IB Biology Exam Prep

Category - Biology

In invertebrates, the speed at which an action potential travels along an axon is directly proportional to the axon's diameter. However, vertebrate axons have narrow diameters, but can still conduct action potentials at very high speeds. This is true because vertebrate axons:
  1. Contain higher concentrations of water that increase the conductivity.
  2. Possess a lipid-rich myelin sheath that functions as electrical insulation.
  3. Operate at higher body temperatures that reduce electrical resistance.
  4. Generate action potentials that use sodium rather than calcium to generate electrical impulses.
Explanation
Correct Response: B. The myelin sheath is a protective covering, composed of proteins and lipids, that surrounds an axon. It speeds up the transmission of electrical impulses by allowing a current to flow only along certain segments of the axon that are exposed to extracellular space. Although water (A) helps in electrical conductivity, it is the myelin sheath that increases the speed of electrical impulses along axons. The temperature of the body cannot be said to significantly affect electrical resistance along vertebrate axons (C), since the body temperatures of cold-blooded and warm-blooded vertebrates vary widely. All organisms use sodium to propagate action potentials along axons (D).
Was this helpful? Upvote!
Login to contribute your own answer or details

Top questions

Related questions

Most popular on PracticeQuiz