chapter 8 Flashcards
development of brain and behavior
brain and behavior appear to develop at similar rates
Does the visual system develop slowly?
no, it develops quickly
What part of the brain is the last to develop?
frontal lobes (ability to plan efficiently, organizing daily activities)
Preformation
the idea that a human embryo is an adult miniature
What do early vertebrate species look like?
similar looking primitive head, a region with bumps or folds and a tail
Zygote
consists of a single cell; when a sperm fertilizes an egg
What happens after a zygote forms?
by the 15th day the cell begins to divide forming an embryonic disc
Embryonic disc
formed by several sheets of cells with a raised area in the middle
Neural Plate
primitive neural tissue formed by day 21; occupies part of the outermost layer of the embryonic cells.
Neural Groove
neural plate folds to form this
Neural tube
neural groove curls to form this;
What forms the brain’s ventricles
the open region in the center of the neural tube remains open and matures into the brain’s ventricles and the spinal canal
7 weeks into development
embryo begins to resemble a miniature person
when do gyri and sulci begin to form?
7 months
When do the genitals begin to form?
7th week after conception; they appear identical (indifferent) in the two sexes at this early stage
sexual dimorphism
structural difference between the sexes
60 days after conception
male and female genitals start to become distinguishable
testosterone
stimulates sexual differentiation in male embryos
gonadal (sex) hormones
prenatal exposure acts to shape male and female brains differently because these hormones activate different genes in the neurons of the two sexes
Neural stem cells
lining the neural tube have an extensive capacity for self-renewal. When a stem cell divides it produces two stem cells; one dies and the other lives to again divide
where do neural stem cells live?
line the ventricles forming the subventricular zone
Progenitor cells
precursor cells; develop from stem cells; it migrates and also can divide and produce neuroblasts and glioblasts
neuroblasts
formed from progenitor cells; form neurons
glioblasts
formed from progenitor cells; form glia
subventricular zone
lining of neural stem cells surrounding the ventricles in adults
When do stem cells work?
well into the aging brain
prolactin
neuropeptide that increases in pregnant rats; stimulates the brain to produce more neurons
Gene expression
a formerly dormant gene becomes activated, resulting in the cell making a specific protein.
gene methylaiton
common epigenetic mechanism; a methyl group (CH3) attaches to the nucleotide base cytosine lying next to guanine on the DNA sequence; resulting in the suppression of gene expressoin
does methylation alter gene expression?
yes, it can do so dramatically during development.
what impacts methylation?
prenatal stress can reduce gene methylation by 10 percent
what impacts cellular differentiation?
neighboring cells, chemicals, hormones
stem cell differentiation
a chemical signal must induce stem cells to produce progenitor cells; another chemical signal induces the progenitor cells to produce either neuroblasts or glioblasts and then a last chemical signal induce the genes to make a specific type of neuron/glia
neurotrophic factors
class of compounds that acts to support growth and differentiation in developing neurons and may act to keep certain neurons alive into adulthood
epidermal growth factor (EGF)
stimulates cells to produce progenitor cells
basic fibroblast growth factor (bFGF or FGF-2)
stimulates progenitor cells to produce neuroblasts
Stages of brain development
- cell birth (neurogenesis; gliogenesis)
- cell migration
- cell differentiation
- cell maturation (dendrite and axon growth)
- synaptogenesis (formation of synapses)
- cell death and synaptic pruning
- myelogenesis (formation of myelin)
neurogenesis
rapid formation of neurons
gliogenesis
rapid formation of glia
migration
when cells travel to their correct locations
when is neurogenesis about finished?
after about 5 months of gestation
what is the exception to when neurogenesis is finished?
the hippocampus–> continues to develop new neurons throughout life
teratogens
chemicals that cause malformations
When can the human brain best cope with injury?
early during development; during neurogenesis. More neurons can be made to replace injured ones or perhaps existing neurons can be allocated differently
when does cell migration begin?
shortly after the first neurons are generated and continues for about 6 weeks in the cerebral cortex and longer the hippocampus
how to neurons migrate?
subventricular zone contains a primitive map of the cortex that predisposes cells formed in a certain ventricular region to migrate to a certain cortical location
how do cells know where the different parts of the cortex were located?
radial glial cells; some follow a chemical signal
radial glial cells
path-making cell that a migrating neuron follows to its appropriate destination
how do cortical layers develop?
from the inside out
Maturing neurons
- grow dendrites to provide surface area for synapses with other cells
- extend their axons to appropriate targets to initiate synapse formation
Dendrite development
dendritic arborization (branching) and the growth of dendritic spines
do dendrites grow fast or slow?
slow
do axons develop fast or slow?
fast; about 1000x as fast
why is it good that axons develop faster than dendrites?
axons can contact its target cell before the cell’s dendrites are completely formed –> may play a role in dendritic differentiation and neuronal function
Autism spectrum disorder
range of cognitive symptoms, from mild to severe, that characterize autism; severe symptoms include greatly impaired social interaction, a bizarre and narrow range of interests, marked abnormalities in language and communication and fixed, repetitive movements
growth cone
growing tip of an axon
filopod (filopodia)
process at the end of a developing axon that reaches out to search for a potential target or to sample the intercellular environment
what are the two cues that growth cones are responsive to?
cell-adhesion molecules and tropic molecules
cell-adhesion molecule (CAM)
a chemical molecule to which specific cells can adhere, thus aiding in migration; can attract or repel growth cones
tropic molecules
signaling molecule that attracts or repels growth cones
netrin
member of the only class of tropic molecules yet isolated
thickness of the cortex
becomes thinner in a caudal-rostral (back to front) gradient; probably due to synaptic pruning
how much is typically eliminated during synaptic pruning?
42% of all synapses in the human cortex
neural Darwinism
hypothesis that the processes of cell death and synaptic pruning are, like natural selection in species, the outcome of competition among neurons for connections and metabolic resources in a neural environment
why do neurons die?
because target cells produce neurotrophic factors that are absorbed by axon terminals–> function to regulate neuronal survival. (ex. nerve growth factor). If many neurons are competing for a limited amount of a neurotrophic factor only some can survive
apoptosis
when neurons are deprived of a neurotrophic factor certain genes seem to be expressed–> resulting in a message for the cell to die
does apoptosis account for synaptic pruning from cells that survive?
no
synaptic pruning and language
young infants can discriminate speech sounds of different languages without previous experience, but this ability declines after year 1. synapses encoding speech sounds not normally encountered in an infant’s daily environment are not active simultaneously with other speech-related synapses and thus are eliminated
when does cortex thinning take place?
age 5-20
does the entire brain thin?
NO! major language regions show an increase in gray matter
frontal lobe development
it is especially sensitive to epigenetic influences; the trajectory of frontal lobe development correlates with adult IQ
IQ and plasticity
children who score highest in intelligence show the greatest plastic changes in the frontal lobe over time
when does myelination occur?
begins just after birth and continues until at least 20 years of age
Flechsig myelination hypothesis
earliest myelinating areas control simple movements or sensory analyses, whereas the latest myelinating areas control the highest mental functions
infant movement: after birth
flexing joins of an arm (scooping)
infant movement: 1-3 months
make spontaneous hand and digit movements that consist of almost all the skilled finger movements of an adult; motor babbling; movement toward objects
infant movement: 8-11 months
grasping becomes more sophisticated as in the pincer grasp
meylination and motor movements
a group of axons from motor-cortex neurons myelinate at about the same time that reaching and grasping with the whole hand develop. Same thing with neurons that control finger movements and the pincer grasp
Language development
- 12 months: start to form vocab (5-10 words; doubles over next 6 months)
- 2 years: vocab ranges from 200-300 words
- 3 years: 1000 words and simple sentences
- 6 years: 2500 words and can understand 20,000-50,000 words
thickening of broca’s area
the left inferior frontal cortex–is associated with enhanced phonological processing (understanding speech sounds)
Jean Piaget
stages of development
object permanence
understanding that objects continue to exist even when out of sight
conservation of liquid volume
develops by age 7; the understanding that the amount of liquid remains constant despite the difference in appearance
Piaget’s stages of cognitive developemtn
- sensorimotor
- preoperational
- concrete operational
- formal operational
stage 1: sensorimotor
birth to 18-24 months; experiences the world through senses and actions (looking, touching, mouthing); object permanence and stranger anxiety
stage 2: preoperational
2-6 years; represents things with words and images but lacks logical reasoning; pretend play, egocentrism, mathematical transformations
stage 3: concrete operational
7-11 years; thinks logically about concrete events, grasps concrete analogies and performs arithmetical operations; conservation, mathematical transformations
stage 4: formal operational
12+ years; reasons abstractly; abstract logic, potential for mature moral reasoning
growth spurts
sporadic period of sudden growth that lasts for a finite time
when do growth spurts occur?
between 3-10 months (30% increase in brain weight); age 2-4; 6-8; 10-12; 14-16+
what leads to increase in brain weight?
brain growth takes place without a concurrent increase in the number of neurons SO probably due to glial cells, blood vessels, myelin and synapses
connection between brain and behavior development
don’t confuse correlation with causation
brain plasticity
brain is plastic in response to external events in addition to internal events (hormones, injury, genetic mutations)
stimulating environments
Hebb– reasoned that people reared in stimulating environments will maximize their intellectual development whereas people raised in impoverished environments will not reach their intellectual potential
Tactile stimulation
important for bonding with caregivers & stimulates brain development
brains of animals from complex environments
larger, have more synapses, have more and larger astrocytes,
Exposure to music
early exposure alters the brain–> perfect pitch
chemoaffinity hypothesis
proposal that neurons of their axons and dendrites are drawn toward a signaling chemical that indicates the correct pathway; each cell has an identifiable biochemical label
neuronal placement
is activity dependent
amblyopia
condition in which vision in one eye is reduced as a result of disuse; usually caused by a failure of the two eyes to point in the same direction
critical period
developmental “window” during which some event has a long-lasting influence on the brain; often referred to as a sensitive period
imprinting
process that predisposes an animal to form an attachment to objects or animals at a critical period in development
deprivation and brain development
depriving young animals specifically of visual input or of maternal contact has devastating consequences for their behavioral development and presumably for their brain development
Harlow & monkeys
separated baby monkeys from their mothers shortly after birth and raised them in individual cages. They were unable to establish normal relations with other animals in adulthood
Androgen
class of hormones that stimulates or controls masculine characteristics; released during a brief period in the course of prenatal brain development for masculinization
masculinization
process by which exposure to androgens (male sex hormones) alters the brain, rendering it identifiably male
estrogens
variety of sex hormones responsible for the distinguishing characteristics of the female
testosterone
changes the structure of cells in many regions of the cortex, with diverse behavioral consequences that include influences on cognitive consequences
experiences for males and females
can impact the brain differently due to the mediating influences of gonadal hormones
gonadal hormones and brain developemtn
gonadal hormones alter the basic development of neurons, shape the nature of experience-dependent changes in the brain, and influence the structure of neurons throughout our lifetimes.
mental disorder onset
peak age 14
why do many mental disorders occur during adolescents?
neurobiological and associated behavioral changes linked with the period of adolescence are designed to optimize the brain for challenges that lie in adulthood but the brain’s plasticity can also make it vulnerable to psychopathologies that can last for the rest of their life
drugs and brain development
prenatal exposure to drugs (of all sorts) likely impact brain development; increase in later drug use
spina bifida
condition in which the genetic blueprint goes awry and the neural tube does not close completely–leads to incompletely formed spinal cord. serious motor problems
anencephaly
failure of the forebrain to develop; front end of the neural tube (forms brain) does not close properly
brains of children with ID
stunted dendrite growth, sparse spines
genetic abormality
error of metabolism chromosomal abnormality; phenylketonuria (PKU), down syndrome
abnormal embryonic development
exposure to a toxin; fetal alcohol syndrome (FAS)
prenatal disease
infection; rubella, retardation
birth trauma
anoxia (oxygen deprivation); cerebral palsy
malnutrition
abnormal brain development; kwashiorkor
environmental abnormality
sensory deprivation; children in Romanian orphaneges
