Musculoskeletal System Part 2 PDF

ANATOMY AND PHYSIOLOGY Musculoskeletal System (Part 2) October 20 1  LEARNING OUTCOMES At the end of the lessons, student will be able to: List the types of muscles present in human body. List basic characteristics of each muscle. Understand mechanism of act...

ANATOMY AND PHYSIOLOGY Musculoskeletal System (Part 2) October 20 1  LEARNING OUTCOMES At the end of the lessons, student will be able to: List the types of muscles present in human body. List basic characteristics of each muscle. Understand mechanism of action potential Identify components of neuromuscular junction and events involved Understand the mechanism of contraction and relaxation of muscle tissue October 20 2 FUNCTIONS OF MUSCULAR SYSTEM Producing body movements Stabilizing body positions Moving substances within the body Producing heat. Support soft tissue Guard body entrance and exit Provide nutrient reserves October 20 3  Types of muscle tissues Skeletal muscle Smooth muscle tissue tissue Cardiac muscle tissue October 20 4  3 types of muscle tissue  Skeletal muscle tissue - primarily attached to bones, it is striated and voluntary.  Cardiac muscle tissue - forms the wall of the heart, it is striated and involuntary.  Smooth muscle tissue - located primarily in internal organs, it is non striated (smooth) and involuntary. October 20 5  Smooth muscle Skeletal muscle Cardiac muscle October 20 6  SKELETAL MUSCLE TISSUE The most abundant tissue in the human body. Under voluntary control. Each skeletal muscle tissue contains skeletal muscle cells, connective tissues, blood vessels, nerves. Each skeletal muscle cell is called skeletal muscle fiber. Each skeletal-muscle fiber is long cylindrical cell, contains many nuclei and striated (alternate light & dark bands). Skeletal muscle fibers bind together and with connective tissue, nerves and blood vessels to form bundles. October 20 7 These bundles, in turn, bind together to form muscles. October 20 8 October 20 9 October 20 10  CARDIAC MUSCLE TISSUE Only found in the heart. Cardiac muscle tissue is made of cardiac muscle cells known as cardiocytes. It is striated. Usually contain centrally located single nucleus. Not under voluntary control. A bundle of specialized muscle cells called the pacemaker cells in the upper part of the heart sends electrical signals through cardiac muscle tissue, causing the heart to rhythmically contract and pump blood through the body. October 20 11 October 20 12 October 20 13  SMOOTH MUSCLE TISSUE Found in many internal organs-abdomen and intestines, and also in the walls of blood vessels. Spindle-shaped and have a single nucleus. Are not striated. Not under voluntary control. The contractions in smooth muscles move food through our digestive tract, control the way blood flows through the circulatory system, and increases the size of the pupils of our eyes in bright light. October 20 14 October 20 15 October 20 16  Skeletal muscle tissue and the Muscular System Three types of muscle Skeletal – attached to bone Cardiac – found in the heart Smooth – lines hollow organs October 20 17  Three Types of Human Muscle Tissue Skeletal Smooth Cardiac October 20 18  Skeletal muscle functions Produce skeletal movement Maintain posture and body position Support soft tissues Guard entrances and exits Maintain body temperature October 20 19 October 20 20  Anatomy of Skeletal Muscle Organization of connective tissues Epimysium surrounds muscle Perimysium sheathes bundles of muscle fibers Epimysium and perimysium contain blood vessels and nerves Endomysium covers individual muscle fibers Tendons attach muscle to bone or muscle October 20 21 October 20 22 October 20 23  Skeletal muscle fibers Sarcolemma (cell membrane) Sarcoplasm (muscle cell cytoplasm) Sarcoplasmic Reticulum (modified ER) → high concentration of Ca+ T-tubules and myofibrils aid in contraction Sarcomeres – regular arrangement of myofibrils October 20 24 October 20 25  Muscle Fiber Thin filaments – Actin – Tropomyosin → Covers active sites on actin – Troponin → Binds to G-actin and holds tropomyosin in place (site for Ca+ attachment) Thick filaments – Bundles of myosin fibers around titan core – Myosin molecules have elongate tail, globular head – Heads form cross-bridges during contraction – Interactions between actin and myosin prevented by tropomyosin during rest October 20 26 Actin and myosin October 20 27 October 20 28  The Contraction of Skeletal Muscle  Created when muscles contract  Series of steps that begin with excitation at the neuromuscular junction  Action potential at the post-synaptic membrane  Calcium release from the sarcoplasmic reticulum  Thick/thin filament interaction  Muscle fiber contraction October 20 29  Axon collateral of Axon terminal somatic motor neuron Nerve impulse Synaptic vesicle Sarcolemma containing Axon terminal acetylcholine Synaptic (ACh) end bulb Motor Synaptic end end bulb Neuromuscular plate junction (NMJ) Synaptic cleft Sarcolemma (space) Myofibril (b) Enlarged view of the neuromuscular junction (a) Neuromuscular junction 1 1ACh is released Synaptic end bulb from synaptic vesicle Synaptic cleft (space) 4 ACh is broken down Motor end plate 2 2 ACh binds to Ach receptor Na+ Junctional fold October 20 3 Muscle action 30 potential is produced (c) Binding of acetylcholine to ACh receptors in the motor end plate  Control of skeletal muscle activity occurs at the neuromuscular junction Action potential arrives at synaptic terminal – ACh (acethylcholine) released into synaptic cleft – ACh binds to receptors on post-synaptic neuron → Ca+ channel to open – Action potential in sarcolemma * Acethylcholine functions as neurotransmitter October 20 31 October 20 32  Animations (audio visual) https://www.youtube.com/watch?v=qccUQGZbyi8 https://www.youtube.com/watch?v=zUUB3nqh79c October 20 33 Take 5! October 20 34  The Contraction of Skeletal Muscle  Created when muscles contract  Series of steps that begin with excitation at the neuromuscular junction  Action potential at the postsynaptic membrane –sarcolemma membrane  Calcium release from the sarcoplasmic reticulum  Thick/thin filament interaction  Muscle fiber contraction October 20 35  Sliding filament theory Thick and thin filaments slide past to another during contraction Cyclic process beginning with calcium release from Sarcoplasmic Reticulum Calcium binds to troponin Troponin moves, moving tropomyosin and exposing actin active site Myosin head forms cross bridge and bends toward H zone ATP allows release of cross bridge October 20 36  Muscle contraction Action potential along T-tubule causes release of calcium from cisternae of Sarcoplasmic Reticulum – Exposure of attachment sites – Cross-bridge formation – Power stroke – ATP binds to myosin head – Cross-bridge release – Recovery stroke Relaxation – Acetylcholinesterase breaks down ACh – Limits the duration of contraction October 20 37  1 Myosin heads Key: hydrolyze ATP and = Ca2+ become reoriented and energized ADP P 2 Myosin heads bind to actin, forming P crossbridges ATP Contraction cycle continues if ATP is available and Ca2+ level in ADP the sarcoplasm is high ATP ADP 4 As myosin heads bind ATP, the crossbridges detach 3 Myosin crossbridges from actin rotate toward center of the sarcomere (power stroke) October 20 38 October 20 39  Audio visual https://www.youtube.com/watch?v=EdHzKYDxrK c https://www.youtube.com/watch?v=sIH8uOg8ddw October 20 40  1 Nerve impulse arrives at axon terminal of motor neuron and triggers release Nerve of acetylcholine (ACh). Muscle action impulse potential 2 ACh diffuses across Transverse tubule synaptic cleft, binds to its receptors in the motor end plate, and triggers a muscle 4 Muscle AP travelling along action potential (AP). transverse tubule opens Ca2+ release channels in the sarcoplasmic reticulum (SR) membrane, which allows ACh receptor calcium ions to flood into the 3 Acetylcholinesterase in Synaptic vesicle synaptic cleft destroys sarcoplasm. filled with ACh ACh so another muscle action potential does not arise unless more ACh is SR released from motor neuron. Ca2+ 9 Muscle relaxes. 8 Troponin–tropomyosin 5 Ca2+ binds to troponin on complex slides back the thin filament, exposing into position where it the binding sites for myosin. blocks the myosin binding sites on actin. Elevated Ca2+ Ca2+ active transport pumps 6 Contraction: power strokes 7 Ca2+ release channels in use ATP; myosin heads bind SR close and Ca2+ active to actin, swivel, and release; transport pumps use ATP thin filaments are pulled toward to restore low level of center of sarcomere. Ca2+ in sarcoplasm. October 20 41  Tension Production Tension production by muscle fibers Amount of tension depends on number of cross bridges formed Skeletal muscle contracts most forcefully over a narrow ranges of resting lengths Twitch Contraction and relaxation of muscle is response to a stimulus 3 phases- lag, contraction & relaxation Repeated stimulation after relaxation phase has been completed October 20 42  Summation Repeated stimulation before relaxation phase has been completed Wave summation = one twitch is added to another Incomplete tetanus = muscle never relaxes completely Complete tetanus = relaxation phase is totally eliminated October 20 43 October 20 44  Motor units and recruitment Motor Units Consists of a motor neuron and the muscle fibers it stimulates The axon of a motor neuron branches out forming neuromuscular junctions with different muscle fibers A motor neuron makes contact with about 150 muscle fibers Control of precise movements consist of many small motor units Muscles that control voice production have 2 - 3 muscle fibers per motor unit Muscles controlling eye movements have 10 - 20 muscle fibers per motor unit Muscles in the arm and the leg have 2000 - 3000 muscle fibers per motor unit The total strength of a contraction depends on the size of the motor units and the number that are activated October 20 45 October 20 46  Fatigue Muscle fibers use ATP faster than they produce Resulting in weaker contraction Binding of new ATP with the head of myosin is necessary to break down to break down the cross bridge Eg; Muscle cramps Rigor mortis (muscle stiffness after death) October 20 47  Types of muscle Contractions Isometric (equal distance) – Tension rises, length of muscle remains constant Isotonic (equal tensions) – Tension rises, length of muscle changes – Resistance and speed of contraction inversely related – Return to resting lengths due to elastic components, contraction of opposing muscle groups, gravity – Concentric and eccentric contraction October 20 48 October 20 49  Muscle Performance Types of skeletal muscle fibers – Fast fibers (type II myosin) Large in diameter Contain densely packed myofibrils Large glycogen reserves Relatively few mitochondria Produce rapid, powerful contractions of short duration Fatigue quickly White muscle October 20 50  Slow fibers (type I myosin) Half the diameter of fast fibers Take three times as long to contract after stimulation Abundant mitochondria Extensive capillary supply High concentrations of myoglobin Can contract for long periods of time Greater resistance to fatigue Red and dark muscle October 20 51 October 20 52 Muscle performance and the distribution of muscle fibers Pale muscles dominated by fast fibers are called white muscles Dark muscles dominated by slow fibers and myoglobin are called red muscles Training can lead to hypertrophy (enlargement of muscle fiber) of stimulated muscle October 20 53 October 20 54  End of Chapter “Patience can't be acquired overnight. It is just like building up a muscle. Every day you need to work on it.” ~ Eknath Easwaran. 55 October 20