Review:

1
Review

• How do receptors, integrators, and effectors
  relate?
• What are positive and negative feedback using
  examples?
• Describe the structure of the nervous system (CNS
  and PNS).
• What are examples of receptors we have in our
  nervous systems?

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Information Flow and the Neuron

• Starr/Taggarts
• Biology
• The Unity and Diversity of Life, 9e
• Chapter 34

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Key Concepts

• Neurons are the basic excitable cells of a
  nervous system.
• With stimulation, the polarity of charge across
  the membrane reverses from negatively charged
  inside the cell to being positively charged. This
  is the electrical basis of the action potential.

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Key Concepts

• Information flow starts with action potentials,
  which self propagate along the plasma membrane.
• Chemical signals called neurotransmitters
  released from a neuron stimulate or inhibit the
  adjoining neuron, muscle cell, or gland cell.
• Information flow depends on integration of
  signals.

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Types of Neurons
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dendrites
INPUT ZONE
cell body
TRIGGER ZONE
axon
axon endings
CONDUCTING ZONE
OUPUT ZONE
Fig. 34.3, p. 576
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Signal Transmission
CHEMICAL ACROSS SYNAPSE
NEW START
ELECTRICAL
START
ELECTRICAL
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A Closer Look at Action Potentials

• Sequence of Events
• Resting Membrane Potential
• Stimulus
• Depolarization to threshold, all or nothing
• Repolarization
• At a synapse neurotransmitters act

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Establishing Resting Membrane Potential

• Membrane of the neuron at rest is
• Negative inside, positive outside
• Membrane potential can be detected by electrodes
  inside and outside the axon
• Usually about 70 millivolts
• Established by the Na/K pump and other proteins

Fig. 34.5, p. 577
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trigger zone
Fig. 34.4, p. 577
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Triggering a Potential

• Sequence of Events
• Stimulus deforms plasma membrane
• Deforming changes ion balance
• Graded signal spreads to trigger zone
• Signal must be at or above threshold to trigger
  action potential

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Action Potential All-or-Nothing Spike
Triggered when threshold potential is
reached Always the same size
During action potential, inside of patch of
membrane becomes more positive then outside
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Propagation of an Action Potential

• Sequence of Events
• Na channels open
• Na rushes inside the axon
• This action depolarizes that section of the cell
  ( inside/ - outside)
• Triggers more depolarization! ( feedback)

NA
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Propagation of an Action Potential

• Sequence of Events
• Triggers more depolarization! ( feedback)
• The wave of depolarization sweeps down the axon

NA
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Propagation of an Action Potential

• Sequence of Events
• The action potential sweeps down the axon until
  it reaches the synapse
• Neurotransmitters must then bridge the gap

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Recovery back to resting potential

• Sequence of Events
• Depolarization eventually causes Na channels to
  shut
• K channels open and K rushes out
• Na /K pump activates!

K
NA
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Chemical Synapses

• Neurotransmitters
• Acetylcholine (ACh)
• Junctions
• Neuron - cell
• Neuron - neuron
• Neuron - muscle
• Neuron - gland
• Excitatory effect
• Inhibitory effect

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A Closer Look at a Chemical Synapse
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A Closer Look at a Chemical Synapse

• Sequence of Events
• Action potential reaches synapse
• Triggers Ca 2 gates, Ca 2 rushes
  into cell
• Vesicles fuse with outer membrane and release
  neurotransmitters
• They diffuse and dock with next neuron
• They are then broken down by enzymes

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DMA (000 to complete)

• None due to assembly schedule.
• We need to begin IMMEDIATELY at the bell!

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Review Questions

• What establishes resting membrane potential?
• What triggers an action potential?
• What causes a depolarization of an axon?
• What causes propagation of an action potential?
• What causes repolarization?
• What causes neurotransmitters to be released?

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Reference Diagram
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Reference Diagram
K
Na
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A Closer Look at a Chemical Synapse

• Sequence of Events
• Action potential reaches synapse
• Triggers Ca 2 gates, Ca 2 rushes
  into cell
• Vesicles fuse with outer membrane and release
  neurotransmitters
• They diffuse and dock with next neuron
• They are then broken down by enzymes

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Examples of Signals

• Neurotransmitters
• Acetylcholine (Ach)
• Norepinephrine (NE)
• Dopamine
• Gamma amino butyric acid (GABA)

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Synaptic Integration

• EPSP (excitatory)
• Depolarizing effect
• IPSP (inhibitory)
• Hyperpolarizing effect
• Synaptic integration
• Excitatory or Inhibitory
• Acetylcholinesterase
• Breaks apart ACh
• ACh is removed from the synaptic cleft

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Structure of a Nerve
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The Myelin Sheath
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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

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Next Topic

• The Endocrine System
• Function
• Structures
• Feedback loops