Muscular System

1. Muscular System

2. 5 Muscular System Functions • Skeletal muscle pulls on the bones of the skeleton, creating movement. • Even when not moving, skeletal muscle is partially contracted, maintaining tone and posture.

3. A wall of skeletal muscle provides protection for the organs of the abdominal cavity.

4. Circular muscles called sphincters control openings in the digestive and urinary systems. • Muscle contractions generate heat, helping to maintain body temperature.

5. Muscle Types • A muscle is an organ that can contract in a coordinated fashion and includes muscle tissue, blood vessels, nerves, and connective tissue. • Their ability to contract and relax not only enables the body to move, but also provides the force that pushes substances, such as blood and food, through the body. • The human body has three types of muscle tissues: skeletal, smooth, and cardiac.

6. Skeletal Muscles • Skeletal muscles consciously control the moving parts of the body and are often referred to as voluntary muscles. • Skeletal muscles are made up of muscle fibers. • Muscle fibers consist of multinucleated elongated cells with light and dark stripes. These stripes are called striations.

7. Smooth Muscle • Smooth muscles are spindle-shaped, have a single nucleus, and interlace to form sheets. • Smooth muscle lacks striations, and the connective tissue that surrounds it cannot form tendons. • Smooth muscle forms the walls of the stomach, intestines, blood vessels, and other internal organs. Because most of its movements cannot be consciously controlled, smooth muscle is referred to as involuntary muscle.

8. Cardiac Muscle • Cardiac muscle makes up the walls of the heart. • Cardiac muscle shares some characteristics with both skeletal muscle and smooth muscle. • As with skeletal muscle, cardiac muscle tissue is striated; as with smooth muscle, it is involuntary and each cell has one nucleus.

9. Three Types of Muscle Tissue

10. Anatomy of a Muscle • Each muscle is covered with epimysium, a layer of collagen fibers that separates it from surrounding organs.

11. The muscle is made of bundles called fascicles. • Each fascicle is divided by another layer called the perimysium. • Nerves and blood vessels are also found here.

12. Individual muscle cells within a fascicle are called muscle fibers. • The endomysium surrounds and each individual muscle fiber.

13. At each end of the muscle, the collagen fibers from all three layers come together to form one of two possible structures: • A bundle of collagen fibers called a tendon, which attaches the muscle to a bone. • A sheet of collagen fibers called a aponeurosis, which attaches the muscle to another muscle.

14. A ruptured tendon will detach a muscle completely from one of its bones, rendering it unusable.

15. Epimysium Perimysium Endomysium Tendon Fiber Muscle Fascicle

16. Muscle fibers are some of the longest cells in the body. • Longest is in the sartorius muscle – 60cm! • Each fiber is multinucleate, meaning there are multiple nuclei in each cell, and amitotic, meaning they cannot divide.

17. The sarcomere is the basic unit of muscle contraction • The sarcolemma, the cell membrane of the muscle fiber, is covered with openings to a network of small tubules called T tubules. • The sarcoplasmic reticulum is a special type of smooth ER that stores calcium ions that signal muscle contraction.

18. Each muscle fiber contains myofibrils, long filaments that have the ability to contract. • Thin, light filaments, made of the protein actin. • Thick, dark filaments, made of the protein myosin.

19. T-Tubules Sarcoplasmic Reticulum Sarcolemma Mitochondria Myosin Actin

20. Muscle Contraction Muscle contractions occur in the following sequence of events: • A signal is passed through motor neuronto a muscle. • This signal is sent to every fiber in the muscle simultaneously through the t-tubules. • The sarcoplasmic reticulum releases calcium ions (Ca2+), initiating muscle contraction.

21. The calcium influx stimulates the myosin filaments to form connections to the actin filaments. • The myosin filaments pull the actin filaments inward, causing the muscle to contract.

22. Muscular Contraction • When a nerve impulse stimulates a muscle to contract, the myosin filaments’ heads attach to points on the actin filaments. • The myosin heads then bend inward, pulling the actin with them. • The myosin heads then let the actin go, bend back into their original position, attach to a new point on the actin filament, and pull again.

23. Muscular Contraction, continued • The action just described shortens the sarcomere, and when all the sarcomeres of a muscle fiber are shortened, the muscle fibers (and thus the muscle) contract. • Muscle contraction requires energy, which is supplied by ATP. • Because myosin heads must attach and detach a number of times during a single muscle contraction, muscle cells must have a continuous supply of ATP energy.

24. Contraction of a Muscle

25. The amount and force of muscle tension depends on: • Frequency of simulation (form the central nervous system). • Number of skeletal muscle fibers involved. • The size of the muscle fibers – larger fibers contain more myofibrils.

26. Muscular Movement of Bones • Muscles are attached to the outer membrane of bone, the periosteum, either directly or by a tough fibrous cord of connective tissue called a tendon. • The point where the muscle attaches to the stationary bone is called the origin. • The point where the muscle attaches to the moving bone is called the insertion.

27. Muscular Movement of Bones, continued • Most skeletal muscles are arranged in opposing pairs, and muscles move bones by pulling them. • The muscle that bends a joint is known as a flexor. • A muscle that straightens a joint is known as an extensor. • In order for smooth movement, one muscle in a pair must contract while the opposing muscle relaxes.

28. Opposing Muscles in the Arm

29. Muscle fatigue has two possible causes: • Running out of ATP . • Limits available glucose to muscle cells. • “Hitting the wall.” • Insufficient oxygen levels. • Forces muscle fibers to rely more onanaerobic respiration • “Out of breath.”

30. Types of Muscle Fibers • Fast-twitch fibers are able to reach peak tension within 0.01 seconds or less of neural stimulation. • Large in diameter. • Densely packed with myofibrils (actin and myosin). • Large glycogen reserves. • Fewer mitochondria. • Fast-twitch fibers produce the most tension, but get fatigued quickly.

31. Slow-twitch fibers can take three times as long to reach peak tension. • Half the diameter of fast-twitch fibers. • Increased network of capillaries, allowing for a greater and more reliable oxygen supply. • Contain a special protein called myoglobin that reserves additional oxygen within the muscle. • Higher numbers of mitochondria. • Produce less power, but much more endurance.

32. Anabolic Steroids • Anabolic steroids are chemical compounds that mimic the effects of testosterone. • This increases protein synthesis in muscle fibers. • As a hormone, testosterone affects many other tissues besides muscles, causing side effects: • Increase in blood cholesterol. • Acne • High blood pressure • Testicular atrophy • Increase in male characteristics in women.

33. Muscular System Disorders • Polio is a viral infection that can infects and destroys motor neurons, causing paralysis. • Considered eradicated due to a vaccine.

34. ALS (Lou Gehrig’s Disease) • Amyotrophic Lateral Sclerosis (ALS), also known as Lou Gehrig’s Disease, is a genetic neurodegenerative disease that damages motor neurons of the peripheral nervous system. • Causes muscle atrophy due to disuse.

35. Muscular Dystrophy • Muscular dystrophy is a group of genetic degenerative disorders that directly affects muscle tissue, causing it to atrophy.

36. Muscle Anatomy

37. How Are Muscles Named? • Some muscles are named based on the direction of their fibers. • Rectus means straight. • Rectus abdominis. • Oblique means diagonally arranged. • External abdominal oblique.

38. Muscles within a group may have different names based on their size. • Maximus indicates a larger muscle. • Minimus indicate a smaller muscle.

39. Muscles may also be named based on their relative location to other muscles. • Medial means towards the midline of the body. • Lateral means towards the sides of the body.

40. Prefixes like bi- and tri- may be used to indicate multiple heads or attachment sites. • Bi – Two attachment sites. • Tri – Three attachment sites.

41. Muscles may also be named based on their origin and insertion bones. • The origin is an attachment to a immoveable bone. • The insertion is an attachment to an movable bone.

42. If a muscle resembles a shape, it can be named after that shape. • Delta is a Greek letter shaped like a triangle. • Trapezius is shaped like a trapezoid. • Serratus means saw-toothed.

43. Finally, muscle names may indicate a specific action they perform. • Flex means to bend a joint. • Extend means to straighten a joint.

44. Zygomatic Bone Face & Neck Temporalis Frontalis • The frontalis raises the eyebrows. • The masseter and temporalisboth elevate the mandible. • Chewing muscles • The buccinator flattens the cheeks during chewing, holding them against the teeth. • The orbicularisoculiperforms all eyelid movements, including opening, closing, blinking, etc. • The orbicularisoris closes the mouth with the lips. • The zygomaticus raises the corners of the mouth when smiling. • The sternocleidomastoid rotates the head and flexes the neck. Orbicularis Oculi Zygomaticus Trapezius Orbicularis Oris Sternoleidomastoid Buccinator Masseter

45. Muscles Of Trunk Sternocleidomastoid Trapezius • The pectoralis majormoves the humerus. • The rectus abdominis flexes the vertebral column and compresses the contents of the abdomen. • The “pushing” muscle of defecation, childbirth, and forced breathing. • Thetransversusabdominis also performs this action. • The external and internal obliques rotate the trunk. Clavicle Sternum Pectoralis Major Deltoid Serratus Anterior Latissimus Dorsi Internal Abdominal Oblique External Abdominal Oblique Rectus Abdominis

46. Muscles Of dorsal Trunk Sternocleidomastoid Trapezius Deltoid • The trapezius elevates and depresses the scapula. • The latissimusdorsimoves the humerus. • The deltoidmoves the arm. Latissimus Dorsi External Oblique

47. Arm • The biceps brachii and brachioradialisflex the arm. • The triceps brachii extends the arm. • The extensor carpiradialis and ulnaris extend the wrist. • The extensor digitorum extends the four non-thumb digits. Deltoid Triceps Brachii Biceps Brachii Brachioradialis Extensor Digitorum Extensor Carpi Radialis Extensor Carpi Ulnaris

48. Gluteus medius Gluteus maximus Posterior Muscles of the Leg Biceps femoris Gastrocnemius Soleus

49. Gluteus medius Sartorius Anterior Muscles of the Leg Rectus Femoris Fibularis Tibialis Anterior Soleus

50. Muscles of the Hip, Thigh, and Leg • The gluteus maximus moves and extends the leg. • The gluteus medius moves the leg. • The hamstring group flexes the knee. • Biceps femoris • The gastrocnemius and soleus extend the foot. • The sartorius flexes, abducts, and laterally rotates the thigh. • The quadriceps group extends the knee. • Rectus femoris • The tibialis anterior and fibularis muscles flex the foot.