Lecture 7: Electrochemical Basis of Neuronal Function

• What is one of the most prominent features of the nervous system?

  Excitability of neurons
• How do neurons communicate within the body?

  Through chemical and electrical means
• What is the potential of inactive cells called?

  Resting membrane potential
• What happens when a neuron receives excitatory or inhibitory signals?

  It generates graded potentials
• What is the action potential in neurons?

  A reversal of membrane potential
• What causes membrane potentials?

  Ion concentration difference across the membrane
• What is the potential difference required in a normal mammalian nerve fiber?

  About 94 millivolts
• What is the resting membrane potential of a neuron?

  –90 millivolts
• What determines the resting membrane potential?

  Concentration gradients of ions and membrane permeability
• Which ions are positively charged cations found in neurons?

  Na+ and K+
• Where are K+ and organic anions found in higher concentrations?

  Inside the cell
• Where are Na+ and Cl- found in higher concentrations?

  Outside the cell
• What creates an electrochemical gradient in neurons?

  Unequal concentrations of ions across the membrane
• How do ions move to create resting membrane potential?

  Through leak channels
• What type of channels are open in resting neurons?

  Leak channels
• Why is the resting potential closer to the equilibrium potential of K+?

  The membrane is more permeable to K+
• What other ions contribute to the resting potential?

  Na+ and Cl-
• What may dissipate the membrane potential?

  Constant movement of ions through leak channels
• How is the negative resting potential maintained inside the cell?

  By the Na+-K+ Pump
• What are brief local changes in postsynaptic membranes called?

  Graded potentials
• How are graded potentials generated?

  In response to neurotransmitters from presynaptic neurons
• What does the amplitude of graded potentials depend on?

  Intensity of the stimulus applied
• What effect do graded potentials have on the postsynaptic neuron?

  They shift the resting membrane potential
• What is a depolarizing graded potential called?

  Excitatory postsynaptic potential (EPSP)
• Which neurotransmitters induce EPSPs?

  Acetylcholine and glutamate
• What do EPSPs do to the postsynaptic membrane potential?

  Drive it toward the threshold
• What neurotransmitters induce inhibitory postsynaptic potentials (IPSPs)?

  GABA and glycine
• What is hyperpolarization in the context of IPSPs?

  A shift toward a more negative potential
• What are synapses that induce IPSPs called?

  Inhibitory synapses
• What factors determine whether the postsynaptic membrane is stimulated or inhibited?

  Transmitter involved and ion permeability change
• How do presynaptic axons affect the postsynaptic neuron?

  They generate thousands of EPSPs and IPSPs
• What are the two modes of summation for graded potentials?

  • Spatial summation: graded potentials from different synapses
  • Temporal summation: graded potentials from successive presynaptic terminals
• What generates an action potential in a nerve fiber?

  Rapid changes in membrane potential
• What is the initial change in membrane potential during an action potential?

  A sudden change to a positive potential
• What happens after the positive potential in an action potential?

  Rapid change back to negative potential
• How does the action potential differ from graded potentials?

  Action potentials are rapid and all-or-nothing
• What are the negatively charged ions inside the axon called?

  Anions
• What is the role of impermeant negatively charged ions in the axon?

  They create a negative charge inside the fiber
• What do calcium pumps do in the cell membrane?

  They pump calcium ions outside the cell
• What type of channels are numerous in cardiac and smooth muscle?

  Voltage-gated calcium channels