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Muscular System > Muscles > Flashcards

Muscles Flashcards

1
Q

What are the three types of muscle tissue?

A

Smooth, cardiac and skeletal

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2
Q

What are the characteristics of smooth muscle?

A

Smooth muscle is involuntary, inherent, rhythmic, unstriated.It is spindle-shaped, has central nucleus, found in the walls of digestive tract, urogenital system and blood vessels.

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3
Q

What are the characteristics of cardiac muscle?

A

Cardiac muscle is involuntary, inherent, rhythmic, striated and is found only in the heart. The cells are striated, branched with centrally located nuclei.

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4
Q

What are the characteristics of skeletal muscle?

A

Skeletal muscle is voluntary, striated, not inherent. Individual cells are striped, multinuclear with nuclei found close to membrane.

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5
Q

What are the terms specific to skeletal muscle and why?

A

Individual cells are referred to as muscle fibers because they can be as long as one foot. The cell membrane of a skeletal muscle is sacrolemma and the sarcoplasmic reticulum has a similar job to the endoplasmic reticulum.

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6
Q

How are skeletal muscles voluntarily controlled?

A

Each skeletal muscle fiber is insulated from all other muscle fibers and controlled directly by a branch of a voluntary nerve=motor neuron. Motor neurons are under conscious control.

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7
Q

What is a motor unit?

A

A motor unit is one motor neuron and all of the muscle fibers it innervates.

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8
Q

What are the features of a motor neuron?

A
  • Axon is myelinated (covered by a myelin sheath)
  • Larger diameter axon=faster propagation
  • As axon approaches muscle, it divides into branches = collaterals. Each collateral forms a junction with one muscle fiber.
  • A single motor neuron innervates many muscle fibers
  • Each muscle fiber is innervated by only one motor neuron
  • All muscle fibers in one motor unit will contract if that motor neuron fires
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9
Q

What is the neuromuscular junction?

A

Sites where the ends of motor nerve fibers connect to muscle fibers=The junction of axon and muscle fiber.

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10
Q

What is the motor end plate?

A

The sarcolemma under the terminal portion of the axon.

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11
Q

What are the fine terminals of the collateral called?

A

Axon terminals.

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12
Q

Describe action potential?

A

Action potential is the message sent along nerves, when it reaches the neuromuscular junction, the vesicles fuse with the axon terminal cell membrane and the neurotransmitter is released into the cleft between the axon terminal and motor end plate.

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13
Q

The transmission of action potential along neuron is what kind of event?

A

An electrical event

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14
Q

The transmission of action potential at the neuromuscular junction is?

A

A chemical event.

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15
Q

At the neuromuscular junction the neurotransmitter is always what?

A

Acetylcholine (ACH)

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16
Q

How does the chemical transmission at the neuromuscular junction go?

A
  1. Axon terminal fills with vesicles of ACH
  2. When AP reaches the NJ, the vesicles fuse with axon terminal cell membrane and ACH is released into the cleft (space between the motor end plate and axon terminal)
  3. ACH diffuses across the cleft and combines with receptors on the motor end plate membrane. ACH must be present for transmission to muscle fiber.
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17
Q

How does the transmission of action potential end?

A

ACH must be removed from the receptors. This is done by acetylcholinesterase=Achase, an enzyme found in the cleft that breaks down ACH, quickly after the ACH is released, removing it from the receptor and splitting it and ending the nerve impulse.

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18
Q

How does curare modify events at the neuromuscular junction?

A

It blocks the receptor sites but does not cause an action potential, nor is it destroyed by Achase. It prevents muscle contraction. Succinyl choline is a curare agent.

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19
Q

How does anti-cholinesterases affect skeletal muscle?

A

Inhibits enzyme Achase so ACH is not destroyed. Instead ACH sits on receptor and maintains transmission of action potential=muscle fiber contraction.

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20
Q

How does botulinus toxin from Clostridia botulinum bacteria affect ACH?

A

It blocks the release of ACH from axon terminals.

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21
Q

What is myasthenia gravis?

A

An autoimmune disease that decreases the number of ACH receptor sites on motor end plate. Clinical signs are skeletal muscle fatigue and weakness.

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22
Q

What are within muscle fibers?

A

several hundred to several thousand independent cylindrical elements called myofibrils, 1-2 um in diameter, but as long as muscle fiber, they are also full of myofilaments, even smaller cylindrical elements.

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23
Q

What causes the striations on skeletal muscle?

A

Striations are result from striations on myofilaments.

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24
Q

What else are the filaments inside the myofibrils responsible for?

A

The myofilaments are contractile protein filaments made up of thin actin filaments and thick myosin filaments.

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25
Q

What is a sarcomere?

A

A sarcomere is a basic contracting unit of skeletal muscle, a unit of the repeating pattern of myosin and actin.

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26
Q

What are the names of the connective tissues surrounding muscle fibers?

A

endomysium is between individual cells, perimysium is around the bundles of fibers and epimysium is the tissue around the entire muscle.

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27
Q

How are the muscle fibers arranged?

A

They can be arranged in sheets (abdominals) or bands (sartorious) or spindle-shaped (gastrocnemious/calf) or peniform (deltoids).

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28
Q

How does the arrangement of muscle fibers affect the muscles capabilities?

A

Parallel fibers produce the greatest distance of shortening but are the weakest. Pennate muscles have more power but at the expense of contraction distance.

29
Q

What are the muscles attachments to bones referred to as?

A

Most muscles have attachments to two different bones: the origin=least movable and the insertion= more movable. In extremities, origin is usually proximal and insertion is distal. Contraction results in movement of origin and insertion together.

30
Q

Describe a FLEXOR muscle

A

A flexor is a muscle located on the side of the limb toward which the joint bends=it flexes/bends a joint

31
Q

Describe an EXTENSOR muscle

A

Extensor muscles extend/straighten joints and are found on the opposite sides of flexor muscles.

32
Q

Describe ADDUCTORS and ABDUCTORS

A

Adductors=inward movers, moves or keeps body part proximal. Abductors=outward movers, moves body part distally.

33
Q

What is a sphincter?

A

A muscle surrounding an opening

34
Q

What are cutaneous muscles?

A

Cutaneous muscles, not found in humans, are muscles in the fascia that move the skin.

35
Q

What are antagonist and antagonist pairs of muscles?

A

Groups of muscles that produce oppositely directed movements of a limb.

36
Q

What are agonists?

A

Agonists are muscles directly responsible for producing desired movement=prime movers.

37
Q

What are synergists?

A

Synergists are muscles that oppose any undesired actions of the agonists, sometimes called fixators since these muscles stabilize one or more bones

38
Q

How do synovial structures play a role in the muscular system?

A

Synovial membrane lined sacs protect structures that rub against each other from friction (tendons), A bursa is a fluid-filled sac, lined with synovial membranes, occurs near joints (shoulder) and structures that move only a short distance. A synovial sheath is an elongated bursa, when tendons travel inches

39
Q

How is skeletal muscle formed embryologically?

A

By fusion of a number of small mononucleated myoblasts. Once fused the resulting muscle fibers no longer have the capacity for cell division but do retain ability to grow in length and diameter=hypertrophy.

40
Q

Describe atrophy

A

Atrophy happens when nerve fibers are severed, denervated muscle fibers become progressively smaller, actin and myosin contents decrease.

41
Q

What is depolarization or end plate potential?

A

The propagation of the action potential at the motor end plate.

42
Q

What is the Sliding Filament Model of Muscle Contraction?

A

Sliding motion accomplished by cross bridges that extend from the surface of the myosin molecules to bind with sites on the actin molecules.

43
Q

How do the cross bridges move?

A

Cross bridges move in an arc, like oars, repeatedly grabbing, pulling and releasing the binding sites of the actin. The bridges movement does not require ATP but the binding and releasing of the actin binding sites do.

44
Q

When the muscle is at rest, how is myosin kept from binding to actin?

A

Myosin is kept from binding to actin by protein molecules called tropomyosin that cover the binding sites on actin

45
Q

What does troponin do?

A

Troponin connects tropomyosin to actin like a hinge, when an ion of calcium binds to troponin, it deforms its shape such that tropomyosin is moved, thus revealing the binding site on the actin.

46
Q

What is Excitation Contraction Coupling?

A

refers to process whereby the action potential in the sarcolemma triggers off a sequences of events leading to cross bridge activity and contraction via an increased availability of calcium.

47
Q

What is the role of the sarcoplasmic reticulum?

A

The SR forms a sleeve around the myofibrils and releases calcium ions during muscle contraction and absorb them during relaxation.

48
Q

What are T-Tubules?

A

T-Tubules=transverse tubules. They join sarcolemma to the sarcoplasmic reticulum. Being tubules, they are filled with extracellular fluid. Transverse (T)-tubules invaginate the sarcolemma, allowing impulses to penetrate the cell and activate the SR.

49
Q

Where is calcium stored in the muscular system?

A

Free calcium concentration in the cytoplasm of a resting muscle is low. Instead, calcium is stored in the sarcoplasmic reticulum.

50
Q

What is the role of calcium in muscle physiology?

A

As an action potential is conducted over the surface of the muscle fiber, it is also done into the interior of the fiber through T-tubules. The action potential causes the SR to release Ca. Ca allows troponin to change shape, thus removing tropomyosin off of the actin binding sites=contraction occurs.

51
Q

How is a muscle contraction turned off?

A

Contraction is turned off by decreasing the concentration of Ca through carier mediated active transport (requires ATP) that pumps Ca from the cytoplasm back into the lumen of the SR.

52
Q

What is the difference between tension and load in regards to muscle contraction?

A

Tension=force exerted by a muscle on an object. Load=force exerted by the object on the muscle. Load and tension are opposing forces. To move a load, the muscle tension must be greater than the load.

53
Q

What is an isotonic contraction?

A

constant tension=muscle shortens and moves a load.

54
Q

What is an isometric contraction?

A

constant length=muscle develops tension but does not shorten.

55
Q

Although different, what is the same about isometric and isotonic contractions?

A

The electrical and chemical events occurring in the muscle fiber during an isotonic and isometric contraction are the same. In both, cross bridges form, and it is the binding and releasing of the cross bridges that uses ATP. Both movements use same amount of ATP.

56
Q

Describe a twitch.

A

The mechanical response to a singe action potential, lasts 10-100msec

57
Q

What are the latent period, contraction and relaxation times?

A

Latent period=interval of milliseconds=times for excitation contraction coupling.
Contraction time=time from stimulus to peak tension
relaxation time=time from peak contraction until tension is zero.
Not all muscle fibers contract at same rate.

58
Q

How is it possible for a second action potential to be initiated while the first twitch is occurring?

A

Muscle action potential lasts 1-2msec and a single twitch lasts 10-100msec. Therefore, it is possible.

59
Q

What is summation?

A

The increase in mechanical response of a muscle fiber to action potentials occurring in rapid succession. The greater the frequency of stimulation, the greater is the intensity of the mechanical response, until a frequency is reached beyond which the response no longer increases. Greatest tension muscle can develop, 3-4x greater than single twitch.

60
Q

What is tetanus?

A

The maximal response to high frequency stimulation.

61
Q

How long can a muscle fiber be maintained in a tetanically contracted state?

A

That depends on the fibers’ ATP supply. As ATP supplies decrease the force of contraction diminishes eventually to zero. Drop in tension with prolonged stimulation=muscle fatigue.

62
Q

What does the total tension a muscle can develop depend on?

A

1) .The amount of tension developed by each contracting fiber, variable, depending upon summation, tension and fatigue. Length-tension relationship.
2) .The number of fibers in the muscle contracting at any given time=the number of motor neurons activated and the # of muscle fibers associated with each motor neuron.=size of motor unit

63
Q

What helps prevent fatigue and allows a muscle to maintain a nearly constant tension?

A

Motor neurons to a given muscle fire asynchronously, so some are active while other are inactive momentarily, helps prevent fatigue.

64
Q

What are the three uses of ATP?

A

1) . Binding of cross bridges of myosin to actin binding sites
2) .Release of actin
3) .Re-accummulation of Ca by SR

65
Q

What are the three sources of ATP?

A 
Creatine phosphate (most rapid, but only enough for single twitches)
Oxidative phosphorylation (36 molecules of ATP with one glucose molecule)
Glycolysis (very rapid, but only produces 2 ATP)
66
Q

How does creatine phosphate produce ATP?

A

When a creatine phosphate molecule is split, the phosphate attaches to ADP to convert it back to ATP. Fast, but limited.

67
Q

How does oxidative phosphorylation create ATP?

A

This takes place in the mitochondria, requires food intake of fatty acids and carbohydrates and oxygen. Good for aerobic exercise, produces 36 ATP. Slow process.

68
Q

How does glycolysis produce ATP?

A

Very rapidly, but produces only two ATP. Glycogen is stored in liver and skeletal muscle so it is readily available. Requires no oxygen, occurs in cytoplasm. Dis=requires large quantity of glucose.

69
Q

What are the types of muscle fibers?

A

Fast twitch=10msec, fatigues readily, high capacity for glycolysis, poor blood supply, white in color
Slow twitch=100msec, good for endurance, high capacity for oxidative phosphorylation, rich blood supply, red in color.

Muscular System (1 decks)

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