Action potentials I & II Flashcards
Most common type of Neuron?
Multipolar neuron
Structure of Neuron:
Large central area?
Cell body or soma, contains nucleus and most organelles
Structure of Neuron:
Numerous short projections from cell body?
Dendrites
Structure of Neuron:
One long projection?
Axon
Structure of Neuron:
Location on cell body where axon connects is
Axon Hillock
Structure of Neuron:
Portion of axon that connects to axon hillock is
Initial Segment or spike initiation zone
Structure of Neuron:
Axons branch out at the ends, these ends are called
terminal branches
Structure of Neuron:
Terminal branches end in small swelling bulbs called
Axon terminal or presynaptic terminal.
Structure of Neuron:
Myelin sheath are made of _______ cells
Glial cells
Structure of Neuron:
Myelin sheath is interupted at intervals by gaps called
Nodes of Ranvier
What are graded potentials?
Where are they produced?
What is their function in neurons?
-Graded potentials are small changes in membrane potential AKA postsynaptic potentials.
-Produced on the dendrites, can also be from cell body.
-They regulate action potential production at the initial segment
Where are action potentials produced?
What is their function?
-Produced at initial segment
-They stimulate the release of neurotransmitters by propagating along the axon to each axon terminal.
Other names for:
-Cell body
-Graded potential
-Presynaptic terminal
-Spike initiation zone
-Soma
-Postsynaptic potential
-Axon terminal
-Initial segment
3 Characteristics of Action Potentials (AP):
-Every AP produced is IDENTICAL
-AP have an ALL-OR-NONE RESPONSE to a stimulus
-AP are TRANSMITTED WITHOUT DECREMENT
Depolarization:
Change in membrane potential to a less negative value than resting potential.
Hyperpolarization:
Change in membrane potential from a depolarized state.
What is needed to reach the threshold?
A depolarization.
Repolarization:
Return to resting potential from a depolarized state.
Typical resting potential for a neuron
-70 mV (milliVolts)
Threshold potential.
-55mv.
Depolarization:
Stimulates action potential
Results in an increase in sodium ion permeability.
Hyperpolarization:
Inhibits action potential
Types of Depolarization stimuli?
Threshold Stimulus
Sub-threshold Stimulus
Suprathreshold Stimulus
Threshold potential:
The membrane potential at which occurrence of the action potential is inevitable.
Threshold Stimulus:
The minimum depolarization needed to induce an action potential, when the membrane is at resting potential.
Sub-threshold Stimulus:
Cannot induce an action potential because it is less than the threshold.
Less than +15mv.
Suprathreshold Stimulus:
A depolarization above the threshold. Geater than 15mv.
What amount of depolarization is typically needed to reach threshold?
+15 mV depolarization
If resting potential is -70 mV (typical) then threshold potential is -55 mV (-70 mV + 15 mV = -55 mV)
Name 3 phases of action potential:
-Depolarization phase
-Repolarization phase
-Undershoot phase
How much mv is needed to go from resting potential to threshold potential?
+15mv.
Alternate names for depolarization phase
-Rapid depolarization phase
-Rising phase
Alternate name for repolarization phase
-Falling phase
Alternate names for undershoot phase
-Hyperpolarizing after potential
-After hyperpolarization phase
What can induce an action potential when the cell is at resting potential?
A threshold and superthreshold stimuli.
Membrane potential during depolarization phase (phase 1)
Depolarizes from threshold (-55 mV) to +30 mV
Membrane potential during repolarization phase (phase 2)
Changes from +30 mV to -70 mV
Membrane potential during undershoot phase (phase 3)
Is slightly hyperpolarized (less than -70 mV)
Na+ Channels can open ______
In response to a depolarization to any change in membrane potential.
The higher the strength of depolarization the higher the chance of opening.
When does Na+ permeability exceed K+ permeability?
At threshold.
This is due to leak channels.
Conductance:
Local changes in membrane permeability to Na+ & K+ that induce and maintain action potential.
What starts the Hodgkin cycle?
When Na+ permeability exceeds that of k+.
It is a positive feedback loop.
The Hodgkin cycle is terminated by
The closing of the inactivation gate.
What causes conductance to occur?
Opening and closing of voltage-gated ion channels within membrane.
Another name for depolarization?
Rising Phase.
Ion channels:
small pores in the membrane that are created by specialized membrane proteins.
Inactivations state:
Activation gate opens, Inactivation gate is closed.
Another name for repolarization:
Falling Phase
Specificity in ion channels mean:
only certain ions can move through particular ion channels.
Ungated ion channels:
always open AKA leak channels
Undershoot:
A slight Hyperpolarization.
K+ channels close slowly.
Potassium ion leak channels:
Responsible for increased permeability of K+ at resting potential.
Gated ion channels:
Can be opened and closed in response to stimulis.
Changes in permeability are called?
Conductance.
Voltage-gated ion channels:
open and close in response to changes in membrane potential
Refractory period:
The initial segment is less important than another stimulus during an action potential.
Reduced responsiveness to stimuli during the action potential.
Phases of the refractory periods:
Absolute refractory
Relative refractory
Absolute refractory period:
Begins @ threshold, and ends at the repolarization phase.
The membrane cannot respond to another stimulus.
Relative refractory period:
Begins at the end repolarization phase and ends in undershoot.
What is required for an action potential in a relative refractory period?
A superthreshold.
What type of cells are in myeline sheets?
Shawn cells.
