Action Potential Animation: Saltatory Conduction Quiz & Flashcards

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Questions and Answers

Which of the following is NOT one of the events that occur during an action potential?

Reversal of the sodium-potassium pump (correct)

Depolarization of the membrane potential

Opening of voltage-gated sodium channels

Increase in potassium permeability

What is the primary function of synaptic vesicles in the presynaptic terminal?

To generate action potentials

To maintain the resting membrane potential

To propagate the action potential along the axon

To store and release neurotransmitters (correct)

Which of the following describes saltatory conduction?

Continuous propagation of the action potential along the axon

Propagation of the action potential through chemical synapses

Discontinuous propagation of the action potential, jumping from node to node (correct)

Propagation of the action potential through electrical synapses

What is the primary function of neurotransmitter receptors on the postsynaptic membrane?

To respond to neurotransmitters and generate postsynaptic potentials Signup and view all the answers

What is the primary difference between an action potential and a graded potential?

Action potentials are all-or-none events, while graded potentials are graded responses Signup and view all the answers

During the resting membrane potential, what is the primary driver for the high concentration of K+ inside the axon?

Active transport by the Na+/K+ ATPase pumping K+ into the axon Signup and view all the answers

What is the primary driving force for the depolarization phase of the action potential?

Influx of Na+ through voltage-gated Na+ channels Signup and view all the answers

During the repolarization phase, what is the primary mechanism that restores the negative resting membrane potential?

Closure of voltage-gated Na+ channels and efflux of K+ through K+ channels Signup and view all the answers

What is the primary role of the voltage-gated Na+ channel's activation gate?

To open the channel when the membrane potential reaches the threshold, allowing Na+ influx Signup and view all the answers

What is the purpose of the voltage-gated Na+ channel's inactivation gate?

To keep the channel closed for 1-2 ms after it has closed, preventing premature reopening Signup and view all the answers

What is the primary role of the K+ leak channels during the action potential?

To establish the resting membrane potential by allowing K+ efflux Signup and view all the answers

What happens when an inhibitory receptor is activated?

Dendrite hyperpolarization Signup and view all the answers

Which type of receptor activation leads to dendrite depolarization?

Excitatory receptor Signup and view all the answers

What is the primary result of graded potentials in the dendrites and cell body?

Summation of excitatory and inhibitory inputs Signup and view all the answers

What property distinguishes graded potentials from action potentials?

Decremental nature over time and distance Signup and view all the answers

When multiple EPSPs from different sites meet at the same time and place on the membrane, what type of summation occurs?

Spatial summation Signup and view all the answers

Why might an action potential not occur even if an EPSP surpasses the threshold?

Absence of Na+ voltage-gated channels Signup and view all the answers

What makes every neuron a complex 'computer' in processing inputs?

Integration of EPSPs and IPSPs at the axon hillock Signup and view all the answers

What is the primary function of synaptotagmin and complexin in the synaptic vesicle fusion process?

To prevent premature fusion and release after zippering of v-SNAREs and t-SNAREs Signup and view all the answers

What is the role of calcium influx in the synaptic vesicle fusion process?

Calcium influx triggers the disengagement of complexin from the SNARE complex Signup and view all the answers

How do the botulinum toxins produced by Clostridium botulinum impair synaptic function?

They prevent the assembly and function of v-SNAREs and t-SNAREs, impairing vesicle fusion Signup and view all the answers

What is the primary mechanism by which neurotransmitters are removed from the synaptic cleft?

Degradation by enzymes, such as acetylcholinesterase Signup and view all the answers

How can different neurotransmitters elicit different effects on the postsynaptic cell?

All of the above Signup and view all the answers

What is the primary mechanism of action for ionotropic neurotransmitter receptors?

They open ion channels when the neurotransmitter binds Signup and view all the answers

How do metabotropic neurotransmitter receptors typically elicit their effects on the postsynaptic cell?

They are linked to G-protein signaling pathways and second messenger systems Signup and view all the answers

What is the primary mechanism by which acetylcholine can have both excitatory and inhibitory effects on the postsynaptic cell?

Acetylcholine can bind to both nicotinic and muscarinic receptors, which have different effects Signup and view all the answers

How do the different types of botulinum toxins (Botox) produced by Clostridium botulinum differ in their medical applications?

The different types are used to treat different muscle spasticity disorders and migraines Signup and view all the answers

What is the primary difference between continuous conduction and saltatory conduction?

In continuous conduction, the action potential progresses by depolarizing each segment of the axon, while in saltatory conduction, it 'jumps' from one node of Ranvier to the next. Signup and view all the answers

What is the primary function of myelin in facilitating saltatory conduction?

Myelin provides insulation, allowing the electrical field from one node of Ranvier to 'jump' to the next. Signup and view all the answers

Which type of nerve fiber would conduct an action potential the fastest?

A-fibers, which are large, myelinated fibers. Signup and view all the answers

What is the primary mechanism by which neurotransmitters are transported to the presynaptic terminal?

Neurotransmitters are packaged into vesicles and transported via fast axonal transport along microtubules. Signup and view all the answers

What is the primary function of the proton gradient in the presynaptic terminal?

It transports neurotransmitters into the synaptic vesicles. Signup and view all the answers

Which of the following statements about the function of neurotransmitters is correct?

Neurotransmitters are released from the presynaptic terminal and bind to receptors on the postsynaptic cell membrane, affecting the postsynaptic cell in various ways. Signup and view all the answers

According to the information provided, which of the following statements about the relationship between axon diameter and conduction velocity is correct?

Conduction velocity in myelinated axons increases linearly with increasing axon diameter, while in unmyelinated axons, it increases with the square root of the diameter. Signup and view all the answers

Which of the following statements about the structure of a chemical synapse is correct?

The presynaptic terminal of the axon is the site of neurotransmitter release, and the dendritic spine expresses the receptors for the neurotransmitter. Signup and view all the answers

Study Notes

Action Potentials and Synaptic Transmission

Myelinated and Unmyelinated Fibers

Velocity of action potentials along myelinated and unmyelinated axons
Velocity of myelinated fiber in m/s = diameter (um) x 4.5
Velocity of unmyelinated fiber in m/s = square root of diameter (um)
Increase in conduction velocity with increased size of axon diameter (true for myelinated and unmyelinated axons)

Saltatory Conduction

Fast conduction due to myelin insulation allowing electrical field to "jump" to next node of Ranvier
Portions covered by myelin do not experience action potentials (no ion channels and myelin keeps ions from crossing the cell membrane)

Fiber Types

A Fibers: largest fibers, 5-20 μm, myelinated, conduct impulses at 12-130 m/sec or 280 miles/hr (large sensory nerves for touch, pressure, position, heat, cold, and motor system)
B Fibers: medium fibers, 2-3 μm, non-myelinated, conduct impulses at 15 m/sec or 32 miles/hr (from viscera to brain and spinal cord, autonomic efferents to autonomic ganglia)
C Fibers: smallest fibers, non-myelinated, conduct impulses at 0.5-2 m/sec or 1-4 miles/hr (pain, touch, pressure, heat, cold from skin and pain impulses from viscera, visceral efferents to heart, smooth muscle and glands)

Chemical Synapses

Associated with excitable cells
Presynaptic neuron releases neurotransmitter (NT) that binds to receptors embedded in post-synaptic cell membrane
NT crosses the synaptic cleft and binds to receptors, affecting the post-synaptic cell in various ways
Synapse is usually between a dendritic spine or an axon terminal, with the dendritic spine expressing the receptor for the NT

Neurotransmitter Vesicles

Synthesized and packaged in rER and Golgi, transported down the axon via microtubules (fast axonal transport)
Neurotransmitters (non-peptide) synthesized in the cytosol of the presynaptic terminal, transported into vesicles
Vesicles bind to actin within the presynaptic terminal cytoskeleton, transported to release sites (active zone) close to the synapse

Basic Steps of NT Release

v-SNARES and t-SNARES "zipper" together
AP → depolarization → Ca+2 VGC opening → calcium influx into the presynaptic terminal
Calcium binds to synaptotagmin → disengagement of complexin
The synaptic vesicle fuses when complexin disengages → release of NT into the synapse
The v-SNAREs and t-SNARES disengage, and the vesicle is re-used

Clinical Relevance - Botox

Toxins produced by Clostridium botulinum impair the assembly and function of v-SNAREs and t-SNARES
Impairs fusion of vesicles with the presynaptic membrane, used therapeutically (in tiny doses) to reduce muscle spasticity, treat migraines, and decrease wrinkles

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Description

Explore the events of the action potential with an animated model showcasing the axon hillock, axon, and synaptic terminals. Learn about sodium voltage-gated channels (Na+ VGC) and potassium voltage-gated channels (K+ VGC) involved in terminating the action potential.

Action Potential: Step-by-Step Animation