muscle cell structure Flashcards
What are the three types of muscle tissue?
skeletal muscle, cardiac, and smooth
- found in voluntary muscles
- cells are called muscle fibers - these are long and cylindrical
- multinucleate
skeletal muscle tissue
contraction of skeletal muscle tissue is dependent on stimulation by somatic motor neurons, these form a chemical synapse called what?
neuromuscular junction
release of __________ induces an action potential, which stimulates contraction of the muscle. (in skeletal muscle)
acetylcholine
- located int he heart
- short, irregular- shaped cells
- single nucleus
cardiac muscle tissue
in cardiac muscle, cells are connected by gap junctions that are located within the __________ ____________
intercalated discs
cardiac muscle is _____________ , meaning that action potentials arise within the muscle tissue itself.
autorhythmic
action potentials within cardiac muscle are transmitted cell to cell via
electrical synapses
- located in the viscera and involved in reflexes
- spindle-shaped and smaller than muscle fibers
- single nucleus
smooth muscle tissue
what are the 2 types of smooth muscle tissue?
single-unit and multi-unit
located in the uterus, GI tract, and small-diameter blood vessels.
- connected by electrical synapses
- autorhythmic
single-unit smooth muscle tissue
-located in large arteries, respiratory airways, iris of the eye, arrector pili muscles of skin
-not connected by electrical synapses
- contraction stimulated by depolarizing postsynaptic potentials
- do not produce action potentials
multi-unit smooth muscle tissue
the plasma membrane of the muscle cell
sarcolemma
the cytosol (ICF) of muscle cell
sarcoplasm
cylindrical structures that extend the length of the muscle fiber and contain the sarcomeres.
myofibrils
what causes the contraction of the muscle fiber?
contraction of sarcomeres
specialized portion of the ER that acts as a calcium ion storage organelle
sarcoplasm reticulum
propagate action potentials from the sarcolemma to the interior of the muscle fiber
transverse tubules (T tubules)
dark crosswire striations on a myofibril
A bands
light crosswire striations on a myofibril
I bands
What gives the myofibrils a striated appearance?
the A and I bands between myofibrils
What are the proteins in the myofibrils organized into?
thick or thin filaments
Thick filaments are surrounded on all sides by thin filaments
yes
Where are thick filaments located?
in the A bands
What is found in the center of each A band?
M line
The central area of an A band (lighter area flanked by darker areas)
H zone
What are the dark areas that flank the H zone?
where the thick and thin filaments meet
Only what kind of filaments are found within the H zone?
thick
Where are thin filaments located?
I band and overlap w A band
What is found in the center of each I band?
Z disk
contractile unit of a myofibril, area between two adjacent Z disks
sarcomere
a chain of Z disks arranged end-to-end
myofibril
What are thin filaments made of?
G-actin, tropomyosin, troponin
a globular protein that can polymerize to form long chains
g-actin
two g-actin chains coiled together form
F-actin
Each G-actin has one
myosin-binding site
A filamentous protein that lies along F-actin, and has the ability to block myosin-binding sites
tropomyosin
Troponin consists of what 3 subunits?
troponin T, troponin I, and Troponin C
which troponin subunits can interact w tropomyosin and alter its position w respect to the myosin-binding sites?
troponins I and T
can bind to calcium ions and regulates the activity of troponins I and T
troponin C
made primarily of the protein myosin
thick filament
what is myosin made of? (its characteristics)
long, thin tail and two heads at the end of the protein
Myosin is composed of how many polypeptides? What are they called and how many are there?
6; 2 heavy chains; 4 light chains
What do the heavy chains form in myosin?
the tails and heads
what do the light chains make up?
they contribute to the head and form a flexible hinge region bw the head and tail.
What sites does the head have on each myosin?
an ATPase site and one G-actin binding site
consists on 200-400 myosin molecules bundled together
1 thick filament
the heads that project from the thick filament are called _______________ because they interact w surrounding thin filaments
cross-bridges
the middle of a thick filament lacks cross-bridges and is referred to as the
bare zone
