Introduction to Neuroscience

Dr Claire Gibson

School of Psychology, University of Leicestercg95@le.ac.uk

PS1000

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1. Functional Neuroanatomy – The Nervous System and Behaviour

2. Development and Plasticity of the Nervous System

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Development of the NS

4 main stages1. Cell proliferation2. Migration3. Differentiation4. Synaptogenesis5. Neuronal cell death6. Synapse rearrangement7. Myelination

….more detailed 7 stages = PS2014/8

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1. Cell Proliferation• 250,000 new cells per minute• Neurogenesis = production of new nerve cells

• Proliferation occurs in the ventricular zone (cells then migrate to final destination)

• Nerve cells themselves do not divide• The cells that produce neurons divide (via mitosis) and =

layer of cells within the ventricular zone• Eventually some cells migrate away from ventricular

zone and begin differentiating into either a neuron or glia cell.

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• Historical opinion - at birth.• But, the human brain weight increases

following birth– simply due to growth in neuronal size, dendrite

branching, increased myelin ???

• NO - Neurogenesis occurs even in adulthood• Neurogenesis is sensitive to experience

– Learning enhances neurogenesis– Social isolation reduces neurogenesis

1. Cell Proliferation – when is it complete?

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• Newly formed neurones migrate from ventricular zone to their final destination

• Radial glial cells• Failure in mechanisms of

migration = behavioural disorders• Cell adhesion molecules (CAMs)

– Promote the adhesion of developing elements of the NS

– Guide migrating cells and growing axons

2. Migration

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3. Differentiation

• Cells reach their final destination – begin to express particular genes

• These enable cells to take on characteristics of a particular neuronal type

• PS2014/8

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4. SynaptogenesisCells undergo extensive growth of axons and dendrites = process

outgrowth and proliferation of synapses (i.e. synaptogenesis)

• Growth cones• Filapodia and lamellipodia – respond to the environment

and pull the growth cone in a particular direction• Chemoattractants• Chemorepellants

• Synaptogenesis occurs rapidly on dendrites and dendritic spines

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5. Neuronal cell death

• Normal part of development

• PS2014/8

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6. Synapse rearrangement

• Not simply elimination• Involves loss of some and formation of others• Human cerebral cortex = net loss of synapses

from late childhood until mid-adolescence

• What determines which synapses are kept and which ones are lost?– Neural activity– Neurotrophic factor = a target-derived chemical that

acts to ‘feed’ neurones

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Development of the NS

• Due to the interaction of intrinsic and extrinsic factors

• Intrinsic (i.e. genes) – originate from within the cell itself

• Extrinsic – originate from outside the developing cell e.g. nutrients, experience

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Genes are the intrinsic factors that influence NS development

• Genome (genotype) • The sum of all the intrinsic genetic information that an

individual possesses• Determined at the moment of fertilisation• Remains constant throughout our lives

• Phenotype• The sum of all the physical characteristics that make up an

individual• Changes constantly as we mature and age• Determined by the interaction of genotype and extrinsic factors

(including experience)

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• So, will two identical twins with identical genotypesa)Have the same phenotype? YES/NO

b)Behave exactly the same? YES/NO

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How does experience modify the NS?

• An individual’s experience during development alters many aspects of behaviour, brain anatomy and neurochemistry

• Much of the change resulting from experience involves reorganisation

• Reorganisation = a shift in connections that changes the function of an area of the brain

• E.g. blind people who read Braille, space in the brain devoted to the index finger increases

• E.g blind people who excel at sound localisation have recruited the unused visual area of their brain to aid in sound localisation

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The ‘plastic’ brain

• So, if experience can ‘reorganise’ the brain = the brain is described as being plastic

• Plasticity = the lifelong ability of the brain to reorganise neural pathways based on new experiences

• Why is this important?• To enable us to learn• As an adaptive mechanism to compensate for lost function

and/or to maximize remaining functions in the event of brain injury.

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Damage and recovery to the CNS

• Scientists are interested in the development of the NS– Hope to find clues about how to repair the NS

when it is damaged by injury, disease or developmental error

– PS2014/8

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Summary

• Neurogenesis, migration, differentiation, synaptogenesis, neuronal death, synapse rearrangement, myelination

• Intrinsic and extrinsic factors

• Role of experience