Muscular Physiology Flashcards
Organization of Skeletal Muscle
fascicles
Myosin
Heads, Crossbridges, Light Chains, and
Heavy Chains
Actin
Binding site for
attachment with myosin
cross bridge
Thin Filament
a polymer of actin with tightly bound regulatory proteins troponin and tropomyosin
Excitation Contraction Coupling
Excitation = AP
• Contraction = Start of Contraction
Calcium Release
Calcium is released from intracellular stores. AP Travels Down T tubule
The Triad
T tubule
• Terminal Cisternae of the SR
Two Key Proteins of Calcium Release
Dihydropyridine receptor and ryanodine receptor
What occurs when a muscle fiber is relaxed
no cross- bridge binding because the cross- bridge binding site on actin is physically covered by the troponin- tropomyosin complex
what occurs when a muscle fiber is excited
released Ca2+ binds with troponin, pulling troponin- tropomyosin complex aside to expose cross-bridge binding site; cross-bridge binding occurs
Cross-Bridge Cycling
Stops When Ca2+ Levels Drop. Muscle contraction based on muscle proteins that slide past each other to generate movement.
Muscle Twitch in a Single Fiber
Stimulates early
Effects of Multiple Stimuli
Treppe
Why Treppe?
“Warm-Up” Ca2+ Levels?
Why Wave Summation?
Ca2+ Levels Already Increased. Cross-Bridges Already Formed
Tetanus
Same as wave summation but more
Changing the Force of a
Contraction in a Whole Muscle
Motor Units and Recruitment
Isometric Contraction
a muscle contraction without motion
Isotonic Contraction
Concentric Contractions and Eccentric Contractions
Series Elastic
acts as a spring to store elastic energy when a tensed muscle is stretched.
Parallel Elastic
consist of the membranes surrounding the contractile components which includes the sarcolemma, sarcoplasmic retinaculum, the perimysium and the epimysium
Why do you need energy?
Myosin ATPase, ATP need to break cross-bridge attachment. Movement of Ca2+ requires energy.
ATP Production Methods
Creatine Phosphate, Glycolysis, Oxidative Phosphorylation
Creatine Phosphate
Creatine Kinase Catalyzes the reaction
Glycolysis
Lactic Acid Production
Oxidative Phosphorylation
Very high energy, but must have O2 and Myoglobin – Storage
Physiological Fatigue (Muscle Fatigue)
Muscle can not contract fully – no matter what
the stimulus.
Psychological Fatigue (Central Fatigue)
Muscle able to contract – human unwilling
Skeletal Muscle Fiber Types
Slow Twitch
Fast Twitch
Slow Twitch
Type I, Oxidative
Fast Twitch
Type IIa, Oxidative
Type IIb, Glycolytic
Smooth Muscle
Lack Striations, Relatively Small, “Spindle Shaped”,
actin, myosin, dense bodies, caveolae
Actin – Lacks troponin
Myosin – Longer than Skeletal Muscle myosin
Dense Bodies – analogous to Z-lines
Caveolae – T-tubule Like???
Smooth Muscle Contraction
Ca2+ dependent mechanism – but very
different than skeletal muscle.
What regulates contraction
Myosin (Light Chain)
EC Smooth
Increased intracellular calcium, Ca2+ binds to calmodulin, Ca2+ - Calmodulin complex activates myosin (light chain) kinase, MLCK phosphorylates myosin, Cross-bridge attachment and cycling occur
Myogenic contraction
Muscle is able to
generate contraction on
it’s own and Single-unit
Neurogenic contraction
Nervous input is
needed to initiate
contractions, For smooth muscle it is ANS innervation,
Multi-unit
Where are Multi-unit Smooth Muscles found
Ciliary muscles, Iris, Large Blood Vessels, Bronchioles
Multi-unit Smooth Muscle
Cells are electrically isolated Varicosities on post-ganglionic neuron near
cells
Where are Single-unit Smooth Muscle found
Everywhere else – gut, the lining of glands and
hollow organs, uterus…
Single-unit Smooth Muscle
Cells are electrically linked,
Pacemaker Potentials, Slow Wave Potentials
Slow-wave potentials
undulating changes in the resting membrane potential in gastrointestinal smooth muscle responsible for triggering an action potential.
Single-unit Smooth Muscle Tone
Helps keep the shape of organs, Tonic vs. Phasic, enough Ca2+ in the
cytosol to maintain some cross-bridge attachment
Single-Unit Rate of Contraction
Regulated by ANS
How long are smooth muscle contractions
Up to 3 sec