Muscular System Flashcards
Skeletal Muscle
Large, elongated, multinucleated fibers; voluntary; neuromuscular junction.
10-100 um in diameter
Activity:
Strong, quick discontinuous voluntary contraction
Cardiac Muscle
Large, fibers branch, one or two nuclei, involuntary, intercalated discs with gap junctions so that all fibers of the atrium or ventricle contract simultaneously.
10-100 um in diameter
Activity:
Strong, quick, continuous involuntary contraction
Smooth Muscle
Small, fusiform fibers with tapering ends, nucleus in the center, involuntary, gap junctions between cells so that all muscles during peristalsis can contract in a unison.
4-5 um in diameter
Activity:
Weak, slow involuntary contraction
Organization of Skeletal Muscle
Fasciculus, fibers, myofibrils, myofilaments (actin, myosin).
Connective Tissue Coverings
Epimysium: surrounding the whole muscle
Perimysium: surrounding each fasciculus
Endomysium, surrounding each fiber.
Function of Connective Tissue
Brings blood vessels and nerves closer to fibers and transmit force of muscle contraction to the tendon and, in turn, to the bone, consequently leading to the flexion or extension of the joint.
Striated Skeletal Muscle in longitudinal section
Striations can be seen nuclei in the periphery
Striated Skeletal Muscle in Transverse( cross) section
Nuclei located in the periphery of each fiber; striations cannot be clearly observed
Nuclei in the periphery are arranged in a row (can be confused with fibroblasts present in the endomysium).
Striations under a microscope
Forms dark and light bands are clearly visible.
A bands
The dark stained bands
contains both thick and thin filaments
(actin and myosin filaments overlapping)
each myosin filaments has 6 actin filaments surrounding it
center of A band only has myosin
I band
the light-stained band
contains only thin filaments;
(only actin filament),
Z line
Thin dark stained
border for the sarcomere
H band
contains only thick filament (middle of A band)
Only myosin filaments
M line
Present in the middle of H band and results from attachment of adjacent myosin filaments
Triad
Each triad consists of a T tubule in the center (cell membrane invagination, extracellular) ) and a SER cisterna on each side (intracellular)
Triads in amphibians
Triads in amphibian muscle are aligned with the Z line in each sarcomere.
Triads In Mammalian Muscle
In mammalian muscle, each sarcomere exhibits 2 triads, one at each A–I band interface.
Sarcomere
Is called a sarcomere, a structural and functional unit of the skeletal muscle. Hence, each muscle fiber contains thousands of sarcomeres along the length (depending upon the length) and hundreds of sarcomeres along the width. Giemsa stain.
Sarcomere is from one Z line to the adjacent one
- the structural and functional unit of the skeletal muscle
SER Cisterna
due to depolarization, Calcium is released which is vital for muscle contraction
The depolarization wave extends along the length of the T tubule and is transmitted to the adjacent SER, from where calcium is released, resulting in muscle contraction
Types of skeletal muscle fibers identified by staining mitochondria with succinate dehydrogenase enzyme. ( can also use atpase)
Red (Type I, aerobic)
White (Type II, anaerobic)
Intermediate
White skeletal muscle fibers (Type II, anaerobic)
Larger, fewer mitochondria, more extensive SER, energy from anaerobic glycolysis, contract and fatigue more rapidly, fast-twitch fibers.
- has more glycogen
Red skeletal muscle fibers (Type I, aerobic):
large amount of myoglobin, numerous mitochondria, energy from oxidative pathway, contract and fatigue slowly, slow-twitch fibers.
posture muscles tend to be red fibers
Intermediate skeletal muscle fibers
Share characteristics of both fibers.
Where are white fibers found
Where are red fibers found
Neuromuscular junction (Motor end plate)
Each branch terminates as a motor end plate on a different muscle fiber.
Hence, all muscle fibers innervated by one axon (one neuron) constitute a motor unit.
Importance of size of a motor unit
The larger the size of the motor unit the cruder the muscle movement (for example, hip muscle, one neuron may innervate hundreds of fibers).
Conversely, the smaller the motor unit, the finer the movement (for example, eye muscles, one neuron may innervate 5-10 muscle fibers).
muscles can be trained to be less crude and more finer
Changes at the distal end of the axon
Dilation of the axon, myelin sheath loss, and aggregation of mitochondria and vesicles containing acetylcholine (Ach).
Changes at the Muscle Fiber
Folding of cell membrane (sarcolemma) enclosing sub-neural clefts, aggregation of mitochondria, and loss of striations.
Events of Impulse Conduction:
1) Depolarization of axolemma
2) release of Ach
3) binding of Ach with Ach receptors on sarcolemma
4) depolarization of sarcolemma
5) extension of depolarization wave to the T tubule and SER cisternae (triad)
6) release of Ca++
7) contraction of myofilaments
8) inactivation of Ach by cholinesterase enzyme present in sub-neural clefts
9) active transport of Ca++ back into SER
10) relaxation of myofilaments
Results of Contraction
1) I band reduces in length
2) sarcomere reduces in length
3) H band disappears
4) and no change in the length of the A band or of actin and myosin filaments.
Huxley’s Sliding Filament Theory of Muscle Contraction
Thick and thin filaments maintain the same length but slide past each other.
What are the three main proteins present in actin filaments
actin, tropomyosin, and troponin.
Actin
Is a globular protein and is polymerized to form a structure resembling double helix;
Each tropomyosin molecule location?
Lies in the double helix groove;
Each troponin (Tn) molecule has
three binding sites: TnC: binds calcium,
TnT: binds tropomyosin, TnI: inhibits actin myosin interaction.
