Muscular System1. Define:EndomysiumEach muscle fiber (skeletal muscle cell) is wrapped in a delicate connective tissue membrane called endomysiumPerimysiumFascicle- consists of a group of endomysium-covered muscle fibers wrapped in a coarse connective tissue membrane called perimysiumEpimysiumSkeletal muscle- consists of a group of fascicles wrapped in a tough connective tissue membrane called epimysiumFasciclesFascicle- consists of a group of endomysium-covered muscle fibers wrapped in a coarse connective tissue membrane called perimysiumTendonsSarcolemmaplasma membrane of muscle fiberSarcoplasmCytoplasm of the muscle fiberSarcoplasmic ReticulumSpecialized smooth endoplasmic reticulum that stores/releases calcium into the sarcoplasm; the expanded ends of sarcoplasmic reticulum are called terminal cisternaeMyoglobinA red pigment that binds and stores oxygenSarcomereStructural units of skeletal muscle=each skeletal muscle is composed of repeated units arranged end to end called sarcomeresThe distance between two successive Z lines=a sarcomereZ lineAnchor the thin filamentsH zoneMiddle region of the A band not overlapping with the thin filamentsA bandThick filamentI bandRegions of the thin filaments not overlapping with the A bandTriadComposed of a transverse tubule in between 2 terminal cisternae: Terminal cisterna-Ttubule-Terminal cisternaFunction: For the release of calcium ions into the sarcoplasm when the sarcolemma depolarizesMotor Unit2. Describe the neuromuscular junction. What is the motor end plate?Neuromuscular junctionThe junction between the axonal terminal of a motor neuron and a skeletal muscle fiber separated by a small space called the neuromuscular cleft (synaptic cleft)Each muscle fiber has only one neuromuscular junctionMotor end plateThe highly folded region of the sarcolemma of the muscle fiber at the neuromuscular junction is called the motor end plate—express acetylcholine receptors on the surfaceA motor neuron and all the muscle fibers it innervates via its axonal terminals is called a motor unit; motor units come in different sizes—small, medium, large3. Name the 3 proteins in a thin filament. What is the function of tropomyosin in a relaxed skeletal muscle?ActinDouble-helical structure that forms the core of the thin filament contains binding sites for myosinTropomyosinA rod-shaped regulatory protein that spirals around the actin and blocks myosin binding sites on actin in a relaxed skeletal muscleTroponinThree complex protein consisting ofTnC—binds calcium ionsTnT—binds to tropomyosinTnI—inhibitory subunit that binds to actinThe function of tropomyosin in a relaxed skeletal muscle is spirals around the actin and blocks myosin binding sites on actinName the 3 subunits of troponin. Which troponin subunit is bound to actin?TnC—binds calcium ionsTnT—binds to tropomyosinTnI—inhibitory subunit that binds to actin4. How are the myosin heads activated?Myosin heads are activated when the myosin heads are attached by ADP+Pi (resulting from ATPase hydrolysis of ATP into ADP+Pi)5. Describe skeletal muscle contractionSize of motor units activated—larger motor units generate more force than smaller motor unitsNumber of motor units activated—force increases as the number of motor units activated increasesRecruitment=smaller motor units are activated first followed by larger motor unitsFrequency of skeletal muscle activation—force increases as the rate of stimulation by motor neurons increasesThe length of the sarcomeres prior to contraction—sarcomeres at the optimum length generate the maximum force; sarcomere length below the optimum length (shortened sarcomeres) results in decreased force; sarcomere length greater than the optimum length (stretched sarcomeres) results in decreased force of contraction6. Give the role of ATP in muscle contractionATP is hydrolyzed by ATPase to produce ADP and Pi to activate theATP is required for crossbridge detachmentATP is required for the sequestration of calcium ions back into the SR for storage (active transport)Differentiate between muscle fatigue and rigor mortisMuscle fatigueMuscle fatigue is a physiological inability of a stimulated skeletal muscle to contract due to ATP deficit—rate of ATP production lags behind ATP demandRigor mortisLack of new ATP results in skeletal muscle contracture termed rigor mortis—occurs when an individual dies and ATP synthesis ceases—actin and myosin are irreversibly cross linked and skeletal muscles remain contracted7. Define the sliding filament mechanism - list structures that a) shortenb) remain the same when a skeletal muscle contractsStates that the sliding of the thin filaments past the A bands results in muscle contractionsAccording to this mechanism when a muscle contracts there is more overlap between the thin filaments and the A bands:H zone decreases or disappearsI bands decrease or disappearSarcomere length shortens=skeletal muscle shortens (contracts)However, the lengths of the A bands and the thin filaments remain the same—they do not shorten8. Discuss the factors that affect the strength of skeletal contraction9. Name and give the characteristics of the 3 types of skeletal muscle fibers:Which type is fatigable and why? Which type is also known as red fiber and why?Three major types of muscle fiber types based on:Speed of contraction—two types:Slow fibers and fast fibers due to the speed at which Myosin ATPase hydrolyzes ATPMajor Pathway for ATP production—two ways:Aerobic respiration=oxidative fibers typesAnaerobic respiration using more glycogen=glycolyic fiber typesBased on the above criteria there are three major skeletal muscles typesSlow Oxidative FibersFast Oxidative FibersFast Glycolytic Fibers10. Define isotonic and isometric contractions.Isotonic contractionsMuscle shortens at a relatively constant force (isotonic=same force); force generated by skeletal muscle exceeds the weight so the skeletal muscle contracts and work is done, such as lifting the weightIsometric contractionsForce (tension) generated by the muscle is increasing at a constant muscle length (“isometric”=same length); occurs when the weight exceeds the force generated by the muscle11. Compare and contrast the structures and mechanism of contraction for skeletal and smooth muscles. What is the function of calmodulin in smooth muscle contraction?12. Name the structures present in skeletal muscle fibers that are absent from smooth muscle cells13. Compare and contrast
View Full Document
Unlocking...