Development of postural control Flashcards
Development in General
- Combination of experience and maturation of systems
- Sensorimotor mapping (motor learning) over time as systems change (cerebellum)
- Seqeuntial order of motor tasks with wide variability and some progression/regression (spiraling)
- Born with some hard-wired movement capabilities (reflexes; spinal cord); Starting point for movement, starts mappping the motor activity in the cerebellum eventually leading to voluntary control.
Normal vs Abnormal infant movement
- Healthy: fidgety, complex patterns; movements are variable in intensity and velocity, shows coordination and fluidity
- Abnormal: less fidgety - atypical monotonous or hypokinetic movements (indicate impaired nervous system)
We want lots of movement for sensorimotor mapping!
Development rate limiting factprs
- CNS maturity (Matures into teenage years)
- Musculoskeletal strength
- Anthrpometrics (Height and mass distribution)
CNS Maturation
Newborn
* Brain is BIG - 25% of adult weight
* Midbrain and spinal cord are myelinated allowing for vital functions, sleep and primative reflexes)
* Touch/Somatosensory tracts myelination has started (Ends at 2 years)
* Trillions of synapses at birth; Synaptogenesis begins at 2 months (primitive reflexes fade and purposeful movement begins)
At what age do babies start to become vision dominant? Why?
- At 3 months!
- Synaptic formation increase in the visual cortex! Start of visually directed movement
- Example: Assymetric Neck Reflex; As the head turns toward the right side, the right arm extends and left arm bends.
At what age does pruning begin and why?
- 10 years old
- Brain eliminates connections to refine, become more efficent and increase speed.
This is why children start to forget childhood memories around 10
Musculoskeletal Strength
- Greatest increase in the number of muscle fibers occurs prenatally (before birth)
- Increase in size and differentiation of muscle fibers postnatally
- Strength increases linearly until 12 years old.
- At 6 months can produce force greater than body weight
Why can children not stand at 6 months if they are strong enough?
They don’t have the coordination and balance systems/connections made yet.
Infant Anthropometrics
- Top heavy!
- Head is 25% of body length
- Head width is close to shoulders and hip width
- Biomechanical challenge (balance due to COM)
Anthropometrics - After 1 Year
- Infant doubles weight
- Length increases by 50%
- Head circumference increases by 30%
Anthropometrics - Birth to adulthood
- Head size doubles
- Trunk length triples
- UE quadruple
- LE quintuple
- Body proportions change and COM lowers as maturation occurs
What do we need to think about with maturation from birth to adulthood?
- The maturation effects coordination.
- This results in progressions/regressions to move toward the next milestone (spiraling)
- Completely normal!
Pattern of Development occurs in what directions? Why?
- Head to foot
- Proximal to distal within segments
- Allows for the child to gain control centrally before moving distal; if we don’t have this we don’t have a proper base of support with movements.
Major Milestones of Development - Sequential
- Crawling (Belly/Army Crawl)
- Sitting
- Creeping (Quadruped motion, what you thought crawling was)
- Pull to Stand
- Independent Stance
- Walking
Windows of achievement for six gross motor milestones
- Wide variability
- 95% Ranges
Specific motor tasks requiring postural control
- Head Control
- Independent Sitting
- Transition to independent stance
Need each of these to accomplish the next, which then leads to mobility.
All precursors to walking
Development of Head Control
- Lack of head control in newborns results from lack of strength and lack of organized (coordinated) muscle activity.
- They lack strength due to being in the womb which does not have the same gravitational impact.
- They don’t have the ability to coordinate extension of the neck extensors.
Development of Head Control - Sensory Contributions
Vision
* Visual and motor connection via optical righting reaction)
* Experience and self produced movment are necessary to refine vision and muscle activity
Vestibular
* Aids in orienting the head vertical (labyrinthine righting)
Somatosensory System
* Proprioceptive/tactile information is used to orient the head and body (body on head righting)
What is optical righting?
Eyes move toward stimulus, head will orient with them in space to align vertically
What is important for parents to do with infants?
- positioning and handling to promote refined control of head movements
Development of Independent Sitting - Stages
- Neck control “spreads” to shoulders/trunk
4 Stages:
* Stage 1: 4-5.5 months: Head and trunk control are present, but not sitting independently; Highly variable COP fluctutations; child exploring what works what doesn’t
* Stage 2: 5-6.5 months: upright breifly, less variable, found one strategy and using it.
* Stage 3: 6-8 months: independent sitting, large sway, more (variable) responses responses to different directions
* Stage 4: 8-9 months: stable sitting with minimal sway, strategy refined
Development of Independent Sitting - Balance
Balance reaction strategies to pertibations
* Available before sitting develops to a limited extent
* 1-4 months: Onset times, directions and response rates are all variable (neural struture refinement)
* 5-9 months (over time or with specific practice) practice improves probability of response, amplitude and consistency of response; synergies are refined
Development of independent sitting - Sensory
Vision
* Infants rely heavily to control sway
* Overrides proprioception and somatosensory
* With experience, reliance diminishes
Somatosensory
* Dominant factor in reacting to seated pertibations (fastest)
Trunk control ____ to legs
“spreads”
As a child gets close to standing, ____ often gets worse
sitting performance
Common regressions in children represent a process of…
recalibrating sensorimotor maps for new skill
The rate limiting factor to independent stance is…
neural coordination required to maintain the center of mass within the base of support.
Development of independent standing - pull to stand to standing
- 2-6 months: early pull to stand - no coordinated response; fall right back down.
- 7-9 months: directionallly appropriate response starts at the ankles
- 9-11 months: independent stance distal to proximal sequence emerges (ankle strategy)
Demonstrates the process of neural refinement to synergies to control COM
Only have AP strategy not ML
Timeline for ankle and hip strategy development
9-11 months: Ankle strategy
7-10 years (up to 13-15): Hip strategy; Multidirectional strategy
What is the rate limiting factor for development of postural strategies? How can we aid in promoting strategies?
- Neural maturation!
- Practice increases the probability of getting postural response but response changes do not change so neural maturation is large factor
How does sensory contributions to stance change as humans age?
- Visual dominance early! Seen at 3 months with assymetric neck reflex.
- Followed by refined ability to integrate multi-modal sensory information. Seen starting at age 3 and into adolescence as speed of processing increases. Requires myelination and experience.
- Somatosensory contributions finish myelination development at 2 years
- Vestibular contributions begin at age 7.
Body morphology and postural sway - children
- Children are shorter and top heavy
- Children sway at a faster rate than adults (static balance is more difficult); more likely to have to use stepping stategy
- After age 7 sway during normal quiet stance is not related to height or mass (vestibular)
Postural Control is essentially “adult like” by age ____
age 7-10 (up to 15) years
Young children’s postural sway is characterized by an increase in…
- Amplitude
- Velocity
- Random variations
Decrease with age into adolescence
Adaptability - Timeline
Response to pertibations
1.5 to 3 years
* Well organized muscle responses
* Large amplitude & slower response latency
* Longer response durations
* More stretch reflex activation is observed; takes time to develop so they rely more on stretch reflexes
4-6 years
Some studies show even slower and more variable than 1.5 - 3 yrs and 7-10 yrs
Regression due to reorganization?
7-10 (15) years
* “Adult like” – ankle, hip, and multi-directional strategies are observable
Development of anticipatory control
- Related to devellopment of reaching and important for walking
-
Sitting:
– Activation of trunk in advance of reach at 9 months -
Standing:
– 10 Months: inconsistent anticipatory action prior to reaching
– 13 months: consistent anticipatory actions (associated with walking)
– 4-6 years: anticipatory adjustments preceding arm movement while standing are mature - Need practice to develop anticipatory control
Children can’t do multiple things at once well but they can….
as they age and develop postural control
____ is one of the hallmarks of development
Variability!
