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The Muscular System By Sam and Jess Functions • • • • • Movement & Circulation Support Posture & Balance Joint Stabilization Heat Production Structure: Skeletal • Responsible for voluntary motion • Striated – Attached to bone via tendons – Ex. Pectorals, deltoids, quadriceps • Many mitochondria/ cell Striations Structure: Cardiac • Responsible for rhythmic contractions of heart • Involuntary • Blend of smooth and striated muscles – Bound together by intercalated disks • Most mitochondria/ cell Intercalated Disks Nucleus Structure: Visceral • Involuntary: controlled by nervous impulses or hormones • Lines walls of hollow organs • Cells spindle shaped: slow + steady contractions – Ex. Vasoconstriction, Vasodilatation Three Types of Muscles (cellular level) Muscle Anatomy Layers of Muscle Myofibrils Muscle Fiber Fascicles held together by perimysium nerves and blood vessels run through Fascia Muscle Fiber Anatomy Muscle Fiber • Many mitochondria • Glycogen stored near sarcolemma – Food for energy • Sarcoplasmic reticulum – Storehouse for Calcium ions The Sarcomere A Band H Band I Band Muscle Contraction • Δvoltage caused by nerve impulse • Calcium ions • Interactions between calcium, troponin, myosin, and actin – ATP required • Fibers pulled shorter: Contraction • Video: http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapt er10/animation__breakdown_of_atp_and_crossbridge_movement_during_muscle_contraction.h tml All-or-None Principle • Strength of muscle contraction does not depend on strength of nerve signal • Cell will contract if voltage threshold is achieved Disease 1: Muscular Dystrophy • Inability to produce dystrophin protein – Inherited or mutation • Muscle weakness and loss of muscle tissue; learning disabilities; inability to walk (age 12); skeletal deformities • Gene therapy? Corticosteroids; mobility aid; physical therapy; surgery Disease 2: Myositis • • • • Autoimmune Inflamed or damaged muscle cells Weakness, swelling, pain Immunosuppressant, immunoglobin, physical therapy, steroids Disease 3: Myasthenia Gravis • • • • Autoimmune Muscle weakness after activity Slow eye, facial, swallowing movements Immunosuppressant drugs, Thymectomy Tetany • Hypocalcaemia: low calcium • How does this affect muscle contraction?? – Normal: calcium binds to sodium to block Δvoltage – Abnormal: less calcium results in lower threshold for Δvoltage • Result constant muscle contractions Fatigue • When muscles run out of energy • No “ingredients” for cell respiration • Lots of waste products – Lactic Acid – ADP • Must pay oxygen debt Muscle Research in Switzerland • “Dirty” muscles mean weak muscles – Healthy cells must clean out waste products and malfunctioning components • Autophagy – Cells with overactive mTORC1 protein (promotes muscle growth) cannot self-clean • Solution: Inject Rapamycin to inhibit mTORC1 and allow cells to clean Alcoholic Skeletal Myopathy Linked to Vitamin D deficiency • • • • • Myopathy: weakness and wasting of muscle tissue 40%-60% of alcoholics experience myopathy Vitamin D deficiency is prevalent in alcoholics Vitamin D deficiency impairs mitochondrial function Shorter phosphocreatine recovery times=better mitochondrial function. • Supplements of vitamin D improve recovery rates Duchenne Muscular Dystrophy (DMD) Research • DMD: fatal, genetic disease where muscles, including heart, progressively deteriorate. • Genetic mutation: absence of vital proteindystrophin • Antisense oligonucleotides (AOs) • DrugDantrolene “A mouse hanging on a wire during a test of muscle strength. Mice with a mutant dystrophin gene, which have a muscular dystrophy-like disease, can only hang for about 20 seconds before they lose their grip and fall to the ground. An antisense oligonucleotide being developed to treat the disease in people only helps a little bit. But if the mice also receive the drug dantrolene (shown as the wire), they are stronger and can hang for 30 seconds or so…It also works in human cells and may help patients with Duchenne's muscular dystrophy.” [CREDIT: G. KENDALL/UCLA; IMAGES: M.C. MICELI, S. NELSON, E. MOKHONOVA, M. SPENCER]
