Physical Growth

Neurological, Physiological, and Motor Development

A. Neurological development:

Neural tube:Prosencephalon (forebrain)Mesocephalon (midbrain)Rhombencephalon (hindbrain)

Neural tube continues developing:

At the end of the bumpy neural tube—telecephalon followed by the diencephalon.

Both make up the forebrain.

Prenatal Neuronal Development:

Neurons & glial cells proliferate rapidly in prenatal development.

Fetus has majority of neurons it will have in life by third trimester (7-8 month).

Neuronal migration—cells migrate to different CNS locations.

What is a neuron?

Prenatal synaptic development

Synapses (synaptogenesis) are formed at a rapid rate.

There are trillions of synapses present at birth. This drops dramatically by adulthood.

What is a synapse:

Why do we lose cells?

1. Programmed cell death- as new synapses are formed, surrounding neurons die to provide space for the new connections.

2. Synaptic pruning- inactive neurons-- removed to free up room for active neurons.

Brain Development: Infancy

Brain Growth:myelination: Areas associated with motor

& mental functions.

cortical & subcortical connections lobe activity neural plasticity: capacity of brain to

change in response to experience & chemicals.

Brain development: Toddlerhood Rapid development 2nd & 3rd yr

Cerebral cortex:

Auditory & Visual cortex

Movement & coordination

Language

Frontal cortex

Brain RegionsBrain Regions

Frontal lobe

Parietal lobe

Temporal lobe

Occipital lobe

Cerebellum

Brain Development: Childhood

By 6 yrs old brain is 90% of adult weight

Increased connections between all brain regions

Communication abilitiesMemory Motor controlCognitive abilities

Brain Development: Adulthood

Aging Brain weight after 30

How?

-loss of white matter or loss of gray matter

Prefrontal cortex connections

Hemispheric Specialization:

Right H. Left H. Left side of body right side of body

Music/melodies language/speech Visual-spatial abilitieslogic, analytic

Infants show hemispheric specialization early.

The majority of newborns process speech sounds by the left hemisphere as measured by scalp potentials.

Neural Plasticity: Rosenzweig study

Rats from same litter put into 1 of 2 environments: enriched (E) or impoverished (I) for 3 months.

“E” environment- large, well-lit, communal cages- with toys (wheels, ladders, platforms) changed daily. Rats also explored a maze once a day.

“I” environment- each rat was placed in a small, isolated, dimly lit cage .

Rosenzweig (1996): Findings 1. “E” rat brains weighed 4% more than “I” rat

brains.

2. Occipital region of “E” rat brains showed greatest gain (6%).

3. Neurotransmitter enzyme levels were greater in the “E” rats.

4. Dendritic connections were grater in “E” rat brains.

B. Motor Development: Infants--born with little motor development.

Within a year, most infants crawl & walk.

Factors Influencing motor development

1. Maturation.

2. Enriched environment–interesting & novel stimuli promotes cortical development.

3. Caregivers—encouragement works.

1. Grasping: Infants vary -grip on an object based on its

size, shape, texture, & their hand size.

For small objects, infants use thumb & index finger. They use all fingers of 1 hand or both hands for larger objects.

Older infants (8 mos.) use visual cues to guide their grasping, younger infants rely on touch.

2. Locomotion:

1.First transition -infants show stepping reflex –ends at 3-4 mos.

2. Second transition- in 2nd half of year, stepping movements occur again.

3. Third transition – Infants walk unsupported (12 mos.+)

Theories as to how we learn to walk? 1. Motor cortex develops– frontal lobe takes 1

year to mature for us to walk.

2. Motor programs– we develop motor programs in spinal cord that guide walking.

3. Cognitive plans—infants have mental representations for walking.

4. Dynamic Systems view—interaction of multiple factors (perceptual, neurological, emotional, etc.)

Factors that promote early walking:

1. Physically handling infants

2. Giving infants practice in motor tasks

Zelazo & coworkers (1972) --mothers of newborns had infants practice stepping reflex a few min. a day.

These babies walked--earlier than a control group given no practice.

C. Physical Growth:

Why do we grow slowly?

We need exposure to social environmental stimulation to develop the frontal lobes.

Growth patterns in development:

1. Cephalocaudal (from head downward).

2.  Proximal-distal (from center outward). Internal organs develop earlier than the arms and hands.

Factors that influence height & weight: 1. Genetic factors – accounts for most of

the variance.

2. Gender- Girls-taller than boys from 2-9 yrs. Girls have growth spurt from 10-14 yrs. Boys show growth spurt from 10+

Weight pattern is similar.

3. Hormonal influences-Growth

Hormone (GH) GH, produced by the pituitary gland

(brain), induces growth in the body.

GH stimulates the liver & skeleton to release somatomedin, which promotes cell duplication in the bones.

This promotes growth beyond (4 feet).

Environmental factors (growth):

1. Nutrition – When healthy food is rationed, growth rates decline.

E.g., During WWII growth rates declined. In prosperous times, when food is easy to come by growth rates increase.

2. Does food supplementation improve growth rates?

Yes!!

Super et al., (1990) showed that giving food supplements to families for 3-4 yrs, prevented growth retardation compared with controls.

Also works with vitamin supplements.

3. Can children with retarded growth catch up to their peers?

Yes. It depends on severity, duration, & timing of deprivation (nutrition) & therapy.

Catch-up growth due to severe malnutrition may be limited to certain aspects of growth.

Children starved early (prenatal+) will show only modest gains if that.

Are we growing heavier? Yes. Obesity rates are rapidly rising.

Appears to have risen in children dramatically within the last decade.

Why? Sedentary lifestyle High-fat food

Why do kids gain too much?

1. Genetics- Adoption studies show biological children of

“heavy” parents reared apart—are more likely to be heavy themselves (Stunkard et al., 1986).

2. Modeling (what & how do parents eat)

3. SES

Critical periods for obesity:

1. Infancy-

2. Child is 4 yrs-old