Muscles Lecture

1. What is muscle tone, and why is it important?

5. muscle tone = sustained, partial contraction in relaxed skeletal muscle - due to spinal reflexes which allows groups of motor units to be activated in response to input from stretch receptors in muscles - keep muscles firm, healthy, and ready to respond to demand - also helps stabilize joints and maintain posture

1. What benefit is provided by a lever that operates at a mechanical advantage? at a mechanical disadvantage?

The benefit provided by a lever that operates at a mechanical advantage is power lever, and the advantage is that a lever allows a given effort to move a heavier load or to move a load further and faster than it otherwise could. A small effort used over a large distance can be used to move a large effort over a small distance--slower, more stable, strength is priority If the load is far from the fulcrum and the effort is applied near the fulcrum, the force exerted by the muscle must be greater than the lad to be moved or supported. This lever system operates at mechanical disadvantage and is a speed lever. These levers allow a load to be moved rapidly over a large distance with wide ROM. Effort farther than load from fulcrum = mechanical advantage. Effort nearer than load to fulcrum=mechanical disadvantage.

1. Relative to muscle function, can you describe the significance of Sharpey's fibers (i.e., perforating fibers)?

a Sharpey's fibers function with muscles because they are a matrix of connective tissue consisting of bundles of strong collagenous fibers connecting periosteum to bone. They are part of the outer fibrous layer of periosteum, entering into the outer circumferential and interstitial lamellae of bone tissue. The tendons of muscles intertwine with these fibers in order to create a strong bond to the bone, which the muscle is responsible for moving via pulling and forceful actions. These are very strong and anchored fibers, which are beneficial when muscles pull on bones so the muscles do not detach.

95. Which type of smooth muscle exhibits rhythmicity and self-excitation?

a Single-unit

1. Classify the three types of muscle tissue (according to location, appearance, and type of nervous system control).

a Skeletal i Attaches to and moves the bony skeleton ii multinucleated iii Striated iv voluntary b Cardiac i Only in heart, contracts to pump blood through the heart and into blood vessels ii Striated iii involuntary c Smooth (viseral) i Walls of interal organs, blood vessels, respiratory passages, etc ii Smooth (non-striated) iii involuntary

1. Where is most of the cell's ATP produced?

a Slow oxidative

1. Classify each muscle fiber type with respect to its predominant pathway for ATP synthesis, the amount of myoglobin present, and the activity of its myosin ATPase.

a Slow oxidative i Aerobic ii High myoglobin iii Slow myosin ATPase activity b Fast oxidative glycolytic i Aerobic ii intermediate myoglobin iii fast myosin ATPase activity c Fast glycolytic i Anaerobic ii Low myoglobin iii fast myosin ATPase activity

1. What changes are induced in skeletal muscle in response to a program of endurance (i.e., "cardio") exercise training? Which muscle fiber type is most responsive to endurance training?

a Slow oxidative fibers are the most responsive, and the number of capillaries that surround the muscle fibers increase. Mitochondria increase. Fiber synthesize more myoglobin. b Most responsive - slow oxidative

1. What are the T tubules? Where are they located?

a T tubules are tunnel-like invaginations of the sarcolemma -extend into sarcoplasm at right angles cell surface - go deep into cell's interior

1. When does a muscle begin to develop (or exert) external tension?

a internal tension is tension produced inside muscle fibers during crossbridge cycling b after internal tension is developed, continued crossbridge cycling can generate external tension c external tension is the tension exerted against the bone at the muscle attachment site -if external tension great enough (to overcome resistance), the muscle contraction will cause movement

1. What factors contribute to the onset of muscle fatigue?

a ionic imbalances, K+ accumulation disturbs the membrane potential of the muscle cells and halts Ca2+ release; inorganic phosphate accumulation; lactic acid

1. What happens to pyruvic acid when there is not enough O2 present to completely hydrolyze it?

a it is converted to lactic acid

1. What specializations of the muscle fiber (at the motor end plate) enable it to respond to signals from the motor neuron?

a junction folds increase SA at NMJ à sarcolemma has millions of ACh receptors so acetylchoninesterase (AChE) breaks down ACh and inactivates it

1. What is the latent period and what is taking place during the latent period?

a latent period - no tension produced; b/t application of threshold stimulus and the onset of tension development in the muscle; action potential being generated (across sarcolemma and thru t tubules and a Ca release and binds to troponin which would pull off tropomyosin and cross bridge cycling); 2 ms

1. What is the function of the T tubules?

a membranous structures specially differentiated for muscle contraction activity b tubes wrap around and pass thru myofibrils c fluid inside in identical to extracellular fluid d membrane continuous w sarcolemma - if action potential passes along sarcolemma, will pass down T tubules too so signal spreads quickly within the muscle cell and they can contract at the same time e T tubules are located at the level of the A band-I band junction

1. What is the effect of load on the velocity of contraction?

a muscle contracts faster when the load is smaller / no load is added to tighten elastic elements faster

1. What is recruitment (i.e., multiple motor unit summation)?

a muscle response to strength of stimulation: multiple motor unit summation (recruitment) 1) in multiple motor unit summation (recruitment), greater external force is achieved by activating more motor units

maximal stimulus

maximal stimulus - the strongest stimulus that increases contractile force; all motor units are recruited

prime mover (agonist)

muscle that bears the major responsibility for effacing a particular movement; a prime mover

antagonist

muscle that reverses or oppose the action of another muscle

1. Describe how the following organelles are modified or adapted for function in skeletal muscle tissue: nucleus; mitochondria; smooth endoplasmic reticulum.

a. Nucleus: muscle fibers (cells) are multinucleated and contain many nuclei just under the sarcolema (plasma membrane); they are not centrally located; important for manufacturing proteins easily b. Mitochondria are sites of oxidative phosphorlyation and ATP production; there are many in the cell because they are used in many steps in contraction therefore there is a high demand for ATP; they lie in rows near contractile proteins of muscle cells c. Smooth endoplasmic reticulum is called the sarcoplasmic reticulum in muscle cells. It regulates the levels of Ca ions in the sarcoplasm by containing an intracellular fluid with a high concentration of Ca ions compared to the sarcoplasm, which can cause contraction. It completely wraps each myofibril like a sleeve.

glycolysis

breakdown of glucose to pyretic acid and anaerobic process

creatine phosphate (CP)

compound that serves as an alternative energy source for muscle tissue

deep fascia

deep fascia - This connective tissue is associated with skeletal muscle and is subdivided into: epimysium, perimysium, intermuscular septum, and retinaculum. aponeurosis

dense bodies

dense bodies - act as anchoring points for thin filaments and therefore correspond to z discs of skeletal muscle

creatine kinase -

enzyme that catalyzes the transfer of phosphate from creatine phosphate to ADP , forming creatine and ATP; important in muscle contraction

synergist

synergist - muscle that aids the action of a prime mover by effecting the same movement or by stabilizing joints across which the prime mover acts, preventing undesirable movements

threshold stimulus

threshold stimulus - the stimulus at which the first observable contraction occurs

Hypertrophy

increase in the volume of an organ or tissue due to the enlargement of its component cells

1. Name the CT sheath that surrounds individual muscle fibers. Of what type of CT is this sheath composed?

a endomysium - inner most sheath - areolar connective tissue and surrounds each muscle fiber in a muscle

1. Name and describe the muscle fiber's three avenues of ATP production.

- Oxidative (aerobic pathways; lots of mitochondria; more myoglobin) or glycolytic (anaerobic glycolysis; creatinine phosphate which is immediate energy source) 1) muscle fibers can be classified by various characteristics -including the predominant pathway for ATP synthesis, speed of the myosin ATPase, & the amount of myoglobing present 2) the three main fiber types a) slow oxidative (SO) fibers -also called slow twitch or fatigue resistant fibers 1 lower intensity, endurance activities (ex. maintaining posture, stabilizing bones and joints); b) fast oxidative glycolytic (FOG) fibers --also called fast-twitch fatigue-resistant fibers 1 medium-intensity activities (ex. sprinting or walking); arms and forearms have more fast glycolytic fibers c) fast glycolytic (FG) fibers --also called fast twitch or fast twitch fatigable fibers 1 short-term intense or powerful movements (ex. hitting a baseball) - most skeletal muscles contain a mix of fiber types, leading to mix of fatigue resistance and contraction levels - diff muscles suited for diff jobs - see above 3) all of the fibers in a single motor unit are of the same type

95. Describe the relationship between resting length and tension development in smooth muscle.

1 Skeletal muscle has a more limited optimal sarcomere length than does smooth muscle a Tension development is not directly related to resting length b/c not organized into sarcomeres like in skeletal muscle 2 Smooth muscle can contract when between half and twice its resting length & still has a lot of force - function of lack of sarcomeres 3 Allows organ to have huge volume changes without becoming flabby when empty

95. Describe the stress-relaxation response.

1 When smooth muscle is stretched, it spontaneously contracts 2 However, the increased tension only lasts briefly -soon, the muscle adapts to new length and relaxes 3 Retains ability to contract when needed 4 Enables organs such as stomach and bladder to fill slowly to accommodate greater volume so they can temporarily store contents

95. What is the role of gap junctions and pacemaker cells in single-unit smooth muscle?

1 the fibers are organized into sheets of cells which contract rhythmically as a single unit a adjacent cells are connected by gap junctions (allow excitation impulses to spread rapidly through the entire sheet) → the sheet functions as a single unit b pacemaker cells are usually present - they set the rhythmic pattern of contraction

1. What is the effect of load and recruitment on the duration of a muscle contraction?

1) internal vs. external tension a) internal tension is tension produced inside muscle fibers during crossbridge cycling b) after internal tension is developed, continued crossbridge cycling can generate external tension c) external tension is the tension exerted against the bone at the muscle attachment site -if external tension great enough (to overcome resistance), the muscle contraction will cause movement - internal tension is greater than external in twitch; external develops peak more slowly; more stimulation again and again=external tension eventually reaches level of internal tension; tetani b/c w/ each contraction, more external tension could develop 2) muscle always have to contract against a load a) muscle contracts faster when the load is smaller / no load is added to tighten elastic elements faster 1 external tension must be slightly greater than the load b) isometric contractions / latent period of contraction are essentially situations in which the velocity of shortening is zero - this phase is longer w/ the greater the load & results in shorter contraction period - would need to recruit more motor units for a big load 1 the greater than load, the slower the speed of shortening 2 if the load is so heavy, not enough external tension can be produced to cause movement 3) recruitment: the more motor units contracting, the faster and more prolonged the contraction can be

1. How does the size of a motor unit influence the strength of contraction and the control of a movement?

1. a. recruitment follows the size principle - small motor neurons activate smaller motor units are recruited first then activate smaller muscle fibers - around threshold w small motor units; then medium motor units & a little larger muscle fibers then large motor units (resulting in large force) are activated - more precise method of controlling the force of a muscle's contraction b. for maximal contraction, all motor units in a muscle must be recruited at the same time (i.e., synchronous activation) -however, in real life, motor unit recruitment is asynchronous - delays fatigue and allows for strong contractions

1. Describe the gross anatomy of a muscle, beginning with the myofibrils.

1. each skeletal muscle is an organ made up of several types of tissue 3. muscle tissue 4. nerve & blood supply - nerves imp b/c is a voluntary muscle; nervous system relies on input from muscles to coordinate muscle reactions - blood supply imp. for oxygen and nutrient coming to the muscle and removing waste products 5. connective tissue sheaths - surround muscle fibers, collections of muscle fibers, and entire muscle i. endomysium - inner most sheath - areolar connective tissue and surrounds each muscle fiber in a muscle ii. perimysium - middle sheath - surrounds each fascicle (collection/cluster of muscle fibers) - dense irreg CT iii. epimysiym most external sheath - dense irreg CT - blends with superficial or deep facia or tendons or aponeuroses which attach muscle to bone **skeletal muscles can be though of having a belly positioned between muscle attachment sites; where muscle cells/fibers are located; connective tissue sheaths extend past the belly and serve as attachment sites 2. muscle attachments - muscles span joints and attach to bones in at least 2 places a. origin vs. insertion - attachment sites i. origin - attachment to immovable or less moveable bone ii. insertion - attachment to movable bone, ex. Biceps at elbow is insertion and biceps at shoulder is origin site 4. direct vs. indirect attachments i. direct - epimysium fused to periosteum of bone or perichondrium of cartilage ii. indirect - may be attached to either ropelike tendon or sheet-like aponeurosis a) tendon - rope/cord-like b) aponeurosis - sheet a. general cell features 1) skeletal muscle fibers are much larger, elongated cylindrical cells - that's why called fibers 2) skeletal muscle fibers are multinucleated - up to 100 or more nuclei which are pushed to the perimeter of the cell, just under the sarcolemma (muscle fiber plasma membrane) 3) both of these features derive from events of embryonic development 1) myoblasts - mesodermal cells differentiate into myoblasts - myoblasts fuse creating a fiber w/ multiple nuclei ; some 2) syncytium 3) satellite cells - MUSCLE STEM CELLS after mucle fibera re formed, primitive myoblasts remain is muscle tissue - some ability to help thru mitosis and diffusion and limited regeneration of skeletal muscle tissue 2. sarcolemma (muscle fiber plasma membrane) encloses cell contents a. sarcoplasm (muscle fiber cytoplasm) contains typical organelles 1) mitochondria - need lots of ATP 2) myoglobin - similar to hemoglobin a) pigment with a high affinity for O2 b) stores & transfers O2 from the blood hemoglobin to the mitochondria 3) glycosomes - cellular inclusions in which glycogen is stored b. other organelles are modified to support specific muscle function: myofibrils, myofilaments, & sarcomeres & T tubules 1) myofibrils are the contractile elements of the muscle fiber - densely packed, rod-like elements that extend the length of the muscle 2) myofibrils consist primarily of two types of protein structures called myofilaments - responsible for 80% muscle fiber volume; extend entire length of muscle a) thin filaments -composed mainly of the protein actin b) thick filaments -composed mainly of the protein myosin - all the myofibrils are anchored to the sarcolemma to the muscle cell by the protein dystrophin; sarcolemma is attached to endomysium which is attached to tendon or aponeurosis or direct attachment that connects the muscle to bone; collagen fibers of the endomysium will transfer tension to the attachment of the muscle; contraction causes enough tension for pulling of muscle 3) myofilaments are arranged in compartments called sarcomeres which do not extend the entire length of the muscle cells - extends from one z disk to the next a) this is the smallest contractile/functional unit of the muscle b) each myofibril is made up of a series of sarcomeres, positioned end to end, side by side 4) the thick and thin filaments overlap each other, producing striations - b/c alternating A and I bands vi. description of the light & dark bands which create the striations in myofibril; bands in each adjacent sarcomere 1) A band -- the dark area (b/c thick and thin filaments overlap) 2) I band -- light area (b/c only thin filaments so a lot of light can get thru) 3) H zone -- a narrow, lighter region in the center of each A band - only thick filaments; changes in length during muscle contraction 4) M line -- a line which divides the H zone in the center vertically; myomesin proteins; anchoring site for components of sarcomere 5) Z disc or Z line -coin-shaped, but looks like a dark line through the middle of the I band a) a single sarcomere extends from one Z disc to the next - anchors thin filaments - connects each myofibril to all surrounding myofibrils throughout width of the muscle fiber b) elastic filaments, composed of the protein titin 1 extend from the Z disc to the tips of thick filaments, then through the thick filament to the M line 2 stabilize myofilaments & enhance extensibility/elasticity of muscle fibers vii. the sarcomere in cross-section 1) each thick filament is surrounded by 6 thin filaments 2) each thin filament is surrounded by 3 thick filaments - contributes to efficient interaction b/t thick and thin filaments 3. molecular structure of myofilaments a. thick filaments i. myosin - each contains 2 heavy and 4 light polypeptide chains 1 heavy chains intertwine to form a myosin tail 2 2 globular heads on the opposite side of heavy chains 3 Flexible hinge region b/t the head and tail allows heads to pivot and change orientation 4 During contraction - light chains link myosin heads to thin filaments, forming cross bridges 5 Making and breaking cross bridges is contraction of sarcomere 6 Myosin heads extend in a spiraling arrangement from the thick filament; tails are oriented towards M line and are ready to anchor the thick filament 7 Each myosin head contains a region that has ATPase function and an ATP binding site ii. consist of a rod-like tail connected to the globular head region by a hinge region which allows the head to pivot iii. during contraction, light chains help link the head to thin filaments, forming crossbridges b. thin filaments i. actin 1) polypeptide subunits of actin are called G actin (globular actin) -polymerized into long actin filaments called F actin and have a myosin-binding site called the active site - to form a thin filament, g actin filaments link together covalently to form long fibrous F actin (filamentous actin); 2 F actin strands twist together to form a thin filament 2) nebulin - protein at core of thin filament and extends the entire length b/t 2 F action strands and helps stabilize F actin and thin filament in general 3) active site 4) regulatory proteins associated with thin filaments a) tropomyosin - rod shaped protein spiraling thin filaments; 2 filaments; covers active sites on G actin subunits b) troponin -consists of 3 globular subunits; complex protein; one subunit binds to tropomyosin and holds the troponin-tropomyosin complex together; one subunit binds to G actin and hold the troponin-tropomyosin complex over active sites on actin; 3rd has binding sites for calcium ion and low calcium levels are low in a resting muscle and calcium binding site is empty; when muscles contract, there's a higher number of calcium ions present in the sarcoplasm and calcium can bind to that binding site on troponin, allowing cross bridges b/t myosin and actin to form e. transverse tubules (T tubules) i. T tubules are tunnel-like invaginations of the sarcolemma -extend into sarcoplasm at right angles cell surface - go deep into cell's interior - - membranous structures specially differentiated for muscle contraction activity - tubes wrap around and pass thru myofibrils - fluid inside in identical to extracellular fluid - membrane continuous w sarcolemma - if action potential passes along sarcolemma, will pass down T tubules too so signal spreads quickly within the muscle cell and they can contract at the same time ii. T tubules are located at the level of the A band-I band junction f. sarcoplasmic reticulum (SR) i. SR is a system of smooth ER that forms a tubular network around individual myofibrils - membranous structures specially differentiated for muscle contraction activity - in skeletal muscle fibers, the sarcoplasmic reticulum is organized to form a tubular network around each myofibril - regulate sarcoplasmic Ca2+ levels - Ca ion pumps pump calcium from the sarcoplasm back into SR - can store high concentrations of Ca b/c calcium concentrating proteins called calsequestrin in the SR - contractions begin when calcium release channels open in the SR and release it into the sarcoplasm - at the A-I band junctions on either side of T tubule, SR forms enlarged chambers -called terminal cisternae (singular = terminal cisterna) - calcium ion and concentration high here iii. triad = a T (transverse) tubule and the 2 terminal cisternae adjacent to it - activate skeletal muscle and trigger contraction thru calcium release 1) integral proteins extending from T tubule membrane into intermembrane space act as voltage sensors 2) integral proteins of terminal cisternae (which also extend into the intermembrane space) are voltage sensors/receptors that regulate the release of Ca2+ from the SR - proteins change shape when action potential - integral proteins protrude into intermembrane space b/t T tubule and terminal cisternae and control Ca release channels so if one of their proteins change shape so does the other and Ca is released - SR helps end contraction process b/c has calcium ion pumps in its membrane to pump calcium back into SR from sarcoplasm

1. Which of the above properties (#3) is muscle's most distinguishing, or unique, characteristic?

Contractibility

1. Name the CT sheath that holds multiple fascicles together to create a muscle. Of what type of CT is this sheath composed?

a epimysiym most -external sheath - dense irreg CT - blends with superficial or deep facia or tendons or aponeuroses which attach muscle to bone

1. Which fiber type has the fastest contraction speed? the slowest?

a fastest: fast glycolytic fiber slowest: slow oxidative fiber

95. How is smooth muscle contraction regulated?

Smooth muscle contraction is controlled by nerves, hormones, and/or local chemical changes 1. smooth muscle contraction may involve neural regulation or regulation by local factors - fibers in a sheet all display synchronized movement - more complex than skeletal muscle regulation a. neural regulation i. in some cases, a neural stimulus activates smooth muscle via neurotransmitter release ii. nerve fibers of autonomic NS and release neurotransmitters in diffuse junctions; neurotransmitters bind to receptors at smooth muscle sarcolemma opening ligand gated channels producing excitation or change in voltage of plasma membrane iii. neurotransmitter binding causes either graded (local) potential (make it less or more likely to be activated but doesn't necessarily trigger contraction) or action potential iv. in both cases the effect results from increased Ca concentration in sarcoplasm v. response depends on neurotransmitter released and type of receptor molecules in smooth muscle sarcolemma vi. parasympathetic and sympathetic nervous system that release diff kinds of neurotransmitters and diff effects in body ii. can produce an action potential or graded potential b. hormones and local chemicals i. not all smooth muscle tissue has a nerve supply 1) depolarize spontaneously or in response to chemical stimuli that bind to G-protein linked receptors 2) chemical factors that can include hormones, high CO2, pH, and low oxygen in body fluids ii. even the smooth muscle that has a nerve supply may also contract in response to local stimuli iii. local factors which may cause contraction include certain hormones, low pH and other chemical factors **some smooth muscles can respond to both neural and chemical stimuli (and also stretch)

1. What is taking place during the relaxation period?

a tension production falls back to resting level; calcium ions being pumped back into SR and active sites being covered up and ability to do cross bridge cycling decreasing; 10-100 ms (longer than contraction period)

1. Describe the location of the sarcoplasmic reticulum (SR) with respect to the myofibrils.

a SR is a system of smooth ER that forms a tubular network around individual myofibrils - membranous structures specially differentiated for muscle contraction activity - in skeletal muscle fibers, the sarcoplasmic reticulum is organized to form a tubular network around each myofibril

1. What causes each of the bands, zones, and lines in a myofibril?

a A band -- the dark area (b/t thick and thin filaments overlap) b I band -- light area (b/c only thin filaments so a lot of light can get thru) c H zone -- a narrow, lighter region in the center of each A band - only thick filaments; changes in length during muscle contraction d M line -- a line which divides the H zone in the center vertically; myomesin proteins; anchoring site for components of sarcomere e Z disc or Z line -coin-shaped, but looks like a dark line through the middle of the I band a) a single sarcomere extends from one Z disc to the next - anchors thin filaments - connects each myofibril to all surrounding myofibrils throughout width of the muscle fiber b) elastic filaments, composed of the protein titin 1 extend from the Z disc to the tips of thick filaments, then through the thick filament to the M line 2 stabilize myofilaments & enhance extensibility/elasticity of muscle fibers

1. What is the advantage of the parallel arrangement of fibers? of the pennate arrangement? the convergent?

a Advantage of a. Parallel arrangement of fibers—Since the fibers run long and parallel to eachother, it is beneficial because the longer and more nearly parallel the muscle fibers are to a muscle's long axis, the more they can shorten; cause large movements and have good endurance (not very strong) b. Pennate arrangement of fibers—pack in a lot of fibers and therefore are very powerful muscles but tire easily c. Convergent arrangement of fibers—allows for maximum force production

1. Which of the above sources (#72) provides energy to fuel prolonged, submaximal activity?

a Aerobic

1. Which of the above sources (#72) provides energy to fuel brief, high-intensity activity?

a Anaerobic

1. Which of the above sources (#72) of ATP are produced anaerobically? Which are produced aerobically?

a Anaerobic - Fast Glycolytic (FG) b Aerobic - Slow Oxidative (SO) & Fast Oxidative-Glycolytic (FOG)

1. Specifically, how do troponin and tropomyosin help regulate the contraction process?

a Ca pour into SR then bonds to troponin which pulls tropomyosin off active sites so crossbridge cycling can occur

1. What two factors permit relaxation?

a Ca2+ levels fall, actin becomes covered again

95. What is the role of myosin light chain kinase (MLCK)?

a Ca2+-calmodulin complexes activate MLCK 2 myosin light chain kinase (MLCK) phosphorylates myosin light chains in myosin heads 3 once it's phosphorylate, myosin light chain increases myosin ATPase activity in the myosin head -promoting crossbridge attachment and crossbridge cycling 4 crossbridge cycling can continue until the myosin light chain is dephosphorylated -dephosphorylation is performed by the enzyme myosin phosphatase 5 dephosphorylated myosin heads can stay attached for a long time to the actin active site, resulting in latch bridges that maintain the contractile tension of the smooth muscle

95. Identify the regulatory protein in smooth muscle which binds to Ca2+ to activate the contraction process.

a Calmodulin

1. What type of tension does a muscle develop when it is acting as an agonist?

a Concentric; A concentric contraction causes muscles to shorten, thereby generating force; (Of a motion), in the direction of contraction of a muscle. (E.g., extension of the lower arm via the elbow joint while contracting the triceps and other elbow extensor muscles. isotonic: Of or involving muscular contraction against resistance in which the length of the muscle changes. Antonym is isometric. Isotonic movements are either concentric (working muscle shortens) or eccentric (working muscle lengthens)

1. What type of tension is being produced when the overall length of the muscle is increasing while the muscle is functioning?

a Eccentric; Eccentric contractions cause muscles to elongate in response to a greater opposing force.; Against or in the opposite direction of contraction of a muscle. (E.g., flexion of the lower arm (bending of the elbow joint) by an external force while contracting the triceps and other elbow extensor muscles to control that movement.

1. Which of the above properties (#3) are protective?

a Extensibility

1. What happens to the A band, I band, H zone, and Z discs during contraction? to sarcomere length?

a I bands shorten b Thin filaments pulled toward M line, thus Z lines/discs get closer together c H zones (in A band) get shorts - and at maximal contraction, H zone disappears altogether d A band does not change in length- bit A bands get closer together b/c length of thick filaments determine its length - but A bands in adjacent sarcomeres get closer together b/c I band shortening

1. What changes are induced in skeletal muscle in response to a program of resistance exercise training? Which muscle fiber types seem to be especially responsive to resistance training?

a Increase size of individual fibers. More mitochondria, myofilaments, myofibrillar, glycogen and more CT between cells. The fast glycolytic fibers are most resistant to this type of training. b Most responsive - fast glycolytic

1. What causes Ca2+ to be released from the terminal cisternae?

a Integral proteins respond to voltage and change shape when there's an action potential. This shape change allows Ca to be released.

1. What type of tension is being produced when internal tension is being developed, but no movement occurs?

a Isometric; Isometric contractions generate force without changing the length of the muscle.; Of or involving muscular contraction against resistance in which the length of the muscle remains the same.

95. Which contracts more quickly -smooth or skeletal muscle? Which is most fatigue resistant?

a Quickly - skeletal b Fatigue resistant - smooth

1. What happens to force production in a muscle that is in extreme stretch or contraction?

a Reduces force

1. What is the function of the SR and terminal cisternae?

a SR - regulate sarcoplasmic Ca2+ levels - Ca ion pumps pump calcium from the sarcoplasm back into SR - can store high concentrations of Ca b/c calcium concentrating proteins called calsequestrin in the SR - contractions begin when calcium release channels open in the SR and release it into the sarcoplasm b at the A-I band junctions on either side of T tubule, SR forms enlarged chambers -called terminal cisternae (singular = terminal cisterna) - calcium ion and concentration high here 1 calcium ion storage and release

1. Describe the difference between indirect and direct muscle attachments.

a direct - epimysium fused to periosteum of bone or perichondrium of cartilage b indirect - may be attached to either ropelike tendon or sheet-like aponeurosis

1. At what point in cross bridge cycling does ATP become hydrolyzed, and provide the energy for activation of the myosin head?

a during step 4, reactivation of the myosin head (becomes cocked/activated)

1. Name and describe the four arrangements of fascicles/fibers within skeletal muscles.

a The four arrangements of fascicles/fibers within skeletal muscles are as follows. The arrangement of a muscles fascicles determines its ROM and its power. The longer and more nearly parallel the muscle fibers are to a muscle's long axis, the more they can shorten. The greater the number of muscle fibers the greater the power. Stocky bi and multipennate muscles shorten very little but are very powerful because pack in many fibers. a. Circular—when fascicles are arranged in concentric rings; muscles with this arrangement surround body openings, which they close by contracting; sphincters (ex. Orbicularis muscles) b. Covergent—has a broad origin and its fascicles converge toward a single tendon of insertion; triangular or fan shaped (ex. Pectoralis major) c. Parallel—the long axis of the fascicles run parallel to the long axis of the muscle; can be straplike or spindle shaped (fusiform mucles) d. Pennate—the fascicles and thus the muscle fibers are short and attach obliquely to a central tendon that runs the length of the muscle. If the fascicles insert into only one side of the tendon the muscle is unipennate (extensor digitorum longus); if the fascicles insert into the tendon from opposite sides the arrangement is bipennate (rectus femoris); multipennate arrangements look like many feathers sitiated side by side (deltoid muscle)

1. What is the most common class of lever system in the in the body? Where is the fulcrum with respect to the load and effort in this lever system?

a The most common lever system in the body is third class lever systems. In these, the effort is applied between the load and the fulcrum. These are speedy and always operate at a mechanical disadvantage. An example in the activity of the biceps muscle of the arm, lifting the distal forearm and anything carried in the hand. Third class muscle systems allow a muscle to be inserted very close to the joint across which movement occurs which allows rapid extensive movements with little shortening of the muscle (which tend to be thicker and more powerful).

1. What is the most prevalent chemical compound (by weight) in muscle?

a The most prevalent chemical compound by weight in a muscle is H2O

1. What is the significance of the Ca2+-release channels and the Ca2+ active transport pumps in the SR?

a They cause muscle contraction

1. Identify the two primary types of myofilaments found in myofibrils.

a Thick and thin filaments a. thick filaments i. myosin - each contains 2 heavy and 4 light polypeptide chains 1 heavy chains intertwine to form a myosin tail 2 2 globular heads on the opposite side of heavy chains 3 Flexible hinge region b/t the head and tail allows heads to pivot and change orientation 4 During contraction - light chains link myosin heads to thin filaments, forming cross bridges 5 Making and breaking cross bridges is contraction of sarcomere 6 Myosin heads extend in a spiraling arrangement from the thick filament; tails are oriented towards M line and are ready to anchor the thick filament 7 Each myosin head contains a region that has ATPase function and an ATP binding site ii. consist of a rod-like tail connected to the globular head region by a hinge region which allows the head to pivot iii. during contraction, light chains help link the head to thin filaments, forming crossbridges b. thin filaments i. actin 1) polypeptide subunits of actin are called G actin (globular actin) -polymerized into long actin filaments called F actin and have a myosin-binding site called the active site - to form a thin filament, g actin filaments link together covalently to form long fibrous F actin (filamentous actin); 2 F actin strands twist together to form a thin filament 2) nebulin - protein at core of thin filament and extends the entire length b/t 2 F action strands and helps stabilize F actin and thin filament in general 3) active site 4) regulatory proteins associated with thin filaments a) tropomyosin - rod shaped protein spiraling thin filaments; 2 filaments; covers active sites on G actin subunits b) troponin -consists of 3 globular subunits; complex protein; one subunit binds to tropomyosin and holds the troponin-tropomyosin complex together; one subunit binds to G actin and hold the troponin-tropomyosin complex over active sites on actin; 3rd has binding sites for calcium ion and low calcium levels are low in a resting muscle and calcium binding site is empty; when muscles contract, there's a higher number of calcium ions present in the sarcoplasm and calcium can bind to that binding site on troponin, allowing cross bridges b/t myosin and actin to form 5) transverse tubules (T tubules) i. T tubules are tunnel-like invaginations of the sarcolemma -extend into sarcoplasm at right angles cell surface - go deep into cell's interior - membranous structures specially differentiated for muscle contraction activity - tubes wrap around and pass thru myofibrils - fluid inside in identical to extracellular fluid - membrane continuous w sarcolemma - if action potential passes along sarcolemma, will pass down T tubules too so signal spreads quickly within the muscle cell and they can contract at the same time ii. T tubules are located at the level of the A band-I band junction f. sarcoplasmic reticulum (SR) i. SR is a system of smooth ER that forms a tubular network around individual myofibrils - membranous structures specially differentiated for muscle contraction activity - in skeletal muscle fibers, the sarcoplasmic reticulum is organized to form a tubular network around each myofibril - regulate sarcoplasmic Ca2+ levels - Ca ion pumps pump calcium from the sarcoplasm back into SR - can store high concentrations of Ca b/c calcium concentrating proteins called calsequestrin in the SR - contractions begin when calcium release channels open in the SR and release it into the sarcoplasm - at the A-I band junctions on either side of T tubule, SR forms enlarged chambers -called terminal cisternae (singular = terminal cisterna) - calcium ion and concentration high here iii. triad = a T (transverse) tubule and the 2 terminal cisternae adjacent to it - activate skeletal muscle and trigger contraction thru calcium release 1) integral proteins extending from T tubule membrane into intermembrane space act as voltage sensors 2) integral proteins of terminal cisternae (which also extend into the intermembrane space) are voltage sensors/receptors that regulate the release of Ca2+ from the SR - proteins change shape when action potential - integral proteins protrude into intermembrane space b/t T tubule and terminal cisternae and control Ca release channels so if one of their proteins change shape so does the other and Ca is released - SR helps end contraction process b/c has calcium ion pumps in its membrane to pump calcium back into SR from sarcoplasm

1. Muscle contraction is currently best described by the sliding filament theory. Why is this name appropriate for the contraction process?

a Thin filaments slide past the thick allowing myosin to overlap to a greater extent ? b the sliding filament theory of muscle contraction -first proposed in 1953 by Huxley - muscle contraction is not muscle shortening (it's sarcomeres shortening & production of tension) - in the relaxed state, thin and thick filaments overlap only slightly at ends of A band (creates darkness in photomicrograph)

1. Which protein covers the active sites on the actin filament in a resting muscle fiber?

a Tropomyosin

1. Which of the proteins identified above (#26) is/are regulatory proteins?

a Tropomyosin and troponin

1. Why is the triad of functional significance?

a a T (transverse) tubule and the 2 terminal cisternae adjacent to it - activate skeletal muscle and trigger contraction thru calcium release 1) integral proteins extending from T tubule membrane into intermembrane space act as voltage sensors 2) integral proteins of terminal cisternae (which also extend into the intermembrane space) are voltage sensors/receptors that regulate the release of Ca2+ from the SR - proteins change shape when action potential - integral proteins protrude into intermembrane space b/t T tubule and terminal cisternae and control Ca release channels so if one of their proteins change shape so does the other and Ca is released - SR helps end contraction process b/c has calcium ion pumps in its membrane to pump calcium back into SR from sarcoplasm

1. Explain the all-or-none law as it relates to skeletal muscle fibers. explain the all-or-none law as it relates to motor units.

a a single nerve impulse elicits a single contraction event in all of the muscle fibers in the motor unit b the all-or-none principle applies to skeletal muscle fibers and to motor units c if Ca released, all myosin heads engage in cross bridging & when no Ca, no cross bridge cycles happening - on or off

1. What is a motor unit?

a a single somatic alpha motor neuron and all of the skeletal muscle fibers it innervates comprise a functional unit called a motor unit - make graded contractions possible

1. Describe the relative positions of actin and myosin when the muscle is at its optimal length for strength production.

a actin is above the myosin heads, length at which is generates maximum source when muscle is slightly stretched; actin and myosin slightly overlap

1. What is the function of the Z disc?

a anchors thin filaments b connects each myofibril to all surrounding myofibrils throughout width of the muscle fiber

1. When is the (ADP + Pi ) which fueled the power stroke released from the myosin head?

a before the power stroke occurs i.e. right before the head bends

1. Describe the entire process of excitation-contraction coupling, beginning with a nerve impulse in a motor neuron.

a contraction in a skeletal muscle is triggered by a nerve impulse b a single somatic alpha motor neuron and all of the skeletal muscle fibers it innervates comprise a functional unit called a motor unit à axons - travel from central nervous system to skeletal muscle and branches end close to muscle fibers forming a neuromuscular junction i Step 1: AP sweeps along the sarcolemma & down T tubules as a result of action potential ii Step 2: when it reaches the triad (consists of a t tubule and the terminal cisternae that lay on either side of the t tubule), the AP causes Ca2+ to flood out of the terminal cisternae of the SR into the sarcoplasm (cause of gated channels) 1 Ca2+ leaves SR so quickly because it is in very high concentration in the SR vs. the sarcoplasm 2 calsequestrin binds to Ca ions so it concentrates Ca in the SR iii Step 3: Ca2+ binds to troponin -causing troponin to change shape & pull tropomyosin away from active sites on actin

1. What structures anchor smooth muscle fibers and transmit the tension they develop?

a dense bodies and intermediate filaments

1. What is a muscle twitch?

a muscle twitch -response of an isolated muscle or motor unit to a single, brief threshold (stimulus is strong enough to elicit a response; subthreshold would not elicit a response) stimulus -is foundational for understanding how muscles produce smooth contractions of varied intensities i twitches and other muscle phenomena can be measured - recorded in a myogram & myogram tracings how the amount of tension/force produced in response to a stimulus - motor units which consist of a single motor neuron and all the muscle fibers it innervates make graded contractions possible ii phases of a twitch response 1 latent period - no tension produced; b/t application of threshold stimulus and the onset of tension development in the muscle; action potential being generated (across sarcolemma and thru t tubules and a Ca release and binds to troponin which would pull off tropomyosin and cross bridge cycling); 2 ms ii. contraction period - sarcomere shortening and muscle tension happening; 10-11 ms iii. relaxation period - tension production falls back to resting level; calcium ions being pumped back into SR and active sites being covered up and ability to do cross bridge cycling decreasing; 10-100 ms (longer than contraction period) iii some muscles have very rapid twitches, while others have much slower twitches -difference due to variations in metabolic properties and enzymes b/t the fibers of muscle

1. What is a sarcomere?

a myofilaments are arranged in compartments called sarcomeres which do not extend the entire length of the muscle cells - extends from one z disk to the next 1 this is the smallest contractile/functional unit of the muscle 2 each myofibril is made up of a series of sarcomeres, positioned end to end, side by side

1. What is the function of myoglobin?

a myoglobin - similar to hemoglobin i pigment with a high affinity for O2 ii stores & transfers O2 from the blood hemoglobin to the mitochondria iii enclosed by sarcolemma

1. What is acetylcholine? What role does it play at the neuromuscular junction?

a neurotransmitter released at the NMJ is acetylcholine (ACh); synaptic vesicles contain ACh b it attaches to ACh receptors which open Na+ channels releasing Na+ into the muscles creating an action potential

1. What causes myosin to detach from actin after the power stroke is completed?

a new ATP binds to the low-energy myosin head at binding site-causing crossbridge to detach from active site on actin - active sit is exposed and a new myosin head can attach

1. Name the CT sheath that surrounds a fascicle. Of what type of CT is this sheath composed?

a perimysium - middle sheath - surrounds each fascicle (collection/cluster of muscle fibers) - dense irreg CT

1. What is muscle fatigue?

a physiological inability to contract even though the muscle still may be receiving stimuli

1. Describe the structure of an actin molecule. How are individual actin monomers arranged to make up a thin filament?

a polypeptide subunits of actin are called G actin (globular actin) -polymerized into long actin filaments called F actin and have a myosin-binding site called the active site - to form a thin filament, g actin filaments link together covalently to form long fibrous F actin (filamentous actin); 2 F actin strands twist together to form a thin filament

1. What role does complete tetanus play in voluntary movements?

a prolonged tetanus leads to muscle fatigue; warming up before exercise to allow for greater force output

1. Identify the ways in which ATP is used to directly power muscle contraction events.

a pumps Ca2+ from sarcoplasm to SR, detachment of ADP activates myosin head, ATP attaches to myosin head causing detachment

1. Describe the process of signal transmission at the neuromuscular junction (i.e., communication of nerve AP to the muscle fiber).

a signal transmission at the NMJ i nerve impulse (i.e., an action potential) triggers ACh release into the synaptic cleft b/c opening of gated channels ii ACh diffuses across the synaptic cleft and binds to receptors on the motor end plate of the sarcolemma iii ACh binding → opening of ligand-gated Na+ channels iv Na+ rushes into the muscle fiber and triggers a muscle action potential / called end plate potential which is required for skeletal muscle fiber to be excited which is turned into an action potential later v All happens quickly b/c AChE breaks down ACh efficiently

1. Which fiber type receives the richest blood supply?

a slow oxidative

1. At what point (#42) does the power stroke occur?

a step 2- after cross bridge attachment when myosin attaches to active site, ADP + Pi is released from myosin head and the head pivots

1. What prevents prolonged stimulation of the muscle fiber by acetylcholine (ACh)?

a synaptic cleft -acetylcholinesterase (AChE) activity in the synaptic cleft breaks down ACh, which prevents continued muscle activation in the absence of additional nervous system activation

1. What is the synaptic cleft?

a synaptic cleft=gel-filled space that separates the axon terminal and muscle fiber in the NMJ

1. Name and compare the two types of indirect muscle attachments.

a tendon - rope/cord-like b aponeurosis - sheet

1. What is the relationship between the initial length of the sarcomere (or muscle fiber) and the amount of tension it can produce?

a tension production in muscle fibers (and also in the muscle as a whole) is dependent on the length of the sarcomeres in the muscle before the contraction begins --called the length-tension relationship - in order for cross bridge cycling to occur, there has to be some degree of overlap of thick and thin filaments (optimal sarcomere length is 80-120% of resting length); less force if length is short on onset b/c no room for thin filaments to move and form cross bridges; less force also if excessively stretched on onset b/c pretty much no overlap of thick and thin filaments b muscle fibers produce greatest tension when there is optimal overlap between thick & thin filaments just prior to the onset of contraction (optimal sarcomere length is 80-120% of resting length - enough overlap that cross bridges can form) - most of the time starting in optimal length c ability to produce tension is greatly reduced when the muscle is in extreme stretch or contraction

1. What is meant by the term excess post-exercise oxygen consumption (EPOC), which was formerly called "oxygen debt"? What accounts for EPOC?

a the extra amount of oxygen that the body must take in for restorative processes

1. What gives skeletal muscle fibers a striated appearance?

a the thick and thin filaments overlap each other, producing striations - b/c alternating A and I bands

1. What happens to the strength of contraction when two or more identical stimuli are delivered to the muscle in rapid succession (i.e., before complete relaxation occurs)? What is this phenomenon called?

a the wave summation WHEN PICK UP HEAVY THINGS -- eventually reaches incomplete tetanus i identical stimuli are delivered to a muscle (or motor unit) so frequently that the muscle doesn't have time to fully relax between stimuli 2) each subsequent contraction is greater than the previous one(s) - stimulus b4 muscle completely relax, so force and tension increase b/t stimuli

1. What is the role of Ca2+ and the regulatory proteins in the sliding filament mechanism?

a thin filaments: primarily of actin (F strands wound together); G actin molecules contain active sites but tropomyosin covers active site; calcium ion concentration in sarcoplasm must increase - Ca pour into SR then bonds to troponin which pulls tropomyosin off active sites so crossbridge cycling can occur

1. What are the sources of the sarcoplasmic Ca2+ which triggers smooth muscle contraction? Which of these is the main source?

a tubules of the SR, also comes in from the extracellular space (main) via membrane channels

1. What is the role of ATP and the myosin head in the sliding filament mechanism?

a. Step 1: crossbridge formation i. activated myosin head attaches to exposed binding site/active site on actin - causes phosphate to drop off the myosin head which initiates step 2 ii. myosin is in its high-energy configuration b. Step 2: power stroke i. when myosin attaches to active site, Pi is released from the myosin head -this initiates the power stroke ii. myosin head pivots -i.e., moves from its high-energy to a low-energy configuration - pulls thin filament toward M line when pivots & ADP drops off myosin head; myosin head now has no ADP or phosphate head; myosin head in low energy state iii. ADP is released c. Step 3: crossbridge detachment i. new ATP binds to the low-energy myosin head at binding site-causing crossbridge to detach from active site on actin - active sit is exposed and a new myosin head can attach ii. exposed active site is ready to interact with another myosin head d. Step 4: re-activation of myosin head i. ATP → ADP + Pi (hydrolysis) due to action of myosin ATPase in myosin head ii. ATP hydrolysis provides energy to move myosin head back into "cocked" position & is ready to bind to another active site via step 1 - Myosin head has a ADP + Pi attached; has a ATPase to hydrolyze ATP thus releasing energy and making ADP; energy moves myosin head into high energy state - arm sticks outward ("cocked") towards Z line of sarcomere in high energy state/activated state - Energy will be used for power stroke in next cross bridge cycle e. sequence repeats as long as Ca2+ levels remain elevated in sarcoplasm (so Ca can bind to troponin) & ATP is available (not ATPà cycle stops between steps 2 and 3 and myosin head cannot detach from thin filament) - at any given time, only half of available myosin heads are involved in cross bridge linking at an active site (others are detaching, finding an active site, or doing their own power stroke) - eventually Ca pumps will take Ca out of sarcoplasm and troponin will detach and the process will stop - rigor mortis illustrates the fact that cross bridge detachment is at dependent

1. Identify the proteins which make up thin filaments.

a. actin b. nebulin - protein at core of thin filament and extends the entire length b/t 2 F action strands and helps stabilize F actin and thin filament in general c. tropomyosin - rod shaped protein spiraling thin filaments; 2 filaments; covers active sites on G actin subunits d. troponin -consists of 3 globular subunits; complex protein; one subunit binds to tropomyosin and holds the troponin-tropomyosin complex together; one subunit binds to G actin and hold the troponin-tropomyosin complex over active sites on actin; 3rd has binding sites for calcium ion and low calcium levels are low in a resting muscle and calcium binding site is empty; when muscles contract, there's a higher number of calcium ions present in the sarcoplasm and calcium can bind to that binding site on troponin, allowing cross bridges b/t myosin and actin to form

1. Describe the structure of the neuromuscular junction.

a. contraction in a skeletal muscle is triggered by a nerve impulse b. a single somatic alpha motor neuron and all of the skeletal muscle fibers it innervates comprise a functional unit called a motor unit - axons - travel from central nervous system to skeletal muscle and branches end close to muscle fibers forming a neuromuscular junction c. the neuromuscular junction (NMJ) --the site of functional contact between axonal endings of an α-motor neuron and the muscle fiber it innervates - nerve fibers enter muscle and branch and each branch activates a muscle fiber - NMJ=a chemical synapse b/t a nerve fiber i. structure of the NMJ 1) axonal endings (where branch ends) are called axonal terminals (large and bludge shaped) or synaptic terminals - synaptic cleft=gel-filled space that separates the axon terminal and muscle fiber 2) synaptic terminals contain mitochondria & synaptic vesicles - synaptic vesicles contain neurotransmitter acetylcholine (Ach) 3) neurotransmitter released at the NMJ is acetylcholine (ACh) ii. motor end plate -i.e., the region of sarcolemma directly opposite synaptic terminal, contains many infoldings called junctional folds - junction folds increase SA at NMJ à sarcolemma has millions of ACh receptors so acetylchoninesterase (AChE) breaks down ACh and inactivates it 1) motor end plate contains many ACh receptors - tightly associated w ligand-gated Na ion channels a Ion channels: play role in changing membrane potentials and information flow at the NMJ i 2 types: chemically-gated ion channels/ligand-gated - ACh binds to its receptor, opening channel & voltage gated ion channels - open of close in response to changes in membrane potential (excitation impulse) 2) the ACh receptors are tightly associated with ligand-gated Na+ channels iii. synaptic cleft -acetylcholinesterase (AChE) activity in the synaptic cleft breaks down ACh, which prevents continued muscle activation in the absence of additional nervous system activation

1. Name and describe the four functional characteristics of muscle.

a. excitability (responsiveness) - ability to receive and respond to stimuli - muscle tissue stimuli are usually chemical like neurotransmitter or hormone or change in local pH for smooth muscle - response is a change is electrical state of the plasma membrane; change is called action potential which causes muscle to contract - nervous tissue is most excitable b. contractility - ability to develop internal tension and/or shorten forcibly when stimulated - generates force that does work externally - allows muscle to produce movement c. extensibility - ability to be stretched by an outside force without damaging the tissue - ex. Most of skeletal muscles are organized in opposing pairs, ex. Biceps and triceps - one contracted, the other extended - a protective property d. elasticity - ability to recoil to resting length after stretching - protective quality

1. What are graded muscle responses? What are the two general ways of producing a graded muscle response?

a. normal movement is smooth and involves sustained muscle contractions of varying intensities, called graded responses b. 2 ways of grading muscle contractions i. changing the frequency of stimulation ii. changing the strength of the stimulus (thru integration process in the brain)

1. What are the four general functions of the muscular system?

a. producing movement - skeletal muscles are responsible for locomotion (moving entire body from one place to another) and manipulation (moving body parts) - cardiac and smooth muscle are responsible for moving materials into, out of, and within the body b. maintaining posture and body position - constant pull of gravity on the body - pull is resisted by muscle tone - partial contraction of skeletal muscles that support parts of the body - antigravity muscles - muscles that support the neck (extenders and flexors), abdominal muscles, muscles of the back, quadriceps and hamstrings, gastrocnemius and soleus - all ensure that the muscles along the long axis of the body can allow the long axis to be erect c. stabilizing joints - especially important at knee and shoulder b/c not complementary bone shapes - stabilizing joints that we don't want movement at so we get desired movement d. thermogenesis - generate heat - heat is byproduct of contractions and muscle metabolism - doesn't capture all energy as ATP, 60% is released as heat; skeletal muscle is 40% of body's mass so most responsible for generating body heat

1. Describe the major structural and functional differences between smooth and skeletal muscle.

a. smooth muscle fibers are smaller in diameter & shorter (1/10 size) b. single nucleus and no striations c. endomysium (surround the smooth muscle fibers) & centrally located nucleus are present in smooth muscle -no perimysium (or fascicles) or epimysium d. nerve innervation is different: innervated by motor neuron of autonomic NS; no neuromuscular junction b/t motor neuron and smooth muscles cells; have axons w usual structures called varicosities that are filled w vesicles that house neurotransmitters and when activated, release them into a wide synaptic cleft near smooth muscle; no specialized region on sarcolemma of smooth muscle like a motor end plate; junction b/t the motor neuron and smooth muscle is called a diffuse junction and is very diff from an NMJ e. the neuromuscular junctions are not highly structured, as they are in skeletal muscle i. nerve fibers end in numerous rounded swellings, called varicosities ii. the varicosities release neurotransmitters in the general region of the smooth muscle cells f. internal organization is different in smooth vs. skeletal muscle fibers i. no T tubules or terminal cisternae -SR forms loose network (less elaborate) through sarcoplasm - no triad relationship; less SR overall and no terminal cisternae - sarcolemma contains pouch-like infoldings called caveolae - higher SA, receptors, voltage and ligand gated channels - allows Ca to flow into sarcoplasm from extracellular fluid mostly, a little from endoplasmic reticulum; SR membrane pumps it back into SR mostly and a little into extracellular fluid when necessary ii. thick & thin filaments are present, but are not organized into myofibrils or sarcomeres - no striations and no sarcomeres but do contain overlapping thick and thin filaments - thick filaments are fewer and have myosin heads along entire length iii. much higher ratio of thin:thick filaments in smooth muscle (10-15: 1 as opposed to 2:1) iv. thick & thin filaments are oriented obliquely (i.e. diagonally) in the muscle fiber (not longitudinally as in skeletal muscle) v. thick filaments have heads along their entire length -the heads extend in different directions on opposite sides of the thick filaments NO troponin complex in thin filaments; tropomyosin is present to help stabilize the thick filament; active sites always open; the protein calmodulin is the Ca binding site & the Ca-calmodulin complex regulates smooth muscle contraction g. smooth muscle has a network of dense bodies and intermediate filaments, which anchor myofilaments and help transmit tension through the tissue - contain lattice-like arrangement of non-contractile intermediate filaments that resist tension - intermediate filaments connect at regular intervals to cytoplasmic structures called dense bodies o intermediate filament-dense body network creates the cytoskeleton for smooth muscle fibers o dense bodies near the sarcolemma anchor the thin filaments to the sarcolemma and correspond to the Z discs of skeletal muscle o dense bodies at the sarcolemma surface also bind to connective tissue outside the cell and to dense bodies in adjacent muscle fiber membranes - helps to ensure synchronous contraction of a smooth muscle sheet - link adjacent cells kind of like desmosomes b/t adjacent smooth muscle cells h. gap junctions and desmosomes are also present between adjacent cells - allow depolarization (the excitation wave) to spread rapidly from cell to cell - in contrast, skeletal muscle fibers are electrically isolated from e/o and must receive signal to contract from alpha motor neuron Contraction in smooth muscle is different from skeletal muscle in following ways: •Decreased Ca2+ in sarcoplasm is not enough to produce relaxation •Some Ca2+ is obtained from SR, but most comes from extracellular space •The regulatory protein is calmodulin -it's associated with the thick filaments •Ca2+ binds to calmodulin, not troponin and Active sites on actin always open •Activated calmodulin then activates myosin light chain kinase (MLCK) •Activated MLCK phosphorylates myosin head, activating it •Leads to crossbridge formation with actin •Thus, activated calmodulin (i.e., Ca2+-calmodulin complexes) regulate crossbridge cycling by determining phosphorylation rates

1. Describe the steps of excitation-contraction coupling in smooth muscle.

i excitation allows influx of Ca ions from extracellular fluid (most) which will open more even more channels in the SR to let Ca in ii ca ions enter by way or voltage gated Ca channels or non voltage gated Ca channels b Ca binds to calmodulin, activating it c Ca-calmodulin complex activates MLCK (present in sarcoplasm) d MLCK phosphorylates light chains in myosin heads, activating the myosin heads e Once the myosin light chain is phosphorylated, it increases myosin ATPase activity (slower than in skeletal muscle usually) which promotes crossbridge formation - myosin head hydrolyze ATP and move head into cocked position then reach out and grab an active site and tug on a thin filament f Crossbridge cycling can continue -even if sarcoplasmic Ca2+ level is falling --until the myosin light chain is dephosphorylated (in skeletal contractions, drops in Ca would stop process b/c active sites would be covered) i Myosin light chain phosphatase is the enzyme that can remove the phosphate g Dephosphorylated myosin releases very slowly from actin, causing cross bridge formation to slow or stop & creating what are called latch bridges i Latch bridges help smooth muscle maintain muscle tone and save energy during prolonged contraction; lock onto active site on action & not allowing thin filament to slide back into resting length; can stay latched on for days and stay in partial contraction state w/o further energy expenditure **Smooth muscle tends to be much less efficient in the short term but good for extended periods so very efficient in long term

1. Describe the structure of a myosin molecule. How are myosin molecules arranged to make up a thick filament?

i myosin - each contains 2 heavy and 4 light polypeptide chains 1 heavy chains intertwine to form a myosin tail 2 2 globular heads on the opposite side of heavy chains 3 Flexible hinge region b/t the head and tail allows heads to pivot and change orientation 4 During contraction - light chains link myosin heads to thin filaments, forming cross bridges 5 Making and breaking cross bridges is contraction of sarcomere 6 Myosin heads extend in a spiraling arrangement from the thick filament; tails are oriented towards M line and are ready to anchor the thick filament 7 Each myosin head contains a region that has ATPase function and an ATP binding site

95. Smooth muscle can be categorized as single-unit smooth muscle (which Marieb calls "unitary smooth muscle) or multi-unit smooth muscle. Describe the ways in which these two types of smooth muscle differ.

i single-unit smooth muscle / unitary (visceral muscle) 1 this is the most common type of smooth muscle 2 found in walls of all hollow organs except heart 3 has all common characteristics of smooth muscle a arranged in opposing (longitudinal and circular) sheets b innervated at diffuse junctions by varicosities of autonomic nerve fibers c often exhibit spontaneous action potentials due to presence of pacemaker cells d cells are electrically coupled by gap junctions and contract as a single unit e response to neurotransmitters or chemical stimuli like pH changes 4 the fibers are organized into sheets of cells which contract rhythmically as a single unit a adjacent cells are connected by gap junctions (allow excitation impulses to spread rapidly through the entire sheet) → the sheet functions as a single unit b pacemaker cells are usually present - they set the rhythmic pattern of contraction ii multiunit smooth muscle 1 consists of smooth muscle fibers that are structurally independent of each other 2 located in large airways in lungs, large arteries, arrector pili muscles, and iris of eye 3 few gap junctions, and spontaneous depolarization is rare (no pacemaker cells) 4 similar to skeleton muscle a independent muscle fibers b innervated by autonomic nervous system, forming motor units c graded contractions occur in response to neural stimuli that involve recruitment 5 diff from skeletal muscle b/c like visceral smooth muscle it is controlled by autonomic nervous system and hormones 6 innervated by nerve fibers from the autonomic nervous system 7 not self-excitatory

95. Where is each type of smooth muscle located?

i. Single-unit - found in walls of all hollow organs except heart ii. Multiunit - located in large airways in lungs, large arteries, arrector pili muscles, and iris of eye

1. What 4 factors influence the amount of force that a muscle generates during contraction?

i. frequency of stimulation -higher frequency of stimulation results in wave summation & tetanus (either incomplete or complete) & greater force ii. the number of fibers activated -i.e., the number of motor units recruited; more=greater force iii. the size of the muscle fibers recruited; larger cross section / large motor unit=more thick and thin filaments in the fiber=greater force/tension iv. muscle and sarcomere length at onset of contraction 1) tension production in muscle fibers (and also in the muscle as a whole) is dependent on the length of the sarcomeres in the muscle before the contraction begins --called the length-tension relationship - in order for cross bridge cycling to occur, there has to be some degree of overlap of thick and thin filaments (optimal sarcomere length is 80-120% of resting length); less force if length is short on onset b/c no room for thin filaments to move and form cross bridges; less force also if excessively stretched on onset b/c pretty much no overlap of thick and thin filaments 2) muscle fibers produce greatest tension when there is optimal overlap between thick & thin filaments just prior to the onset of contraction (optimal sarcomere length is 80-120% of resting length - enough overlap that cross bridges can form) - most of the time starting in optimal length o example: basketball player crouching over slightly before making basket so get more force out of jump 3) ability to produce tension is greatly reduced when the muscle is in extreme stretch or contraction

1. What is the difference between unfused tetanus and complete tetanus? How is complete tetanus achieved in a muscle fiber?

i. unfused, or incomplete, tetanus - NORMAL MOVEMENT 1) occurs when frequent stimulation continues and muscle is not allowed to relax completely between them 2) tension reaches a peak, but vacillating level - explained by fact that Ca levels are high for an extended period of time and there's no chance for thin filaments to move back ii. complete/fused tetanus 1) stimulation occurs so frequently that relaxation phase is eliminated altogether 2) results in smooth, continuous contraction with no evidence of relaxation - doesn't happen in the body (except potentially for very short time) b/c muscle fatigue - muscles produce unfused tetanus

oxidative phosphorylation

process of ATP synthesis during which an inorganic phosphate group is attached to ADP; occurs via the electron transport chain within the mitochondria