Bio 217 Focus Outline Chapter 9 PDF

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Focus Outline Chapter 9 Muscles and Muscle Tissue 9.1 Overview of muscle types, special characteristics, and functions Compare and contrast the three basic types of muscle tissue. Skeletal muscle

Cardiac muscle

Smooth muscle

-Skeletal muscle  tissue  is packaged into skeletal muscles: organs that are attached to bones and skin

- Cardiac muscle tissue is found only in heart

- Smooth muscle tissue: found in walls of hollow organs

-Makes up bulk of heart walls

-Examples: stomach, urinary bladder, and airways

-Skeletal muscle  fibers  are the longest of all muscles and have striations (stripes) -Also called voluntary muscle: can be consciously controlled -Contract rapidly; tire easily; powerful - Key words for skeletal muscle: skeletal, striated, and voluntary - Body location: attached to bone (or some facial muscles) to skin - Cell shape appearance: single, very long, cylindrical, multinucleate cells with obvious striations.

-Striated -Involuntary: cannot be controlled consciously - Contracts at steady rate due to heart’s own pacemaker, but nervous system can increase rate

-Not striated -Involuntary: cannot be controlled consciously - Can contract on its own without nervous system stimulation

- Key words for cardiac muscle: cardiac, striated  , and involuntary - Body location: walls of the heart

-Branching chains of cells; uni- or binucleate; striations.

-unitary muscle in walls of hollow visceral organs (other than the heart); multi unit muscle in intrinsic eye muscles, airways, large arteries - single, fusiform, unicleate; no striations

*List four important functions of muscle tissue. • Four important functions ❖ Produce movement: responsible for all locomotion and manipulation ▪ Example: walking, digesting, pumping blood ❖ Maintain posture and body position ❖ Stabilize joints ❖ Generate heat as they contract • Additional functions – Protect organs, form valves, control pupil size, cause “goosebumps”

Skeletal muscle 9.2 Gross and microscopic anatomy Describe the gross structure of a skeletal muscle.

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Skeletal muscle is an organ made up of different tissues with 3 features: nerve and blood supply, connective tissue sheaths, and attachments. Nerve and blood supply: One nerve, one artery, and one or more veins serve each muscle. Consciously controlled skeletal muscle has nerves supplying every fiber to control activity. Skeletal muscle has a rich blood supply. Contracting muscle fibers use huge amounts of energy and require almost continuous delivery of oxygen and nutrients via the arteries. And also need waste products to remove quickly. Connective tissue sheaths: - Each skeletal muscle, as well as each muscle fiber, is covered in connective tissue - Support cells and reinforce whole muscle - Sheaths from external to internal:

+Epimysium: dense irregular connective tissue surrounding entire muscle; may blend with fascia +Perimysium: fibrous connective tissue surrounding fascicles (groups of muscle fibers) +Endomysium: fine areolar connective tissue surrounding each muscle fiber Attachments: -Muscles span joints and attach to bones -Muscles attach to bone in at least two places + Insertion: attachment to movable bone + Origin: attachment to immovable or less movable bone - Attachments can be direct or indirect + Direct (fleshy): epimysium fused to periosteum of bone or perichondrium of cartilage + Indirect: connective tissue wrappings extend beyond the muscle as ropelike tendon or sheetlike aponeurosis 9.3 Intracellular structures and sliding filament model Describe the microscopic structure and functional roles of the myofibrils, sarcoplasmic reticulum, and T tubules of skeletal muscle fibers.

Myofibrils: -The microscopic structure: + are densely packed, rodlike ligaments +single muscle fiber can contain 1000s + accounts for ~80% of muscle cell volume +Myofibrils features: 1. Striations: stripes formed from repeating series of dark and light bands along the length of each myofibril. - A bands: dark regions; H zone: lighter region in the middle of dark A band; M line: line protein (myomesin) that bisects H zone vertically.

2. 3. + + + + 4. -

I bands: lighter regions Z disc (line) : coin shaped sheet of protein on the midline of light I band Sarcomere: Are the smallest contractile unit (functional unit) of muscle fiber Contains A band with half of an I band at each end: consists of area between between Z disc Individual sarcomere aligns end to end along myofibril, like boxcars of train Myofilaments: Orderly arrangement of actin and myosin myofilaments within sarcomere Actin myofilaments: thin filaments across I band and part way in A band Anchored to Z discs Myosin myofilaments: thick filaments Extend length of A band Connected at M line Sarcomere cross section shows hexagonal arrangement of one thick filament surrounded by six thin filaments Molecular composition of myofilaments Thick filaments: composed of protein myosin that contains two heavy and four light polypeptide chains +Heavy chains intertwine to form myosin +Light chains form myosin globular head

During contraction, heads link thick and thin filaments together, forming cross bridges +Myosins are offset from each other, resulting in staggered array of heads at different points along thick filament - Thin  filaments: composed of fibrous protein actin + Actin is polypeptide made up of kidney-shaped G actin (globular) subunits + G actin subunits bears active sites for myosin head attachment during contraction ▪ G actin subunits link together to form long, fibrous F actin (filamentous) ▪ Two F actin strands twist together to form a thin filament + Tropomyosin and troponin: regulatory proteins bound to actin 5. Molecular composition of myofilaments -

Other proteins help form the structure of the myofibril + Elastic filament: composed of protein titin Holds thick filaments in place; helps recoil after stretch; resists excessive stretching + Dystrophin Links thin filaments to proteins of sarcolemma + Nebulin, myomesin, C proteins bind filaments of sarcomeres together Maintain alignment of sarcomere

Sarcoplasmic  Reticulum: Network of smooth endoplasmic reticulum tubules surrounding each myofibril -

Most run longitudinally Terminal cisterns form perpendicular cross channels at the A-I band junction Sarcoplasmic reticulum functions in regulation of intracellular Ca2+ levels Stores and releases Ca 2+ T  tubules: – Tube formed by protrusion of sarcolemma deep into cell interior ▪ Increase muscle fiber’s surface area greatly ▪ Lumen continuous with extracellular space ▪ Allow electrical nerve transmissions to reach deep into the interior of each muscle fiber – Tubules penetrate cell’s interior at each A–I band junction between terminal cisterns ▪ Triad: area formed from terminal cistern of one sarcomere, T tubule, and terminal cisterns of neighboring sarcomere Triad relationships:

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T tubule contains integral membrane proteins that protrude into intermembrane space (space between tubule and muscle fiber sarcolemma) ▪ Tubule proteins act as voltage sensors that change shape in response to an electrical current SR cistern membranes also have integral membrane proteins that protrude into intermembrane space ▪ SR integral proteins control opening of calcium channels in SR cisterns When an electrical impulse passes by, T tubule proteins change shape, causing SR proteins to change shape, causing the release of calcium into the cytoplasm

*Describe the sliding filament model of muscle contraction. -

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Contraction: the activation of cross bridges to generate force Shortening occurs when tension generated by cross bridges on thin filaments exceeds forces opposing shortening Contraction ends when cross bridges become inactive

In the relaxed state, thin and thick filaments overlap only slightly at the ends of A band Sliding filament model of contraction states that during contraction, thin filaments slide past thick filaments, causing actin and myosin to overlap more – Neither thick or thin filaments change length, just overlap more When nervous system stimulates muscle fiber, myosin heads are allowed to bind to actin, forming cross bridges, which cause sliding (contraction) process to begin Cross bridge attachments form and break several times, each time pulling thin filaments a little closer toward the center of the sarcomere in a ratcheting action

Causes shortening of muscle fiber -

Z discs are pulled toward M line I bands shorten Z discs become closer H zones disappear A bands move closer to each other

9.4 How does a nerve impulse causes a muscle fiber to contract?

The nerve impulse causes the release of acetylcholine from the motor end plate. This causes the depolarization of the membrane of the adjacent muscle cells. Depolarization triggers the release of calcium ions from the terminal cisternae and sarcoplasmic reticulum inside the muscle cell. In the presence of ATP, the high calcium level causes the myosin heads to bend, dragging actin filaments towards the middle of the unit of contraction.

#The muscle cell, including the T tubules are polarized. Stimulation of the motor end plate on a muscle cell by ACh triggers depolarization resulting in contraction of the sarcomeres *Explain

how muscle fibers are stimulated to contract by describing events that occur at the neuromuscular junction. - When the action potential arrives at the axon terminal, the voltage change of the membrane occurs. This causes voltage-gated channels open that make calcium ions enter the axon terminal. - Synaptic vesicles fuse to membrane of axon terminal, and then Acetylcholine is released into the synaptic cleft. - Ach binds to receptor sites on the motor end plate( on the junctional folds of the sarcolemma) ACh binding opens chemically gated ion channels that allow the passage of Na+ into the muscle fibers and K+out of muscle fibers. =>Motor end plates becomes depolarized (decrease in MP) => this called an end plate potential EPP - The EPP spreads to the adjacent sarcolemma and triggers an AP there.

- After ACh binds to the ACh receptors, Acetylcholine diffuses away from its receptor site, the ion channels closes, and Acetylcholine is then broken down by Acetylcholinesterase. ❖ ACh diffuses away from the ACh receptor, which is a part of the chemically regulated ion channel. As the ACh falls off the receptor, the ion channel on the receptor closes, preventing further flow of Na+ and K+ ions. ❖ The ACh binds to the enzyme Acetylcholinesterase ❖ The Acetylcholinesterase breaks down ACh into two pieces, inactivating it. After the ACh has broken down, its part is taken back up into the axon terminal where they can be reassembled into ACh again. - An action potential is generated which propagates along the sarcolemma in all directions and down the T tubules. - The action potential causes the release of calcium ions from the terminal cisternae into the cytosol - Calcium ions trigger a contraction of muscle cells

Describe how an action potential is generated.

1. An end plate potential EPP is generated at the neuromuscular junction: The EPP causes a wave of depolarization that spreads to the adjacent sarcolemma. 2. Depolarization: generating and propagating an action potential AP Depolarization of the sarcolemma opens voltage-gated Na+ channels: Na+ enters. At a certain membrane voltage. An AP is generated. The AP spreads to adjacent areas of the sarcolemma and opens voltage-gated Na+ channels there, propagating the AP. The AP propagates along the sarcolemma in all directions. 3. Repolarization: Restoring the sarcolemma to its initial polarized state ( negative inside, positive outside). The repolarization wave is also a consequence of opening and closing ion channels - voltage-gated Na+ channels close and voltage-gated K+channels open. The K+ ion concentration is higher inside the cell than in the extracellular fluid, so K+ diffuses out of the muscle fiber. This restores the negatively charged conditions inside that are characteristic of sarcolemma at rest

Follow the events of excitation-contraction coupling that lead to cross-bridge activity Excitation-Contraction Coupling:  is the sequence of events by which transmission of an action potential along the sarcolemma causes myofilament to slide

1. The action potential propagates along the sarcolemma and down the T tubules 2. Calcium ions are released in the terminal cisternae of the sarcoplasmic reticulum SR, allowing the Ca2+ to flow into the cytosol. 3. Calcium binds to troponin, then troponin changes shape, exposing myosin-binding sites on the actin thin filament => removes the blocking action of tropomyosin. 4. Myosin binding to actin form cross bridges and contraction begins (cross bridge cycling) begins. At this point E-C coupling is over. Muscle fiber contraction: Cross Bridge Cycling: Step 1: Exposure of binding sites on Actin: 1.Presence of an action potential in the muscle cell membrane 2. Release of calcium ions from the terminal cisternae 3. Calcium ions rush into the cytosol and bind to the troponin 4. There is a change in the conformation of the troponin-tropomyosin complex 5.This tropomyosin slides over, exposing the binding sites on actin Step 2: Binding of Myosin to Actin: The hinge on the tail of the myosin bending and the energized myosin head binding into the actin During the entire step, the myosin head is in its high energy, upright position. If it was tilted backward, in its low energy position, the actin binding site would not be in the proper position to bind the actin Step 3: Power stroke of the cross bridge: The ADP and Pi are released from the actin -> The myosin head (cross bridge) tilts backward -> The power stroke occurs as the thin filament is pulled inward toward the center of the sarcomere, which cause muscle contraction Step 4: Disconnecting the Cross Bridge: ATP binds to the cross bridge, allowing the cross bridge to disconnect from the actin Step  5: Re-energizing of the Cross Bridge: ATP is hydrolyzed into ADP and phosphate. The energy is transferred from the ATP to the myosin cross bridge, which points upward. Step 6: Removal of Calcium Ions: Calcium ions fall off the troponin -> Calcium is taken back up into the sarcoplasmic reticulum -> Tropomyosin covers the binding sites on actin

9.5 What are the properties of whole muscle contraction? Frequency of stimulation, number of motor units recruited, degree of muscle strength: length-tension relationship.

Wave summation and motor unit recruitment allow smooth, graded skeletal muscle contractions *Define

motor unit and muscle twitch, and describe the events occurring during the three phases of a muscle twitch. -

Motor unit: consists of one motor neuron and all the muscle fibers it innervates, or supplies. The size of a motor unit can vary.

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Muscle twitch: is the response of a muscle to a single stimulus of adequate strength. The muscle fibers contract quickly and then relax.

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The events occuring during the three phases of a muscle twitch: 1. Latent period: events of excitation contraction coupling ● The Sarcolemma and T tubules depolarize ● Calcium ions are released into the cytosol ● Cross bridges begin to cycle but there is no visible shortening of the muscle 2. Contraction phase: cross bridge formation, tension increases ● Myosin cross bridge cycling causes sarcomeres to shorten 3. Relaxation: ca2+ reentry into SR; tension declines to zero ● Calcium ions are actively transported back into the terminal cisternae ● Cross bridge cycling decrease and end. ● Muscle return to its original length Explain how smooth, graded contractions of a skeletal muscle are produced.

Muscle contraction can be graded in two ways: - Most skeletal muscle contractions are tetanic, smooth, because rapid nerve impulses are reaching the muscle , the muscle cannot relax completely between contractions, the strength of the contractions reflexes the amount of muscle cells contracting, more stronger. -

An increase in the frequency of stimulation causes temporal summation. The higher the frequency, the greater the strength of contraction of a given motor unit

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An increase in the strength of stimulation causes recruitment. The stronger the stimulation, the more motor units are activated, and the stronger the contraction.

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*Differentiate between isometric and isotonic contractions Isometric contractions: If muscle tension develops but the load is not moved , the contraction is called isometric contractions. Tension may build to the muscle’s peak tension-producing capacity, but

the muscle neither shortens or lengthens because the loads is greater than the force (tension) the muscle is able to develop

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Isotonic contractions: If the muscle tension developed overcomes the load and muscle shortening occurs, the contraction is called isotonic contractions. Isotonic contractions come in 2 “flavors”: + Concentric contractions: are those in which the muscle shortens and does work + Eccentric contractions: in which the muscle generates force as it lengthens, are equally important for coordination and purposeful movements

9.6 How do muscles generate ATP? 1. Direct phosphorylation of ADP by creatine phosphate: Hydrolysis of creatine phosphate 2. Anaerobic glycolysis, which converts glucose to lactic acid 3. Aerobic respiration: The Krebs cycle and oxidative phosphorylation

*Describe three ways in which ATP is regenerated during skeletal muscle contraction. 1. Hydrolysis of Creatine Phosphate:

The immediate source of energy for rebuilding ATP is the high energy molecule creatine phosphate. The phosphate in creatine phosphate, can be transferred from ADP to ATP in a process called substrate phosphorylation. However, there is not much creatine phosphate stored in muscle cells. Net gain - 1 ATP molecule - Oxygen use: None - products : 1 ATP per CP, creatine Creatine Phosphate + ADP --------------------> creatine + ATp (creatine kinase) 2. Glycolysis:

-Glycolysis is a reaction where sugar (glucose) is broken down (lysed). -This reaction requires 2 ATP to be put in the formation of 4 ADP giving a net chain of 2 ATP molecules. -Advantages of glycolysis are that it uses readily available reactants and does not require oxygen. Two sources of glucose to muscles: 1. Blood glucose 2. Breakdown of glycogen into glucose within the muscle cell Glucose is stored in the body in the molecule glycogen Glycogen---> Glucose--------------------> 2 Pyruvic Acid + 2 ATP (GLYCOLYSIS) | | Lactic acid

3. The Krebs cycle and oxidative phosphorylation: Aerobic pathway:

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In the presence of oxygen, the products of glycolysis can continue to make more ATP- a net gain of 33-36 ATP by going through the kreb cycle and oxidative phosphorylation. The combination of glycolysis, the kreb cycle and oxidative phosphorylation is also known as aerobic cellular respiration. Sources of Oxygen: - The oxygen needed for aerobic metabolism is available to muscle cells from the blood or an oxygen binding protein called myoglobin Glucose (from glycogen breakdown or delivered from blood)+ O2-->Pyruvic acid→ Aerobic respiration in mitochondria (fatty acids,amino acids in)---> CO2+ H20+32 Atp glucose--->2ATP+2pyruvic acid ; pyruvic acid--->kreb cycle+ETC--->CO2+H2O+36ATP (glycolysis) (needed O2) *Define -

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EPOC and muscle fatigue. List possible causes of muscle fatigue.

EPOC (Excess Postexercise Oxygen Consumption): The extra amount of oxygen that the body

must take in for these restorative processes, formerly called the oxygen debt. EPOC re...