Question

13). Describe the structural & functional differences between a myofilament & a myofibril?

14). List four (4) proteins found in the myofilaments & describe their physical arrangement with respect to each other.

15). Describe the overlapping pattern of thick & thin myofilaments & explain how this overlap pattern accounts for the A band, I band, H band & Z disc appearances.

16). What differences would you expect to see between a motor unit where muscular strength is more important than fine control & another motor unit where fine control is more important than muscular strength?

Answer 1

13)

Myofibrils : They are the formed by the bundle of myofilaments

The cells of the msucle are called myocyte , the myocyte is composed of rod like structure called Myofribils

The function of the myofibril is to contract with stimuli , because it is composed of proteins that are capable for the contraction

Myofilaments: Myofilaments are the basic unit of the myofibril

structurally it is composed of Thick filaments(myosin) and thin filaments(actin)

Functionally it is meant for muscle contraction

14)The four proteins in the myofilaments are

ACTIN:

MYOSIN

TROPOMYOSIN

TROPONIN

Actin is a linear polymer of g-actin monomer , the tropomysin is the linear protien that is bound to the surface of the Actin. Each tropomyosin contain Troponin(I,T,C)

when the muscle is stimulated by an impulse , the sarcoplasmic reticulum releases calcium ion , calcium will bind to the troponin and help in the movement of the tropomyosin from above the actin filament and it causes the exposure of the actin Binding site.Myosin protein will bind with the actin binding site to produce the muscle contraction

3)the thin filament is composed of mainly actin protein and the thick filament s composed of myosin protein. When the sarcoplasmic reticulum releases teh calcium ion , the calcium bind with the troponin and the cative site of the actin filament get exposed, the myosin will bind with the actin and produce the sliding of ctin filament over the myosin filament(sliding filament theory)

The actin is bound to the z line when muscle contract the actin filament comes closer above the myosin filament and soem bads are created, they are

1)A band(anisotrophic)- it is the dark band , it is composed of both actin filament and myosin filament

I band(isotrophic) - light band , it is composed of only the actin filament

H band is the central area of the sarcomere, when the muscle contract the actin filament comes closer and the H band disappear

16) motor unit where muscular strength is more important than fine control

This type of muscle are our quadriceps muscle , leg muscle they are mainly disigned for stability.

This muscle fibres are supplied by a single motor unit

A motor unit comprises of motor neuron and muscle fibers

But the muscle that requires fine movement is suuplied by more than one motor unit

that is a single motor unit only supply few muscle fibers, the whole muscle is supplied by more number of motor unit.

thsi can be explained by the innervation ratio( that is number of muscle fiber supplied by the motor unit)

innervation ratio for the muscle whose strength is more important is high

innervation ratio of the fine muscles are low