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27 Cards in this Set

  • Front
  • Back
Define Resting
Membrane Potential.
def. the voltage difference that occurs across the PM when the cell is at rest; expressed in mV
How is a membrane potential created?
- charge separation across a membrane
- process:
1. diffusion of key ions
(Na+, K+, A-)down
their concentration
(conc. gradient)
2. result: charge
separation, creating
membrane potential
(electrical gradient)
3. electrical gradient =
conc. gradient
-> equilibrium
Factors Contributing to Concentration Gradient
1. High Intracellular
Macromolecular anions (A-)
-> net negative charge IC
2. High Extracellular Na+
due to Na+/K+ ATPase
-> net positive charge EC
3. High Intracellular K+
due to Na+/K+ ATPase
-> net negative charge IC
Function of Na+/K+ ATPase
- establishing and maintaining concentration gradients
Funciton of Leak Channels
- permit ions to flow down concentration gradients
Describe the relative
Permeability of the Membrane
to Na+, K+, and A-
- A- : impermeable,
infinite resistance
- Na+: permeable,
high resistance
- K+ : permeable,
low resistance
Equilibrium potential for K+
- Ek = -90 mV
- diffusion of K+
1. Conc. gradient
-> pushes K+ outward
2. Electrical gradient
-> pushes K+ inward
Equilibrium potential for Na+
- Ek = +60 mV
- diffusion of Na+
1. conc. gradient
-> pushes Na+ inward
2. electrical gradient
-> pushes Na+ outward
Define equilibrium potential.
- def. occurs when the concentration gradient and transmembrane voltage becomes equal and opposite
- calculated using Nernst equation: Vm= 61 log [co]/[ci}
Vm = transmembrane voltage
co = EC conc of ionic species
ci = IC conc of ionic species
What factor will shift Vm toward equilibrium for a particular ion?
- transient changes in the permeability of the membrane to that particular ion
Structure of a neuron.
1. soma - cell body of a neuron
2. dendrite - membranous processes extending from the soma tha receive synaptic inputs from other neurons
3. axon - a single specialized membranous processes that conducts AP; 2 parts
a. axon hillock - part of
axon that extends from
the soma where AP are
b. axon terminals -
distal end of axonal
fibers that releases
synaptic fibers
Define Graded Potentials.
- short distance changes in
membrane potentials
- occur as a depolarization or
hyperpolization as a result
from chemical synaptic
Define Action Potentials.
- brief all-or-nothing
reversal in membrane
potential caused by rapid
changes in membrane
permeability via voltage
gated channels
- long distance signaling
- signal transmission lasts ~1
Initiation of an Action Potential.
- initiated in axonal or
somatic membrane in response
to depolization beyond a
threshold potential
Define Threshold
def. the membrane potential, which, when reached, leads ineveitably to the occurence of a spike
Define the Absolute Refractory Period for AP
def. a brief period during a spike in which a second spike cannot be generated due to inactivation
Define the Inactivation Period for AP
def. occurs more slowly than channel opening (activation) and contributes to the termination of a spike
Define the after hyperpolarization period (AHP)for AP
def. a brief period at the end of a spike in which the membrane potential is more negative than at rest
Define the Relative Refractory Period of AP
def. a brief following a spike during which a higher intensity stimulus is needed to generate a second spike
Propagation of AP
- propagation occurs when locally generated depolarizing current spreads to adjacent regions of memrbane causing it to depolarize
- conduction velocity proportional to axonal diameter and increased by myelin
2 types of AP propagation
1. contiguous conduction
2. saltatory conduction
Define contiguous conduction.
-propagation of AP in unmyelinated fibers
-relatively slow & inefficient
Define Saltatory Conduction
-propagation of AP in myelinated fibers b yjumping from node to node
- current flow at regular interval
Define myelin.
def. a multilayered sheath of PM, derived from specialized glial cells, that wraps around axonnal fibers and acts as an insulator to the flow of current
- They occur at regular interval, but is interrupted by gaps in the insulation called Nodes of Ranvier that contains high densities of voltage-gated Na+ and K+ channels and can generate AP
Define Schwann Cells
def. myelin-forming glial cells in the peripheral nervous system
Define Oligodendrocytes
def. myelin-forming glial cells in the CNS
Define demyelinating Diseases
def. disease, such as multiple sclerosis, resulting from the degeneration of myelin