anatomy & physiology

• Functions of the Nervous System

  • Controls voluntary and involuntary movement of the body
  • Homeostasis
  • Sensing stimuli
  • Responding to stimuli
• Central Nervous System (CNS)

  Brain and spinal cord
• Components of the Peripheral Nervous System

  • Afferent (sensory)
  • Efferent (motor)
• Components of the Somatic Nervous System

  • Voluntary motor
• Components of the Autonomic Nervous System

  • Parasympathetic (rest and digest)
  • Sympathetic ("Fight or flight")
• Characteristics of Nervous Tissues

  • Excitable
  • Able to send/receive electrochemical signals that provide the body with information
• Neuron

  Cell body, dendrites, axons (nerve fiber), axon hillock
• Nissl bodies


  Help in protein synthesis of neurons, discrete clumps of rough endoplasmic reticulum and free ribosomes in nerve cells
• Axolemma

  Conveys signals between the neuron and its Schwann cells
• Axon terminals

  Ends of axons which transmit messages to other cells via use of neurotransmitters at synapses
• Myelin sheath

  Protects axons and helps speed nerve transmissions
• Nodes of Ranvier

  Specialized regions in the axonal membrane that are not insulated by myelin
• Structural Classification of Neurons

  • Multipolar (most common in the CNS, form autonomic ganglia, single axon with several symmetrically tapering dendrites)
  • Bipolar (one axon and one dendrite)
  • Unipolar (only has one nerve process extending from the cell body: an axon that extends into dendrites)
• Functional Classification of Neurons

  • Sensory (afferent limb of somatosensory neural pathways)
  • Motor (located in CNS, controlling a variety of downstream targets)
  • Interneurons (connect spinal motor and sensory neurons)
• Astrocytes


  CNS, parorm metabolic
• Microglial cells


  • CNS, first to respond
  • When things go wrong
• Ependymal cells


  CNS, control production and flow of cerebrospinal fluid
• Oligodendrocytes


  CNS, allow fast and efficient transfer of neuronal communication through the myelination of axons
• Schwann cells


  PNS, maintain PUS
• Satellite cells

  PNS, muscle regeneration throughout the lifespan
• Ganglia

  Groups of nerves or brain
• Tracts

  A system of body parts or organs that act together to perform some function
• Nerves


  Cables that carry electrical impulses between your brain and the rest of your body
• White matter


  Made up of myelinated axons
• Gray matter


  Made up of neuronal cell bodies
• Neurophysiology


  The study of how the nervous system works
• Neurons


  The functional units of the nervous system
• Neurons


  • Use electrical signals and chemicals to communicate
  • Electrical signals are produced when ions move across membranes
• Gated ion channels


  Can be either open or closed
• Types of gated ion channels

  • Ligand-gated
  • Mechanically-gated
  • Voltage-gated
• Membrane potential


  The charge difference across a membrane
• Resting membrane potential


  About -70 millivolts (negative membrane potential means inside is more negative than outside)
• Na+/K+ pump


  Pumps about 3 Na ions out of cell for every 2 K+ ions pumped into the cell, making the inside of the cell more negative
• Graded potentials


  Short-distance signals
• Action potentials


  Long-distance signals, transient reversals of the membrane potential
• Action potentials


  • All or none events caused by the diffusion of Na+ and K+ ions
  • Threshold (about -55 millivolts) is the membrane potential that must be reached for the AP to begin
• Phases of an action potential

  1. Depolarization

  2. Repolarization

  3. Hyperpolarization
• Continuous conduction


  Slower conduction in unmyelinated axons
• Saltatory conduction


  Faster conduction in myelinated axons, action potentials jump over myelinated regions
• Factors affecting conduction speed

  • Diameter of the axon (thick faster, thin slower)
  • Amount of myelination (heavily myelinated faster, slightly myelinated medium, unmyelinated slowest)