chapter-12.4- 12.5 Membrane Potential Flashcards
Extracellular fluid contains—-concentrations of —and——
high
Na+
Cl-
Cytosol contains————–and ———–
high concentration of K+
negatively charged proteins
What are the passive processes acting across cell membranes
- Chemical gradients
- Concentration gradients of ions (Na+, K+)
- Electrical gradients
- Charges are separated by cell membrane
- Cytosol is negative relative to extracellular fluid
- Electrochemical gradient
- Sum of chemical and electrical forces acting on an ion across the
membrane - A form of potential energy
What is the function of the sodium-potassium pump?
- Powered by ATP
- Ejects 3 Na+ for every 2 K+ brought in
- Balances passive forces of diffusion
- Stabilizes resting membrane potential (–70 mV)
- When ratio of Na+ entry to K+ loss through passive channels is
3:2
Describe the passive ion channel
These are also called leak channels and are always open and permeability changes with conditions.
Describe active ion channels
These are also called gated ion channels which open and close in response to stimuli. Most are closed at resting membrane potential.
What are the types of active channels
- Chemically gated ion channels
- Voltage-gated ion channels
- Mechanically gated ion channels
Describe the chemically gated ion channels
the chemically gated ion channels are also called ligand-gated ion channels which open when they bind to specific chemicals. These are found on cell bodies and dendrites of neurons.
Describe the voltage-gated ion channel
They are found in the axons of neurons and sarcolemma of skeletal and cardiac muscle cells which respond to changes in membrane potential
Describe the mechanically gated ion channels
these respond to membrane distortion and found in sensory receptors that respond to touch, pressure or vibration
Explain hyperpolarization
Results from opening potassium ion channels
* Positive ions move out, not into cell
* Opposite effect of opening sodium ion channels
* Increases the negativity of the resting potential
What is the threshold for an axon
-60 to -55
At which mv do sodium channels closed and what also open at the same time
sodium channels close and potassium channels open.
potassium moves out of cytosol and repolarization begins
What is value for hyperpolarization
-90
what is absolute refractory period
all voltage-gated sodium channels are open or inactivated
the membrane cannot respond to further stimulation
What is a relative refractory period
This begins when sodium channels regain resting condition and continues until membrane potential stabilizes.
only a strong stimulus can initiate another action potential.
What is propogation
moves an action potential along an axon in a series of steps
what are the two types of propagation
continuous propagation
saltatory propagation
Describe continuous propagation
It occurs in unmyelinated axons and it happens in each segment. Therefore as one segment is repolarizing the other segment is depolarizing
Describe saltatory propagation
this occurs in myelinated axons
it is faster that continuous propagation and requires less energy
What are the types of fibers
- Type A fibers
- Type B fibers
- Type C fibers
Describe the types of fibers
Type A fibers
* Myelinated
* Large diameter
▪ Type B fibers
* Myelinated
* Medium diameter
* Transmit information at intermediate speeds (18 m/sec)
▪ Type C fibers
* Unmyelinated
* Small diameter
* Transmit information slowly (1 m/sec)
* Example: most sensory information
