Anatomy Exam II Chapter 9: Muscles

Learning Objectives of Anatomy Exam II- (Tuesday, Oct. 25th) These are the learning objectives for Anatomy Exam II. Each objective will require you to go back to your chapter PowerPoints, with respective chapter section readings, class notes and any additional resources for elaboration, context, and details. For best study results, study with the goal of relating information to previous knowledge and seek true understanding, rather than “rote memorizing”. Muscles I (Chapters 9 and 10) Chapter 9 SUGGESTIONS ON HOW TO STUDY MUSCLE - LEARN THE PARTS OF THE MUSCLE, LEARN THE LOCATION OF OTHER RELATED MUSCLE AREAS AND THE LEARN THE FUNCTIONS. WATCH VIDEOS, USE YOUR BODY AS A CHEAT MODEL. ~Karina What are the functions (give all) of muscle? Skeletal muscles are contractile organs directly or indirectly attached to bones of the skeleton. Skeletal muscles have the following functions: 1) Produce skeletal movement: Muscle contractions pull on tendons and move the bones of the skeleton. The effects range from simple motions, such as extending the arm, to the highly coordinated movements of swimming, skiing, or texting. 2) Maintain posture and body position: Skeletal muscle contraction maintains body posture. Without constant muscular contraction, we could not sit upright without collapsing or stand without falling over. 3) Support soft tissues: The abdominal wall and the floor of the pelvic cavity contain layers of skeletal muscle. These muscles support the visceral organs and protect internal tissues from injury. 4) Regulate the entry and exit of material: Skeletal muscles encircle the openings, or orifices, of the digestive and urinary tracts. These muscles provide voluntary control over swallowing, defecation, and urination. 5) Maintain body temperature: Muscle contractions require energy, and some of that energy is converted to heat. This heat released by contracting muscles helps maintain the body’s normal temperature. 1. What is a muscle fiber? Muscle fibers are Muscle Cell , especially one of the cylindrical, multi-nucleate cells that make up skeletal muscles and are composed of numerous myofibrils that contract when stimulated. -can be 30-40cm in length -multinucleate (each muscle cells has hundreds of nuclei) -nuclei are located just deep to the sarcolemma 2. What are the three types of muscle fibers? How are they different? Why? Be familiar with locations in the body of each type. Page 248 & see slides

Slow oxidative / Slow Fibers (Red Fibers) - associated with leg muscles (slow contractions) -Smaller diameter than fast fibers (half the size) -Darker color d/t myoglobin (creates the red color) -Take three times longer to contract after stimulation -Specialized to continue contracting for extended periods of time, long after a fast muscle fatigues -fatigue resistant / slowly d/t their mitochondria continue producing ATB throughout the contraction process -Mitochondria absorb O2 & generate ATP by AEROBIC METABOLISM -Contain larger# of mitochondria than fast muscles Ex: leg muscles of marathon runners are dominated by slow muscle fibers Oxygen required comes from 2 sources: 1. Have larger network of capillaries than muscles dominated by fast muscle fibers MEANING: greater blood flow to the muscle & RBCs can deliver more O2 to the active muscle fibers 2. Myoglobin. This globular protein like Hgb binds O2 molecules resulting to slow muscle fibers contain large O2 reserves that are mobilized during a contraction Intermediate glycolytic / Intermediate Fibers (pink fibers) - fast and slow fibers Ex: intermediate fibers contract faster than slow fibers but slower than fast fibers. Similar to fast fibers: -have low myoglobin content -have high glycolytic enzyme concentration -contract using anaerobic metabolism Similar to slow fibers: -have lots of mitochondria -have greater capillary supply -resist fatigue Fast Glycolytic / Fast Fibers (white fibers) - associated w/ eye muscles (fast contractions) - large diameter -densely packed myofibril -large glycogen reserves -fatigue easily -Can contract in 0.01 second or less after stimulation -Relatively few mitochondria -fast-fiber muscles produce powerful contractions (sprinters) -Contractions use large amounts of ATP but mitochondria unable to meet demand -Muscle Contractions instead are supported primarily by Anaerobic Metabolism (GLYCOLYSIS) -Glycolysis - Does not require O2 & converts stored glycogen to lactic acid -Fast fibers fatigue rapidly d/t glycogen reserves are limited & lactic acid builds up resulting acidic pH interferes with the contraction mechanism

3. How are muscle fibers unique? Why do you think this is so? 4. What do the prefixes “myo” and “sarco” mean and when do we use them? Myo - refers to muscle - frequently used in medical terms in the anatomy Sarco - means flesh (muscle) - often used in biology 5. Know what it means when we say a muscle is “excitable” Muscle cells are excitable - the ability to respond to stimulation.

Its function is to produce force and cause motion, either locomotion or movement within internal organs. A characteristic feature of an excitable tissue is the presence of resting membrane potential. Ex: skeletal muscles respond to stimulation by the nervous system, and some smooth muscles respond to circulating hormones. 6. A muscle cell and a nerve cell differ greatly. How are they alike? How do they differ? The main difference between muscle cells and nerve cells is that muscle cells are responsible for the contraction and relaxation of muscles whereas nerve cells are responsible for the coordination of the functions of the body through the transmission of nerve impulses between the body and the central nervous system. How are they alike? Muscle cells and nerve cells are two types of specialized cells in the animal body. Both muscle cells and nerve cells form tissues. Both muscle cells and nerve cells contain mitochondria and endoplasmic reticulum. Both muscle cells and nerve cells work together to coordinate the functions of the body. Nerve cells and muscle cells are excitable. Their cell membrane can produce electrochemical impulses and conduct them along the membrane. In muscle cells, this electric phenomenon is also associated with the contraction of the cell.

7. What is the structure of skeletal muscle? Be sure you know the connective tissue membranes that surround each muscle fiber, fascicle, and muscle. a) The epimysium (ep-i-MIS-ē-um; epi– , on, + mys , muscle) is a layer of dense irregular connective tissue surrounding the entire skeletal muscle. i. The epimysium separates the muscle from surrounding tissues and organs and is connected to the deep fascia. b) The connective tissue fibers of the perimysium (per-i-MIS-ē-um; peri– , around) divide the muscle into internal compartments. i. Each compartment contains a bundle of muscle fibers called a fascicle (FAS-i-kul; fasciculus , bundle). ii. The perimysium contains collagen and elastic fibers, and numerous blood vessels and nerves supply each fascicle. c) The endomysium (en-dō-MIS-ē-um; endo– , inside, + mys , muscle) surrounds each skeletal muscle fiber (individual skeletal muscle cell), binds each muscle fiber to its neighbor, and supports the capillaries that supply the individual fiber. i. The endomysium consists of a delicate network of reticular fibers. ii. Scattered myosatellite cells that lie between the endomysium and the muscle fibers are stem cells that repair damaged muscle tissue.

A skeletal muscle consists of bundles of muscle fibers (fascicles) enclosed within a connective tissue sheath, the epimysium. Each fascicle is then ensheathed by the perimysium, and within each fascicle the individual muscle fibers are surrounded by the endomysium. Each muscle fiber has many nuclei as well as mitochondria and other organelles. TEST YOURSELF::::

8. How are muscles named? Be able to give examples. The name of a skeletal muscle provides important clues about that specific muscle. Learn the names of muscles and what they mean rather than simply memorizing them. Skeletal muscles are named according to several criteria introduced in Table 9.2. 1) Orientation of the muscle fibers (direction of fascicles) a) For example, rectus means “straight,” and rectus muscles are parallel muscles whose fibers run along the longitudinal axis of the body. Because there are several rectus muscles, the name includes a second term that refers to a precise region of the body. The rectus abdominis is on the abdomen, and the rectus femoris is on the thigh. Other directional indicators include transversus (fibers run at right angles), and oblique (fibers run at angles) for muscles whose fibers run across or at an oblique angle to the longitudinal axis of the body. 2) Number of Origins: a) A biceps muscle has two tendons of origin ( bi –, two, + caput , head), the triceps has three, and the quadriceps four. 3) Muscle Shape: a) Shape is often an important clue in the muscle’s name; trapezius (tra-PĒ-zē-us), deltoid , rhomboideus (rom-BOYD-ē-us), and orbicularis (or-bik-ū-LA-ris) refer to prominent muscles that look like a trapezoid, triangle, rhomboid, and circle, respectively. 4) Muscle Size: a) Long muscles are called longus (long) or longissimus (longest), and teres muscles are both round and long. Short muscles are called brevis ; large ones magnus (big), major (bigger), or maximus (biggest/largest); and small ones are called minor (smaller) or minimus (smallest). 5) Muscles location: bone or body region with which the muscle is associated. Example: temporalis (over temporal bone). a) Muscle visible at the body surface are external and often called externus or superficialis (superficial), whereas those lying beneath are internal, termed internus or profundus . Superficial muscles that position or stabilize an organ are called extrinsic muscles; those that operate within the organ are called intrinsic muscles. 6) Location of attachments a) Muscle names identify their origins and insertions: the first part of the name indicates the origin and the second part the insertion. For example, the genioglossus originates at the chin ( geneion ) and inserts in the tongue ( glossa ). b) Example: sternocleidomastoid attaches to sternum and clavicle, with insertion on the mastoid process. 7) Muscle Action names: a) flexor , extensor , and adductor , indicate the primary function of the muscle. These are such common actions that the names also include other clues about the appearance or location of the muscle. For example, the extensor carpi radialis longus is a long muscle found along the radial (lateral) border of the forearm. When it contracts, its primary function is extension at the wrist. 8) Muscle movements: a) A few muscles are named after the specific movements associated with special occupations or habits.

b) For example, the sartorius (sar-TŌR-ē-us) is active when crossing the legs. Before sewing machines were invented, a tailor would sit on the floor cross-legged; the name of the muscle was derived from sartor , the Latin word for “tailor.” On the face, the buccinator (BUK-si-nā-tor) compresses the cheeks, as when you purse your lips and blow forcefully. Buccinator translates as “trumpet player.” Finally, another facial muscle, the risorius (ri-SOR-ē-us), was supposedly named after the mood expressed. However, the Latin term risor means “laughter,” while a more appropriate description for the effect would be “grimace.” 9. What are the muscle types based on the orientation of fibers?

10. What are the functional groups of muscle by action? Levels of Functional Organization in a Skeletal Muscle Fiber

11. Describe the microstructure of muscle. a) Sarcolemma (sar-kō-LEM-a; sarkos , flesh, + lemma , husk) - the plasma membrane in the skeletal muscle cell

i. Within the sarcolemma is the cytoplasm, which in a muscle cell is called the sarcoplasm. b) Skeletal muscle fibers are large compared with the cells of other tissues. A fiber in a leg muscle could have a diameter of 100 μ m and a length equal to that of the entire muscle (30–40 cm, or 12–16 in.). c) Skeletal muscle fibers are multinucleate (containing more than one nucleus). d) During development, groups of embryonic cells called myoblasts fuse to form individual skeletal muscle fibers. e) Each skeletal muscle fiber contains hundreds of nuclei deep to the sarcolemma. f) This characteristic distinguishes skeletal muscle fibers from cardiac and smooth muscle fibers. g) Some myoblasts do not fuse with developing muscle fibers, but remain in adult skeletal muscle tissue as stem cells called myosatellite cells . h) When a skeletal muscle is injured, these stem cells differentiate and assist in repairing and regenerating the muscle.

12. What is a sarcomere? Be able to describe it. a) Sarcomeres - Myofibrils are organized in repeating units. i. Sarcomeres are the smallest functional units of muscle fibers. ii. Differences in the size, density, and distribution of the thin and thick filaments give the sarcomere a banded appearance Sarcomere Structure: a) The dark bands are called A bands and the light bands are called I bands. b) These names are derived from the terms anisotropic (A band) and isotropic (I band), which refer to their appearance when viewed using polarized light microscopy. c) The thick filaments are at the center of each sarcomere, in the A band. d) The A band contains the M line, H band, and zone of overlap.

e) The M line is the center of the A band; the M stands for middle . Proteins of the M line connect the central portion of each filament to the neighboring thick filaments. M lines stabilize the positions of the thick filaments. f) The H band is the lighter region on each side of the M line. The H band contains thick filaments, but no thin filaments. g) The zone of overlap is the dark region where thin filaments are found between the thick filaments. Here, three thick filaments surround each thin filament, and six thin filaments surround each thick filament. Two tubules encircle each sarcomere, and the triads containing them are found in the zones of overlap. As a result, calcium ions released by the SR enter the area where thin and thick filaments interact. h) The I band is the region of the sarcomere that contains thin filaments but no thick filaments. The I band extends from the A band of one sarcomere to the A band of the next sarcomere. Z lines, or Z discs , bisect the I bands and mark the boundary between adjacent sarcomeres. Z lines are made up of proteins called actinin, which interconnect thin filaments of adjacent sarcomeres. Strands of the elastic protein titin extend from the tips of the thick filaments to the attachment sites at the Z line.

13. What are thick filaments? What are thin filaments? a) Each thin filament is a twisted strand 5–6 nm in diameter and 1 μ m long. i. A single thin filament contains four proteins: F-actin, nebulin, tropomyosin, and troponin. ii. Filamentous actin, or F-actin, is a twisted strand composed of two rows of 300–400 globular molecules of G-actin. iii. G-actin is the globular (G) subunit of the actin molecule. iv. A slender strand of the protein nebulin extends along the F-actin strand in the cleft between the rows of G-actin molecules. v. Nebulin holds the F-actin strand together. vi. Each molecule of G-actin contains an active site where myosin in the thick filaments can bind.

vii. A thin filament also contains the regulatory proteins tropomyosin and troponin ( trope , turning). viii. Tropomyosin molecules form a long chain that covers the active sites on G-actin, preventing actin-myosin interaction. ix. Troponin holds the tropomyosin strand in place. x. Before a contraction can begin, the troponin molecules must change position, moving the tropomyosin molecules and exposing the active sites. b) Each thick filament is 10–12 nm in diameter and 1.6 μ m long and is composed of a bundle of myosin molecules, each made up of a pair of myosin subunits twisted around one another. c) The long tail is bound to the other myosin molecules in the thick filament. d) The free head, with two globular protein subunits, projects outward toward the nearest thin filament. e) When the myosin heads interact with thin filaments during a contraction they are known as cross-bridges. f) Thick filaments have a core of titin. g) On both sides of the M line, a strand of titin extends the length of the filament and attaches at the Z line. h) In the resting sarcomere, the titin strands are completely relaxed; they become tense only when some external force stretches the sarcomere. i) When the sarcomere stretches, the titin strands maintain the normal alignment of the thick and thin filaments. j) When the tension is removed, the titin fibers help return the sarcomere to its normal resting length. 14. What is a motor unit? a) Motor Unit - is a single motor neuron and all of the muscle fibers it controls. i. Some motor neurons control a single muscle fiber, but most control hundreds.

ii. The smaller the size of a motor unit, the finer the control of movement will be. In the eye, where precise muscular control is critical, a motor neuron may control only two or three muscle fibers. iii. We have less precise control over power-generating muscles, such as our leg muscles, where a single motor neuron may control up to 2000 muscle fibers. 15. What is the motor end plate? A) The motor endplate is a modified area of the muscle fibre membrane at which a synapse occurs. A motor nerve axon ending may have up to 50 synaptic knobs (boutons) but a single muscle fibre has only one endplate. The neurotransmitter is acetylcholine. B) The motor end plate is the basic component of a nerve-muscle junction, which functions as a synapse with chemical transmission; a stimulus is transmitted from nerve to muscle by means of a mediator, and it contracts. C) The area made up of an axon terminal of a neuron, a specialized region of the plasma membrane called the motor end plate, a narrow space in between called the synaptic cleft, and the membrane of the muscle fiber. Each muscle fiber has one neuromuscular junction, usually located midway along its length. At the NMJ, the axon terminal of the neuron attaches to the motor end plate of the skeletal muscle fiber. The motor end plate is a specialized area where the axon of a motor neuron establishes synaptic contact with a skeletal muscle fiber. 16. Where are calcium ions stored in muscle cells? What role do calcium ions play in muscle contraction? The Events in Muscle Contraction 1) At the neuromuscular junction ACh released by the axon terminal binds to receptors on the sarcolemma. 2) The resulting change in the membrane potential of the muscle fiber leads to the production of an action potential that spreads across its entire surface and along the T tubules.

3) The sarcoplasmic reticulum (SR) releases stored calcium ions, increasing the calcium concentration in the sarcoplasm and around the sarcomeres. 4) Calcium ions bind to troponin, producing a change in the orientation of the troponin-tropomyosin complex that exposes active sites on the thin (actin) filaments. Myosin cross-bridges form when myosin heads bind to active sites. 5) Repeated cycles of cross-bridge binding, pivoting, and detachment occur, powered by the hydrolysis of ATP. These events produce filament sliding, and the muscle fiber shortens. This process continues for a brief period, until: 6) Action potential generation stops as ACh diffuses out of the synapse or is broken down by AChE. 7) The sarcoplasmic reticulum (SR) reabsorbs calcium ions, and the concentration of calcium ions in the sarcoplasm decreases. 8) When calcium ion concentrations near normal resting levels, the troponin- tropomyosin complex returns to its normal position. This change covers the active sites and prevents further cross-bridge interaction. 9) Without cross-bridge interactions, further sliding does not take place, and the contraction ends. 10) Muscle relaxation occurs, and the muscle fiber returns passively to resting length. · 17. What is the sliding-filament theory with respect to muscle contraction? How can we observe this by looking at a slide of the sarcomere? The sliding filament theory explains the physical changes occurring between thick and thin filaments during contraction.

18. What is a cross bridge? What is the role of ATP? Acetylcholine? What are the T-tubules associated with the SR? Function? (SEE QUESTION #16) WATCH VIDEO ON ANATOMY MY LAB VERY HELPFUL. Cross-Bridges - is when the myosin heads interact with thin filaments during a contraction - The cross bridge cycle is responsible for the contraction of muscles. The sarcomere is what actually contracts. -An action potential is a sudden change in the membrane potential that travels the length of an axon. The stimulus for ACh release is the arrival of an action potential. When an action potential arrives at the axon terminal, ACh is released into the synaptic cleft. The ACh

diffuses across the synaptic cleft and binds to receptor sites on the motor end plate, generating an action potential in the sarcolemma and into each T tubule. Action potentials continue to be generated, one after another, until ACh is removed from the synaptic cleft. This removal occurs in two ways: ACh diffuses away from the synapse or is broken down by AChE. 19. What happens at the neuromuscular junction that induces muscle contraction? At the neuromuscular junction, the nerve fiber is able to transmit a signal to the muscle fiber by releasing ACh (and other substances), causing muscle contraction. Muscles will contract or relax when they receive signals from the nervous system. The neuromuscular junction is the site of the signal exchange. Each skeletal muscle fiber is stimulated by a nerve fiber at a neuromuscular junction.

20. How do muscles enlarge through exercise? What happens during muscle hypertrophy? Muscle cells increase the amount of intracellular contractile proteins in response to exercise. This increase in cell size is called hypertrophy. Exercise increases the activity of muscle spindles and may enhance muscle tone. As a result of repeated, exhaustive stimulation, muscle fibers develop a greater number of myofibrils and mitochondria, a higher concentration of glycolytic enzymes, and larger glycogen reserves. The net effect is an enlargement, or hypertrophy of the stimulated muscle. Hypertrophy occurs in muscles that have been repeatedly stimulated to produce near-maximal tension; the intracellular changes that occur increase the amount of tension produced when these muscles contract. The muscles of a champion weight lifter or bodybuilder are an excellent example of muscular hypertrophy. 21. How do muscle behave as levers? Know the parts of a lever and the examples of the first-, second- and third-class lever system muscles given in class. The force, speed, or direction of movement that a muscle contraction produces can be modified by attaching the muscle to a lever. A lever is a rigid structure—such as a board, a crowbar, or a bone—that moves on a fixed point called the fulcrum. In the body, each bone is a lever and each joint a fulcrum. In addition to levels and fulcrums, mechanical pulleys can change the direction of a force to accomplish a task more easily and efficiently. In the body, tendons act like lines that convey the forces produced by muscle contraction. The presence of bones or bony processes can change the path that a tendon takes. Bony structures that change the direction of applied forces are called anatomical pulleys.

22. What is so special about cardiac muscle? What are intercalated disks? What do they contain? Why? -Cardiac muscle is striated. Cardiac muscle cells have a single central nucleus, numerous mitochondria, and large amounts of stored glycogen; intercalated discs form junctions between adjacent cardiac muscle cells. -Cardiac muscle cells are connected to neighboring cells at specialized cell junctions called intercalated discs . Intercalated discs are unique to cardiac muscle tissue. The arrangement of these specialized cell-to-cell junctions and the extensive interlocking of the adjacent cardiac plasma membranes give intercalated discs a jagged appearance. >Intercalated discs contain gap junctions and desmosomes.The gap junctions, which are protein lined tunnels, allow direct transmission of the depolarizing current from cell to cell, across the chambers of the heart, so that the cells contract in unison.

23. Compare and contrast the origin, insertion and action of a muscle. Page 251 What is the belly of a muscle? Each muscle begins at an origin, ends at an insertion, and contracts to produce a specific action. Origin (of a muscle) - remains stationary Insertion - moves >Origin is proximal to the insertion When a muscle contracts, the origin pulls the insertion closer . Always! Muscles pull. The origin is the fixed point that doesn’t move during contraction, while the insertion does move. Your bones are the levers and your muscles are the pulley. The belly of the muscle is the fleshy part of the muscle in between the tendons that does the actual contraction. What is meant by the belly of a muscle ? The widest part of a muscle is called the belly . The origin and insertion deal with the tendon attachments. 24. With respect to origin and insertion, what happens to them when a muscle contracts? (Review from page 251-252 & slide) When a skeletal muscle contracts to produce a movement, it plays one of four roles: Agonist, Antagonist, Synergist, or Fixator. These roles can and do changes as the movement changes. Grouped by Primary Actions: 1. Agonist or Prime Mover - muscle whose contraction is mostly responsible for producing movement such as: flexion at the elbow 2. Antagonist - muscle who action OPPOSES that of the agonist. a) Ex: if agonist produces flexion, ANTAGONIST PRODUCES EXTENSION. b) Ex: the biceps brachii acts as an agonist when it contracts, flexing the elbow. The triceps brachii, on the opposite side of the humerus, is the antagonist and acts to stabilize the flexion movement and to produce the opposing action, extension of the elbow. 3. Synergist - contracts, it assists the agonist in performing that action

4. Fixators - when agonists and antagonists contract simultaneously, stabilizing a joint and creating an immovable base a) Ex: muscles of the hand contract to firmly grasp an object in the fingers 25. Why is it appropriate to think of muscles in opposite pairs? What does this mean? Give an example a) Opposing Muscles mean muscles that work opposite to each other. These muscles are found on opposite sides of the joint or body. When one such muscle contracts the other stretches or relaxes. This is also known as antagonistic pairs. Examples of opposing muscles are the chest and back, biceps and triceps, and quadriceps and hamstrings . b) When physiologists say that muscles work in opposable pairs, they mean that muscles work in a location opposite of another muscle. For example, the bicep and tricep. These muscles are located opposite from each other and therefore work as a pair. c) Antagonistic Muscles - muscles that work in opposite pairs d) Synergists - Muscles that work together 26. What is an aponeurosis? Be able to recognize the examples given in class. Aponeurosis - muscle to muscle - sheet like tendon. At each end of the muscle, the collagen fibers of the epimysium, perimysium, and endomysium come together and form a tendon that attaches the muscle to bone, cartilage, skin, or another muscle. Tendons that form thick, flattened sheets are called aponeuroses. Aponeurosis/Aponeuroses - broad tendinous sheets that may serve as the origins and insertions of a skeletal muscle Tendon - A collagenous band that connects a skeletal muscle to an element of the skeleton