Ch 10: Muscular Tissue Flashcards
There are three major types of muscle:
(1) skeletal or striated muscle, (2) cardiac muscle, and (3) smooth or visceral muscle.
Skeletal muscle cells
very long, multinucleated fibers, cylindrically shaped and with diameters up to 100 μm.
The sarcolemma of each fiber is surrounded by an external lamina and thin connective tissue, endomysium, containing capillaries.
Groups of fibers called fascicles are surrounded by
perimysium; all fascicles are enclosed within a dense connective tissue epimysium.
Internally each muscle fiber has:
is filled with myofibrils, composed of thousands of thick myosin filaments and thin actin filaments, highly organized into contractile units called sarcomeres.
Within sarcomeres
thick and thin filaments interdigitate; globular myosin heads project from the thick filaments toward the F-actin filaments, which are associated with tropomyosin and troponin.
Sarcomeres are separated
by Z discs that bisect the light-staining I bands that contain mainly the thin filaments attached to α-actinin in the Z disc
Between the two I bands of a sarcomere
is the dark-staining A band with the thick myosin filaments; alternating light and dark bands appear as microscopic striations along the fibers.
In the sarcoplasm between parallel myofibrils are mitochondria and cisternae of smooth ER, called
the sarcoplasmic reticulum(SR) specialized for Ca2+ sequestration and release.
At each sarcomere, two terminal cisterns of SR contact a deep invagination of the sarcolemma called a transverse or T-tubule
what does this cause?
a forming a triad that triggers Ca2+ release when the sarcolemma is depolarized.
Ca2+ binding to troponin causes tropomyosin to change shape and
allow the myosin heads to bind the actin subunits, forming crossbridges between thick and thin filaments.
The myosin heads then pivot with ATP hydrolysis, which pulls the thin filaments along the thick filaments.
With Ca2+ and ATP present, a contraction cycle ensues in which:
myosin heads repeatedly attach, pivot, detach, and return, causing the filaments to slide past one another, shortening the sarcomere.
When the membrane depolarization ends, Ca2+ is again sequestered, this causes….
the ending contraction and allowing the sarcomeres to lengthen again as the muscle relaxes.
Synapses of motor axons with skeletal muscle are called:
motor end plates (MEPs), neuromuscular junctions (NMJs), or myoneural junctions; the neurotransmitter used is acetylcholine.
A motor axon may form many terminal branches, each ending on an MEP of a muscle fiber, but….
all fibers innervated by branches of that axon comprise a motor unit.
Muscle Spindles & Tendon Organs
These are both sensory proprioceptors in which sensory axons wrap around intrafusal fibers in small specialized fascicles or around myotendinous collagen bundles, respectively.
Muscle Fiber Types
Skeletal muscles contain fibers that can be physiologically classified as the three main types:
1) slow, oxidative (type I);
(2) fast, intermediate oxidative-glycolytic (type IIa);
(3) fast, glycolytic (type IIb).
Cardiac Muscle
Cardiac muscle fibers are also striated, but they consist of individual cylindrical cells, each containing one (or two) central nuclei
and linked by adherent and gap junctions at prominent intercalated discs.
Sarcomeres of cardiac muscle are organized and function similarly to those of skeletal muscle.
Cardiac Muscle
Contraction of cardiac muscle is intrinsic at
at nodes of impulse-generating pacemaker muscle fibers; autonomic nerves regulate the rate of contraction.
Smooth Muscle
Smooth muscle fibers are individual small, fusiform (tapering) cells,
they are linked by…..
numerous gap junctions.
Thin and thick filaments in smooth muscle fibers do not form sarcomeres, and no striations are present.
Smooth Muscle
Thin actin filaments attach to α-actinin located in dense bodies that are located ….
throughout the sarcoplasm and near the sarcolemma; contraction causes cells to shorten individually.
Smooth Muscle
Sarcoplasmic reticulum is less well-organized in ….
smooth muscle fibers, and there is no transverse tubule system.
Smooth Muscle
Troponin is lacking in smooth muscle; proteins controlling the sliding filaments here include….
myosin light-chain kinase (MLCK) and the Ca2+-binding protein calmodulin.
Regeneration of Muscle Tissue
Repair and regeneration can occur in….
skeletal muscle because of a population of reserve muscle satellite cells that can proliferate, fuse, and form new muscle fibers.
Regeneration of Muscle Tissue
Cardiac muscle lacks
satellite cells and has little capacity for regeneration.