Postural Control In Neuromuscular Disorders Flashcards
What is the relationship between CoM and BoS?
fundamental to maintaining balance and stability in both static and dynamic situations
For a person to maintain balance, the CoM must remain within the BoS
If the CoM shifts outside the BoS, the person will likely lose balance and fall unless corrective actions are taken
in dynamic activities, such as walking or running, the CoM moves relative to the BoS, but stability is maintained through adjustments in posture, gait, and movements
to stay balanced, the body makes postural adjustments to ensure that the CoM remains within the BoS. These adjustments involve shifting weight, altering body posture, or adjusting the BoS (e.g., moving feet or changing stance width)
Center of Mass (CoM):
The point where the mass of an object or body is concentrated. For the human body, it is typically located just anterior to the sacrum in the pelvis
*S2
It is where the gravitational forces act and is central to the body’s balance
Base of Support (BoS):
The area between and including the points of contact with the supporting surface
For a standing person, this is the area defined by the feet. A larger BoS generally provides greater stability
Neuromuscular Control:
The nervous system continuously monitors the CoM relative to the BoS and makes rapid adjustments through muscle activation and coordination to maintain balance.
Feedback Mechanisms:
Sensory feedback from visual, vestibular, and proprioceptive systems helps the body detect shifts in the CoM and initiate corrective actions to maintain stability.
Balance Strategies:
ankle
hip
stepping
Ankle Strategy:
Involves small adjustments using the ankles to maintain CoM within the BoS, useful for minor perturbations.
Hip Strategy:
Involves larger movements at the hips to maintain balance when the CoM is significantly displaced.
Stepping Strategy:
Involves taking a step to enlarge the BoS when the CoM has moved too far outside the BoS to maintain stability.
Center of Pressure (CoP):
The point of application of the resultant ground reaction force acting on the body
It is the average location of the vertical forces exerted by the ground through the base of support (BoS)
It represents the point where the pressure is effectively concentrated during standing or dynamic activities
CoM vs. CoP:
CoM: Represents the point where the body’s mass is concentrated and where gravity acts.
CoP: Represents where the ground reaction forces are applied. In static conditions, the CoP needs to be within the BoS to maintain balance.
The CoP shifts in response to movements and adjustments to keep the CoM within the BoS.
Measuring CoP:
Force Plates: CoP is often measured using force plates, which capture the distribution of forces exerted by the feet and calculate the location of the CoP. This measurement is valuable in assessing balance and postural control.
In clinical settings, CoP measurements can help evaluate balance disorders, the effectiveness of interventions, and the risk of falls.
Resources required for postural stability and orientation:
biomechanical constraints
cognitive processing
control of dynamics
orientation in space
sensory strategies
movement strategies
biomechanical constraints:
degrees of freedom = number of independent ways a system (like a joint or a body segment) can move
strength = ability of muscles to produce force, essential for generating movement and maintaining posture
limits of stability = boundaries within which the body can maintain balance without changing its base of support (like stepping or reaching)
> distance a person can lean or shift their center of mass while maintaining balance
cognitive processing:
attention = Effective postural control requires cognitive resources to monitor and adjust posture. Attention to body position and environmental changes is necessary for balance maintenance
learning = The ability to recall and apply learned strategies for maintaining balance and orientation is essential, especially in novel or challenging situation
control of dynamics:
gait = Gait is a dynamic process that involves the coordination of muscles, joints, and sensory feedback to maintain balance and propel the body forward
proactive = body’s ability to anticipate and prepare for changes in movement based on previous experience or environmental cues
> body uses sensory input (vision, proprioception) to predict obstacles or changes in terrain, and adjusts movements accordingly before encountering them
orientation in space:
perception = involves integrating sensory input from multiple systems, including vision, the vestibular system (inner ear), and proprioception (sensory feedback from muscles and joints)
gravity, surfaces, vision = estibular system, specifically the otolith organs in the inner ear, detects changes in head position relative to gravity
> Proprioceptive feedback from the body and contact with surfaces (such as the ground) informs the brain about how the body interacts with the environment
verticality = perception of uprightness and alignment with respect to gravity
sensory strategies:
sensory integration = brain’s ability to combine information from different sensory systems—vision, vestibular (inner ear), and somatosensory (proprioception and touch)—to form a coherent understanding of the body’s position and movement in space
sensory reweighting = body’s ability to adjust the relative importance of different sensory inputs based on the situation or the reliability of the available information
> when walking in the dark, visual input becomes unreliable, so the brain “reweights” the sensory inputs, relying more on proprioception and vestibular information
movement strategies:
reactive = automatic responses that occur after a disturbance or loss of balance
> ankle, hip, stepping
anticipatory = pre-programmed movements that occur before a voluntary action or an expected disturbance, allowing the body to prepare for potential challenges to balance
> important for smooth, coordinated movement and preventing falls during tasks that require planning, like reaching for something on a high shel
voluntary = conscious, intentional movements aimed at accomplishing a specific task, such as walking, reaching, or changing posture
> controlled by higher brain centers and are goal-directed, allowing flexibility and adaptability in complex environments
Postural control- involves multiple systems = postural control system
1) Sensory Systems:
-vision’
-vestibular
-proprioception
-exteroception
2) Sensory Integration and Weighting
3) Brain Areas Involved in Postural Control
- Pre-frontal Cortex
- Primary Motor Cortex
- Frontal and Pre-motor Cortex
- Cerebellum
- Brainstem
4) Pathways
- Dorsal
- Ventral
5) Motor response = body generates a motor response (e.g., adjusting posture or movement) to maintain stability
Ventral pathway =
“WHAT” Pathway
involved in object identification and recognition, helping us understand what we are looking at
processes information related to the form, color, and details of objects
starts in the occipital lobe (where visual information first arrives) and travels to the temporal lobe, an area associated with recognition of objects, faces, and scenes
It answers questions like:
“What is this object?”
“Is this familiar to me?”
“What are the object’s characteristics (color, texture, shape)?”
Dorsal pathway =
“WHERE” Pathway
involved in spatial awareness, helping us determine where objects are in relation to ourselves and guiding our movements
starts in the occipital lobe and moves towards the parietal lobe, an area involved in processing spatial location and motion
It answers questions like:
“Where is this object located?”
“Is it moving? In what direction?”
“How can I interact with it (e.g., reaching, grasping)?”
Dorsal Pathway to Posterior Parietal Cortex:
Supports spatial awareness and attention, allowing the body to understand “where” it is in space
Ventral Pathway to Inferotemporal Cortex:
Involved in object recognition and identification, processing “what” is in the environment
Vision:
Provides visual input about the environment, helping the body understand its position relative to objects and surroundings
Vestibular System:
Located in the inner ear, it helps detect changes in head position, motion, and orientation relative to gravity
Proprioception:
Involves the sensory feedback from muscles, joints, and tendons, giving the body awareness of its position in space
Exteroception:
Provides information from external sensory receptors in the skin, contributing to the awareness of environmental contact (such as pressure or texture from the ground)
Pre-frontal Cortex:
Involved in decision-making and planning movements
Primary Motor Cortex:
Responsible for the execution of voluntary motor movements
Frontal and Pre-motor Cortex:
Involved in the planning and initiation of movement
Cerebellum:
Coordinates timing and precision of movements and fine-tunes motor responses
Brainstem:
Regulates automatic postural responses and integrates sensory and motor signals
Sensory Signals:
Sources: Visual, vestibular, auditory, proprioception, touch, and visceral systems provide sensory feedback to the brain about the body’s position and movement relative to its environment.
Proprioceptive and Skin Afferents: These signals convey information from the body’s joints, muscles, and skin, helping the central nervous system understand its spatial orientation and posture.
Basal Ganglia:
Central to motor control, the basal ganglia play a major role in initiating and regulating voluntary movements. It processes sensory input and sends signals to the cerebral cortex and other brain areas to refine motor actions. Dopamine from the basal ganglia affects movement regulation.
Cerebral Cortex:
The cognitive reference is represented by the cerebral cortex, which governs voluntary movements and cognitive processes involved in postural adjustments. The cortex integrates sensory feedback and decision-making processes, which are essential for initiating and modifying movements.
Thalamus:
Serves as a relay station, transmitting sensory signals (e.g., proprioceptive feedback) to the cortex for processing and integrating them with motor commands.
Limbic System:
The emotional reference is represented by the limbic system, which influences emotional motor behavior. Emotional states can directly affect posture and movement, integrating emotional responses with motor control.
Automatic Processes:
Midbrain, Pons, Medulla: These areas are involved in automatic postural adjustments and reflexive movements. The cerebellum fine-tunes movements and coordinates balance.
Spinal Cord & Central Pattern Generators (CPGs): The spinal cord houses CPGs, which control rhythmic movements such as walking. These generators help maintain automatic locomotion without conscious effort, regulated by sensory feedback and brain input.
Spinal Locomotor Network:
Involved in automatic and rhythmic movements, the spinal locomotor network is essential for walking and maintaining posture, allowing for dynamic adjustments based on proprioceptive and sensory feedback.
Motor Outputs:
Automatic Movements: Controlled by subcortical structures (brainstem, cerebellum, spinal cord), these involve reflexive and rhythmic activities, like maintaining posture while standing or walking.
Voluntary Movements: Controlled by the cerebral cortex and basal ganglia, voluntary actions are goal-directed and consciously initiated, such as deciding to change posture or walking toward an object.
Postural control in Stroke
83% of pts. 2-4 wks post stroke -> balance disability
Motor control impairments (caused by reduction in # and firing rate of motor units): slow movements, weakness, fatigue, incoordination, decreased force production, co-contractions
Reduction in the Number and Firing Rate of Motor Units:
Damage to the brain affects the recruitment and activation of motor units, which are responsible for muscle contraction.
Slow Movements (Bradykinesia):
Movements become slower due to a reduced ability to activate muscles rapidly. This can limit the speed and efficiency of postural adjustments.
Weakness (Paresis):
Muscle weakness is a hallmark of stroke, particularly on one side of the body (hemiparesis), and is associated with reduced muscle strength and endurance, contributing to postural instability.
Fatigue:
Stroke patients often experience physical and mental fatigue, which further impairs their ability to maintain posture, particularly during prolonged activities.
Incoordination:
Loss of motor coordination results in jerky or uncoordinated movements, impairing the ability to execute smooth postural adjustments and movements.
Decreased Force Production:
Muscles affected by the stroke produce less force, making it difficult to perform actions that require strength, such as standing, walking, or reaching.
