Exam 1 Flashcards
What is a “membrane potential”?
a membrane potential is the voltage difference between the inside and outside of a cell.
The membrane potential has two basic functions:
- Allows a cell function a a battery, providing power to operate a variety of “molecular devices” embedded in the membrane
- In electrically excitable cells such as neurons, it is used for transmitting signals between different parts of a cell.
Three types of membrane potentials:
- Resting membrane potential
- Action potentials
- Synaptic potentials
Resting potential
this is used to refer to the membrane potential of nerve and muscle cells not actively signaling.
Why does the resting potential exist?
Membrane potential result from a separation of positive and negative charges (ions) across the membrane.
Nernst Equation
The equilibrium potential for an ion can be calculated using this
The Goldman Equation
infers that the membrane potential of an excitable cell is most strongly influenced by the concentration difference of the ion to which the membrane is most permeable since each permeant ion attempts to drive the membrane potential towards it own equilibrium potential.
Action potentials play an important role in:
- Information coding
2. Information transfer
What information is encoded by action potentials?
Intensity (strength)
Timing
Quality
Where are action potentials generated?
Action potentials are generated at the axon hillock. Once generated, they propagate down the axon away from the cell body and towards the axon terminals.
How are action potentials generated?
By the movement of Na+ and K+ ions through voltage-gated ion channels.
R(o)
Represents the resistance of the extracellular fluid to ion flow down the length of the axon.
R(l)
represents the resistance of the cytoplasm to ion flow down the length of the axon
R(m)
represents the resistance to ion flow across the membrane (membrane resistance)
C(m)
represents the capacity of the membrane to store charge (membrane capacitance).
Increasing axon diameter…
decreases R(l)
Increasing axon diameter increases the conduction velocity of action potentials
Decreasing axon diameter decreases the conduction velocity of action potentials
Myelin is formed by…
Schwann cells (peripheral nervous system) oligodendrocytes (central nervous system)
Myelination…
increases Rm and decreases Cm
Rm is determined by..
the number of open ion channels in the axonal membrane through which ions can pass
the larger the number of open ion channels the small the Rm
A capacitor is…
an electrical component comprised of two conductive plates separated by an insulating material (dielectric).
Capacitors store “charge” via electrostatic interactions.
The amount of charge stored in a capacitor depends upon:
- Surface area of plates (larger area, greater capacitance).
- Thickness of the dielectric (thicker the dielectric, smaller capacitance.
What does the thickness of the lipid bilayer as a result of the myelin sheath do?
This decreases the membrance capacitance Cm, reducing the amount of charge that can be stored across the membrane
More ions are available to move down the length of the axon contributing to rapid depolarization of membrane at the nodes of Ranvier and subsequent action potential formation
Synaptic transmission
synaptic potentials represent the transfer of info from one neuron to another at a specialized region called a synapse
synaptic potentials are..
changes in the membrane potential of the postsynaptic terminal of a synapse due to activity in a presynaptic neuron
they function to initiate or inhibit action potential formation in the postsynaptic neuron
