Nervous System Part 1

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Nervous System Part 1

• Organization
• Resting Membrane Potential
• Signaling
• Graded Potentials
• Action Potentials

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Organization

• Control System that receives info about internal
  and external environment, integrates, and directs
  activities to respond.
• Divided into the CNS and the PNS.

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Organization

• Consists of 2 classes of cells
• Neurons (20) communication
• Neuroglia (80) many fnctns structurally
  supporting, nurturing, insulating, protecting
  neutons
• Nerves Bundles of neurons in the PNS

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Organization

• 3 types on neurons
• Afferent (sensory) neurons
• Interneurons
• Efferent (motor) neurons

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Organization

• Main parts of a neuron

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Resting Membrane Potential

• A charge difference across the membrane of
  -70mV at rest.
• Has the potential to do work.
• K and Na leak channels in the cell membranes
  establish electrochemical gradients.

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Resting Membrane Potential
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Resting Membrane Potential

• If the cell only had K channels the equilibrium
  potential of the cell would be 90mV.

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Resting Membrane Potential

• If the cell only had Na channels the equilibrium
  potential of the cell would be 60mV.

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Resting Membrane Potential

• There are more K leak channels so Vm is closer
  to EK than ENa.

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Resting Membrane Potential

• Active transport Na/K pumps maintain the ion
  concentrations as seen in table 6-2.

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Signaling

• Changes in a cells membrane potential produce
  electrical signals.
• Graded potentials signaling over short
  distances.
• Action potentials signaling over long distances
• Terms for the direction
• of changes relative to resting potential are
  seen to the right.

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Graded Potentials

• Changes in membrane potential confined to a small
  region of a neuron.
• They are graded, meaning they can vary in
  magnitude.

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Action Potentials

• If the minimum threshold voltage is reached, a
  graded potential becomes an action potential.

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Action Potentials

• Voltage-gated sodium and potassium channels are
  responsible for the depolarization and
  repolarization of the membrane.

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Action Potentials
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Action Potentials

• Always an all-or-nothing event.
• Propagates away from a neurons trigger zone.

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Nervous System Part 1 (cont.)

• Action Potentials Review
• Synapse

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Action Potentials Review

• http//outreach.mcb.harvard.edu/animations/action
  potential.swf

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Action Potentials Review

• A typical neuron would have a resting membrane
  potential of about
• (A) 70 mV
• (B) 70 V
• (C) -70 mV
• (D) -70 V
• (E) All of the above are observed at rest.

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Action Potentials Review

• At the peak of the action potential, the membrane
  potential is
• (A) exactly at the Na equilibrium potential
• (B) close to but more positive than the Na
  equilibrium potential
• (C) close to but less positive than the Na
  equilibrium potential
• (D) exactly at 0 mV
• (E) the same as the resting membrane
  potential

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Action Potentials Review

• True or False Threshold voltage for opening is
  approximately the same for voltage-gated Na and
  K channels.
• Voltage-gated Na and K channels open at the
  approximately the same threshold voltage K
  channels are just much more slower at opening
  wide and closing completely than Na channels.

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Action Potentials Review

• Schwann cells are glia cells that that for the
  myelin sheath.
• They insulate the axons of neurons and increase
  the rate of action potential propagation.

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Synapse

• Synapse the narrow gap b/w 1 neuron the next.
• Neurotransmitter the chemicals that cross the
  synapse

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Synapse
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Synapse

• Response by postsynaptic cell depends on
• Type of neurotransmitter
• Conc. of neurotransmitter
• Type of receptor
• Number of receptors
• Responsiveness of the receptors

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Synapse

• Many axon terminals synapse onto one neuron.
• Excitatory and inhibitory signals are integrated
• All synaptic potentials are graded potentials

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Synapse

• EPSP excitatory post-synaptic potentials
  depolarization
• IPSP inhibitory post-synaptic potentials
  hyperpolarizing
• When threshold is reached an action potential is
  fired down the post-synaptic neuron.

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Synapse

• Neurotransmitters need to be removed ASAP after
  signal is complete.
• Many helpers
• Diffusion
• Enzymes
• Protein pumps