Muscle spindle

Gamma motor neurons innervate intrafusal fibers of the muscle spindle, which monitors muscle length. 

Stretching of the muscle is sensed in the muscle spindle and leads to firing in muscle spindle afferent. These nerves travel via the dorsal root and synapse in the anterior horn of the spinal cord directly with the motor neurone to that muscle. They stimulate firing of the motor neurones, which causes contraction of the muscle that has just been stretched. The muscle spindle afferent also synapses with inhibitory interneurons, which inhibit the antagonistic muscles. This is called reciprocal innervation. 

Muscle spindles are composed of nuclear bag (dynamic) and chain (static) fibres known as intrafusal fibres and these are innervated by y motor neurones. Extrafusal fibres make up the muscle bulk and are innervated by a motor neurones. Stimulation of the muscle spindle leads to increased skeletal muscle contraction, which opposes the initial stretch and maintains the length of the fibre. This feedback loop oscillates at 10 Hz, which is the frequency of a physiological tremor. 

In the same way that muscle spindles are responsible for the maintenance of muscle length, Golgi tendon organs are responsible for maintenance of muscle tension. 

Raines, A., HeIke, C.J., ladarola, M.J., Britton, L.W., and Anderson, R.J. Blockade of the tonic hindlimb extensor component of maximal electroshock and pentylenetetrazol-induced seizures by drugs acting on muscle and muscle spindle systems a perspective on method. Epilepsia 17 395-402, 1976. 

Nerves differ in their sensitivity to local anaesthetics. When lidocaine (lignocaine) is applied to a mixed peripheral nerve the onset of the block is in the order, vasodilatation (B fibres), loss of pain and temperature (C and A6 fibres), muscle spindle reflex (Ay fibres), motor and pressure (A(3 fibres) and large motor and proprioception (Aa fibres). This phenomenon is called differential block. There are other minor variations in this ranking order among the local anaesthetics. The basis of differential block is thought to be the result of variability in the sensitivity of different nerves to the same agent. 

Botulinum toxin induces weakness of striated muscles by inhibiting transmission of motor neurons at the neuromuscular junction. This has led to its use in conditions with muscular overactivity, such as dystonia. Transmission is also inhibited at y neurons in muscle spindles, which may alter reflex overactivity. 

Hets sensory neuropathy with muscle spindle deficiency. Horn neonatal lethality Loa, Cml, Swl (68-70)... 

This means that CC will be regulated until CI=CO, so the system always ends up with perfect control no matter the gain. As shown later, many hormonal control systems and metabolic pathways utilize variants of integral control. Even some types of voluntary movements, for example length control via the muscle spindle, are dominated by integral control. 

Muscle relaxants may also contribute to anesthesia. Pancuronium 0.1 mg/kg has been reported to lower the MAC for halothane by 25% (135). It was conjectured that this could be due to a central effect or peripheral effect, through reduction of afferent input from muscle spindles to the reticular activating system. Recently, however, a similar though not identical study (SEDA-15, 124) (136) failed to confirm that pancuronium, vecuronium, or atracurium lowers the MAC for halothane. 

An arousal pattern can occur on the electroencephalogram, possibly as a result of increased afferent traffic from muscle spindles. This has been speculated as the cause of perioperative dreaming in children in whom an intermit-tent-suxamethonium technique has been used during hght anesthesia (SEDA-13,102) (32). Suxamethonium must be used with caution in neurological disease and is better avoided altogether when there is a risk of a dangerous rise in serum potassium. A transient rise in intracranial pressure has been observed after injection of... 

The cause of the pain is unknown, although there are many hypotheses such as damage to muscle (43,44) resulting from asynchronous contractions of adjacent muscle fibers (45), irreversible damage to muscle spindles (46), potassium flux (47), lactic acid (48), serotonin (49), calcium influx-associated damage to muscle spindles (50), and prostaglandins (51,52). The pain appears not to be related to the extent or intensity of the observed fasciculations. 

Rack PM, Westbury DR. The effects of suxamethonium and acetylcholine on the behaviour of cat muscle spindles during dynamics stretching, and during fusimotor stimulation. J Physiol 1966 186(3) 698-713. 

Stretch receptor A sensory receptor that monitors the degree of stretch, e.g. muscle spindle. 

Motor endplates in Duchenne dystrophy show no adequate morphological evidence to support the neurogenic theory.23 Muscle spindle innervation appeared normal in Duchenne dystrophy.24... 

Systemically, nerve agents produce fascicula-tion and then blockade at the neuromuscular junction with weakness and paralysis. Paralysis of the muscles of respiration (see above) may interfere with respiration and is potentially life-threatening. Some of these effects may be mediated by direct actions at the receptor-ion channel complex. Soman and sarin were reported by Goldstein et al. (1987) to alter muscle spindle function. 

In contrast, naked antibodies are not systemically toxic per se. Of course, a particular antibody can be toxic by its biological effect on the chosen target - either at the intended tumor site or at another site where the target is expressed. For example, Herceptin shows incidence of cardiotoxici-ty, especially in combination with anthra-cyclines [113]. This is caused by HER2 being expressed in cardiac myoblasts, where it is involved in muscle spindle maintenance. 

Kubota, K., Sato, Y Masegi, T., Kobayashi, M. and Shishido, Y. (1978) Electron microscopic study of the snout muscle spindles of the mole following denervation. Anat. Anz. 144 81-96. 

Tower, S.S. (1932) Atrophy and degeneration in the muscle spindle. Brain 55 77-90. 

Muscle spindle primary endings Often et al. [1995] extended the Frankenhaeuser-Huxley model with modifications to reproduce repetitive firing in sensory endings in addition to the fast sodium current, fast potassium current and leakage currents of the FH model a slowly activating delayed rectifier current was required. 

Otten, E., M. Hulliger, and K.A. Scheepstra (1995). A model study on the influence of a slowly activating potassium conductance on repetitive firing patterns of muscle spindle primary endings. J. Theor. Biol. 173,67-78. 

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