Chapter 8: The Muscular System Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins Cohen: Memmler’s The Human Body in Health and Disease Types of Muscle Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins Cohen: Memmler’s The Human Body in Health and Disease Types of Muscle Pop Quiz 8.1 Which type of muscle tissue is striated and involuntary? A) Cardiac B) Intercalated C) Smooth D)Skeletal Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins Cohen: Memmler’s The Human Body in Health and Disease Types of Muscle Pop Quiz Answer 8.1 Which type of muscle tissue is striated and involuntary? A) Cardiac B) Intercalated C) Smooth D)Skeletal Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins Cohen: Memmler’s The Human Body in Health and Disease The Muscular System Skeletal Muscle Has Three Primary Functions: • Skeletal movement • Posture maintenance • Heat generation Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins Cohen: Memmler’s The Human Body in Health and Disease The Muscular System Muscle Structure • Fascicles – Bundles of muscle cells (fibers) that make up a whole muscle • Connective tissue – Hold fascicles and whole muscle together – Three layers • Endomysium • Perimysium • Epimysium • Tendons Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins Cohen: Memmler’s The Human Body in Health and Disease Figure 8-1 Structure of a skeletal muscle. What is the innermost layer of connective tissue in a muscle? What layer of connective tissue surrounds a fascicle of muscle fibers? Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins Cohen: Memmler’s The Human Body in Health and Disease Exit Ticket What are the three types of muscle? Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins Cohen: Memmler’s The Human Body in Health and Disease Do Now What are the three main functions of skeletal muscle? What are the three types of muscle? Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins Cohen: Memmler’s The Human Body in Health and Disease The Muscular System Muscle Cells in Action • Motor unit: A single neuron and all the muscle fibers it stimulates – Small motor units used for fine movements – Large motor units used for broad movements Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins Cohen: Memmler’s The Human Body in Health and Disease The Muscular System Muscle Cells in Action • Neuromuscular junction (NMJ): The point at which a nerve fiber contacts a muscle fiber – A type of synapse – NMJ anatomy • Motor neuron • Neurotransmitter (acetylcholine; ACh) • Motor end plate (on muscle fiber) Contains acetylcholine receptors Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins Cohen: Memmler’s The Human Body in Health and Disease The Muscular System Muscle Cells in Action • NMJ allows motor neuron to stimulate muscle fiber to become electrically excited (action potential) • Action potential stimulates muscle contraction • Events at the NMJ – Ach is released from motor neuron into synaptic cleft – Ach diffuses across synaptic cleft towards motor end plate – Ach binds to receptors on motor end plate and stimulates action potential Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins Cohen: Memmler’s The Human Body in Health and Disease Figure 8-2 Nerve supply to a skeletal muscle and the NMJ. Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins Cohen: Memmler’s The Human Body in Health and Disease Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins Cohen: Memmler’s The Human Body in Health and Disease The Muscular System Pop Quiz 8.2 A single neuron and all the muscle fibers it stimulates comprise a(n): A) Motor end plate B) Motor unit C) Neuromuscular junction D) Synapse Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins Cohen: Memmler’s The Human Body in Health and Disease The Muscular System Pop Quiz Answer 8.2 A single neuron and all the muscle fibers it stimulates comprise a(n): A) Motor end plate B) Motor unit C) Neuromuscular junction D) Synapse Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins Cohen: Memmler’s The Human Body in Health and Disease The Muscular System Muscle Cells in Action • The sarcomere is the functional unit of contraction in the skeletal muscle fiber • Sarcomere anatomy: – Thick filaments (myosin) – Thin filaments (actin) – Regulatory proteins • Troponin • Tropomyosin Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins Cohen: Memmler’s The Human Body in Health and Disease Figure 8-3 Detailed structure of a skeletal muscle cell. Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins Cohen: Memmler’s The Human Body in Health and Disease The Muscular System Muscle Cells in Action • Sarcomeres contract via the sliding filament mechanism: – Myosin heads bind to actin, forming cross-bridges – Using stored energy, myosin heads pull actin filaments together within the sarcomeres and the cell shortens – New ATP is used to detach myosin heads and move them back into position for another “power stroke” Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins Cohen: Memmler’s The Human Body in Health and Disease Figure 8-4 Sliding filament mechanism of skeletal muscle contraction. Sliding filament mechanism of skeletal muscle contraction. Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins Cohen: Memmler’s The Human Body in Health and Disease The Muscular System Muscle Cells in Action • Calcium regulates sarcomeric contraction within the muscle cell: – Action potential from NMJ travels to sarcoplasmic reticulum (SR) – SR releases calcium into cytoplasm – Calcium shifts troponin and tropomyosin off of thin filament so that binding sites on actin are exposed – Sliding filament mechanism now able to proceed – Muscle relaxes when stimulation ends and calcium is pumped back into SR Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins Cohen: Memmler’s The Human Body in Health and Disease Figure 8-5 Role of calcium in muscle contraction. Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins Cohen: Memmler’s The Human Body in Health and Disease The Muscular System Summary of Events in a Muscle Contraction 1. ACh is released from neuron ending into synaptic cleft at NMJ 2. ACh binds to motor end plate and produces action potential 3. Action potential travels to sarcoplasmic reticulum (SR) 4. SR releases calcium into cytoplasm 5. Calcium shifts troponin and tropomyosin so that binding sites on actin are exposed Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins Cohen: Memmler’s The Human Body in Health and Disease The Muscular System Summary of Events in a Muscle Contraction (continued) 6. Myosin heads bind to actin, forming cross-bridges 7. Using stored energy, myosin heads pull actin filaments together within sarcomeres and cell shortens 8. New ATP is used to detach myosin heads and move them back to position for another “power stroke” 9. Muscle relaxes when stimulation ends and calcium is pumped back into SR Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins Cohen: Memmler’s The Human Body in Health and Disease The Muscular System Pop Quiz 8.3 The two filaments that form cross-bridges are A) Actin and troponin B) Tropomyosin and myosin C) Actin and myosin D) Troponin and tropomyosin Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins Cohen: Memmler’s The Human Body in Health and Disease The Muscular System Pop Quiz Answer 8.3 The two filaments that form cross-bridges are A) Actin and troponin B) Tropomyosin and myosin C) Actin and myosin D) Troponin and tropomyosin Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins Cohen: Memmler’s The Human Body in Health and Disease Exit Ticket What is the name of the special synapse in which a nerve cell makes contact with a muscle cell? What neurotransmitter is involved in the stimulation of skeletal muscle cells? Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins
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