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Cystone

By X. Ugrasal. Maryville University of Saint Louis.

Type II gamma motor neurons reside in the ventral horns of the axons innervate mainly nuclear chain fibers and have nerve spinal cord and in nuclei of the cranial motor nerves generic 60caps cystone otc. This high number reflects the com- ings of both primary and secondary sensory axons of the plex role of the spindles in motor system control. Intrafusal muscle spindles respond to stretch by generating action po- muscle fibers likewise constitute a significant portion of the tentials that convey information to the central nervous sys- total number of muscle cells, yet they contribute little or tem about changes in muscle length and the velocity of nothing to the total force generated when the muscle con- 94 PART II NEUROPHYSIOLOGY A R Ia Response Passive stretch of muscle fibers from resting length Tension Wt. T Passive stretch B Ia response ceases R Stimulate alpha Ia Response motor neuron Tension Wt. T Stimulate C Ia responsiveness is maintained Stimulate alpha R and Ia Response gamma motor neurons Tension Wt. A, The Ia C, Concurrent alpha and gamma motor neuron activation, as oc- sensory endings from the muscle spindles discharge at a slow rate curs in normal, voluntary muscle contraction, shortens the muscle when the muscle is at its resting length and show an increased fir- spindle along with the extrafusal fibers, maintaining the spindle’s ing rate when the muscle is stretched. Rather, the contractions of intrafusal fibers play a spindle were reinstituted, the Ia nerve endings would re- modulating role in sensation, as they alter the length and, sume their sensitivity to stretch. This is accomplished by coordinated activation discharge of action potentials. Contraction of the muscle of the alpha and gamma motor neurons during muscle con- increases the firing rate in type Ib axons from Golgi tendon traction (see Fig. Ia endings report both the velocity and the length of stretch, type Ia endings show a greater firing rate increase, while muscle stretch; type II endings report length. B, With the release CHAPTER 5 The Motor System 95 types of endings, each located distal to the sensory endings on the striated poles of the spindle’s muscle fibers (see Fig. The nerve terminals are either plate endings or trail endings; each intrafusal fiber has only one of these two types of endings. Plate endings occur predominantly on bag1 fibers (dynamic), whereas trail endings, primarily on chain fibers, are also seen on bag2 (static) fibers.

Bowel and Bladder Function Motor difficulty in structures related to speech may affect the individual’s ability In some instances control of bladder or to speak buy cystone 60caps on-line. Coordination and accuracy of bowel function may be lost (inconti- movement of the muscles, lips, tongue, nence) after brain damage. At times prob- or other parts of the speech mechanism lems are caused by the individual’s may be impaired secondary to weakness inability to recognize the need to urinate or paralysis of the muscles needed to or defecate. Paralysis or weakness of mus- or bowel retraining, or the need for indi- cles may also cause vocal cord dys- viduals to wear or utilize a catheter (tube function, which in turn can affect voice inserted into the bladder to drain urine). Other motor problems can cause artic- Posttraumatic Seizures ulation disorders in which there is no sig- nificant weakness or lack of coordination Seizures may be experienced in the peri- for reflexive action but rather the inabil- od immediately after the brain damage. In some instances, seizures may be able to scrape a food particle off occurring in the immediate postdamage their teeth with their tongue, but they phase resolve after swelling of the brain may be unable to coordinate the muscles recedes. In many other cases, however, indi- that move the tongue to produce a pho- viduals continue to have seizures, a condi- netic sound. It results from dysfunc- Language impairment may differ tion of the language centers in the brain, depending on the area of the brain dam- rather than impairment in the muscu- aged. Individuals may nitive skills: be able to understand and read simple material; however, as the complexity or • Memory length of the message increases, difficul- • Attention and concentration ty becomes more apparent. Although • Self-awareness they are able to comprehend, they may • Problem solving and decision making have difficulty expressing thoughts in • Information processing and concept speech and writing because of difficulty formation putting words and sentences together log- • Judgment ically. Speech may be labored, slow, and/or difficult to Memory encompasses the ability to understand, and small connecting words, store and retrieve information. Memory and increased verbal output, but with for both new and old information may be reduced information content, so that affected. Immediate memory lasts only sec- Wernicke’s aphasia are typically unaware onds or minutes unless converted in- of their communication difficulties. An example In some instances individuals may ex- of immediate memory is remember- perience global aphasia, in which there ing a phone number long enough to is severe difficulty communicating because dial the number, but then not com- of both the inability to use language (to mitting it to memory for later use. Short-term memory lasts from min- to wipe the same spot on a counter until utes to hours, but it is then lost if not someone intervenes.


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