Lecture 4: Graded And Action Potentials Flashcards
What kind of signals are critical to nervous system and muscles
Electrical
Why use ion permeability changes and not hormones/cell-cell signaling in the brain
Faster = survival
Where are neurotransmitters released
Synaptic cleft
4 functional regions o neuron
-cell body
-dendrites
-axon
-presynaptic terminal
Cell body function
Make proteins to maintain neuron
Dendrites function
Receive signals from neighboring neurons and deliver across axon to next neuron
Axon function
Integrate signal from dendrites and transmit action potential along cell
Presynaptic terminal function
Signal adjacent cells
2 types of ion channels involved in graded and action potentials
-ligand gated
-voltage gated
Graded potential vs action potential
-action potential large depolarization over long distance
-graded potential amplitude depends on strength of stimulus, shorter distances
Step 1 of graded potential (3)
-resting membrane exposed to stimulus (i.e. neurotransmitter)
-opens chemically gated channels
-changes membrane potential (depolarization or hyperpolarization)
Step 2 of graded potential
-ions move through channel to produce current
-depolarizes/hyperpolarizes nearby regions of cell membrane
-change in potential is proportional to stimulus
Graded potentials can lead to
Action potentials
Repolarization definition
Return to resting potential after depolarization
2 types of postsynaptic potentials: graded potentials
-EPSP
-IPSP
EPSP
-excitatory postsynaptic potential
-right after depolarization
IPSP
-inhibitory postsynaptic potential
-right after hyperpolarization
Graded potential: threshold
Amount of graded potentials required to create an action potential
Where does integration of post-synaptic potentials occur
Initial segment of axon
Typical EPSP voltage and how long it lasts
0.5 mV
20 seconds
A typical neuron would need ________ to reach threshold
30
Temporal summation definition
Occurs when single synapse receives many EPSPs in short period of time
Spatial summation definition
Occurs when single synapse receives many EPSPs from many presynaptic cells
Action potential features
-one way
-all or none
-signal propagates non decrementally
“Signal propagates non decrementally” meaning
-impulse propagates along axon
-amplitude of impulse is maintained
2 gates within voltage gated Na+ channels
-activation gate
-inactivation gate
How many gates do voltage gated K+ channels have
1 (open OR closed)
When are voltage gated channel gates triggered to respond
At threshold
3 conformations of voltage gated Na+ channels
-resting
-activated
-inactivated
Activated voltage gated Na+ channel at threshold: what happens
-Influx of Na+
-activation gate opens
-inactivation gate starts to close before equilibrium is reached
K+ channels have a ________ opening while Na+ channels have a _________ opening (hint: timing)
Delayed, rapid
Opening Na+ channels at threshold is what kind of feedback cycle
Positive
Positive feedback cycle for opening Na+ channels at threshold
depolarization —> opening of some voltage gated Na+ channels —> influx of Na+ which further decreases membrane potential —> depolarization —> repeat
2 types of refractory periods
-absolute
-relative
Absolute refractory period: definition
-when no stimulus can elicit an action potential
State of voltage gated Na+ channels during absolute refractory period
Inactivated
Supranormal stimulus definition
Stimulus that elicits a stronger response than original stimulus
Relative refractory period definition
Interval when supranormal stimulus is required to elicit action potential
Importance of refractory period (2)
-ensures one way propagation
-limits frequency of an action potential to conserve energy and prevent seizures
How does Hyperkalemia cause muscle paralysis
-depolarization of skeletal muscle = increased excitability
-spontaneous APs occur
-voltage gated Na+ channels inactivate
-cells unable to fire APs (exhausted)
2 things that determine speed of conduction
-diameter of fiber
-myelination
2 types of fibers (conduction)
-rapid
-slow
How does diameter affect speed of conduction
Larger diameter = lower internal resistance for current flow = faster conduction
Are rapid or slow fibers larger in diameter
Rapid
Where are rapid fibers found
Motorneurons
Where are slow fibers found
Internal organs
How does myelination affect speed of conduction
-Decreases capacitance of axon
-restrict action potential generation to nodes of ranvier
-increases conduction velocity
Diameter of myelinated vs unmyelinated axons
Larger in myelinated
2 types of conduction
-contiguous
-saltatory
Which type of conduction occurs in myelinated fibers
Saltatory
Which type of conduction occurs in unmyelinated fibers
Contiguous
Contiguous conduction definition
AP spreads along every portion of membrane
Saltatory conduction definition
Impulse jumps over sections of fiber covered with insulating myelin
Is contiguous or saltatory conduction faster (and by how much)
Saltatory, 50 times
Degenerative myelopathy definition and clinical signs
-Progressive disease of spinal cord causing progressive paralysis
-begins with ataxia in hind limbs
-dog with wobble when walking, knuckle over or drag feet
All or none principle: 2 conditions
-if stimulus exceeds threshold, AP will be initiated (AP is triggered or not)
-AP will always be same magnitude for particular axon no matter how large the stimulus
