Muscular System PDF

Muscular System © 2013 Pearson Education, Inc.  Muscle Tissue Nearly half of body's mass Transforms chemical energy (ATP) to directed mechanical energy  exerts force Three types – Skeletal – Cardiac – Smooth...

Muscular System © 2013 Pearson Education, Inc.  Muscle Tissue Nearly half of body's mass Transforms chemical energy (ATP) to directed mechanical energy  exerts force Three types – Skeletal – Cardiac – Smooth Myo, mys, and sarco - prefixes for muscle © 2013 Pearson Education, Inc.  Types of Muscle Tissue Skeletal muscles – Organs attached to bones and skin – Elongated cells called muscle fibers – Striated (striped) – Voluntary (i.e., conscious control) – Contract rapidly; tire easily; powerful – Require nervous system stimulation © 2013 Pearson Education, Inc.  Types of Muscle Tissue Cardiac muscle – Only in heart; bulk of heart walls – Striated – Can contract without nervous system stimulation – Involuntary © 2013 Pearson Education, Inc.  Types of Muscle Tissue Smooth muscle – In walls of hollow organs, e.g., stomach, urinary bladder, and airways – Not striated – Can contract without nervous system stimulation – Involuntary © 2013 Pearson Education, Inc.  Table 9.3 Comparison of Skeletal, Cardiac, and Smooth Muscle (1 of 4) © 2013 Pearson Education, Inc.  Table 9.3 Comparison of Skeletal, Cardiac, and Smooth Muscle (2 of 4) © 2013 Pearson Education, Inc.  Table 9.3 Comparison of Skeletal, Cardiac, and Smooth Muscle (3 of 4) © 2013 Pearson Education, Inc.  Table 9.3 Comparison of Skeletal, Cardiac, and Smooth Muscle (4 of 4) © 2013 Pearson Education, Inc.  Special Characteristics of Muscle Tissue Excitability (responsiveness): ability to receive and respond to stimuli Contractility: ability to shorten forcibly when stimulated Extensibility: ability to be stretched Elasticity: ability to recoil to resting length © 2013 Pearson Education, Inc.  Muscle Functions Four important functions – Movement of bones or fluids (e.g., blood) – Maintaining posture and body position – Stabilizing joints – Heat generation (especially skeletal muscle) Additional functions – Protects organs, forms valves, controls pupil and lumen size, causes "goosebumps" © 2013 Pearson Education, Inc.  Skeletal Muscle Each muscle served by one artery, one nerve, and one or more veins – Enter/exit near central part and branch through connective tissue sheaths – Every skeletal muscle fiber supplied by nerve ending that controls its activity – Huge nutrient and oxygen need; generates large amount of waste © 2013 Pearson Education, Inc.  Figure 9.1 Connective tissue sheaths of skeletal muscle: epimysium, perimysium, and endomysium. Epimysium Epimysium Bone Perimysium Tendon Endomysium Muscle fiber in middle of a fascicle Blood vessel Perimysium wrapping a fascicle Endomysium (between individual muscle fibers) Muscle fiber Fascicle Perimysium © 2013 Pearson Education, Inc.  Skeletal Muscle: Attachments Attach in at least two places – Insertion – movable bone – Origin – immovable (less movable) bone Attachments direct or indirect – Direct—epimysium fused to periosteum of bone or perichondrium of cartilage – Indirect—connective tissue wrappings extend beyond muscle as ropelike tendon or sheetlike aponeurosis © 2013 Pearson Education, Inc.  Microscopic Anatomy of a Skeletal Muscle Fiber Long, cylindrical cell – 10 to 100 µm in diameter; up to 30 cm long Multiple peripheral nuclei Sarcolemma = plasma membrane Sarcoplasm = cytoplasm – Glycosomes for glycogen storage, myoglobin for O2 storage Modified structures: myofibrils, sarcoplasmic reticulum, and T tubules © 2013 Pearson Education, Inc.  Myofibrils Densely packed, rodlike elements ~80% of cell volume Contain sarcomeres - contractile units – Sarcomeres contain myofilaments Exhibit striations - perfectly aligned repeating series of dark A bands and light I bands © 2013 Pearson Education, Inc.  Figure 9.2b Microscopic anatomy of a skeletal muscle fiber. Diagram of part of a muscle fiber Sarcolemma showing the myofibrils. One myofibril Mitochondrion extends from the cut end of the fiber. Myofibril Dark Light Nucleus A band I band © 2013 Pearson Education, Inc.  Striations H zone: lighter region in midsection of dark A band where filaments do not overlap M line: line of protein myomesin bisects H zone Z disc (line): coin-shaped sheet of proteins on midline of light I band that anchors thin filaments and connects myofibrils to one another Thick (myosin) filaments: run entire length of an A band Thin (actin) filaments: run length of I band and partway into A band Sarcomere: region between two successive Z discs © 2013 Pearson Education, Inc.  Sarcomere Smallest contractile unit (functional unit) of muscle fiber Align along myofibril like boxcars of train Contains A band with ½ I band at each end Composed of thick and thin myofilaments made of contractile proteins © 2013 Pearson Education, Inc.  Figure 9.2c Microscopic anatomy of a skeletal muscle fiber. Thin (actin) filament Z disc H zone Z disc Small part of one myofibril enlarged to show the myofilaments responsible for the banding pattern. Each sarcomere Thick I band A band I band M line extends from one Z (myosin) Sarcomere disc to the next. filament © 2013 Pearson Education, Inc.  Figure 9.2d Microscopic anatomy of a skeletal muscle fiber. Sarcomere Thin Z disc M line Z disc (actin) filament Enlargement of Elastic one sarcomere (titin) (sectioned length- filaments wise). Notice the myosin heads on Thick the thick filaments. (myosin) filament © 2013 Pearson Education, Inc.  Myofibril Banding Pattern Orderly arrangement of actin and myosin myofilaments within sarcomere – Actin myofilaments = thin filaments Extend across I band and partway in A band Anchored to Z discs – Myosin myofilaments = thick filaments Extend length of A band Connected at M line PLEASE NOTE: the following darkened slides are condensed and simplified in the “Muscle Physiology” powerpoint. © 2013 Pearson Education, Inc.  Figure 9.3 Composition of thick and thin filaments. Longitudinal section of filaments within one sarcomere of a myofibril Thick filament Thin filament In the center of the sarcomere, the thick filaments lack myosin heads. Myosin heads are present only in areas of myosin-actin overlap. Thick filament. Thin filament Each thick filament consists of many myosin A thin filament consists of two strands of actin molecules whose heads protrude at oppositeends of the subunits twisted into a helix plus two types of filament. regulatory proteins (troponin and tropomyosin). Portion of a thick filament Portion of a thin filament Myosin head Tropomyosin Troponin Actin Actin-binding sites Heads Tail ATP- Active sites binding Actin subunits for myosin site Flexible hinge region attachment Myosin molecule Actin subunits © 2013 Pearson Education, Inc.  Figure 9.5 Relationship of the sarcoplasmic reticulum and T tubules to myofibrils of skeletal muscle. Part of a skeletal I band A band I band muscle fiber (cell) Z disc H zone Z disc M line Myofibril Sarcolemma Triad: T tubule Terminal Sarcolemma cisterns of the SR (2) Tubules of the SR Myofibrils Mitochondria © 2013 Pearson Education, Inc.  Sliding Filament Model of Contraction Generation of force Does not necessarily cause shortening of fiber Shortening occurs when tension generated by cross bridges on thin filaments exceeds forces opposing shortening © 2013 Pearson Education, Inc.  Sliding Filament Model of Contraction In relaxed state, thin and thick filaments overlap only at ends of A band Sliding filament model of contraction – During contraction, thin filaments slide past thick filaments  actin and myosin overlap more – Occurs when myosin heads bind to actin  cross bridges © 2013 Pearson Education, Inc.  Sliding Filament Model of Contraction Myosin heads bind to actin; sliding begins Cross bridges form and break several times, ratcheting thin filaments toward center of sarcomere – Causes shortening of muscle fiber – Pulls Z discs toward M line I bands shorten; Z discs closer; H zones disappear; A bands move closer (length stays same) © 2013 Pearson Education, Inc.  Figure 9.6 Sliding filament model of contraction. Slide 2 1 Fully relaxed sarcomere of a muscle fiber Z H Z I © 2013 Pearson Education, Inc. A I  Figure 9.6 Sliding filament model of contraction. Slide 3 2 Fully contracted sarcomere of a muscle fiber Z Z © 2013 Pearson Education, Inc. I A I  Physiology of Skeletal Muscle Fibers For skeletal muscle to contract – Activation (at neuromuscular junction) Must be nervous system stimulation Must generate action potential in sarcolemma – Excitation-contraction coupling Action potential propagated along sarcolemma Intracellular Ca2+ levels must rise briefly © 2013 Pearson Education, Inc.  Figure 9.7 The phases leading to muscle fiber contraction. Action potential (AP) arrives at axon terminal at neuromuscular junction ACh released; binds to receptors on sarcolemma Phase 1 Ion permeability of sarcolemma changes Motor neuron stimulates muscle fiber Local change in membrane voltage (see Figure 9.8). (depolarization) occurs Local depolarization (end plate potential) ignites AP in sarcolemma AP travels across the entire sarcolemma AP travels along T tubules Phase 2: SR releases Ca2+; Ca2+ binds to Excitation-contraction troponin; myosin-binding sites coupling occurs (see (active sites) on actin exposed Figures 9.9 and 9.11). Myosin heads bind to actin; contraction begins © 2013 Pearson Education, Inc.  The Nerve Stimulus and Events at the Neuromuscular Junction Skeletal muscles stimulated by somatic motor neurons Axons of motor neurons travel from central nervous system via nerves to skeletal muscle Each axon forms several branches as it enters muscle Each axon ending forms neuromuscular junction with single muscle fiber – Usually only one per muscle fiber © 2013 Pearson Education, Inc.  Figure 9.8 When a nerve impulse reaches a neuromuscular junction, acetylcholine (ACh) is released. Slide 1 Myelinated axon of motor neuron Action potential (AP) Axon terminal of neuromuscular junction Sarcolemma of the muscle fiber 1 Action potential arrives at axon terminal of motor neuron. 2 Voltage-gated Ca2+ channels Synaptic vesicle open. Ca2+ enters the axon terminal containing ACh moving down its electochemical Axon terminal Synaptic gradient. of motor neuron cleft Fusing synaptic 3 Ca2+ entry causes ACh (a vesicles neurotransmitter) to be released by exocytosis. ACh Junctional folds of 4 ACh diffuses across the synaptic sarcolemma cleft and binds to its receptors on Sarcoplasm of the sarcolemma. muscle fiber 5 ACh binding opens ion Postsynaptic channels in the receptors that membrane allow simultaneous passage of ion channel opens; Na+ into the muscle fiber and K+ ions pass. out of the muscle fiber. More Na+ ions enter than K+ ions exit, which produces a local change in the membrane potential called Degraded ACh the end plate potential. ACh Ion channel closes; ions cannot pass. 6 ACh effects are terminated by its breakdown in the synaptic cleft by acetylcholinesterase and Acetylcho- © 2013 Pearson Education, Inc. diffusion away from the junction. linesterase  Neuromuscular Junction (NMJ) Situated midway along length of muscle fiber Axon terminal and muscle fiber separated by gel-filled space called synaptic cleft Synaptic vesicles of axon terminal contain neurotransmitter acetylcholine (ACh) Junctional folds of sarcolemma contain ACh receptors NMJ includes axon terminals, synaptic cleft, junctional folds © 2013 Pearson Education, Inc.  Events at the Neuromuscular Junction Nerve impulse arrives at axon terminal  ACh released into synaptic cleft ACh diffuses across cleft and binds with receptors on sarcolemma  Electrical events  generation of action potential © 2013 Pearson Education, Inc.  Destruction of Acetylcholine ACh effects quickly terminated by enzyme acetylcholinesterase in synaptic cleft – Breaks down ACh to acetic acid and choline – Prevents continued muscle fiber contraction in absence of additional stimulation © 2013 Pearson Education, Inc.  Figure 9.9 Summary of events in the generation and propagation of an action potential in a skeletal Slide 4 muscle fiber. Open Na+ Closed K+ channel channel Na + – – – – – ––– – – – –– – – – ––– + + + + ACh-containing + + + ++ ++ + + + + + + + + + – – – – synaptic vesicle K + Axon terminal of neuromuscular Action potential Ca2+ junction Ca2+ Synaptic cleft 2 Depolarization: Generating and propagating an action potential (AP). The local depolarization current spreads to adjacent areas of the sarcolemma. This opens voltage-gated sodium channels there, so Na+ enters following its electrochemical gradient and initiates the AP. The AP is propagated as its local depolarization wave spreads to adjacent areas of the sarcolemma, opening voltage-gated channels there. Again Na+ diffuses into the cell following its electrochemical gradient. Wave of depolarization Closed Na+ Open K+ 1 end plate potential is generated at the channel channel An neuromuscular junction (see Figure 9.8). Na+ + + + + + + + + + + + + + + + + + + + ++ + – – – – – ––– – – – – – –– –– –– – –– K+ 3 Repolarization: Restoring the sarcolemma to its initial polarized state (negative inside, positive outside). Repolarization occurs as Na+ channels close (inactivate) and voltage-gated K+ channels open. Because K+ concentration is substantially higher inside the cell © 2013 Pearson Education, Inc. than in the extracellular fluid, K+ diffuses rapidly out of the muscle fiber.  Figure 9.10 Action potential tracing indicates changes in Na + and K+ ion channels. +30 Membrane potential (mV) Na+ channels close, K+ channels Depolarization open due to Na+ entry 0 Repolarization due to K+ exit Na+ channels open K+ channels closed –95 0 5 10 15 20 © 2013 Pearson Education, Inc. Time (ms)  Excitation-Contraction (E-C) Coupling Events that transmit AP along sarcolemma lead to sliding of myofilaments AP brief; ends before contraction – Causes rise in intracellular Ca2+ which  contraction Latent period – Time when E-C coupling events occur – Time between AP initiation and beginning of contraction © 2013 Pearson Education, Inc.  Events of Excitation-Contraction (E-C) Coupling AP propagated along sarcomere to T tubules Voltage-sensitive proteins stimulate Ca2+ release from SR – Ca2+ necessary for contraction © 2013 Pearson Education, Inc.  Figure 9.11 Excitation-contraction (E-C) coupling is the sequence of events by which transmission of an Slide 3 action potential along the sarcolemma leads to the sliding of myofilaments. Steps in E-C Coupling: Sarcolemma 1 The action potential (AP) Voltage-sensitive T tubule tubule protein propagates along the sarcolemma and down the T tubules. Ca2+ 2 Calcium ions are released. release Transmission of the AP along the channel T tubules of the triads causes the Terminal voltage-sensitive tubule proteins to cistern change shape. This shape change of SR opens the Ca2+ release channels in the terminal cisterns of the sarcoplasmic reticulum (SR), allowing Ca2+ to flow into the cytosol. Actin Troponin Tropomyosin blocking active sites Myosin 3 Calcium binds to troponin and removes the blocking action of tropomyosin. When Ca2+ binds, troponin changes shape, exposing binding Active sites exposed and sites for myosin (active ready for myosin binding sites) on the thin filaments. 4 Contraction begins: Myosin binding to actin forms cross bridges and contraction (cross bridge Myosin cycling) begins. At this cross point, E-C coupling is over. bridge The aftermath When the muscle AP ceases, the voltage-sensitive tubule proteins return to their original shape, closing the Ca2+ release channels of the SR. Ca2+ levels in the sarcoplasm fall as Ca2+ is continually pumped back into the SR by active transport. Without Ca2+, the blocking action of tropomyosin is restored, myosin-actin interaction is inhibited, and relaxation occurs. Each © 2013 Pearson Education, Inc. time an AP arrives at the neuromuscular junction, the sequence of E-C coupling is repeated.  Channels Involved in Initiating Muscle Contraction Nerve impulse reaches axon terminal  voltage- gated calcium channels open  ACh released to synaptic cleft ACh binds to its receptors on sarcolemma  opens ligand-gated Na+ and K+ channels  end plate potential  Opens voltage-gated Na+ channels  AP propagation  Voltage-sensitive proteins in T tubules change shape  SR releases Ca2+ to cytosol © 2013 Pearson Education, Inc.  Role of Calcium (Ca2+) in Contraction At low intracellular Ca2+ concentration – Tropomyosin blocks active sites on actin – Myosin heads cannot attach to actin – Muscle fiber relaxed © 2013 Pearson Education, Inc.  Role of Calcium (Ca2+) in Contraction At higher intracellular Ca2+ concentrations – Ca2+ binds to troponin Troponin changes shape and moves tropomyosin away from myosin-binding sites Myosin heads bind to actin, causing sarcomere shortening and muscle contraction – When nervous stimulation ceases, Ca2+ pumped back into SR and contraction ends © 2013 Pearson Education, Inc.  Cross Bridge Cycle Continues as long as Ca2+ signal and adequate ATP present Cross bridge formation—high-energy myosin head attaches to thin filament Working (power) stroke—myosin head pivots and pulls thin filament toward M line © 2013 Pearson Education, Inc.  Cross Bridge Cycle Cross bridge detachment—ATP attaches to myosin head and cross bridge detaches "Cocking" of myosin head—energy from hydrolysis of ATP moves myosin head into high-energy state © 2013 Pearson Education, Inc.  Figure 9.12 The cross bridge cycle is the series of events during which myosin heads pull thin filaments Slide 1 toward the center of the sarcomere. Actin Ca2+ Thin filament Myosin cross bridge Thick filament Myosin 1 Cross bridge formation. Energized myosin head attaches to an actin myofilament, forming a cross bridge. ATP hydrolysis 4 Cocking of the myosin head. As 2 The power (working) stroke. ADP and ATP is hydrolyzed to ADP and Pi, the Pi are released and the myosin head pivots myosin head returns to its prestroke and bends, changing to its bent high-energy, or “cocked,” position. * low-energy state. As a result it pulls the actin filament toward the M line. In the absence of ATP, myosin heads will not detach, causing rigor mortis. *This cycle will continue as long as ATP is available and Ca2+ is 3 Cross bridge detachment. After ATP bound to troponin. attaches to myosin, the link between myosin and actin weakens, and the myosin head © 2013 Pearson Education, Inc. detaches (the cross bridge “breaks”). Principles of Muscle Mechanics Contraction may/may not shorten muscle – Isometric contraction: no shortening; muscle tension increases but does not exceed load – Isotonic contraction: muscle shortens because muscle tension exceeds load Force and duration of contraction vary in response to stimuli of different frequencies and intensities Motor unit = motor neuron and all (four to several hundred) muscle fibers it supplies – Smaller number = fine control  Homeostatic Imbalance Myasthenia gravis – Complex autoimmune disorder in which antibodies destroy neuromuscular junctions – Affects voluntary muscles, especially those in the eyes, mouth, throat, and limbs © 2013 Pearson Education, Inc.  Homeostatic Imbalance Strain = muscle; sprain = ligament Rigor mortis – Cross bridge detachment requires ATP – 3–4 hours after death muscles begin to stiffen with weak rigidity at 12 hours post mortem Dying cells take in calcium  cross bridge formation No ATP generated to break cross bridges © 2013 Pearson Education, Inc.  Muscular Dystrophy Duchenne muscular dystrophy (DMD): – Most common and severe type – Inherited, sex-linked, carried by females and expressed in males (1/3500) as lack of dystrophin Cytoplasmic protein that stabilizes sarcolemma Fragile sarcolemma tears  Ca2+ entry  damaged contractile fibers  inflammatory cells  muscle mass drops – Victims become clumsy and fall frequently; usually die of respiratory failure in 20s © 2013 Pearson Education, Inc.  Polio Fecal-oral contamination virus Causes muscle paralysis by destroying motor neurons © 2013 Pearson Education, Inc.  Muscle Action Type Agonist - the main mover of the joint Antagonist – a muscle that oppose or reverse joint actions Synergist – muscles that help the agonist Fixator – muscles that hold bones stable for an agonist at another joint © 2013 Pearson Education, Inc.  Muscle Names Location Size Shape Direction of fibers Number of origins Attachments (origins then insertions) Movement actions © 2013 Pearson Education, Inc. How Are Muscles Named? Some muscles are named based on the direction of their fibers. Rectus means straight. – Rectus abdominis. Oblique means diagonally arranged. – External abdominal oblique.  Muscles within a group may have different names based on their size. Maximus and longus indicates a larger muscle. Minimus and brevis indicate a  Muscles may also be named based on their relative location to other muscles. – Medial means towards the midline of the body. – Lateral means towards the sides of the body.  Prefixes like bi- and tri- may be used to indicate multiple heads or attachment sites. – Bi – Two attachment sites. – Tri – Three attachment sites.  Muscles may also be named based on their origin and insertion bones. – The origin is an attachment to a immoveable bone. – The insertion is an attachment to  If a muscle resembles a shape, it can be named after that shape. – Delta is a Greek letter shaped like a triangle. – Trapezius is shaped like a trapezoid.  Finally, muscle names may indicate a specific action they perform. – Flex means to bend a joint. – Extend means to straighten a joint. – Abductors  Zygo Fronta Temp matic lis oralis Bone Orbiculari s Oculi Zygom aticus Trape Orbic zius ularis Oris Sternocleid Bucci Masse omastoid nator ter Head and Neck Muscles The frontalis raises the eyebrows. The masseter and temporalis both elevate the mandible. – Chewing muscles The buccinator flattens the cheeks during chewing, holding them against the teeth. The orbicularis oculi performs all eyelid movements, including opening, closing, blinking, etc. The orbicularis oris closes the mouth with the lips.  Trapeziu Sternocleidomas s toid Clavicle (Sternum) Pectoralis Deltoid Major Latissimus Serratus Dorsi Anterior External Internal Abdominal Abdominal Rectus Oblique Oblique Abdominis  Muscles of the Trunk The pectoralis major adducts the humerus. The rectus abdominis flexes the vertebral column and compresses the contents of the abdomen. – The “pushing” muscle of defecation, childbirth, and forced breathing. – The transversus abdominis also performs this action. The external and internal obliques rotate the trunk.  Sternocleidomast oid Trapezius Deltoid Infraspinatu Teres Major s Latissim us Dorsi External Oblique Muscles of the Dorsal Trunk The trapezius elevates and depresses the scapula. The latissimus dorsi adducts the humerus. The deltoid abducts the arm. The teres major and infraspinatus rotate and adduct the humerus. Anterior Muscles of the Arm The biceps brachii and brachioradialis flex the arm. The triceps brachii extends the arm. The extensor carpi radialis and ulnaris extend the wrist. – Each muscle has a flexor antagonist that flexes the wrist. The extensor digitorum extends the four non-thumb digits.  Front Side Posterior Deltoid Biceps Triceps Brachii Brachii Brachio- Brachioradialis Extensor radialis Digitorum Extensor Extensor Digitorum Flexor carpi carpi radialis Extensor carpi ulnaris Flexor ulnaris carpi ulnaris Muscles of the Hip, Thigh, and Leg The gluteus maximus abducts the leg. The gluteus medius abducts the leg. The hamstring group flexes the knee. – Biceps femoris – Semitendinosus – Semimembranosus The gastrocnemius and soleus extend the foot.  Gluteus medius Gluteus maximus Posterior Semitendino Muscles Biceps sus of the Leg Semimembranos femoris us Gastrocnemiu s Soleus Muscles of the Hip, Thigh, and Leg The gracilis adducts and rotates the hip. The tensor fascia latae abducts the hip. The sartorius flexes, abducts, and laterally rotates the thigh. – Look at the bottom of your foot while standing to demonstrate these actions. The quadriceps group extends the knee. – Rectus femoris – Vastus medialis – Vastus lateralis – Vastus intermedialis (a deep muscle) The tibialis anterior and fibularis muscles flex the foot.  Gluteus medius Tensor Fascia Latae Gracili Sartorius Anterior s Rectus Muscles of Femoris Vastus the Leg Medialis Vastus Lateralis Fibularis Tibialis Soleus Anterior  Temporali Frontalis s Orbicularis Oculi Zygomaticus Masseter Orbicularis Oris Sternocleidomastoid Pectoralis Major Deltoid Biceps Brachii Rectus Abdominis External Oblique Internal Oblique Gluteus Medius Tensor Fascia Latae Adductor (Groin)Gracili s Sartorius Rectus Femoris Vastus Lateralis Vastus Medialis Tibialis Anterior Fibularis Longus Soleus  Muscle Movements Muscles move joints in specific ways, according to the orientation of the muscle, its origin(s), and its insertion(s). Flexor vs Extensor Abductor vs Adductor Rotator (pronator vs supinator) There are others, just the movements are less common (levator vs depressor...) © 2013 Pearson Education, Inc.  Muscle Fiber Type Classified according to two characteristics – Speed of contraction: slow or fast fibers (slow/fast twitch) according to Speed at which myosin ATPases split ATP Pattern of electrical activity of motor neurons – Metabolic pathways for ATP synthesis Oxidative fibers—use aerobic pathways Glycolytic fibers—use anaerobic glycolysis © 2013 Pearson Education, Inc.  Exercise Isotonic vs isometric – Same tone/ tension vs same distance – E.g. pushups vs plank Anaerobic vs aerobic – Anaerobic respiration is done without oxygen and results in lactic acid formation Fermentation Oxygen debt – Aerobic respiration requires oxygen, and uses a different pathway in the mitochondria © 2013 Pearson Education, Inc.