Muscle neural influence

Braithwaite, A.W., Harris, A.J. (1979). Neural influence on acetylcholine receptor clusters during embryonic development of skeletal muscles. Nature (Land.) 279 549-51. 

These external neural influences on intestinal motility are common targets for prokinetic drugs, but events within the bowel can have important effects on intestinal motility and cause the bowel to be refractory to traditional prokinetic therapy. Release of cytokines from activated inflammatory cells is probably an important feature of ileus in many cases. Ileus secondary to reperfusion injury is an anticipated response in horses with small intestinal obstruction. However, even apparently mild intestinal injury can initiate cellular responses that lead to impaired motility. Mild intestinal insult by gentle surgical manipulation activated adhesion molecules on leukocytes and increased the expression of P-selectin and intercellular adhesion molecule 1 on endothelial cells within the vasculature of the muscularis layer of the intestine (Kalff et al 1999). Surgical manipulation of the rodent small intestine resulted in substantial extravasation of leukocytes into the intestinal muscularis, consisting mainly of polymorphonuclear neutrophils, monocytes and mast cells and lasting for days. This cellular inflammatory response within the intestinal muscularis externa was associated with a marked decrease in jejunal circular muscle activity (Kalff et al 1998). 

Denervation and dysinnervation abnormalities are usually neurogenous (but, atypically, sometimes can be myogenous see Chapter 1). Conceptually, denervation is a complete loss of neural influence on the muscle fiber (which initially can be reversible by... 

Although many smooth muscles are still rhythmically active when separated from extrinsic innervation, most are quiescent if completely denervated. Net excitatory neural modulation of smooth muscle is the rule. To make things more complex, the influences of innervation to smooth muscle are carried by a rather large number of different transmitters, whose effects are still being investigated. This presumably... 

In some types of rhythm disorders, antiar-rhythmics of the local anesthetic, Na+-channel blocking type are used for both prophylaxis and therapy. These substances block the Na+ channel responsible for the fast depolarization of nerve and muscle tissues. Therefore, the elicitation of action potentials is impeded and impulse conduction is delayed. This effect may exert a favorable influence in some forms of arrhythmia, but can itself act arrhythmogenically. Unfortunately, antiarrhythmics of the local anesthetic, Na+-channel blocking type lack suf -cient specificity in two respects (1) other ion channels of cardiomyocytes, such as K1 and Ca+ channels, are also affected (abnormal QT prolongation) and (2) their action is not restricted to cardiac muscle tissue but also impacts on neural tissues and brain cells. Adverse effects on the heart include production of arrhythmias and lowering of heart rate, AV conduction, and systolic force. CNS side effects are manifested by vertigo, giddiness, disorientation, confusion, motor disturbances, etc. 

Techniques have been developed for study of the renal microcirculation. These techniques have distinct advantages over in vitro endothelial and vascular smooth muscle cell preparations. They allow study of important anatomic and physiologic relationships that are lost in isolated cell systems. For example, the effects of both pressure and flow can be determined and the spatial relahonship between the endothelium and smooth muscle is maintained. These techniques permit functional assessment of the resistance micro-vasculature without destroying vessel integrity while eliminating the confounding influence of undetected circulating, neural and parenchymal factors. The techniques are demonstrated in Table 8. 

From the joint moments, multijoint dynamics can be used to compute the accelerations, velocities, and angles for each joint of interest. Cta the feedback side, the neural command is influenced by muscle length (via muscle spindles) and tendon force (via (jolgi tendon organs). Many other sensory organs play a role in this as well, but these two are generally the most influential. 

Existence of ChAT (acetyl-CoA-choline O-acetyl-transferase, EC 2.3.1.6) in skeletal muscles is probably of neural origin, and its activity varies among skeletal muscles. ChAT activity can be altered by increased or decreased neuromuscular activity. It appears that neuromuscular activity exerts a regulatory influence on neuronal production of ChAT. Alterations in ChAT activity in response to variations in muscular activity represent changes in enz3une synthesis, although effects on catabolism of the enzyme or on exoplasmic transport... 

The muscle activity and the EMG signal associated may vary according to the number of Motor Units (MU) recruited and their activation frequency. A MU is the smallest functional unit, which describes the neural control of muscle contraction. During voluntary muscle contraction, two independent parameters modulates the force applied the first one represents the number of recruited MUs and the second one is MU activation frequency. Considering an experiment, which involves the same muscle activity and the same applied force, is unlikely to observe the same pattern signal. The main parameters that influences EMG signals are ... 

The muscle activation is linked to the activity of neural cells. The twitch is an indication of force development by the muscle (Figure 24.7). After a short latent period, the force becomes evident and rises to a peak then, it declines over a slightly longer time course to zero. The time course of the development of force in the twitch is influenced by the interaction of the contractile components of the muscle fibrils with the elastic components of the muscle. 

---