A&P I Ch 11 Pt 2
Resting potential
The transmembrane potential of resting cell.
Sodium-potassium Pump
Moves Na+ and K+ against gradients.
Graded potential
Temporary, localized change in resting potential - Caused by stimulus.
Resting Potential
The axolemma contains both voltage- gated sodium channels and voltage- gated potassium channels that are closed when the membrane is at the resting potential.
Saltatory Propagation
The movement of an action potential along a myelinated axon, "jumping" from node to node. Action potential along myelinated axon. Myelin insulates axon, prevents continuous propagation. Local current "jumps" from node to node. Depolarization occurs only at nodes. Faster and uses less energy than continuous propagation.
Action Potential - The Refractory Period
The time period. From beginning of action potential. To return to resting state. During which membrane will not respond normally to additional stimuli.
Action Potential - Powering the Sodium-Potassium Exchange Pump
To maintain concentration gradients of Na+ and K+ over time. Requires energy (1 ATP for each 2 K+/3 Na+ exchange)
Repolarization
When the stimulus is removed, transmembrane potential returns to normal.
Action Potential occurs when
a stimulus of sufficient strength depolarizes the cell. Opens Na+ channels, and Na+ diffuses into cell. Inside becomes more positive.
Resting Membrane Potential
-70 milivolts (on average)
Graded Potentials "local potentials"
Changes in transmembrane potential. That cannot spread far from site of stimulation.
Hyperpolarization
Increasing the negativity of the resting potential. Result of opening a potassium channel. Opposite effect of opening a sodium channel. Positive ions move out, not into cell.
Ion Channels at rest (non activated)
Most sodium channels are closed. Na+ stays out.
Powering the Sodium-Potassium Exchange Pump - Without ATP
Neurons stop functioning.
Action Potential All-or-none law
Once a nerve impulse is initiated, it will travel the length of the neuron. No matter how large the stimulus, an action potential is either triggered, or not.
Graded Potentials "local potentials" From the resting state...
Opening sodium channel produces graded potential. Resting membrane exposed to chemical. Sodium channel opens. Sodium ions enter the cell. Transmembrane potential rises. **Depolarization** occurs.
Resting Membrane Potential is determined by
Permeability of plasma membrane to ions. Difference in ion concentrations across membrane Na+, K+, Cl-, and Ca++.
Resting Membrane Potential is maintained by sodium-potassium pump
Potassium tends to diffuse out of cell. **Na+/K+ pump moves 2 K+ in and 3 Na+ out**
Sodium-potassium ATPase (exchange pump)
Powered by ATP. Carries 3 Na+ out and 2 K+ in. Balances passive forces of diffusion. Maintains resting potential (-70 mV)
Action potential
Produced by graded potential - Propagates along surface of axon to synapse.
Step 1: Depolarization to threshold Step 2: Activation of Na+ channels
Rapid depolarization. Na+ ions rush into cytoplasm. Inner membrane changes from negative to positive.
Synaptic activity
Releases neurotransmitters at presynaptic membrane - Produces graded potentials in postsynaptic membrane.
Graded Potentials **if not strong enough**
Repolarization or Hyperpolarization
Information processing
Response (integration of stimuli) of postsynaptic cell.
Five Main Membrane Processes in Neural Activities
Resting potential, graded potential, action potential, synaptic activity, information processing.
Repolarization in Action Potential
Return to resting membrane potential. K+ leaves the cell rapidly. Na+ channels close.
Four Steps in the Generation of Action Potentials
**Step 1: Depolarization to threshold. Step 2: Activation of Na+ channels. Step 3: Inactivation of Na+ channels and activation of K+ channels. Step 4: Return to normal permeability**
Ion Channels - some potassium channels are
**open** **K+ "leaks" out**
Graded Potentials **if strong enough**
to meet the threshold, then will stimulate an Action potential.