FUNCTIONAL ORGANIZATION OF THE NERVOUS SYSTEM

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• FUNCTIONAL ORGANIZATION OF THE NERVOUS SYSTEM
• 1. Overview The Central and Peripheral Nervous
  Systems
• The central nervous system
• Brain
• Spinal cord
• The peripheral nervous system
• Peripheral nerves
• somatic portion

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The nervous system consists of the central
nervous system (CNS) and the peripheral nervous
system (PNS).
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• autonomic portion
• sympathetic nerves
• parasympathelic nerves
• Ganglia
• 2. Cells of the Nervous System
• A. Neurons
• Structures
• Dendrites
• Cell body - soma
• Axon
• Synaptic terminal

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• Classification
• By structure
• Multipolar
• Bipolar
• Unipolar
• By function
• Sensory neuron (afferent neuron)
• Motor neuron (efferent neuron)
• Interneuron

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• Axonal transport
• Antigrade transport
• Fast 400mm/day (organelles synaptic vesicles,
  mitochondria, etc.)
• Slow1-2mm/day (structural proteins actin,
  microtubules, etc.)
• Kinesin a protein motor
• Retrograde transport
• Dynein

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Axonal transport of membranous organelles occurs
in two forms slow axonal transport, and fast
axonal transport.
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• B. Glia (Glial cells)
• Oligodendroglia (CNS)/Schwann cells (PNS)
• Myelination
• Nodes of Ranvier
• astroglia
• Fibrous astrocyte
• Protoplasmic astrocyte
• Microglia

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In the CNS, oligodendrocytes form myelin around
portions of several interneuron axons.
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Structural map of the location and function of
glial cells.
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• 3. The Membrane Potential and the Action
  Potential
• A. Resting membrane potential (RMP)
• RMP -60 TO -90 mV
• predominately diffusion potential (largely K)
• Ion channels of nervous membranes
• Passive ion channels
• found in all areas of the nerve cell
• channel specificity
• Chemical activated ion channels
• located predominantly on dendrites and the soma

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• normally closed
• also known as receptors
• Voltage-activated ion channels
• found in axons and soma
• open at certain voltage
• responsible for generating and propagating action
  potential
• Electrochemical gradients across the cell
  membrane
• e.g. K
• RMP Equilibrium potential (E), can be
  mathematically calculated

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• Nernst equation
• Eion RT/zF x ln(iono/ioni)
• where z is the ion valance and F is the faraday
  constant
• or EK 58 x log10(Ko/ Ki) at 20 C
• e.g. EK -75mV, ENa 55 mV
• Goldman equation

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• B. The action potential
• A temporary change in the membrane potential
• Components of action potential
• Resting potential ?membrane depolarization ?
  threshold ? action potention ? repolariztion ?
  hyperpolarization
• Ion channels and the action potential
• Na channel
• Resting state
• Activation state
• Inactivation state

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• K channel
• Resting state
• Slow activation state
• Phases of the action potential and corresponding
  movements of ions
• Refractory periods
• Absolute refractory period
• Relative refractory period
• Propagation of the action potential

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Diagram indicates the membrane potential events
and the changes in membrane ion permeability
during an action potential.
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• Velocity of the action potential
• Unmyelinated axon diameter
• Myelinated nerve fibers
• Diameter of the axon
• Distance between nodes of Ranvier -
• saltatory conduction

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• Communication between nerve cells synaptic
  transmission
• Electrical synapses
• Gap junctions
• Connexon
• Connexin
• Communication between adjacent cells
• By passing molecules between cells
• Found between
• axons/soma
• axons/dendrites
• dendrites/dendrites
• soma/soma

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• Provide a rapid communication between cells
• Synchronize the activity of many adjoining cells
• Chemical synapses
• Mediate communication between distant cells by
  transmitter-receptor interaction
• Components of chemical synapses
• Presynaptic cell
• Postsynaptic cell
• Synaptic cleft

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Action potential invading synaptic terminal ?
activation of voltage-sensitive Ca2 channels ?
Ca2 in the terminal ? release of
neurotransmitters ? coupling of the transmitter
with the receptor ? change in postsynaptic
potential
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• Postsynaptic potential
• Single channel current
• Synaptic current
• Unitary postsynaptic potential
• Summation of postsynaptic potential
• Excitatory postsynaptic potentials (EPSPs)
• Inhibitory postsynaptic potentials (IPSPs)
• Termination of synaptic transmission
• Reuptake
• Degradation

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