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  • Answer: c. myofibrils
  • Answer: a. sarcomere
  • Answer: b. titin
  • Answer: d. store calcium ions
  • Answer: a. muscle fibers
  • Answer: d. Lemma
  • Answer: b. Skeletal
  • Answer: c. Cardiac and skeletal
  • Answer: d. Heat generation
  • Answer: b. nerve
  • Answer: c. Myofibrils
  • Answer: a. sarcomere
  • Answer: b. Titin
  • Answer: d. Store calcium ions
  • Answer: c. the H zone becomes less obvious and the Z-discs move closer together
  • Answer: c. binding of acetylcholine to membrane receptors on the sarcolemma
  • Answer: b. depolarization
  • Answer: a. sodium ions
  • Answer: a. latent period
  • Answer: a. Calcium binds to troponin, changing its shape and removing the blocking action of tropomyosin.
  • Answer: b. ATP hydrolysis promotes myosin head detachment from actin
  • Answer: a. small
  • Answer: b. recruitment occurs and more motor units respond to stronger stimuli
  • Answer: d. maintaining an upright posture
  • Answer: a. anaerobic; aerobic
  • Answer: d. fast oxidative
  • Answer: c. calcium ion influx occurs mostly from the extra cellular fluid in smooth muscle
  • Answer: b. gap junctions

Muscle Muscle Presentation Transcript

  • Why do I care?
    • You like to move
  • Muscle Similarities
    • Skeletal and smooth muscle cells are elongated and are called muscle fibers
    • Muscle contraction depends on two kinds of myofilaments – actin and myosin
    • Muscle terminology is similar
      • Sarcolemma – muscle plasma membrane
      • Sarcoplasm – cytoplasm of a muscle cell
      • myo, mys, and sarco all refer to muscle
  • Skeletal Muscle Tissue
    • Attach to the skeleton
    • Striations
    • Voluntary
    • Contracts rapidly, tires easily
    • Is responsible for movement
    • Is extremely adaptable and can exert a wide range of forces
  • Cardiac Muscle Tissue
    • In the heart
    • Striated
    • Involuntary
    • Contracts at a steady rate set by the pacemaker
    • Neural controls allow the heart to respond to changes in bodily needs
  • Smooth Muscle Tissue
    • Found in the walls of hollow organs, such as the stomach, urinary bladder, and respiratory passages
    • Forces food and other substances through internal body channels
    • It is not striated and is involuntary
    • muscle cells are referred to as?
    • muscle fibers
    • What prefixes mean muscle?
    • mys, myo, sarco
    • What type of muscle is subject to conscious control?
    • Skeletal
    • What muscle types appear striated?
    • skeletal and cardiac
  • Functional Characteristics of Muscle Tissue
    • Excitability– the ability to receive and respond to stimuli
    • Contractility – the ability to shorten
    • Extensibility – the ability to be stretched
    • Elasticity – the ability to recoil
    • Identify four important functions of muscle tissue
    • Locomotion
    • Maintain posture
    • Stabilize joints
    • Generate heat
    • pumping blood
    • blood pressure, peristalsis
    • Describe the structure and function of the gross and microscopic structures of skeletal muscle
  • Skeletal Muscle
    • Each muscle is a discrete organ composed of muscle tissue, blood vessels, nerve fibers, and connective tissue
  • Figure 9.2a InterActive Physiology ®: Anatomy Review: Skeletal Muscle Tissue, pages 4-6 PLAY
  • Table 9.1a
  • Myofibrils Figure 9.3b InterActive Physiology ®: Anatomy Review: Skeletal Muscle Tissue, pages 7-8 PLAY
  • Structure and Organization Table 9.1b
  • Microscopic Anatomy of a Skeletal Muscle Fiber
    • Each fiber is a long, cylindrical cell with multiple nuclei just beneath the sarcolemma
  • Microscopic Anatomy of a Skeletal Muscle Fiber
    • Sarcoplasm has numerous glycosomes and a unique oxygen-binding protein called myoglobin
    • Fibers contain the usual organelles, myofibrils, sarcoplasmic reticulum, and T tubules
  • Myofibrils
    • Myofibrils are densely packed, rodlike contractile elements
    • They make up 80% of the muscle volume
    • Dark A bands and light I bands appear because of the arrangement of myofibrils
  • Sarcomeres Figure 9.3c InterActive Physiology ®: Anatomy Review: Skeletal Muscle Tissue, page 9 PLAY
    • The smallest contractile unit of a muscle
    • The region of a myofibril between two successive Z discs
    • Composed of myofilaments made up of contractile proteins
    • Thick filaments (Myosin)– extend the entire length of an A band
    • Thin filaments (Actin) – extend across the I band and partway into the A band
    • Z-disc – coin-shaped sheet of proteins (connectins) that anchors the thin filaments and connects myofibrils to one another
    • H zone- no overlap
  • Figure 9.3c,d
    • 1. What is the smallest functional unit of skeletal muscle?
    • 2. Give 4 functions of skeletal muscle.
  • Ultrastructure of Myofilaments: Thick Filaments Figure 9.4a,b
  • Thick Filaments
    • Thick filaments are composed of the protein myosin
    • Each myosin molecule has a rod-like tail and two globular heads
      • Tails – two interwoven, heavy polypeptide chains
      • Heads – two smaller, light polypeptide chains called cross bridges
  • Ultrastructure of Myofilaments: Thin Filaments Figure 9.4c
  • Thin Filaments
    • Thin filaments are made of actin
    • Each actin molecule is a helical polymer of globular subunits called G actin
    • The subunits contain the active sites to which myosin heads attach during contraction
    • Tropomyosin and troponin are regulatory subunits bound to actin
  • Arrangement of the Filaments in a Sarcomere Figure 9.4d
  • Sarcoplasmic Reticulum (SR)
    • Smooth ER that surrounds each myofibril
    • stores calcium
  • T Tubules
    • Continuation of sarcolemma
    • Conduct impulses to the deepest part of the muscle
    • These impulses cause the release of Ca 2+
  • Which of the following components accounts for the bulk muscle fiber volume (up to 80%)?
    • a. glycosomes
    • b. mitochondria
    • c. myofibrils
    • d. sarcoplasm
  • The functional unit of a muscle fiber is the __________.
  • The thin filaments are not comprised of which of the following components?
    • a. actin
    • b. titin
    • c. troponin
    • d. tropomyosin
  • What is the major function of the sarcoplasmic reticulum?
    • a. store sodium ions
    • b. store potassium ions
    • c. expel calcium ions from the cell
    • d. store calcium ions
  •  
  • Important steps
    • Action potential comes from nerve
    • Acetylcholine is released
    • Action potential is generated in the muscle
    • Action potential travels down the T-tubules
    • Calcium is released
  • Skeletal Muscle Contraction Figure 10–9 (Navigator)
  • Skeletal Muscle Innervation Figure 10–10a, b (Navigator)
  • Neuromuscular Junction Figure 9.7 (a-c)
  • Neuromuscular Junction
    • When a nerve impulse reaches the neuromuscular junction Acetylcholine (Ach) is released
    InterActive Physiology ®: The Neuromuscular Junction, pages 3-5 PLAY
  • Destruction of Acetylcholine
    • ACh destroyed by the enzyme acetylcholinesterase
    • This prevents continuous contraction
    InterActive Physiology ®: The Neuromuscular Junction, pages 6-10 PLAY
  • Ion Channels
    • protein channels in the cell membrane that can be opened by chemicals or electrically
  • Action Potential
    • An electrical signal that is spread by the difference in charge across a membrane
  • Na+ K+
  • Action potential
    • At rest, cell has negative charge
    • ACh causes Na channels to open, positive Na ions come into the cell, making the inside of the cell more positive
    • This causes more Na channels to open, more positive Na ions come into the cell, and the current spreads down the cell
    • When Na channels close the inside of the cell is negative again
  • Action potential review
    • At rest, the inside of the cell has negative charge
    • ACh causes Na channels to open, positive Na ions come into the cell, making the inside of the cell more positive
    • This causes more Na channels to open, more positive Na ions come into the cell, and the current spreads down the cell
    • When Na channels close the inside of the cell becomes negative again
  • Excitation-Contraction Coupling
    • Once generated, the action potential:
      • Travels along the sarcolemma, down the T tubules
      • Triggers Ca 2+ release
    • Ca 2+ binds to troponin and causes Actin binding sites to be exposed
  • Excitation-Contraction Coupling
    • Myosin cross bridges alternately attach and detach
    • Thin filaments move toward the center of the sarcomere
    • Hydrolysis of ATP powers this cycling process
    • Ca 2+ is removed into the SR, tropomyosin blockage is restored, and the muscle fiber relaxes
  • Role of (Ca 2+ )
    • At low [Ca 2+ ] Tropomyosin blocks the binding sites on actin
      • Myosin cross bridges cannot attach
    Figure 9.11a
  • At high [Ca 2+ ]
    • Calcium binds to troponin
    • Troponin changes shape
    • tropomyosin moves away from actin’s binding sites
    Figure 9.11b
  • Figure 9.10 Synaptic cleft Synaptic vesicle Axon terminal ACh ACh ACh Neurotransmitter released diffuses across the synaptic cleft and attaches to ACh receptors on the sarcolemma.
  • Figure 9.10 Net entry of Na + Initiates an action potential which is propagated along the sarcolemma and down the T tubules. T tubule Sarcolemma Synaptic cleft Synaptic vesicle Axon terminal ACh ACh ACh Neurotransmitter released diffuses across the synaptic cleft and attaches to ACh receptors on the sarcolemma. 1
  • Figure 9.10 Net entry of Na + Initiates an action potential which is propagated along the sarcolemma and down the T tubules. T tubule Sarcolemma SR tubules (cut) Synaptic cleft Synaptic vesicle Axon terminal ACh ACh ACh Neurotransmitter released diffuses across the synaptic cleft and attaches to ACh receptors on the sarcolemma. Action potential in T tubule activates voltage-sensitive receptors, which in turn trigger Ca 2+ release from terminal cisternae of SR into cytosol. SR Ca 2+ Ca 2+ Ca 2+ Ca 2+ Ca 2+ Ca 2+ Ca 2+ Ca 2+ 1 2
  • Figure 9.10 Net entry of Na + Initiates an action potential which is propagated along the sarcolemma and down the T tubules. T tubule Sarcolemma SR tubules (cut) Synaptic cleft Synaptic vesicle Axon terminal ACh ACh ACh Neurotransmitter released diffuses across the synaptic cleft and attaches to ACh receptors on the sarcolemma. Action potential in T tubule activates voltage-sensitive receptors, which in turn trigger Ca 2+ release from terminal cisternae of SR into cytosol. Calcium ions bind to troponin; troponin changes shape, removing the blocking action of tropomyosin; actin active sites exposed. SR Ca 2+ Ca 2+ Ca 2+ Ca 2+ Ca 2+ Ca 2+ Ca 2+ Ca 2+ Ca 2+ 1 2 3
  • Figure 9.10 Net entry of Na + Initiates an action potential which is propagated along the sarcolemma and down the T tubules. T tubule Sarcolemma SR tubules (cut) Synaptic cleft Synaptic vesicle Axon terminal ACh ACh ACh Neurotransmitter released diffuses across the synaptic cleft and attaches to ACh receptors on the sarcolemma. Action potential in T tubule activates voltage-sensitive receptors, which in turn trigger Ca 2+ release from terminal cisternae of SR into cytosol. Calcium ions bind to troponin; troponin changes shape, removing the blocking action of tropomyosin; actin active sites exposed. Contraction; myosin heads alternately attach to actin and detach, pulling the actin filaments toward the center of the sarcomere; release of energy by ATP hydrolysis powers the cycling process. SR Ca 2+ Ca 2+ Ca 2+ Ca 2+ Ca 2+ Ca 2+ Ca 2+ Ca 2+ Ca 2+ 1 2 3 4
  • Figure 9.10 Net entry of Na + Initiates an action potential which is propagated along the sarcolemma and down the T tubules. T tubule Sarcolemma SR tubules (cut) Synaptic cleft Synaptic vesicle Axon terminal ACh ACh ACh Neurotransmitter released diffuses across the synaptic cleft and attaches to ACh receptors on the sarcolemma. Action potential in T tubule activates voltage-sensitive receptors, which in turn trigger Ca 2+ release from terminal cisternae of SR into cytosol. Calcium ions bind to troponin; troponin changes shape, removing the blocking action of tropomyosin; actin active sites exposed. Contraction; myosin heads alternately attach to actin and detach, pulling the actin filaments toward the center of the sarcomere; release of energy by ATP hydrolysis powers the cycling process. Removal of Ca 2+ by active transport into the SR after the action potential ends. SR Ca 2+ Ca 2+ Ca 2+ Ca 2+ Ca 2+ Ca 2+ Ca 2+ Ca 2+ Ca 2+ Ca 2+ 1 2 3 4 5
  • Figure 9.10 ADP P i Net entry of Na + Initiates an action potential which is propagated along the sarcolemma and down the T tubules. T tubule Sarcolemma SR tubules (cut) Synaptic cleft Synaptic vesicle Axon terminal ACh ACh ACh Neurotransmitter released diffuses across the synaptic cleft and attaches to ACh receptors on the sarcolemma. Action potential in T tubule activates voltage-sensitive receptors, which in turn trigger Ca 2+ release from terminal cisternae of SR into cytosol. Calcium ions bind to troponin; troponin changes shape, removing the blocking action of tropomyosin; actin active sites exposed. Contraction; myosin heads alternately attach to actin and detach, pulling the actin filaments toward the center of the sarcomere; release of energy by ATP hydrolysis powers the cycling process. Removal of Ca 2+ by active transport into the SR after the action potential ends. SR Tropomyosin blockage restored, blocking myosin binding sites on actin; contraction ends and muscle fiber relaxes. Ca 2+ Ca 2+ Ca 2+ Ca 2+ Ca 2+ Ca 2+ Ca 2+ Ca 2+ Ca 2+ Ca 2+ 1 2 3 4 5 6
    • NMJ 14
  • EC coupling review
    • Action potential comes from nerve
    • Acetylcholine is released
    • Action potential is generated in the muscle
    • Action potential travels down the T-tubules
    • Calcium is released
  • Action potential review
    • Describe the sliding filament model of muscle contraction
    • SF19-28
  • 5 Steps of the Contraction Cycle
    • Exposure of active sites
    • Formation of cross-bridges
    • Pivoting of myosin heads (power stroke)
    • Detachment of cross-bridges
    • Reactivation of myosin
  • Sliding Filament Model of Contraction
    • Thin (actin) filaments slide past the thick (myosin) ones so that the filaments overlap
    • When relaxed filaments overlap only slightly
    • Upon stimulation, myosin heads bind to actin and sliding begins
  • Figure 9.12 ATP ADP ADP ATP hydrolysis ADP ATP P i P i Myosin head (high-energy configuration) Myosin head attaches to the actin myofilament, forming a cross bridge. Thin filament As ATP is split into ADP and P i , the myosin head is energized (cocked into the high-energy conformation). Inorganic phosphate (P i ) generated in the previous contraction cycle is released, initiating the power (working) stroke. The myosin head pivots and bends as it pulls on the actin filament, sliding it toward the M line. Then ADP is released. Myosin head (low-energy configuration) As new ATP attaches to the myosin head, the link between myosin and actin weakens, and the cross bridge detaches. Thick filament 1 4 2 3
  • 5 Steps of the Contraction Cycle
    • Exposure of active sites
    • Formation of cross-bridges
    • Pivoting of myosin heads
    • Detachment of cross-bridges
    • Reactivation of myosin
  • Contraction
    • Refers to the activation of myosin’s cross bridges. Shortening occurs when the tension produced is greater than load
    • Ends when cross bridges become inactive
    • describe the different types of muscle contraction
  • Contraction of Skeletal Muscle
    • The two types of muscle contractions are:
      • Isometric contraction – increasing muscle tension (length doesn’t change)
      • Isotonic contraction – decreasing muscle length (length changes)
  • Isotonic Contractions Figure 9.19a
  • Isometric Contractions Figure 9.19b
    • Describe muscle twitch, tetanus and motor unit
  • Motor Unit
    • A motor unit is a motor neuron and all the muscle fibers it supplies
  • Motor Unit InterActive Physiology ®: Contraction of Motor Units, pages 3-9 Figure 9.13a
    • Muscles that control fine movements (fingers, eyes) have small motor units
    • Large weight-bearing muscles (thighs, hips) have large motor units
    PLAY
  • Muscle Twitch
    • A muscle twitch is the response of a muscle to a single stimulus
    • There are three phases to a muscle twitch
      • Latent period
      • Period of contraction
      • Period of relaxation
  • Phases of a Muscle Twitch
    • Latent period -EC coupling
    • Period of contraction – cross bridges form; muscle shortens
    • Period of relaxation – Ca 2+ reabsorbed; muscle tension goes to zero
    Figure 9.14a
  • Figure 9.14b
  • Graded Muscle Responses
    • Graded muscle responses are:
      • Variations in the degree of muscle contraction
      • Required for proper control of skeletal movement
    • Responses are graded by Changing the frequency or strength of stimulation
    • A single stimulus results in a single contractile response – a muscle twitch
    • Frequently delivered stimuli (muscle can’t relax) increases contractile force – wave summation
    Figure 9.15
    • More rapidly delivered stimuli result in incomplete tetanus
    • If stimuli are given quickly enough, complete tetanus results
    Figure 9.15
  • Stimulus Intensity and Muscle Tension Figure 9.16
    • Threshold stimulus – the minimum stimulus for contraction to occur
    • Muscle contracts more vigorously as stimulus strength is increased
    • Force of contraction is controlled by the number of motor units recruited (activated)
    • Recruitment activates more and more muscle fibers
  • Force of Muscle Contraction
    • The force of contraction is affected by:
      • The number of muscle fibers contracting
      • The relative size of the muscle
      • Degree of muscle stretch
  • Length Tension Relationship Figure 9.22 There is an optimal length
  •  
    • describe the types of skeletal muscle fibers (fast-twitch, slow-twitch)
    • mm25
  • Muscle Fiber Type: Functional Characteristics
    • Speed of contraction –
      • slow and fast fibers
    • ATP-forming pathways
      • Oxidative fibers (red)
      • Glycolytic fibers (white)
      • We have 3 types of fibers- slow oxidative, fast oxidative, and fast glycolytic
    InterActive Physiology ®: Muscle Metabolism, pages 25-27 PLAY
  •  
  •  
  •  
  •  
  •  
    • Describe the methods that are used to produce ATP for muscle contraction
  • Muscle Metabolism
    • ATP is the energy source for contractile activity
    • As soon as available stores of ATP are used (4-6 seconds), they are regenerated by:
      • Creatine phosphate (CP)
      • Anaerobic glycolysis
      • Aerobic respiration
    InterActive Physiology ®: Muscle Metabolism, pages 15
  • Energy for Contraction Figure 9.20
  • Energy Source Creatine Phosphate Anaerobic glycolyis Aerobic respiration Oxygen Use no no yes Products 1 ATP creatine 2 ATP lactic acid 36 ATP CO 2 , H 2 O Duration 15 Seconds 30-60 seconds Hours
    • compare the gross, microscopic anatomy, and contractile mechanisms of smooth muscle and cardiac muscle to skeletal muscle
  • Smooth Muscle
    • spindle-shaped fibers
    • have fine endomysium
    • Organized into two layers (longitudinal and circular)
    • Found in walls of hollow organs
    • Have essentially the same contractile mechanisms as skeletal muscle
  • Smooth Muscle Figure 9.24
  • Peristalsis
    • Peristalsis – alternating contractions and relaxations of smooth muscles that mix and squeeze substances through the lumen of hollow organs
  • Microscopic Anatomy
    • Plasma membranes have pouchlike infoldings called caveoli
    • Ca2+ is held in the extracellular space near the caveoli, allowing rapid influx when channels are opened
    • No sarcomeres
    • Thin and thick filaments are present
  • Myofilaments in Smooth Muscle
    • Ratio of thick to thin filaments is lower than in skeletal muscle
    • Thick filaments have heads along their entire length
    • No troponin
  • Myofilaments
    • Thick and thin filaments are arranged diagonally
    • intermediate filament bundles attach to dense bodies (analogous to Z discs)
  • Contraction of Smooth Muscle
    • Whole sheets of smooth muscle exhibit slow, synchronized contraction
    • They are electrically coupled with gap junctions
    • Some cells are self-excitatory and act as pacemakers
    • Ca 2+ binds to calmodulin and activates it
    • Calmodulin activates the kinase enzyme
    • Kinase transfers phosphate from ATP to myosin cross bridges
    • Phosphorylated cross bridges interact with actin to produce shortening
    • Smooth muscle relaxes when intracellular Ca 2+ levels drop
    Contraction of Smooth Muscle
  • Smooth Muscle
    • Unique characteristics of smooth muscle include:
      • Smooth muscle tone
      • Slow, prolonged contractile activity
      • Low energy requirements
      • Response to stretch
  • Table 9.3.1
  • Table 9.3.2
  • Table 9.3.3
  • Table 9.3.4
  •  
  •  
  • Muscle cells are referred to as ________.
    • muscle fibers
    • muscle spindles
    • muscle myosin
    • muscle actin
    Copyright © 2010 Pearson Education, Inc.
  • Which of the following is not a prefix used to refer to muscle?
    • Mys
    • Myo
    • Sarco
    • Lemma
    Copyright © 2010 Pearson Education, Inc.
  • Of the following muscle types, which is the only one subject to conscious control?
    • Smooth
    • Skeletal
    • Cardiac
    • All of these muscle types are subject to conscious control.
    Copyright © 2010 Pearson Education, Inc.
  • Which two types of muscle appear striated when examined under a microscope?
    • Smooth and skeletal
    • Smooth and cardiac
    • Cardiac and skeletal
    • Skeletal muscle is the only striated muscle type.
    Copyright © 2010 Pearson Education, Inc.
  • Which of the following muscular functions serves a metabolic function?
    • Movement
    • Posture maintenance
    • Joint stabilization
    • Heat generation
    Copyright © 2010 Pearson Education, Inc.
  • In order to receive a signal to contract, each skeletal muscle must be served by a(n) ________.
    • artery
    • nerve
    • vein
    • ligament
    Copyright © 2010 Pearson Education, Inc.
  • Which of the following components accounts for the bulk of muscle fiber volume (up to 80%)?
    • Glycosomes
    • Mitochondria
    • Myofibrils
    • Sarcoplasm
    Copyright © 2010 Pearson Education, Inc.
  • The functional unit of a muscle fiber is the __________.
    • sarcomere
    • myofibril
    • fascicle
    • myofilament
    Copyright © 2010 Pearson Education, Inc.
  • The thin filaments are not comprised of which of the following components?
    • Actin
    • Titin
    • Troponin
    • Tropomyosin
    Copyright © 2010 Pearson Education, Inc.
  • What is the major function of the sarcoplasmic reticulum?
    • Store sodium ions
    • Expel sodium ions from the cell
    • Expel calcium ions from the cell
    • Store calcium ions
    Copyright © 2010 Pearson Education, Inc.
  • During a muscle contraction, the sliding filament theory would be apparent in a sarcomere because __________.
    • the I bands get longer
    • the A bands get shorter
    • the H zone becomes less obvious and the Z discs move closer together
    • the Z discs get pulled closer to the I bands and the H zone becomes more obvious
    Copyright © 2010 Pearson Education, Inc.
  • At the neuromuscular junction, the muscle contraction initiation event is ______.
    • a release of calcium ions from the sarcoplasmic reticulum
    • conduction of an electrical impulse down the T tubules
    • binding of acetylcholine to membrane receptors on the sarcolemma
    • sliding of actin and myosin filaments past each other
    Copyright © 2010 Pearson Education, Inc.
  • In a muscle fiber, the key intracellular event that stimulates muscle contraction is known as ________.
    • polarization
    • depolarization
    • repolarization
    • potential
    Copyright © 2010 Pearson Education, Inc.
  • During depolarization, the sarcolemma is most permeable to _______.
    • sodium ions
    • potassium ions
    • calcium ions
    • chloride ions
    Copyright © 2010 Pearson Education, Inc.
  • The time period between action potential initiation and mechanical activity of a muscle fiber is called the _________.
    • latent period
    • refractory period
    • action potential
    • excitation period
    Copyright © 2010 Pearson Education, Inc.
  • What is calcium’s function during muscle contraction?
    • Calcium binds to troponin, changing its shape and removing the blocking action of tropomyosin.
    • Calcium binds to troponin to prevent myosin from attaching to actin.
    • Calcium depolarizes the muscle fiber.
    • Calcium flows down the T tubules to stimulate the influx of sodium from the sarcoplasmic reticulum.
    Copyright © 2010 Pearson Education, Inc.
  • Corpses usually exhibit rigor mortis because __________.
    • ATP hydrolysis is stimulating myosin head attachment to actin
    • a lack of ATP hydrolysis prevents myosin head detachment from actin
    • calcium stores become deficient
    • sodium stores become deficient
    Copyright © 2010 Pearson Education, Inc.
  • Small precise movements are controlled by ______ motor units.
    • small
    • large
    • many
    • few
    Copyright © 2010 Pearson Education, Inc.
  • A muscle contraction increases in strength up to a point because ________.
    • stronger stimuli inhibit motor unit activation
    • recruitment occurs and more motor units respond to stronger stimuli
    • more calcium is available in the sarcoplasm
    • additional neurons begin stimulating each muscle fiber
    Copyright © 2010 Pearson Education, Inc.
  • Isometric contractions come into play when an individual is ________.
    • jumping
    • walking uphill
    • lifting a heavy object
    • maintaining an upright posture
    Copyright © 2010 Pearson Education, Inc.
  • A sprinter is more likely to depend on _______ respiration to generate ATP, whereas a Tour de France cyclist is more likely to rely on __________ respiration.
    • anaerobic; aerobic
    • aerobic; anaerobic
    • aerobic; aerobic
    • anaerobic; anaerobic
    Copyright © 2010 Pearson Education, Inc.
  • Sprinters typically possess more ________ muscle fibers.
    • slow glycolytic
    • fast glycolytic
    • slow oxidative
    • fast oxidative
    Copyright © 2010 Pearson Education, Inc.
  • A major difference between smooth muscle fibers and skeletal muscle fibers in terms of calcium influx is that ______.
    • smooth muscle fibers have a sarcoplasmic reticulum
    • calcium ions are stored in the sarcoplasm of smooth muscle
    • calcium ion influx occurs mostly from the extracellular fluid in smooth muscle
    • smooth muscle contraction does not involve calcium
    Copyright © 2010 Pearson Education, Inc.
  • A major cellular feature in smooth muscle that contributes to its rhythmicity and ability to participate in peristalsis is the presence of _________.
    • troponin complex
    • gap junctions
    • varicosities
    • caveolae
    Copyright © 2010 Pearson Education, Inc.