THE NERVOUS SYSTEM

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THE NERVOUS SYSTEM
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Objective 1
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Illustrate And/Or Label The Following Parts Of A
Neuron And Identify Or Indicate Their
FunctionsCell Body, Dendrite, Axon, Nucleus,
Axon Hillock, Axon Terminals, Nodes Of Ranvier,
Schwann Cell, Myelin Sheath, Neurilemma, Receptor
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(No Transcript)
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Functions Of Nerve Cell Parts
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The Nerve Cell Body

• An enlarged part of the nerve cell containing
  abundant cytoplasm and cell organelles. It is
  sometimes called the soma.
• Receives information from dendrites and sends
  messages out through the axon.
• The primary site for maintaining the life of the
  nerve cell which support the dendrites and axon.

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The Dendrite

• An incoming nerve cell process that can act as a
  receptor or connect to separate specialized
  receptors.
• Conducts stimulus information to the nerve cell
  body.
• Produces voltage changes in response to various
  stimuli and assists in nerve impulse formation.

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The Axon

• Conducts nerve impulses away from the nerve cell
  to the axon terminals.
• Is very small in diameter, but can be very long
  (e.g. the length of a leg).
• Each nerve cell has only one axon.
• If an axon is cut, the distal portion degenerates
  due a disruption of the cytoplasm extending from
  the cell body.

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Axon Terminals

• Axon terminals are bulbous distal endings of the
  many branches that extend from the end of an
  axon. These bulb-like structures can also be
  called synaptic knobs, boutons or even end
  feet.
• The axon terminal serves as a secretory component
  that releases neurotransmitters in response to
  nerve impulses.

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Nodes of Ranvier

• A Node of Ranvier is a space or gap found on a
  nerve cell process (axon or dendrite) and is
  located between the myelin sheaths formed by
  cells such as the Schwann Cell.
• The exposed cell membrane located in the node can
  facilitate the formation and transmission of
  nerve impulses.

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The Myelin Sheath

• The Schwann Cell wraps around a section of nerve
  cell fiber in jellyrollfashion resulting in a
  tight coil of concentric membranes called the
  Myelin Sheath.
• The whitish, fatty myelin material acts as an
  excellent insulator and protector of the nerve
  cell fiber.

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The Neurilemma

• The most external portion of the plasma or cell
  membrane of the Schwann Cell.
• This specialized membrane surrounds the myelin
  sheath.
• The neurilemma is sometimes called the sheath of
  the Schwann Cell or a neuron husk.

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Receptor

• A specialized part of a nerve cell or the nervous
  system that detects stimuli and produces voltage
  changes that can lead to nerve impulses.
• The tips of dendrites, the nerve cell body and
  sections of the axon can possess receptors.
• The voltage produced by receptors are called
  graded or generator potentials.

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Objective 2
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Identify Or Draw And Label A Spinal Cord
Cross-Section Depicting A Simple Reflex Arc And
Include The Followingsensory (afferent)
neuron, motor (efferent) neuron, synapse, central
canal, dorsal (posterior) root, ventral
(anterior) root, gray matter, white matter,
posterior horn, anterior horn and interneuron.
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Spinal Cord Diagram
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Spinal Cord Diagram
White Matter
Gray Matter
Dorsal Horn
Dorsal Root
Ventral Horn
Ventral Root
Dorsal Root Ganglion
Central Canal
Spinal Nerve
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Objective 3
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Describe Or Recognize The Sequence Of Events
Which Occur During The Utilization Of A Reflex
Arc.
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The Reflex Arc

• The key components of a reflex arc are receptor,
  sensory neuron, interneuron (may be absent),
  motor neuron and effector (e.g. muscle).
• The receptor detects stimuli and produces graded
  potentials that cause the formation of nerve
  impulses in the neurons.
• The nerve impulses then produce rapid responses
  in muscle (jump due to sound).

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Characteristics of the Nerve Impulse

• An electrochemical event that occurs in nerve
  cells following proper stimulation.
• An all-or-none process which is fast acting and
  quick to recover.
• An event that is described by a voltage curve
  that is called an action potential.
• The nerve impulse can be conducted the entire
  length of a nerve cell without diminishment
  (domino effect).

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Characteristics of a Nerve Impulse Continued

• The nerve impulse serves as the primary
  information signal used by the nervous system to
  provide communication about stimuli, nerve cell
  activity, neurotransmitter release and to
  generate various output responses (motor action,
  glandular secretion, etc.).
• Typically initiated by graded or generator
  potentials from a stimulus.

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The Synapse

• The nerve synapse is a specialized junction that
  transfers nerve impulse information from a pre
  synaptic membrane to a postsynaptic membrane
  using neurotransmitters and enzymes
• The synapse operates as an on/off switch and as
  a filter for information flow.

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Acetylcholine

• A chemical that operates as a common excitatory
  neurotransmitter.
• Released from vesicles in the presynaptic
  membrane.
• Stimulates receptors in the postsynaptic
  membrane.
• Broken down by the enzyme Acetylcholinesterase.

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Excitatory Neurotransmitter

• A chemical that accumulates in the synapse from
  presynaptic neurons and which stimulates the
  postsynaptic neuron to produce nerve impulses.
• A common example is Acetylcholine.
• Excitation is produced through the formation of
  excitatory postsynaptic potentials (EPSPs).

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Anesthetic

• A Chemical that alters nerve cells in such a way
  that nerve impulse formation and transmission are
  suppressed.
• When anesthetics operate in pain pathways, loss
  of sensation occurs.
• Barbiturates are anesthetics which suppress the
  reticular activating system in the brain and lead
  to unconsciousness.