The Nobel Prize in Physiology or Medicine is given for discoveries deemed particularly important in the fields of physiology or medicine. In 1906, this award was given to two biologists for their groundbreaking work in the field of neuroanatomy. Despite using the same technique to visualize neurons, the two biologists formed opposing theories regarding organization of the nervous system.Hypothesis 1: Reticular TheoryBiologist 1 developed a neural staining technique that was carried out by fixing brain tissue from older animals with primarily myelinated nerve fibers in potassium dichromate (K2Cr2O7) before treating this tissue with silver nitrate (AgNO3). A silver chromate (Ag2CrO4) precipitate deposited within the neurons, making them appear black. This silver impregnation method was revolutionary because of two features. First, only a random subset of neurons within a given tissue sample (~1% of the total cell population) was subject to silver impregnation. Second, the impregnated cells were stained in their entirety, allowing for visualization of the complete neuron. Biologist 1 concluded that his findings supported the idea that the nervous system is a single reticulum of fused neural processes that transmit information via cytoplasmic continuity.Hypothesis 2: Neuron DoctrineBiologist 2 modified the silver impregnation method by first subjecting the brain tissue to two rounds of staining ("double impregnation") rather than one. Where Biologist 1 studied the brain tissue of older animals with myelinated nerve fibers, Biologist 2 employed the silver stain on brain tissue from younger animals, which made it easier for the silver to impregnate the neural processes due to a relative lack of myelination. Biologist 2 reasoned that the nervous system is not a single web of interconnected fibers but rather is made up of discrete neural units that communicate via close, but not continuous, contact.The neuron doctrine was later proven correct with the advent of electron microscopy, which allowed scientists to visualize the synapse (ie, the point of communication between two distinct neurons). Further investigation allowed researchers to ultimately discover that there are two types of synapses: electrical and chemical. Question 43Which of the following synaptic events would likely contribute most directly to the generation of an action potential in a postsynaptic neuron?A.The presynaptic neuron releases large quantities of gamma-aminobutyric acid (GABA).B.Postsynaptic neurotransmitter-gated Na+ and Ca2+ channels open.C.Neurotransmitter reuptake into the presynaptic cell and surrounding glia is increased.D.Neurotransmitter binding activates G protein–coupled receptors on the postsynaptic membrane.
Question
The Nobel Prize in Physiology or Medicine is given for discoveries deemed particularly important in the fields of physiology or medicine. In 1906, this award was given to two biologists for their groundbreaking work in the field of neuroanatomy. Despite using the same technique to visualize neurons, the two biologists formed opposing theories regarding organization of the nervous system.Hypothesis 1: Reticular TheoryBiologist 1 developed a neural staining technique that was carried out by fixing brain tissue from older animals with primarily myelinated nerve fibers in potassium dichromate (K2Cr2O7) before treating this tissue with silver nitrate (AgNO3). A silver chromate (Ag2CrO4) precipitate deposited within the neurons, making them appear black. This silver impregnation method was revolutionary because of two features. First, only a random subset of neurons within a given tissue sample (~1% of the total cell population) was subject to silver impregnation. Second, the impregnated cells were stained in their entirety, allowing for visualization of the complete neuron. Biologist 1 concluded that his findings supported the idea that the nervous system is a single reticulum of fused neural processes that transmit information via cytoplasmic continuity.Hypothesis 2: Neuron DoctrineBiologist 2 modified the silver impregnation method by first subjecting the brain tissue to two rounds of staining ("double impregnation") rather than one. Where Biologist 1 studied the brain tissue of older animals with myelinated nerve fibers, Biologist 2 employed the silver stain on brain tissue from younger animals, which made it easier for the silver to impregnate the neural processes due to a relative lack of myelination. Biologist 2 reasoned that the nervous system is not a single web of interconnected fibers but rather is made up of discrete neural units that communicate via close, but not continuous, contact.The neuron doctrine was later proven correct with the advent of electron microscopy, which allowed scientists to visualize the synapse (ie, the point of communication between two distinct neurons). Further investigation allowed researchers to ultimately discover that there are two types of synapses: electrical and chemical. Question 43Which of the following synaptic events would likely contribute most directly to the generation of an action potential in a postsynaptic neuron?A.The presynaptic neuron releases large quantities of gamma-aminobutyric acid (GABA).B.Postsynaptic neurotransmitter-gated Na+ and Ca2+ channels open.C.Neurotransmitter reuptake into the presynaptic cell and surrounding glia is increased.D.Neurotransmitter binding activates G protein–coupled receptors on the postsynaptic membrane.
Solution
The synaptic event that would likely contribute most directly to the generation of an action potential in a postsynaptic neuron is B. Postsynaptic neurotransmitter-gated Na+ and Ca2+ channels open.
Here's why:
An action potential is essentially an electrical signal that travels along the neuron. It's generated when the neuron's membrane potential (the difference in electric charge across the membrane) changes dramatically. This change is triggered by the flow of ions in and out of the neuron.
When neurotransmitter-gated channels open, they allow specific ions to flow across the neuron's membrane. In this case, the opening of Na+ (sodium) and Ca2+ (calcium) channels would allow these positively charged ions to flow into the neuron. This influx of positive charge depolarizes the membrane (makes the inside of the neuron less negative relative to the outside), which is the first step in generating an action potential.
The other options (A, C, and D) are less likely to directly generate an action potential:
A. GABA is an inhibitory neurotransmitter, meaning it tends to make neurons less likely to fire an action potential, not more.
C. Neurotransmitter reuptake would decrease the amount of neurotransmitter available to bind to postsynaptic receptors, which would likely decrease the chances of an action potential.
D. While G protein–coupled receptors can play a role in neuron signaling, they typically do so through slower, indirect pathways, not by directly causing an action potential.
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