The Nervous System

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The Nervous System
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4 Functions of the Nervous System

• Gathers information both from the outside world
  and from inside the body.
• Transmits the information to the processing area
  of the brain and spinal cord.
• Processes the information to determine the best
  response. 
• Sends information to muscles, glands, and organs
  (effectors) so they can respond correctly. 

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The Central Nervous System (CNS)

• consists of the Brain and the Spinal Cord
• the Spinal Cord carries messages from the body to
  the Brain where they are analyzed and interpreted
• response messages are then passed from the Brain
  through the Spinal Cord and to the rest of the
  Body.

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The Peripheral Nervous System (PNS)

• consists of the neurons NOT Included in the Brain
  and Spinal Cord
• Afferent Neurons Collect Information from the
  Body and Transmit it TOWARD the CNS. 
• Efferent Neurons Transmit Information AWAY from
  the CNS. 

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The Somatic Nervous System

• regulates activities that ARE UNDER CONSCIOUS
  CONTROL, movement of skeletal muscles.
• many nerves within this system are part of
  reflexes and can act automatically.

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The Autonomic Nervous System

• regulates involuntary activities
• are not under conscious control
• is responsible for maintaining homeostasis in the
  functioning of organs
• EXAMPLES  heart beat, digestion, breathing

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Sympathetic Nervous System

• generally ACTIVATES ORGANS or SPEEDS UP

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Parasympathetic Nervous System

• generally RETARDS ORGANS or SLOWS DOWN
• Most organs are under control of both Sympathetic
  and Parasympathetic Neurons.

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The Neuron
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The Cell Body

• contains the nucleus and much of the cytoplasm
• responsible for most of the metabolic activity of
  the cell, including the generation of ATP and
  synthesis of protein

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Dendrites

• short branch extensions spreading out from the
  cell body
• dendrites receive STIMULI and carry IMPULSES from
  the environment or from other neurons and carry
  them TOWARD the cell body.
•  

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AXON

• long fiber that carries impulses AWAY from the
  cell body
• each neuron has only ONE AXON
• ends in a series of small swellings called AXON
  TERMINALS
• Axons of most Neurons are covered with a Lipid
  Layer known as the MYELIN SHEATH.

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The Myelin Sheath

• both Insulates and Speeds Up transmission of
  Action Potentials through the Axon
• In the PNS, is produced by SCHWANN CELLS, which
  surround the Axon
• GAPS in the Myelin Sheath along the length of the
  Axon are known as the NODES OF RANVIER

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Characteristics of Neurons

• Nervous messages are called impulses. 
• A Neuron carries impulses in only ONE direction
• Impulses are in the from of electric signals

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Types of Neurons

• Interneurons, Efferent or Motor Neurons, Afferent
  or Sensory Neurons

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Afferent Neurons(Sensory)

• carry impulses from the SENSE ORGANS to the Brain
  and Spinal Cord
• detect external or internal changes and send the
  information to the Central Nervous System by way
  of the Afferent Neurons

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Efferent Neurons(Motor)

• carry impulses from the Brain and Spinal Cord to
  MUSCLES or GLANDS
• in response to impulses, Muscles Contract and
  Glands Secrete

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Interneurons

• Connect Sensory and Motor neurons and carry
  impulses between them 
• are found entirely within the Central Nervous
  System