Multiple Choice
In the context of cell signaling and reflex arcs, which component is primarily responsible for determining the response to a stimulus?
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10. Cell Signaling
Introduction to Cell Signaling
Multiple Choice
Which brain defense mechanism restricts substances from entering the brain via the vascular system?
A
Meninges
B
Myelin sheath
C
Blood-brain barrier
D
Cerebrospinal fluid
Verified step by step guidance1
Understand the problem: The question is asking about a brain defense mechanism that restricts substances from entering the brain through the vascular system. This means we need to identify the structure or system responsible for controlling the passage of substances from the bloodstream into the brain.
Clarify the options: Review each option provided: (1) Meninges, which are protective layers surrounding the brain and spinal cord; (2) Myelin sheath, which insulates nerve fibers to enhance signal transmission; (3) Blood-brain barrier, a selective barrier that regulates the entry of substances into the brain; and (4) Cerebrospinal fluid, which cushions the brain and spinal cord and provides nutrients.
Focus on the correct concept: The blood-brain barrier is a specialized structure formed by endothelial cells lining the brain's capillaries. These cells are tightly joined, creating a selective barrier that allows essential nutrients to pass while blocking harmful substances.
Explain the mechanism: The blood-brain barrier functions through tight junctions between endothelial cells, supported by astrocytes. It uses selective transport mechanisms to allow molecules like glucose and amino acids to enter while preventing toxins and pathogens from crossing.
Conclude the reasoning: Based on the description and function, the blood-brain barrier is the correct answer because it specifically restricts substances from entering the brain via the vascular system, unlike the other options which serve different roles in brain protection or function.
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