Nervous System (Part 1)

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Chapter 13

• Nervous System (Part 1)

An electro -
- chemical system.
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Review

• Overview of the Nervous System
• Central Nervous System
• The Spinal Cord
• The Brain
• The Limbic System and Higher Mental Functions
• Peripheral Nervous System
• - Somatic / Autonomic Systems
• Drug Therapy and Drug Abuse

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Overview of the Nervous System
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• Nervous system function?
• allows us to receive, integrate (process), and
  react to environmental stimuli to maintain
  homeostasis.
• Component parts?
• Central nervous system (CNS)
• includes the brain and spinal cord
• Peripheral nervous system (PNS)
• Somatic sensory and motor neurons to skeletal
  muscles (voluntary)
• Autonomic sensory and motor neurons go to smooth
  muscles and glands (involuntary)

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Nervous Tissue

• Nervous Tissue contains two types of cells.
• Neurons transmit nerve impulses between parts of
  the nervous system.
• Neuroglia support, protect, and nourish neurons.
  (neuroglial cells or glial cells)
• Have different specific names based on their
  shape, location, function.

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Neuron Structure

• Neurons are classified according to function.
• Sensory neurons take impulses from a sensory
  receptor to the CNS. (afferent, at)
• Interneurons receive input from sensory neurons,
  and other neurons, and then communicate with
  motor neurons. (association, connector)
• Motor neurons take nerve impulse away from the
  CNS to an effector that carries out responses to
  environmental change. (efferent, exit)

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Types of Neurons
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Neuron Structure

• Neurons contain three basic parts.
• Cell body contains nucleus and other organelles.
• Dendrites receive signals from sensory receptors
  or other neurons.
• Axon conducts nerve impulses away for the cell
  body.

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Myelin Sheath

• Some axons are covered by a protective myelin
  sheath.
• Formed by Schwann cells containing myelin in
  plasma membranes.
• (neurolemmocytes)
• Nodes of Ranvier are gaps on the axon with no
  myelin sheath. (neurofibril node)

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Myelin Sheath
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The Nerve Signal

• The nervous system uses the nerve impulse to
  convey information.
• Resting potential is the voltage level when an
  axon is not conducting an impulse.
• Sodium-potassium pump causes greater
  concentration of Na outside the axon, and
  greater concentration of K inside the axon.
• Unequal ion distribution causes inside of axon to
  be negative relative to the outside.

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Action Potential

• An action potential is a rapid change in polarity
  across an axomembrane as the nerve impulse
  occurs.
• All-or-none once threshold is reached.
• Sodium gates open, allowing Na to move inside
  the axon.
• Potassium gates open, allowing K to move outside
  the axon.
• The charge flips becomes on the inside, (-)
  on the outside . . .

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Propagation of an Action Potential

• Each preceding portion causes an action potential
  in the next portion of an axon.
• Rather than moving continuously along the axon,
  the electrical impulse jumps from node to node
  saltatory conduction.
• As soon as an action potential has moved on, the
  previous portion of an axon undergoes a
  refractory period in which the sodium gates are
  unable to open thus the impulse can only move
  away from the cell body.

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The Synapse

• Transmission across a synaptic cleft is carried
  out by neurotransmitters stored in synaptic
  vesicles (which are released into the cleft
  because of the release of Ca) - norepinephrine
  (NE) or acetylcholine (ACh).
• Depending on the neurotransmitter and the
  receptor, the response of the postsynaptic neuron
  can be towards excitation or inhibition summary
  (net) effect.
• Integration is the summing of signals received by
  a postsynaptic neuron.

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Synaptic Integration
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Historical Focus

• Artist and Scientist Santiago Ramon y Cajal
  (1852-1934)

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The Central Nervous System

• The central nervous system (CNS) is made up of
  the spinal cord and the brain.
• Both are wrapped in protective membranes,
  meninges, with spaces between meninges filled
  with cerebrospinal fluid which also fills 4
  cavities in the brain (called ventricles) and act
  as reservoirs.
• CNS is composed of two types of nervous tissue.
• Gray matter Short, nonmyelinated fibers.
• White matter - Myelinated axons.

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Computer Assisted Tomography (CAT) scan
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Magnetic Resonance Imaging (MRI) scan
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The Spinal Cord

• The spinal cord extends from the base of the
  brain through the foramen magnum into the
  vertebral canal.
• Components
• Central canal filled with cerebrospinal fluid
• Grey matter butterfly shaped
• White matter contains interneurons grouped in
  tracts (ascending and descending) which cross
  over so that left side of brain controls right
  side of body.

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Functions of the Spinal Cord

• The spinal cord (1) provides a means of
  communication between the brain and the
  peripheral nerves that leave the cord
• and (2) is a center for reflex actions.