NERVOUS SYSTEM

• Nervous System Functions


  • Receiving sensory input
  • Integrating information
  • Controlling muscles and glands
  • Maintaining homeostasis
  • Establishing and maintaining mental activity
• Main Divisions of Nervous System

  • Somatic Nervous System
  • Autonomous Nervous System
  • Enteric Nervous System
  • Central Nervous System (CNS)
  • Peripheral Nervous System (PNS)
  • Sensory Division
  • Motor Division
• Somatic Nervous System

  Transmits action potentials from the CNS to skeletal muscles
• Autonomous Nervous System


  Transmits action potentials from the CNS to cardiac muscle, smooth muscle, and glands
• Enteric Nervous System


  A special nervous system found only in the digestive tract
• Central Nervous System (CNS)


  Brain and spinal cord
• Peripheral Nervous System (PNS)


  All the nervous tissue outside the CNS
• Sensory Division


  Conducts action potentials from sensory receptors to the CNS
• Motor Division


  Conducts action potentials to effector organs, such as muscles and glands
• Cells of the Nervous System

  • Neurons
  • Glial Cells
• Neurons


  Receive stimuli, conduct action potentials, and transmit signals to other neurons or effector organs
• Glial Cells

  Supportive cells of the CNS and PNS, do not conduct action potentials but carry out different functions that enhance neuron function and maintain normal conditions within nervous tissue
• Structural Types of Neurons

  • Multipolar neurons
  • Bipolar neurons
• Multipolar neurons


  Have many dendrites and a single axon, most neurons within the CNS and nearly all motor neurons are multipolar
• Bipolar neurons

  Have two processes: one dendrite and one axon, located in some sensory organs such as the retina of the eye and in the nasal cavity
• Glial Cells

  • Astrocytes
  • Ependymal cells
  • Microglial cells
  • Oligodendrocytes
  • Schwann cells
• Astrocytes

  Serve as the major supporting cells in the CNS, can stimulate or inhibit the signaling activity of nearby neurons and form the blood-brain barrier
• Ependymal cells


  Line the cavities in the brain that contains cerebrospinal fluid
• Microglial cells

  Act in an immune function in the CNS by removing bacteria and cell debris
• Oligodendrocytes

  Provide myelin to axons of neurons in the CNS
• Schwann cells

  Provide myelin to axons of neurons in the PNS
• Myelin Sheath

  Specialized layers that wrap around the axons of some neurons, formed by oligodendrocytes in the CNS and Schwann cells in the PNS, an excellent insulator that prevents almost all ion movement across the cell membrane
• Nodes of Ranvier

  Gaps in the myelin sheath where ion movement can occur, myelination of an axon increases the speed and efficiency of action potential generation along the axon
• Multiple sclerosis

  A disease of the myelin sheath that causes loss of muscle function
• Unmyelinated neurons

  Axons that lack myelin sheaths, rest in indentations of the oligodendrocytes in the CNS and the Schwann cells in the PNS
• Organization of Nervous System

  • Gray matter
  • White matter
• Gray matter

  Consists of groups of neuron cell bodies and their dendrites, where there is very little myelin
• White matter

  Consists of bundles of parallel axons with their myelin sheaths, which are whitish in color
• Resting Membrane Potential


  The electrical property of the cell membrane when the cell is at rest, with the inside of the membrane having a negative charge relative to the outside
• Leak channels


  Ion channels that are always open so ions can diffuse across the membrane, down their concentration gradient
• Gated channels


  Ion channels that are closed until opened by specific signals, including chemically gated channels and voltage-gated channels
• In most cells the inside of the membrane has a negative charge relative to the outside of the membrane which has a positive charge, and this voltage is called the resting membrane potential
• Nerve Cell Communication


  Nerve cells are excitable and can change their resting membrane potential in response to stimuli, using action potentials to communicate with other cells
• Action Potentials


  Electrical signals conducted along the cell membrane, generated by the opening and closing of voltage-gated Na+ and K+ channels
• Action Potential Conduction


  • Continuous conduction
  • Saltatory conduction
• Continuous conduction

  Action potentials travel along the entire membrane of unmyelinated axons
• Saltatory conduction


  Action potentials on myelinated axons occur in a jumping pattern at the nodes of Ranvier
• Synapse

  A junction where the axon of one neuron interacts with another neuron, with a presynaptic terminal, synaptic cleft, and postsynaptic membrane
• Neurotransmitters


  Chemical substances stored in synaptic vesicles in the presynaptic terminal and released into the synaptic cleft to bind to receptors on the postsynaptic membrane
• Neuronal Pathways

  • Converging pathway