Week 2 material

• What is the flow of the signal in nervous system?

  dendrites to cell body to axon to axon terminal to next cell via synapse
• Microtubules


  backbone of an axon
• afferent neurons


  Nerve cells that carry impulses towards the central nervous system
• efferent neurons


  Nerve cells that conduct impulses away from the central nervous system
• interneurons


  Central nervous system neurons that internally communicate and intervene between the sensory inputs and motor outputs
• Glial Cells


  make up 90% of the cells in the nervous system. They don't convey information. Rather they serve to support nerve cells
• Schwann cells


  myelinate peripheral neurons (PNS)
• Oligodendendrocytes


  myelinate CNS neurons
• Ependymal cells


  Form sheets that line the brain ventricles (cavities)
• Astrocyte


  control composition of CNS extracellular fluid (ion and glucose concentration, permeability of capillaries)
• Microglia


  immune functions in brain
• voltage gated channels


  open and close in response to changes in membrane voltage potential
• ligand gated channel


  Open in response to binding of small chemical messengers
• What two forces do you need to consider when ions are moved in or out of cell?

  Concentration gradient and electrical potential
• membrane potential


  By convention the ECF is defined as zero voltage, so the excess of + or - charges in the cell defines this
• Electrical potential


  The ability (used or not) to move electrical charges (units of volts, V)
• electrical current


  When charges move this is the result (I)
• Ohm's Law


  I = V/R where for a given potential, the amount of current will be a function of the resistance (R) of the media
• Resistance (R) in Ohm's law

  For a cell, it is a function of the number of open ion channels
• Which ion are cells more permeable to and why?

  More permeable to K+ than Na+ because of leak channels
• What does the Na+/K+ ATPase maintain?

  Resting potential of the cell. Unequal transport of 3Na+ out and 2K+ in generates part of the membrane potential
• When is a cell at equilibrium potential?

  force of the concentration gradient and the electrical potential exactly balance each other out. There is no net movement of ions in and out of cells
• Nernst equation


  E(ion) = 61/z * log[ C out / C in ]

  Finds the equilibrium potential of a given ion in mVolts. Tells how much electrical potential could build up given the concentration differences
• Driving force


  Determines if an ion will enter or exit a cell

  Driving force = membrane potential - ion potential
• What does a negative DF mean?


  A cation will enter the cell while an anion will exit the cell
• What does a positive DF mean?


  An anion will enter the cell while a cation will exit the cell
• What does it mean if membrane potential is equal to ion potential

  No net movement will occur
• resting potential


  Membrane potential of a neuron or other excitable cell when it is not signaling. Characterized by higher K+ permeability than Na+ permeability
• Synapse


  Points of connection between neurons
• Convergence


  One nerve cell can have thousands of of synaptic inputs
• Divergence


  One nerve cell can contact many other cells at synapses
• What are the two types of synapses?

  chemical and electrical
• Electrical synapse


  simpler, less abundant, and faster than chemical synapses

  the cytoplasm of the pre- and post-synaptic cells are joined by gap junctions.

  Proteins called connexins form hollow tubes that allow for cytoplasms of adjacent cells to be interconnected. This allows direct flow of current from one cell to the next.

  Electrical synapses are found in neural systems that require the fastest possible response (example is defensive reflexes) and are used for simple behaviors.
• Chemical synapse


  Involve a synaptic cleft/gap where a neurotransmitter (chemical signal) is released into it due to the arrival of an action potential to the axonal terminus. The neurotransmitter then binds to a receptor on the post-synaptic cells which may cause either depolarization or hyperpolarization. There is a brief delay in synaptic transmission because of the time it takes for the release, diffusion, and binding of the neurotransmitter.

  
  

  Chemical synapses allow for the biological computations that underlie both unconscious behaviors and conscious thought.
• Acetylcholine (Ach)


  Excitatory neurotransmitter

  Two types of receptors: nicotinic, muscarinic

  Regulation of muscle movement
• Dopamine (DA)


  A catecholamine (synthesize from tyrosine) that acts in a reward pathway in the central nervous system
• Norepinephrine (NE)


  A catecholamine (synthesize from tyrosine) that is involved in the fight or flight response
• Epinephrine


  A catecholamine (synthesize from tyrosine) that usually acts as a hormone and has similar effects to norepinephrine
• Serotonin


  Derived from tryptophan, can be excitatory or inhibitory, and helps with control of mood
• Glycine


  Inhibitory and receptor is a Cl- channel. Acts primarily in the spinal cord. It is an antioxidant and an AA