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• Structural classification subdivisions


  • Central nervous system
  • Peripheral nervous system
• Central nervous system (CNS)


  • Consists of the brain and spinal cord
  • Occupies the dorsal body cavity
  • Acts as the integrating and command centers of the nervous system
  • Interpret incoming sensory information and issue instructions based on past experience and current conditions
• Peripheral nervous system (PNS)


  • Includes all parts of the nervous system outside the CNS
  • Consists mainly of the nerves that extend from the spinal cord and brain
  • Spinal nerves carry impulses to and from the spinal cord
  • Cranial nerves carry impulses to and from the brain
  • Serve as communication lines linking all parts of the body by carrying impulses from the sensory receptors to the CNS and from the CNS to the appropriate glands or muscles
• Functional classification subdivisions

  • Sensory division
  • Motor division
• Sensory division (afferent division)


  • Consists of nerves that convey impulses to the central nervous system from sensory receptors located in various parts of the body
  • Keeps the CNS constantly informed of events going on both inside and outside the body
  • Somatic sensory fibers deliver impulses from the skin, skeletal muscles, and joints
  • Visceral sensory fibers transmit impulses from the visceral organs
• Motor division (efferent division)


  • Carries impulses from the CNS to effector organs, the muscles and glands
  • Activates muscles and glands, effecting a motor response
• Somatic nervous system


  Allows conscious, voluntary control of skeletal muscles
• Autonomic nervous system (ANS)


  Regulates automatic, involuntary events like smooth muscle, cardiac muscle, and glands
• Parts of the autonomic nervous system

  • Sympathetic
  • Parasympathetic
• Sympathetic and parasympathetic divisions

  Typically bring about opposite effects; what one stimulates, the other inhibits
• Nervous system subdivisions are made for convenience, but it acts as a coordinated unit both structurally and functionally
• Nervous tissue is made up of two principal types of cells: supporting cells and neurons
• Supporting cells in the CNS

  • Neuroglia (glial cells or glia)
• Neuroglia in the CNS

  • Astrocytes: abundant star-shaped cells that account for nearly half of neural tissue
• Microglia


  Spiderlike phagocytes that monitor the health of nearby neurons and dispose of debris, such as dead brain cells and bacteria
• Debris


  • Dead brain cells
  • Bacteria
• Ependymal cells


  Neuroglia that line the central cavities of the brain and the spinal cord
• Ependymal cells


  • The beating of their cilia helps to circulate the cerebrospinal fluid that fills those cavities and forms a protective watery cushion around the CNS
• Nervous System


  The master controlling and communicating system of the body
• Nervous System Functions


  • Monitors changes inside and outside the body using sensory receptors
  • Processes and interprets sensory input and makes decisions - integration
  • Effects a response by activating muscles or glands - motor output
• Structural Classification of Nervous System

  • Central Nervous System (CNS)
  • Peripheral Nervous System (PNS)
• Functional Classification of Nervous System

  • Sensory or Afferent division
  • Motor or Efferent division
• Supporting Cells in the CNS

  1. Astrocyte - protect neurons, control chemical environment

  2. Microglia - monitor neuron health, dispose debris

  3. Ependymal cells - circulate cerebrospinal fluid, form protective cushion

  4. Oligodendrocytes - produce myelin sheaths
• Supporting Cells in the PNS

  1. Schwann cells - form myelin sheaths

  2. Satellite cells - act as protective, cushioning cells
• Neurons


  • Nerve cells specialized to transmit messages
  • Common features: cell body, dendrites, axons
  • Myelin sheath protects and insulates nerve fibers, increases transmission rate
• Multiple sclerosis is a condition where myelin sheaths around nerve fibers are gradually destroyed, leading to loss of muscle control
• Terminology


  • CNS: Cell bodies, Nuclei, Tracts
  • PNS: Ganglia, Nerve fibers, Nerves
• Classification of Neurons by Function

  • Sensory or afferent neuron
  • Motor or efferent neuron
  • Association (interneuron)
• Types of Sensory Receptors are classified
• Types of Neurons


  1. Sensory receptors

  2. Classification of Neurons: STRUCTURE
• Types of Neurons based on structure

  • Multipolar neuron
  • Bipolar neuron
  • Unipolar neuron
• Multipolar neuron


  Several processes, most common structural type, found in motor and association neurons
• Bipolar neuron


  With two processes, rare in adults, found in special organs like the eye and nose for sensory processing
• Unipolar neuron


  One single process, found in sensory neurons in PNS ganglia
• Nerve Impulses


  Neurons have two major functional properties: Irritability and Conductivity
• Irritability


  The ability to respond to a stimulus and convert it into a nerve impulse
• Conductivity


  The ability to transmit impulse to other neurons, muscles, or glands
• Saltatory conduction is a faster type of electrical impulse propagation that happens on myelinated fibers
• Alcohol, sedatives, and anesthetics block nerve impulses by reducing permeability to sodium ions
• Cold and continuous pressure hinder impulse conduction by interrupting blood circulation to the neurons