Lecture 3 Flashcards
Muscle Types?
-Skeletal
-Smooth
-Cardiac
Skeletal Muscle is Not Uniform?
True
Skeletal is Striated, thus it?
Appears to have stripes
(myocyte –> myofibril –> sarcomere –> actin/myosin)
Large Bundles of muscle are composed of individual muscle cells that each contain many?
Myofibrils
Myofibrils each contain many?
Sarcomeres that are arranged end-to-end in series
Each Sarcomere is composed of?
(smallest functioning unit of muscle)
Actin, Myosin, and other molecular machinery
Actin?
Thin
Myosin?
Thick
Thin Filaments?
Actin helix with tropomyosin and troponin complex attached
Thick Filaments?
Myosin II = ATPase because breakdown ATP for energy
Thin and Thick filaments interact to produce?
Force
AChR causes?
Depolarization in skeletal muscle cells
Neuromuscular Junction?
1) Nerve axon innervating each muscle fiber
2) Release actylcholine (ACh)
3) ACh binds to AChR which is permeable to Na+, K+, and Ca2+
Each Muscle Cell innervated by?
1 Nerve
Initiation of Skeletal Muscle Contraction?
1) Ca2+ release from SR
2) Ca2+ binds to Troponin C and initiates a conformational change
3) Tropomyosin slides into groove between actin strands
4) Myosin can now bind actin
Muscle Relaxed?
-Z-bands become wider
-I-bands widen
-A-bands remain the same
-H-bands widen
Muscle Contraction?
-Z-bands move closer together
-I-bands narrow
-A-bands remain the same
-H-bands narrow
(Skeletal Muscle Relaxation) SERCA?
(Sarcoplasmic Endoplasmic Reticulum ATPase)
-A calcium pump that sequesters myoplasmic Ca2+ into SR
-Pumps 2 Ca2+ into lumen/ATP while extruding 2 H+
(Skeletal Muscle Relaxation) Calsequestrin?
Ca2+ binding protein near RyR (holds Ca2+ into SR in preparation for next contraction)
(Skeletal Muscle Relaxation) Sarcalumenin?
Transfers Ca2+ from uptake sites to release sites (transport of Ca2+ from SERCA to RyR)
(Initiation of Smooth Muscle Contraction) Ca2+ initiates smooth muscle contraction by?
Myosin light chain kinase (MLCK) is required to?
-Binding to calmodulin (can bind 4 molecules of Ca2+)
Skeletal Muscle: T-tubules carry charge to SR to stimulate?
Ca2+ release from internal stores
Smooth Muscle: Caveolae bring?
External Ca2+ to the SR (when refills SR)
Factors Affecting Force Production in Skeletal Muscle?
1) Initial Length of Muscle Fiber
2) Fiber Type
3) Motor Unit Recruitment
4) Speed of Contraction
5) Muscle Fiber Arrangement
Dynamic Actions?
-Concentric
-Eccentric
Concentric?
-Muscle develops Tension and Muscle shortens and pulls weight up
-Muscle Force > External Force
Eccentric?
-Muscle develops Tension and Muscle lengthens lowering weight gently
-Braking Action= hiking downhill, spring-like storage of energy
-Muscle Force < External Force
Static Action - Isometric?
-Muscle develops Tension with no change in Length
-Muscle Force = External Force
Passive Force is Mediated by Titin?
(largest known protein)
-Elastic protein that runs from Z line to M line of the sarcomere (halfway)
-Acts as a molecular spring that is responsible for producing passive force in muscle
Increased O2?
Increased ATP
Motor Unit?
All Muscle Fibers Innervated by a Single Motor Neuron, all move together when AP fires
Summation?
How muscle increases force
Temporal Summation?
-Increased frequency of stimulation
-Increased AP firing rate
-Single AP releases Ca2+ for a short duration to cause a twitch
(Tetany)
Spatial Summation in Skeletal Muscle?
-All muscle fibers in a motor unit are activated simultaneously
-All or None
-Not all motor units are available at same time
Recruitment?
Not all muscle fibers are participating all the time; some are inactive
Tetany?
-Maximum force
-Spasmic Muscles
-Stimulating a muscle with an AP before muscle has had time to totally relax leads to
Tonic?
-Continuously active to maintain a level of tone
-Ex. blood vessels, respiratory tract, some sphincters
-Multiunit
Phasic?
-Rhythmic or intermittent contractions
-Ex. GI tract, urogenital, lymphatic
-Single unit
1 Sarcomere is bounded by 2?
Z-lines
I-Band decreases?
Increased overlap
(I-Band has only actin)
H-Zone decreases?
Increased overlap
(H-Zone has only myosin)
Sarcoplasmic Reticulum in Myocytes is?
Ca2+ storage cell
T-tubules maximize SA of cell membrane contact with SR to couple?
Electrical activity from nerve with Ca2+ release
Intermediate filaments desmin or vimentin form a?
Cytoskeleton network connecting dense bodies (dense bodies also contain a-actinin, which binds actin)
Smooth Muscle Relaxation?
-Similar to skeletal Muscle, Ca2+ must be resequestered in SR and can also pump Ca2+ out of cell
-Additional Step: MLCP (to remove phosphate from myosin to inactivate)
Muscle Energy Sources During Exercise?
1) ATP (small but replenishable pool)
2) Creatine Phosphate (ATP buffer system that keeps ATP constant)
3) Glycogen (from muscle cells)
4) Plasma glucose + glycogen
5) Plasma Free Fatty Acids
