GIDADO JENNIFER BUSAYO 18/MHS01/166 NURSING PHYSIOLOGY

Discuss the physiology of balance

The is the sensory apparatus of the inner ear that helps the body maintain its postural equilibrium. The information furnished by the vestibular system is also essential for coordinating the position of the head and the movement of the eyes. There are two sets of end organs in the inner ear, or labyrinth: the semicircular canals, which respond to rotational movements (angular acceleration); and the utricle and saccule within the vestibule, which respond to changes in the position of the head with respect to gravity (linear acceleration). The information these organs deliver is proprioceptive in character, dealing with events within the body itself, rather than exteroceptive, dealing with events outside the body, as in the case of the responses of the cochlea to sound. Functionally these organs are closely related to the cerebellum and to the reflex centres of the and brainstem that govern the movements of the eyes, neck, and limbs.

Although the vestibular organs and the cochlea are derived embryologically from the same formation, the otic vesicle, their association in the inner ear seems to be a matter more of convenience than of necessity. From both the developmental and the structural point of view, the kinship of the vestibular organs with the lateral line system of the fish is readily apparent. The lateral line system is made up of a series of small organs located in the skin of the head and along the sides of the body of fishes. Each organ contains a crista, sensory hair cells, and a cupula, as found in the ampullae of the semicircular ducts. The cristae respond to waterborne vibrations and to pressure changes.

The anatomists of the 17th and 18th centuries assumed that the entire inner ear, including the vestibular apparatus, is devoted to . They were impressed by the orientation of the semicircular canals, which lie in three planes more or less perpendicular to one another, and believed that the canals must be designed for localizing a source of sound in space. The first investigator to present evidence that the vestibular labyrinth is the organ of equilibrium was French experimental neurologist Marie-Jean-Pierre Flourens, who in 1824 reported a series of experiments in which he had observed abnormal head movements in pigeons after he had cut each of the semicircular canals in turn. The plane of the movements was always the same as that of the injured canal. Hearing was not affected when he cut the nerve fibres to these organs, but it was abolished when he cut those to the basilar papilla (the bird’s uncoiled cochlea). It was not until almost half a century later that the significance of his findings was appreciated and the semicircular canals were recognized as sense organs specifically concerned with the movements and position of the head. stimulated when the head moves and the relationship to gravity changes.

There is a small dense area of nerve fibers called the macule located in each of the saccule and utricle. The macule of the saccule is oriented vertically while the utricle macule is horizontal. Each macule consists of fine hair bundles which are covered by an otolithic membrane that is jelly-like and covered by a blanket of calcium crystals.

The calcium crystals are the structures that ultimately stimulate the position hairs and provoke nerve impulses created by the position changes and transmit that information to the stem and cerebellum.

Balance Balance is a choreographed arrangement that takes sensory information from a variety of organs and integrates it to tell the body where it is in related to gravity and the earth.Information from the vestibular system of the inner ear (semicircular canals, the saccule and the utricle) is sent to the brainstem, cerebellum, and spinal cord. Potential balance abnormalities do not require conscious input from the cerebrum of the brain. Abnormal vestibular signals cause the body to try to compensate by making adjustments in posture of the trunk and limbs as well as making changes in eye movement to adjust sight input into the brain. There are three semicircular canals in the inner ear positioned at right angles to each other like a gyroscope. They are able to sense changes in movement of the body. With such changes, endolymph waves within the canals cause hair cells located within their base to move. Position of the head is sensed by hair cells of the utricle and saccule which isstimulated when the head moves and the relationship to gravity changes.There is a small dense area of nerve fibers called the macule located in each of the saccule and utricle. The macule of the saccule is oriented vertically while the utricle macule is horizontal. Each macule consists of fine hair bundles which are covered by an otolithic membrane that is jelly-like and covered by a blanket of calcium crystals.The calcium crystals are the structures that ultimately stimulate the position hairs and provoke nerve impulses created by the position changes and transmit that information to the brain stem and cerebellum.

Disturbances of the vestibular system The relation between the vestibular apparatus of the two ears is reciprocal. When the head is turned to the left, the discharge from the left horizontal canal is decreased, and vice versa. Normal posture is the result of their acting in cooperation and in opposition. When the vestibular system of one ear is damaged, the unrestrained activity of the other causes a continuous false sense of turning (vertigo) and rhythmical, jerky movements of the eyes (nystagmus), both toward the uninjured side. When the vestibular hair cells of both inner ears are injured or destroyed, as can occur during treatment with the antibiotics gentamicin or streptomycin, there may be a serious disturbance of posture and gait (ataxia) as well as severe vertigo and disorientation. In younger persons the disturbance tends to subside as reliance is placed on vision and on proprioceptive impulses from the muscles and joints as well as on cutaneous impulses from the soles of the feet to compensate for the loss of information from the semicircular canals. Recovery of some injured hair cells may occur. Routine tests of vestibular function traditionally have involved stimulation of the semicircular canals to elicit nystagmus and other vestibular ocular reflexes. Rotation, which can cause vertigo and nystagmus, as well as temporary disorientation and a tendency to fall, stimulates the vestibular apparatus of both ears simultaneously. Because otoneurologists are usually more interested in examining the right and left ears separately, they usually employ temperature change as a stimulant. Syringing the ear canal with warm water at 44 °C (111 °F) or with cool water at 30 °C (86 °F) elicits nystagmus by setting up convection currents in the horizontal canal. The duration of the nystagmus may be timed with a stopwatch, or the rate and amplitude of the movements of the eyes can be accurately recorded by picking up the resulting rhythmical variations in the corneoretinal direct current potentials, using electrodes pasted to the skin of the temples—a diagnostic process called electronystagmography. An abnormal vestibular apparatus usually yields a reduced response or no response at all.

The vestibular system may react to unaccustomed stimulation from the motion of an aircraft, a ship, or a land vehicle to produce a sense of unsteadiness, abdominal discomfort, nausea, and vomiting. Effects not unlike motion sickness, with vertigo and nystagmus, can be observed in the later stages of acute alcoholic intoxication. Vertigo accompanied by hearing loss is a prominent feature of the periodic attacks experienced by patients with Ménière , which, until the late 19th century, was confused with epilepsy. It was referred to as apoplectiform cerebral congestion and was treated by purging and bleeding. Other forms of vertigo may present the otoneurologist with more difficult diagnostic problems.

Since the advent of space exploration, interest in experimental and clinical studies of the vestibular system has greatly increased. Investigators are concerned particularly about its performance when persons are exposed to the microgravity of spaceflight, as compared with the Earth’s gravitational field for which it evolved. Investigations include the growing use of centrifuges large enough to rotate human subjects, as well as ingeniously automated tests of postural equilibrium for evaluating the vestibulospinal reflexes. Some astronauts have experienced relatively minor vestibular symptoms on returning from spaceflight. Some of these disturbances have lasted for several days, but none have become permanent.

Mechanical There are five sensory organs innervated by the vestibular nerve; three semicircular canals (Horizontal SCC, Superior SCC, Posterior SCC) and two otolith organs (Saccule and Utricle). Each semicircular canal (SSC) is a thin tube that doubles in thickness briefly at a point called osseous ampullae. At their center-base each contains an ampullary cupula. The cupula is a gelatin bulb connected to the stereocilia of hair cells, affected by the relative movement of the endolymph it is bathed in. Since the cupula is part of the bony labyrinth, it rotates along with actual head movement, and by itself without the endolymph, it cannot be stimulated and therefore, could not detect movement. Endolymph follows the rotation of the canal, however, due to inertia its movement initially lags behind that of the bony labyrinth. The delayed movement of the endolymph bends and activates the cupula. When the cupula bends, the connected stereocillia bend along with it, activating chemical reactions in the hair cells surrounding crista ampullaris and eventually create action potentials carried by the vestibular nerve signalling to the body that it has moved in space. After any extended rotation the endolymph catches up to the canal and the cupula returns to its upright position and resets. When extended rotation ceases, however, endolymph continues, (due to inertia) which bends and activates the cupula once again to signal a change in movement.[3] Pilots doing long banked turns begin to feel upright (no longer turning) as endolymph matches canal rotation; once the pilot exits the turn the cupula is once again stimulated, causing the feeling of turning the other way, rather than flying straight and level. The HSCC handles head rotations about a vertical axis (the neck), SSCC handles head movement about a lateral axis, PSCC handles head rotation about a rostral-caudal axis. E.g. HSCC: looking side to side; SSCC: head to shoulder; PSCC: nodding. SCC sends adaptive signals, unlike the two otolith organs, the saccule and utricle, whose signals do not adapt over time.[citation needed] A shift in the otolithic membrane that stimulates the cilia is considered the state of the body until the cilia are once again stimulated. E.g. lying down stimulates cilia and standing up stimulates cilia, however, for the time spent lying the signal that you are lying remains active, even though the membrane resets. Otolithic organs have a thick, heavy gelatin membrane that, due to inertia (like endolymph), lags behind and continues ahead past the macula it overlays, bending and activating the contained cilia.Kinocilium are the longest stereocilia and are positioned (one per 40-70 regular cilia) at the end of the bundle. If stereocilia go towards kinocilium depolarization occurs causing more neurotransmitter, and more vestibular nerve firings as compared to when stereocilia tilt away from kinocilium (hyperpolarization, less neurotransmitter, less firing).[8][9]

Neural First order vestibular nuclei (VN) project to IVN, MVN, and SVN.The inferior cerebellar peduncle is the largest center through which balance information passes. It is the area of integration between proprioceptive, and vestibular inputs to aid in unconscious maintenance of balance and posture.Inferior olive nucleus (also known as the olivary nucleus) aids in complex motor tasks by encoding coordinating timing sensory info; this is decoded and acted upon in the cerebellum. Cerebellar vermis has three main parts: vestibulocerebellum (eye movements regulated by the integration of visual info provided by the superior colliculus and balance info), spinocerebellum [integrates visual, auditory, proprioceptive, and balance info to act out body and limb movements. Trigeminal and dorsal column (of spinal cord) proprioceptive input, midbrain, , reticular formation and vestibular nuclei (medulla) outputs], and cerebrocerebellum (plans, times, and initiates movement after evaluating sensory input from, primarily, motor cortex areas, via pons and cerebellar dentate nucleus. It outputs to thalamus, motor cortex areas, and red nucleus) Flocculonodular lobe is a cerebellar lobe that helps maintain body equilibrium by modifying muscle tone (continuous and passive muscle contractions). MVN and IVN are in the medulla, LVN and SVN are smaller and in pons. SVN, MVN, and IVN ascend within medial longitudinal fasciculus (MLF). LVN descend the spinal cord within the lateral vestibulospinal tract and end at sacrum. MVN also descend the spinal cord, within the medial vestibulospinal tract, ending at lumbar. Thalamic reticular nucleus distributes information to various other thalamic nuclei, regulating the flow of information. It is speculatively able to stop signals, ending transmission of unimportant info. The thalamus relays info between pons (cerebellum link), motor cortices, and insula.Insula is also heavily connected to motor cortices; insula is likely where balance is likely brought into .

The oculomotor nuclear complex refers to fibers going to tegmentum (eye movement), red nucleus (gait (natural limb movement)), substantia nigra (reward), and cerebral peduncle (motor relay). Nucleus of Cajal are one of the named oculomotor nuclei, they are involved in eye movements and reflex gaze coordination. Abducens solely innervates the lateral rectus muscle of the eye, moving the eye with trochlear. Trochlear solely innervates the superior oblique muscle of the eye. Together, trochlear and abducens contract and relax to simultaneously direct the pupil towards an angle and depress the globe on the opposite side of the eye (e.g. looking down directs the pupil down and depresses (towards the brain) the top of the globe). The pupil is not only directed but often rotated by these muscles. (See )

The thalamus and superior colliculus are connected via lateral geniculate nucleus. Superior colliculus (SC) is the topographical map for balance and quick orienting movements with primarily visual inputs. SC integrates multiple . Other animals Some animals have better equilibrioception than humans, for example a cat uses its inner ear and tail to walk on a thin fence.

Equilibrioception in many marine animals is done with an entirely different organ, the statocyst, which detects the position of tiny calcareous stones to determine which way is "up".

In plants Plants could be said to exhibit a form of equilibrioception, in that when rotated from their normal attitude the stems grow in the direction that is upward (away from gravity) while their roots grow downward (in the direction of gravity) this phenomenon is known as gravitropism and it has been shown that for instance poplar stems can detect reorientation and inclination.

Sensation and perception

Stimulus Sensory receptor

Sensation Transduction (physiology) Processes and Active sensory system

Multimodal integration

Perception Cognition Feeling Qualia

Eyes Ears Inner ear

Sensory organs Nose Mouth Skin

Visual system (sense of vision) (sense of hearing)

Sensory systems () Gustatory system (sense of ) (sense of touch)

Optic (II) Vestibulocochlear (VIII) Olfactory (I)

External Sensory cranial and spinal Facial (VII) nerves Glossopharyngeal (IX) Trigeminal (V) Spinal

Visual cortex Auditory cortex Vestibular cortex

Cerebral cortices Olfactory cortex Gustatory cortex Somatosensory cortex

Visual perception (vision) Auditory perception (hearing) Equilibrioception (balance) Olfaction (smell) Gustation (taste or flavor) Touch mechanoreception nociception () )

Vestibular system () Hunger

Internal Thirst Suffocation Nausea

Electroception Magnetoreception Echolocation Infrared sensing in vampire bats

Animal Infrared sensing in snakes Surface wave detection Frog hearing Toad vision

Photomorphogenesis

Plant Gravitropism

Robotic sensing

Artificial Computer vision Machine hearing

Baroreceptor Mechanotransduction Lamellar corpuscle sensory

Mechanoreceptor Tactile corpuscle Merkel nerve ending Bulbous corpuscle Campaniform sensilla Slit sensilla Stretch receptor

Photoreceptor cell Cone cell Rod cell Photoreceptor ipRGC Photopigment Aureochrome

Taste receptor

Chemoreceptor Olfactory receptor Osmoreceptor

Cilium

Thermoreceptor TRP channels

Nociceptin receptor

Nociceptor Juxtacapillary receptor

Visual impairment Alice in Wonderland syndrome Amaurosis Anopsia Color blindness Diplopia Hemeralopia and Nyctalopia Optic neuropathy

Visual Oscillopsia Palinopsia Papilledema Photophobia Photopsia Polyopia Scotoma Stereoblindness Amblyaudia Auditory agnosia Auditory Auditory verbal agnosia

Auditory Hearing loss Microwave auditory effect Music-specific disorders Palinopsia Spatial hearing loss Tinnitus

Vertigo BPPV

Vestibular Labyrinthine fistula Labyrinthitis Ménière's disease

Anosmia Dysosmia Hyperosmia

Olfactory Hyposmia Olfactory reference syndrome Parosmia

Ageusia Hypergeusia

Gustatory Hypogeusia Parageusia

Astereognosis CMT disease

Tactile Hyperesthesia Hypoesthesia Paresthesia Tactile hallucination

Hyperalgesia Nociception Hypoalgesia (pain) Pain dissociation Phantom pain

Asomatognosia syndrome Proprioception Somatoparaphrenia Supernumerary phantom limb

Multimodal