Skeletal muscles Flashcards
Muscle
Made up of multiple fascicles
Perimysium
Connective tissue surrounding individual fascicle
Fascicle
Bundle of myofibers
Endomysium
Delicate connective tissue around each myofiber
Myofiber
multi nucleated muscle cells
Sarcolemma
cell membrane of myofiber
Myofibril
Chain of sarcomere
Sarcomere
bundle of myofilaments (actin and myosin)
Sarcomere organization
Sarcolemma
T-tubules: invagination of sarcolemma
Form triad with cisternae (enlarged area of sarcoplasmic reticulum)
2 triads per sarcomere
Sarcomere banding
Z discs (Z lines): anchor actin filaments, located at end of sarcomere I band: composed entirely of actin;width changes during contraction A band: composed of actin and myosin; do not change width H band: composed entirely of myosin; width changes during contraction, can disappear at maximum contraction M lines: separated H bands
Sliding filament mechanisms
make sure you go through the whole process from the nerve to the end
Preload
Load in the relaxed state before muscle contracts
Afterload
Load the muscle works against
Types of tension
Passive: produced by preload
Active: produced by cross bridge cycling
Total: sum of active and passive tension
Cross bridge cycling
Starts when free calcium is available and attaches to troponin
Contraction is the continuous cycle of cross bridge
ATP not required to form the cross bridge linking to actin
ATP required to break the link with actin
Continues until withdrawal of calcium ions or ATP depletion
Energetics of muscle contraction
ATP required for:
-sliding filament mechanism
-pumping calcium ions from sarcoplasm back to SR
-Pumping of sodium, potassium ions through sarcolemma to reestablish resting potential
4 mmol—> maintain contraction for 1-2 seconds
Energy for rephosphorylation
phosphocreatine releases energy rapidly and reconstitutes ATP
ATP+phosphocreatine provides energy for 5-8 seconds contraction
Glycolysis :lactic acid build up,sustain contraction for 1 minute
Oxidative metabolism (krebs cycle, ETC)
provide more than 95% of all energy needed for long term contraction
Types of muscle contraction
Isometric: increase in tension but not length
Isotonic: change in length
Eccentric—>muscle lengthens
Concentric—> muscle shortens
Epimysium
Connective tissue surrounding entire muscle
Types of myofiber
Dark, slow fibers (red fibers)
Light, fast fibers (white fibers)
Characteristic of fast ( white) fibers
Contract rapidly but less endurance Fewer mitochondria Use anaerobic respiration primarily Little myoglobin Large concentration of ATPase
Characteristics of slow (red ) fibers
Contract slowly but more endurance More mitochondria Use aerobic respiration---> pyruvic and lactic acids build up More myoglobin Smaller concentration of ATPase
What is a motor unit?
Neuron and myofibers it innervates form the motor unit
A neuron may innervate from a few o several hundred myofibers
What is summation?
Additional spike adding to the effects of the previous spikes due to electrical events occurring faster than mechanical events which cause an increase in the total calcium ions in the cytosol and cycling cross-bridges—>Increases muscle tension
