BIOL 252 Exam 2 Practice Questions and Correct Answers
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Course
BIO 252
Institution
BIO 252
Myocyte Muscle cell
Sarcolemma Plasma membrane of myocyte
Sarcoplasm Cytoplasm of myocyte
Myofibril Tightly packed filament bundles found within skeletal muscle fibers. Contractional unit of a muscle cell.
Sarcoplasmic reticulum Site of calcium storage in a muscle cell. Surrounds the myofibrils...
BIOL 252 Exam 2 Practice Questions and
Correct Answers
Myocyte ✅Muscle cell
Sarcolemma ✅Plasma membrane of myocyte
Sarcoplasm ✅Cytoplasm of myocyte
Myofibril ✅Tightly packed filament bundles found within skeletal muscle fibers.
Contractional unit of a muscle cell.
Sarcoplasmic reticulum ✅Site of calcium storage in a muscle cell. Surrounds the
myofibrils
Transverse tubules (T-tubule) ✅Inward extensions of the sarcolemma that dive into the
muscle fiber and surround each myofibril to form a tunnel-like network within the muscle
fiber
Terminal cisternae ✅Enlarged portions of the sarcoplasmic reticulum that flank each
side of a T-tubule
Triad ✅Combination of a T-tubule and it's two terminal cisternae on either side
Organization of muscles and muscle cells ✅Muscle (organ) --> fascicle --> myocyte
(cell) --> myofibril (organelle)
Myofilament ✅Collection of myofibrils; protein bundles
Endomysium ✅Connective tissue over the myocytes
Proteins found in myofilaments ✅Contractile proteins
Regulatory proteins
Structural proteins
Contractile proteins ✅Produce tension
Regulatory proteins ✅Control when the muscle fiber can contract
Structural proteins ✅Hold the myofilaments in their proper places and ensure the
structural stability of the myofibril and the muscle fiber
,Three types of myofilaments ✅Thick filaments
Thin filaments
Elastic filaments
Thick filaments ✅- largest diameter
- many units of myosin
- contractile protein
Myosin ✅Motor protein for muscle contraction
Thin filaments ✅- made up of contractile and regulatory proteins
- contains actin, tropomyosin, and troponin
Actin ✅Bead-shaped protein with an area called the active site that binds to a myosin
head
- strung together like beads on a necklace to form the largest part of the thin filament
- appears as two intertwining strands
Tropomyosin ✅Long rope-like regulatory protein that spirals around the two actin
strands so that it covers the active sites on actin
Troponin ✅Regulatory protein that holds tropomyosin in place
Elastic filaments ✅- thinnest type
- composed of a single massive structural protein called titin
Titin ✅- spring shaped
- runs through core of thick filament to help stabilize myofibril
- resists excessive stretching
- provides elasticity to muscle fiber
I band ✅Light region of a striation that contains only thin filaments
Z-disc ✅Dark line in I bands that is composed of structural proteins
- anchors thin filaments in place and to one another
- attachment point for elastic filaments
- attaches myofibrils to one another across the whole diameter of the muscle fiber
A band ✅Dark region of a striation that contains thick filaments
H zone ✅Middle area of A band that is slightly lighter, contains only thick filaments
, M line ✅Dark line in the middle of A bands that consists of structural proteins that hold
the thick filaments in place, serve as an anchoring point for the elastic filaments
Sarcomere ✅Functional unit of contraction where muscle tension is produced
- section of myofibril that extends from one Z-disc to the next Z-disc
- includes full A band and half of two I bands
Fascia ✅Thick layer of connective tissue that encloses skeletal muscles, anchoring
them to surrounding tissues and holding groups of muscles together
Epimysium ✅Layer of connective tissue deep to the fascia that surrounds the whole
muscle
Perimysium ✅Deeper layer of connective tissue that blends with the epimysium;
surrounds individual fascicles (groups of muscle fibers)
What do the epimysium and perimysium form? ✅Tendons
Sliding-filament mechanism ✅Interaction of thin and thick filaments during muscle
contraction and relaxation
What happens to the sarcomere with each contraction? ✅Grows progressively shorter
Which part of the sarcomere shortens during a contraction? ✅I band
Dystrophin ✅Linking protein that links thin filaments to proteins of sarcolemma
Which neurotransmitter is found at the neuromuscular junction? ✅Acetylcholine
Motor end plate ✅Specialized region of the sarcolemma whose folded surface proteins
contain ACh receptors. "Dendrite" of a muscle fiber.
Excitation ✅Sarcolemma of a muscle fiber must be stimulated by ACh from a motor
neuron to have an action potential
Excitation phase ✅1. action potential arrives at the axon terminal, triggers calcium
channels to open
2. calcium ion entry triggers exocytosis of synaptic vesicles
3. synaptic vesicles release acetylcholine into synaptic cleft
4. acetylcholine binds to ligand-gated ion channels in the motor end plate
5. ion channels open, sodium ions enter the muscle fiber
6. entry of sodium ions depolarizes the sarcolemma and produces an end-plate
potential
- multiple end-plate potentials --> functional contraction of a muscle fiber
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