Npb_Resting Potential And Graded Potential

Front 1

Define Resting
Membrane Potential.

Back 1

def. the voltage difference that occurs across the PM when the cell is at rest; expressed in mV

Front 2

How is a membrane potential created?

Back 2

- charge separation across a membrane
- process:
1. diffusion of key ions
(Na+, K+, A-)down
their concentration
gradient
(conc. gradient)
2. result: charge
separation, creating
membrane potential
(electrical gradient)
3. electrical gradient =
conc. gradient
-> equilibrium

Front 3

Factors Contributing to Concentration Gradient

Back 3

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

Front 4

Function of Na+/K+ ATPase

Back 4

- establishing and maintaining concentration gradients

Front 5

Funciton of Leak Channels

Back 5

- permit ions to flow down concentration gradients

Front 6

Describe the relative
Permeability of the Membrane
to Na+, K+, and A-

Back 6

- A- : impermeable,
infinite resistance
- Na+: permeable,
high resistance
- K+ : permeable,
low resistance

Front 7

Equilibrium potential for K+

Back 7

- Ek = -90 mV
- diffusion of K+
1. Conc. gradient
-> pushes K+ outward
2. Electrical gradient
-> pushes K+ inward

Front 8

Equilibrium potential for Na+

Back 8

- Ek = +60 mV
- diffusion of Na+
1. conc. gradient
-> pushes Na+ inward
2. electrical gradient
-> pushes Na+ outward

Front 9

Define equilibrium potential.

Back 9

- 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

Front 10

What factor will shift Vm toward equilibrium for a particular ion?

Back 10

- transient changes in the permeability of the membrane to that particular ion

Front 11

Structure of a neuron.

Back 11

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
generated
b. axon terminals -
distal end of axonal
fibers that releases
synaptic fibers

Front 12

Define Graded Potentials.

Back 12

def.
- short distance changes in
membrane potentials
- occur as a depolarization or
hyperpolization as a result
from chemical synaptic
transmission

Front 13

Define Action Potentials.

Back 13

def.
- 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
ms

Front 14

Initiation of an Action Potential.

Back 14

- initiated in axonal or
somatic membrane in response
to depolization beyond a
threshold potential

Front 15

Define Threshold

Back 15

def. the membrane potential, which, when reached, leads ineveitably to the occurence of a spike

Front 16

Define the Absolute Refractory Period for AP

Back 16

def. a brief period during a spike in which a second spike cannot be generated due to inactivation

Front 17

Define the Inactivation Period for AP

Back 17

def. occurs more slowly than channel opening (activation) and contributes to the termination of a spike

Front 18

Define the after hyperpolarization period (AHP)for AP

Back 18

def. a brief period at the end of a spike in which the membrane potential is more negative than at rest

Front 19

Define the Relative Refractory Period of AP

Back 19

def. a brief following a spike during which a higher intensity stimulus is needed to generate a second spike

Front 20

Propagation of AP

Back 20

- 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

Front 21

2 types of AP propagation

Back 21

1. contiguous conduction
2. saltatory conduction

Front 22

Define contiguous conduction.

Back 22

def.
-propagation of AP in unmyelinated fibers
-relatively slow & inefficient

Front 23

Define Saltatory Conduction

Back 23

def.
-propagation of AP in myelinated fibers b yjumping from node to node
- current flow at regular interval

Front 24

Define myelin.

Back 24

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

Front 25

Define Schwann Cells

Back 25

def. myelin-forming glial cells in the peripheral nervous system

Front 26

Define Oligodendrocytes

Back 26

def. myelin-forming glial cells in the CNS

Front 27

Define demyelinating Diseases

Back 27

def. disease, such as multiple sclerosis, resulting from the degeneration of myelin