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Neurons And Glia (The Building Blocks Of The Brain) Notes

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Lecture 5 Neurons and glia are the building blocks of the brain

Structure of neurons o General
 Electrically excitable, use electricity to relay messages
 Polarised (dendrites- input; axons- output)
 Terminally differentiated (don't divide- postmitotic)

• When neurons die, don't produce more. Fewer when die than born
 Actual CNS neuron: axon length >0.5m
 In peripheral nervous system= longer o Structural classes of neurons
 Polarity refers to number of processes coming from the cell body (i.e. dendrites and axons)
 UNIPOLAR

• E.g. Dorsal root ganglion sensory neuron (primary afferent)
 BIPOLAR

• E.g. Retinal bipolar cell (special senses)
 MULTIPOLAR

• E.g. Spinal motor neuron
 NB. May also be described structurally according to shape (e.g. pyramidal cells, granule cells, stellate cells) Ionic basis of electrical activity o (Resting) Membrane potential
 Neurons maintain (negative inside, ~-70mV) membrane potential at rest
 Key determinant of membrane potential

• Ionic conc. gradient

• Ionic electrical gradient (2 together= electrochemical gradients)

• Selective membrane ionic permeability
 Key charged ion species

• Na; K; Cl; Organic ions (largely protein), Ao Sodium-potassium ATPase establishes electrochemical gradient
 3 Na out; 2 K in
 Critical for balance of osmotic pressures
 ATPase so requires energy (ATP)
 Energy efficiency is problem for NS. Human brain (-2% body mass) consumes

• 15% CO

• 20% total body oxygen consumption

• 25% total body glucose utilisation under low physical exertion o In average neuron at rest
 Ion Intracellular Extracellular Out/In Na 15mM 145mM 10 K 155mM

4.5mM

0.03 Ca

0.0001mM 1mM 10000 Cl 5mM 120mM 6 o Nernst Equation

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