Brain Growth and Motor Development

Myelin

-Axons of neurons become coated with myelin, a fatty substance that, like the insulation on an electric wire, provides protection and speeds the transmission of nerve impulses. -Contributes to increased weight of brain Even though many neurons are lost, the increasing size and complexity of the remaining ones contribute to impressive brain growth. -A baby's brain triples its weight during his or her first 2 years of life, and it reaches more than three-quarters of its adult weight and size by the age of 2.

Brain Growth and Cognitive Development

-Myelination of the reticular formation, an area of brain associated with attention and concentration, is completed by the time children are about 5. May be associated with children's growing attention spans as they approach school age. The improvement in memory that occurs during preschool years may also be associated with myelination: During the preschool years, myelination is completed in hippocampus, an area associated with memory. -Significant growth in nerves connecting the cerebellum, a part of brain that controls balance and movement, to cerebral cortex, the structure responsible for sophisticated information processing. The growth in these nerve fibers is related to significant advances in motor skills that occur during the preschool years, as well as to advances in cognitive processing.

Comparing Individual to Group Norms

-Represent the average performance of a large sample of children of a given age. -Permit comparisons between a particular child's performance on a particular behavior and the average performance of the children in the norm sample. -Must be interpreted with caution.

Neuron Doctrine

-The brain is composed of separate neurons and other cells that are independent structurally, metabolically, and functionally. -Information travels from cell to cell across tiny gaps.

Motor Development in Infancy

-Young infants still are able to accomplish some kinds of movement. -When placed on their stomachs they wiggle their arms and legs and may try to lift their heavy heads. -As their strength increases, they are able to push hard enough against the surface on which they are resting to propel their bodies in different directions. -They often end up moving backwards rather than forwards, but by the age of 6 months they become rather accomplished at moving themselves in particular directions. -These initial efforts are the forerunners of crawling, in which babies coordinate the motions of their arms and legs and propel themselves forward. -Crawling appears typically between 8 and 10 months. -Walking comes around the age of 9 months; most infants are able to walk by supporting themselves on furniture, and half of all infants can walk well by the end of their first year of life. -Most are able to sit without support by the age of 6 months.

Prefrontal cortex

-undergoes considerable development throughout adolescence which is not fully developed until around the early 20s. -is the part of the brain that allows people to think, evaluate, and make complex judgments in a uniquely human way. -It underlies the increasingly complex intellectual achievements that are possible during adolescence. -During adolescence, the prefrontal cortex becomes increasingly efficient in communicating with other parts of the brain. This helps build a communication system within the brain that is more distributed and sophisticated, permitting the different areas of the brain to process information more effectively.

The Synapse

3 components of the synapse: Presynaptic membrane (end on the signaling neuron) Postsynaptic membrane (dendrite of the receiving neuron) A gap (20-40nm) between the pre- and postsynaptic membrane.

Neurons

Approx. 100 billion in the adult nervous system Role is to receive, process and transmit information Generate & Propogate electrical impulses

How great brains grow!

Birth: -Approx100 billion neurons -Relatively few neurons-neuron connections During first two years: -Billions of new connections established and become more complex By year 2: -The intricacy of neural connections continues to increase throughout life. In fact, in adulthood a single neuron is likely to have a minimum of 5,000 (and up to 10,000) connections to other neurons or other body parts. -Proximodistal development, Principle of independence of Systems)

Use It or Lose It

Brain produces oversupply of gray matter during adolescence which is later pruned back at a rate of one to two percent per year *Brain changes Growth spurts -Number of neurons (the cells of the nervous system) continue to grow. -Interconnections become richer and more complex. -Adolescent thinking becomes more sophisticated.

Major Systems of the Brain

Brain stem (developed and working at birth) Limbic system Cerebral cortex

Structure of the Neuron: Dendrites

Cellular extensions, like branches on a tree, that receiveinput from other neurons

Brazelton

Flexible approach advocating waiting until signs of readiness appear

Do boys and girls differ in motor skills?

Gender differences in gross motor skills became increasingly pronounced during middle childhood, -Boys outperform girls -Little or no difference when equal participation in exercise/activities -Influenced by societal expectations *American Academy of Pediatrics suggests that boys and girls should engage in the same sports and games, and that they can do so together in mixed-gender groups. There is no reason to separate the sexes in physical exercise and sports until puberty, when the smaller size of females begins to make them more susceptible to injury in contact sports.

Growing Brain

Grows at a faster rate than any other part of the body -Increase in interconnections among cells and myelin -Corpus callosum becomes thicker (improves communication b/w the two hemipheres. -Lateralization improves *By age 5, children's brains weigh 90 percent of average adult brain weight. -In comparison, the average 5-year-old's total body weight is just 30 percent of average adult body weight. -Interconnections allow for more complex communication between neurons, and they permit the rapid growth of cognitive skills that we'll discuss later in the chapter. -Corpus callosum, a bundle of nerve fibers that connect the two hemispheres of the brain, becomes considerably thicker, developing as many as 800 million individual fibers that help coordinate brain functioning between the two hemispheres. -Two-year-olds have brains that are about three-quarters the size and weight of an adult brain. -Lateralization, the process in which certain functions are located more in one hemisphere than the other.

Gross Motor Development in Middle Childhood

Improved muscle coordination

Ratio of glial to neurons

It is debated. The higher order brains (primates and humans) that can perform higher order functions have more glial cells supporting each neurons. When we say that brain has evolved and expanded, we are talking about more glail cells supporting each neurons. They serve a supportive role. Glail cells part of the blood brain barrier.

Structure of the Neuron: Axon

Long extension which transmits electrical impulses away from the cell body

Glial

Name comes from the Greek glia meaning "glue" 3 times as many glial cells as there are neurons Perform critical role to neuronal function & survival

Nervous System: 2 types of cells

Neurons and glial

Form and Function: Brain Growth

Neurons reposition themselves with growth, becoming arranged by function -Cerebral cortex -Subcortical levels -Each neuron may be connected to up to 10,000 other neurons, passing signals to each other via as many as 1,000 trillion synaptic connections. -Estimates of the human brain's memory capacity vary wildly from 1 to 1,000 terabytes (for comparison, the 19 million volumes in the US Library of Congress represents about 10 terabytes of data). *Some move into the cerebral cortex, the upper layer of the brain, while others move to subcortical levels, which are below the cerebral cortex. As time passes, however, the cells in the cerebral cortex, which are responsible for higher-order processes such as thinking and reasoning, become more developed and interconnected. The subcortical levels, which regulate such fundamental activities as breathing and heart rate, are the most fully developed at birth. Myelination of the reticular formation, an area of brain associated with attention and concentration, is completed by the time children are about 5. May be associated with children's growing attention spans as they approach school age. The improvement in memory that occurs during preschool years may also be associated with myelination: During the preschool years, myelination is completed in hippocampus, an area associated with memory. Significant growth in nerves connecting the cerebellum, a part of brain that controls balance and movement, to cerebral cortex, the structure responsible for sophisticated information processing. The growth in these nerve fibers is related to significant advances in motor skills that occur during the preschool years, as well as to advances in cognitive processing.

Glial cells

Originally thought to simply provide structural support to neurons, it is now realized that glia serve much more diverse and necessary functions...they are certainly more than just "glue" Types: Astrocyte (star shaped) Microglial cell Oligodendrocyte Schwann cell Ependimal

Left Hand, Right Hand

PET scans illustrates activity in right or left hemisphere of brain differs according to task in which person is engaged *Each of two hemispheres also begins to process information in a slightly different manner. -Left hemisphere processes information sequentially, one piece of data at a time. -Right hemisphere processes information in a more global manner, reflecting on it as a whole. -In most respects the two hemispheres act in tandem. -They are interdependent, and the differences between the two are minor. -Even hemispheric specialization in certain tasks is not absolute. -Each hemisphere can perform most of the tasks of the other. -There are also individual and cultural differences in lateralization.

How is prefrontal cortex related to adolescent impulse control?

Prefrontal cortex provides for impulse control Adolescence prefrontal cortex is biologically immature = ability to inhibit impulses is not fully developed *Rather than simply reacting to emotions such as anger or rage, an individual with a fully developed prefrontal cortex is able to inhibit the desire for action that stems from such emotions.

Ethnic and Cultural Differences and Similarities in Reflexes

Reflexes -Genetically determined -Universal Cultural variations in ways displayed -Moro reflex Multiple purposes -Diagnostic tool -Social function -Survival function

Rosemond

Rigid approach advocating quick and early training

Moro Reflex

Some differences reflect cultural and ethnic variations. -Caucasian infants show a pronounced response to situations that produce the Moro reflex. Not only do they fling out their arms, but they also cry and respond in a generally agitated manner. -Navajo babies react to the same situation much more calmly. Their arms do not flail out as much, and they cry only rarely. -Diagnostic tools for pediatricians. Because reflexes emerge and disappear on a regular timetable, their absence—or presence—at a given point of infancy can provide a clue that something may be amiss in an infant's development.

Structure of the Neuron: Axon terminals

Swelling at the end of the axon which communicate the cells activity to other cells.

Myelination

The axon of a neuron conducts an electrical impulse and thus must be insulated. This is accomplished with help from oligogendrocytes. Myelination speeds up the electrical current passing along the axon. If myelination of the axons is disrupted, the resulting symptoms include: Memory impairment Depression Dizziness Fatigue Numbness Visual impairment Bladder and bowel dysfunction

Structure of the Neuron: Cell body

The brains of the operation, containing nucleus

The first actions

The earliest movements of the newborn are reflexes, involuntary responses to environmental stimuli such as touch, sound, and light

Primitive reflexes

are necessary for survival and include reflexes that provide nourishment, such as rooting and sucking.

Nervous System: Central Nervous system

brain and nerves that extend throughout the body (Peripheral nervous system) Information --> Sensory --> and chemical. (convert sensory information to the language of the brain) Peripheral cause muscles to move and body to react.

Synaptic pruning

elimination of unused neurons that allows established neurons to build more elaborate communication networks with other neurons. Unlike most other aspects of growth, then, the development of the nervous system proceeds most effectively through the loss of cells. -Neurons that do not become interconnected with other neurons as the infant's experience of the world increases become unnecessary. They eventually die out, increasing the efficiency of the nervous system.

Stages of preschool artistic renderings

from top of pyramid to bottom pictures designs shapes scribbles

Reflexes

learned and involuntary responses that occur automatically in presence of certain stimuli.

Postural reflexes

maintain body orientation and include stepping and body righting

Brazelton Neonatal Behavior Assessment Scale (NBAS)

one of the most widely used techniques to determine infants' normative standing; measure designed to determine infants' neurological and behavioral responses to their environment; provides a supplement to the traditional Apgar test.

Myelination

the process in which nerve cells are insulated by a covering of fat cells—increases and continues to make the transmission of neural messages more efficient. -Both the pruning process and increased myelination contribute to the growing cognitive abilities of