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What is the function of connective tissue in a skeletal muscle?
It surrounds and protects muscular tissue.
What is the subcutaneous layer (hypodermis)?
A layer of connective tissue that separates muscle from skin.
What is the function of the subcutaneous layer (hypodermis)?
It provides a pathway for nerves, blood vessels, and lymphatic vessels to enter and exit muscles.
What are the functions of the subcutaneous layer's (hypodermis) adipose tissue?
1. Stores most of the body's triglycerides.
2. Serves as an insulating layer that reduces heat loss.
3. Protects muscles from physical trauma.
What is fascia?
A dense sheet or broad band of irregular connective tissue that lines the body wall and limbs and supports and surrounds muscles and other organs of the body.
What are the functions of fascia?
1. Allows free movement of muscles.
2. Carries nerves, blood vessels, and lymphatic vessels.
3. Fills spaces between muscles.
What are the three layers of connective tissue in a skeletal muscle?
What are the functions of epimysium, perimysium, and endomysium?
They protect and strengthen skeletal muscle.
What is epimysium?
The outermost layer of dense, irregular connective tissue that encircles the entire muscle.
What is perimysium?
The middle layer of dense, irregular connective tissue that surrounds groups of 10 to 100 or more muscle fibers and separates them into fascicles.
What is endomysium?
The innermost layer of connective tissue that penetrates the interior of each fascicle and separates individual muscle fibers from one another.
What are epimysium, perimysium, and endomysium all continuous with?
The connective tissue that attaches a skeletal muscle to other structures, such as bone or another muscle.
What is a tendon?
A white fibrous cord of dense regular connective tissue that attaches muscle to the bone.
What is an aponeurosis?
The connective tissue elements extended as a broad, flat, sheetlike tendon, joining one muscle with another or with bone.
What is fibromyalgia?
A chronic, painful, nonarticular rheumatic disorder that affects the fibrous connective tissue components of muscles, tendons, and ligaments.
What is a striking sign of fibromyalgia?
Pain that results from gentle pressure at specific tender points.
What are some symptoms of fibromyalgia?
1. Even without pressure, there is pain, tenderness, and stiffness of muscles, tendons, and surrounding soft tissues.
2. Severe fatigue.
3. Poor sleep.
5. Irritable bowel syndrome.
6. Inability to carry out daily activities.
What are some treatments for fibromyalgia?
1. Stress reduction.
2. Regular exercise.
3. Application of heat.
4. Gentle massage.
5. Physical therapy.
6. Medication for pain.
7. Low-dose antidepressant to help improve sleep.
Generally, how many arteries and veins accompany each nerve that penetrates a skeletal muscle?
An artery and one or two veins.
Where does the threadlike axon of a somatic motor neuron extend from and go to?
Its axon extends from the brain or spinal cord to a group of skeletal muscle fibers.
What does each branch of the axon of a somatic motor neuron extend to?
A different skeletal muscle fiber.
What is the function of blood capillaries?
They bring in oxygen and nutrients and remove heat and the waste products of muscle metabolism.
How do capillaries aid in the process of muscle contraction?
Especially during contraction, a muscle fiber synthesizes and uses considerable ATP (adenosine triphosphate). These reactions require oxygen, glucose, fatty acids, and other substances that are delivered to the muscle fiber in the blood.
What is a myoblast?
A small mesodermal cell that creates a skeletal muscle fiber when it fuses with other myoblasts during embryonic development.
What happens to a skeletal muscle fiber once fusion occurs?
It loses its ability to undergo cell division.
Does your body create more skeletal muscle fibers after birth?
No. The number of skeletal muscle fibers is set before you are born.
Why can't more skeletal muscle fibers be created after birth?
Because once fusion occurs, skeletal muscle fibers lose their ability to undergo cell division.
What are transverse (T) tubules?
Small, cylindrical invaginations of the sarcolemma of striated muscle fibers (cells) that conduct muscle action potentials toward the center of the muscle fiber.
How do muscle action potentials spread throughout a muscle fiber?
They travel along the sarcolemma and through the T tubules.
What is myoglobin?
The oxygen-binding, iron-containing protein present in the sarcoplasm of muscle fibers (cells); contributes the red color to muscles.
What is the function of myoglobin?
It binds oxygen molecules that diffuse into muscle fibers from interstitial fluid. It then releases this oxygen when it is needed by the mitochondria for ATP production.
Where are the mitochondria located in a skeletal muscle fiber?
They lie in rows throughout the muscle fiber, strategically close to the contractile muscle proteins that use ATP during contraction so that ATP can be produced as quickly as needed.
What is a myofibril?
A threadlike structure, extending longitudinally through a muscle fiber (cell), consisting mainly of thick filaments (myosin) and thin filaments (actin, troponin, and tropomyosin). The contractile organelles of skeletal muscle.
What is the sarcoplasmic reticulum (SR)?
A network of saccules and tubes surrounding myofibrils of a muscle fiber (cell), comparable to endoplasmic reticulum; functions to reabsorb calcium ions during relaxation and to release them to cause contraction.
How does the sarcoplasmic reticulum trigger muscle contraction?
By releasing calcium ions (Ca2+) from its terminal cisterns.
What are terminal cisterns?
Dilated end sacs of the sarcoplasmic reticulum that butt against the T tubules from both sides.
How do terminal cisterns trigger muscle contraction?
The sarcoplasmic reticulum triggers it to release calcium ions (Ca2+).
In the regions of filament overlap, how many thin filaments are there for every thick filament?
There are two thin filaments for every thick filament.
What is a sarcomere?
A contractile unit in a striated muscle fiber (cell), especially of a skeletal muscle fiber; the basic functional unit of a myofibril.
What are Z discs?
Narrow, plate-shaped regions of dense material that separates one sarcomere from the next.
What does the extent of overlap of the thick and thin filaments depend on?
On whether the muscle is contracted, relaxed, or stretched.
What creates the visible striations in single myofibrils and whole muscle fibers?
The overlap patterns of the thick and thin filaments.
What is the A band?
The dark, middle part of sarcomere that extends the entire length of thick filaments and includes those parts of thin filaments that overlap thick filaments.
What is the zone of overlap?
Where the thick and thin filaments lie side by side toward each end of the A band.
What is the I band?
The lighter, less dense area of sarcomere that contains a remainder of thin filaments but no thick filaments; a Z disc passes through the center of each I band.
What is the H zone?
The narrow region in center of each A band that contains thick filaments but no thin filaments.
What is the M line?
The region in center of H zone that contains proteins that hold thick filaments together at center of sarcomere.
How do existing muscle fibers enlarge through muscular hypertrophy?
From increased production of myofibrils, mitochondria, sarcoplasmic reticulum, and other organelles.
How does muscular hypertrophy occur?
From very forceful, repetitive muscular activity, such as strength training.
What are hypertrophied muscles capable of more forceful contractions?
Because there are more myofibrils.
What stimulates an increase in the size of skeletal muscle fibers during childhood?
Human growth hormone, testosterone, and other hormones.
What are satellite cells?
Flat, neuroglial cells that surround cell bodies of peripheral nervous system ganglia to provide structural support and regulate the exchange of material between a neuronal cell body and interstitial fluid.
How can functional muscle fibers be regenerated?
Satellite cells can fuse with one another or with damaged muscle fibers, but the number of new skeletal muscle fibers that satellite cells can form is not enough to compensate for significant skeletal muscle damage or degeneration.
How do skeletal muscle fibers regenerate when satellite cells aren't enough?
Skeletal muscle tissue undergoes fibrosis.
What is fibrosis?
The process by which fibroblasts synthesize collagen fibers and other extracellular matrix materials that aggregate to form scar tissue. It replaces damaged skeletal muscle fibers with fibrous scar tissue.
How does muscular atrophy occur?
Individual muscle fibers decrease in size as a result of progressive loss of myofibrils.
What can cause disuse atrophy?
Bedridden individuals and people with casts experience this because the flow of nerve impulses (nerve action potentials) to inactive skeletal muscle is greatly reduced.
What is denervation atrophy?
Muscular atrophy that occurs because a nerve supply to a muscle is disrupted or cut.
What happens to a muscle when it is atrophied by denervation atrophy?
Over a period of six months to two years, the muscle shrinks to about one-fourth its original size, and the muscle fibers are irreversibly replaced by fibrous connective tissue.
What is exercise-induced muscle damage?
Torn sarcolemmas in some muscle fibers, damaged myofibrils, and disrupted Z discs after intense exercise. There is also an increase in blood levels of proteins, such as myoglobin and the enzyme creatine kinase, that are normally confined within muscle fibers.
What is delayed onset muscle soreness (DOMS)?
Stiffness, tenderness, and swelling of skeletal muscles 12 to 48 hours after a period of strenuous exercise.
What are the causes of delayed onset muscle soreness?
Causes are not completely understood, but microscopic muscle damage appears to be a major factor.
What happens to muscle fibers in response to exercise-induced muscle damage?
Muscle fibers undergo repair. New regions of sarcolemma are formed to replace torn sarcolemmas, and more muscle proteins (including those of the myofibrils) are synthesized in the sarcoplasm of the muscle fibers.
Myofibrils are built from what three kinds of proteins?
1. Contractile proteins.
2. Regulatory proteins.
3. Structural proteins.
What are structural proteins?
1. Keep the thick and thin filaments of myofibrils in the proper alignment.
2. Give the myofibril elasticity and extensibility.
3. Link the myofibrils to the sarcolemma and extracellular matrix.
What is myosin?
A contractile protein that makes up thick filament; molecule consists of a tail and two myosin heads, which bind to myosin-binding sites on actin molecules of thin filaments.
What is a motor protein?
A protein that pulls various cellular structures to achieve movement by converting chemical energy in ATP to the mechanical energy of motion, that is, the production of force.
What part of the thick filament do the parallel myosin tails of a myosin molecule form?
The shaft of the thick filament.
Where are the myosin heads located?
They project outward from the shaft in a spiraling fashion, each extending toward one of the six thin filaments that surround each thick filament.
What is actin?
A contractile protein that is the main component of thin filament; each actin molecule has a myosin-binding site where myosin head of thick filament binds during muscle contraction; individual actin molecules join to form an actin filament that is twisted into a helix.
What is a myosin-binding site?
A site on each actin molecule of a thin filament where a myosin head can attach.
What is tropomyosin?
A regulatory protein that is a component of thin filament; when skeletal muscle fiber is relaxed, tropomyosin covers myosin-binding sites on actin molecules, thereby preventing myosin from binding to actin.
What is troponin?
A regulatory protein that is a component of thin filament; when calcium ions (Ca2+) bind to troponin, it changes shape; this conformational change moves tropomyosin away from myosin-binding sites on actin molecules, and muscle contraction subsequently begins as myosin binds to actin.
What does a myosin-binding site look like in a relaxed muscle?
Strands of tropomyosin cover the myosin-binding sites on actin, blocking myosin from binding to actin.
When tropomyosin strands cover the myosin-binding sites on actin, what holds them in place?
How is a muscle contraction initiated in a myofibril?
1. Calcium ions (Ca2+) bind to troponin.
2. Troponin changes shape.
3. Tropomyosin moves away from myosin-binding sites on actin.
4. Myosin binds to myosin-binding site on actin.
5. Muscle contraction begins.
Why does tropomyosin move away from myosin-binding sites on actin?
Because the shape of troponin, which is holding the strands in place, changes.
What are the five key structural proteins on a myofibril?
What is titin?
A structural protein that connects Z discs to M line of sarcomere, thereby helping to stabilize thick filament position; can stretch and then spring back unharmed, and thus accounts for much of the elasticity and extensibility of myofibrils.
What are the functions of titin in a myofibril?
1. It helps stabilize thick filament position.
2. It accounts for much of the elasticity and extensibility of myofibrils.
3. Probably helps the sarcomere return to its resting length after a muscle has contracted or been stretched.
4. May help prevent overextension of sarcomeres.
5. Maintains the central location of A bands.
How much of a sarcomere does each titin molecule span?
Half of a sarcomere, from a Z disc to an M line.
What is α-actinin?
A structural protein of Z discs that attaches to actin molecules of thin filaments and to titin molecules.
What is myomesin?
A structural protein that forms M line of sarcomere; binds to titin molecules and connects adjacent thick filaments to one another.
What is the function of myomesin?
It connects adjacent thick filaments to one another, holding them in alignment at the M line.
What is nebulin?
A long, nonelastic structural protein that wraps around entire length of each thin filament; helps anchor thin filaments to Z discs and regulates length of thin filaments during development.
What are the functions of nebulin?
1. Helps anchor thin filaments to Z discs.
2. Regulates length of thin filaments during development.
What is dystrophin?
A structural protein that links thin filaments of sarcomere to integral membrane proteins in sarcolemma, which are attached in turn to proteins in connective tissue matrix that surrounds muscle fibers; is thought to help reinforce sarcolemma and help transmit tension generated by sarcomeres to tendons.
What are the functions of dystrophin?
1. Thought to help reinforce the sarcolemma.
2. Thought to help transmit tension generated by sarcomeres to tendons.
What protein helps to transmit tension generated by sarcomeres to tendons and how?
Dystrophin. It links thin filaments of the sarcomere to integral membrane proteins in the sarcolemma, which are attached in turn to proteins in connective tissue matrix that surrounds muscle fibers.
Which proteins are present in the I band?
Actin, tropomyosin, troponin, titin, α-actinin, nebulin, and dystrophin.
Which proteins are present in the A band?
Myosin, actin, tropomyosin, troponin, titin, myomesin, and nebulin.
Which proteins are present in the zone of overlap?
Myosin, actin, tropomyosin, troponin, titin, nebulin, and dystrophin.
What part of the sarcomere does myosin make up?
The thick filaments. Parallel myosin tails form the shaft of the thick filament.
What is the physical description of myosin?
It consists of a myosin tail and myosin heads that look like twisted golf clubs.
What is the function of myosin?
It binds to myosin-binding sites on actin during muscle contraction.
What is the location/position of myosin?
Myosin tails point outward from shaft in spiraling fashion. Each myosin head extends toward one of the six surrounding thin filaments.
How does actin connect to myosin in a sarcomere?
During contraction, myosin heads bind to its myosin-binding sites.
How does titin connect to myosin in a sarcomere?
It connects a Z disc to the M line, thereby helping to stabilize thick filaments.
How does myomesin connect to myosin in a sarcomere?
It connects adjacent thick filaments to one another, holding them in alignment at the M line.
What is the function of actin?
Each molecule has a myosin-binding site where a myosin head of a thick filament binds during muscle contraction.
What proteins is actin connected to in a sarcomere?
Myosin, tropomyosin, troponin, α-actinin, nebulin, and dystrophin.
How does myosin connect to actin in a sarcomere?
During muscle contraction, its heads bind to actin's myosin-binding sites.
How does tropomyosin connect to actin in a sarcomere?
When skeletal muscle is relaxed, it covers actin's myosin-binding sites, preventing myosin from binding to actin. Its strands wrap around an actin filament.
How does α-actinin connect to actin in a sarcomere?
It attaches to actin molecules of thin filaments.
How does nebulin connect to actin in a sarcomere?
It wraps around the entire length of a thin filament. It helps anchor thin filaments to Z discs and regulates the length of thin filaments during development.
How does dystrophin connect to actin in a sarcomere?
It links thin filaments of a sarcomere to integral membrane proteins in the sarcolemma, which are attached in turn to proteins in connective tissue matrix that surrounds muscle fibers.
What is the physical description of tropomyosin?
It is a strand that wraps around each actin filament.
What is the function of tropomyosin?
When skeletal muscle is relaxed, it covers myosin-binding sites on actin molecules, preventing myosin from binding to actin. When calcium ions (Ca2+) bind to troponin, troponin changes shape, moving it away from myosin-binding sites on actin, and muscle contraction subsequently begins as myosin binds to actin.
How does actin connect to tropomyosin in a sarcomere?
Tropomyosin strands are wrapped around its filaments. In a relaxed skeletal muscle, tropomyosin covers myosin-binding sites on it.
How does troponin connect to tropomyosin in a sarcomere?
Tropomyosin strand are held in place by it. When calcium ions (Ca2+) bind to it, it changes shape, moving tropomyosin away from myosin-binding sites on actin, and muscle contraction subsequently begins as myosin heads bind to actin's myosin-binding sites.
How does nebulin connect to tropomyosin in a sarcomere?
It wraps around the entire length of each thin filament. It helps anchor thin filaments to Z discs and regulates the length of thin filaments during development.
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