Muscle Physiology II PDF - BIOL 101

Anatomy & Physiology BIOL 101 6. Muscle Physiology Dr. Stephen Onigbinde [email protected] Session ID:  Your Objectives will show here!...

Anatomy & Physiology BIOL 101 6. Muscle Physiology Dr. Stephen Onigbinde [email protected] Session ID:  Your Objectives will show here! 11. Identify and describe the components of the neuromuscular junction 12. Identify and describe the events that occur at the neuromuscular junction 13. Identify and describe the role of the nerve cell components in the excitation-contraction coupling process 14. Describe the roles of the sarcolemma, transverse tubules, sarcoplasmic reticulum and filaments in the excitation-contraction coupling process 15. Outline and explain how calcium release results in muscle contraction 16. List and define the steps of the contraction cycle 17. Describe the sliding filament theory for muscle contraction Biol 101. Block 1. Lecture 2. Cell Physiology 18. Describe the changes that occur in the different bands/zones of the sarcomere during the contraction cycle 19. Discuss the determinants that influence the force of skeletal muscle contraction 20. Explain the concept of length-tension relationship  Your Objectives will show here! 21. List and explain the different types of skeletal muscle contraction 22. Briefly describe isotonic and isometric muscle contraction 23. List and briefly describe the 3 different types of metabolism that occurs in skeletal muscle 24. Briefly discuss muscle fatigue and the factors that contribute to it Physiology 25. Describe the 3 different types of muscle fibres Physiology II 26. Describe the main histological, structural and functional characteristics of cardiac muscle 2. Cell 27. Describe the main histological, structural and functional 6 Muscle 1. Lecture characteristics of smooth muscle 28. Compare and contrast skeletal and smooth muscle Lecture 101. Block contraction BIOL101. Biol  Objective 11 Neuromuscular Junction The neuromuscular junction is formed by: 1. Axon terminal End of motor neuron axon Terminals have small membranous sacs (synaptic vesicles) These vesicles contain neurotransmitters (e.g. acetylcholine - ACh) BIOL101. Lecture 6 Muscle Physiology II 2. The motor end plate A specific part of the sarcolemma that contains ACh receptors Axonal ends and muscle fibers are always separated by a space called the synaptic cleft Session ID: BIOL101. Lecture 6 Muscle Physiology II Neuromuscular Junction Objective 11,12  Objective 11, 12 Myasthenia Gravis Autoimmune neuromuscular disease against the nicotinic acetylcholine receptor More common in women aged 20-40 with possible links to thymus gland tumors Begins with double vision and BIOL101. Lecture 6 Muscle Physiology II swallowing difficulties, with progression to paralysis of respiratory muscles Treatment: acetylcholinesterase inhibitors, immunosuppressant  Objective 13,14,15 Excitation-Contraction coupling 1) Nerve impulse reaches an axon terminal and synaptic vesicles release acetylcholine (ACh) 2) ACh diffuses to receptors on the sarcolemma and Na+ channels open and Na+ rushes into the cell 3) A muscle action potential spreads over sarcolemma and down into the transverse tubules 4) The sarcoplasmic reticulum releases calcium ions (Ca++) into the BIOL101. Lecture 6 Muscle Physiology II sarcoplasm and they bind to troponin 5) Troponin then moves tropomyosin away from the myosin binding sites on actin 6) Once the binding sites are “free”, there is a start to the contraction cycle (the repeating sequence of events that causes the filaments to slide)  Objective 16 Contraction Cycle Repeating sequence of events that cause the thick and thin filaments to move past each other Four steps to the contraction cycle: ATP hydrolysis Attachment of myosin to actin to form cross-bridges Power stroke BIOL101. Lecture 6 Muscle Physiology II Detachment of myosin from actin The cycle keeps repeating as long as there is ATP available and there is a high Calcium ion level near the filaments BIOL101. Lecture 6 Muscle Physiology II Objective 16  Objective 17,18 The Sliding Filament Mechanism Muscle contraction occurs because myosin heads attach to and “walk” along the thin filaments at both ends of a sarcomere, progressively puling the thin filaments toward the M line. As the thin filaments slide inward, the I band and H zone narrow and eventually disappear altogether when the muscle is maximally contracted. BIOL101. Lecture 6 Muscle Physiology II The width of the A band and the individual lengths of the thick and thin filaments remain unchanged. BIOL101. Lecture 6 Muscle Physiology II Summary chart Objective 17,18 BIOL101. Lecture 6 Muscle Physiology II Summary chart Objective 12,13,14,15 BIOL101. Lecture 6 Muscle Physiology II Relaxation Objective 16  Objective 19 Determinants of the force of skeletal muscle contraction Muscle contraction is regulated by the somatic nervous system The strength of skeletal muscle contraction is determined by these factors: Metabolic conditions (e.g. fatigue) Amount of load BIOL101. Lecture 6 Muscle Physiology II Recruitment of motor units Initial length of muscle fibers Frequency of stimulation  Objective 20 Length-tension relationship The amount of tension that can be generated is determined by the extent of actin-myosin myofilament overlap If the sarcomere is shortened, the actin and myosin have less room to overlap and develop tension BIOL101. Lecture 6 Muscle Physiology II If the muscle is stretched to a point at which actin and myosin no longer overlap, no cross-bridges can be formed and no tension can develop  Objective 21 Twitch contraction A twitch contraction is the brief contraction of all muscle fibers in a motor unit in response to a single action potential in its motor neuron A record of a muscle contraction is called a myogram and includes three periods: latent, contraction, and relaxation. BIOL101. Lecture 6 Muscle Physiology II The refractory period is when a muscle temporarily loses excitability following contraction.  Objective 21 Types of Contraction Twitch Electrical stimulation of myocytes above the threshold potential results in a limited efflux of calcium from the sarcoplasmic reticulum into the cytoplasm, stimulating a single contraction Summation and tetanus If muscle is stimulated at a high enough frequency, individual BIOL101. Lecture 6 Muscle Physiology II muscle twitches combine (summate) to produce sustained contraction (tetanus) Graded The strength of contraction depends primarily on the number of muscle fibers recruited rather than the strength of the muscle fibers BIOL101. Lecture 6 Muscle Physiology II Frequency of stimulation Objective 21  Objective 22 Isometric muscle contraction A constant force is produced while the muscle is held so that it does not change in length and can only exert tension Active tension is produced by cross-bridge cycling, but muscle length does not change e.g. pushing against an immovable object such as a wall Isotonic muscle contraction A constant force is produced while the muscle length is changing BIOL101. Lecture 6 Muscle Physiology II As muscle tension increases, the muscle shortens and lifts the loads e.g. biceps curls in weight lifting  Objective 21 Mechanism of Tetanus The muscle is stimulated repeatedly. Cumulative increase in intracellular calcium ions released from the sarcoplasmic reticulum. Extended time for cross-bridge cycling. As a result, the muscle does not relax (tetanus). BIOL101. Lecture 6 Muscle Physiology II  Objective 23 Metabolism 1. Aerobic metabolism 95% of cell demand Kreb's cycle 1 pyruvic acid molecule: yields 17 ATP 2. Anaerobic metabolism Glycolysis yields 2 pyruvic acids + 2 ATP BIOL101. Lecture 6 Muscle Physiology II Provides substrates for aerobic metabolism As pyruvic acid builds up, it is converted to lactic acid 3. Creatine phosphate  Objective 23 Creatine Molecule capable of storing ATP energy BIOL101. Lecture 6 Muscle Physiology II BIOL101. Lecture 6 Muscle Physiology II Objective 23  Objective 24 Muscle fatigue When muscles can no longer perform a required activity, they are fatigued Factors that contribute to muscle fatigue Depletion of metabolic reserves such as oxygen, glycogen Depletion of creatine phosphate Reduced calcium concentration in the sarcoplasm resulting from BIOL101. Lecture 6 Muscle Physiology II inadequate release from sarcoplasmic reticulum Build up of lactic acid and ADP Failure of action potential in the motor neuron to release acetylcholine  Objective 25 Classification of Muscle Fibers Muscle fiber type Slow oxidative Oxidative-glycolytic Fast glycolytic (slow-twitch) (fast-twitch A) (fast twitch B) Color Red Red White Mitochondria, Abundant Abundant Low myoglobin and blood vessels Use Prolonged, Split ATP at very fast Anaerobic sustained rates; for walking and movements for BIOL101. Lecture 6 Muscle Physiology II contractions for sprinting short duration; maintaining weight lifting posture  Objective 23 Muscle Rigor Muscle fibers are completely depleted of ATP and phosphorylcreatine and develop a state of rigidity called rigor. When this occurs after death, the condition is BIOL101. Lecture 6 Muscle Physiology II called rigor mortis BIOL101. Lecture 6 Muscle Physiology II Objective 26, 27 BIOL101. Lecture 6 Muscle Physiology II Objective 26, 27  Objective 28 Smooth muscle contraction Slower onset of contraction and a longer contraction period compared to skeletal muscle. Can stretch and shorten to a greater degree than skeletal muscles These differences are a result of the following: Smooth muscles contain very few sarcoplasmic reticulum. BIOL101. Lecture 6 Muscle Physiology II Calcium ions flow into smooth muscle cytosol from the interstitial fluid and sarcoplasmic reticulum. Smooth muscles have caveolae (not transverse tubules) It takes longer for calcium ions to reach the filaments in the center of the fiber and trigger the contractile process.  Objective 28 Smooth muscle contraction Calmodulin, a regulatory protein, takes the role of troponin in smooth muscle. After binding to calcium, calmodulin activates myosin light chain kinase. Myosin light chain kinase adds phosphoryl group to the myosin head using ATP allowing myosin to bind to actin. BIOL101. Lecture 6 Muscle Physiology II In addition to action potential from the autonomic nervous system, many smooth muscle fibers contract or relax in response to Stretching, hormones, or local factors such as changes in pH, oxygen and carbon dioxide levels, temperature, and ion concentrations BIOL101. Lecture 6 Muscle Physiology II Objective 3d