Passage
In 1906, the Nobel Prize in Physiology or Medicine was awarded 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 nervous system organization.Hypothesis 1: Reticular TheoryBiologist 1 developed a neural staining technique that was carried out by fixing brain tissue in potassium dichromate (K 2 Cr 2 O 7 ) before treating it with silver nitrate (AgNO 3 ). A silver chromate (Ag 2 CrO 4 ) precipitate deposited within the neurons, making them appear black. The 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. Second, 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 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 (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.
-Compared to the axons investigated by Biologist 2, the axons studied by Biologist 1 most likely had:

Question

Passage
In 1906, the Nobel Prize in Physiology or Medicine was awarded 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 nervous system organization.Hypothesis 1:  Reticular TheoryBiologist 1 developed a neural staining technique that was carried out by fixing brain tissue in potassium dichromate (K 2 Cr 2 O 7 ) before treating it with silver nitrate (AgNO 3 ).  A silver chromate (Ag 2 CrO 4 ) precipitate deposited within the neurons, making them appear black.  The 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.  Second, 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 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 (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.
-Compared to the axons investigated by Biologist 2, the axons studied by Biologist 1 most likely had:

Quizplus · Accepted Answer

11ecba2d_0fb2_e6a5_a3bf_3367c285d91c_MD0008_00 The myelin sheath is a multilayered, segmented covering that surrounds and insulates axons to increase the conduction speed of an action potential (AP). The sheath is produced by glial cells that wrap their plasma membranes tightly around the axon. Because myelin is a lipid substance, the sheath functions as an insulator (fat is a poor conductor of electrical current) that keeps the current within the axon by preventing the dissipation of electrical charge across the membrane. However, the insulation is not perfect and some charge does leak across the sheath back into extracellular space, weakening the current as it propagates down the axon. To ensure the membrane potential does not fall below the threshold before it reaches the axon terminal, the AP is regenerated at the nodes of Ranvier, which are gaps in the sheath where voltage-gated ion channels are concentrated. This type of conduction, where the AP "leaps" from node to node rather than flows down the entirety of the axon, is called saltatory conduction. In unmyelinated axons, ions quickly dissipate back into the extracellular space, causing rapid weakening and decay of the propagating electrical signal. Accordingly, unmyelinated axons have voltage-gated ion channels positioned along the entirety of the axon to continually regenerate the AP. However, it takes time for each channel to open and for ions to move inward, so this repeated AP regeneration greatly decreases the speed of the signal. Other than myelin, increasing axon diameter can also increase AP speed by reducing intracellular electrical resistance. According to the passage, Biologist 1 stained neurons with myelinated axons (which contain voltage-gated ion channels that are clustered at the nodes of Ranvier) whereas Biologist 2 stained unmyelinated axons (which contain voltage-gated ion channels that are evenly distributed across the entire axon). Due to the lack of myelination, the axons studied by Biologist 2 were fully exposed to extracellular space (Choice B), were more susceptible to rapid weakening of the electrical signal (Choice A), and conducted APs at a slower rate (Choice C). Educational objective: The myelin sheath increases the speed of action potential (AP) propagation by acting as an electrical insulator that prevents dissipation of charge across the membrane. APs in myelinated axons travel via saltatory conduction.

Passage In 1906, the Nobel Prize in Physiology or Medicine Was