This question concerns nerve impulses, signals that propagate along nerve fibers

Question

This question concerns nerve impulses, signals that propagate along nerve fibers consisting of many axons (fiber-like extensions of nerve cells) connected end-to-end. The speed of the signal depends on whether the axon has a sheath called myelin around it or not. Nerve impulses move along axons with myelin at 100 m/s , one hundred times as quickly as on axons without it. The figure shows small portions of three nerve fibers consisting of axons of equal size. Fiber A is unmyelinated. Two-thirds of the axons in Fiber B are myelinated. Fiber C is fully myelinated. Suppose that the nerve fibers in the figure connect a finger to your brain, a distance of 1.2m. What is the travel time of a nerve impulse from finger to brain along the fiber A? What is the travel time of a nerve impulse from finger to brain along the fiber C? For fiber B, 2/3 of the length will be composed of myelinated axons, 1/3 unmyelinated axons. Compute the travel time for a nerve impulse on this fiber. When you touch a hot stove with the finger, the sensation of pain must reach your brain as a nerve signal along a nerve fiber before your muscles can react. Which of the three fibers gives you the best protection against a burn?
This question concerns nerve impulses, signals that propagate along nerve fibers consisting of many axons (fiber-like extensions of nerve cells) connected end-to-end. The speed of the signal depends on whether the axon has a sheath called myelin around it or not. Nerve impulses move along axons with myelin at 100 m/s , one hundred times as quickly as on axons without it. The figure shows small portions of three nerve fibers consisting of axons of equal size. Fiber A is unmyelinated. Two-thirds of the axons in Fiber B are myelinated. Fiber C is fully myelinated. Suppose that the nerve fibers in the figure connect a finger to your brain, a distance of 1.2m. What is the travel time of a nerve impulse from finger to brain along the fiber A? What is the travel time of a nerve impulse from finger to brain along the fiber C? For fiber B, 2/3 of the length will be composed of myelinated axons, 1/3 unmyelinated axons. Compute the travel time for a nerve impulse on this fiber. When you touch a hot stove with the finger, the sensation of pain must reach your brain as a nerve signal along a nerve fiber before your muscles can react. Which of the three fibers gives you the best protection against a burn?

Explanation / Answer

Speed along nerve A = 1 m/s

Speed along nerve C = 100 m/s

Speed along nerve B= (100*2/3 + 1*1/3) m/s = 67 m/s.

Time required for an impulse to travel a distance of 1.2 metres along:

A is tA = 1.2/1 = 1.2 s

C is tC = 1.2/100 = 0.012 s

B is tB = 1.2/67 = 0.018 s

We can see that the fastest response can be obtained in case of fully myelinated nerve fibre C. This gives the best protection against a burn.

Related Questions

Navigate

• Browse (All)
• Browse T
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.