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A/P I: Chapter 11 & 17
Receptor Responses and Membrane Potentials
32
Anatomy
Undergraduate 2
09/23/2009

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Cards

Term
Ligand
Definition
Chemical Signal
Term
Function/Characteristics of Ligands
Definition

Allow for communication between cells.

Act to produce reaction w/in another cell.

Classified by receptor site.

Term
Two classifications of ligands
Definition

Membrane-bound

Intracellular

Term
Ligand-gated Ion Channel
Definition
Ligand receptor binds and stimulates opening of channel.
Term
G Protein
Definition
Three subunits linked to a membrane bound receptor that activate a response in the cell.
Term

Three actions of the alpha subunit

in a G Protein

Definition

1. Alter membrane permeability

2. Activate Intracellular mediators

3. Alter functional cellular pathways

Term
Four steps of the G Protein activation process
Definition
  • 1. Chemical binds with integral protein causing conformational change.
  • 2. γ, β and α subunits separate.
  • 3. α subunit is energized by binding GTP and dephosphorilating to GDP and Pi
  • 4. α subunit leaves the membrane and works in cell or shifts over within the membrane.
Term
Example of a Ligand-gated ion channel
Definition
Acetylcholine and Na+ ion channel
Term
How Acetylcholine and Na+ ion channel works.
Definition
  • 1. Na+ channel is closed
  • 2. Acetylcholine binds to receptor sites on channel.
  • 3. Channel opens and Na+ diffuses through the open channel.
Term
Intracellular mediators
Definition
Ions or molecules that enter cell or are produced in a cell.
Term
Four common intracellular mediators
Definition

Cyclic guanine monophosphate (cGMP)

Cyclic adenosine monophosphate (cAMP)

Inositol triphosphate (IP3)

Nitric oxide (NO)

Term
Membrane bound receptors
Definition
Directly effect intracellular enzymes
Term
Four primary types of ion channels.
Definition

Non-gated

Voltage-Gated

Ligand-Gated

Other-gated

Term
Non-gated Ion Channel
Definition

Also known as leak channels.

Always open.

Permeable to specific ions.

 

Term
Voltage Gated Ion Channel
Definition
Open and close in response to small voltage changes across plasma membrane.
Term
Ligand Gated Ion Channels
Definition

Open or close in response to a ligand binding to a receptor.

 

Common in glands and nervous and muscle tissue.

Ex: acetylcholine-sodium ion channel.

 

Term
Other-gated ion channels
Definition

Gated ion channels that respond to stimuli other than ligands or voltage changes.

Present in specialized electrically excitable tissues.

Term
Local Potential
Definition
Either depolarization or hyperpolarization of a plasma membrane confined to a small area. Graded in nature and decreases in strength as it moves away from stimuli.
Term
Action Potential
Definition
Occurs when local potential exceeds a depolarization threshold. Occurs at a constant strength throughout the membrane.
Term
Phases of Action Potential
Definition

Depolarization

Repolarization

After Potential

Term

Depolarization Phase

(Voltage Gated Ion Channels)

Definition
  1. Voltage gated Na+ ion channels open. 
  2. Na+ ions enter cell.
  3. Voltage-gated K+ channels begin to open.
  4. Na+ ions reduce electrical gradient between intracellular and extracellular fluid.

 

 

Term

Repolarization Phase

(Voltage Gated Ion Channels)

Definition
  1. Voltage-gated Na+ ion channels close.
  2. Voltage-gated K+ ion channels remain open until RMP is re-established.
  3. K+ ions move out of cell.
Term
After-potential
Definition
Plasma membrane is slightly hyperpolarized for a short period due to K+ ion channels closing slowly.
Term
Resting Membrane Potential (RMP)
Definition
The difference in charges between the extracellular and intracellular fluid in the immediate area of the plasma membrane.
Term
Typical normalized RMP
Definition

Charge is naturally negative on the inside of the cell membrane.

 

Between -70 and -90 mV

Term
Depolarization
Definition
Movement of RMP towards zero.
Term
Hyperpolarization
Definition
Movement of RMP away from zero.
Term
Sodium-Potassium Exchange Rate for each ATP in Na+/K+ ATPase pump
Definition

3 Na+ out

2 K+ in

Term
Absolute Refractory Period
Definition
A refractory period when, no matter how strong the stimuli, a second action potential cannot occur.
Term
Refractory Period
Definition
A window of time when a second action potential cannot occur due to the depolarization of membrane.
Term
Relative refractory period
Definition
Stronger than threshold stimuli causes a second action potential to occur, during the afterpotential period.
Term
Accommodation
Definition
When cells begin to ignore a stimulus.
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