Hockenbury Discovering Psychology 5th txtbk

Development During Infancy and Childhood375ForebrainMidbrainHindbrainSpinal cordForebrainMidbrainHindbrainFigure 9.2 The Sequence of Fetal BrainDevelopment The human brain begins asa fluid-filled neural tube at about threeweeks after conception. The hindbrainstructures are the first to develop, followedby midbrain structures. The forebrainstructures develop last, eventuallycoming to surround and envelop the hindbrainand midbrain structures.(a) 3 weeks (in utero)(b) 11 weeks (in utero)ForebrainMidbrain (hidden)Hindbrain(c) at birthDuring the final two months of the fetal period, the fetus will double in weight,gaining an additional three to four pounds of body fat. This additional body fat willhelp the newborn adjust to changing temperatures outside the womb. It alsocontributes to the newborn’s chubby appearance. As birth approaches, growthslows and the fetus’s body systems become more active.At birth, the newborn’s brain is only about one-fourth the size of an adult brain,weighing less than a pound. After birth, the neurons grow in size and continue todevelop new dendrites and interconnections with other neurons. Myelin forms onaxons in key areas of the brain, such as those involved in motor control. Axons alsogrow longer, and the branching at the ends of the axons becomes more dense. Butthe process of neural development has only begun. The development of dendritesand synapses, as well as the extension of axons, continues throughout the lifespan.Development During Infancy and ChildhoodKey Theme• Although physically helpless, newborn infants are equipped with reflexesand sensory capabilities that enhance their chances for survival.Key Questions• How do the senses and the brain develop after birth?• What roles do temperament and attachment play in social and personalitydevelopment?• What are the stages of language development?The newly born infant enters the world with an impressive array of physical andsensory capabilities. Initially, his behavior is mostly limited to reflexes that enhancehis chances for survival. Touching the newborn’s cheek triggers the rooting reflex—