ampullaris. There are two types of hair cells, type 1 and type 2 hair cells. Hair cells of semicircular canals, utricle,- saccule receive both afferent and efferent nerve terminals.\n<ul>\n<li><strong>Type 1 hair cells:<\/strong> Type 1 hair cells are flask-shaped. The afferent nerve terminates in the form of a calyx that surrounds the cell body. The efferent nerve terminal ends on the surface of the calyx.<\/li>\n<li><strong>Type 2 hair cells:<\/strong> These cells have a cylindrical or test tube shape. Both afferent and efferent nerve fibers terminate on the surface cell body without forming a calyx.<\/li>\n<li><strong>Cilia of hair cells: <\/strong>The apex of each hair cell has a cuticular plate. From this plate, about 40-60 cilia arise which are called stereocilia. Each stereocilium is attached at its tip to the neighboring taller one by means of a fine process called tip link. Because of the tip links, all the stereocilia are held together. One of the cilia is very tall which is named kinocilium.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<ul>\n<li><strong>Cupula: <\/strong>From crista ampullaris, a dome-shaped gelatinous structure extends up to the roof of the ampulla. It is known as a cupula. The cupula encloses the cilia of hair cells. The cilia of hair cells are projected in the cupula.<\/li>\n<\/ul>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-21560\" src=\"https:\/\/anatomystudyguide.com\/wp-content\/uploads\/2023\/08\/Vestibular-Apparatus-Crista-Ampullaris.png\" alt=\"Vestibular Apparatus Crista Ampullaris\" width=\"409\" height=\"444\" srcset=\"https:\/\/anatomystudyguide.com\/wp-content\/uploads\/2023\/08\/Vestibular-Apparatus-Crista-Ampullaris.png 409w, https:\/\/anatomystudyguide.com\/wp-content\/uploads\/2023\/08\/Vestibular-Apparatus-Crista-Ampullaris-276x300.png 276w\" sizes=\"auto, (max-width: 409px) 100vw, 409px\" \/><\/p>\n<p>2. <strong>Receptor Organ In Otolith Organ Macula<\/strong><\/p>\n<p>acceptor organ in the otolith organ is called the macula. Like cMsia ampullaris, the macula is also formed by neuroepithelium and supporting cells. The neuro-epithelium of the macula also has two types of hair cells, type 1 and type 2 hair cells.<\/p>\n<p>1.<strong> Otolith Membrane:<\/strong><\/p>\n<ul>\n<li>Like the crista ampullar, the macula is also covered by a gelatinous membrane called the otolith membrane. It is a flat structure and not dome-shaped like a cupula. The stereocilia and kinocilium of each hair cell are embedded in the otolith membrane.<\/li>\n<li>The Otolith membrane contains some crystals, which are called ear dust, otoconia or statoconia. The otoconia are mainly constituted by calcium carbonate.<\/li>\n<\/ul>\n<p>2. <strong>Situation of Macula:<\/strong> The situation of the macula is different in utricle and saccule.<\/p>\n<ul>\n<li><strong>Macula in utricle:<\/strong> In the utricle, the macula is situated in the horizontal plane, so that the cilia from hair cells are in the vertical direction.<\/li>\n<li><strong>Macula In Saccule:<\/strong> In the case of the saccule, the macula is in the vertical plane and the cilia are in the horizontal direction.<\/li>\n<\/ul>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-21561\" src=\"https:\/\/anatomystudyguide.com\/wp-content\/uploads\/2023\/08\/Vestibular-Apparatus-Hair-Cells-Of-Vestibular-Apparatus.png\" alt=\"Vestibular Apparatus Hair Cells Of Vestibular Apparatus\" width=\"413\" height=\"467\" srcset=\"https:\/\/anatomystudyguide.com\/wp-content\/uploads\/2023\/08\/Vestibular-Apparatus-Hair-Cells-Of-Vestibular-Apparatus.png 413w, https:\/\/anatomystudyguide.com\/wp-content\/uploads\/2023\/08\/Vestibular-Apparatus-Hair-Cells-Of-Vestibular-Apparatus-265x300.png 265w\" sizes=\"auto, (max-width: 413px) 100vw, 413px\" \/><\/p>\n<h2><span class=\"ez-toc-section\" id=\"Nerve_Supply_To_Vestibular_Apparatus\"><\/span>Nerve Supply To Vestibular Apparatus<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>The impulses from the hair cells of the crista ampullar and maculae are transmitted to the medulla oblongata and other parts of the central nervous system through the fibers of the vestibular division of the vestibulocochlear (8 cranial) nerve.<\/p>\n<p>1.<strong> First Order Neuron:<\/strong><\/p>\n<ul>\n<li>The first-order neurons of the sensory pathway are bipolar in nature. The soma of the bipolar cells is situated in the vestibular or Scarpa\u2019s ganglion. The Scarpa\u2019s ganglion is situated in the internal auditory meats.<\/li>\n<li>The dendrites of the bipolar cells reach the receptor organs, i.e. crista ampullaris and maculae in the vestibular apparatus. The branches of the dendrites have close contact with the basal part of hair cells.<\/li>\n<li>The dendrites terminating on type I hair cells are comparatively larger than those ending on type 2 hair cells. The axons of the first-order neurons (bipolar cells) form the vestibular division of the vestibulocochlear nerve.<\/li>\n<li>These fibers reach the medulla oblongata and terminate in the vestibular nuclei. These nerve fibers are called primary vestibular fibers.\n<ul>\n<li><strong>Vestibular Nuclei:<\/strong>\n<ul>\n<li>There are four vestibular nuclei in the medulla oblongata, viz. superior, inferior, lateral, and medial nuclei. Most of the primary vestibular fibers reaching superior and medial nuclei come from crista ampullaris of semicircular canals.<\/li>\n<li>The lateral vestibular nucleus receives the fibers mostly from the maculae of the otolith organ and, the inferior vestibular nucleus receives fibers from both the crista ampullar and maculae.\n<ul>\n<li><strong>Efferent nerve fibers to hair cells: <\/strong>Some of the neurons in vestibular nuclei send efferent fibers which run back to the hair cells along with primary vestibular fibers (see above). It is believed that the efferent fibers to hair cells provide tonic inhibition of hair cells.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<li><strong>Fibers to Cerebellum:<\/strong> The fibers from some bipolar cells reach the cerebellum directly and terminate in the flocculonodular lobe or the fastigial nucleus in the cerebellum.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-21563\" src=\"https:\/\/anatomystudyguide.com\/wp-content\/uploads\/2023\/08\/Vestibular-Apparatus-Macula-In-Otolith-Organ.png\" alt=\"Vestibular Apparatus Macula In Otolith Organ\" width=\"591\" height=\"460\" srcset=\"https:\/\/anatomystudyguide.com\/wp-content\/uploads\/2023\/08\/Vestibular-Apparatus-Macula-In-Otolith-Organ.png 591w, https:\/\/anatomystudyguide.com\/wp-content\/uploads\/2023\/08\/Vestibular-Apparatus-Macula-In-Otolith-Organ-300x234.png 300w\" sizes=\"auto, (max-width: 591px) 100vw, 591px\" \/><\/p>\n<p>2.<strong> Second Order Neuron:<\/strong><\/p>\n<p>The second-order neurons of this pathway are located in the four vestibular nuclei. The axons from the vestibular nuclei form the secondary vestibular fibers. The secondary vestibular fibers form four tracts:<\/p>\n<ol>\n<li>Vestibulo-ocular tract<\/li>\n<li>Vestibulospinal tract<\/li>\n<li>Vestibuloreticular tract<\/li>\n<li>Vestibulocerebellar tract.<\/li>\n<\/ol>\n<p>&nbsp;<\/p>\n<ol>\n<li><strong>Vestibulo-ocular Tract:<\/strong> Fibers from superior, medial, and inferior vestibular nuclei descend downwards for a short distance along with the vestibulospinal tract. Afterward, the fibers ascend through the medial longitudinal fasciculus and terminate in the nuclei of 3, 4, and 6 cranial nerves, thus forming the vestibule-ocular tract. This tract is concerned with the movements of the eyeballs in relation to the position of the head.<\/li>\n<li><strong>Vestibulospinal Tract:<\/strong> Fibers from the lateral nucleus descend downwards and form the vestibulospinal tract. Some fibers from this nucleus ascend upward and join the medial longitudinal fasciculus. The fibers of the vestibulospinal tract are involved in reflex movements of the head and body during postural changes.<\/li>\n<li><strong>Vestibuloreticular Tract:<\/strong> Some fibers from vestibular nuclei reach the reticular formation of the brainstem forming the reticulospinal tract. These fibers are concerned with the facilitation of muscle tone.<\/li>\n<li><strong>Vestibulocerebellar Tract:<\/strong> Some of the fibers arising from all four vestibular nuclei reach the cerebellum and terminate in the flocculonodular lobe and fastigial nuclei. The fibers of this tract are involved in the coordination of movements according to body position.<\/li>\n<\/ol>\n<h2><span class=\"ez-toc-section\" id=\"Functions_Of_Vestibular_Apparatus\"><\/span>Functions Of Vestibular Apparatus<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>The receptors of semicircular canals give a response to rotatory movements or angular acceleration of the head. And, the receptors of the utricle and saccule give a response to linear acceleration of the head. Thus, the vestibular apparatus is responsible for detecting the position of the head during different movements. It also causes reflex adjustments in the position of the eyeball, head, and body during postural changes.<\/p>\n<p>1. <strong>Functions Of Semicircular Canals: <\/strong>Semicircular canals are concerned with angular (rotatory) acceleration. Semicircular canals sense rotational movement. Each semicircular canal is sensitive to rotation in a particular plane.<\/p>\n<ul>\n<li><strong>Superior Semicircular Canal:<\/strong> Superior semicircular canal gives a response to rotation in the anteroposterior plane (transverse axis), i.e. front to back movements like nodding the head while saying \u2018Yes &#8211; yes\u2019.<\/li>\n<li><strong>Horizontal Semicircular Canal:<\/strong> This semicircular canal gives a response to rotation in the horizontal plane (vertical axis), i.e. side to side movements (left to right or right to left) like shaking the head while saying \u2018No &#8211; no\u2019.<\/li>\n<li><strong>Posterior Semicircular Canal:<\/strong> This semicircular canal gives a response to rotation in the vertical plane (anteroposterior axis) by which the head is rotated from shoulder to shoulder.<\/li>\n<li><strong>Mechanism Of Stimulation Of Receptor Cells In Semicircular Canal:<\/strong>\n<ul>\n<li>At the beginning of the rotation, the receptor cells are stimulated by the movement of endolymph inside the semicircular canals. However, the receptors are stimulated only at the beginning and at the stoppage of rotatory movements. And during rotation at a constant speed, these receptors are not stimulated.<\/li>\n<li>When a person rotates in a clockwise direction in the horizontal plane (vertical axis), the horizontal canal moves in a clockwise direction. But, there is no corresponding movement of endolymph inside the canal at the beginning of the rotation.<\/li>\n<li>Because of the inertia, endolymph remains static. This phenomenon causes relative displacement of endolymph in the direction opposite to that of the rotation of the head. That is, the fluid is pushed in an anticlockwise direction.<\/li>\n<li>Thus, in the right horizontal semicircular canal, the endolymph flows towards the ampulla and, in the left canal, the fluid moves away from the ampulla.<\/li>\n<li>The movement of endolymph in the semicircular canal, in turn, causes the corresponding movement of the gelatinous cupula. Thus, in the right horizontal canal, the cupula moves towards the ampulla. Whereas in the left canal, the cupula moves away from the ampulla.<\/li>\n<li>In any semicircular canal, when the cupula moves towards the ampulla, the stereocilia of hair cells are pushed towards the kinocilium leading to stimulation of hair cells. When the cupula moves away from the ampulla, the stereocilia are pushed away from the kinocilium, and hair cells are not stimulated.<\/li>\n<li>Thus, at the commencement of rotation in a clockwise direction around a vertical axis, the hair cells at the ampulla of the horizontal canal in the right ear are stimulated. But, the hair cells in the horizontal canal of the left ear are not stimulated.<\/li>\n<li>Because of stimulation, the hair cells in the right horizontal canal send information (impulses) through sensory nerve fibers to vestibular, cerebellar, and reticular centers. Now, these centers send proper instructions to various muscles of the body to maintain the equilibrium of the body during angular acceleration (rotation).<\/li>\n<li>On the other hand, rotation in an anticlockwise direction causes stimulation of hair cells in the ampulla of the horizontal canal in the left ear only. The hair cells of the horizontal canal in the right ear are not stimulated. Stimulation of hair cells in the left ear is followed by the process as in the case of clockwise rotation.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-21567\" src=\"https:\/\/anatomystudyguide.com\/wp-content\/uploads\/2023\/08\/Vestibular-Apparatus-Movement-Of-Fluid-And-Excitation-Of-Crista-Ampullaris-In-Horizontal-Semicircular-Canals-During-Clockwise-Rotation.png\" alt=\"Vestibular Apparatus Movement Of Fluid And Excitation Of Crista Ampullaris In Horizontal Semicircular Canals During Clockwise Rotation\" width=\"403\" height=\"454\" srcset=\"https:\/\/anatomystudyguide.com\/wp-content\/uploads\/2023\/08\/Vestibular-Apparatus-Movement-Of-Fluid-And-Excitation-Of-Crista-Ampullaris-In-Horizontal-Semicircular-Canals-During-Clockwise-Rotation.png 403w, https:\/\/anatomystudyguide.com\/wp-content\/uploads\/2023\/08\/Vestibular-Apparatus-Movement-Of-Fluid-And-Excitation-Of-Crista-Ampullaris-In-Horizontal-Semicircular-Canals-During-Clockwise-Rotation-266x300.png 266w\" sizes=\"auto, (max-width: 403px) 100vw, 403px\" \/><\/p>\n<ul>\n<li><strong>Electrical Potential in Hair Cells &#8211; Mechanotransduction:<\/strong>\n<ul>\n<li>Mechanotransduction is a type of sensory transduction in the hair cell (receptor) by which the mechanical energy (movement of cilia in hair cells) caused by the stimulus is converted into action potentials in the vestibular nerve fiber.<\/li>\n<li>The resting membrane potential in hair cells is about- 60 mV. The movement of stereocilia of hair cells towards kinocilium causes the opening of mechanically gated potassium channels. It is followed by an influx of potassium ions from endolymph which contains a large amount of potassium ions. Potassium ions cause the development of mild depolarization in hair cells up to &#8211; 50 mV.<\/li>\n<li>The depolarization is called receptor potential. Besides potassium ions, calcium ions also enter the hair cells from endolymph.<br \/>\nThe receptor potential in hair cells is nonpropagative. But, it causes the generation of action potential in nerve fibers distributed to hair cells.<\/li>\n<li>Depolarization of hair cells causes them to release a neurotransmitter which generates the action potential in the nerve fibers. It is believed that the probable neurotransmitter may be glutamate. Movement of stereocilia in the opposite direction (away from kinocilium) causes hyperpolarization of hair cells.<\/li>\n<li>Calcium may play a role in the development of hyperpolarization. Hyperpolarization in hair cells slops generation of action potential in the nerve fibers.<\/li>\n<\/ul>\n<\/li>\n<li><strong>Adaptation of Receptors in Semicircular Canal during Rotation:<\/strong>\n<ul>\n<li>The hair cells of crista ampullaris generate impulses even at rest. But, the frequency of discharge is very low at resting conditions. It is about 50-100 impulses per minute.<\/li>\n<li>At the commencement of rotation, the discharge of impulses reaches a higher frequency of 600-800 per minute, depending upon the speed of rotation. However, the rapid discharge of impulses lasts only for the first 20-25 seconds of rotation. Afterward, even if rotation continues, the frequency of impulses falls back to the resting level. It is because of the adaptation of receptors during continuous rotation.<\/li>\n<li><strong>Cause for adaptation of receptor cells:<\/strong>\n<ul>\n<li>At the onset of rotation, the endolymph inside the semicircular canal does not move along with the semicircular canal because of the inertia of the fluid. So semicircular canal moves leaving the endolymph behind which is like moving in the opposite direction.<\/li>\n<li>Now the endolymph is pushed into the ampulla towards the utricle. It causes the stimulation of hair cells but, after about 20 seconds due to the accumulation of endolymph, pressure is developed in the ampulla. Due to the back pressure, the endolymph starts moving away from the ampulla, i.e. it starts moving along with the semicircular canal at the same speed.<\/li>\n<li>It causes the adaptation of the hair cells. The hair cells of the crista ampullar of vertical semicircular canals are stimulated during the rotation of the head in the anteroposterior or transverse axis. However, the mechanism involved is similar to that of the hair cells of the crista ampullar of horizontal canals.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-21568\" src=\"https:\/\/anatomystudyguide.com\/wp-content\/uploads\/2023\/08\/Mechanotransduction-In-Hair-Cell-Of-Vestibular-Apparatus.png\" alt=\"Mechanotransduction In Hair Cell Of Vestibular Apparatus\" width=\"428\" height=\"599\" srcset=\"https:\/\/anatomystudyguide.com\/wp-content\/uploads\/2023\/08\/Mechanotransduction-In-Hair-Cell-Of-Vestibular-Apparatus.png 428w, https:\/\/anatomystudyguide.com\/wp-content\/uploads\/2023\/08\/Mechanotransduction-In-Hair-Cell-Of-Vestibular-Apparatus-214x300.png 214w\" sizes=\"auto, (max-width: 428px) 100vw, 428px\" \/><\/p>\n<ul>\n<li><strong>Nystagmus: <\/strong>Nystagmus is the rhythmic oscillatory involuntary movements of the eyeball. It is common during rotation. It is due to the natural stimulatory effect of the vestibular apparatus during rotational acceleration. Nystagmus occurs both in physiological and pathological conditions.\n<ul>\n<li><strong>Vestibulo-ocular reflex and nystagmus: <\/strong>The nystagmus is a reflex phenomenon that occurs in order to maintain visual fixation. Since the movements of eyeballs occur in response to the stimulation of the vestibular apparatus this reflex is called the vestibular- ocular reflex.<\/li>\n<li><strong>Movement of the eyeball during nystagmus: <\/strong>Nystagmus has two components of movement.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<ol>\n<li style=\"list-style-type: none;\">\n<ol>\n<li style=\"list-style-type: none;\">\n<ol>\n<li>Slow component<\/li>\n<li>Quick component<\/li>\n<\/ol>\n<\/li>\n<\/ol>\n<\/li>\n<\/ol>\n<p>1.<strong> Slow component:<\/strong><\/p>\n<ul>\n<li>At the beginning of the rotation, since the eyes are fixed at a particular object (point), the eyeballs rotate slowly in the direction opposite to that of the rotation of the head.<\/li>\n<li>It is called the slow component of nystagmus. It is due to the vestibulo-ocular reflex. This reflex is because of labyrinthine impulses reaching the ocular muscles via vestibular nuclei and 3, 4, and 5 cranial nerves.<\/li>\n<\/ul>\n<p>2. <strong>Quick component:<\/strong><\/p>\n<ul>\n<li>When the slow movement of eyeballs is limited, the eyeballs move to a new fixation point in the direction of rotation of the head. This movement to a new fixation point occurs with a jerk.<\/li>\n<li>So, it is called the quick component. The quick component of nystagmus is due to the ach&#8217;janon of some centers in the brainstem. The slow and quick components of nystagmus occur alternately.<\/li>\n<\/ul>\n<p><strong>Postrotatory nystagmus: <\/strong>Nystagmus that occurs immediately after the stoppage of rotation is called postrotatory nystagmus. It is due to the movement of the cupula in the opposite direction caused by the endolymph when rotation is stopped. Postrotatory nystagmus can be demonstrated by Barany&#8217;s chair (see below for details).<\/p>\n<ul>\n<li><strong>Postrotatory Reactions: <\/strong>After the end of the rotatory movement, two reactions occur:<\/li>\n<\/ul>\n<ol>\n<li>The feeling of rotation in the opposite direction<\/li>\n<li>Postrotatory nystagmus.<\/li>\n<\/ol>\n<p>&nbsp;<\/p>\n<ol>\n<li><strong>The feeling of rotation in the opposite direction:<\/strong>\n<ul>\n<li>When rotation in a clockwise direction is stopped suddenly, the endolymph moves in the direction of rotation in the right horizontal semicircular canal although the semicircular canal stops moving. So, the cupula moves away from the utricle. However, in the case of the left horizontal semicircular canal, the endolymph moves into the ampulla.<\/li>\n<li>There, it pushes the cupula towards the utricle and stimulates the hair cells in the crista of the left canal. It causes the feeling of rotation in the opposite direction when the rotation is stopped.<\/li>\n<\/ul>\n<\/li>\n<li><strong>Postrotatory nystagmus:<\/strong> It is already explained above<\/li>\n<\/ol>\n<ul>\n<li><strong>Nystagmus in Pathological Conditions:<\/strong> Nystagmus is very common in the lesions of the cerebellum and in the lesions of the brainstem involving vestibular nuclei or vestibular nerve. It occurs due to the damage of the labyrinth also.<\/li>\n<\/ul>\n<p>2. <strong>Function Of Otolith Organ: <\/strong>Otolith organ is concerned with linear acceleration and detects acceleration in both horizontal and vertical planes. Utricle responds during horizontal acceleration and saccule responds during vertical acceleration.<\/p>\n<ul>\n<li><strong>The function of Utricle:<\/strong>\n<ul>\n<li>The position of hair cells of the macula helps the utricle to respond to horizontal acceleration. In the utricle, the macula is situated in the horizontal plane with the hair cells in the vertical plane.<\/li>\n<li>While moving horizontally, because of inertia the otoconia move in opposite directions and pull the cilia of hair cells resulting in stimulation of hair cells.<\/li>\n<li>For example, when the body moves forward, the otoconia fall back in the otolith membrane and pull the cilia of hair cells backward. Pulling of cilia causes stimulation of hair cells. Hair cells send information (impulses) to vestibular, cerebellar, and reticular centers.<\/li>\n<li>These centers in turn send instructions to various muscles to maintain the equilibrium of the body during the forward movement.<\/li>\n<\/ul>\n<\/li>\n<li><strong>The function of Saccule:<\/strong>\n<ul>\n<li>The Macula of the saccule is situated in the vertical plane with the cilia of hair cells in the horizontal plane. While moving vertically, as in the case of the utricle, the otoconia of the saccule move in the opposite direction and pull the cilia resulting in the stimulation of hair cells.<\/li>\n<li>For example, while climbing up, the otoconia move down by pulling the cilia downwards. It stimulates the hair cells which in turn send information to the brain centers. And the action follows as in the case of movement in the horizontal plane.<\/li>\n<\/ul>\n<\/li>\n<li><strong>Role of Otolith Organ in Resting Position: <\/strong>During resting conditions (in the absence of head movement), the hair cells are stimulated continuously because of the pulling of otoconia by gravitational force. Stimulation of hair cells produces reflex movements of the head and limbs for the maintenance of posture in relation to gravity. Because of this function, the receptors of the otolith organ are called gravity receptors.<\/li>\n<\/ul>\n<h2><span class=\"ez-toc-section\" id=\"Effects_Of_Stimulation_Of_Semicircular_Canals\"><\/span>Effects Of Stimulation Of Semicircular Canals<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>Under experimental conditions, the semicircular canals can be stimulated by the two methods.<\/p>\n<ol>\n<li>Rotational movement<\/li>\n<li>Caloric stimulation<\/li>\n<\/ol>\n<p>1.<strong> Rotational Movement:<\/strong> Semicircular canal can be stimulated by rotational movement with the help of a Barany chair.<\/p>\n<ul>\n<li><strong>Barany Chair: <\/strong>It is a revolving chair. The subject is seated on this chair with the head tilted forward at 30\u00b0. Both eyes are closed. The chair is rotated at a speed of 30 RPM for about 20 seconds and then stopped.<\/li>\n<li><strong>Effects of Stimulation of Semicircular Canals by Rotation:<\/strong> The simulation of semicircular canals during rotation in the Barany chair produces some effects both during rotation and after the end of the rotation.<\/li>\n<li><strong>Postrotatory Reactions: <\/strong>Twenty seconds after the stoppage of rotation in Barany&#8217;s chair the following reactions occur.\n<ul>\n<li><strong>Postrotatory nystagmus:<\/strong> The eyes are closed during rotation by the Barany chair. When the eyes are opened after the sudden stoppage of rotation, nystagmus starts. The postrotatory nystagmus exists for about 30 seconds.<\/li>\n<li><strong>Dizziness:<\/strong> Immediately after the stoppage of rotation, there is a feeling of unsteadiness. It is called dizziness. Dizziness is associated with the feeling of rotation in the opposite direction.<\/li>\n<li><strong>Vertigo:<\/strong> After the end of the rotation, there is a feeling of the environment whirling around or, there is a feeling of rotation of the person himself.<\/li>\n<li><strong>Other effects:<\/strong> Rotation for a longer period causes nausea and vomiting, The blood pressure falls by about 10-15 mm Hg. And the heart rate is reduced by 10-12 beats per minute.<\/li>\n<\/ul>\n<\/li>\n<li><strong>Reaction during Rotation with Opened Eyes:<\/strong> If the Barany chair is rotated with opened eyes, the nystagmus occurs continuously throughout the period of rotation.<\/li>\n<\/ul>\n<p>2. <strong>Caloric Stimulation: <\/strong>The semicircular canals can be stimulated by bypassing hot or cold water into the ear by using a syringe. The transmission of change in temperature into the labyrinth alters the specific gravity of endolymph. This in turn causes movement of the cupula and stimulation of receptor cells.<\/p>\n<ul>\n<li><strong>Effects of Caloric Stimulation:<\/strong> The effects of stimulation of semicircular canals by thermal stimulus cause nystagmus, vertigo, and nausea. During the treatment for ear infection, the temperature of fluid instilled into the ear must be equal to body temperature, so that, such symptoms of caloric stimulation are avoided.<\/li>\n<\/ul>\n<h2><span class=\"ez-toc-section\" id=\"Applied_Physiology_Effect_Of_Labyrinthectomy\"><\/span>Applied Physiology Effect Of Labyrinthectomy<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<ul>\n<li><strong>Bilateral Labyrinthectomy:<\/strong> Removal of labyrinthine apparatus on both sides leads to complete loss of equilibrium. The equilibrium could be maintained only by visual sensation. The postural reflexes are severely affected. There is a loss of hearing sensation too.<\/li>\n<li><strong>Unilateral Labyrinthectomy:<\/strong> Removal of labyrinthine apparatus on one side causes less effect on postural reflexes. However, severe autonomic symptoms occur. The autonomic symptoms are due to the unbalanced generation of impulses from the unaffected labyrinthine apparatus.\n<ul>\n<li>The symptoms are nausea, vomiting, and diarrhea. During movement, the symptoms become very severe. The unaffected labyrinthine apparatus starts compensating the loss of functions of the affected labyrinth. Hence, the symptoms disappear slowly after a few months.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<h2><span class=\"ez-toc-section\" id=\"Motion_Sickness\"><\/span>Motion Sickness<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p><strong>Motion Sickness Definition: <\/strong>Motion sickness is defined as the syndrome of physiological response during movement (travel) to which the person is not adapted. It can occur while traveling in any form of vehicle like an automobile, ship, aircraft, or spaceship. The motion sickness that occurs while traveling in a watercraft is called seasickness.<\/p>\n<p><strong>Motion Sickness Cause: <\/strong>Motion sickness is due to excessive and repeated stimulation of the vestibular apparatus. Excessive and repeated stimulation of the vestibular apparatus occurs because of:<\/p>\n<ul>\n<li>Rapid and repeated change in the rate of motion while traveling<\/li>\n<li>Rapid and repeated change in direction.<\/li>\n<\/ul>\n<p>Psychological factors like anxiety about unfamiliar modes of travel may be added up to cause motion sickness.<\/p>\n<p><strong>Motion Sickness Symptoms:<\/strong><\/p>\n<ul>\n<li>Nausea<\/li>\n<li>Vomiting<\/li>\n<li>Sweating<\/li>\n<li>Diarrhea<\/li>\n<li>Pallor (paleness)<\/li>\n<li>Salivation<\/li>\n<li>Discomfort<\/li>\n<li>Headache<\/li>\n<li>Disorientation<\/li>\n<\/ul>\n<p><strong>Motion Sickness Prevention:<\/strong><\/p>\n<ul>\n<li>The responses of motion sickness can be prevented by avoiding greasy and bulky food before travel and by taking antiemetic drugs (drugs preventing nausea and vomiting).<\/li>\n<li>In experimental animals, motion sickness is abolished by bilateral removal of the vestibular apparatus, sectioning of the vestibular nerve, or ablation of the flocculonodular lobe.<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>Vestibular Apparatus Introduction The vestibular apparatus is the part of the labyrinth or inner ear. It plays an important role in maintaining posture and equilibrium through statokinetic reflexes. The other part of the labyrinth is the cochlea, which is concerned with the sensation of hearing. Read And Learn More:\u00a0Medical Physiology Notes Labyrinth The labyrinth (inner [&hellip;]<\/p>\n","protected":false},"author":14,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_genesis_hide_title":false,"_genesis_hide_breadcrumbs":false,"_genesis_hide_singular_image":false,"_genesis_hide_footer_widgets":false,"_genesis_custom_body_class":"","_genesis_custom_post_class":"","_genesis_layout":"","_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[46],"tags":[],"class_list":{"0":"post-21515","1":"post","2":"type-post","3":"status-publish","4":"format-standard","6":"category-physiology","7":"entry","8":"has-post-thumbnail"},"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v23.6 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>Vestibular System: Structure and Function Notes - Anatomy Study Guide<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/anatomystudyguide.com\/vestibular-system-structure-and-function-notes\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Vestibular System: Structure and Function Notes - Anatomy Study Guide\" \/>\n<meta property=\"og:description\" content=\"Vestibular Apparatus Introduction The vestibular apparatus is the part of the labyrinth or inner ear. 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