Psych 4

• Camillo Golgi


  Staining tissue showed an "interconnected net of fibres", called it a "nerve net"
• Santiago Ramón y Cajal


  Staining embryonic cells showed discrete cells of many sizes, proposed the Neuron Hypothesis

  
• Neuron Hypothesis


  • Neurons are the nervous system's functional units
  • Discrete cells that make up all of the nervous system
  • Today's accepted theory of brain organization

  
• Cell body (soma)


  Core region of cell, contains organelles for basic cell functions (including nucleus), integrates information
• Dendrites


  Branching extensions that collect information from other cells
• Axon


  Main projection from soma, carries messages to other cells
• Axon hillock


  Juncture of the soma and axon, where the action potential begins

  
• Axon collaterals


  Branches of an axon
• Telodendria


  End branches of an axon
• Terminal button


  Knob at the tip of an axon, conveys information to other neurons (aka end foot)
• Dendritic spine


  Protrusion from dendrite, greatly increases surface area, usual point of contact with axons of other cells
• Synapse


  Gap between one neuron and the next, usually between an end foot of the axon of one neuron and a dendritic spine of another neuron
• Types of Neurons


  • Motor neuron
  • Sensory neurons
  • Interneurons

  
• Stellate (star-shaped) cell


  Small; many dendrites extend around the cell body; larger brains contain more (behavioral complexity)
• Pyramidal cell


  Has a long axon, a pyramid-shaped cell body, and two sets of dendrites, apical and basal; carries information from cortex to rest of brain and spinal cord

  
• Purkinje cell


  Distinctively shaped with extremely branched dendrites that form a fan; carries information from cerebellum to rest of brain and spinal cord
• Glial Cells


  • Ependymal cell
  • Astrocyte
  • Microglial cell
  • Oligodendroglial cell
  • Schwann cell
• Ependymal Cells


  Small, ovoid; found in the walls of the ventricles, make and secrete cerebrospinal fluid (CSF)
• Astrocytes (aka Astroglia)


  Star shaped, symmetrical, provide structural support for neurons, transport substances between neurons and capillaries (blood–brain barrier), enhance brain activity by providing fuel to active brain regions, promote healing of damaged brain tissue
• Microglia


  Originate in the blood as offshoot of immune system, involved in scavenging of debris (e.g., dead cells); phagocytosis, monitor the health of brain tissue and play the role of its immune system, identify and attack foreign tissue, invade the area to provide growth factors that aid in repair when brain cells are damaged
• Oligodendrocytes


  Glial cells which produce myelin in the brain and spinal cord, almost 75% of glial cells in the brain are oligodendrocytes

  
• Schwann cells


  Glial cells which produce myelin in the rest of the nervous system

  
• Polarization


  A state in which there is a difference in electrical charge between the inside and outside of the neuron
• Voltage


  Measure of the difference in electrical charge between two points
• Resting potential


  Difference in charge between inside & outside of membrane of a neuron at rest

  
• Voltmeter


  Device that measures the difference in electrical potential between two bodies
• Ions


  Atoms that have lost or gained electrons, positive (Na+, K+), negative (Cl-, A-)
• Force of diffusion


  Tendency of ions to move through membrane to less concentrated side

  
• Electrostatic pressure


  Force where ions are repelled from similarly charged, attracted to oppositely charged
• Sodium potassium pump


  Large protein molecules that move sodium ions through cell membrane to outside, potassium ions back inside
• Ion channels


  Gated pores in the membrane formed by proteins, limit the flow of ions into and out of the cell, can be chemically gated or electrically gated

  
• Voltage-Activated Ion Channels


  Gated protein channels that open or close only at specific membrane voltages, sodium (Na+) and potassium (K+) channels, closed at membrane's resting potential, Na+ channels are more sensitive than K+ channels and, therefore, open sooner

  
• Local potential


  Partial depolarization, polarity in an area shifts toward zero when disturbed, is a graded potential, varies in magnitude with the strength of the stimulus that produced it
• Action potential


  Abrupt depolarization of membrane that allows neuron to communicate, is ungraded, all-or-none law, nondecremental, propagated at each successive point along the way
• Hyperpolarization


  Increase in electrical charge across a membrane (more negative), usually due to the inward flow of chloride ions or outward flow of potassium ions
• Absolute refractory period


  Sodium ion channels are unresponsive to further stimulation, a new action potential cannot occur
• Relative refractory period


  Sodium ion channels could support another action potential, but potassium channels are still open, a new action potential can occur, if the stimulation is sufficiently strong enough to overcome the charge
• Rate law


  Axon encodes stimulus intensity not in the size of its action potential but in its firing rate
• Excitatory postsynaptic potential (EPSP)

  When receptors open sodium channels to produce a partial depolarization of the dendrites and cell body
• Inhibitory postsynaptic potential (IPSP)


  When receptors open potassium channels, chloride channels, or both to produce a hyperpolarization of the dendrites and cell body