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Human Biology, 13th Edition - Sylvia S. Mader > Ch 12 - Muscular System > Flashcards

Ch 12 - Muscular System Flashcards

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1
Q

What are the three types of muscle tissue?

A
  1. Skeletal muscle
  2. Smooth muscle
  3. Cardiac muscle
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2
Q

What are the main characteristics of cardiac muscle?

A

Striated cells
Single nucleus
Only in the heart
Intercalated disks w/ gap junctions

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3
Q

What are the main characteristics of skeletal muscle?

A

Striated cells
Multiple nuclei
Attached to muscle
No cell-to-cell junctions

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4
Q

Why doesn’t skeletal muscle have cell-to-cell junctions?

A
  1. They have the T-tubule system to conduct nerve impulses, and thus don’t need to communicate with other cells via junctions. Cardiac muscle on the other hand needs gap junctions in order for heart contractions to spread quickly throughout the heart wall
  2. Skeletal muscles aren’t single cells and thus don’t need them
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5
Q

What are muscle cells called?

A

Myocytes (myo = “muscle”). Also simply called muscle fibers because they’re long and thin

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6
Q

What are the functions of skeletal muscles?

A
  1. Support – maintain our bodies upright
  2. Movements of bone and other body structures via contractions
  3. Maintenance of body temp – Contractions cause muscle to break down ATP, which releases heat that gets distributed throughout the body
  4. Helps move blood and lymph throughout the cardiovascular and lymphatic systems via muscle contractions.
  5. Protects internal organs (muscular wall, the abs, protects internal organs) and stabilizes joints
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7
Q

What is the structure of a muscle?

A

Whole muscle contains bundles of fascicles. Fascicles contain bundles of skeletal muscle fibers (muscle cells). All of these fibers are connected to one another by connective tissue.

Muscle > Fascicle > Muscle fiber > Myofibril > Sarcomere > Myofilament

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8
Q

What is the “origin” and the “insertion?” Provide an example of both.

A

Origin = the origin of a muscle is on a stationary bone. For example, the tricep’s origin is on the scapula (shoulder blade), and the insertion connects the tricep (via a tendon) to the ulna, which is a bone in the forearm. Therefore, when the tricep contracts, the forearm moves rather than the shoulder blade, which stays put.

Insertion = the connection of a muscle to a bone that moves. See example above

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9
Q

For any particular movement, what is the primary muscle called that does most of the work? What about the other muscles that help the primary muscle carry out its function?

A

The prime mover vs. the synergists, which make the prime mover’s action more effective

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10
Q

Why can’t muscles push, but rather only pull?

A

When muscles contract, they shorten.

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11
Q

What is the muscle called that acts opposite to a prime mover? Provide an example.

A

The antagonist. For example, the biceps vs. the triceps. The former flexes the forearm (bends it) and the latter extends the forearm.

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12
Q

How are muscles characterized?

A

Size
Shape
Location
Direction of muscle fiber (straight in abs vs. circular in eye)
Attachment (what bone the muscle is attached to)
# of attachments
Action (extend vs. adduct, for example)

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13
Q

What are the major skeletal muscles of the human body?

A

See pg. 264 in textbook

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14
Q

What are the cell membrane, cytoplasm and endoplasmic reticulum of a muscle fiber called?

A

Sarcolemma = cell membrane
Sarcoplasm = cytoplasm
Sarcoplasmic reticulum = ER

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15
Q

What is the role of the sarcolemma?

A

The plasma membrane, which forms T tubules. These tubules are vital for muscle contractions by nerve impulses

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16
Q

What is contained in the sarcoplasm of a muscle fiber?

A
  1. Organelles
  2. Myofibrils, which contain bundles of myofilaments that contract (myosine and actin)
  3. Glycosomes, which store glycogen for energy use
  4. Myoglobin, which stores oxygen and can withstand the heat produced by ATP when muscles contract (hemoglobin cannot)
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17
Q

What are T (transverse) tubules?

A

Extensions of the sarcolemma that extend into the muscle fiber/cell and convey impulses that cause Ca2+ to be released from the sarcoplasmic reticulum (which allows nerve pulses to travel throughout the fiber to contract myofilaments)

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18
Q

What role does the the sarcoplasmic reticulum play?

A

It’s the smooth ER of a muscle fiber that stores Ca2+. When T tubules are stimulated, that enacts the release of Ca2+, allowing nerve signals to stimulate the myofilaments within a muscle fiber.

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19
Q

What causes striations to appear on muscle fibers?

A

Myofilaments’ structure. More specifically, the dark striations in a muscle fiber (the central A band) appear due to the overlapping of the myosin and actin filaments, causing a thicker, darker appearance compared to the lack of overlapping as we approach the z-lines, which mark the outer boundaries of a sarcomere

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20
Q

What portion of the muscle fiber contracts?

A

Myofibrils, which contain myofilaments

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21
Q

Why is calcium so important for muscle contractions? Where is it stored?

A

Calcium ions are how nerve impulses are able to travel through our bodies. Calcium is stored in the sarcoplasmic reticulum.

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22
Q

What are the two main proteins called that compose the myofilaments? What are the two other proteins called that wrap around the _____ filament?

A

Myosin and actin, myosine is a thicker protein. Tropomyosin wraps around the actin filament and troponin scatters throughout this filament as well

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23
Q

A sarcomere extends between two vertical lines called the ____ ?

A

The Z lines

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24
Q

Which bands create the contrast of light and dark bands that create the striations?

A

The I bands are light, and the A bands are dark

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25
Q

What is the structure of the motor unit?

A
  1. The axon of a nerve cell branches off into multiple axon branches, each with their own axon terminals. The axon branches connect to multiple muscle fibers via the axon terminals
  2. Each axon terminal has a synapses where the synaptic vesicles release the neurotransmitter acetylcholine into the synaptic cleft
  3. The synaptic cleft is the gap between the axon terminal and the sarcolemma of the muscle fiber (they don’t actually touch)
  4. The sarcolemma of the muscle fiber is folded where the synaptic cleft is, and those folds contain ACh receptors
26
Q

How does a muscle get stimulated?

A

When muscles are stimulated, electrical signals travel across the sarcolemma and then down a T tubule. This signals calcium to be released from the sarcoplasmic reticulum. The muscle fiber then contracts, as the sarcomeres within myofibrils shorten. Myosin filaments break down ATP to pull actin filaments closer toward the center of the sarcomere.

27
Q

What is the sliding filament model?

A

The movement of actin filaments in relation to myosin filaments.

28
Q

What is the neuromuscular junction?

A

The region where the synapses of the axon branches/terminals connect with the sarcolemma in the muscle fiber.

29
Q

What structure do T tubules lie adjacent to?

A

The sarcoplasmic reticulum, however, they do not connect

30
Q

What happens with the sarcomeres when a muscle fiber is stimulated?

A
  1. Stimulation occurs, and T tubules cause the release of Calcium2+ from the sarcoplasmic reticulum, which causes the sarcomeres to contract

What happens with actin filament when stimulated…

  1. Ca2+ attaches to troponin, which is scattered across an actin filament. This action pulls on tropomyosin (which is wrapped around actin filaments), thereby shifting it slightly to reveal myosin-binding sites

How sarcomeres contract…

  1. Starts off with the myosin filament HEAD disconnected from the actin filament. This myosin filament head contains ATP (as ATP is needed to stop muscles from contracting, thus during rest, an ATP molecule is present)
  2. As a nerve stimulates the muscle fiber, that ATP is separated into ADP + P, causing a cross-bridge to be formed between myosin and actin filaments. They connect.
  3. ADP + P get released, which causes a power stroke where myosin pulls actin inward (like pulling a rope)
  4. Once ATP binds to the myosin filament once again, the head returns to its resting position. ATP was used to force the cross-bridge to disconnect

This cycle recurs until calcium ions are actively returned to the calcium storage sites (this uses ATP as well)

31
Q

What is the all-or-none law?

A

All muscle fibers in a motor unit are stimulated at once. They either all contract or do not contract at all.

32
Q

What is a muscle twitch?

A

When a motor unit is stimulated by infrequent electrical impulses, a single contraction occurs

33
Q

What is summation? How does that relate to tetanus?

A

Increased muscle contraction via a motor unit until maximal sustained contraction, which is called tetanus.

34
Q

How long does tetanus continue for, and what happens afterward?

A

Tetanus continues until the muscle fatigues due to depletion of energy reserves. Fatigue comes after tetanus, and is marked by relaxation of the muscles even though stimulation continues

35
Q

What is the infection called tetanus?

A

Caused by the bacterium Clostridium tetani. In this infection, death occurs because the muscles (incl. respiratory muscles) become fully contracted and don’t relax.

36
Q

What is recruitment?

A

A muscle usually contains many motor units. As the intensity of nervous stimulation increases, more motor units in a muscle are activated. This is called recruitment because more motor neurons are being recruited.

37
Q

What would maximum contraction of an entire muscle look like, and why doesn’t that occur?

A

It would require all motor units to be undergoing tetanic contraction, but that rarely happens because the motor units could all fatigue at the same time. Usually what happens is that some motor units are contracting maximally while others are resting. This allows sustained contractions to occur.

38
Q

What are the four energy sources of muscle?

A

Stored in muscle:

  1. Glycogen
  2. Triglycerides

Acquired from blood:

  1. Glucose
  2. Fatty acid
39
Q

Which energy sources are used the most at the beginning of exercise? Once those start depleting, what other energy sources do we begin to use?

A

Beginning (0-1 hrs):

Used LESS over time (these deplete):
Muscle glycogen = 45% of energy expenditure
Muscle triglycerides = 25% of energy expenditure

Used MORE over time:
Plasma fatty acids = 25% of energy expenditure
Blood glucose = 5% of energy expenditure

Over time, these stores of glycogen and triglycerides get used up.

After 4 hrs:
Plasma fatty acids = 50% of energy expenditure
Blood glucose = 45% of energy expenditure
Muscle triglycerides = 5% of energy expenditure
Glycogen = 0%

The amount of fat burn increases the longer we exercise.

40
Q

What are the three sources of ATP once the stored ATP is used up?

A
  1. Formation of ATP by the creatine phosphate (CP) pathway
  2. Formation of ATP by fermentation
  3. Formation of ATP by cellular respiration, which involves use of O2 by mitochondria
41
Q

What is the CP pathway?

A

The quickest way for muscle to produce ATP because it only consists of one reaction. It’s used during high-intensity exercise that lasts less than 5 seconds. It’s created in the midst of sliding filaments, and can only be formed when a muscle is resting

42
Q

What is formation of ATP by fermentation?

A

Fermentation produces 2 ATP molecules from the anaerobic breakdown of glucose to lactate. It’s most likely to begin with glycogen. Hormones tell muscles cells to break down glycogen into glucose for use as energy.

Lactate is eventually transported to the liver, where 20% of it is broken down into CO2 and H2O. The ATP gained by this respiration is then used to reconvert 80% of the lactate to glucose and then to glycogen

43
Q

What is the cellular respiration pathway?

A

The slowest of all three pathways, but the most efficient. Makes use of glucose from the breakdown of stored muscle glycogen, glucose taken up from blood, and/or fatty acids from fat digestion.

44
Q

What are slow-twitch fibers vs. fast-twitch fibers?

A

Some muscle fibers use one method more than the other to provide myofibrils with ATP. Fast-twitch fibers rely on the CP pathway and fermentation. Slow-twitch fibers rely on cellular respiration.

Fast-twitch fibers:

  • Rely on anaerobic pathways
  • Less mitochondria
  • Less myoglobin (b/c if there’s no mitochondria, we don’t need myoglobin to provide oxygen)

Slow-twitch fibers:

  • Rely on aerobic pathways
  • More mitochondria
  • More myoglobin b/c mitochondria need energy to function. Myoglobin also makes them darker in color
  • Slow-twitch fibers are most helpful in endurance sports, such as long-distance running, biking, jogging, and swimming
  • Have a substantial reserve of glycogen and fat, so their abundant mitochondria can maintain prolonged production of ATP when O2 is available
45
Q

Why does hemoglobin transfer oxygen to myoglobin in muscle fibers?

A

Because the increase in temperature and the more acidic pH in muscles, hemoglobin loses it’s ability to bind to oxygen. Myoglobin can withstand that heat and acidity

46
Q

How does having more muscle prevent fat accumulation?

A

Muscle tissue metabolizes faster than other tissues

47
Q

What is rigor mortis?

A

Muscle death, “stiffness of death.” Muscles can’t relax unless they have a supply of ATP. Without ATP, the muscles remain fixed in their last state of contraction. Therefore, stiffness of the body occurs after someone dies for 24-36 hrs until lysosomes release enzymes that break the bonds between the muscle proteins actin and myosin.

48
Q

Which are the first tissues to die after someone dies?

A

The ones that have the highest oxygen requirement (brain and nervous tissues)

49
Q

What is DOMS?

A

Delayed onset muscle soreness that appears 24-48 hours after strenuous exercise. It’s associated with any activity that causes muscles to contract while they’re lengthening.

50
Q

What are anabolic steroids, and what are the most common health effects of using them?

A 
A class of steroids that generally cause tissue growth (esp. muscles) by promoting protein production. Most common side effects are:
High blood pressure
Jaundice
Acne
Increased risk of cancer
Shrinking of the testicles
Increased aggressive behavior
Violent mood swings
51
Q

What are spasms? Provide example.

A

Sudden and involuntary muscle contractions most often accompanied by pain. A spasm o the smooth muscle in the intestinal tract is a type of colic sometimes called a bellyache. Multiple spasms are called seizures or convulsions.

52
Q

What are cramps?

A

Strong, painful spasms, especially of the leg and foot, usually due to strenuous activity.

53
Q

What are facial tics?

A

Periodic eye blinking and head turning, for example, are spasms that can be controlled voluntarily, but only with a great amount of effort.

54
Q

What is a strain?

A

Caused by stretching or tearing a muscle.

55
Q

What is a sprain?

A

Twisting of a joint that leads to swelling and injury, not only of muscle but also of ligaments, tendons, blood vessels, and nerves. Usually ankle and knee get sprained.

56
Q

What is tendinitis?

A

When a tendon is inflamed by a sprain. It can irritate the bursa underlying the tendon, causing bursitis.

57
Q

What is myalgia and fibromyalgia?

A

Myalgia is achy muscles caused by overuse or overstretching of a muscle or group of muscles. It can also be due to viral infections.

Fibromyalgia is a chronic condition whose symptoms include achy pain, tenderness, and stiffness of muscles

58
Q

What is muscular dystrophy?

A

A broad term applied to a group of disorders characterized by a progressive degeneration and weakening of muscles. As muscle fibers die, fat and connective tissue take their place.

Duchenne muscular dystrophy is the most common type, and it’s inherited through a flawed gene on the X chromosome. The lack of a protein called dystrophin causes the condition because calcium leaks into the cell and activates an enzyme that dissolves muscle fibers.

59
Q

What is myasthenia gravis?

A

An autoimmune disease characterized by weakness that especially affects the muscles of the eyelids, face, neck, and extremities. Muscle contraction is impaired because the immune system mistakenly produces antibodies that destroy acetylcholine (ACh) receptors. Causes drooping of the eyelids and double vision

60
Q

What are the soft tissue sarcomas?

A

Cancers that originate in muscle or the connective tissue associated with muscle. Occur in smooth muscle or skeletal muscle.

A common form of smooth muscle cancer is leiomyoma, which occurs in the uterine wall.

Rhabdomyosarcomas are a rare form of cancer that may originate in the skeletal muscle or move into the muscle from another location in the body.

61
Q

Why does shivering occur?

A

It’s caused by temperature-sensitive neurons in the hypothalamus of the brain. Shivering = involuntary skeletal muscle contractions. Skeletal muscle contractions require ATP, and using ATP generates heat.

62
Q

Why are goosebumps useful to other species but not humans?

A

Arrector pili muscles contract to make goosebumps. They make hairs stand up when we’re scared or when we’re cold. In animals, their “bigger” hair will make them look like a bigger threat to predators, and bigger hair will also shield them more from the cold.

Human Biology, 13th Edition - Sylvia S. Mader (16 decks)

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