Podcast
Questions and Answers
Which of the following is NOT one of the events that occur during an action potential?
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?
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?
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?
What is the primary function of neurotransmitter receptors on the postsynaptic membrane?
What is the primary difference between an action potential and a graded potential?
What is the primary difference between an action potential and a graded potential?
During the resting membrane potential, what is the primary driver for the high concentration of K+ inside the axon?
During the resting membrane potential, what is the primary driver for the high concentration of K+ inside the axon?
What is the primary driving force for the depolarization phase of the action potential?
What is the primary driving force for the depolarization phase of the action potential?
During the repolarization phase, what is the primary mechanism that restores the negative resting membrane potential?
During the repolarization phase, what is the primary mechanism that restores the negative resting membrane potential?
What is the primary role of the voltage-gated Na+ channel's activation gate?
What is the primary role of the voltage-gated Na+ channel's activation gate?
What is the purpose of the voltage-gated Na+ channel's inactivation gate?
What is the purpose of the voltage-gated Na+ channel's inactivation gate?
What is the primary role of the K+ leak channels during the action potential?
What is the primary role of the K+ leak channels during the action potential?
What happens when an inhibitory receptor is activated?
What happens when an inhibitory receptor is activated?
Which type of receptor activation leads to dendrite depolarization?
Which type of receptor activation leads to dendrite depolarization?
What is the primary result of graded potentials in the dendrites and cell body?
What is the primary result of graded potentials in the dendrites and cell body?
What property distinguishes graded potentials from action potentials?
What property distinguishes graded potentials from action potentials?
When multiple EPSPs from different sites meet at the same time and place on the membrane, what type of summation occurs?
When multiple EPSPs from different sites meet at the same time and place on the membrane, what type of summation occurs?
Why might an action potential not occur even if an EPSP surpasses the threshold?
Why might an action potential not occur even if an EPSP surpasses the threshold?
What makes every neuron a complex 'computer' in processing inputs?
What makes every neuron a complex 'computer' in processing inputs?
What is the primary function of synaptotagmin and complexin in the synaptic vesicle fusion process?
What is the primary function of synaptotagmin and complexin in the synaptic vesicle fusion process?
What is the role of calcium influx in the synaptic vesicle fusion process?
What is the role of calcium influx in the synaptic vesicle fusion process?
How do the botulinum toxins produced by Clostridium botulinum impair synaptic function?
How do the botulinum toxins produced by Clostridium botulinum impair synaptic function?
What is the primary mechanism by which neurotransmitters are removed from the synaptic cleft?
What is the primary mechanism by which neurotransmitters are removed from the synaptic cleft?
How can different neurotransmitters elicit different effects on the postsynaptic cell?
How can different neurotransmitters elicit different effects on the postsynaptic cell?
What is the primary mechanism of action for ionotropic neurotransmitter receptors?
What is the primary mechanism of action for ionotropic neurotransmitter receptors?
How do metabotropic neurotransmitter receptors typically elicit their effects on the postsynaptic cell?
How do metabotropic neurotransmitter receptors typically elicit their effects on the postsynaptic cell?
What is the primary mechanism by which acetylcholine can have both excitatory and inhibitory effects on the postsynaptic cell?
What is the primary mechanism by which acetylcholine can have both excitatory and inhibitory effects on the postsynaptic cell?
How do the different types of botulinum toxins (Botox) produced by Clostridium botulinum differ in their medical applications?
How do the different types of botulinum toxins (Botox) produced by Clostridium botulinum differ in their medical applications?
What is the primary difference between continuous conduction and saltatory conduction?
What is the primary difference between continuous conduction and saltatory conduction?
What is the primary function of myelin in facilitating saltatory conduction?
What is the primary function of myelin in facilitating saltatory conduction?
Which type of nerve fiber would conduct an action potential the fastest?
Which type of nerve fiber would conduct an action potential the fastest?
What is the primary mechanism by which neurotransmitters are transported to the presynaptic terminal?
What is the primary mechanism by which neurotransmitters are transported to the presynaptic terminal?
What is the primary function of the proton gradient in the presynaptic terminal?
What is the primary function of the proton gradient in the presynaptic terminal?
Which of the following statements about the function of neurotransmitters is correct?
Which of the following statements about the function of neurotransmitters is correct?
According to the information provided, which of the following statements about the relationship between axon diameter and conduction velocity is correct?
According to the information provided, which of the following statements about the relationship between axon diameter and conduction velocity is correct?
Which of the following statements about the structure of a chemical synapse is correct?
Which of the following statements about the structure of a chemical synapse is correct?
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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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