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Seminar Workbook Muscle Session Objectives. What you will cover • Characteristics and basic functions of skeletal muscle • Structure of muscle fibres • Types of contraction • Motor units • Muscle fibre types Your objectives are • Differentiate skeletal muscle, cardiac muscle and smooth muscle based on their basic properties • State the basic functions of skeletal muscle • State the basic properties of muscle tissue • Explain why muscle is an organ • Label typical skeletal muscle fibres • Identify the functions of the organelles found in skeletal muscle fibres • Explain the relationship of actin and myosin fibres to the structure of sarcomeres • Describe isotonic, isometric and isokinetic muscle contractions and give examples of each. • Describe sliding filament theory in terms of actin and myosin fibres • Describe the molecular events of the contraction cycle of skeletal muscle • Relate sarcomere lengths to the tension generated by the muscle • Describe events at the neuromuscular junction • Describe the structure and function of motor units • Explain the function of recruitment • Describe a simple muscle twitch. • Describe and differentiate wave summation, incomplete tetanus, complete tetanus and treppe. • Describe a simple reflex arc • Identify the fibres and neurons associated with muscle spindles • State the function of muscle spindle reflexes with reference to muscle tone • Identify the muscle fibre types from descriptions of their properties. Suggested reading: Tortora, Ch 10; Ch 15 Marieb Ch 9, Ch 13 14 Generic_Muscle04.doc Dr Marjorie L Wilson, University of Teesside, 2004 Seminar Workbook Muscle Muscles are the specialised tissues that facilitate body movement. Most muscle in the body is skeletal, being attached to the bony skeleton. Other muscle types are cardiac and smooth. Task Characteristics of Muscle. Identify the muscle tissue type described by choosing the correct responses. Complete the table using the responses. Some may be used more than once. Striated appearance Arranged in longitudinal and circular layers Coordinated activity to act as pump The muscular system SKELETAL MUSCLE Dense connective tissue packing Involuntary Move bones and facial skin Voluntary CARDIAC MUSCLE SMOOTH MUSCLE Task Four properties of muscle tissue. Identify the property of muscle tissue from the definition that has been given. Definition Property The ability to return to it’s original length The ability to stretch without being damaged The ability to contract forcefully The ability to respond to signals [chemical or electrical] 15 Generic_Muscle04.doc Dr Marjorie L Wilson, University of Teesside, 2004 Seminar Workbook Looking more closely at muscles – Muscle Fibres. Skeletal muscles are made of many muscle cells or fibres. Muscle fibres are just very highly modified and specialised cells. They have some organelles which look the same as a typical cell, such as mitochondria. They also have specialised organelles. Task. Label the diagram of a typical skeletal muscle fibre. Use the words given to complete the diagram. One has been done for you. Sarcoplasmic reticulum Myofibril Sarcoplasm Mitochondria Sarcolemma Triad T-tubules Sarcoplasm Task. Write in the functions of the organelles found in skeletal muscle. ORGANELLE FUNCTION IN SKELETAL MUSCLE Sarcolemma T-tubule Sarcoplasmic Reticulum Myofibril 16 Generic_Muscle04.doc Dr Marjorie L Wilson, University of Teesside, 2004 Seminar Workbook Thick and Thin Filaments of the Sarcomere These are the parts that pull on one another to generate tension in a muscle fibre. Here are images of the thick and thin filaments. Task What proteins are the thick and thins filaments made of respectively? What is the function of the troponin complex? What happens to the troponin-tropomyosin complex when calcium ions bind onto it? Where do the calcium ions get released from in the muscle fibre? Why therefore do we need calcium ions for muscle contraction? 17 Generic_Muscle04.doc Dr Marjorie L Wilson, University of Teesside, 2004 Seminar Workbook Sarcomeres and Sliding Filament Theory Sliding filament theory attempts to explain what happens to a sarcomere during a contraction. The diagram shows what happens to a sarcomere when a muscle carries out a concentric contraction. It may help you to label the top diagram with the bands I and A. Use the diagram on the previous page to help you. Task. State what happens to the sizes of the A band, the I band, the Z discs and H zones when a muscle contracts. It may help to look at some animations of sliding filament theory on the Internet. There are web-links given at the end of the chapter, and links on the intranet site. A band I band Z disc H zone 18 Generic_Muscle04.doc Dr Marjorie L Wilson, University of Teesside, 2004 Seminar Workbook Sarcomeres and Muscle Length –Tension Relationships. During normal movement, our skeletal muscles are active over a broad range of intermediate lengths. When two tug-o-war teams pull on a rope, the tension generated in the rope is proportional to the number of people pulling on the rope. Task What do you think generates the tension in a muscle fibre? The length of the sarcomere in a muscle fibre determines the amount of pulling power that each fibre can generate. Task. Use the diagram of length tension relationships shown above at points (a), (c) and (e) to complete the table. POINT PERCENTAGE TENSION GENERATED LENGTH OF SARCOMERE [µm] EXPLANATION FOR TENSION GENERATED (a) (c ) (e) Task What happens to the ability to generate tension in a muscle fibre when it is over-stretched? 19 Generic_Muscle04.doc Dr Marjorie L Wilson, University of Teesside, 2004 Seminar Workbook Muscle Motor Units A typical skeletal muscle is made up of thousands of muscle fibres. Each of these muscle fibres receives an input from the central nervous system [brain & spinal cord] via a motor neuron [bundle of nerves]. Activity in the motor neuron causes the fibre to contract. Task Multiple motor unit summation, or recruitment is used by muscle to perform specific movements, such as when you flex your arm. Explain what happens during recruitment. During what sort of activity might you expect to see maximal motor recruitment in the triceps muscle group? Task Write in the spaces under the diagrams what type of stimulation is being observed. 20 Generic_Muscle04.doc Dr Marjorie L Wilson, University of Teesside, 2004 Seminar Workbook Muscle Fibres and Stretch Reflexes. We all probably know about and have experienced the patellar tendon stretch reflex [the knee jerk reflex]. Stretch reflexes allow us to regulate the length of muscle fibres. There is communication to and from the central nervous system at the level of our spinal cord through specialised neurons. Task Why is it important for us to be able to regulate the length of our skeletal muscles? Monosynaptic reflexes Task Look at the diagram above about and then answer the questions below about monosynaptic reflexes. How many neurons are there in a reflex arc? What type of neuron is shown at step 2? What does activity in a motor neuron cause in the skeletal muscle it is attached to? 21 Generic_Muscle04.doc Dr Marjorie L Wilson, University of Teesside, 2004 Seminar Workbook When a skeletal muscle is stretched, the fibres elongate and muscle tone increases. Muscles have to maintain and readjust the resting tone in the fibres so that the fibres are not overstretched or torn. These constant fine adjustments are regulated by muscle spindles. There are specialised muscle fibre cells that sense/monitor and detect changes in muscle tone. They allow the rest of the muscle fibres around them to contract or relax in response to the changes and prevent overstretching or contractures. Task. Label the diagram of a muscle spindle with the selected words provided. Gamma efferent neuron Type Ia sensory neuron Extrafusal fibre Intrafusal fibre 22 Generic_Muscle04.doc Alpha motor neuron Dr Marjorie L Wilson, University of Teesside, 2004 Seminar Workbook Task What are meant by the terms afferent and efferent when speaking about the nervous system? What is the function of the intrafusal muscle fibres? Where are the Type Ia sensory fibres located in a muscle spindle? What is the function of the Type Ia sensory fibres? What type of muscle fibre is innervated by the gamma motor efferent neurons? Web pages (accessed July 2003) http://physioweb.med.uvm.edu/muscle_physio/ - This is an excellent link. Choose the ‘muscle contractions’ option to go to the link for animation of muscle contraction. http://physioweb.med.uvm.edu/muscle_physio/muscle_contraction/mscl_cntrct_fil aments.htm http://srs.dl.ac.uk/OTHER/OW/MUSCLE/ - has some interesting animations of sliding filament theory. http://3dotstudio.com/zz.html - good animation of what happens to the I and A bands http://w3.uokhsc.edu/human_physiology/presentation/muscle1ani.gif This link is a good demonstration of how the myosin heads ‘walk’ along the actin filaments. A must see! http://www.accessexcellence.com/AB/GG/myosin_Actin.html - A clear description of the cycle of attachment of actin and myosin. 23 Generic_Muscle04.doc Dr Marjorie L Wilson, University of Teesside, 2004
