ZOO 331 Muscles
Describe a muscle fiber action potential and be able to graph the change in membrane potential over time
#44
Be able to draw a sarcomere with A bands, I bands, Z discs, H zones and M lines
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Describe three ways in which ATP is regenerated during skeletal muscle contraction.
- ATP only source used directly for contractile activities - move and detach cross bridge - Ca pumps in SR - return of Na+ & K+ after E-C coupling - available stores depleted in 4-6 seconds - ATP regenerated by: 1) Hydrolysis of creatine phosphate - high energy molecule stored in muscle - combine w/ stored ATP allows maximal muscle power for 15 seconds 2) Anaerobic pathway (glycolysis & lactic acid) - glycolysis: doesnt require oxygen - at 70% of max contractile activity bulging muscles compress blood vessels; oxygen delivery impaired ; pyruvic acid converted to lactic acid (yields only 5% as much ATP as aerobic respiration but produces 1.5x faster) 3) Aerobic respiration (krebs cycle & oxidative preparation) - breaks glucose into CO2, H2O, & large amount of ATP - requires oxygen - 95% of ATP during rest & light to moderate exercise Muscle fatigue: physiological inability to contract despite continued stimulation - short duration ex: ionic imbalances (K+ in T tubules) halts Ca2+ release from SR - not due to lactic acid - prolonged low intensity ex may damage SR & interface w/ Ca2+
What is botulism, what causes it, and what area of the NMJ does it affect?
- Clostridum botulinum: soil & water - spores are present on food - botulinum toxin released - blocks release of ACh on NMJ - Symptoms: flaccid paralysis
What is rigor mortis and what causes it?
- Cross bridge detachment requires ATP - 3 to 4 hours after death, muscles begin to stiffen - peak rigidity at 12 hours post mortem - dying cells take in Ca2+ --> cross bridge formation - no ATP generated to break cross bridges - 48 to 60 hrs muscle proteins break down leading to loss of rigidity
What 4 factors affect the force of muscle contraction?
- Depends on number of cross bridges attached which is affected by: 1) Frequency of stimulation 2) Number of muscle fibers stimulated (recruitment) 3) Relative size of fibers -- hypertrophy of cells increases strength vs. atrophy (enlarging) 4) Degree of muscle stretch
Describe the sliding filament model of muscle contraction
- During contraction: - thin filaments slide past thick filaments --> actin & myosin overlap more - occurs when myosin heads bind to actin --> cross bridges
Define motor unit and muscle twitch, and describe the events occurring during the three phases of a muscle twitch. What is a myogram?
- each muscle served by at least one motor nerve, which contain axons of up to hundreds of motor neurons Motor Unit: - motor neuron + all muscle fibers it innervates (smaller number = fine control) - muscle fibers from motor unit spread throughout muscle so single motor unit causes weak contraction of entire muscle -motor units contract asynchronously to prevent fatigue Myogram: graphical representation of muscle contractions Muscle twitch (motor units response to single AP of motor neuron) - latent period - contraction - relaxation
Follow the events of excitation-contraction coupling that lead to cross bridge activity
- events that transmit AP along sarcolemma lead to sliding of myofilaments - AP brief; ends before contraction --> causes rise in intracellular Ca2+ which causes contraction - NMJ sets stage for E-C by providing excitation from released ACh on sarcolemma which triggers AP 1) AP propogates along sarcolemma and down T tubules 2) Ca2+ released 3) Ca2+ binds to troponin & removes blocking action of tropomyosin -- when Ca2+ binds, troponin changes shape, exposing binding sties for myosin (active sites) on thin filaments 4) contraction begins: myosin binding to actin forms cross bridges and contraction beings -- E-C- is over now Summary: #51
Explain how muscle fibers are stimulated to contract by describing events that occur at the neuromuscular junction
- muscle fiber must be activated - muscle fiber must generate an action potential - action potential must be linked to contraction: excitation - contraction coupling NMJ: 1) AP arrives at axon terminal of motor neuron 2) volt-gated Ca2+ channels open, Ca2+ enters axon terminal 3) Ca2+ entry causes ACh to be released by exocytosis 4) ACh diffuses across synaptic cleft & binds to receptor on sarcolemma 5) ACh binding opens ion channels in the receptors that allow simultaneous passage of Na+ into the muscle fiber and K+ out of muscle fiber 6) ACh effects are terminated by its breakdown in the synaptic cleft by acetylcholinesterase and diffusion away from the junction
Compare and contrast the three basic types of muscle tissue as discussed in class regarding tissue location, cell shape and size and regulation of contraction.
-Nearly half of body's mass -transforms chemical E (ATP) to mechanical E - 3 types: skeletal, cardiac, smooth
Be able to describe the events that occur in the cross bridge cycle?
1) Cross bridge formation: energized myosin head attaches to actin myofilament, forming a cross bridge 2) Power Stroke: ADP and Pi are released and myosin head pivots and bends, changing to its bent, low energy state -- pulls actin filament towards M line 3) Cross bridge detachment: After ATP attaches to myosin, the link between myosin and actin weakens and myosin head detaches (cross bridge breaks) 4) Cocking of myosin head: As ATP is hydrolyzed to ADP and Pi, myosin head returns to its prestroke high energy or cocked position --> cycle will continue as long as ATP is available and Ca2+ is bound to troponin
Describe how an action potential is generated. What is an end plate potential? How is the action potential propagated?
1) End plate potential = local deplorization - ACh binding opens chemically (ligand) gated ion channels - simultaneous diffusion of Na+ (inward) and K+ (outward) - more Na+ diffuses in so interior of sarcolemma becomes less negative 2) Depolarization - end plate potential spreads to adjacent membrane areas - voltage gated Na+ channels open - Na+ influx decreases membrane voltage toward threshhold --> if threshold is reached, AP initated, then unstoppable --> AP spreads across sarcolemma --> voltage gated Na+ channels open in adjacent patch, causing it to depolarize to threshold 3) Repolarization - Na+ channels inactivate and voltage - gated K + channels open - K+ efflux rapidly restores resting polarity - fiber cannot be stimulated - in refractory period until repolarization complete - ionic condition of resting state restored by Na+ - K+ pump Summary: #45
List four main functions of muscle tissue, as well as the additional functions described in class.
1) movement of bones or fluids 2) maintaining posture or body position 3) stabilizing joints 4) heat generation + protects organs + goosebumps
Explain how smooth, graded contractions of a skeletal muscle are produced. What is fused and unfused tetany.
1] Frequency of stimulation: - Temporal summation: increased stimulus frequency (muscle does not completely relax between stimuli) --> 2nd contraction of greater force - Additional Ca2+ release w/ second stimulates more short - if stimuli are given quickly enough ,muscle reaches maximal tension --> fused (complete tetany) results - smooth sustained contractions - no muscle relaxation leads to muscle fatigue --> muscle can't contract so zero tension - motor units are activated asynchronously --> at any one time, some are infused tetanus and some are resting to prevent or delay fatigue
What are the adaptations that occur with aerobic exercise?
Aerobic (endurance) exercise: - leads to increased: muscle capillaries and myoglobin synthesis - results in greater endurance, strength, and resistance to fatigue - may convert fast glycolytic fibers into fast oxidative
Know the definitions of an agonist, antagonist and synergist and give an example of each during flexion of the elbow.
Agonist (prime mover) -major responsibility for producing specific movement -biceps brachii, brachialis Antagonist -opposes or reverses particular movement - agonist & antagonist on opposite sides of joints across which they act -triceps brachii Synergist -helps prime movers -adds extra force to same movement -reduces undesirable or unnecessary movement -brachioradialis
Describe three types of skeletal muscle fibers and explain the relative value of each type.
Classified according to: 1) Speed of contraction: slow or fast fibers -- speed at which myosin ATPase split ATP ; pattern of electrical activity of motor neurons 2) Metabolic pathways for ATP synthesis -- oxidative (aerobic), glycolytic (anaerobic) - most muscles contain mixture of fiber types --> range of contractile speed, fatigue resistance - all fibers in one motor unit are all the same type - genetics dictate individual % Myoglobin: red appearing proteins, oxygen binding Three types of skeletal muscle fibers: 1) Slow oxidative fibers - slow speed of contarction - slow myosin ATPase activity - high myoglobin content & extensive blood supply - slow to fatigue - red due to myoglobin 2) Fast glycolytic fibers - fast fibers are quick to contract -fast myosin ATPase activity - low myoglobin content - white in color - fatigue easily -anaerobic glycolysis 3) Fast oxidative fibers - fast speed of contraction -fast myosin ATPase activity - high myoglobin content - aerobic - intermediate role of fatigue - pink
Describe the gross structure of a skeletal muscle including the muscle shapes based on the fascicle arrangement and surrounding connective tissue.
Convergent: fascicles come together into a common tendon (pectoralis major) Circular = sphincter: fascicles are in concentric rings around a body opening (orbicularis oris) Parallel: fascicles run parallel to long axis of muscle (sartorius) Unipennate: tendon runs through the body and fibers come off one side (extensor digitorum longus) Bipennate: more common, fibers come off both sides of tendon (rectus femoris) Multipennate: many pennate muscles together (deltoid) -pennate = more force - parallel = more movement
What is hypertrophy and atrophy. What changes occur in the muscle fibers?
Hypertrophy: - increased size of muscle fibers (from resistance exercise) - more myofribrils & myofilaments - more mitochondria & blood supply Atrophy: - loss of muscle mass - loss of proteins - never regain those cells - Length-tension relationship: muscle fibers generate maximal force at 80-120% normal resting length
Differentiate between isometric and isotonic contractions
Isometric: - does not change in height - muscle tension increases but doesn't change the load Isotonic: - muscle shortens because muscle tension exceeds load
Understand the concepts presented in the malignant hyperthermia case study.
Malignant Hyperthermia: -inherited autosomal dominant disease - can cause rapid rise in temperature during general anesthesia - life threatening - due to mutation in RYR1 gene - causes calcium release channels in the sarcoplasmic reticulum to open more easily and close more slowly in presence of certain anestetics
Describe the microscopic structure and functional roles of the sarcolemma, myofibrils, myofilaments, sarcoplasmic reticulum, and T tubules of skeletal muscle fibers.
Muscle fiber: long cylindrical cell up to 30 cm long Sarcolemma: plasma membrane Sarcoplasm = cytoplasm Sarcoplasmic Reticulum - network of smooth endoplasmic reticulum surrounding each myofibril - functions in regulation of intracellular Ca2+ levels (stores & releases) Myofibril - densely packed, rodlike elements -perfectly aligned repeating series of dark A bands and light I bands give muscle fiber strations Sarcomere - smallest contractile unit - **functional unit of muscle fiber - region between 2 successive Z discs T Tubules: - continuations of sarcolemma - lumen continuous with extracellular space - associate with paired (2) terminal cisterns to form triads that encircle each sarcomere
Know the various ways muscles are named
Muscle location: bone or body region with which muscle associated Muscle shape: deltoid muscle (deltoid=triangle) Muscle size: maximus, minimus, longus, brevis Direction of muscle fibers or fascicles: rectus (straight), transversus (right angles), oblique (angles) Number of origins: biceps (2), triceps (3) Location of attachments: origin & insertion Muscle action: flexor vs. extensor
Define muscle tension and load.
Muscle tension: muscle force exerted by contracting muscle on an object Load: opposing force worked on muscle by the weight of an object contraction may or may not shorten muscle: 2 types = isometric, isotonic
Be able to discuss what occurs at the neuromuscular junction. (skeletal muscle attachment)
Origin: attachment that is more proximal / more stationary Insertion: attachment that is more distal or more mobile Belly = body = main region that shortens & thickens when it contracts -- creates the action
How does recruitment occur in the lab and in the body? What is the benefit of recruitment?
Recruitment controls force of contraction - works on size principle: motor units w/ smallest muscle fibers recruited first -- largest motor unit activated only for most powerful contraction In lab: recruitment achieved by delivering stronger & stronger stimulus to muscle In body: activation of increasingly larger # of motor units -- contraction force controlled by recruitment
Know the characteristics of muscle as described in Table 9.3 from the text.
SKELETAL -attached to bones or skin - single, very long, cylindrical multinucleate cells w/ obvious striations -voluntary -requires nervous system stimulation CARDIAC -intercalated discs: cell to cell comm
Describe the structure of the thick and thin filaments including troponin, tropomyosin, actin and myosin. What is titan and what does it do?
Thick filament - composed of myosin molecules (protein) - myosin tails - myosin heads: binding sites for actin & ATP Thin filament: - twisted double strand of fibrous protein, actin - tropomyosin and troponin - regulatory proteins bound to actin -- control myoson-actin interaction Elastic filament - composed of protein TITIN - extends from Z disc to thick filament to M line - holds thick filaments in place - helps recoil after stretch -resists excessive stretching