BIOL125 Lecture Notes - Lecture 15: Long-Term Memory, Neurofibrillary Tangle, Prefrontal Cortex
8 Jun 2018
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Changes in Lifespan
• 3.50. Anatomical changes with aging
o The adult human brain
• 100 billion neurons
• 20 billion in the cerebral cortex
• Each cortical neuron has on average 7000 synaptic connections
• Initially development of CNS is dependent on
▪ Recruitment of embryonic cells to form neural plate
▪ Connections formed between specific types of nerve cells
▪ Differentiation of brain regions
• Changes occur across the life span, at critical periods or times when brain is
sensitive to change
• Early development
▪ NS develops from 3rd week of gestation
▪ Cells differentiate from early embryonic cells and process continues
throughout adulthood
▪ Embryonic development involves overproduction of glial cells and
neurons and if no longer useful they die
▪ Each region of the brain undergoes critical or sensitive periods at
different ages
▪ Most critical period for CNS development is birth - 1 year
• Most vulnerable to change
• Influences the NS structurally and functionally
• Birth to first year
▪ Increase in growth - increases to more than half the size of an adult
brain during the first year
▪ Increased myelination within the brain
▪ Increase in neuronal size
▪ Development, particularly in cerebral cortex, may emerge out of
environmental demands and the need to solve problems (tasks)
▪ Consequently, experiences can alter neural networks, and more
complex experiences lead to increasing complexity of neural structures
▪ 3 phases of development through to adulthood
• Neural division and migration
• Includes neurogenesis, proliferation, migration and folding
• From gestation (embryo) to foetal mid term
• New neurons created at rate of 250000/minute
• Migrate towards brain surface
• Not enough of them to cause folding by mid term
• 3rd week of gestation
• Neurulation starts -> ectoderm -> neural plate -
> neural groove -> neural tube
• By end of 4th week
• precursors of spinal cord and brain are evident
• 5th week
• Developing neurons grow out of spinal cord,
make permanent contact with developing
skeletal muscles and structures that will
become the skin
• 8th week
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• 2 distinct hemispheres, cerebral cortex begins
• Somatic system begins first and autonomic NS
development lags behind by 1-2 weeks
• Neuronal connectivity
• From week 12 to 2 years
• Week 12
• Thickening of cortex and cortical layers form
• Many new connections formed and cortex expands
• Mid-term
• Cortex makes contact with rest of CNS
• Folding commences Gyrification/primary sulci
• 6 months
• Brain myelination commences
• Synaptogenesis and synaptic pruning
• Normal processes that occur throughout life
• Nervous tissue has plasticity
• Synaptogenesis - expanding/new connections which
decreases over time
• Commences in 6 month of foetus
• Greater rate after birth due to learning and
maturation
• Synaptic pruning - clipping back, remodelling unused
pathways - customising neural tissue base on experiences
• Commences around birth
• Continues until post puberty
• Influences by environmental factors
• Associated with learning
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Document Summary
Anatomical changes with aging: the adult human brain, 100 billion neurons, 20 billion in the cerebral cortex, each cortical neuron has on average 7000 synaptic connections. Influences the ns structurally and functionally: birth to first year. Increase in growth - increases to more than half the size of an adult brain during the first year. Somatic system begins first and autonomic ns development lags behind by 1-2 weeks: neuronal connectivity. From week 12 to 2 years: week 12, thickening of cortex and cortical layers form, many new connections formed and cortex expands, mid-term, cortex makes contact with rest of cns. Folding commences gyrification/primary sulci: 6 months, brain myelination commences. Synaptogenesis and synaptic pruning: normal processes that occur throughout life, nervous tissue has plasticity. Synaptogenesis - expanding/new connections which decreases over time: commences in 6 month of foetus, greater rate after birth due to learning and maturation.
