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Introduction to Nerves and the Nervous Systems

Introduction to Nerves and the Nervous System

Role of the Nervous System

  • Controls the functions of the human body
  • Analyzes incoming stimuli
  • Integrates internal and external responses

Makeup of the Nervous System

  • Central nervous system (CNS)
    • Composed of the brain and spinal cord
  • Peripheral nervous system (PNS)
    • Sensory receptors bring information into the CNS
    • Motor nerves carry information away from the CNS
  • Autonomic nervous system (ANS)
    • Uses components of the CNS and PNS to regulate automatic or unconscious responses to stimuli

Functions of the Cells That Make Up the Nervous System

  • Allow movement
  • Allow realization of various sensations
  • Provide response to internal and external stimuli
  • Stimulate learning, thinking, and emotions





Types of Axons

  • Afferent fibers
    • Nerve axons that run from peripheral receptors into the CNS
  • Efferent fibers
    • Nerve axons that carry nerve impulses from the CNS to the periphery to stimulate muscles or glands

Action Potential

Action Potential
Action Potential



Electrolytes Involved in Nerve Cell Action

  • Sodium
  • Potassium
  • Calcium

Movement of Electrolytes With Action

  • Rest/repolarization
    • Membrane is impermeable to sodium
    • Membrane is permeable to potassium
  • Action/depolarization
    • Sodium goes into the cell
    • Potassium leaves the cell

Formation of Myelin Sheath

Formation of Myelin Sheath
Formation of Myelin Sheath



Nerve Synapse

  • Presynaptic nerve
  • Synaptic cleft
  • Postsynaptic effector cell


  • Acetylcholine
    • Communicates between nerves and muscles
  • Norepinephrine and epinephrine
    • Catecholamines released by nerves in the sympathetic branch of the ANS
  • Dopamine
    • Involved in the coordination of impulses and responses
  • Gamma-aminobutyric acid (GABA)
    • Inhibits nerve activity and is important in preventing overexcitability or stimulation such as seizure activity
  • Serotonin
    • Important in arousal and sleep and in preventing depression and promoting motivation

Central Nervous System

  • Made up of brain and spinal cord
  • Structures are covered by meninges
  • Blood–brain barrier
  • Blood supply to the brain

Anatomy of the Brain

Anatomy of the Brain
Anatomy of the Brain




  • Runs from the top of the spinal cord into the midbrain
  • Most primitive part of the brain: contains the brain stem
  • Controls basic vital functions:
    • Breathing
    • Blood pressure
    • Swallowing
    • RAS


  • Contains the thalamus, the hypothalamus, and the limbic system
    • The thalamus sends direct information into the cerebrum to transfer sensations
    • The hypothalamus acts as the major sensor of activity in the body
      • Temperature regulation
      • Water balance
      • Appetite
      • Endocrine function

Limbic System

  • Contains high levels of the neurotransmitters:
    • Epinephrine
    • Norepinephrine
    • Serotonin
  • Controls expression of emotions


  • Made up of 2 cerebral hemispheres joined together by the corpus callosum
  • Receives and sends nerve impulses, coordinates speech and communication, and facilitates learning

Spinal Cord

  • Made up of 31 pairs of spinal nerves
  • Each spinal nerve has 2 components or roots
    • Sensory fiber (dorsal root)
      • Brings information into the CNS from the periphery
    • Motor fiber (ventral root)
      • Causes movement or reaction

Functions of Central Nervous System

  • Sensory functions
  • Motor functions
  • Intellectual and emotional functions

Intellectual and Emotional Function

  • Two hemispheres of the brain process information differently
  • Right side
    • Artistic
  • Left side
    • Analytical
  • When learning takes place, an actual change occurs in a neuron
  • Some degree of stress facilitates learning
  • Increased stress inhibits learning
  • The limbic system plays a role in learning
  • Emotions associated with memory and the present have an impact on stimulus response

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