Signaling in the Nervous System
Chapter 1 was devoted to giving an account of what a neuron is in itself. Now we come to consider how neurons are concerned in receiving and in giving signals. In Figure 2.1A the diagram of the spinal cord is partly transverse and partly longitudinal, and below there is a muscle which has a stretch receptor or annulospiral ending (cf. A-S in Figure 4.1, Section 4.1). When you give a brief pull to a muscle, as when you make a knee jerk, impulses run up in the primary afferent fibers from the stretch receptors and excite nerve cells in the spinal cord (the so-called motoneurons) which fire impulses out to the muscles that are thus made to contract, the reflex circuit being indicated by arrows. That is the knee jerk. It is the very simplest central reflex pathway, and we will be dealing with it in Chapter 4.
KeywordsNerve Fiber Myelin Sheath Initial Segment Myelinated Fiber Nerve Impulse
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