2008 Wiring the brain

2008 Wiring the brain - Number of cells in the nervous...

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Number of cells in the nervous system • Of the order of 100 billion (10 11 ) nerve cells • At least that many more glial cells responsible for making myelin, buffering ions, etc. • Each cell receives and makes up to thousands of synapses, i.e., contact many but not all the other cells in the brain. • Achieving specificity of connections is a major problem for development and recovery of function after injury or degeneration.
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Brain size/cell size • Brain volume (incl spinal cord)= 15,000cc= 15,000* 10 12 μm 3 • Number of cells in brain= 100 billion= 10 11 • Average volume/ cell= 15000*10 12 *10 -11 = 150,000 μm 3 • If the cell were a sphere, it would have a diameter of 62 μm [Volume (sphere)= 4/3 π (d/2) 3 ] • In fact most of the volume is in the axon and dendrites so that the average soma volume is considerably smaller: <10 μm 3
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Wiring of the brain is crucial for brain function Hard wiring: connectivity Sensory input from peripheral organs Motor output to muscles Reflex patterns connecting sensory and motor systems: stretch reflex, flexor reflex, pupillary reflex Connections between different processing regions, e.g., cerebellum and motor cortex Failure for accurate wiring to occur leads to developmental deficits: motor, sensory, cognitive, etc.
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Stretch reflex pathway
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Intricate connections between cells in stretch reflex pathway
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Limb withdrawal
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Limb withdrawal leads to extension of the opposite limb to maintain balance
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Precise wiring of sensory pathways from vibrissae
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Precise wiring of the visual system to achieve binocular vision: input from a given point in space through both eyes must project to same place in the brain
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When wiring from the retina to the brain is reversed…rotate the eye after initial projections are established
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Amputation can lead to loss of precise wiring because of reorganization
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Organism begins as a single cell. How do specific connections develop
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This note was uploaded on 07/15/2009 for the course BIO 208 taught by Professor Lorne-mendell,s during the Fall '08 term at SUNY Stony Brook.

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2008 Wiring the brain - Number of cells in the nervous...

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