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How Nerve Signals Maintain Homeostasis. Chapter 9. The Nervous System Intro. Every single stimulus (light, touch, feeling of muscles moving, pressure, blinking, etc.) involves your nervous system.

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the nervous system intro
The Nervous System Intro
  • Every single stimulus (light, touch, feeling of muscles moving, pressure, blinking, etc.) involves your nervous system.
  • Coordinated motions (which do not seems to be coordinated) are controlled mostly by the nervous system.
  • nervous system + endocrine system control the actions of the body.
the nervous system
The Nervous System
  • Elaborate communication system
    • Contains 100 billion nerve cells in the brain alone.
    • Humans: memory, learning, language, etc.
vertebrate nervous system
Vertebrate Nervous System
  • 2 main divisions:
    • Central nervous system (CNS)
      • Brain + spinal cord  coordinating centre
        • Incoming and outgoing info.
    • Peripheral nervous system (PNS)
      • Info between organs of body and CNS.
        • Two peripheral divisions:
          • Somatic
            • Skeletal muscles, bones, and skin
              • Sensory somatic PNS: relay info about environment to CNS.
              • Motor somatic PNS: initiate appropriate responds.
          • Autonomic
            • Motor nerves which control internal organs of body.
              • Sympathetic
              • Parasympathetic
nerve cells
Nerve Cells
  • Glial cells
    • Nonconducting cells  structural support and metabolism of nerve cells.
  • Neurons
    • Functional units of nervous system (conduct electricity)
      • Sensory neurons
        • “afferent neurons”
        • Sense and relay info (stimuli) from environment to CNS
          • (ex// photoreceptors, chemoreceptors, thermoreceptors, etc.)
          • Ganglia: clusters of sensory receptors.
      • Interneurons
        • Integrate and interpret sensory and motor neurons (found mostly in the CNS)
      • Motor neurons
        • “efferent neurons”
        • Relay info to effectors: muscles, organs, and glands (can produce a response)
anatomy of a nerve cell neuron
Anatomy of a Nerve Cell (Neuron)
  • All neurons contain:
    • Dendrites
      • Receive info from other nerve cells
      • Conduct info towards the neuron’s cell body
    • Soma: neuronal cell body (containing nucleus)
    • Axon
      • Extension of cytoplasm
      • Carries nerve impulse towards other neurons or effectors.
      • Creates an “attachment” to other neurons.
      • Super super thin (100 could fit inside single human hair!)
myelin sheath
Myelin Sheath
  • Insulation
    • Myelin sheaths are formed by special glial cells called Schwann cells
    • Myelin sheaths prevents the loss of ions from axon.
      • (important when you understand how these cells work!)
      • Made of ‘fatty protein’
nodes of ranvier
Nodes of Ranvier
  • Between sections of myelin sheath
  • Nerve impulses jump from one node to another  speed up movement of nerve impulses.
    • Nerve impulses move much faster along myelinated nerve fibres than nonmyelinated ones.

(Nerve impulses move much faster along smaller diameter axons)

  • Thin membrane which surrounds the axon in peripheral nervous system
    • Promotes regeneration of damaged axons
    • Severed neurons can be rejoined.
    • (feeling gradually returns to your finger following a paper cut)
white and grey matter
White and Grey Matter
  • White matter
    • Nerve cells within the brain that contain myelinated fibres and neurilemma
      • Myelinated axons white in appearance
  • Grey matter
    • Nerve cells within the brain and spinal cord referred to as grey matter: lack myelin sheath and neurilemma do not regenerate after injury
      • Damage to grey matter is usually permanent.
categories of neurons
Categories of Neurons
  • Sensory Neurons: AFFERENT neurons: relay info from environment  CNS
    • Located in clusters called ganglia
      • Photoreceptors (eyes)
      • Chemoreceptors (tongue and nose)
      • Thermoreceptors (skin and hypothalamus)
  • Interneurons
    • Interpret sensory info and send info to outgoing motor neurons (mostly in CNS)
  • Motor neurons: EFFERENT neurons: relay info from interneurons effectors (produce a response)
    • Muscles
    • organs,
    • glands
organization of nerves
Organization of Nerves
  • Most nerves are part of many neurons/axons held together in a ‘bundle.’
neural circuits
Neural Circuits
  • Reflex
    • Involuntary and often unconscious
  • Example: touching a hot stove
    • How long does it take you to remove your hand?
    • Nerve impulse is carried to the spinal chord  motor neuron (skipping brain)  sensation felt after removing hand.
reflex arc
Reflex arc
  • Simplest nerve pathway.
  • Occurs without brain coordination
  • Five essential components:
    • Receptor
    • Sensory neuron
    • Interneuron (spinal chord)
    • Motor neuron
    • Effector
seatwork homework
  • Page 417

1) # 1-6, 8.

2) Draw/ Label a general neuron: dendrite(s), soma, nucleus, axon, myelin sheath, axon terminals, direction of impulse.

3) Read page 415 article. Make brief notes.