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Week 1 Elluminate Presentation
The vestibular system is responsible for the human sense of motion and balance. It is located in the inner ear alongside the auditory system. While similar in using fluid and hair cells, the vestibular system is more intricate with five parts - the utricle, saccule, and three semicircular canals. It serves four main functions: as an organ of equilibrium, sensing motion, influencing posture control, and affecting eye movement through the vestibulo-ocular reflex. The system works through fluid movement and hair cell stimulation in the semicircular canals and otolith organs to detect head movement and orientation.
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Week 1 Elluminate Presentation
- 1. AUD 831 WeekOne Chat Lisa M Koch, AuD
- 2. Introduction to thevestibular system • Responsible for every sense of motion that humans have – standing up – lying down – walking forward – riding in an elevator – driving a car
- 3. Characteristics in commonwith the auditory system • encased in the same part of the skull • fluid-filled organs • have tiny hair cells within them • depend on the inner ear’s ability to convert the mechanical energy of the hair cells to electrical energy
- 4. Difference between thevestibular system and the auditory system • The vestibular (balance) system is a much more intricate structure. • Each of the vestibular systems is comprised of five parts – Utricle – saccule – three semi-circular canals
- 5. Functions of theVestibular System 1. Organ of equilibrium 2. Sensation of motion 3. Influence on posture control 4. Influences eye movement
- 6. What does thevestibular system look like? •
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- 13. 2 Types of“Equilibrium” Rotational Movement
- 14. Static Equilibrium Receptors forstatic Equilibrium are the maculae.
- 15. Maculae in Saccule& utricle Saccule Utricle
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- 22. Mechanism of actionof an otolith organ
- 23. Mechanism of actionof a horizontal semicircular duct and the resulting reflex eye movement.
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- 35. Vestibular nerve fiberdischarge 1.
- 38. What gives usbalance? • Visual System – Oculomotor nuclei – Eye muscles • Vestibular System – Semicircular Canals – Otoliths (Utricle and saccule) – Vestibular nerves – Vestibular nuclei • Proprioceptor System (Tells us where we are in space) ‐ Spinal cord ‐ Muscles ‐ Joints
- 39. Questions/ Comments? lkoch@atsu.edu or740-441-7579
Editor's Notes
- #6 THE 3 FUNCTIONS OF THE VESTIBULAR SYSTEM 1. IT IS THE PRIMARY ORGAN OF EQUILIBRIUM 2. PLAYS A MAJOR ROLE IN THE SUBJECTIVE SENSATION OF MOTION AND SPATIAL ORIENTATION 3. VESTIBULAR INPUT TO AREAS OF THE NERVOUS SYSTEM INVOLVED IN MOTOR CONTROL ELICITS ADJUSTMENTS OF MUSCLE ACTIVITY AND BODY POSITION TO ALLOW FOR UPRIGHT POSTURE SO THE VESTIBULAR SYSTEM IS IMPORTANT IN POSTURE CONTROL TOO 4. VESTIBULAR INPUT TO REGIONS OF THE NERVOUS SYSTEM CONTROLLING EYE MOVEMENTS HELPS STABILIZE THE EYES IN SPACE DURING HEAD MOVEMENTS. THIS REDUCES THE MOVEMENT OF THE IMAGE OF A FIXED OBJECT ON THE RETINA
- #7 The peripheral vestibular apparatus consists of the saccule, utricle, and semicircular canals. The purpose of the vestibular system is to check the position and motion of our head in space. There are two components, one detecting rotation through the three semicircular canals, the other detecting motion along a line through the utricle and saccule organs. An important role of the vestibular system is to keep our eyes still in space while our head moves. The vestibular system exerts direct control over the eyes through three pairs of muscles. The direction of these eye muscles is exactly in line with the direction of the three semicircular canals, so that in general a single canal controls a single pair of eye muscles. Directly or indirectly, the vestibular system influences nearly everything we do. It is the unifying system in our brain that modifies and coordinates information received from other systems and has a great impact on our behavior. THE SEMICIRCULAR CANALS SENSES ANGULAR ACCELERATION THEN FEEDS THAT INFORMATION TO THE CENTRAL NERVOUS SYSTEM THE UTRICLE AND SACCULE SENSE LINEAR ACCELERATION AS WELL AS THE HEADS POSITION REALATED TO GRAVITY 5 RECEPTOR ORGANS IN EACH LABYRINTH 3 SEMICIRCULAR CANALS, ONE UTRICLE AND ONE SACCULE SEMICIRCULAR CANALS ARE SO ARRANGED THAT THEY LIE IN PLANES ORTHOGONAL TO ONE ANOTHER
- #11 Anatomy of the inner ear is dominated by large fluid-filled spaces. Perilymph/endolymph. Perilymph in the bony labyrinth, separates bony lab from membranous lab. Endolymph is the fluid in the membranous lab (in orange in this pic). Imbalance between perilymph and endolymph results in Meniere’s disease (vertigo, tinnitus, hearing loss, perception of fullness in the ear)
- #12 Perilymph Similar to extracellular fluid K+=10mM, Na+=150mM Unclear whether this is ultrafiltrate of CSF or blood Endolymph Similar to intracellular fluid K+=150mM, Na+=2mM Produced from dark cells in the cristae and maculae In this picture, perilymph is orange, endolymph is blue. Endolymphatic space is completely bounded by tissues and there are no connections between perilymph and endolymph. perilymphatic chamber of the vestibular system has a wide connection to scala vestibuli, which in turn connects to scala tympani by an opening called the helicotrema at the apex of the cochlea. Scala tympani is then connected to the cerebrospinal fluid (CSF) of the subarachnoid space by the cochlear aqueduct. endolymphatic system of the cochlea (scala media) is connected to the saccule by the ductus reuniens and from there connects to the endolymphatic sac, which lies in a bony niche within the cranium. The endolymph of the utricle and semi-circular canals also connects to the endolymphatic sac.
- #14 Static equilibrium: is concerned with the orientation of the body relative to the ground (Linear acceleration) Dynamic equilibrium is concerned with the maintenance of posture, especially in the head (Rotational movement)
- #15 1- Supporting cells 4- otolithic membrane 2- Hair cell 5- nerve fibers 3- Cilia 6- Otoliths or otoconia Each maculae contains supporting cells and scattered receptors called hair cells Each of the hair cells has a major process called a kinocilium and several smaller stereocilia. Lying over the supporting and hair cells is a gelatin-like otolithic membrane. This membrane slides over the hair cells and stimulates them when the head is moved.
- #16 The Maculae are responsible for linear acceleration forces. The Maculae are in the Saccule : is responsible for vertical acceleration Utricle: is responsible for horizontal acceleration
- #17 When the head starts or stops moving in a linear acceleration, the otolithic membrane slides backward or forward over hair cells, so the hair cells will bend You can see the position of the macula with head upright and with the head tilted forward in this photo.
- #18 This slide shows the nerve action potential for linear acceleration stimuli. When the hair bends towards the kinocilium the hair cell depolarize faster steam of impulse is sent to the brain When the hair bends in the opposite direction the hair cells hyperpolarize Slower impulse generation
- #19 The receptors for Dynamic equilibrium are the ampulla which is found in the semicircular canals. In each ampulla is a small elevation called a crista. Each crista is made up of hair (receptor) cells and supporting cells, and covered by a jelly-like material known as the cupola. Movement of the cupola stimulates the hair cells
- #20 The ampulla is responsible for the change in rotational movement, as continuous rotation does not stimulate the ampulla. When the head starts moving rotationally, the endolymph in the semicircular ducts move in the direction opposite to the body’s direction deforming the crista in the duct, causing depolarization If the body continues to rotate at a constant rate, the endolymph moves at the same direction and speed as the body and stops the movement of hair cells
- #21 When we stop moving, endolymph keeps on moving in the opposite direction, causing hyperpolarization of the hair cells that will tell the brain that we have stopped movement. Note that all hair cells have the same orientation in a given cupula Head rotation (angular acceleration) carries the membranous SSC along with it, while the inertia of the endolymph and cupula tend to keep these elements stationary in space. the endolymph is inside the membranous labyrinth so that during angular acceleration there is a swelling of the membrane just next to the ampulla (to the right in the above picture), so that there can be a small displacement of the endolymph, in spite of the barrier formed by the cupula. 2 things act to accelerate the endolymph in the same direction that the head is turning The elastic push from the distended cupula as it pushes against the endolymph The viscous drag exerted on the endolymph at its interface with the wall of the membranous canal
- #22 Vestibular nerve contains bipolar ganglion cells of first order neurons No primary vestibular afferents cross the midline Afferent fibers terminate in the vestibular nuclei in floor of fourth ventricle Superior vestibular, Lateral vestibular, medial vestibular, Descending vestibular nuclei Vestibular nuclei project to Cerebellum Extraocular nuclei Spinal cord Contralateral vestibular nuclei
- #23 A change in direction of the force of gravity (above) or a linear acceleration (below) causes the otolithic membrane to shift its position with respect to its macula, thereby generating a new pattern of action potentials in the utricular or saccular nerve. Shifting of the otolithic membranes can elicit compensatory vestibulo-ocular reflexes and nystagmus, as well as perceptual effects.
- #24 Angular acceleration to the right increases the frequency of action potentials originating in the right ampullary nerve and decreases those in the left. This pattern of neural signals causes extraocular muscles to rotate the eyes in the direction opposite that of head rotation. Thus stabilizing the retinal image with a compensatory eye movement. Angular acceleration to the left has the opposite effect.
- #25 Kinocilia are located closest to utricle in lateral canals and are on canal side in other canals Ampullopetal flow (toward the ampulla) excitatory in lateral canals, inhibitory in superior/posterior canals Ampullofugal flow (away from the ampulla) has opposite effect
- #26 Semicircular canals are paired Horizontal canals Right superior/ left posterior Left superior/ right posterior Allow redundant reception of movement Explains compensation after unilateral vestibular loss
- #27 Cupula is gelatinous mass extending across at right angle Extends completely across, not responsive to gravity Crista ampullaris is made up of sensory hair cells and supporting cells
- #28 In contrast to the otoliths, the semicircular canals detect the rate of head rotation (angular acceleration), and are therefore dynamic in function when the head is initially moved, the ampulla (and therefore the hair cells) turns with it the endolymph remains in its initial position due to inertia, causing movement of the stereocilia against the cupula and altering the receptor potential (could be depolarizing or hyperpolarizing, depending upon direction) once the head is moving at a constant velocity, the duct fluid moves at the same rate as the hair cells, and the stereocilia are not deflected when the head stops moving, the fluid keeps moving (inertia again), and the receptor potential is again altered, this time in the opposite direction to what occurred at the start of the rotation
- #29 Saccule The saccule is an almost globular-shaped sac that lies in the spherical recess on the medial wall of the vestibule. It is connected anteriorly to the cochlear duct by the ductus reuniens and posteriorly to the endolymphatic duct via the utriculosaccular duct. The saccular macula is an elliptical thickened area of sensory epithelium that lies on the anterior vertical wall of the saccule. Utricle The utricle is larger than the saccule and lies posterosuperiorly to it in the elliptical recess of the medial wall of the vestibule. It is connected anteriorly via the utriculosaccular duct to the endolymphatic duct. The 3 semicircular canals open into it by means of 5 openings; the posterior and the superior semicircular canals share one opening at the crus commune. The macula of the utricle lies mainly in the horizontal plane and is located in the utricular recess, which is the dilated anterior portion of the utricle.
- #30 Stereocilia are not true cilia, they are graded in height with tallest nearest the kinocilium.
- #31 The sense organs within the saccule and utricle are called maculae both the saccular macula and utricular macula are covered by a gelatinous mass called the otolithic membrane The otolithic membrane contains calcium Carbonate called otoconia or otoliths This loading of the cilia by inertial mass makes the organs sensitive to linear acceleration and changes of position of the head in the gravitational field Calcium carbonate or calcite Central region of otolithic membrane is called the striola
- #32 Vestibulo--ocular reflex ––Membranous labyrinth moves with head motion–– Endolymph does not causing relative motion –– Cupula on right canal on deflected towards utricle causing increase in firing rate, left deflects away causing a decrease in firing rate.–– Reflex causes movement of eyes to the left with saccades to right ––Stabilizes visual image
- #33 Effectively 3 synapses in horizontal VOR: SCC -> vestibular nucleus -> motoneurons -> muscle. When turning head right, the right horizontal SCC hair cells depolarize the right VN firing rate increases the motoneurons (right 3rd and left 6th nuclei) fire at higher frequency, the left lateral rectus & right medial rectus contract the eyes turn left. Note that SSC operate in conjugate pairs: Push-Pull. So replace all text above with right <-> left and increase -> decrease, contract -> relax
- #35 With large head rotations (360-deg body turn) compensatory eye movements take another form. Initially, VOR directs the eyes slowly in direction opposite to head motion (slow phase). When the eye reaches the limit of the orbit, it springs back rapidly to a central position, moving in the same direction as that of the head (fast phase). Another slow phase then begins. This combination of slow compensatory phases punctuated by fast return phases is called nystagmus
- #36 Discharge rate of the vestibular nerve fibers at rest and as a function of displacement of stereocilia (sensory hairs) relative to kinocilium.
- #37 Sensory cells are either Type I or Type II Type I cells are flask shaped and have chalice shaped calyx ending One chalice may synapse with 2-4 Type I cells Type II cells – cylinder shaped, multiple efferent and afferent boutons
- #39 Several systems are involved: