multiple systmens interact and neural connections are strenthened

pathway depends on the environment and the task

synaptic overgrowth

synaptic pruing

Synaptic pruning is the reduction in the number of unused neurons in the brain that occurs as we age

two types: apoptosis

Axon retraction

the selective eximination of synaptic connections that occurs in normal development.  It reinforces functional pathways that develop as a result of interactions between individual, task and environment.

It occurs in healthy neurons. 

Extraneous axonal connections are eliminated

• the pairing of sensory and motor information that begins in fetal development.
• A sequence of reflexive motor behavior that is seen in early infancy and provides a substrate for development or functional movement
• movement patterns oberserved in infancy
• follow an orderly sequence of appearance and disappearance

when do primitive reflexes reappear

List three theories that try to explain this phenomenon

• primitive reflexes oftem reappear after a brain injury
• theoretical explanations for this have changed:
• Hierarchical
• Maturational
• Dynamic systems

• the sequential appearance of reflexes is infancey reflects maturation of brain centers from lower to higher

• reflexes disappear because they are ultimately suppressed by cortex
• Reappear if "called on" by cortex to support voluntary movement
• reappear if "released" from CNS control by brain injury

• the expression orf reflexes in infancy is influenced by practice and body dimension
• practice of some reflexes promotes development
• reflex movement that occures with brain injury is not isomorphic with reflex movement seein in typical development
• note: isomorphic means that something is simialar in appearance but genetically different

• distributed model of CNS control
• Numerous interconnections within CNS
• Movement emerges as a result of intrinsic and extrinsic factors
• primitive reflexes "re-appear" with pathology as residual structures reorganize

• Asymmetric tonic neck reflex
• symmetric tonic neck reflex
• palmar grasp
• plantar grasp
• flexor withdrawal
• babinski

• head turning that results in extension of the limbs on the face side and flexion of the limbs on the skull side
• sometimes called the fencer posture
• if this reflex doesn't dissapear it can interfere with movement and posture; it is important to address to minimize any negiative impacts on function

• neck extension results in arm extension and leg flexion
• Can interfere with reciprocal crawling

• Palmar: tactile pressure to the palm results in finger flesion; if retained there is difficulty with object release
• Plantar: tactile pressure to the plantar surface results in toe flexion; when retained can lead to problems with standing and have the potential for skin break down

• touch to the sole of the food results in extension and abducion of the toes
• re-appearance of reflexees in pathology
• represent UMN problem
• Motor system attemps to reorganize after injury

• They are coordinative structures that limit the degrees of freedom at joints
• they are one of the substrates for motor control

• it is a reorganization mechanism that is involved in synaptic pruning, collateral sprouting, and new synapse formation.  PT attempts to use reorganization potential in the recovery of function.
• Because the brain is reorganzing it can cause positive or negative change.  Intervention shortly after injury is important because of the impact on the reorganization state

• neural tube develops from specialized ectoderm at 3 weeks gestational age (GA)
• neurons of the spinal cord and brain stem develop by the 10th week
• newurons of the cerebral hemispheres develop by 20 weeks
• development of the fetal nervous system at risk from teratogens, infection, mal-nutrition
• note: teratogens are substances in the environment that can cause birth defects

• brain weight doubles in the first 6 months of life
• critical periods for brain growth between 3-10 months and 15-24 months
• brain growth correlates with cognitive and language development in the first 2 years
• Myelination of brain continues into young adulthood
• richness of experiences are critical to cognitive development
• prime time for language development
• infant needs lots of experiance from proper development

• more development of skills as brain myelination continues
• develop quicker response time in childhood
• practice is a variable across all ages
• Critical periods of brain growth at: 6-8yrs, 10-12 yrs, 18yrs
• Language development continues to be related to brain growth
• brain directs other body systems via hormones to change at puberty

• CNS: braing weight and volume begin to decline at age 20; loss of brain mass related to loss of myelin; decreases can be moderated by overall good health
• PNS: nerve conduction velocity decreases; this is seen in motor nerves at age 20 and sensory nerves around age 30

• age-related decline in brain weight and volume continues
• increased neural atrophy, cell death, and ventricular enlargement
• rate of volume loss decrease as age 65
• frontal lobes afected by ageing and impact memory and executive function
• intellectual ability is presearved into mid-70's
• memory loss is common
• decreased reaction time: premotor time is slower and motor time is task dependent

neurofibrillary tangles

neuritic plaques