an AP develops in the motor nerve released from The nerve terminal EPP de-velops on the post June tonal membrane if it (the EPP) is of sufficient magn

muscles when repeated contractions are attempted, muscular weakness and even frank neuromuscular transmission block. Besides, DFP. as slated above, heavy dose of corlisol (in the hope of destroying the antibody) is also used for treatment 7. Muscle relaxants During surgical operations in the abdomen. muscles should be satisfactory lelaxed. as this helps adequate re-, traction of the abdominal wound. This, of course can be achieved by deepening the level of anesthesia, but this is not preferred. An alternative procedure is to use the muscle relaxants which (by different mechanisms) can produce a neuromuscuJar block so that the tone of all the skeletal muscfes iincluding the muscles of respiration) are reduced wilhout using a heavy dose of anesthesia. As can be understood, possibility of the respiratory paralysis has to be guarded against. recall, this enzyme destroys ACh. SUMMARY & HIGHLIGHTS Under light microscopes, some differences are seen between skeletal and canjiac muscles, but EM features and mechanism of contraction (called ratchet or sliding theory) of these two types of muscles aie remarkably similar. Contractile elements are. (i) myosin. and (2) actin. When an AP develops on sarcolemma more free Ca++ ions become available within thecytosol of muselee ell uncovering of the active sites of theaclin modules attachment ol the myosin heads into the active sites, occur, New, these heads rotate-> actin filament moves forward (towards the H zone) the head deatlaches ->again reattaches to a new active site and so Ihe sarcomere length reduces and the muscle as a whole shortens. ATPs are required for the rotation and deattachment of the heads.Neuromuscular transmitter is ACh. When an AP develops in the motor nerve released from The nerve terminal EPP de-velops on the post June tonal membrane if it (the EPP) is of sufficient magnitude, an AP of the muscle develops contraction occurs. This neuromuscular transmission can be abolished by succinyl choline [(depalarizing blocker, a twitch followed by paralysis)] curare [(competitive antagonist), no twitch before the paralysis] and so on. 1. Introduction 2 Instruments for study.3. Some commonly used terms. The properties. A. Mechanical (i) Response to a single stimulus. The simple muscle curve. ii. Summation. (@ Clonus and tetanus - Response to repeated stimuli, (iv) all or none' law. v) Fatigue. (9 Effect of terrnpeiature and load. (>o Force of contraction. Factors influencing force of contraction. Length tension relationship. Force velocity relationship. (viii) Lever action of muscles, (ix) Summary. B. Thermal properties.C. Electrical properties.5. EMG 6. Energy expenditure during muscular contraction. Introduction Studying the properties of skeletal muscles, forms the basis of 'nerve muscle physiobgy' of the undergraduate students of medical physiology. In the practical classes it is commonly performed on frog's skeletal muscle. There are a number of reasons why the frog is chosen as an experimental animal for this purpose : (i) the animal is cheap, but more important reason is (ii) a skeletal muscle separated from this animal's body (and thus bereft of its vascular supply) remains alive at room temperatures of Indian laboratories for several hours. A mammalian skeletal muscle preparation. once isolated, dies quickly. For this reason, if experiments are intended on mammalian sketetal muscles, elaborate arrangements, (which are often not very practicable for a mass of students) are necessary. Nevertheless, the informations obtained Irom such isolated nerve muscle preparations of frogs, are reasonably dose to those from the mammalian muscles. In the following pages. properties (Characteristics) of skeletal muscles will be discussed. These properties should be compared and contrasted with those of the cardiac muscles (chap.2. sec. V) and the smooth muscles (chap. 4. sec. IX). Procedure and instruments for study Commonly, the frog is made unconscious by a sharp stun on the laboratory bench (stunning). This is followed by pithing In pithing, a sharp needle is introduced through the foramen magnum of the animal into its cranial cavity. By manipulating the needle, the brain is destroyed. The aim of stunning is to make the animal unconscious in quickest possible time; pithing is done while the animal is still unconscious. The twin procedures ensure that during subsequent procedures the animal does not feel pain and thus an avoidable cruelty is avoided. Subsequently, the spinal cord of the animal is destroyed by introducing the needle within the vertebral canal and rotating it re-peatedly. This destruction ensures loss of all spinal leflexes (which may. otherwise, be elicited in Ihe subsequent procedures) and thus prevents premature fatigue. It also makes the limbs toneless (flaccid) which facilitates dissection. Subsequently, the gastiocnemius soleus ('calf muscles') of one leg. together with the sciatic nerve (with its branch supplying the gastrocnemius soleus) is dissected out and isolated from the body. The branch supplying the gastrocnermius arises just above the knee joint and care must be taken to see that this twig to the calf muscle is not Tom during the preparation. Such a preparation is called the 'gastrocnemius sciatic' preparation. Instruments The aim is to give a single electrical shock to the sciatic nerve. The nerve is thus stimulated and generates an action potential. Eventually the nerve impulse crosses the neuromuscular junction and causes the muscle to contract. Arrangements for giving the electrical shock are as follows : A steady DC current is led off from a source, which is usually a dry cell battery. This current is led to a solenoid called the 'primary coil'. Superimposing the primary coil. there is another solenoid called the 'secondary coil'. The wires of the secondary are apposed but not in physical contact with the primary. As a result, when a DC current starts to flow or stops to flow (i.e. changes