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Chapter 05: Development & Plasticity of the Brain
 

Chapter 05: Development & Plasticity of the Brain

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Growth and differentiation of the brain as well as brain damage and recovery.

Growth and differentiation of the brain as well as brain damage and recovery.

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    Chapter 05: Development & Plasticity of the Brain Chapter 05: Development & Plasticity of the Brain Presentation Transcript

    • Development of The Brain
    • Growth of the Brain
      • CNS Begins Forming in the Embryo at About 2 Weeks
      • The Neural Tube forms around a fluid-filled cavity
      • Eventually it sinks under the skin & develops into the hindbrain, midbrain, & forebrain
      • The fluid-filled cavity becomes the central canal & the 4 ventricles
    • Neurogenesis
      • 5 Steps in Neuron Development
      • Proliferation
      • Production of New Cells
      • Migration
      • Movement of Primitive Neurons & Glia to Final Destination
      • Differentiation
      • Neurons Develop Axons & Dendrites
      • Myelination
      • Glial Cells Produce Myelin Sheaths Around Axons
      • Synaptogenesis
      • Formation of Synapses
    • Neuronal Survival
      • Nerve Growth Factor
      • Promotes Neuronal Survival
      • Axons not Receiving Enough NGF Degenerate & Die (Apoptosis)
      • Neurotrophin
      • NGF-like Chemical the Promotes Neuronal Survival Activity
      • Work in Several Ways:
      • Prevent Apoptosis Early in Development
      • Increases Axonal Branching
      • Increases Regrowth of Axons after Damage
    • Developing Nervous System
      • Developing Nervous System Produces 2-3X as Many Neurons as Needed
      • Allows for Errors to be Corrected
      • Compensates for Unpredictable Body Size Variations
    • Competition Among Axons
      • Postsynaptic Cells Strengthen Synapses of Some Cells & Weaken Others
      • Neural Darwinism
      • During development, synapses form randomly before a selection process keeps some & rejects others
      • Synapse formation is also influenced by chemical guidance & trophic factors
      Signalling Molecules >
    • Fine-tuning by Experience
      • Plasticity of the Brain
      • The brain can redesign itself (within limits) through experience
      • Experience Creates Dendritic Branches
      • Enriched environments create more dendrites and improved performance
      • Exercise releases neurotrophins
      • Generation of New Neurons
      • Adult vertebrate brain develops new neurons
      • Stem cells can form new glia or neurons
    • Effects of Experience
      • Practice
      • Practice makes one more adept at a particular skill
      • Brain changes identified with expertise at a skill
      • Chemical & Experiential Effects
      • 2 stage process for making synaptic connections
      • 1. Axons find approximate targets by following chemical gradients
      • 2. Experience strengthens or discards some connections
      • Exceptions:
      • Some axons produce spontaneous action potentials when reaching destination which are important for deciding what synaptic connections are appropriate in some areas of the brain
    • Brain Growth
      • Human Brain is Similar to Other Species
      • Nearly all neurotransmitters found in the human brain are found throughout the animal kingdom
      • Ion channels are much the same in all other species & bacteria
      • Brain structures are in same locations & have similar functions
      • Size
      • The human brain is larger than most mammals, but smaller than whales, dolphins, & elephants
    • The Primate Brain
      • Primates Have a Larger Cerebral Cortex in Comparison to the Brain of Insects
      • Some Differences in Brain Size are Due to the Way of Life
      • Development of Any Brain Depends on 2 Factors:
      • How long the embryonic development of the brain lasts
      • The number of new neurons produced per day
    • Vulnerability of the Developing Brain
      • Developing Brain is Vulnerable to Malnutrition, Toxic Chemicals, & Infections
      • Fetal Alcohol Syndrome
      • Decreased alertness, hyperactivity, facial abnormalities, mental retardation, motor problems, & heart deficiencies
      • Cocaine Exposure
      • Lower IQ scores & decreased language skills
      • Cigarette Exposure
      • Low birthweight. SIDS, ADHD, intellectual deficits, impaired immune system, delinquency & crime later in life
    • Causes of Brain Damage
      • Closed Head Injury
      • Sharp blow to the head that does not actually puncture the brain
      • Most common cause of brain damage in young people
      • Damages the brain because of rotational forces driving brain tissue against the inside of the skull
    • Causes of Brain Damage
      • Stroke
      • Strokes destroy neurons by killing cells in the immediate vicinity of the stroke immediately and those in the surrounding area die over the next few days
      • Ischemia: Most common type of stroke caused by loss of blood flow due to a clot or other obstruction
      • Hemmorage: Bleeding due to rupture of an artery
    • Recovery from Brain Damage
      • The Kennard Principle
      • Recovery from brain damage earlier in life is better than the same damage later
      • Exceptions: Younger brains are more vulnerable to forces that interfere with its development & organization
      • In essence, the elderly do not recover as well as younger adults
      Normal Exercising Damaged Limb
    • Mechanisms of Recovery
      • Some Behavioral Improvement Seen After Damage
      • Due to structural changes in the surviving neurons & learned changes in behavior
      • Learned Adjustments in Behavior
      • Much of the recovery after damage is learned
      • Learn to make better use of unimpaired abilities
      • May also learn to use that at first appear lost but were only impaired
    • Mechanisms of Recovery
      • Diaschisis
      • Decreased activity of surviving neurons after other neurons are destroyed
      • Drugs may sometimes improve behavioral deficits
      • Regrowth of Axons
      • Damaged axons rarely regenerate in CNS
      • Myelin in PNS secretes chemicals stimulating growth
    • Mechanisms of Recovery
      • Collateral Sprouting
      • Newly formed branches from an uninjured axon attaching to a synapse vacated when the original axon was destroyed
      • Reorganization of Sensory Representations
      • (Phantom Limb) Amputation of a limb results in axonal sprouts forming not only in the cortex but also in the spinal cord, brainstem, & thalamus
    • Therapies
      • Behavioral Interventions
      • Consists mainly of supervised practice of impaired behaviors
      • Drugs
      • New drugs aided recovery with animals: Mimodipine, gangliosides, & pregesterone
      • Brain Grafts
      • Replacing dead cells with healthy donor cells