Lecture 4 -- Graded Potentials and Action Potentials Flashcards
(28 cards)
What is hyperpolarization?
An increase in membrane potential (the interior of the neuron becomes even more negative).
What is depolarization?
A decrease in membrane potential (the interior of the neuron becomes less negative).
What happens to graded local potentials as they spread across the membrane?
They decrease in size, like ripples in a pond because electric signals lose strength when spread out.
What is an action potential and how is it different from a graded potential?
A rapid reversal of membrane potential, making the inside of the neuron temporarily positive when a sudden influx of Na+ ions through voltage-gated Na+ channels occurs.
It is actively propagated and does not diminish with distance.
What does the all-or-none property mean?
An action potential either fires at full amplitude or not at all, regardless of stimulus strength.
How do neurons encode stronger stimuli?
By increasing the number of action potentials, not their size.
What are afterpotentials?
Small voltage changes after the spike due to ion movement.
What returns the membrane to resting potential after reaching peak?
After the peak of the action potential (around +40 mV), the voltage-gated Na⁺ channels close, and voltage-gated K⁺ channels open.
K⁺ ions move out of the cell, because the inside of the neuron is now more positive than the outside.
This efflux of K⁺ returns the inside of the cell toward a more negative resting potential (repolarization).
Often, too much K⁺ exits, causing hyperpolarization (temporarily more negative than the resting potential)
Sodium-Potassium pumps restore the original ion distribution after action potentials.
What limits the frequency of action potentials?
The refractory period. (Sodium-Potassium pumps do their job)
What is the absolute refractory period?
A time when no new action potential can be initiated, no matter the stimulus because Na+ channels are shut until resting potential.
What is the relative refractory period? Why does it occur
The short period after the absolute refractory period, during which a stronger-than-usual stimulus is required to trigger another action potential.
Occurs because Na⁺ channels reset, so another action potential can occur—but not easily.
Why are cell bodies and dendrites poor at conducting action potentials?
They have few voltage-gated Na+ channels.
If hyperpolarization means an increase in membrane potential, why is the action potential voltage decreasing?
Resting potential: ~–65 mV
Hyperpolarization: –75 mV
- membrane potential is the intercellular change to extracellular.
- the inside is now even more negative relative to the outside
- voltage difference (or potential) across the membrane increased in strength
How is the action potential propagated along the axon?
It is actively regenerated in a chain reaction by voltage-gated Na⁺ channels at each segment of axonal membrane.
How is the action potential propagated along the axon?
Depolarization is actively regenerated in a chain reaction by voltage-gated Na⁺ channels responding to local depolarization at each segment of axonal membrane
Why does the action potential travel only one direction down the axon?
The previous segment becomes refractory, so it can’t fire again immediately.
What is saltatory conduction?
When action potentials “jump” from one node of Ranvier to the next along myelinated axons because myelin insulation prevents ion leakage, forcing depolarization to jump between nodes of Ranvier.
Why is saltatory conduction faster than conduction in unmyelinated axons?
fewer action potentials need to be generated—signal travels faster between nodes.
What two factors increase conduction velocity of action potentials?
Larger axon diameter and myelination.
What causes multiple sclerosis (MS), and how does it affect action potentials?
MS is caused by the immune system attacking myelin, which disrupts saltatory conduction, slowing or blocking action potential propagation.
What are the symptoms of MS, and how does myelin damage impact conduction?
Early symptoms include blurred vision, tingling, stiffness, fatigue, and difficulty walking.
Myelin damage impairs saltatory conduction, preventing efficient action potential transmission between nodes.
Symptoms vary and worsen unpredictably, but there is no cure for MS. Treatments focus on managing symptoms.
What is multiple sclerosis?
A chronic autoimmune disease that affects the CNS and neural function.
How do EPSPs and IPSPs contribute to neuronal firing?
EPSPs bring the neuron closer to threshold (excitatory), while IPSPs move it further away from threshold (inhibitory). The neuron’s action potential depends on the balance between these signals.
What determines whether a neurotransmitter is excitatory or inhibitory?
The effect depends on the type of receptor on the postsynaptic cell. Some transmitters are excitatory at one synapse and inhibitory at another.
