Chapter Five-Module 1Development of the Brain

Chapter Fourteen-Module 1Lateralization & Function

Development of the Brain-Growth and Differentiation of the Vertebrate Brain

Early Beginnings CNS begins to form at two weeks gestation Development of the neural tube (figure 5.2) At birth, brain weighs 350g, at one year

1,000g (figure 5.3) Growth and Development of Neurons

Proliferation-production of new cells Migration-move toward final destination Differentiation-form axons and dendrites Myelination-addition of insulating sheath

Figure 5.2  Early development of the human central nervous systemThe brain and spinal cord begin as folding lips surrounding a fluid-filled canal. The stages shown occur at approximately age 2 to 3 weeks.

Figure 5.3  Human brain at five stages of developmentThe brain already shows an adult structure at birth, although it continues to grow during the first year or so.

Video

Development of the Brain-Neuronal Survival

Determinants of Neuron Survival Must make correct connections Must receive support from nerve growth factor

neurotrophins act in several ways– early in development cause cells to survive and

grow– increase the branching of incoming axons– decrease pain and increase regrowth of damaged

axons apoptosis-programmed cell death that occurs when

connections are not reinforced Competition Among Axons as a General Principle

We produce redundant synapses the most successful axons and combinations survive

Development of the BrainPathfinding Axons

Pathfinding by Axons Chemical Pathfinding by Axons

Example: Weiss and the grafted salamander leg

Specificity of Axon Connections Example: Sperry and the rotated eye of

newt (figure) Chemical Gradients

cell surface molecule chemical attractants (e.g. TOPDV) Neurotrophins

Figure 5.7  Summary of Sperry’s experiment on nerve connections in newtsAfter he cut the optic nerve and inverted the eye, the optic nerve axons grew back to their original targets, not to the targets corresponding to the eye’s current position.

Development of the Brain Fine-Tuning by Experience

Fine-Tuning by Experience Genetic Instruction are “only approximate”

Effects of Experience on Dendritic Branching Enriched environments increase dendritic branching (figure

5.10) & dendritic spine growth (5.11) thus a thicker cortex What is an enriched human environment? Effects?

Generation of New Neurons Can the adult brain generate new neurons? Olfactory cells must…. Why? stem cells in the interior of the brain scientists have observed new cells in hippocampus and

cerebral cortex in monkeys of ages. Possible meaning of new neural development?

Development of the Brain Effects of Experience on Human Brain Structures

Example: music training on temporal lobe development identifying “absolute pitch” and temporal cortex growth

Example: somatosensory cortex (post-central gyrus) in violin players MEG: D5 dipole strength, age of first playing, and control

groups (figure 5.13b)

Combinations of Chemical and Experiential Effects not always a clear 2-stage process of chemical pathfinding

and experiential strengthening

e.g., the identification by lateral geniculate cells of activating retinal neurons (spontaneous embryonic firing)

Development of the Brain The Vulnerable Developing Brain

Fetal Alcohol Syndrome decreased alertness, hyperactivity, varying degrees

of mental retardation, motor problems, heart defects, and facial abnormalities

Fetal Nicotine Exposure low birthweight, SIDS, decreased intelligence,

hyperactivity Fetal Cocaine Exposure

decrease in IQ and language skills

Module 1 Conclusions

Chapter Fourteen- Module 1Lateralization

Lateralization of Function

Some Definitions Lateralization-Division of labor between the two

hemispheres Commissures-Cross-over points of information in the

brain

Corpus Callosum Anterior Commissure Hippocampal Commissure

Figure 14.1  Two views of the corpus callosumThe corpus callosum is a large set of axons conveying information between the two hemispheres. (a) A sagittal section through the human brain. (b) A dissection (viewed from above) in which gray matter has been removed to expose the corpus callosum.

Figure 14.4  The anterior commissure and hippocampal commissuresThese commissures allow for the exchange of information between the two hemispheres, as does the larger corpus callosum.

Visual Connections to the Hemispheres

Visual Field-what is visible at any moment Right visual field-->left half of each retina-->left

hemisphere Left visual field-->right half of each retina-->right

hemisphere Cutting the Corpus Callosum

Sometimes done to treat severe epilepsy Behavior is abnormal only when sensory stimuli are

limited to one side of the body

Figure 14.2  Connections from the eyes to the human brain Route of visual input to the two hemispheres of the brain. Note that the left hemisphere is connected to the left half of each retina and thus gets visual input from the right half of the world; the opposite is true of the right hemisphere.

Split Hemispheres

Competition Soon after surgery you may see competition

between activities on the two sides of the body Hemispheric Specialization

Left Speech Happiness

Detail-oriented Right

Emotional content of speech Recognizes emotions in others Expresses fear and anger Spatial Relationships Music perception

Animation