Threadlike shape, many mitochondria, several nuclei
Shape and Structure of Muscle Cell
Fusion of many small cells
How is a muscle cell formed?
DNA & RNA for protein synthesis
Why are there so many nuclei?
Plasma membrane of muscle fibers
Network of tubules & sacs Extend across sarcoplasm perpendicular to long axis of muscle fiber Formed by inward extensions of sarcolemma Ion pumps continually transport Ca2+ inward from sarcoplasm Allow electrical impulses traveling along sarcolemma to move deeper into cell
Numerous fine fibers packed close together in sarcoplasm Each myofibril contains thousands of thick & thin myofilaments
Sarcoplasmic reticulum (SR)
Pumps Ca2+ ions from sarcoplasm & stores ions for later release
Triplet of tubules Sandwiched between two sacs of SR Allows electrical impulse traveling along T tubule to stimulate membranes of adjacent sacs of SR
Segment of myofibril between two successive Z disks Each myofibril consists of many sarcomeres Contractile unit of muscle fibers
Dark stripes H zone runs across midsection of A band
Light stripes Z disk extends across center of I band
Muscle Plasma Membrane
Temorarily Stores Calcium
Piece of sarcolemma that indents
Made up of thousands of thick myofilaments. Packed closely together.
Thick filaments are made up of only
Thin filaments are anchored by
Thick filaments a called
Thin Filaments are called
Thick filaments are anchored by
Actin, Tropomyosin, Troponin
Thin Filaments are made up of
Globular protein that Forms two fibrous strands twisted around each other
Blocks active sites on actin molecules
Holds tropomyosin molecules in place
Makes up almost all thick filaments, Heads chemically attracted to actin molecules, Heads aka cross bridges when attached to actin.
I shortens, A stays the same length
How are the bands effected when a muscle contracts?
Immediately after Ca2+ is released, SR begins actively pumping it back into sacs. Ca2+ is removed from troponin molecules, thereby shutting down contraction
Small motor control
Less fibers in a unit, fine muscle control, precise movement
Large motor control
More fibers in a unit, fine muscle control, more powerful contaction
Tonic contraction. Continual, partial contraction of muscle. Small number of muscle fibers within muscle contract & produce tightness, or muscle tone. Muscles with less tone than normal are flaccid. Muscles with more tone than normal are spastic. Muscle tone is maintained by negative feedback mechanisms.
Tension within a muscle remains same as length of muscle changes. All energy of contraction is used to pull on thin myofilaments & thereby change length of fiber's sarcomeres. Most body movements occur as result of both types of contractions. Two Types are Concentric & Eccentric.
Muscle shortens as it contracts. Type of isotonic contraction.
Muscle lengthens while contracting
Concentric & Eccentric
What are the two types of Isotonic Contractions?
Energy source. Binds to myosin head. Transfers energy to perform work of pulling thin filament during contraction. Continually resynthesized from breakdown of creatine phosphate. Catabolism by muscle fibers requires glucose & O2. At rest, excess O2 in sarcoplasm is bound to myoglobin.
Energy source. Occurs when adequate O2 is available Slower than anaerobic respiration Supplies energy for long term
Energy source. Very rapid. Provides energy during first minutes of maximal exercise. Low levels of O2.
Formation of lactic acid
Energy source. Occurs in Anaerobic respiration. Requires O2 to convert back to glucose. Produces "oxygen debt," or excess post-exercise O2 consumption.
Skeletal muscle contraction
What produces heat & can be used to help maintain set point body temperature?