HANSON, J. T h e effects of repetitive stimulation on. the action potential and the twitch of rat muscle. Acta physiol. scand. 1974. 90. 387-400. Membrane potentials and contraction curves of different types of rat muscle fibre have been studied a t body and room temperatures with special regard to the effects of repetitive stimulation. Fast fibres (from the surface of the extensor muscles of the antebrachium) have a higher resting membrane potential, a higher amplitude and shorter duration of the spike of the action potential and a larger early negative after-potential than soleus fibres. I n the fast fibres stimu-B~R~N Y , M., ATPase activity of myosin correlated with speed of muscle shortening. A comparison between the effects of sympathomimetic amines on fast-and slow-contracting mammalian muscle. Brit. J. Pharma-BROWN, G. L. and U. S. VON EULER, The after-effects of a tetanus on mammalian muscle. units: Physiological-histochemical correlation in three types in cat gastrocnemius. Science CHAPMAN R. A., Experimental alteration of the relationship between the external calcium concentration and the contractile force generated by auricular trabeculae isolated from the heart of the frog, Rana pipiens. , Influence of temperature on isometric contractions of rat skeletal muscles. Nature (Lond.) 1968 a. 217. 1179-1 180. CLOSE, R. I. and J. F. Y . HOH, The after-effects of repetitive stimulation on the isometric twitch contraction of rat fast skeletal muscle. J. Physiol. (Lond.) 1968 b. 197. 4 6 1 4 7 7 .CONNOLLY, R., W. GOUGH and S. WINEGRAD, Characteristics of the isometric twitch of skeletal muscle immediately after a tetanus.

HANSON, J. Effects of repetitive stimulation on membrane potentials and twitchin human and rat intercostal muscles. Acta physiol. scand. 1974. 92. 238-248. Membrane potentials of human and rat external intercostal muscles have been studied in vitro at body temperature, and contraction curves at both body and room temperature. Histochemical staining of the entire preparation used in the experiment was performed. The resting membrane potential was on the average somewhat higher in human than in rat intercostal muscle fibres.l'he mean duration of the spike was 1.50 ms for the human fibres and 0.89 ms for the rat fibres. The mean contraction times were 79 and 11 ms, respectively. In the randomly taken Neurosurg. Psychiat. 1971. 34. 113-120. S~O M I C ,A., A. ROSENFALCK and F. BUCHTHAL, Electrical and mechanical responses of normal and myasthenic muscle. Brain Res. 1968. 10. 1-78. TAKAMORI, M., L. GUTMANN and S. R. SAANE, Contractile properties of human skeletal muscle.

Hanson, J. and L. Widén. Afferent fibres in the hypoglossal nerve of cat. Acta physiol. scand. 1970. 79. 24–36. Electrical stimulation of the hypoglossal nerve in cat elicited bilateral twitching of the vibrissae and suppression of shivering. The afferent fibres which mediate these reflexes have a higher stimulus threshold than the motor fibres. They travel to the brain stem via anastomoses between the hypoglossal nerve and the vagus group in the region of the ganglion nodosum. Unitary activity was recorded in the spinal trigeminal nucleus after stimulation of the hypoglossal nerve. The reflexes are probably nociceptive reactions since similar reflexes can be evoked from the greater part of the body surface by pain stimuli. Stimulation of a peripheral branch of the hypoglossal nerve also elicited a local reflex response in the styloglossus muscle. The reflex is polysynaptic. Any tonic background activity in the muscle is inhibited by the stimulation. It is shown that this inhibition is probably not recurrent but mediated by afferent fibres via anastomoses to the vagus group. Afferent impulses evoked by stretching the tongue were recorded in the proximal part of the hypoglossal nerve trunk. These units behaved like muscle spindles. In cat these units are sparse and probably of secondary importance for movements of the tongue.

Transversal sections of the inferior oblique muscle from kittens of various ages and from adult cats were stained for myofibrillar ATP-ase at Ph 9.4 and 4.35, succinic dehydrogenase (SDH) and fat. The same muscles had previously been submitted to studies of contractional and fatigue properties. With ATPase the fibers could be differentiated into types I, II and II C. The percentages of each fiber type remained approximately the same from birth onwards. In the inner, global layer of the muscle, type I fibers showed a linear increase in size, but types II and IIC fibers an accelerated growth after age 20 weeks. In the outer, orbital layer, where no type I fibers were seen, type II and II C fibers showed the same growth pattern as in the global layer. The fiber content of SHD and fat was low at birth but increased after two weeks of age. Type I fibers were poor and type II C fibers rich in SDH and fat. Type II fibers showed varying amounts of these substances. Provided that type I fibers are slow, type II fast and type II C intermediate in speed of contraction, like in other muscles, the findings on fiber growth and SDH content seem to support the idea that slow, fatigue resistant components in eye muscles reach maturity earlier than fast components.

The postnatal development of the inferior oblique muscle in the cat has been studied with physiological and histochemical techniques. This paper describes the changes with age in isometric twitch and tetanic response characteristics. The twitch amplitude increased and the twitch contraction time (ct) and half-relaxation time (hrt) decreased almost linearly from birth to adulthood. The relation between the strength of nerve stimulation and twitch ct and hrt changed during development with a threshold slow response appearing at 10 weeks. Twitch responses in cats 6 weeks of age or older were of longer duration than in younger cats, in spite of the longer ct and hrt in young cats. Fusion frequency of the tetanic response reached a constant level in muscles 6 weeks or older. The maximum rate of tension rise remained the same from birth to 6 weeks of age and later increased markedly up to 20 weeks of age. The contracture induced by succinylcholine was the same in muscles of all ages. These data were related to previous findings on the postnatal development of fast and slow muscles and motor units in the hindlimb of the cat. A differentiation of the development of fast and slow eye muscle fibers is suggested. Slow fibres seemed to have completed their maturation at about ten weeks of age, while the development of fast fibre properties continued, probably up to the adult stage.