Development of Brain & Nervous System PDF

Development of Brain and Nervous System CNS (BRAIN & SPINAL CORD) IS KEY FACTOR IN DEVELOPMENTAL CHANGES IN BEHAVIOR  Nervous system Nervous system controls, stimulates and coordinates all other body systems Nervous tissue is made up of NEURONS. Neurons receive and transmit messages from o...

Development of Brain and Nervous System CNS (BRAIN & SPINAL CORD) IS KEY FACTOR IN DEVELOPMENTAL CHANGES IN BEHAVIOR  Nervous system Nervous system controls, stimulates and coordinates all other body systems Nervous tissue is made up of NEURONS. Neurons receive and transmit messages from one part of the body to another. Neurons can vary in size from a fraction of a centimeter to greater than 2 meters in length, depending on where they are located in the body People are born with 100 billion neurons.  Development of the Brain and Nervous System ◦ Each neuron has a cell body, dendrites, and an axon ◦ Dendrites ◦ Short fibers that extend from cell body and receive incoming information from other parts of the nervous system ◦ Axon ◦ Extends trunk-like from the cell body and accounts for much of the difference in length in neurons ◦ Neurotransmitters ◦ Message-carrying chemicals released from axon terminals Fig. 4-2, p. 76  Myelin Myelin sheath ◦ Fatty, whitish substance that encases and insulates axons Myelination ◦ Process by which axons are coated with myelin ◦ Not completed at birth (part of the maturation process) ◦ Myelination of brain’s prefrontal matter continues into the 2nd decade of life ( the breakdown of myelin is believed to associated with Alzheimer’s Disease) Also…..Multiple sclerosis ◦ Myelin is replaced by hard, fibrous tissue that disrupts the timing of neural transmission, interfering with muscle control  Structures of the Brain Medulla ◦ Vital in the control of basic functions such as heartbeat and respiration ◦ Part of brain stem ◦ Nerves that connect spinal cord to higher levels of the brain pass through here Cerebellum ◦ Helps child maintain balance, control motor behavior, and coordinate eye movements with bodily sensations Cerebrum ◦ Two hemispheres that become more wrinkled as child develops, coming to show ridges and valleys called fissures ◦ Contributes to human learning, thought, memory, and language Young Brain is very responsive to environmental influences and continues in diminishing quantity throughout the lifespan Mc Graw (1945)- “Heiarchial Model” of development ◦ Suggests that as the CNS matures the behavior displayed represents the function at that level Hubel & Wiesel (1962)- Neuroplasticity ◦ The ability of the brain to change as a result of experience. Structural and functional changes in the brain were driven by environmental experience. ◦ The child spontaneously engages in challenging activity because of maturation of the brain.  Brain Development in Infancy Myelination contributes to what infants are able to do. Reflexive functions such as breathing due to myelination Myelination of motor pathways allows neonates to show stereotyped reflexes. Myelination will allow the disorganized movements of the neonate to come under increasing control. ◦ Myelination of motor area of the cerebral cortex begins at the 4th month of prenatal development. ◦ Myelination of the nerves to muscles is largely developed by the age of 2 years. ◦ Some myelination continues to some degree into adolescence.  Infant Reflexes Moro Grasp Sucking Rooting Stepping Reflexes Growth Spurts of the Brain Formation of neurons completed at birth First growth spurt ◦ During 4th and 5th month of prenatal development ◦ Due to formation of neurons Second growth spurt ◦ Between 25th week of prenatal development and the end of the 2nd year of life after birth ◦ Due to proliferation of dendrites and axon terminals  Brain Development in Infancy (cont’d) Sensory development ◦ Vision, hearing, and skin senses are less well myelinated at birth. ◦ Myelination progresses and allows for increasingly complex and integrated sensorimotor activities. ◦ Hearing ◦ Myelination begins at 6th month ◦ Continues through age 4 ◦ Vision ◦ Myelination begins only shortly before full term ◦ Completes process by 5th or 6th month  Nature and Nurture in Brain Development Sensory stimulation and physical activity during early infancy sparks growth of the cortex. Infants have more connections among neurons than adults. ◦ Connections activated by experience survive ◦ Others are pruned Lack of stimulation ◦ Can impair motor development and adaptability Sensory and Perceptual Development Visual Acuity, Peripheral Vision, and Preference Neonates ◦ Extremely nearsighted at about 20/600 ◦ Have poor peripheral vision ◦ Expands to 45 degrees by the age of 7 weeks ◦ Prefer stripes and curved lines ◦ Prefer and identify mother’s face ◦ After 8 hours of contact over 4 days ◦ Prefer edges of face such as chin ◦ May be due to attention to movement and contrast Most dramatic gains in visual acuity made between birth and 6 months of age ◦ Acuity reaches about 20/50 By 3 to 5 years, ◦ visual acuity generally approximates adult levels about 20/20  Depth Perception Infants generally respond to depth cues by 6 to 8 months Visual cliff study, Gibson and Walk (1960) ◦ Identified age at which infants have depth perception ◦ Ability to crawl indicated in ability to perceive depth Campos et al. (1970) study ◦ Heart rate increased when infants placed on edge of cliff at 9 months of age ◦ Newly walking infants more afraid of falling off ◦ Different postures involve the brain in different ways and influence infants’ avoidance (Adolph, 2000) Fig. 4-9, p. 85  Development of Perceptual Constancies Perceptual constancy: ◦ The tendency to perceive an object you are familiar with, to be the same even though the sensations produced by the object may differ under various conditions Size constancy ◦ Tendency to perceive the same objects as being the same size even though their retinal sizes vary as a function of their distance ◦ Present in early infancy (Bower, 1974) Shape constancy ◦ Tendency to perceive that the shape of objects remains the same regardless of the retinal image being received ◦ At 4 to 5 months old, infants grasp shape constancy under certain conditions. Development of Hearing 1 month ◦ Infants perceive differences between speech sounds that are similar. ◦ Infants exposed to normal backdrop of moderate noise levels become habituated to them and not likely to awaken unless there is a sharp, sudden noise. 3 ½ months ◦ Can discriminate parent’s voices 18 months ◦ Hearing is similar to adults’ Exposure to native language causes gradual loss of capacity to discriminate sounds that are not in their native language Development of Coordination of the Senses Young infants recognize that objects experienced by one sense are the same as those experienced through another sense. Five-month-old infants look at novel stimulation longer than familiar sources of stimulation. ◦ Infants looked at unfamiliar objects longer than objects they had held in their hands. ◦ This shows a transfer of information from the sense of touch to the sense of vision  The Role of Nature and Nurture Evidence for the role of nature Neonates born with sensory skills and perceptual skills ◦ can see nearby objects, hearing is fine, able to track moving objects, prefer certain kinds of stimuli Sensory and motor changes linked to maturation of nervous system Evidence for the role of nurture Children have critical periods in their perceptual development. ◦ Failure to receive adequate sensory stimulation can result in permanent sensory deficits Health problems with vision in child’s eye where patch is needed extensively can result in permanent visual impairment MOTOR DEVELOPMENT  Motor Development Physical development refers to children’s growth and refinement of motor skills. (children’s ability to use and control their bodies) Gross motor skills – involve use of large muscle groups in the arms, legs and torso. Involve “whole body” movement like walking, jumping, kicking and crawling. Fine motor skills – involve use of small muscle of the hands and fingers. These skills progress as a child’s sensory perception develops. Examples of fine motor movement would be cutting, scribbling, stringing beads. Particularly important for development in self-care activities. development occur as a result of both physical maturity (strength) and brain growth and development.  Motor development follows cephalocaudal and proximodistal patterns and differentiation. Neonates (0-4 weeks old), can lift head up aiding in avoiding suffocation. ◦First, they lift head ◦Then, they lift chest Heads must be supported when held ◦Can hold up head independently between 3 to 6 months old Control of the Hands: Getting a Grip 3 months ◦ Infants make clumsy, swiped movements toward objects ◦ Ulnar grasp 4 to 6 months ◦ Infants are more successful at grasping objects ◦ Can transfer objects back and forth between hands. ◦ Good age for giving rattles, large plastic spoons, mobiles, and other brightly colored hanging toys that are kept out of reach 9 to 12 months ◦ Pincer grasp gives infants ability to pick up tiny objects ◦ Oppositional thumb comes into play 15 to 24 months ◦ Children show progression in stacking ability Locomotion 6 months ◦ Infants roll over, turn from back to stomach ◦ Infants can sit if supported 7 months ◦ Infants usually sit on their own 8 to 9 months ◦ Infants begin to crawl or creep ◦ Standing overlaps with crawling and creeping ◦ May walk with support of adult 11 months ◦ Infants can pull themselves up  Locomotion (cont’d) 12 to 15 months ◦ Walk on their own, earning the name of toddler ◦ Run in bowlegged manner ◦ Fall easily because they are top heavy ◦ Some toddlers fall without notice and get back up ◦ Others cry Toddlers differentiate between shallow slopes and steep ones, choosing to slide or crawl down steep ones Age 2 ◦ Child can climb one step at a time, run well, walk backward, kick a large ball, and jump several inches Motor Development Myelination and differentiation of the motor areas of the cortex must occur to master skills Neonate’s stepping and swimming reflexes ◦ disappear when cortical development inhibits some functions of the lower brain ◦ reappear later, yet differ in quality Effects of training ◦ Early introduction to extensive motor skills training levels off (Arnold Gesell study, 1929) Iranian infants (unlike Hopi children) in orphanage were exposed to extreme social and physical deprivation ◦ They did not overcome motoric retardation (Dennis study, 1960)  Motor Development Motor skill does not develop in a vacuum. Motor development depends on: 1.Individual child factors (physiology, cognition, temperament) 2.Environmental factors (family, home, surroundings, peers) 3.Ecosystem Environment (extended family, neighbourhood, school) 4.Macrosystem Environment ( community, economic system, culture) - Pediatric therapist must consider the layers of influence that build behavior. Motor Development in Children Homework: Read Motor Development chapters 5 & 8, from “Children, Canadian Edition”, Kail & Zolner, 2005. (provided by instructor) - Questions on these chapters will be posted on blackboard, under week #2. We will take up answers next class.