Principles of Animal Physiology

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Principles of Animal Physiology
Neuronal Physiology
Introduction
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Principles of Animal Physiology
Neuronal Physiology
Introduction

• Two types of cells use the membrane potential
• Membrane potential undergo rapid, transient
  changes
• These fluctuations serve as signaling mechanisms
• Cells that produce electrical signals when
  stimulated are called Excitable Tissues. These
  are
• Nerve cells
• Muscle cells

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Principles of Animal Physiology
Neuronal Physiology
Introduction

• Terminology
• Normal, unpolarized, equlibrium
• No difference in polarity, charge or
  concentration
• Polarized
• Differences in charge ( or -) across membrane
• Membrane potential not 0 mV
• Resting Membrane Potential
• Membrane potential of the cell at rest
• Depolarization
• Membrane potential becomes less negative than
  resting level
• Repolarization
• Membrane potential returning to resting level
• Hyperpolarization
• Membrane potential more negative than resting
  level

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Principles of Animal Physiology
Neuronal Physiology
Introduction

• Terminology - changes in membrane potential

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Principles of Animal Physiology
Neuronal Physiology
Introduction

• Electrical signals via movement of ions across
  plasma membrane
• Changes in membrane potential cause by changes in
  ion movement across plasma membrane
• Changes in ion movement caused by changes in
  permeability of the membrane
• Changes in permeability cause by a triggering
  event (stimulus)

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Principles of Animal Physiology
Neuronal Physiology
Introduction

• Stimulus may be caused by
• Sound waves stimulating nerve endings
• A change in the electrical field in neural
  endings
• An interaction of a ligand with a receptor
• Spontaneous change in potential cause by leak
  channels

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Principles of Animal Physiology
Neuronal Physiology
Introduction

• Two types of channels
• Leak channels (nongated channels)
• Remain open
• Gated channels
• Open and close in response to some triggering
  event
• At least 3 kinds
• Voltage-gated ion channels
• Chemically (ligand) gated channels
• Mechanically gated channels
• Respond to stretch or other mechanical
  deformation
• There are two basic electrical signals generated
  by the movement of ions across the membrane
• Graded potentials
• Action potentials

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Principles of Animal Physiology
Neuronal Physiology
Graded Potentials

• Graded potentials local changes in membrane
  potential that occur in varying grades or degrees
  of magnitude or strength.
• Amplitude directly related to level of stimulus
• Amplitude inversely related with distance
• Local event
• Active area
• Begins at a point where ions enter ECF
• Duration directly related to duration of stimulus
• Different graded potentials can be added Summed
• Graded potential can travel to Trigger zone
• Can be depolarizing or hyperpolarzing

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Principles of Animal Physiology
Neuronal Physiology
Graded Potentials

• Magnitude and duration of graded potentials

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Principles of Animal Physiology
Neuronal Physiology
Graded Potentials
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Principles of Animal Physiology
Neuronal Physiology
Graded Potentials

• Current flow during graded potential

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Principles of Animal Physiology
Neuronal Physiology
Graded Potentials

• Current loss and decrement of graded potential

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Principles of Animal Physiology
Neuronal Physiology
Graded Potentials

• Graded potentials
• Decremental gradually decreases from initial
  site
• Passive conduction
• Electronic conduction
• Nonspiking of local circuit
• Limited signal distance
• Types of graded potentials
• Postsynaptic potentials
• Receptor potentials
• End-plate potentials
• Pacemaker potentials
• Slow-wave potentials

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Principles of Animal Physiology
Neuronal Physiology
Graded Potentials

• Summation of graded potentials

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Principles of Animal Physiology
Neuronal Physiology
Action Potentials

• Components/characteristics
• Resting Membrane Potential
• Depolarizing stimulus
• Threshold
• Rapid Na entry (depolarization)
• Isopotential
• Overshoot
• Repolarization (K moves out)
• Absolute refractory period
• Relative refractory peroid

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Principles of Animal Physiology
Neuronal Physiology
Action Potentials
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Principles of Animal Physiology
Neuronal Physiology
Action Potentials

• Changes to voltage-gated sodium and potassium
  channels during an AP

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Principles of Animal Physiology
Neuronal Physiology
Action Potentials

• Positive-feedback cycle

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Principles of Animal Physiology
Neuronal Physiology
Action Potentials

• Ionic movements responsible for changes in
  membrane potential during an action potential