Vestibular System and Balance

The vestibular system, located in the oval central position of the bony labyrinth, is a specialized proprioceptive system.
Functions:
- Maintains equilibrium.
- Directs eye gaze to preserve a constant plane of vision.
- Modifies muscle tone.
Information sources:
- Eyes
- General proprioceptors throughout the body
- Vestibular receptors of the inner ear
Hearing and equilibrium are interconnected as the inner ear serves both functions.

Static Equilibrium:
- Maintains body position, such as holding the head upright against gravity.
Dynamic Equilibrium:
- Maintains body position in response to sudden movements.
- Examples: rotation, acceleration, deceleration.

Located on the walls of the utricle and saccule.
Consist of two cell types:
- Hair cells: Possess long extensions in the central membrane with fine, hair-like projections.
  - 40-70 stereocilia and one kinocilium, which is the most important receptor, anchored at the basal end.
- Supporting cells: Secrete the otolithic membrane, a thick, gelatinous protein layer resting on the hair cells.
Head movements cause the otolithic membrane to slide over hair cells, pulling stereocilia and initiating a nerve impulse in the vestibular branch.

Concerns maintenance of body and head position relative to gravity and uniform linear motion.
When the head tilts, the otolithic membrane slides, bending the stereocilia and triggering a nerve impulse.

Maintains body position in response to movement.
Semicircular canals are responsible for detecting head rotation, whether self-induced or from external forces.
Canals are positioned at right angles to each other in three planes (two vertical, one horizontal) to detect rotation, acceleration, and deceleration.
Filled with fluid (endolymph).

Each canal has a bulbous expansion at its base called the ampulla.
The ampulla houses the crista, the receptor surface of the canal.
The crista contains receptor cells with fine hairs extending into the cupula, a gelatinous mass.
The cupula forms a barrier through which the endolymph cannot pass.

Head turns cause endolymph movement, which is blocked by the cupula, causing it to distort.
This distortion displaces hair fibers within the crista, creating a nerve impulse.
The impulse travels along the vestibular branch of the eighth cranial nerve.

Activated hair cells of the crista ampullaris (afferent axon fibers) move to the vestibulocochlear nerve.
The vestibulocochlear nerve projects to:
- Vestibular nuclei (in the medulla): Receives input from eyes and somatic proprioceptors for coordination and control of eye, neck, and limb movement.
- Cerebellum: Also receives input from eyes and somatic proprioceptors to regulate head position, posture, and balance.

Two-directional pathways connect the vestibular nuclei and cerebellum.
Fibers from the vestibular nuclei form the medial longitudinal tracts, extending to cranial nerves for control of eye movement (oculomotor, trochlear, abducens) and head/neck movement (accessory).
Pathways travel from the medulla to the cortex (near primary somatosensory and motor areas) via the thalamus.
These pathways integrate body movements with eye and visual input.

Vestibular receptors, visual receptors, and somatic receptors work together to maintain balance and orientation.
These receptors enable reflexive body responses.

Vestibular dysfunction is largely linked to an inability to maintain balance.
Balance maintenance involves coordination of musculoskeletal, sensory-motor, and neural systems.
Impairments in sensation or muscle strength negatively affect balance, leading to reliance on vision for compensation.
Neurologically, balance is controlled by sensory and motor systems processing input from vestibular, visual, tactile, and proprioceptive systems.
The vestibulocochlear nerve plays a key role in balance and spatial orientation.
Proprioception helps detect body position and movement, crucial for stability; its decline with aging increases fall risk and gait disturbances.
Balance difficulties have multiple causes and require a thorough understanding of the client's medical history.
Fear of falling can impact stability.
A comprehensive multifactorial assessment is recommended to identify specific needs.

There is a lack of commonly accepted methods for occupational therapists to assess and document sitting balance.
Objective skills documentation is important for referrals and third-party reimbursements.
Baseline balance performance should be recorded at initial evaluation to measure progress and plan for discharge.
Interventions are motor-based and encourage neuroplasticity when balance issues are not limited to vestibular dysfunction.

Scientists developed a neurostimulation device for vision and vestibular function.
Mitch, a team member, used an adapted vision device (with an accelerometer in a hat) to address his own balance issues resulting from an infection.
The hat fed positional information to a computer, then to a tongue device stimulating different areas based on head position.
Cheryl Schlitz, with severe vestibular damage, trialed the device.
The device provided orientation information that went directly to the brainstem, processing touch and balance.
With training and practice, neuroplasticity occurred, leading to new brain circuits and complete recovery after two and a half years.

Compensatory strategies:
- Safe weight shifting techniques.
- Using contralateral upper extremity for support.
- Dressing while lying on the bed.
- Completing body dress steps in sitting before standing.
- Minimising bending during dressing.
- Performing toileting hygiene in sitting.
Environmental modifications:
- Installing grab rails.
- Using electronic lift chairs.
- Adding toilet safety frames.
- Using a shower chair.
Optimising the home environment:
- Arranging spaces within reach.
- Setting up areas for seated task completion.
- Placing grooming and hygiene tools within reach from a chair.
Collaboration ensures adaptations are tailored to individual needs and environments.
Functional mobility training: Improves movement in bed, transitions between sitting and standing, and performing daily activities while standing or walking.
Balance is crucial for safe functional mobility and independent mobility.
Interventions align with balance training, incorporating strength building and postural adjustments.