trasmission within neurons

• Sensory neurons


  Carry information from the body to the central nervous system
• Motor neurons


  Carry information from the central nervous system to the body
• Interneurons


  Link sensory and motor neurons
• Neuron


  • Soma (cell body)
  • Dendrites (receive messages)
  • Axon (carries information as action potential from soma to terminal buttons)
  • Myelin sheath (wraps around axon)
  • Terminal buttons (at end of axon branches)
• Glia (glial cells)


  Supporting cells including astrocytes, oligodendrocytes, and microglia
• Oligodendrocytes


  Produce the myelin sheath that insulates axons
• Node of Ranvier


  Naked axon
• Glia


  • Provide support, waste services, supply of nutrients and chemicals
• There are 86 billion neurons in the human brain (Azevedo et al., 2009)
• Neurons and glia (astrocytes, oligodendrocytes) do all the information processing and information transmitting
• The central nervous system (CNS) is the brain and spinal cord, the peripheral nervous system (PNS) is all other nerves
• Cells have an electrical charge, with the inside more negative than the outside
• Resting potential


  The difference in electrical potential inside and outside the cell, which is a store of energy
• Membrane potential


  The difference in electrical potential inside and outside the cell
• Ions


  Charged molecules, including cations (positively charged) and anions (negatively charged)
• Intercellular fluid contains potassium ions (K+) and anions (A-), extracellular fluid contains sodium (Na+) and chloride (Cl-) ions
• Diffusion


  The movement of ions down their concentration gradient
• Electrostatic pressure


  The attraction or repulsion of ions due to their charge
• The resting potential of a neuron is -70 mV
• Action potential


  A rapid change in the membrane potential, an 'all or none' process that is how information is sent through an axon
• Action potential transmission


  1. Depolarization (decrease from normal resting potential)

  2. Sodium channels open, sodium ions enter cell

  3. Potassium channels open, potassium ions leave cell

  4. Sodium channels close, potassium channels close

  5. Membrane becomes hyperpolarized (more negative than resting potential)

  6. Sodium-potassium pump restores resting potential
• Saltatory conduction


  Action potential regenerated along the axon at nodes of Ranvier, enabling fast and energy-efficient transmission
• Synaptic transmission


  Neurotransmitters are released from one neuron and attach to another neuron, initiating a reaction that ultimately results in postsynaptic potentials
• Synapse


  The junction between two neurons (terminal buttons & membrane)
• Synaptic transmission


  1. Neurotransmitter binding

  2. Postsynaptic potential generation
• Neurotransmitter binds to binding site on post-synaptic membrane (lock and key)
• EPSP


  Excitatory postsynaptic potential
• IPSP


  Inhibitory postsynaptic potential
• Ionotropic receptor


  • Contains a binding site and an ion channel. This opens when molecule attaches to binding site.
• Metabotropic receptor


  • Contains a binding site. Initiates a chain reaction that eventually opens ion channels. Requires energy.
• Postsynaptic potentials produced by metabotropic receptors are slower than those produced by ionotropic receptors
• Termination of neurotransmitter


  1. Enzymatic deactivation/degradation

  2. Reuptake
• Enzymatic deactivation/degradation


  • Acetylcholinesterase breaks down Ach into choline and acetic acid
• After diffusing across the cleft, neurotransmitter attaches to a binding site
• An ionotropic receptor is a direct method of opening a channel
• In the terminal button, neurotransmitter is contained in vesicles
• Ca2+ ion enters at the terminal button on arrival of the action potential
• Excitatory


  Increases likelihood of neuron firing
• Inhibitory


  Decreases likelihood of neuron firing
• Neural integration


  Summation of PSPs in control of neuron firing