B. White communicating rami contain myelinated preganglionic sympathetic fibers. They are found from T-l to L-3 (the extent of the lateral horn and the intermediolat-era I cell column).
II. TERMINATION OF THE CONUS MEDULLARIS (see Figure 2-1) occurs in the newborn at the level of the body of the third lumbar vertebra (L-3). In the adult, it occurs at the level of the lower border of the first lumbar vertebra (L-l).
Peripheral \ nerve
Preganglionic \ fibers (GVE)
^Postganglionic \ neuron
Arrector pili muscle
< White ramus
Dorsal root ganglion cells
Paravertebral ganglion (sympathetic trunk)
Spinal nerve GSE fiber
Free nerve ending (pain)
Muscle spindle (proprioception)
Alpha motor neuron of ventral horn (GSE)
Figure 6-1. The four functional components of the thoracic spinal nerve: general visceral afferent (GVA), general somatic afferent (GSA), general somatic efferent (GSE), and general visceral efferent (GVE). Proprioceptive, cutaneous, and visceral reflex arcs are shown. The muscle stretch (myotatic) reflex includes the muscle spindle, GSA dorsal root ganglion cell, GSE ventral horn motor neuron, and skeletal muscle.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.