Nerve & Muscle Preparation PDF

Dr. Maryam Mosad Elmasry Lecturer of physiology  Nerve & Muscle preparation The contractile property of the muscle is studied by using: The frog’s gastrocnemius –sciatic nerve preparation. Frog’s dissection  Apparatus Kymograph Electric st...

Dr. Maryam Mosad Elmasry Lecturer of physiology  Nerve & Muscle preparation The contractile property of the muscle is studied by using: The frog’s gastrocnemius –sciatic nerve preparation. Frog’s dissection  Apparatus Kymograph Electric stimulator Adjust stimulus intensity and frequency  Simple Muscle twitch (SMT) Single contraction followed by single relaxation of the muscle produced by single maximum stimulation  Phases of a simple muscle Twitch 1) Latent period: time between application of the stimulus and the start of muscle contraction Recorded as an isoelectric line in which the muscle show no mechanical activity. occur due to time needed for: 1. Transmission of action potential through nerve. 2. Neuromuscular transmission. 3. Transmission A.P of muscle. (0.01 second) 2) Contraction Period: shortening of muscle occurs Recorded as an upward deflection from the baseline (0.04 seconds) 3) Relaxation period: the muscle returns to its original length (0.05 seconds) Recorded as a downward deflection back to the baseline  Simple Muscle twitch Point of stimulation Relaxation period Contraction Period Latent period Contraction time < the relaxation time  Factors affecting SMT 1- Type of muscle fibers 2- Initial length of the muscle fiber 3- Temperature 4- Fatigue 1) Types of skeletal muscle fibers Fast (white) muscle fiber as extraocular muscle has shorter duration & Slow (red) muscle fiber as soleus muscle has longer duration 10 2) Initial length of the muscle fiber Lmax: is the optimal length of the sarcomere that give maximal muscle contraction = 2.2 U More than 2.2 U 11  3) Effect of Temperature warm COLD Shorter longer duration duration Higher lower amplitude amplitude  These effects are due to changes in: Rate of chemical reactions (Hot increase chemical reactions, cold decrease chemical reactions) Muscle viscosity (Hot decrease viscosity, Cold increase viscosity)  4) Effect of Fatigue When the nerve muscle preparation is stimulated repeatedly a fatigue curve is obtained  Staircase effect (Treppe response) ⚫ If a resting muscle is repeatedly stimulated with successive stimuli at a rate which does not produce fatigue , the first few contractions become progressively stronger. ⚫ The Staircase phenomenon is caused by: 1-Increased Ca ++ inside the fibers 2-Heat which is liberated as a result of muscle contraction , increases the strength of subsequent contractions. 15 Fatigue: It is the decrease in the muscular activity due to repeated stimulus Causes: 1. Depletion of Ach at the neuromuscular junction. 2. Accumulation of metabolites e.g. lactic acid. 3. Depletion of muscle ATP or glycogen. 4. Psychogenic.  Latent Amplitude Duration period Room Normal Normal Normal temp. Warmth Cold & Fatigue  A case of Myasthenia Gravis: A 35-year-old woman came to the doctor complaining of (symptoms) recurrent double vision (diplopia), difficulty in chewing food and swallowing, difficulty in breathing (dyspnea) and progressive fatigue on doing household errands. Her symptoms improved by rest (or sleep). Examination (signs), of cranial nerves revealed impaired movement of the left eye and unilateral ptosis (drooping of upper eye lid) , which worsen with repetitive eye movements.  Investigation 1- Nerve conduction test: will detect abnormalities in neuromuscular transmission. 2- Lab investigations: immunologic studies : serologic tests to detect the presence of Anti-AChR antibodies (+ve in 90% of myasthenic patients)  Pathophysiology of Myasthenia Gravis Serious & sometimes fatal disease Skeletal muscles are weak and easily fatigue. May involve extra-ocular ms only cause diplopia, or generalized. May affect respiratory muscle cause dysnea, suffocation & death. Other symptoms include difficulty in chewing, swallowing, progressive fatigue & ptosis. Caused by circulating antibodies against nicotinic receptors (Ach receptor) at the MEP destroying them. Symptoms appears at the end of the day with depletion of circulating Ach & disappear during rest.  Treatment 1) short acting anticholinesterase (neostigmine) ( each dose lasts 3-6 hours) 2) Immunosuppressive drugs (takes weeks to bring about effect) 3) Usually combined therapy ( 1 & 2) 4) corticosteroids