ABSTRACT
In Chapter 11, we discussed the sensory receptors that provide environmental information to the circadian system. In Chapter 12, we discussed the cells and molecules that make up the master pacemaker and the multiple peripheral slave pacemakers. In this chapter, we will discuss the pathways through which the receptors send information to the master pacemaker (the afference) and the pathways through which the pacemaker sends information to the various effector organs (the efference). We will make frequent use of some technical terms that are reviewed in Figure 13.1. For conduction of nerve impulses, the term “orthodromic” refers to the movement of impulses in the natural direction of the nerve (that is, from the cell body to the axon), whereas the term “antidromic” refers to the movement of impulses in the opposite direction (that is, from the axon to the cell body). Notice that the physical direction of movement is reversed in the efferent pathway as compared to the afferent pathway. For transport of practically everything else (including substances moving along the axon of a neuron), the terms “anterograde” and “retrograde” are used instead of orthodromic and antidromic. Anterograde transport refers to movement of substances from dendrites (or cell body) to the axon of a neuron, whereas retrograde transport refers to movement of substances from the axon to the cell body.
