Physiology of Muscle - 2 Flashcards
Actions of muscle
Contraction or shorting of muscle fibers, convert chemical energy onto mechanical energy
Relaxation
Passive process of a muscle contraction
Structure of skeletal muscle
Bundles or sheets of tissue (fascia), fascia composed of many fibers, individual fibers composed of myofibrils, myofibrils are made of up end to end sarcomeres, sarcomers - the smallest repetitive subunit of contractile unit, sarcomeres are composed of thin and thick filaments
Thin filaments
Actin
Thick filaments
Myosin
Largest to smallest
Muscle, fascia, fibers, myofibrils, sarcomeres, filaments, thin actin / thick myosin
Myofibrils
Specialized contractile organelle that can constitute up to 90% the volume of muscle fiber, total volume in a fiber dictates potential force
Sarcomeres
Functional unit of muscle, smallest component of muscle, give the striated appearance
Thin filaments three proteins
Actin, tropmyosin, tropnin
Actin proteins
Connected end to end into two long thin filaments, twisted to create double helical form, binding site for myosin
Tropomyosin
Thread like proteins that lie end to end, two polypeptide chain, positioned along actin filaments to facilitate the binding of the myosin cross bridge for contraction to occur
Troponin
Protein complex that consists three polypeptide units
Three troponin units
T, I, C
Troponin T
Binds tightly to tropmyosin
Troponin I
Binds tightly to actin, inhibiting the actin/myosin interaction durning the relaxed state
Troponin C
Binds to Ca to expose the myosin binding site on the actin molecule, initiating muscle contraction
Myosin
Make up large thick filaments of the sarcomere, consitis of hundreds of proteins in a specific arrangement, Tesoro heavy chains and two light chains , composed of two identical subunits, both shaped like a golf club with heads on opposite ends
Myosin head
Two globular heads projected at one end, represents binding site to actin during contraction, each head has two binding sites
Two types of binding sites
Actin binding site, ATPase binding site
Actin binding site
Binds the globular head to the actin molecule
ATPase binding site
Bound ATP is hydrolyzed, yielding energy for contraction
Sarcoplasmic Reticulum
Supplies Ca needed for contractions, interconnected tables surrounding each myofibrils like sleeve, end of each expands called lateral sacs
Transverse tubules
Finger like invaginations of the sarcolemma, run perpendicular from surface, transferring actin potential, releases Ca to bind with troponin C
Steps of contractions
Action potential is sent, causes nerve ending to release ACH, binds to receptor, causes action to be spread, T Tubules transfer actin uniformly, spread of actin to the SR causes immediate release of Ca, Ca binds to Troponin C, ATP cleaved to yield energy for contractions, causes shortlist of muscle
Steps for relaxation
Ca is pumped back in SR, Ca is released from Troponin C, breakdown of myosin/actin linkage, filaments expand back to relaxed state
What are the 5 lines and bands of sacromere
I-band, A-band, Z-line, M-line, H-zone
I-band
Acting filaments, light bands
A-band
Myosin filaments, dark bands
Z-line
Defines the outer edges of the sarcomere
M-line
Cross connections of myosin filaments that hold myosin filaments
H-zone
Short section where actin does not overlap myosin filaments
Two type of muscle contraction
Isometric, isotonic
Isometric contractions
Muscle re sins the same, length when held stationary against equal resistance or tension
Isotonic contractions
Tension in the muscle stays the same but the length changes
Types of isotonic contractions
Concentratic, eccentric
Concentric contractions
Common form, where the force generated by the muscle moves a bone or segment by shortening
Eccentric contractions
The force generated by the muscle is nit sufficient and the external force (or gravity) causes the fibers to lengthen
Types of smooth muscle
Single unit/ unitary, multi-unit
Single- unit
Hundreds of millions fibers the contraction together, make up 99% of smooth muscle, fibers are joined with gap junctions
Gap junctions
Transmit action potential from fiber to fiber
Multi-unit
Consist of distinct single fibers, gap joints are not prevalent, each fiber operates independently,
Smooth muscle contractions — than skeletal muscle
Slower
How much more force does smooth muscle generate compared to skeletal muscle
4-6x greater
