Lecture 14: Muscular System PDF

LECTURE -14 Muscular System Dr.Pugazhandhi Bakthavatchalam Assistant Professor of Anatomy and Physiology, AUACAS, American University of Antigua LEARNING OUTCOMES  Describe the Mechanism of contraction and relaxation of skeletal muscle fibers...

LECTURE -14 Muscular System Dr.Pugazhandhi Bakthavatchalam Assistant Professor of Anatomy and Physiology, AUACAS, American University of Antigua LEARNING OUTCOMES  Describe the Mechanism of contraction and relaxation of skeletal muscle fibers.  Describe the Neuro Muscular Junction (NMJ) Muscle Contraction  Physiology of Muscle Contraction Contraction of a Skeletal Muscle  Muscle fiber contraction is “all or none”  Within a skeletal muscle, not all fibers may be stimulated during the same interval  Different combinations of muscle fiber contractions may give differing responses  Graded responses – different degrees of skeletal muscle shortening Rapid stimulus = constant contraction or tetanus  Muscle force depends upon the number of fibers stimulated More fibers contracting results in greater muscle tension  Muscles can continue to contract unless they run out of ATP or Ca2+ One molecule of ATP supplies enough energy for one actin and myosin cross-bridge Energy for Muscle Contraction  Muscles use stored ATP for energy Bonds of ATP are broken to release energy Only 4-6 seconds worth of ATP is stored by muscles  Three ways for muscle to make energy (ATP) ATP production for Muscle Contraction Fermentation Creatine Cellular (Anaerobic Phosphate Respiration Respiration) 1. Creatine Phosphate  Creatine phosphate is a high-energy compound and is the fastest way to make ATP available for muscles  Used for activities lasting < 15 seconds  Anaerobic (no oxygen needed)  Creatine phosphate is made when a muscle is at rest 2. Cellular Respiration  Mitochondria use glucose molecules to make ATP in the presence of oxygen Provides most of a muscle’s ATP  Aerobic (needs oxygen)  Used for activities lasting hours  1 glucose = 36 ATP 3. Anaerobic Respiration/ Fermentation  Reaction that breaks down glucose without oxygen  Used for activities lasting 30 – 60 seconds  Anaerobic (no oxygen)  Lactic acid is also produced and causes pain in the muscle  Heavy breathing after exercise is a sign of oxygen deficiency  A marathon runner is exhausted after crossing the finish line because they have depleted not only their oxygen but their glucose as well  It takes up to two days to replace all of the glucose in the muscles and glycogen in the liver Muscles and Body Movements  Movement is attained due to a muscle moving an attached bone  Muscles are attached to at least two points Insertion – attachment to a moveable bone Origin – attachment to an immovable bone Types of Ordinary Body Movements  Flexion – decreases angle of joint and brings two bones closer together  Extension- increases angle of joint  Rotation- movement of a bone in longitudinal axis, shaking head “no”  Abduction – moving away from the midline  Adduction - moving toward the midline  Circumduction - cone- shaped movement, proximal end doesn’t move, while distal end moves in a circle. Types of Muscles  Muscles work in opposing pairs Ex. Biceps (flexion of arm) and Triceps (extension of arm)  Prime mover – muscle that does most of the work Synergist – muscle that helps a prime mover in a movement  Antagonist – muscle that opposes or reverses a prime mover Naming of Skeletal Muscles  Direction of muscle fibers Example: rectus (straight), orbicularis (circular)  Relative size of the muscle Example: maximus (largest), minimus (smallest), longus (long), brevis (short)  Location of the muscle Example: pectoralis (chest), external (outside), frontalis (frontal)  Number of origins Example: triceps (three heads)  Location of the muscles origin and insertion Example: sterno (on the sternum)  Shape of the muscle Example: deltoid (triangular)  Action of the muscle Example: flexor and extensor (flexes or extends a bone) Affects of Aging on Muscles 1. Muscles that are not used are replaced by connective tissue then by fat 2. With age comes degeneration of mitochondria due to exposure to oxygen and free radicals 3. Changes in the nervous system and endocrine system also effect structure and function of muscles 4. Muscles become weaker as we age but exercise can stimulate muscle build-up  She is 86 years young and a body builder.  He is 80, and the oldest Iron man triathlon participant. (1.2 mile swim, a 56-mile bike and a 13.1 mile run = 70.3 miles.) Disorders relating to the Muscular System  Muscular Dystrophy: inherited, muscle enlarge due to increased fat and connective tissue, but fibers degenerate and atrophy  Duchenne MD: lacking a protein to maintain the sarcolemma  Myasthemia Gravis: progressive weakness due to a shortage of acetylcholine receptors Sprain verses Strain  Strain – overstretching of a muscle near a joint  Sprain – twisting of a joint leading to swelling and injury to ligaments, tendons, blood vessels and nerves  Myalgia and Tendinitis  Myalgia – inflammation of muscle tissue (arthritis on previous slide)  Tendinitis – inflammation of the tendon due to strain of repeated activity