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BIO102 Unit 3: Muscle Assignment
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BIO102 Unit 3: Muscle Assignment1. Describe the organization of skeletal muscle at the tissue level.
Bodies contain numerous skeletal muscle organs, the muscles that move and support our body,
are attached to bones at each end by what we call tendons. These tendons are composed of
connective tissue, which not only attaches the bone to the muscle, but also wraps around inside
the muscle that separates the organ into smaller components. Inside each skeletal muscle fibers
are organized into individual bundles, called a fascicle, by a middle layer of connective tissue
called the perimysium. This fascicular organization is common in muscles of the limbs; it allows
the nervous system to trigger a specific movement of a muscle by triggering a subset of muscle
fibers within a bundle, or fascicle of the muscle. Inside each fascicle, each muscle fiber is
encased in a thin connective tissue layer of collagen and reticular fibers called the endomysium.
The endomysium contains the extracellular nutrients and fluid to support the muscle fiber. These
nutrients are supplied by blood to the muscle tissue.
2. Describe and provide a function for muscle's associated connective tissues.
Muscles have 3 layers of connective tissues the epimysium -an exterior collagen layer connected
to the deep fascia which separates the muscle from surrounding tissues. The perimysium
surrounds bundles of muscles fibers called fascicles. Perimysium holds the blood vessels and
nerves that supply the fascicles. The endomysium, surrounds individual muscle cells, the muscle
fibers), contains the capillaries and nerve fibers that link the muscle cells. Endomysium also has
stem cells that repair damaged muscles. At each end of the muscle, the endomysium,
perimysium and epimysium come together to form a connective tissue attachment to the bone
matrix, either a tendon or a bundle or an aponeurosis, a sheet. Skeletal muscles are voluntary
muscles, operated by nerves from the central nervous system. An extensive vascular system
supplies large amounts of oxygen to muscles and carries away waste material.
3. How is a muscle attached to the bone? Describe the structures and their functions.
Muscle is attached to the bone by tendons. Skeletal muscles are attached to the ends of bones
that meet at a joint. These muscles span the joint and connect the bones. When the muscles
contract, they pull on the bones, causing them to move.
Identify the structural components of a sarcomere.
Sarcomeres are composed of long, fibrous proteins as filaments that slide past each other when a
muscle contracts or relaxes. Two of the important proteins are myosin, which forms the thick filament,
and actin, which forms the thin filament. Myosin has a long, fibrous tail and a globular head, which binds
to actin.
4. Describe the structural components of a thin filament and a thick filament.
, Each thick filament is approximately 15 nm in diameter, and each is made of several hundred molecules
of myosin. Thin filaments, 7 nm in diameter, consist primarily of the protein actin, specifically fibrous
actin. Each actin strand is composed of a string of subunits called globular actin.
5. What role does Calcium play in the activation of muscle contraction?
When calcium binds to troponin, the troponin changes shape, removing tropomyosin from the binding
sites. The sarcoplasmic reticulum stores calcium ions, which it releases when a muscle cell is stimulated;
the calcium ions then enable the cross-bridge muscle contraction cycle.
6. What role doe Magnesium plain in overall muscle activity?
Magnesium also plays a role in regulating muscle contractions. Just like in the heart, magnesium acts as a
natural calcium blocker to help muscles relax. In your muscles, calcium binds to proteins such as
troponin C and myosin. This process changes the shape of these proteins, which generates a contraction
7. Identify the components of the neuromuscular junction, and summarize the events involved in
the neural control of skeletal muscles.
When an action potential reaches a neuromuscular junction, it causes acetylcholine to be released into
this synapse. The acetylcholine binds to the nicotinic receptors concentrated on the motor end plate, a
specialized area of the muscle fibre's post-synaptic membrane.
8. What is the major neurotransmitter for muscle contraction?
Neuromuscular junction (NMJ) Location where motor neuron controls a skeletal muscle fiber. One NMJ
per muscle fiber, but each motor neuron may branch and control multiple muscle fibers. Neuromuscular
junction components. Axon terminal synaptic terminal of motor neuron. Has vesicles with acetylcholine
(ACh) Neuromuscular junction components. Motor end plate of muscle fiber. Has junctional folds,
creases that increase # of Ach receptors. Contains acetylcholinesterase (AChE); breaks down ACh
Neuromuscular junction components. Synaptic cleft is the space between axon terminal and motor end
plate. Activities at neuromuscular junction. Electrical impulse action potential arrives at axon terminal.
Change in membrane permeability causes Ach vesicles to fuse with neuron plasma membrane. Ach
released exocytosis Ach diffuses across synaptic cleft. Binds ACh-receptor membrane channels at motor
end plate. Changes sarcolemma Na+permeability. Na+ enters muscle fiber sarcoplasm. Na+influx
generates action potential in sarcolemma. Ach diffuses away or breaks down (AChE). ACh-receptor
membrane channels closes. Action potential (AP) generated at motor end plate immediately spreads
across entire sarcolemma. Brief event, Ach was cleared from receptors; no other stimulus occurs until
another AP occurs Action potential moves down T tubules between terminal cisternae of sarcoplasmic
reticulum (SR). Changes permeability of SR. 6.SR releases stored Ca2+into sarcomeres; begins
contraction. Excitation-contraction coupling excitation action potential is coupled with contraction sliding
filaments shorten sarcomeres.
9. Describe the role of ATP in a muscle contraction, and explain the steps involved in the
contraction of a skeletal muscle fiber. "Sliding filament mechanism"
Resting sarcomere: Myosin heads are all “energized” and “cocked”. Cocking head requires breakdown of
ATP –Myosin head acts as ATPase; ADP and P stay attached to head. Contraction cycle begins. Calcium
ions arrive from SR3.Active sites exposed. Calcium binds to troponin. Troponin changes position, moves
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