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Cell Division and Mitosis - PowerPoint by decree


									  Information Flow and
       the Neuron

The Unity and Diversity of Life,   9e
           Chapter 34
Key Concepts:

Neurons are basic units of communication
 in nervous system
Neurons are excitable cells
With stimulation, the polarity of charge
 across the membrane reverses from
 negatively charged inside the cell to being
 positively charged
Key Concepts:
Action potentials are changes in the
 polarity of the cell membrane
Information flow starts with action
 potentials, which self propagate along the
 plasma membrane
Chemical signals released from a neuron
 stimulate or inhibit the adjoining neuron,
 muscle cell, or gland cell
Information flow depends on integration
 of signals

    sensory        interneurons        motor    muscle cells,
    neurons       (e.g., the brain)   neurons    gland cells

              NERVOUS SYSTEM                      response
                                                                Slide 4
            INPUT ZONE
cell body
            TRIGGER ZONE


              CONDUCTING ZONE

                                OUPUT ZONE
Types of Neurons
Resting Membrane Potential

Negative inside, positive outside
Can be detected by electrodes placed inside and
outside axon
Usually about -70 millivolts
             Restoring and
          Maintaining Readiness
Potential is
established and
maintained by
pumping and
leaking of Na+
and K +
   Restoring and
Maintaining Readiness
  Ion Concentrations At Resting Potential
           A Closer Look at
           Action Potentials
Voltage changes    All or nothing
Na+, K+              Action potential
Graded response    Depolarization
Local response     Repolarization
Threshold level
Action Potential
              Action Potential
             All-or-Nothing Spike

Triggered when
potential is

Always the
same size

During action potential, inside of patch of
membrane becomes more positive then outside
  Propagation of
an Action Potential
  Propagation of
an Action Potential
        Chemical Synapses
  Acetylcholine (ACh)
  Neuron - cell
  Neuron - neuron
  Neuron - muscle
  Neuron - gland
Excitatory effect
Inhibitory effect
     A Closer Look
at a Chemical Synapse
Channels Open
       Examples of Signals
  Acetylcholine (Ach)
  Norepinephrine (NE)
  Gamma amino butyric acid (GABA)
         Synaptic Integration
  Depolarizing effect
  Hyperpolarizing effect
Synaptic integration
  Excitatory or Inhibitory
  Breaks apart ACh
  ACh is removed from the synaptic cleft

                         myelin sheath

nerve’s outer wrapping

     blood vessels

        nerve fascicle

                           Slide 19
Structure of a Nerve
The Myelin Sheath
            Reflex Arcs

Reflex - Automatic movement made in response
 to stimulus
Simplest reflexes - Sensory neurons synapse
 directly on motor neurons
Stretch reflex
Most reflex pathways include interneurons
receptor     peripheral    cell   axon   axon         cell   axon    cell       axon            axon
endings        axon        body          ending       body           body                       endings

       SENSORY NEURON                             INTERNEURON       dendrites          MOTOR NEURON

                                                                                                          Spinal cord
           Biceps stretches.

                                                                                  Biceps contracts

                                                                                                      Slide 23
In Conclusion

 The nervous system consists of sensory
 neurons, interneurons, and motor neurons,
 which activate muscle and glands
 A neuron’s dendrites and cell body are
 input zones and the axon ending is the
 output zone
 Channels exist in the membrane for Na+
 and K+
In Conclusion
 There is a voltage difference across the
  plasma membrane in a resting neuron
 An action potential is a reversal of the
  voltage difference across the membrane
 Stimuli can cause local graded potentials
  or to the threshold of an action potential
 When Na+ channels open, allowing Na+ to
  enter a cell, the voltage difference across
  the membrane reverses abruptly
In Conclusion
 Sodium/Potassium Pumps restore the
    gradients after an action potential
 Neurotransmitters released into a synaptic
    cleft may excite or inhibit the cell’s plasma

   developed by M. Roig

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