Posture and Balance Flashcards
What is posture?
The relative position of body parts with respect to each other, the environment, and gravity.
What is postural equilibrium?
A state where all forces acting on the body are balanced.
What are the two types of postural equilibrium?
Static (still) and dynamic (during movement).
What type of muscle tone is essential for posture?
Extensor tone – extensor muscles remain active to maintain upright posture.
What pathways are involved in postural control?
Ventromedial pathways:
Vestibulospinal
Tectospinal
Pontine reticulospinal
Medullary reticulospinal
What do ventromedial tracts control?
Posture by affecting axial and proximal musculature.
What is the function of the vestibulospinal tract?
Maintains upright posture and balance via leg extensors; originates from vestibular nuclei.
What is the function of the tectospinal tract?
Directs head/eyes toward visual or auditory stimuli (orienting reflex); originates from superior colliculus.
What is the function of the pontine reticulospinal tract?
Enhances antigravity reflexes and facilitates extensors for standing.
What does the medullary reticulospinal tract do?
Inhibits extensor muscles, counteracts pontine effects, and allows voluntary movement.
What is decerebrate rigidity?
Excessive extensor tone due to loss of cerebral inhibition over brainstem nuclei.
What causes decerebrate rigidity in humans?
Severe cortical damage leading to unopposed brainstem control.
What are the main vestibular structures?
Otolith organs (utricle & saccule) and semicircular canals.
What do otolith organs detect?
Head tilt and linear acceleration (utricle = horizontal, saccule = vertical).
What do semicircular canals detect?
Angular (rotational) acceleration.
What are otoconia?
Calcium carbonate crystals on the otolith organs that respond to gravity.
What is the ampulla?
The sensory region in semicircular canals containing hair cells embedded in cupula.
What is the function of the Vestibulo-Ocular Reflex (VOR)?
Keeps vision stable during head movement by moving eyes in opposite direction of head rotation.
What cranial nerves are involved in Vestibulo-Ocular Reflex (VOR)?
CN III (oculomotor), CN VI (abducens), CN VIII (vestibulocochlear).
What is caloric testing?
A method to stimulate the VOR by irrigating the ear with warm or cold water.
What is a protective postural reflex?
Reflex extending arms/legs to protect the body during falls.
What initiates the limb placing reflex?
Contact of foot/limb with ground triggers muscle stiffening via brainstem and spinal circuits.
What is the hopping reaction?
Movement to a new position to restore balance when posture is destabilised.
What is anticipatory postural control?
The body prepares for movement by adjusting posture before voluntary motion.
What is the difference between feedback and feedforward in posture?
Feedback: Reaction to postural disturbance.
Feedforward: Anticipatory adjustment in preparation for movement.
What does posture platform testing study?
Muscle responses and balance control when the platform or visual input is altered.
What is vestibular plasticity?
The ability of the vestibular system to adapt to new environments (e.g. sea or space).
What causes Ménière’s Syndrome?
Endolymphatic hydrops – excess endolymph in the inner ear.
What are Ménière’s symptoms?
Vertigo, tinnitus, temporary hearing loss.
What causes BPPV?
Dislodged otolith crystals disrupt semicircular canal function.
What are symptoms of BPPV?
Sudden dizziness when changing head position.
What is vestibular neuronitis vs. labyrinthitis?
Neuronitis: Vestibular branch inflammation
Labyrinthitis: Affects both vestibular and cochlear branches (hearing + balance affected)
What is the difference between static and dynamic postural equilibrium?
Static: maintaining balance while still.
Dynamic: maintaining balance during movement.
What type of muscles primarily maintain posture?
Extensor muscles (through continuous low-level contraction).
What is the function of postural systems?
To stabilise and maintain the position of the body automatically.
Which brainstem nuclei are responsible for posture?
Vestibular, reticular, and tectal nuclei.
Which tract originates in the superior colliculus and directs head/eye orientation?
Tectospinal tract.
What is the role of the lateral vestibular nucleus?
Facilitates extensor tone in trunk and limbs to maintain upright posture.
What is a decerebrate preparation?
Brain transection at the midbrain, removing cerebral input, leaving brainstem and spinal cord functional.
What is the effect of decerebrate preparation on muscle tone?
Increased extensor tone (decerebrate rigidity) due to loss of cortical inhibition.
What part of the vestibular system detects linear acceleration and head tilt?
Otolith organs – utricle and saccule.
What detects angular (rotational) acceleration?
Semicircular canals (anterior, posterior, and lateral).
What are otoconia?
Calcium carbonate crystals that move in response to gravity/acceleration and stimulate hair cells.
What happens when vestibular hair cells bend toward the kinocilium?
They depolarize and increase firing of the vestibular nerve.
What happens when they bend away from the kinocilium?
They hyperpolarize and reduce firing.
What is the purpose of the VOR?
Stabilize gaze during head movement to maintain clear vision.
What triggers the VOR?
Rotational acceleration sensed by semicircular canals.
In the VOR, what muscles move the eyes?
Right lateral rectus and left medial rectus when head turns left (eyes move right).
