Balance

Balance: 

Important for: standing walking, performing complex movement, allows us to maintain our body main support, 

Systems contributing to balance: all help us stay upright

• Vestibular system

  • Function: head position signals 

  • Head movement and equilibrium

  • Located: inner ear (the CORE component!)

    • Detects changes in head position and movement 

  • Anatomical structures:

    • Semicircular canals: rotational movement

    • Otolith organs

      • The utricle: horizontal plane (linear motion in horizontal plane, like a care moving forward and backward)

      • The saccule: vertical plane (motion in vertical plane, elevator moving up and down)

        • fluid moves in these structure simulating hair cells, which then send signals to the brian letting the brain know where the head is positioned (why inner ear problems cause dizziness or balance issues)

• Proprioceptive system:

  • Function: Internal GPS, Uses receptors in muscles, tendons and joints to tell us where our body parts are positioned even when we are not looking at them

  • Feedback on body position, movement, and equilibrium through specialized sensory receptors

    • Muscle spindles: detect changes in muscle length and contribute to postural control

      • Receptors located in skeletal muscles

      • Detect changes in muscle length 

      • Contribute to postural control provide information on lead positioning 

    • Golgi tendon organs: sense tension and force

      • Receptors located in tendons 

      • Sense tension and force within muscles, helps regulate muscles contractions and  provides stability

    • Joint receptors: signal joint position and movement 

      • Located in ligaments and joint capsules

      • Signal joint position and movement (esp in weight bearing joints like knees and ankles)

      • Relayed through spinal nerves to spinal cord and then to brian, integrated with data from the vestibular and visual system.

• Visual system

  • Function: Gives us spacial awareness, Input on body position

  • Retina: detects light and relays information about visual environment via CN II to the brain

  • Superior colliculus and visual cortex: integrates visual information and balance data from vestibular and proprioceptive systems.

    • Visual system works closely with the vestibular and proprioceptive systems to maintain balance

      • Ex. visual input conflicts like looking at moving objects while standing still, the brian might have an issues maintaining its orientation leading to disorientation

Cranial Nerves: sensory input facialting muscles movements and stabilizing vision

• CNs III, IV, & VI: control eye movement and maintain stable vision during head movements (achieved through the vestibulo-ocular reflex

  • works by stabilizing the eyes my moving them in the opposite direction of head movements to maintain a steady gaze

• CN VIII: Transmits information from vestibular organs (semicircular canals and otolith organs) to the brain.

  • Vestibular part of this brain carries balance information to the brain stem, where it is processed to determine the heads position relative to gravity and motion

• CN XI: Controls neck and shoulder muscles and supports head posture.

  • Sternocleidomastoid and the trapezius 

  • Stabilize head posture which indirectly supports balance 

• CNs IX & X: (indirect involvement) contribute to autonomic responses related to vestibular input.

  • Nausea and vomiting in cases of extreme vertigo and motion sickness

Central processing in the brain

• Brainstem: integration

  • Acts as a processing center coordinating reflexes and sending commands to adjust posture 

• Cerebellum: fine tune motor activity and coordination

  • Receives input from brainstem processes it and send it up to motor areas in the brain, 

  • Ensure smooth and precise movements essential for maintaining balance during activities like walking and running

• Cerebral cortex: voluntary movement and spatial awareness

  • Sensory and motor cortex and involved in voluntary movement and spacial awareness

  • Integrates sensory input with motor output to plan and execute movements that maintain balance 

• Basal ganglia: automatic postural response

  • Coordination automatic postural responses

  • Enabling adjustments to be made quickly and subconsciously

Interactions of Systems for Balance

• Constant communication between the sensory system and central processing centers

  • Vestibular dysfunction: loss of accurate head position information (vestibular neuritis, veneer stasis)

  • Visual impairments: reduced spatial awareness (increase fall risk)

  • Proprioceptive deficits: inability to detect limb and joint positioning

Balance during movement:

• Dynamic balance: stability during activities like walking or running 

• Role of gait patterns: coordinated movement across joints

• Adjustments: muscle and joint adjustments based on feedback

Factors affecting balance: 

• Age: slower reflexes and sensory decline

• Health conditions: vestibular disorders, visual impairments, nerve damage

• Environmental factors: surface, lighting and obstacles

Disorders of balance:

• Vestibular disorders: vertigo, meniere's disease vestibular neuritis (effecting balance)

• Neurological disorders: stroke parkinson’s disease, multiple sclerosis (coordination and even reflexes)

• Musculoskeletal issues: weakness, joint injuries (balance)

Vestibular tests:

• Romberg test:

  • A person requires 2 out of three inputs to the cortex

  • Visual confirmation of position, Non visual confirmation of position 

    • Including proprioceptive and vestibular input, normally functioning cerebellum

  • Ex. if a patient loses balance with their eyes closed but can maintain balance with their eyes open, then there is likely to be a lesion in the cerebellum