Motor Development - PowerPoint PPT Presentation

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Motor Development

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Life span motor development – PowerPoint PPT presentation

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Title: Motor Development


1
AFP/Getty Images
  • The Genetics, Evolution, and Development of the
    Human Brain

2
Humans Have 23 Pairs of Chromosomes
3
Major Principles of Genetics
  • DNA sequences, or genes, provide instructions for
    producing proteins.
  • Ribosomes "read" DNA sequences that have been
    transcribed onto RNA in order to construct
    proteins.
  • Alternative versions of a gene, or alleles, may
    be dominant or recessive.

4
Genes Direct Protein Synthesis
5
The Roles of Heredity and Environment
  • Comparisons of identical twins and fraternal
    twins.
  • Adoption studies.
  • Identical twins raised either apart or together
    are very similar, whether the correlation for a
    particular trait is high or low.

6
Lifespan Development
Pascal Goetgheluck/Photo Researchers, Inc.
7
Blastocyst
8
Early Differentiation
  • Within the first week following conception, the
    human embryo has divided into three germ layers
  • Ectoderm
  • Mesoderm
  • Endoderm
  • Inducing factors differentiate the ectoderm layer
    into skin and nervous tissue.
  • The neural tube will be retained in the mature
    brain as the ventricle system and central canal
    of the spinal cord.

9
The Closing of the Neural Tube
10
Neural Tube Related Birth Defects
Anterior neural pore
failure to close anencephaly
Posterior neural pore
failure to close spina bifida
11
Overview of Neural Development
  • Neurogenesis
  • Migration
  • Differentiation
  • Synaptogenesis
  • Apoptosis
  • Myelination
  • Refinement of synapses

12
Neurogenesis and Migration
  • New neural cells are produced in the ventricular
    zone lining the neural tube.
  • Some daughter cells remain in the ventricular
    zone and continue to divide.
  • Other daughter cells migrate away from the
    ventricular zone along radial glia.

13
Neurogenesis
14
Migration
15
Differentiation
  • Daughter cells differentiate into neurons or
    glia.
  • The neural tube differentiates in two directions
  • along the rostral-caudal axis.
  • between the dorsal and ventral halves.
  • Many genes, inducing chemicals, and types of
    input responsible for differentiation have been
    identified.

16
Synaptogenesis
  • Growth cones respond to the chemical and physical
    properties of the extracellular environment in
    order to reach their destinations.
  • Once axons and dendrites are in place, both pre-
    and postsynaptic structures influence synaptic
    development.
  • The identity of a cell's major neurotransmitter
    substance appears to be influenced by the
    postsynaptic neuron.

17
The Growth Cone
From Bridgman, P.C. and Dailey, M.E., The
organization of myosin and actin in rapid frozen
nerve growth cones, Journal of Cell Biology,
108, pp. 95109
18
Growth Cones Respond to External Cues
19
A Synapse Is Formed
20
Apoptosis
  • Significant numbers of new neurons die during the
    development process.
  • Neurons appear to compete for nerve growth
    factors, and those that fail to obtain this
    stimulation die.
  • Synapses follow a similar pattern of
    overproduction followed by "pruning."

21
Visual Synapses Peak at 1 Year of Age
22
Myelination
  • Myelination occurs from the spinal cord rostrally
    towards the forebrain.
  • Sensory systems are myelinated before motor
    systems.
  • Although the majority of myelination occurs very
    early in childhood, human myelination is not
    complete until about the age of 30 years.

23
Experience Affects Development
  • In some cases, the ability to rearrange synapses
    is limited to a critical window, while in other
    systems, plasticity continues throughout the
    lifespan.
  • Examples of systems with critical windows
  • Vision
  • Language
  • Effects of an enriched environment
  • Imprinting

24
Humans Need Social Interaction
Cynthia Johnson/Getty Images
25
Ending a Critical Period
  • Although we dont know exactly why a critical
    period ends, several hypotheses appear promising.
  • Axon growth may end in an area.
  • Synapses may mature.
  • The presence or absence of neurotrophins may
    influence plasticity.

26
Disorders of Development
  • As the neural tube closes early in development,
    mistakes may occur, leading to spina bifida and
    anencephaly.
  • Genetic disorders affecting development include
    trisomy 21, or Down syndrome, fragile X and
    phenylketonuria.
  • Environmental toxins, including alcohol, tobacco
    and other legal and illegal substances, can
    interfere with the normal course of development.

27
Fetal Alcohol Syndrome May Produce Physical and
Intellectual Abnormalities
Courtesy Dr. Sterling K. Clarren
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