1. Assumption College Mathayom 4, Universal Biology Miss Anna The Muscular System Lesson 32.2

2. Key Questions What are the principle types of muscle tissue? How do muscles contract? How do muscle contractions produce movement?

3. Vocabulary Muscle fiber Myofibril Myosin Actin Sarcomere Neuromuscular junction Acetylcholine Tendon

4. What are the principal types of muscle tissue? There are three different types of muscle tissue: skeletal, smooth, and cardiac, and each has a specialized function in the body About 1/3 of the mass of an average person is made of muscle! Figure 32-6 shows each type of muscle

5. Three types of muscle tissue

6. Skeletal Muscles Usually attached to bones Usually under voluntary control Striated under a microscope (light and dark bands) Many nuclei, vary in length Movements are consciously controlled by the nervous system Because skeletal muscle cells are long and slender, they are often called muscle fibers

7. Skeletal Muscle

8. Smooth Muscles Do not have striations and look “smooth” under a microscope Spindle-shaped, single nucleus Movements usually involuntary Form the walls of hollow structures such as the stomach, blood vessels and intestines Example: smooth muscles move food throughout your digestive tract, control the way blood flows through your circulatory system, and decrease the size of your pupils in bright light

9. Smooth Muscles Continued Most smooth muscle cells can function without direct stimulation by the nervous system The cells in smooth muscle tissue are connected to one another by gap junctions that allow electrical impulses to travel directly from one muscle cell to a neighboring muscle cell

10. Smooth Muscle

11. Cardiac Muscle Cardiac muscle is found in just one place in the body – the heart Cardiac muscle is striated like skeletal muscle, although its cells are smaller and usually have just one or two nuclei Cardiac muscle is not under the control of the central nervous system, just like smooth muscle; cardiac muscle cells can contract on their own and are connected to their neighbors by gap junctions

12. Cardiac Muscle

13. Three types of muscle tissue

15. Question: What is the key difference between control of skeletal muscle contraction and smooth muscle contraction?

16. Answer: Most skeletal Muscle contractions are voluntarily controlled by the central nervous system. Smooth muscle contractions are usually involuntary.

17. Muscle Contraction Muscles produce movement by shortening (or contracting) from end to end Cells generate force to do this through the interaction of muscle protein filaments

18. Muscle fiber structure Skeletal muscles (or fibers) are filled with tightly packed filament bundles called myofibrils Each myofibril contains thick filaments of a protein called myosin and thin proteins of a protein called actin These filaments are arranged in an overlapping pattern that produces the stripes or striations visible through a microscope

19. Muscle fiber structure The thin actin filaments are bound together in areas called Z lines Two Z lines and the filaments between them make up a unit called a sarcomere Figure 32-7 on page 930 in your book shows the structure of a muscle fiber

20. Muscle fiber structure

21. The sliding-filament model Myosin and actin are tiny force-producing engines During a muscle contraction, myosin filaments form cross-bridges with actin filaments The cross bridges then change shape, pulling the actin filaments toward the center of the sarcomere As Figure 32-8 on page 931 shows, this action decreases the distance between the Z lines, and the fiber shortens; for this reason, the process is called the sliding-filament model of muscle contraction

22. The sliding filament model continued When hundreds of thousands of myosin cross-bridges repeat these actions, the muscle fiber shortens with considerable force Contractions like these enable you to run, lift weights, and turn a page in a book Since one molecule of ATP supplies just enough energy for one interaction between a myosin cross-bridge and an actin filament, a muscle cell needs plenty of ATP

23. The Sliding-Filament Model

24. Control of Muscle Contraction Skeletal muscles must contract in a controlled fashion in order for them to be voluntary Remember: motor neurons connect the central nervous system to the skeletal muscle cells Impulses from these motor neurons control the contraction of muscle fibers

25. Control of muscle contraction continued A motor neuron and a skeletal muscle cell meet at a type of synapse known as a neuromuscular junction (see Figure 32-9 on page 931) When a motor neuron is stimulated, its axon terminals release a neurotransmitter called acetylcholine (Ach) Acetylcholine molecules diffuse across the synapse, producing an impulse (action potential) in the cell membrane of the muscle fiber The impulse causes the release of calcium ions within the fiber These ions affect regulatory proteins that allow myosin cross-bridges to bind to actin

26. Control of muscle contraction continued A muscle cell contracts until the release of Ach stops and an enzyme produced at the axon terminal destroys any remaining Ach Then, the muscle pumps calcium back into storage, the cross- bridges stop forming, and the contraction ends

27. Review: action potential In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and endocrine cells In muscle cells, for example, an action potential is the first step in the chain of events leading to contraction.

28. How do muscle contractions produce movement? Muscles produce force by contracting in ONE direction Skeletal muscles are joined to bones by tough connective tissues called tendons Tendons are attached in such a way that they PULL on bones Skeletal muscles generate force and produce movement by pulling on body parts as they contract

29. How muscles and bones interact? We can use our muscles to push as well as pull; most skeletal muscles work in opposing pairs When one muscle in the pair contracts, the other muscle in the pair relaxes Figure 32-10 on page 932 shows an example of this dual action with biceps and triceps When the biceps muscle contracts, it opens (or extends) the elbow joint. When the triceps muscle contracts, it opens (or extends) the elbow joint. A controlled movement requires the involvement of both muscles

30. Opposing muscle pairs

31. Types of Muscle Fibers There are 2 principal types of skeletal muscle fibers: red and white Red muscle (or slow-twitch muscle) contains many mitochondria and a generous supply of oxygen; useful for endurance activities like long-distance running White muscle (or fast-twitch muscle) contracts more rapidly and has fewer mitochondria; useful for activities that require great strength or quick bursts of speed, like sprinting

32. Types of muscle fibers

34. Exercise and health Regular exercise helps to maintain strength and flexibility Aerobic exercise (such as running and swimming) help to make our hearts and lungs more efficient Exercise also helps to strengthen our bones Resistance exercises (such as weight lifting) increase muscle size and strength

35. End of Lesson 32.2 Homework: Please complete questions #1-3 on page 933 in your notebooks, and pick FIVE vocabulary words to define