Igray And White Communicating Rami Figure

A. Gray communicating rami contain unmyelinated postganglionic sympathetic fibers. They are found at all levels of the spinal cord.

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).

Lateral Horn Ganglion

Peripheral \ nerve

Preganglionic \ fibers (GVE)

^Postganglionic \ neuron

Digestive tube


Arrector pili muscle

Sweat gland

Lateral horn

Dorsal root ganglion,


Postganglionic fibers

Blood vessel

< White ramus

Gray ramus

-GSA fibers

Dorsal root ganglion cells

Paravertebral ganglion (sympathetic trunk)

Prevertebral ganglion

Spinal nerve GSE fiber

Free nerve ending (pain)

Muscle spindle (proprioception)

Motor endplate

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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Essentials of Human Physiology

Essentials of Human Physiology

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