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Neurodevelopment ((Critical periods (now sensitive periods) period when…

- - - - Males
        SRY Gene (sex determining region of Y chromosome)
        causes primitave gonads to become testes
        once formed testes, produce testosterone
        testosterone causes wolffian ducts to become vas deferens and seminal vesicles
        MIH (Mullerian inhibiting Hormone) causes degeneration of mullerian ducts (oviducts, uterus, upper vagina)
      - Hormones
        organisation and activation effects
        Androgens (testosterone) determine masculinisation of fetus
        (external genetalia & brain) default animal is female
        Testosterone sexual behaviour
        Estrogens predominates in females
        Hormomes reach distant targets
        
        Organising effects
        rats - shortly before, and after birth
        Humans - 3rd 4th month before birth, also in puberty
        Activating effects
        any time of life when hormone is present
        temporarily activates response
        
        Female rats injected w/ T after birth exhibit male behaviour
        (mounting instead of lordosis)
        Male rats without androgen receptors (or T antagonists)
        female typical behaviour
        Alcohol interferes with T effects
        substances which mimic E (e.g. BPA)
  - - - Regrowth of axons
        Better in young brains
        better in PNS than in CNS/brain
        Damaged cell bodies not replaced
        recovery involves collateral sprouting
        
        Collateral Sprouting
        new branching formed by non-damaged axons
        attach to vacant spots on dendrites and cell bodies
        cells secrete neurotrophins which allow collateral sprouting
        very fast in first 2 weeks #
      - reorganisation
        monkey finger amputated
        somatosensory cortex reorganised
        other fingers became more sensitive #
    - - Hebb(1947)
        rats in enriched environment vs lab (impoverished)
        better to solve mazes
        thicker cortex, more dendritic branching
        enhancement due to physical activity
        dendritic branching improved ability to learn
      - Adaptation
        Blind since infancy = enhanced tactile and auditory
        deaf people better tactile & vision
        
        Musicians
        temporal cortex of professionals 30% larger right hemisphere
        thicker grey matterin hand control and vision for piano
        larger postcentral gyrus right hemisphere (movement left hand string control)
  - - - time to make decisions = less impulsive
        Peers affect ability
      - prefrontal cortex immature (decision making)
        Nucleus Accumbens developed (pleasure & reward)
        compared to children & adults
        less responsive to small rewards, more sensitive to large
      - Antisaccade task
        look away from powerful attention-grabber
        Children can't do this well
        ADHD can't do this
        gradually improves during teenage
        Adolescents can perform well, but more effort
      - Increased synaptic pruning - reorganising
        starting from the back - caudal to rostral
        increased myelination
        second phase of 'use it or lose it'
        environment important
        occurs faster in girls than boys
    - - Alzheimer's
        severe and rapid dementia
        Genetic component
      - age-associated memory impairment (AAMI)
        less severe cognitive decline
        seen in general population
        
        No issues with:
        Implicit memory tasks - subconscious learning
        short-term memory tasks - repeating lists of words
        recognition memory tasks - recognise stimulus from large group stimuli
        
        issues with:
        free or cued recall
        recall of original context (know him from somewhere)
        prospective memory tasks (carry out task in future)
        Working memory tasks - recall words in order
  - - - Not produced readily in cortex
        controversial
        (exceptions maybe folling injury or stroke)
        Rather reorganisation
- - - - Brain weight
        At birth - 350g
        1st year - 1,000g
        Adult - 1,200 - 1,400g
  - - - At destination, neurons (neuroblasts) differentiate
        stem cells acquire charecteristics of cells around it if implanted early (Parkinsons)
        grow axon and then later, dendrites
        dendritic arborisation (branching)
        Dendrtitic spines grow
    - - after differentiation, synapses between neurons form
        occurs throughout life (slows down with age)
        form new connections and discard old (synaptic pruning)
        Growing end of axon called growth cone
        develop filopodia which make contact with target cell
        growth cones attracted to chemical signals
        Cell adhesion molecules (CAM)
        Tropic molecules (attract or repell growth cones)
        
        pathfinding
        when axons reach target, form many synapses
        more neurons & synapses than are needed
        Nerual Darwinism - successful connections kept, others lost
    - - migrate by
        chemical signals (Cytokines & immunoglobulins)
        physical support provided by radial glia
        from inside to outside
        form layers (I - VI)
    - - protiens secreted by target cells promote growth (survival signals)
        Neurotrophic factors:
        Nerve growth Factor (NGF)
        Brain derived neurotrophic factor
        if axon does not recieve survival signal (neurotrophic factor) it dies
        apoptosis - programmed cell death (PCD)
        
        Apoptosis
        Doesn't cause damage to brain
        Necrosis
        explosive, after trauma
        damages other cells
        
        active communication with other neurons needed to strengthen synapses
        Hebbian learning
        Dendritic branches not fixed - extend, retract, disappear
        Dendritic Spines also appear and disappear
        Related to learning and experinece
    - - at peak, 250,000 neurons born a minute
        neural tube lined with stem cells
        Neuroblasts or glioblast cells
        migrate out of ventricular zone
    - - Produced by glia
        fatty sheath covering axons
        speeds up transmission of nerual impulse
        occurs back to front
        spinal chord (Schwann cells)
        hindbrain (oligodendroglia)
        midbrain
        forebrain
        slow process
        occurs for decades
        18 years to finish
        early to mid 20s for prefrontal cortex
        
        Whole Schwann cell in PNS
        just feet/legs of oligodendroglia