Physiology of balance

Kunal shah

What is balance ?

• Balance is a complex process involving the reception and integration of sensory inputs and the planning and execution of movements to achieve a goal requiring an upright posture.

Visual input

Proprioceptiual

input

Vestibular input

labyrinths.

equilibrium

Peripheral sensory inputs

• Somatosensory receptors – present in joints , ligaments , muscle and skin

• provide information about muscle length , stretch , tension and contraction; pain , temperature, pressure and joint position.

• it is the dominant sense for upright postural control and triggering autonomic postural reactions.

• Visual receptors in eyes- • Peripheral (ambient) vision detects motion of

the self in relation to the environment, including head movement and postural sways.

• Central (focal) vision allows environmental orientation, contributing to the perception of verticality and object motion, as well as hazards and opportunities presented by environments.

• Vestibular system – provides central nervous system with information about the position and motion of the head.

• Position of the head in relation to gravity • Horizontal and vertical acceleration such as

riding in a car and an elevator• Angular acceleration

• Orientation to wider environment primarily from vision, allows feedforward or anticipatory adjustments .

• detection of head movement by the vestibular and cervical somatosensory system and of body sways by somatosensory and visual system provides feeedback for responsive action.

CNS

• Multisensory integration or sensory organization. – Brain processes all the environmentally available sensory information gathered by peripheral receptors.

• Central sensory structures function first to compare available inputs between two sides and among three sensory systems.

• Somatosensory system alone is not able to distinguish surface tilts from body tilts.

• Visual system by itself cannot discriminate movement of the environment from movement of the body.

• Vestibular system by itself cannot tell if head movement through space is produced by neck motion or trunk/hip motion.

• Brain needs information from all three senses to distinguish correctly self motion from motion in environment.

• Push pull function considered to “match”.• Change in environment results in change in

relative availability, accuracy, and usefulness of information.

• Adaptive process or multisensory reweighting.

• Sensory conflict can arise when information between sides or between system is not synchronous.

• Brain recognize any discrepancies and select the correct inputs on which to base motor response.

• Vestibular system is used as an internal reference to determine accuracy of the other two senses when there is conflict.

Semicircular canals

• Semicircular Canals (SCC)– Horizontal– Anterior– Posterior

• Cupula– End organ receptors

• Endolymph

Utricle

• Utricle– Connected to SCC– Contains endolymph– Otoliths (otoconia)

• Calcium carbonate• Attached to hair cells• Macule (end organ)

Vestibular system

• Tells brain which way the head moves without looking– SCC: angular acceleration– Utricle: linear acceleration

Vestibular pathway and connections

• 1st order • 2nd order • Connection with vestibular nuclei - occulomotar nuclei - ant horn cells in spinal cord - cerebellar cortex - temporal lobe cortex - autonomic nervous system

• sup and med vestibular nuclei • lat vestibular nuclei • inf vestibular nuclei

• Vestibulopostural reflex • Vestibulooccular reflex

Other factors

• Neck proprioceptors • Proprioceptive information from other pars of

body • Visual information