Equilibrium Sensation (Vestibular Sense) PDF

Equilibrium sensation (vestibular sense) Asghar Ghasemi  Functions of vestibular sense 1. Provide information about head orientation (head position) with respect to gravity 2. Provide information about head movement (head motion) in space 3. Help to control eye movement Vestibular...

Equilibrium sensation (vestibular sense) Asghar Ghasemi  Functions of vestibular sense 1. Provide information about head orientation (head position) with respect to gravity 2. Provide information about head movement (head motion) in space 3. Help to control eye movement Vestibular sense is a meta-sense in that it requires the integration of several sensations (vestibular, visual, proprioceptive, tactile) to arrive at its expression and appreciation  = little bag = little sac Ampullae of semicircular ducts are located at the base of the semicircular canals next to the utricle  From left From above Lateral (horizontal) semicircular Anterior semicircular canal canal Posterior semicircular canal When the head is bent forward about 30° : The lateral semicircular ducts are horizontal with respect to the surface of the Earth Cochlea is located The anterior ducts are in vertical planes that anteromedial relative to the project forward and 45° outward semicircular canals The posterior ducts are in vertical planes that project backward and 45° outward. Otoconia (staconia, otolith, ear stone): Small crystals of calcium carbonate in the saccule and utricle of the vestibular system. The calcified statoconia have a 2-3 times the specific gravity of the surrounding fluid and tissues What is the difference between cochlear hair cells and vestibular hair cells? Unlike cochlear hair cells, vestibular hair cells in addition to about 100 small cilia called stereocilia, has one large cilium, the kinocilium The kinocilium is always located to one side, and the stereocilia become progressively taller toward the kinocilium Stimulation and inhibition of vestibular hair cells  Macula: for Detecting Orientation of the Head With Respect to Gravity (heal tilting) Head is upright → utricular macula Lying down position → saccular macula Linear acceleration (translational head movements) Horizontal → utricular macula Vertical → saccular macula Linear acceleration: Changes in velocity during movement in a straight line Utricular macula detects head tilting when head is upright Tonic activity (Signals head orientation with respect to gravity) Utricular macula detects translational head movements in horizontal plane Moving and stopping a car  In each macula, each of the hair cells is oriented in a different direction so that: Some of the hair cells are stimulated when the head bends forward Some are stimulated when it bends backward Others are stimulated when it bends to one side A different pattern of excitation occurs in the macular nerve fibers for each orientation of the head in the gravitational field and apprises the brain of the head’ s orientation in space.  Maculae— Sensory Organs of the Utricle and Saccule The macula of the utricle The macula of the saccule Lies in the horizontal plane on theIs located mainly in a vertical inferior surface of the utricle plane of the saccule Plays a role in determining head Signals head orientation when the orientation when the head is person is lying down upright Detects horizontal linear Detects vertical linear acceleration acceleration (e.g., when the body (e.g., going up and down in an is suddenly thrust forward like escalator; going from sit to stand) moving and stopping a car) Maintaining static equilibrium Maintaining static equilibrium particularly when the head is in the particularly when the head is in the near-vertical position near-vertical position Do not operate for the detection of Do not operate for the detection of linear velocity linear velocity Crista Ampularis Semicircular Ducts for detecting: Angular (rotational) acceleration Angular acceleration: Changes in velocity during rotation Endolymph pressure Effect of Leftward Head Rotation on the Activity of Vestibular Afferent Fibers Supplying Hair Cells in the Horizontal Semicircular Canals  All semicircular ducts detect is that the person’ s head is beginning or stopping to rotate in one direction or another. Semicircular ducts along with flocculonodular lobes of the cerebellum predicts disequilibrium to provide anticipatory correction Both semicircular ducts and flocculonodular lobes of the cerebellum participate in dynamic equilibrium during rapid changes in direction of motion  Summary Otolith organs Located at the base of the vestibular labyrinth and comprised of the utricle and saccule. Provide information regarding linear acceleration (dynamic equilibrium) as well as static position of the head relative to gravity (static equilibrium) Uvula in the cerebellum is also involved in static equilibrium Semicircular canals Located in inner ear, these three canals (horizontal, superior, and posterior) provide sensory information related to angular (rotational) acceleration of the head and dynamic equilibrium Flocculonodular lobes of the cerebellum participate in dynamic equilibrium Vestibular pathways Thank you