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Medicine Notes Neurology Notes

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

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

Neurology Notes

Neurology

Approximately 117 pages

These notes helped me achieve a mark of 76% in my neurology exam, which is the equivalent of a 1st. The notes are based on a series of 49 lectures on the subject. This is a very good, thorough and in depth review of the nervous system. They are very clearly laid out and easy to follow. They cut out unnecessary information on the topic, making the notes very concise, and fast to get through. Anyone studying medicine, or any other subject requiring knowledge of the nervous system (e.g. physiology o...

The following is a more accessible plain text extract of the PDF sample above, taken from our Neurology Notes. Due to the challenges of extracting text from PDFs, it will have odd formatting:

Lecture 5

Neurons and glia are the building blocks of the brain

  • Structure of neurons

    • 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

    • 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

    • (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), A-

    • 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

    • 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

  • Nernst Equation

    • Calculates equilibrium or Nernst potential for ion across membrane- no net ion movement

    • Ex = RT/zF in [X]extracellular/[X]intracellular

      • R= Universal gas constant (8.314 J per Kelvin per mole)

      • T= Absolute temp (C + 273.15 K)

      • Z= Ion charge

      • F= Faraday’s constant (96485 coulombs per mole)

      • E= Electrical potential

      • NB: RT/F (at 37C)= 0.0267 joules/coulomb= 26.7mV

    • Favourite ion species

      • Na

        • (-61.4/1)*log(15/145)= +60mV

      • K

        • (-61.4/1)*log(154/4.5)= -94mV

      • Cl

        • (-61.4/1)*log(5/120)= -85mV

      • But resting Em= -60 to -90mV

        • Potential for each ion are the potentials that would balance the conc. gradient if each was the only ion involved

        • Membrane potential not close to that of Na as membrane not very permeable to it (more so to K)

  • Permeability

    • Controlled by protein ion channels in neuronal plasma membrane

    • Specific channels for specific ions

    • State of channels controlled by conformation of constituent proteins

  • Three major factors that influence movement of ions across cell membrane

    • Conc. gradient

    • Voltage gradient

    • Membrane permeability

    • Em=RT log Pk[K]o + Pk[Cl]o + PNa[Na]o

zF Pk[K]i + Pk[Cl]i + PNa[Na]i

  • Neurons as information processors

    • Changes in RMP

      • Depolarisation: RMP becomes less negative

      • Hyperpolarisation: RMP more negative

      • Permeability changes for an ion when permeability for specific ion increases, RMP will move towards that ions equilibrium potential (K= hyperpolarising; Na= depolarising)

    • Action potentials

      • Check notes, basic physiologic principles of APs

    • Basic properties of AP

      • THRESHOLD= membrane voltage at which AP initiated

      • RAPID DEPOLARISATION= explosive depolarising change in potential

      • OVERSHOOT= magnitude of positive change in membrane potential

      • ALL-OR-NONE RESPONSE= membrane reaches threshold, stereotypic AP occurs, if threshold not reached, no AP occurs

      • ABSOLUTE REFRACTORY PERIOD= when 2nd AP cannot be produced

      • RELATIVE REFRACTORY PERIOD= time when more difficult but not impossible to produce 2nd AP at membrane site

    • Ionic imbalance leads to pathological excitability changes

      • Na:E= +61mV; K:E= -95mV

      • HYPOKALAEMIA= more negative (hyperpolarised) closer to AP threshold (e.g.) muscle trouble

      • HYPERKALAEMIA= more positive (depolarised) closer to AP threshold hyperexcitability (prolonged...

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