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Muscle physiology
The document outlines muscle physiology, discussing the three main types of muscle tissue - skeletal, cardiac, and smooth muscle. It focuses on skeletal muscle, describing its general functions including movement, protection, and posture maintenance. The functional anatomy of skeletal muscle is explained down to the sarcomere level. The physiology of skeletal muscle contraction is summarized in three steps: 1) events at the neuromuscular junction, 2) the excitation-contraction coupling process, and 3) the contraction-relaxation cycle at the sarcomere level.
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Introduction to muscle physiology including function, characteristics, types, and outline of skeletal, cardiac, and smooth muscle.
Muscle functions include movement, thermogenesis, protection, posture maintenance, and joint stabilization.
Muscle tissues share four key characteristics: excitability, contractility, elasticity, and extensibility.
Three primary types of muscle tissue: skeletal, cardiac, and smooth muscle.
Skeletal muscle functions include voluntary movement, protection of underlying structures, and stabilizing joints.
Involuntary functions include thermogenesis through shivering and maintenance of posture through reflexes.
Functional anatomy details including the smallest unit (sarcomere) and its microfilament composition.
Components of the sarcomere, titin's role, and the function of myosin and actin filaments.
Contraction mechanics involving NMJ events, excitation-contraction coupling, and the contraction-relaxation cycle.
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Muscle physiology
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- 2. Lecture Outline • MuscleFunction • Muscle Characteristics • Muscle Tissue Types • Skeletal Muscle – General Functions of Skeletal Muscle – Functional Anatomy – Physiology – Skeletal Muscle Types – Energetics – Adaptive Responses • Cardiac Muscle Physiology • Smooth Muscle Physiology
- 3. Muscle Function • Movement –Depends on type of muscle tissue – Depends on location of muscle tissue • Thermogenesis • Protection • Posture Maintenance • Joint Stabilization
- 4. Muscle Tissue Characteristics Allmuscle tissues share basic characteristics 1.Excitability 2.Contractility 3.Elasticity 4.Extensibility
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- 6. Skeletal Muscle General Functions- Voluntary • Movement – Only have contractility in one direction • Requires multiple muscles to create movements from the simple – flexion and extension • To the complex – Circumduction • Stabilizing Movements & Joints – The result of synergistic muscles
- 7. Skeletal Muscle General Functions •Protection – of underlying structures • abdominal viscera – Stronger muscles = greater protection, increased joint stability
- 8. Skeletal Muscle General Functions- Involuntary • Shivering Thermogenesis (shivering reflex) – asynchronous & involuntary – Initiated by hypothalamic nuclei in the primary motor center for shivering (posterior nuclei) • Normally inhibited by the heat center in the hypothalamus (preoptic nuclei) when body temp is in range (96.8-99.5) – Receives cold signals from skin and spinal cord - - Skeletal Muscle preoptic nucleus posterior nucleus Damage to the posterior nuclei would cause?
- 9. Skeletal Muscle General Functions- Involuntary • Maintenance of Posture – Involves stretch reflexes • Static reflexes – Long term sustained contractile events • Phasic reflexes – Dynamic and short term corrective responses • Regulated by gamma neurons which adjust tension in the muscle spindles
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- 13. Skeletal Muscle • Thesmallest functional unit of skeletal muscle is the sarcomere
- 14. Skeletal Muscle • Sarcomereis composed of various microfilaments and supporting structures • Titin – largest known elastomeric protein – Connects myosin to z-disc – thought to be critical in the development of sarcomeres
- 15. Skeletal Muscle • Myosinmolecule consists of tail, hinge and heads – Heads contain active sites for • Actin • ATP • M-line consists of myomesin and skelemin proteins – stabilize the myosin filaments – theorized to aid in transmission of force from sarcomere to cytoskeletal intermediate filaments
- 16. • Thin filamentsare composed of – g-actin molecules in a helical arrangement • Contain myosin binding sites – nebulin • Filament that forms internal support and attachment for actin – tropomyosin filaments – troponin (complex of three molecules) attached to tropomyosin • Has binding sites for Ca2+ Skeletal Muscle
- 17. Skeletal Muscle Functional Anatomy •The Z-disc – Anchors the filaments and interacts with cytoskeletal framework
- 18. Skeletal Muscle Functional Anatomy •Transmission of force from the sarcomere to the tissue at large – Sarcomeres linked by dystrophin to sarcolemma, then via membrane proteins interacting with cytoskeletal framework Muscular Dystrophy?
- 19. Skeletal Muscle Physiology ofContraction • How does all this functional anatomy work? – 1st – synaptic transmission at the neuromuscular junction – 2nd – excitation-contraction coupling – 3rd – contraction-relaxation cycle
- 20. Skeletal Muscle Physiology ofContraction - NMJ 1. Events at the neuromuscular junction (NMJ) a. action potential arrives at the pre-synaptic membrane b. depolarization of membrane opens voltage gated Ca2+ channels c. calcium influxes into synaptic bulb d. calmodulin is activated by Ca2+ which e. activates protein kinase II (PK II) f. PKII phosphorylates synapsin (motor protein) g. vessicle binds to membrane proteins (SNAREs) h. exocytosis of ACh i. ACh binds to nicotinic receptors j. Na+ influx creates an End Plate Potential (EPP) k. EPP spreads to edge of the motor end plate and initiates an action potential in the sarcolemma
- 21. Skeletal Muscle Physiology ofContraction – Excitation-Contraction Coupling 2. Excitation-Contraction Coupling Process a. Action potential spreads along sarcolemma and down t- tubules b. Depolarization of membrane alters membrane protein dihydropyridine L (DHP) configuration c. Altered DHP configuration signals ryanodine Ca2+ receptors (RyR Ca2+ ) in the terminal cisternae of the sarcoplasmic reticulum • Neatly, these are near the I and A bands of the sarcomere! a. Ca2+ is released into the sarcoplasm and b. binds to troponin c. initiates a conformational change in the troponin-tropomyosin complex exposing the binding sites for myosin on actin d. Myosin binds to actin (electrostatic attraction)
- 22. Skeletal Muscle Physiology ofContraction – Contraction-Relaxation Cycle 3. Contraction-Relaxation Cycle a. Myosin upon attaching to actin is hydrolized (phosphate coming from the splitting of ATP by Myosin ATPase) b. This changes the conformation of myosin causing it to bend at the neck towards the m-line c. ADP is released by the conformational change during the “power stroke” d. ATP binding site is now available for another ATP (along with magnesium Mg2+ ) e. Splitting of ATP to ADP + P by myosin detaches and returns myosin to its active state f. This single event creates a twitch
- 23. Skeletal Muscle Physiology ofContraction