Nervous System

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Nervous System

• A basic overview

Mrs. S. Taylor
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What does it do?

• Allows us to
• Think, feel, remember, move, being aware of the
  world around us
• How?
• Sensory receptors bring messages to the Central
  Nervous System(CNS) from both inside and outside
  sources.
• CNS determines course of action and sends a
  message out to where it need to go so that the
  action can happen.

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So... it is the master control?

• Yep, it sure is and it is also our means of
  communication, too.
• How does it work? Well....
• Sensory input monitoring stimuli
• This is all the data the receptors collect... you
  know... pain, pressure, temperature... that sort
  of stuff
• Integration interpretation of sensory input
• The data is brought together to create memories,
  sensations, produce thoughts.. stuff like that
  and then we make decisions about it, either
  consciously or subconsciously
• Motor output response to stimuli
• This is how we act on what we have sensed... like
  running to the restroom, jerking our hand back
  from a hot stove...

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Okay... so what are the parts?

• The major players are the Nerve cells
  (technically called the neurons) that use
  electrochemical impulses (nerve impulses) to pass
  messages from one to another and to the effectors
  (the things that respond to the message)?
• They make up the brain, spinal cord, motor
  nerves, sensory nerves... anything that sends and
  receives messages in us has a nerve.

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1st major classification

• Are they of the CNS (central nervous system)?
• Brain and spinal cord
• Integration and command center
• Or are they the PNS (peripheral nervous system)?
• Paired spinal and cranial nerves (peripheral
  nerves)?
• Carries messages to and from the spinal cord and
  brain

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The PNS is further divided

• Sensory (afferent) division
• Sensory afferent fibers carry impulses from
  skin, skeletal muscles, and joints to the brain
• Visceral afferent fibers transmit impulses from
  visceral organs to the brain
• Motor (efferent) division
• Transmits impulses from the CNS to effector organs

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The motor division gets to do it again....

• Somatic nervous system
• Conscious control of skeletal muscles
  (Voluntary)?
• Autonomic nervous system (ANS)?
• Regulates smooth muscle, cardiac muscle, and
  glands (Involuntary)?
• Divisions (once again...-)?
• Sympathetic- prepares the body for
  energy-expending, stressful, or emergency
  actions
• Parasympathetic- used in ordinary restful
  conditions, and returning to that after the
  sympathetic division has had its way.

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Okay Okay Okay... we got that, but what does the
nerve look like?

• Well... it has three main parts
• Dendrites
• Cell body
• Axon
• And some ancillary parts too
• Nodes of Ranvier
• Schwann cells the Neurilemma
• Myelin sheaths

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Let's start with the main parts

• Dendrites
• They are the short, tapering, and diffusely
  branched processes (extensions)?
• receive the messages from where ever (sensory
  receptors, other nerves...) and carries them to
  the Cell body
• Axon
• It is the slender processes of uniform diameter
  arising from the hillock (If long called a nerve
  fiber)?
• Typically only one and it is usually unbranched
• Takes messages from the Cell body to the next
  stop (dendrites or the effector)?

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So, what about the Cell body?

• Contains the nucleus and a nucleolus,
  mitchondria, gogli apparatus... those sorts of
  things
• Is the focal point for the outgrowth of neuronal
  processes (Those things we just finished talking
  about)?
• Has no centrioles (hence its amitotic nature
  that means it can't divide to make new cells)?
• Has well-developed Nissl bodies (kind of like
  rough ER)?
• Contains an axon hillock cone-shaped area from
  which axons arise

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The Ancillaries? First up... the Myelin sheaths

• Whitish, fatty (protein-lipoid), segmented sheath
  around most long axons
• It functions to
• Protect the axon
• Electrically insulate fibers from one another
• Increase the speed of nerve impulse transmission
• It is created by Schwann cells in PNS
• Can repair the axon if damages
• It is created by oligodendrocytes in the CNS
• Axons usually cannot repair

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Schwann cells?

• A Schwann cell
• Envelopes an axon in a trough
• Encloses the axon with its plasma membrane
• Has concentric layers of membrane that make up
  the myelin sheath
• Neurilemma remaining nucleus and cytoplasm of a
  Schwann cell

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So, what are these node things?

• The Nodes of Ranvier (AKS Neurofibral nodes)?
• Gaps in the myelin sheath between adjacent
  Schwann cells

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So, what if the axon is short?

• It is called unmyelinated.
• A Schwann cell surrounds nerve fibers but coiling
  does not take place
• In the brain they are called gray matter (the
  myelinated are called white matter)?