Membrane Potentials: Chapter 11 Flashcards
Action Potential
- electrical impulses that are carried along the entire length of axons
- always the same amplitude regardless of strength of stimulus
- CNS interpretation and response is impulse frequency based
Voltage
(V) measure of potential energy generated by separate charge (ie battery)
Potential difference
voltage measured between two points
Current
(I) the flow of electrical charge between two points
Resistance
(R) hindrance to charge flow
Insulator
substance with high electrical resistance
Conductor
substance with low energy resistance
What does the electrical current and the body reflect?
Flow of Ions (NOT ELECTRONS)
What is needed to have a potential of electrical flow through a membrane?
- the number of ions is different across the membranes
- the membrane provides resistance to ion flow
What is the importance of Ion channels?
It allows ions to pass through membranes
Passive or Leakage Channels
- always OPEN!
- Ions flow along the concentration gradient for the particular ion
- When gradient is equal on both sides then it will stop
Chemically Gated Channels:
-open with binding of a specific neurotransmitter or hormone
IE: NA+ -K+ gated channel
-Closed when a neurotransmitter/hormone is not bound to extracellular receptor
Voltage Gated Channels:
- open and close in response to a specific membrane potential… (- inside, + outside)
- IE: NA channel
- Closed when intracellular environment is negative (NA cannot enter, nor K exit cell)
- Open when a neurotransmitter is attached to receptor (NA enters, K exits)
Mechanically Gated Channels:
open & close in response to physical deformation of receptors (as in sensory receptors for touch & pressure)
-IE: Merkel cells deform in response to touch, opening NA channels
What happens when a gated channel is open?
- Ions move quickly across membrane
- movement along electrochemical gradients
- electrical currant is created
- voltage changes across membrane?
Chemical concentration gradient
when ions diffuse passively from an area of higher concentration to an area of lower concentratoin
Electrical Gradients
ions move toward an ear of opposite electrical charge
Electrochemical Gradienat
when electrical and concentration gradients taken together
Resting Membrane Potentials
potential difference across membrane is -70mV
-inside is negative, outside is positive
Polarized membrane
inside negative, outside positive
What are the primary reasons for ionic differences in membranes?
-Differential permeability of plasma membrane
higher concentration of sodium on outside
Sodium-Potassium Pump
pump stabilizes the resting membrane potential by maintaining concentration gradients for sodium and potassium.
- requires ATP
- Pumps agains gradient
Concentration of potassium:
higher on inside of cell
-nerve plasma membrane is very permeable to K+ leaving out
Concentration of Sodium:
higher on outside of cell
-membrane is only slightly permeable to NA leaking in
How is membrane equilibrium reached?
- Sodium potassium pump
- maintaining concentration gradient
- maintaining negative resting membrane potenial
What type of signals do membrane potentials send when there are changes?
- graded potentials
- action potentials
graded potential:
short distance incoming signals to dendrites or nerve cell bodies
action potential
long-distance signals of the axons
What causes a change in membrane potential?
- changes in membrane permeability to ions
- alterations of ion concentration across membrane
What are the three events that can change the membrane potential?
- Depolarization
- Repolarization
- Hyperpolarization
Depolarization
the inside of membrane becomes less negative relative to the outside
Repolarization
membrane returns to its resting potential (-70mV)
Hyperpolarization
inside of membrane becomes more negative than resting potential
