Posture And Equilibrium Flashcards
A disturbing force to equilibrium is…..
Acceleration (or deceleration)
What are types of acceleartion?
Linear
Angular (rotatory)
Describe mechanism of stimulation of maculae
- Hair cells with its cilia act as stretch receptors. When these cilia bend due to displacement of otolith by effect of gravity, hair cells are stimulated
- Stimulation of hair cells generates action potential transmitted along the vestibular n
- Cilia are arranged in different positions. Each position of head stimulatea certain group of cilia helping the brain to detect orientation of head in space.
Describe mechanism of determination of orientation of head in space
- Head in central position: there is minimal equal discharge from both maculae so head is percieved in central position
- Head tilt to the right: the right maculae ia stretched more than the left one leading to unequal discharge from both and head is felt tilted to right.
- Head tilt to left: opposite
Compare role of utricle and saccule in head orientation
- Utricle is oriented in horizontal plane thus responds to changes of head position away from vertical plane, when person is upright.
- Saccule is oriented in vertical plane thus responds to changes of head position away from horizontal plane, when person is lying down.
Compare role of utricle and saccule in linear acceleration.
Utricle respond to horizontal acceleration
Saccule respond to vertical acceleration
Mention postural reflexes done by macula
Righting reflex
Labyrinthine statotonic reflex
Bending of stereocilia towards kinocilium…..hair cells while bending away from kinocilium…..hair cells.
Depolarizes
Hyperpolarizes
In horizontal SCCs, bending towards…..causes stimulation of hair cells. In vertical SCCs, bending towards…….causes stimulation.
Utricle
Canal side
With respect rotatory movements, horizontal SCC gives response to rotation in….., while superior in…., while posterior in…..
Horizontal plane
Anteroposterior plane
Vertical plane
Describe mode of action of SCC during rotation from left to right
- At start of motion endolymph moves in opposite direction of motion due to inertia so right discharge is more than left and rotation is percieved in correct direction.
- When rotating at constant speed endolymph has same speed as receptors so cupulae return to resting position amd no rotation is detected.
- When ending rotation the fluid moves in direction of rotation so left is stimulated more than right leading to false sense of opposite direction rotation.
- After stopping the endolymph stops moving and cupulae restore their position,vertigo disappears.
Enumerate methods of stimulation of SCCs
Mechanical, caloric, electrical
List connections of labyrinth via vestibualr nuclei
- MLB
- Reticular formation
- Spinal cord
- Cerebellum
- Cerebral cortex
Explain the slow component of nustagmus
Via connection of vesticular nuclei with MLB which is connected to CN III,IV,VI to stabilize images on the retina during head movements thus produce correction movements of the eyes every time the head rotates. It causes stimulation of ipsilateral occulomotor nucleus & contralateral abducent nucleus causing slow equal movement of both eyes opposite direction of rotation.
Imp: image tracking, it is a vestibular reflex
Mention importance of connection of vestibular nuclei with each of the following:
1. Reticular formation
2. Spinal cord
- Via vestibuloreticular tract stimulating autonomic effects and adjusts circulation and breathing due to body position. Also, impulses descend down to spinal cord through reticulosponal tract causing changes in muscle tone.
- Via vestibulospinal tract producing changes in muscle tone. It is involved in reflex head and body movements during postural changes.
List effects of stimulation of SCC
- Vertigo
- Nystagmus
- Autonomic effects
- Alteration in muscle tone
- Post-rotatory reactions
Describe alteration in muscle tone in response to SCC stimulation
Inc tone of extensors of the same side of rotation and dec that of opposite side. This is reflex mechanism to support the body on the side of stimulation which maintains balance during rotation.
Define past pointing of Baraney
After stoppage of rotation if you ask the patient to touch a certain point with closed eyes, he points to same direction of rotation. Thus past pointing exact tested point to compensate for false sense of counter rotation.
Post rotatory nystagmus lasts….
20 sec
Mention pathological causes of nystagmus
-inner ear disease (Meniere’s disease)
-motion sickness
-defective vision (error of refraction)
-overdose of steptomycin
-chronic alcoholism
Mention nervous pathways of vertigo
- Vestibulo-cerebello-thalamo-cortical
- Vestibulo-reticulo-thalamo-cortical
Proove: Rotatory nystagmus is a vestibulo-ocular reflex
It occurs in blind subjects
Enumerate physiological and pathological causes of nystagmus
Physio: rotatory, optokinetic
Patho: congenital or aquired (due to neocerebellar syndrome, vestibulocerebellum damage, Meniere’s disease, defective vision, lesion in labyrinth or vestibular pathway.
Mention the 2 main types of postural reflexes
Static and statokinsetic reflexes
Enumerate the spinal reflexes
- Stretch reflex
- Crossed extensor reflex
- Stepping reflex
- Positive supporting reaction
Enumerate the medullary reflexes
Neck statotonic reflex
Labyrinthine statonic reflex
Enumerate the midbrain reflexes
They correct body position thus called righting reflexes:
Labyrinthine, body on head, neck on body, body on body righting reflexes
Enumerate the cortical postural reflexes
- Visual righting reflex
- Hopping reaction
- Placing reaction
