II Ia III in Microsoft Office

Painting Denso QR Bar Code in Microsoft Office II Ia III

5 20 3 6 2 5 1 3 03 11

30 70 15 30 12 30 3 15 05 2

Touch, pressure Spindle afferents Pain and temperature, soma touch (Sharp, lancinating, prickly pain) Slow pain and temperature (Dull, burning, poorly localized pain)

(C bers) form a discrete bundle, the tract of Lissauer (Fig 8-1A) That Lissauer s tract is predominantly a pain pathway is shown (in animals) by the ipsilateral segmental analgesia that results from its transection, but it contains deep sensory or propriospinal bers as well Although it is customary to speak of a lateral and medial division of the posterior root (the former contains small pain bers and the latter, large myelinated bers), the separation into discrete functional bundles is not complete, and in humans the two groups of bers cannot be differentially interrupted by selective rhizotomy

(See Fig 9-1, page 129) Each sensory unit (the sensory nerve cell in the dorsal root ganglion, its central and peripheral extensions, and cutaneous and visceral endings) has a unique topography that is maintained throughout the sensory system from the periphery to the sensory cortex The discrete segmental distribution of the sensory units permits the construction of sensory maps, so useful to clinicians (see Fig 9-1) This aspect of sensory anatomy is elaborated in the next chapter, which includes maps of the sensory dermatomes and cutaneous nerves However, as a means of quick orientation to the topography of peripheral pain pathways, it is useful to remember that the facial structures and anterior cranium lie in the elds of the trigeminal nerves; the back of the head, second cervical; the neck, third cervical; the epaulet area, fourth cervical; the deltoid area, fth cervical; the radial forearm and thumb, sixth cervical; the index and middle ngers, seventh cervical; the little nger and ulnar border of hand and forearm, eighth cervical rst thoracic; the nipple, fth thoracic; the umbilicus, tenth thoracic; the groin, rst lumbar; the medial side of the knee, third lumbar; the great toe, fth lumbar; the little toe, rst sacral; the back of the thigh, second sacral; and the genitoanal zones, third, fourth, and fth sacrals The distribution of pain bers from deep structures, though not fully corresponding to those from the skin, also follows a segmental pattern The rst to fourth thoracic nerve roots are the important sensory pathways for the heart and lungs; the sixth to eighth thoracic, for the upper abdominal organs; and the lower thoracic and upper lumbar, for the lower abdominal viscera

segmental sensory impulses From these cells of termination, second-order axons connect with ventral and lateral horn cells in the same and adjacent spinal segments and subserve both somatic and autonomic re exes The main bundle of secondary neurons subserving pain sensation projects contralaterally (and to a lesser extent ipsilaterally) to higher levels; this constitutes the spinothalamic tract, discussed below In recent years, a number of important observations have been made concerning the mode of transmission and modulation of pain impulses in the dorsal horn and brainstem Excitatory amino acids (glutamate, aspartate) and nucleotides such as adenosine triphosphate (ATP) are the putative transmitters at terminals of primary A- sensory afferents Also, A- pain afferents, when stimulated, release several neuromodulators that play a role in the transmission of pain sensation Slower neurotransmission by C neurons involves other substances, of which the most important is the 11 amino acid peptide known as substance P In animals, substance P has been shown to excite nociceptive dorsal root ganglion and dorsal horn neurons; furthermore, destruction of substance P bers produces analgesia In patients with the rare condition of congenital neuropathy and insensitivity to pain, there is a marked depletion of dorsal horn substance P A large body of evidence indicates that opiates are important modulators of pain impulses as they are relayed through the dorsal horn and through nuclei in the medulla and midbrain Thus, opiates have been noted to decrease substance P; at the same time, exor spinal re exes, which are evoked by segmental pain, are reduced Opiate receptors of three types are found on both presynaptic primary afferent terminals and postsynaptic dendrites of small neurons in lamina II Moreover, lamina II neurons, when activated, release enkephalins, endorphins, and dynorphins all of which are endogenous, morphine-like peptides that bind speci cally to opiate receptors and inhibit pain transmission at the dorsal horn level The subject of pain modulation by opiates and endogenous morphinelike substances is elaborated further on