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Lecture 4

Psychology 2040A/B Lecture Notes - Lecture 4: Blastocyst, Habituation, Middle Ear


Department
Psychology
Course Code
PSYCH 2040A/B
Professor
Laura Reid
Lecture
4

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Physical Development in Infancy
Physical
Motor
Sensory, perceptual
Babies have large heads because brain develops early on
More than other parts of the body
General Patterns of Physical Development
Different parts of the body grow at different rates
Two growth patterns:
-Cephalocaudal trend top to bottom (head to tail)during the prenatal period the
head develops earlier and faster than the lower parts, head takes up 1/4th of the
body and the legs 1/3rd. By age 2, the head accounts for only 1/5th and legs for ½
-Proximodistal trend centre of the body to outward (near to far)during the
prenatal period the head, chest and trunk grow first, then the arms and legs and
finally hands and feet
Eyes and brains earlier than jaws
Trunk first, arms, fingers
Brain Development
Brain Growth Spurt: last 3 months of prenatal development to first 2 years of life
Brain is 75% of adult weight reached by 2 years of age
Brain growth understood by 2 points
1) Microscopic level of individual brain cells
2) Larger level of the cerebral cortex (responsible for the highly developed
intelligence of our species
Neurons
Human brain=100-200 billion neurons (nerve cells) that store and transmit
information
Not tightly packed together, between them are synapses
People can grow new neurons, not a major way things change in the brain

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In the prenatal period, neurons are produced in the embryos primitive neural
tubethen migrate to form major parts of the brain
Neruons send messages to each other by releasing chemicals called
neurotransmitters
Half the brains volume consists of glial cells=support brain cellswhich are
responsible for myelination=coating of neural fibres with an insulating fatty
sheath called myelin sheath=helps travel faster, acts like an insulator
Dendrites=collect messages from other neurons (branches: collect to other
neurons)
Neuronal Development
250 000 neurons “born” each minute during embryonic stage
Present at birth=all you would ever need
When a neuron is “born” determines its eventual location and in turn, its function
Early on: Not actually functioning
Formed during embryonic stage
Result from mitosis
Position
Blastocyst
Special=geographical location in blastocyst
Ectoderm=nervous system
Neural Migration
Genes determine neuronal migration
Migration/location dictates function
Location and function
What its going to do and where
Neuronal Function
Neurons in isolation

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Neurons have potential for any function
Neurons become specialized
-Will develop axons and dendrites
-Will take on a certain function
Start out unspecialized
Develop more fully as they grow
Back of brain=visual information
Communicating with other neurons
Myelinization
Myelin sheath=improves the efficiency of message transfer, coating of neural
fibers with an insulating (insulation for neurons) fatty sheath
Long
Increases rate of transmission of electrical impulses
Continues throughout childhood
Plays a role in more efficient motor control, cognitive processing
Long for myelin coating to develop
Neural Pruning
Hebb’s Rule: “Neurons that fire together, wire together”
Neurons that communicate connections, get stronger and stronger
Half of the neurons in the infants brain will die (and not be replaced) over the first
few years of life
Evolved brains-excess of neurons, more than we need
Ready to receive anything
Brain reacts by firing neurons
Active=sending messages to other neuron
Die offleads to differentiation
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