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APHY 101 Exam 4a
Ch. 9 Muscles and Muscle Tissue
| Term | Definition |
|---|---|
| I band | thin filaments only |
| H zone | thick filaments only |
| M line | thick filaments linked by accessory proteins |
| outer edge of A band | thin and thick filaments overlap |
| facial muscles | occipitofrontalis, correlation supercilii, orbicularis oculi, zygomaticus major/minor, buccinator, orbicularis oris, mentalis, temporalis, masseter, medial & lateral pterygoid |
| forearm muscles | brachioradialis, flexor carpi radialis, palmaris longus, flexor carpi ulnaris, flexor digitorum superficialis; extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris |
| arm muscles | biceps brachii, brachialis, triceps brachii, deltoid at shoulder, pectoralis major, latissimus dorsi, supraspinatus, infraspinatus, teres minor, subscapularis |
| rotator cuff muscles | supraspinatus, infraspinatus, teres minor, subscapularis |
| neck muscles | trapezius, sternocleidomastoid, splenius capitus |
| abdomen muscles | rectus abdominis, internal/external abdominal oblique, transversus abdominis |
| thigh muscles | sartorius, tensor fascia lata, rectus femoris, vastus medialis, vastus intermedius, vastus lateralis, biceps femoris, semi membranosus, semitendinosus, adductor magnus & longus, gracilis, piriformis, iliopsoas |
| buttock muscles | gluteus maximus, gluteus medius, piriformis |
| leg muscles | gastrocnemius, soleus, tibialis anterior, peroneus (fibularis) brevus/longus/tertius |
| back muscles | erector spinae muscles: iliocostalis, longissimus, and spinalis |
| categories of how skeletal/cardiac/smooth muscle differ | in structure, location, function, and means of activation |
| sarcolemma | muscle plasma membrane |
| sarcoplasm | cytoplasm of a muscle cell |
| prefixes for muscle | myo, mys and sarco |
| skeletal muscle | striated, voluntary, contracts rapidly but tires easily; is extremely adaptable and can exert forces from a fraction of an oz to over 70 pounds |
| cardiac muscle controlled by | neural controls that allow the heart to respond to changes in bodily needs |
| smooth muscle functions | helps maintain blood pressure, and peristalsis of food and feces through organs |
| additional functions of muscles | maintain posture, stabilize joints, and generate heat such as exercising or shivering |
| the three connective tissue sheaths | epimysium, perimysium, endomysium |
| epimysium | overcoat of dense regular connective tissue continuous with tendon on outside of muscle, covers entire muscle |
| perimysium | surrounds groups of muscle fibers called fascicles, segregated from the rest of the muscle by a connective tissue sheath |
| endomysium | fine sheath of connective tissue composed of RETICULAR fibers that surrounds sarcolemma of an individual muscle cell/fiber |
| myofibril | rodlike contractile element that is an organelle composed of bundles of myofilaments; composed of sarcomeres end to end; make up most of the muscle volume |
| arrangement of myofibrils within a fiber | such that the dArk A bands and lIght I bands is evident |
| sarcomere | segment of a myofibril; aka the region of a myofibril between 2 successive Z discs; the smallest contractile unit responsible for muscle contraction; composed of myofilaments made of contractile proteins |
| myofilament or filament (extended macromolecular structure) 2 types | thick myosin and thin actin, and elastic for recoil |
| skeletal muscle composition | each muscle is a discrete organ composed of muscle tissue, blood vessels, nerve fibers, and connective tissue |
| each skeletal muscle is served by how many nerves? | one nerve ending that controls contraction, an artery, and one or more veins (not true of cardiac and smooth) |
| true | |
| skeletal muscle attachments | most skeletal muscles span joints and are attached to bone in at least two places |
| principle of skeletal muscle movement | the movable bone aka insertion moves toward the immovable vone aka orgin |
| skeletal muscles attach directly and indirectly to where? | directly to epimysium of the muscle fused to the periosteum of a bone; indirectly with connective tissue wrappings extending beyond the muscle as a tendon or aponeurosis |
| how long is a skeletal muscle fiber? | 10-100 micrometers in diameter, and up to hundreds of centimeters long |
| the fusion of embryonic cells in a skeletal muscle fiber is termed a what? | syncytium (sin-sih-shee-um); myoblasts came together and fused creating a syncytium |
| myoglobin protein | essential for oxygen binding, storage, and delivery to mitochondria during activity; provides muscles with necessary O2 is responsible for the red color in meat |
| where is myoglobin located? | sarcoplasm with numerous glycosomes, the granules of stored glycogen that provide glucose during the period of muscle fiber activity |
| skeletal muscle fibers contain what features? | the usual organelles, myofibrils, sarcoplasmic reticulum, and T tubules |
| banding pattern of thin filaments | thin filaments extend across the I band and partway into the A band |
| banding pattern of Z disc | coin-shaped sheet of proteins (connectins) that anchors the thin filaments and connects myofibrils to one another |
| banding pattern of myofilaments | thin filaments do not overlap thick filaments in the lighter H zone; M lines appear darker due to protein myomesin or desmin |
| myomesin and desmin functions (not in ppt) | molecular bridge that connects myosin thick filaments to the elastic protein titin, maintaining sarcomere integrity; a mechanical scaffold for thick filaments |
| ultrastructure of myofilaments - thick filaments | myosin molecules have a rod-like tail and two globular heads; tail = two interwoven, heavy polypeptide chains; head = two smaller, light polypeptide chains called cross bridges |
| ultrastructure of myofilaments - thin filaments | actin protein with each molecule as a helical polymer of globular subunits called G actin; the subunits contain active sites where myosin wants to attach |
| what are the regulatory subunits bound to actin? | tropomyosin the gate, and troponin the sensor complex that changes shape |
| SR (sarcoplasmic reticulum) | an elaborate, smooth endoplasmic reticulum that mostly runs longitudinally and surrounds each myofibril; paired terminal cisternae form perpendicular cross channels |
| function of the SR | regulation of intracellular calcium levels |
| what penetrates into the cell's interior at each A band I band junction? | elongated tubes called T tubules |
| triads | where T tubules associate with the paired terminal cisternae |
| Z disc location | in the middle of the I band |
| T tubules are continuous with? | the sarcolemma |
| T tubules function | conduct impulses to the deepest regions of the muscle; these impulses signal for the release of Ca2+ from adjacent terminal cisternae |
| sliding filament model of contraction | thin filaments slide past the thick ones so that the actin and myosin filaments overlap to a greater degree (in the relaxed state, they overlap only slightly)--upon stimulation, myosin heads bind to actin and sliding begins |
| true or false: each myosin head binds and detaches several times during contraction | true |
| event that occurs throughout the sarcomeres making the muscle shorten | each myosin head binds and detaches like a ratchet to generate tension and propel thin filaments to the center of the sarcomere |
| in order to contract, a skeletal muscle must | be stimulated by a nerve ending; propagate an electrical current (AP) along its sarcolemma; have a rise in intracellular Ca2+ levels--the final trigger |
| excitation-contraction coupling | links the electrical signal to the contraction. is the physiological process converting an electrical stimulus (AP) into a mechanical response (muscle contraction) (see notes if needed) |
| NMJ: neuromuscular junction | each axonal branch forms an NMJ with a single muscle fiber; axons of motor neurons branch profusely as they enter muscles |
| what do the motor neuron axons do? | travel in nerves to muscle cells to stimulate the skeletal muscles |
| what are an NMJ's components? | axonal endings, which have the synaptic/axonal vesicles that contain ACh, and the motor end plate of a muscle part of the sarcolemma that contains ACh receptors |
| synaptic cleft | though exceedingly close, axonal ends and muscle fibers are separated by a space called the synaptic cleft |
| what is the enzyme that cleans up acetylcholine? | acetylcholinesterase |
| what does acetylcholinesterase prevent? | prevents continued muscle fiber contraction in the absence of additional stimuli |
| what happens 1st at the NMJ when a nerve impulse reaches the end of an axon? | 1, voltage-regulated calcium channels open and allow Ca2+ to enter the axon |
| what happens 2nd at the NMJ when a nerve impulse reaches the end of an axon? | 2, Ca2+ inside the axon terminal causes synaptic/axonal vesicles to fuse with the axonal membrane |
| what happens 3rd at the NMJ when a nerve impulse reaches the end of an axon? | 3, The fusion of those vesicles releases Ach into the synaptic cleft via exocytosis |
| what happens 4th at the NMJ when a nerve impulse reaches the end of an axon? | 4, ACh diffuses across the synaptic cleft to ACh receptors on the sarcolemma |
| what happens 5th at the NMJ when a nerve impulse reaches the end of an axon? | 5, Binding of ACh to its receptors initiates an action potential in the muscle |
| action potential | transient depolarization event that includes polarity reversal of a sarcolemma (or nerve cell membrane) and the propagation of an action potential along the membrane |
| ACh in depolarization 1 of 3 | ACh binds its receptors at the motor end plate |
| ACh in depolarization 2 of 3 | Binding opens chemically ligand gated channels |
| ACh in depolarization 3 of 3 | Na+ diffuses in and K+ diffuses out along their concentration gradients, and the interior of the sarcolemma becomes less negative |
| Who cleans up the mess afterward after depolarization? aka, how is the ionic concentration of the resting state restored? | Na+-K+ pump! |
| depolarization is initially a local electrical event called what? | end plate potential |
| what does depolarization later ignite? | an action potential that spreads in all directions across the sarcolemma |
| what are the electrical conditions of a polarized sarcolemma? | the extracellular face is positive, while the inside face is negative = this is called the resting membrane potential |
| what is the predominant extracellular ion? | Na+ |
| what is the predominant intracellular ion? | K+ |
| true or false, the sarcolemma is relatively permeable to both ions | false (impermeable) |
| specifically, how does depolarization occur at the cellular membrane? | an axonal terminal of a motor neuron releases ACh and causes a patch of the sarcolemma to become permeable to Na+ (sodium channels open); Na+ enters the cell and the resting potential is decreased (depolarization occurs) |
| what determines whether an action potential is initiated? | if the stimulus is strong enough |
| how is the rest of the cell depolarized? | voltage-regulated Na+ channels open in the adjacent patches to the ligand-gated sodium channels (polarity reversal of the initial patch changes the adjacent) |
| the action potential is unstoppable once initiated, and ultimately results in what? | the contraction of a muscle |
| what happens immediately after the depolarization wave passes? | the sarcolemma permeability changes: Na+ channels close and K+ channels open, restoring the polarity (repolarization) |
| true or false: repolarization occurs in the same direction as depolarization | true |
| refractory period | repolarization must occur here before muscle can be stimulated again |
| true | |
| what powers the process of cross-bridge cycling? | hydrolysis of ATP |
| end of excitation-contraction coupling | Ca²⁺ is actively transported back into the sarcoplasmic reticulum, tropomyosin resumes blocking the myosin-binding sites on actin, and cross-bridge cycling ceases, resulting in muscle relaxation |
| role of ionic calcium in the contraction mechanism at low intracellular Ca2+ concentration | tropomyosin blocks actin's binding sites and myosin bridges are prevented; the relaxed state of the muscle is enforced |
| role of ionic calcium at higher intracellular Ca2+ concentrations | inactive troponin binds two Ca2+); calcium-activated troponin binds an additional two Ca2+ at a separate regulatory site; calcium-activated troponin undergoes a conformational change, permitting myosin to now bind |
| sequential events of contraction | cross bridge formation, power stroke toward M line, cross bridge detachment, and cocking of the myosin head |
| contraction | refers to the activation of myosin's cross bridges (force-generating sites) |
| shortening | occurs when the tension generated by the cross bridge exceeds forces opposing shortening |
| when does contraction end? | when cross bridges become inactive, the tension generated declines, and relaxation is induced |
| the 2 general types of muscle contraction | isometric (no further subtypes) = muscle does not shorten, and isotonic contraction (has 2 subtypes) = muscle length changes |
| what are the 2 types of isotonic contraction? | concentric = muscle shortens (typical); eccentric = muscle lengthens while tension is generated (setting down an object or walking down stairs) |
| motor unit | the nerve-muscle functional unit; a motor neuron and all the muscle fibers it supplies |
| what is the range of numbers of muscle fibers per motor unit? | four to several hundred (small motor units = fine movements in the fingers and eyes, large motor units for large weight-bearing muscles such as thighs, hips) |
| why does contraction of a single motor unit cause weak contraction of the entire muscle? | because muscle fibers from a motor unit are spread through the muscle |
| muscle twitch | a fast contraction that is not very useful; response of a motor unit to a single action potential of its motor neuron |
| what are the periods of muscle contraction in a twitch? | latent period, period of contraction, period of relaxation |
| latent period | first few milliseconds after stimulation when excitation-contraction coupling is occuring. no shortening of muscle as a whole is seen |
| period of contraction | cross bridges active from onset to peak of tension; if tension overcomes the load, muscle shortening is seen |
| period of relaxation | Ca2+ re-enters the terminal cisternae of the sarcoplasmic reticulum, muscle tension drops to zero |
| our muscles generally operate by single twitches, true or false | false |
| 2 ways to cause normal muscle contractions | temporal wave summation, and recruitment/multiple motor unit summation |
| temporal wave summation | multiple individual twitches combine due to the FREQUENCY of stimulation--slow, medium, or fast |
| slow frequency of stimulation results in | individual twitches that relax completely between stimuli |
| medium frequency of stimulation results in | unfused or incomplete tetanus, seen in normal muscle contractions; "stairstep" phenomenon: each subsequent stimulus causes a contraction that rides on the heels of the previous one, making twitches stronger & stronger |
| fast frequency of stimulation results in | maximal contraction that leads quickly to fatigue, aka fused or complete tetanus rarely seen in the body and only in cases of superhuman feats of strength during emergencies; NOT the normal way muscles contract |
| recruitment or multiple unit summation | in which the strength of contraction is determined by the NUMBER of motor units activated. |
| in recruitment, subthreshold stimuli to the muscle's nerve produce no contraction | true |
| threshold stimuli | strong enough signals that create action potentials in motor neurons |
| a small threshold stimulus | only recruits small motor units whose neurons are easily excited (by small depolarizations) --> produces a weak muscle contraction |
| larger stimuli do what? | recruit more (and larger) motor units whose neurons need a stronger stimulus (larger depolarization) in order to fire --> this activates more mucsle fibers and produces a stronger muscle contraction |
| muscle tone | relaxed muscles are not truly relaxed, a few of their fibers are generating tension to keep the muscle at an optimal length so when stimulated, it can contract efficiently |
| fact, an overstretched or understretched muscle has trouble contracting well when stimulated | true |
| sarcomeres need to be an optimal length which muscle tone (set by the CNS) maintains | also true |
| length-tension relationship | principle: the amount of force a muscle fiber produces depends on its initial sarcomere length since force is determined by the degree of overlap between actin and myosin |
| muscles only pull, never push | true |
| skeletal muscles work together or in opposition | true |
| as muscles shorten, the insertion generally moves toward the origin | true |
| whatever a muscle or group of muscles does, there's another muscle or group that "undoes" it | true |
| somatic | nervous system having to do with voluntary movement |
| functional groups of muscle classification | prime movers (agonists), antagonists, synergists |
| synergists | add force to a movement/help, and reduce undesirable or unnecessary movement |
| fixators | synergists that immobilize a bone or muscle's origin |
| muscle naming features | location, shape, size, direction of fibers, number of origins, location of attachments, action (flexor or extensor) |
| rule of muscle movement | in order for a muscle to move a joint, it must span that joint |
| arrangement of fascicles | parallel, fusiform, pennate, convergent, circular |
| parallel arr. of fascicles | fascicles run parallel to the long axis of the muscle e.g. sartorius |
| fusiform arr. of fascicles | spindle-shaped muscles e.g. biceps brachii |
| pennate arr. of fascicles | short fascicles that attach obliquely to a central tendon running the length of the muscle e.g. extensor digitorum longus, unipennate, rectus femoris bipennate, deltoid multipennate |
| convergent arr. of fascicles | fascicles converge from a broad origin to a single tendon insertion e.g. pectoralis major |
| circular arr. of fascicles | fascicles are arranged in concentric rings e.g. orbicularis oris |
| bone-muscle relationships lever systems comprisal | lever, effort, load |
| lever | a rigid bar (bone) that moves on a fulcrum (joint) or fixed point |
| effort | force applied to a lever (by the muscle and depending what kind) |
| load | resistance moved by the effort (whether a dumbbell or whatever) |
| first-class lever | the fulcrum is between the load and the effort |
| first-class lever examples | teetertotter, scissors, weight of your face falling forward |
| second-class lever | the load is between the fulcrum and the effort |
| second-class lever examples | wheelbarrow, gastrocnemius where fulcrum is the toe |
| third-class lever | the effort is in the middle applied between the fulcrum and the load |
| third-class lever examples | most muscles where the muscle is between the joint and weight/load of the limb; tweezers being squeezed at the middle |
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