During a neurobiology lecture, a professor repeatedly refers to group A and group B fibers, absolute refractory period, and myelin sheath gaps. Define these terms.

Video transcript

Hi, everyone. Welcome back. Here's our next question based on the relation between conducting velocity and diameter. Nerve fibers, nerve fibers are classified into three major groups. Group A group B and group C. What is the function of group A fibers A transmit less urgent sensory information. B transmit fast and precise sensory and motor information. C mediate involuntary reflexes or d maintain the directionality of action potentials. So, a useful place to start is recalling the difference between groups A B and C group A involves nerve cells, nerve fibers, excuse me with large diameter. And that are myelinated. Group B refers to nerve fibers with an intermediate diameter and that are less myelinated than group A and group C is nerve fibers that have small diameter and are not myelinated. Let's recall that myelin is the insulation that allows electrical signals to be uh conducted through very efficiently without a loss of that strength of that signal. So with that in mind, seeing that we are talking about group a large diameter myelinated, the large diameter would mean that the signal is conducted with high velocity rapidly and very efficiently with little loss of strength. So that will point us to our correct answer here, which is choice B that they transmit fast and precise sensory and motor information. The large diameter means that signal moves with great velocity. And the insulated axons mean you have little loss or degradation of signal. So we can eliminate choice A since that's exactly the opposite here that says, transmit less urgent sensory information. But again, we have these axons that can move very rapid, move a signal very rapidly. So you want that for more urgent information, choice C says mediate involuntary reflexes, but group A fibers mediate voluntary movements. So that's why that's not our answer. And then finally, choice D says maintain the directionality of action potentials. But that's not a result of the characteristics of our nerve fibers. The directionality of action potentials is maintained by the refractory period when action potentials, new action potentials can only be generated ahead uh of the neuron. So maintaining that directionality and the specificity of the ion channels that create the action potential. So choice D is not our correct answer. So again, we know that our nerve fibers can be classified as one of three groups of nerve fibers. The function of the group A fibers is choice B to transmit precise fast and precise sensory and motor information. See you in the next video.