18. AP FA18 - UNIT 5 - Chapter 11 Part II Lecture Notes.pdf...

BIOL 2401 Human Anatomy and Physiology I Dr. Newsome
Chapter 11 Part II
Action Potentials
As discussed in the muscle tissue section, neurons can initiate action potentials. Review the terms given
below using the Chapter 9 course notes on electrical activity in the last unit (thank goodness this is
review and not the initial lecture over this material!).
• Sodium and potassium influence on electrical activity – these ions create the potential for electrical
activity in muscle cells and neurons. Potassium concentration is higher inside the cell and sodium is
higher outside of the cell. At rest, sodium does not easily enter the cell, but potassium can exit
through open leak channels.
• Sodium-potassium pump – active transport pump on the membrane that pumps out 3 Na+ and
brings in 2 K+ into the cell. This activity maintains concentrations of Na+ and K+ and helps create the
resting membrane potential. Requires ATP.
• Resting membrane potential – different ion permeabilities and different concentrations in and
outside of the cell create a more negative charge on the inside and a more positive charge on the
outside of the neuron. A resting membrane is also said to be polarized (oppositely charged on the
inside and outside of the membrane).
• Depolarization – shift in membrane potential to a more positive charge on the interior of the
membrane due to sodium gates opening and allowing sodium entry into the cell.
• Action potential – a depolarization that spreads down the entire cell (neuron); requires a threshold
stimulus.
• Threshold stimulus – depending on the type of neuron, usually about 100 millivolts.
• All or none response – a depolarization either causes an action potential or doesn ’t cause a change
in the neuron that can spread (propagate) along the entire membrane.
• Repolarization – return to resting membrane potential by establishing the sodium and potassium
levels inside and outside of the cell (sodium is moved out of the cell).
• Refractory period – period of time when the membrane cannot respond to an action potential
• Hyperpolarized – membrane potential is shifted towards a more negative value (e.g. -70mV shifts to
the more negative -90mV). Direct result of chloride gates opening on the membrane allowing more
Cl- to enter the cell or the opening of all K+ gates to allow K+ to exit the cell.
Effects of Anesthetics, Sedatives, and Alcohol on the Action Potential
Remember the last time you had a filling, or a tooth extracted at the dentist?
(maybe you don't want to remember!). The dentist "numbs" or anesthetizes your
mouth before she begins to drill or work on your teeth. You know that funny
feeling of numbness. Dental anesthetics such as lidocaine and novocaine inactivate
the sodium gates so action potentials cannot occur . Drilling or pulling of teeth
produces many action potentials interpreted as PAIN by the brain. Without novocaine, the drilling on
your teeth would cause a barrage of action potentials carrying pain information to the brain and create