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.
Regeneration of Muscle Tissue
egeneration is rapid in smooth muscle because ….
the cells/fibers are small and relatively less differentiated, which allow renewed mitotic activity after injury.
The basal lamina of a muscle fiber is part of which structure?
a. Perimysium
b. Epimysium
c. Fascia
d. Endomysium
e. Sarcoplasmic reticulum
With the transmission electron microscope skeletal muscle fibers can be seen to contain structures called triads. What do the two lateral components of a triad represent?
a. Attachment sites for thick myofilaments
b. Sites for calcium sequestration and release
c. Sites for impulse conduction into the fiber
d. Sites for ATP production
e. Sites for synthesis of proteins to be secreted outside the cell
Which characteristic is unique to cardiac muscle?
a. Contain centrally located nuclei
b. Striated
c. Often branched
d. Multinucleated
e. Lack T-tubules
In smooth muscle calcium released by the smooth ER initiates contraction by binding to what protein?
a. Actin
b. Calmodulin
c. Desmin
d. Myosin light chain kinase
e. Tropomyosin
Which feature typifies T-tubules?
a. Evaginations of the sarcoplasmic reticulum
b. Sequester calcium during muscle relaxation, releasing it during contraction
c. Carry depolarization to the muscle fiber interior
d. Overlie the A-I junction in cardiac muscle cells
e. Rich supply of acetylcholine receptors
Which characteristic is unique to smooth muscle?
a. T-tubules lie across Z lines
b. Each thick filament is surrounded by six thin filaments
c. Thin filaments attach to dense bodies
d. Cells are multinucleated
e. Cells have centrally located nuclei
In one type of muscle, numerous gap junctions, desmosomes, and adherens junctions are specifically localized in which structures?
a. Myofilaments
b. Dense bodies
c. Sarcomeres
d. Neuromuscular spindles
e. Intercalated discs
A 66-year-old man who lives alone has a severe myocardial infarction and dies during the night. The medical examiner’s office is called the following morning and describes the man’s body as being in rigor mortis. This state of rigor mortis is due to which one of the following?
a. Inhibition of Ca2+ leakage from the extracellular fluid and sarcoplasmic reticulum
b. Enhanced retrieval of Ca2+ by the sarcoplasmic reticulum
c. Failure to disengage tropomyosin and troponin from the myosin active sites
d. Absence of ATP preventing detachment of the myosin heads from actin
e. Increased lactic acid production
A 5-year-old boy sustains a small tear in his gastrocnemius muscle when he is involved in a bicycle accident. Regeneration of the muscle will occur through which of the following mechanisms?
a. Dedifferentiation of muscle cells into myoblasts
b. Differentiation of muscle satellite cells
c. Fusion of damaged myofibers to form new myotubes
d. Hyperplasia of existing muscle fibers
e. Differentiation of fibroblasts to form myoblasts
A healthy 32-year-old man lifts weights regularly as part of his workout. In one of his biceps muscle fibers at rest, the length of the I band is 1.0 μm and the A band is 1.5 μm. Contraction of that muscle fiber results in a 10% shortening of the length of the sarcomere. What is the length of the A band after the shortening produced by muscle contraction?
a. 1.50 μm
b. 1.35 μm
c. 1.00 μm
d. 1.90 μm
e. 0.45 μm
