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Pathophys quiz 3 > Muscles > Flashcards

Muscles Flashcards

1
Q

3 classifications of muscles

A
  • skeletal
  • smooth
  • cardiac
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2
Q

muscle fiber=

A

muscle cell

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3
Q

myofibrils=

A

the organized actin/myosin strands within the muscle fiber

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4
Q

sarcomeres=

A

“chunks” of myofibrils. exist between Z lines

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5
Q

Characteristics of a Skeletal Muscle Fiber:

A
  1. Big! (One muscle cell can be up to 8 inches long!)
  2. Multinucleated (why?)
  3. It contains many mitochondria (why?)
  4. It has special structures called Transverse tubules (T tubules)
  5. It has myofibrils and sarcomeres
  6. Special names:
    Sarcolemma = Plasma membrane
    Sarcoplasm = Cytoplasm
    Sarcoplasmic reticulum =
    Smooth ER
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6
Q

How does a muscle fix itself?

A

Satellite Cells–

  • undifferentiated myoblasts hanging out near the basement membrane of muscle fibers.
  • They only activate/differentiate if the muscle they’re close to is strained or injured.
  • Typically they don’t form new cells– instead they fuse with the remaining cells (damaged ones or remaining “well cells” to make them bigger/ stronger (Hypertrophy).
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7
Q

Hypertrophy

A

making lager

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8
Q

Hyperplagia

A

reproducing cells

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9
Q

A “muscle” is….

A

a number of muscle fibers bound together by connective tissue

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10
Q

Which shortens during a muscle contraction–

actin, or myosin?

A

Neither! They slide past each other like a sliding glass door.

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11
Q

does a muscle always shorten when it’s working?

A

No… sometimes it’s exerting force but staying the same length– e.g., when you’re holding something heavy but keeping it in place.

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12
Q

What’s going on in a muscle that’s working, but maintaining its length?

A

Cross-bridges between actin and myosin are being maintained.

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13
Q

Actin

A

globular polypeptides strung together in a strandlike protein like a string of pearls.

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14
Q

Myosin

A

thick protein filament that’s firmly attached to the center fo a sarcomere and is immobile– HOWEVER, it has “heads” that can grab actin and pull the actin against it in a sliding motion.

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15
Q

Troponin

A

another globular protein, but not a strand. Attached to actin and tropomyosin… BUT– when it binds calcium, it changes its shape and lets go of tropomyosin.

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16
Q

Tropomyosin

A

a ropelike microtubular structure. When it’s bound to troponin, It’s wrapped around actin and covers up the sites where myosin likes to grab on. If troponin lets go of it, it moves out of the way.

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17
Q

Calcium

A

stored n the smooth ER of muscle cells. When there’s very little of it around, tropomyosin is in the way of actin-myosin binding. When it’s out of the way, actin and myosin bind easily.

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18
Q

How the Sliding Filament Process Works:

A
  1. When a muscle fiber is at rest, actin binding sites are covered up by a strand of tropomyosin, so that myosin heads can’t bind to them. Tropomyosin is attached to a molecule of troponin, which holds it in the way of the myosin.
  2. When a muscle fiber is stimulated by the nervous system, each myofibril releases stored calcium from its sarcoplasmic reticulum into the cytoplasm– where the actin and myosin is. When calcium is present, troponin eagerly binds to calcium at another binding site. This process changes its shape, causing it to “let go” of tropomyosin. Tropomyosin then moves out of the way, so that myosin heads can grab the actin molecule and pull it against the myosin like a sliding door. This process uses ATP– the myosin heads hydrolyze ATP to ADP and use the energy to “flex and slide.”
  3. At the end of the “flex and slide” action, myosin heads release their ADP. If calcium is still present, they remain attached to their actin sites and await another ATP. When they get one, they grab further down the actin and do it again.
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19
Q

If Ca++ remains and more ATP is available:

A

Myosin will let go of actin in order to grasp a new ATP. This changes its shape to “unflexed.” It re-grasps actin at a new binding site and “flexes” again.

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20
Q

If Ca++ disappears:

A

While Myosin is “letting go” to grab another ATP, actin binding sites will again become covered. Myosin will hold its ATP, detached from actin, and await another chance to bind. The muscle relaxes.

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21
Q

If Ca++ is present but no ATP is available:

A

Myosin will remain attached to its actin binding site in its “flexed” position, until a new ATP arrives.

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22
Q

the Story of rigor Mortis

A
  1. An animal dies.
  2. After a while, within individual myofibrils (muscle cells), calcium diffuses out of the smooth ER (the sarcoplasmic reticulum) because there’s no energy to maintain the high concentration there.
  3. The now-leaked calcium causes crossbridges to form, and the muscle contracts.
  4. IF THIS ANIMAL WERE ALIVE AND HAD AVAILABLE ATP, the crossbridge would let go in order to bind to new ATP and be ready for the next job.
  5. Without ATP, however, the crossbridge just sits there, attached (contracted) but with no orders to do anything new
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23
Q

Why the latent period? What’s going on in there?

A

It takes time for the electrical message to travel down the T-Tubules into the sarcoplasmic reticulum to release its calcium stores, then for the calcium stores to reach the muscle fibers.

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24
Q

Excitiation-contraction coupling relies on…

A

sarcoplasmic reticulum

t-tubules

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25
Q

Sarcoplasmic reticulum

A

an immediate source of Calcium ions that can flood the sarcomeres when it’s time.

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26
Q

T Tubules

A

A way to rapidly let the whole cell know when it’s time to contract.
-“pipes”

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27
Q

endoplasmic reticulum

A

specialized to store calcium until it’s needed.

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28
Q 
One motor neuron innervates many 
muscle fibers (cells), but \_\_\_ muscle fiber is innervated by only one motor neuron.
A

one

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29
Q

One large muscle=

A

many motor units (the example has two). Strength of contraction may depend on how many of these motor units are activated at once.

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30
Q

More motor neurons=

A

better muscle coordination

31
Q

Skeletal muscles have no pacemaker– they have to be stimulated by a nerve or …

A

they won’t contract

32
Q

The nerve cells that innervate skeletal muscle fibers are ______ (or somatic efferent neurons). Their cell bodies are located in either the brainstem or the spinal cord (always the CNS).

A

motor neurons

33
Q

Motor neurons are myelinated and are the largest-diameter (and ____) nerves in the body.

A

fastest

34
Q

poliomyelitis

A

is a viral disease that destroys motor neurons, leading to the paralysis of skeletal muscle, and may result in death due to respiratory failure.

35
Q

The neuromuscular Junction steps:

A
  1. Motor neuron action potential
  2. Ca2+ enters voltage-gated channels
  3. Acetylcholine release
  4. Acetylcholine binding opens ion channels
  5. Na+ entry
  6. Local current between depolarized end plate and adjacent muscle plasma membrane
  7. Muscle fiber action potential initiation
  8. Propagated action potential in muscle plasma membrane
  9. Acetylcholine degradation
36
Q

So… how do you “turn one off”? i.e., how do you get a muscle to stop doing what it’s doing?

A
  1. Stop the action potential and get rid of the ACh that’s in the motor end plate.
  2. Use the opposing muscle if necessary (antagonistic muscle groups)
    - No IPSPs for muscle cells
37
Q

A muscle fiber generates force called ______ in order to oppose a force called the _______, which is exerted on the muscle by an object.

A

tension, load

38
Q

The mechanical response of a muscle fiber to a single action potential is known as a ________.

A

twitch

39
Q

3 phases to a twitch contraction:

A

Latent, contraction, relaxation

40
Q

Latent Period

A

-from the action potential to the onset of contraction. The time delay is due to the excitation-contraction coupling.

41
Q

Contraction phase

A

the time that tension is developing due to the cross-bridge cycling.

42
Q

relaxation

A

-the time that the tension is decreasing (i.e., relaxing). It’s longer than the contraction phase because of the amount of time it takes to get all the Ca2+ sequestered.

43
Q

Isometric twitches

A

do generate tension but do not shorten the muscle (load and force are perfectly balanced… i.e., postural muscles). (constant length)

44
Q

Isotonic twitches

A

do shorten the muscle, because the tension generated is greater than the load it is opposing (constant tension).

45
Q

Too much summation =

A

Tetany

-A maintained contraction in response to repetitive stimulation is known as a tetanus (tetanic contraction).

46
Q

When a skeletal muscle fiber is repeatedly stimulated, the tension that the fiber can develop eventually ________–even with continued stimulation.

A

decreases

47
Q

Muscle fatigue

A

decline in muscle tension

48
Q

Additional characteristics of fatigued muscle:

A
  • decreased shortening velocity (shortening takes longer)

- slower rate of relaxation

49
Q

Rate of onset of fatigue depend on:

A
  • type of muscle fiber,
  • intensity and duration of contractile activity
  • degree of an individual’s fitness.
50
Q

Conduction Failure

A

can happen if K+ builds up in T Tubules, which can happen during repetitive depolarizations (remember, Na+ goes into muscle cell and K+ goes out). This causes inability to repolarize.

51
Q

Lactic Acid Buildup

A

decreased pH may change the shape (and thus the activity) of key proteins– like the ones that release Ca++ from the SR.

52
Q

Inhibition of Cross-Bridge Cycling

A

The buildup of ADP and Pi within muscle fibers during intense activity may directly inhibit cross-bridge formation by getting in the way of ATP binding to myosin.

53
Q

Central Command Fatigue:

A
  • happens when the appropriate regions of the cerebral cortex fail to send excitatory signals to the motor neurons.
  • An athlete’s performance depends on both the physical state of the appropriate muscle groups and the ability to initiate central commands to muscles during a period of increasingly distressful sensations.
54
Q

Voluntary movements

A

accompanied by a conscious awareness of what we are doing

55
Q

Involuntary movements

A

often characterized as unconscious, automatic or a “reflex.”

56
Q

Local Control of Motor Neurons

A

Local control systems receive instructions from higher brain centers, then make adjustments based on information received from sensory receptors in the muscles, tendons, and joints of the body part to be moved.

57
Q

over 90% of the spinal cord neurons are_____

A

interneurons

58
Q

The interneuron processes the data, then sends its “reduced” message to the motor neurons

A

FOR NOW PLEASE KNOW:

  • interneurons
  • Upper and lower neuron input
  • It’s complicated
59
Q

the muscle spindle made of:

A

some specialized muscle fibers that are wrapped with the ends of sensory neurons.

60
Q

the muscle spindle mission:

A

detect length, and change in length, of muscles.

61
Q

stretch=

A

firing

62
Q

contraction=

A

absence of firing

63
Q

persistent contraction

A

firing

64
Q

the take home message:

A

Muscles are motor organs, but they contain sensory organs within them that give your brain information about how long a particular muscle fiber is. This contributes significantly to proprioception

65
Q

4 different activities of stretch reflex:

A
  • Monosynaptic response
  • reciprocal innervation
  • synergistic muscle recruitment
  • Ascending information
66
Q

sensorimotor cortex =

A

the parts of the cerebral cortex that act together to control muscle movement.

67
Q

Primary motor cortex and Premotor Cortex:

A

made up of neurons that give rise to descending pathways for motor control

68
Q

The cortical neurons that control movement form a neural network, meaning ______

A

many neurons participate in each single movement.

69
Q

Role of the basal ganglia

A
  • establish the programs that determine the specific sequence of movements needed to accomplish a desired action.
  • They manage cortical loops that send a steady flow of information from:
  • Sensorimotor cortex
  • Basal Nucleus
  • Thalamus
  • Back to Sensorimotor Cortex
70
Q

Parkinson Disease

A

destroys the substantia nigra

-Drugs used to treat Parkinson disease are designed to restore dopamine activity in the basal nuclei:

71
Q

Cerebellum=

A

balance and smooth motion

72
Q

Where does the cerebellum send input:

A
  • to the brainstem nuclei
  • via the thalami to the motor cortex
  • down the descending pathways via the motor cortex
73
Q

Cerebellum receives input from:

A
  • from the sensorimotor cortex (relayed via brainstem nuclei)
  • from the vestibular system, eyes, skin, muscles, joints, and tendons.

Pathophys quiz 3 (3 decks)

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