Biological Psychology-Lecture Slides 09-Psychology-Andrew Weeks, Slides of Biological Psychology

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9.1 Phases of Neurodevelopment

9.2 Postnatal Cerebral Development in Human Infants

9.3 Effects of Experience on the Early Development, Maintenance, and Reorganization of Neural Circuits

9.4 Neuroplasticity in Adults

9.5 Disorders of Neurodevelopment: Autism and Williams Syndrome

Topics

The Case of Genie

Illustrates the impact

of severe deprivation

on development

• At age 13, Genie weighed 62 pounds and could not chew solid food
• Beaten, starved, restrained, kept in a dark room, denied normal human interactions
• Even with special care and training after her rescue, her behavior never became normal

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Phases of Development

 Ovum + sperm = zygote

 Developing neurons accomplish

these things in five phases

 Induction of the neural plate

 Neural proliferation

 Migration and aggregation

 Axon growth and synapse

formation

 Neuron death and synapse

rearrangement

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Neural Proliferation

• Neural plate folds to form the

neural groove, which then fuses

to form the neural tube

• Inside will be the cerebral

ventricles and neural tube

• Neural tube cells proliferate in

species-specific ways: three

swellings at the anterior end in

humans will become the

forebrain, midbrain, and hindbrain

• Proliferation is chemically guided

by the organizer areas – the roof

plate and the floor plate

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• Once cells have been created through

cell division in the ventricular zone of

the neural tube, they migrate

• Migrating cells are immature, lacking

axons and dendrites

igration

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Migration

FIGURE 9.3: Somal Translocation and Glia-Mediated Migration

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Neural Crest

• A structure dorsal to the

neural tube and formed from

neural tube cells

• Develops into the cells of the

peripheral nervous system

• Cells migrate long distances

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Axon Growth and Synapse Formation

• Once migration is complete

and structures have formed

(aggregation), axons and

dendrites begin to grow

• Growth cone – at the

growing tip of each

extension, extends and

retracts filopodia as if finding

its way

• Chemoaffinity hypothesis –

postsynaptic targets release

a chemical that guides

axonal growth, but this does

not explain the often

circuitous routes often

observed

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Axon Growth and Synapse Formation

• Mechanisms underlying axonal growth are the same across species
• A series of chemical signals exist along the way – attracting and repelling
• Such guidance molecules are often released by glia
• Adjacent growing axons also provide signals

FIGURE 9.5: Sperry’s classic study of eye rotation and regeneration.

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Synapse Formation

Formation of new synapses:

• Depends on the presence of glial

cells

• High levels of cholesterol are

needed—supplied by astrocytes

• Chemical signal exchange

between pre- and postsynapctic

neurons is needed

• A variety of signals act on

developing neurons

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The human brain

Neuron Death and Synapse Rearrangement

• ~50% more neurons than are needed are produced – death is normal
• Neurons die due to failure to compete for chemicals provided by targets: - The more targets, the fewer cell deaths - Destroying some cells increases survival rate of remaining cells - Increasing number of innervating axons decreases the proportion that survives

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• Neurons that fail to establish correct connections are particularly likely to die
• Space left after apoptosis is filled by sprouting axon terminals of surviving neurons
• Ultimately leads to increased selectivity of transmission

Life-Preserving Chemicals

FIGURE 9.8: The effect of neuron death and synapse rearrangement on the selectivity of synaptic transmission

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Postnatal Cerebral Development in Human Infants

• Postnatal growth is a

consequence of:

• Synaptogenesis
• Myelination – sensory areas and then motor areas. Myelination of prefrontal cortex continues into adolescence
• Increased dendritic branches
• Overproduction of synapses

may underlie the greater

plasticity of the young brain