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Week 8
Lecture 2
46
Anatomy
Undergraduate 2
10/30/2014

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Term
What is potential energy?
Definition
the separation of positive and negative charges which results in stored energy which is referred to as voltage
Term
What is kinetic energy?
Definition
when the potential energy is released and work is done; allowing the separated charges to move freely will create a current
Term
What is resistance?
Definition
the force which slows down the current flow
Term
What is an insulator?
Definition
substance which inhibits current flow
Term
What is a conductor?
Definition
substance with promotes current flow
Term
What is Ohm's law?
Definition
basic equation that states that:
-current=voltage/resistance
-current varies as the voltage varies
Term
What is the ion flow in a living system equivalent to?
Definition
the current flow
Term
What creates the potential energy situation in living systems?
Definition
the charge separation across a membrane
Term
What is the equivalent of an insulator in a living system?
Definition
the plasma membrane
Term
What is the equivalent of a conductor in a living system?
Definition
the proteins embedded in the plasma membrane
Term
What are passive channels?
Definition
(AKA leakage channels) typically always open and allow specific ions to flow through them
Term
What are active channels?
Definition
(AKA gated channels) only open when they are stimulated; chemically gated channels and voltage gated channels
Term
What are chemically gated channels?
Definition
opens when something binds to the particular transmembrane protein; after it opens, it provides a pathway for ions to flow in or out
Term
What are voltage gated channels?
Definition
opened by a change in potential energy; opens because there is a change in ion distribution at or about the membrane
Term
What are the two factors that influence current flow?
Definition
-electrical charge movement
-chemical diffusion
Term
What is electrical charge movement?
Definition
ions that are charged will move to an area that contains an opposite charge
Term
What is chemical diffusion?
Definition
diffusing from an area of high concentration to low concentration
Term
What do both electrical charge movement and chemical diffusion do?
Definition
together they create an electrochemical gradient
Term
What is the resting membrane potential?
Definition
created by unequal concentrations of ions of both charges that exist in a narrow band around each side of the cytoplasmic and extracellular sides of the plasma membrane
Term
What is the composition of a resting membrane potential?
Definition
potential energy is created by separation of charges and a concetration gradient; it is created due to the chemical and electrical forces that develop by separating these ions
Term
What are the charges on either side of the membrane?
Definition
inside the cell is slightly negative and outside is slightly positive
Term
What is polarization of the membrane?
Definition
basis of electrical conductivity of cells that are capable of conducting action potentials
Term
What is the resting membrane potential of the typical cell?
Definition
-70 mV
Term
What is polarization?
Definition
specific ions are separated at different concentrations immediately around the membrane
Term
What generates concentration differences?
Definition
Na+/K+ pump and # of passive potassium channels vs # of passive sodium channels
Term
How does the presence of Na+/K+ pumps in the plasma membrane generate concentration differences?
Definition
-pump requires ATP because moves ions agains concentration gradient
-pumping prevents equilibrium from being reached
-maintains an unequal distribution of ions and therefore creates an electrochemical gradient
Term
How does the # of passive potassium channels vs # of passive sodium channels generate concentration differences?
Definition
-# of K+ passive channels is greater
-K+ is able to move more freely than sodium, from in to out
-Na+ has been pumped out of cell but wants to go back in but can't because there isn't as many channels
-this leaves an unequal concentration gradient where plasma membrane is slightly - on inside and slightly + on outside
Term
Why are some cells capable of altering their plasma membrane potential?
Definition
they are either carrying a message of going to do a specific type of work; have gated channels
Term
What are characteristics of a polarized cell?
Definition
-charge is separated across membrane
-any cell at RMP is polarized because cell has different concentrations of ions across membrane
-RMP= -70 mV
Term
What are characteristics of a depolarized cell?
Definition
-charges have been allowed to flow across membrane
-0 mV
Term
What are characteristics of a hyperpolarized cell?
Definition
-cell that is more polarized than it would normally be
-potential energy is greater
-separated more ions than normally would have been
Term
What are characteristics of a repolarized cell?
Definition
-membrane has returned to normal from having been somewhere else
Term
What are mechanisms of change in plasma membrane potential?
Definition
-graded potential
-action potential
Term
What are characteristics of graded potential cell membranes?
Definition
-chemically gated channels
-channels open and few ions move across
-no voltage gated channels
-change in potential is relatively small
-can be depolarized (move in -> out) or hyperpolarized (move out -> in)
Term
What are characteristics of action potential cell membranes?
Definition
-voltage gated channels
-specific for single ion
-at least two types of channels (Na+ and K+ are necessary)
-different ions move in opposite directions
-has to be initiated by change in voltage
Term
What are the 4 phases of an action potential?
Definition
1. resting phase
2. active phase: depolarization
3. active phase: repolarization
4. active phase: hyperpolarization
Term
What happens in the resting phase of an action potential?
Definition
cell is at rest, meaning that it is at its resting membrane potential and all of the gated channels are closed
Term
What happens in the active phase: depolarization of an action potential?
Definition
chemically gated channels have opened and Na+ enters which then depolarizes the membrane and causes the Na+ voltage gated channels to open
Term
What happens in the active phase: repolarization of an action potential?
Definition
Na+ channels close and the K+ voltage channels open
Term
What happens in the active phase: hyperpolarization of an action potential?
Definition
K+ ions continue to flow out of voltage gated channels, which stay open a while; have more polarization than would be necessary to return to baseline
Term
What is action potential propogation?
Definition
in the case of skeletal muscle, action potential will travel down both sides while others will just go in one direction and go around
Term
What is the action potential threshold?
Definition
must have enough of the stimulus in order to open the voltage gated channels
Term
What is the all or none rule?
Definition
once the voltage gated channels have opened, the action potential will proceed, no matter what
Term
What is the refractory period?
Definition
-period of time where we have just completed an action potential and we have hyperpolarized or repolarized
-period of time when Na+ and K+ ATPases are working and restoring membrane back to its original concentration
Term
What is the absolute refractory period?
Definition
immediate period directly after the action potential stimulus has passed through and because the ions are on the wrong side of the membrane, that particular membrane is capable of generating an action potential
Term
What is the relative refraactory period?
Definition
a little later than absolute period; period where Na+ and K+ ATPase have had a little chance to work to restore the ion concentrations to where it's supposed to be; large stimulus can then generate and action potential
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