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Kaplan MCAT Biology > Musculoskeletal System: Muscular System (HY) > Flashcards

Musculoskeletal System: Muscular System (HY) Flashcards

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1
Q

what are the three types of muscle?

A
  1. skeletal muscle
  2. smooth muscle
  3. cardiac muscle
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2
Q

what is the difference between red/slow-twitch fibers and white/fast-twitch fibers?

  1. reasoning for color
  2. rate of contraction and fatigue
A
  1. red fibers have high myoglobin content, a red color, and many mitochondria for oxidative phosphorylation for aerobic energy consumption.
    white fibers have lower myoglobin content and a white color.
  2. red fibers: slower contraction, sustained activity
    white fibers: faster contraction, faster fatigue
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3
Q

what are two types of fibers within skeletal muscle?

A
  1. red/slow-twitch fibers

2. white/fast-twitch fibers

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4
Q

what is myogenic activity?

A

when muscle cells (myocytes) initiate their own contraction without nervous system input or another external signal

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5
Q

what types of muscles exhibit myogenic activity?

A
  1. smooth muscle

2. cardiac muscle

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6
Q

what is a tonus state of muscle?

A

constant state of low-level contraction

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7
Q

is smooth muscle or skeletal muscle able to undergo more sustained contractions?

A

smooth muscle

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8
Q

what are cardiac muscle cells connected?

A

connected by intercalated discs that contain gap junctions connecting cytoplasms of adjacent cells for ion flow

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9
Q

what does the vagus nerve do to heart rate?

A

slows heart rate

associated with parasympathetic nervous system

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10
Q

what do norepinephrine and epinephrine (aka. adrenaline) do to heart rate?

A

both increase heart rate by binding to adrenergic receptors
(sympathetic nervous system)

epinephrine increases intracellular calcium levels in cardiac myocytes

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11
Q

For the three types of muscles, list the following: striation, in/voluntary, innervation type, # nuclei per cell, Ca2+ req?

A

skeletal muscle: striated, voluntary, somatic innervation, multiple nuclei, requires Ca2+

smooth muscle: nonstriated, involuntary, autonomic innervation, 1 nucleus, requires Ca2+

cardiac muscle: striated, involuntary, autonomic innervation, 1-2 nuclei, requires Ca2+

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12
Q

identify the following lines, bands, and zone of the sarcomere: Z-line, M-line, H-zone, I-band, A-band

A

Z-line: boundaries of sarcomere
M-line: cuts through middle of sarcomere and myosin filaments
H-zone: contains only thick filaments
I-band: contains only thin filaments
A-band: contains all of the thick filaments even when they overlap with thin filaments

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13
Q

during contraction, what happens to the distance between Z-lines and M-lines and the size of the I-band, H-zone, and A-band?

A

Distance between Z-lines and M-lines decreases
Size of I-band and H-zone deccreases
Size of A-band stays the same

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14
Q

what are thick filaments made of?

A

myosin

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15
Q

what are thin filaments made of?

A

actin, troponin, and tropomyosin

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16
Q

what is the function of troponin and tropomyosin?

A

troponin and tropomyosin are bound to one anotehr and regulate interaction between actin and myosin

17
Q

what is the function of titin in the sarcomere?

A

prevents excessive stretching by anchoring actin and myosin filaments together

18
Q

what are myofibrils?

A

sarcomeres attached end-to-end

19
Q

what is the sarcoplasmic reticulum?

A

a modified endoplasmic reticulum that surrounds myofibrils and contains a high concentration of Ca2+

20
Q

what is the sarcolemma?

A

cell membrane of a myocyte that can propagate action potentials

21
Q

what are transverse tubules (T-tubules)?

A

system of tubules perpendicular to myofibrils that can distribution actin potential from sarcolemma to sarcoplasmic reticulum

22
Q

what’s the order of muscle structure starting with sarcomeres?

A

sarcomeres –> myofibrils –> myocytes/muscle cell/muscle fiber –> muscle

23
Q

What are the three stages of muscle contraction?

A
  1. initiation
  2. shortening of the sarcomere
  3. relaxation
24
Q

what occurs during initiation of muscle contraction?

A
  1. motor/efferent neuron sends a signal to the neuromuscular junction
  2. acetylcholine is released from the nerve terminal and binds to receptors on sarcolemma, causing depolarization
  3. depolarization triggers action potential through sarcolemma, through T-tubules, and then sarcoplasmic reticulum
  4. Ca2+ release upon action potential reaching sarcoplasmic reticulum
  5. Ca2+ binds to troponin –> conformational change of tropomyosin
  6. myosin-binding sites on actin thin filament become exposed
25
Q

what is the motor end plate?

A

another name for the nerve/axon terminal specifically in the neuromuscular junction

26
Q

what is a motor unit?

A

a nerve terminal + the group of myocytes that the nerve terminal controls

27
Q

what are the four steps of the actin-myosin cross-bridge cycle that allows for shortening of the sarcomere?

A
  1. Resting stage: ADP+Pi bound to myosin
  2. Ca2+ binding: Ca2+ binds to troponin, myosin binds to actin
  3. Powerstroke: ADP+Pi dissociation from myosin provides energy for powerstroke/sarcomere contraction/actin filament sliding over myosin filament
  4. ATP stage: ATP binding to myosin leads to myosin dissociation from actin; ATP hydrolysis leads to recocking of myosin head
28
Q

what is the sliding filament model?

A

sequential shortening of the sarcomere due to repetitive binding and release of myosin head

this is what actually occurs in muscle contraction

29
Q

what enzyme degrades acetylcholine in the neuromuscular junction during muscle relaxation?

A

acetylcholinesterase

30
Q

what happens during muscle relaxation?

A
  1. signal termination due to acetylcholine degradation by aceylcholinesterase
  2. sarcolemma repolarizes
  3. calcium release stops
  4. sarcoplasmic reticulusm takes up calcium from sarcoplasm, controlling intracellular calcium contraction and preventing excessive contraction
  5. ATP binds to myosin heads, dissociating myosin from actin and allowing sarcomere to return to original width
31
Q

what is simple twitch? what are its three periods?

A

response of a single muscle fiber to a brief stimulus at/above threshold

  1. latent period
  2. contraction period
  3. relaxation period
32
Q

what is the latent period of simple twitch?

A

time between stimuli reaching threshold value and muscle contraction
during this time, action potential goes through muscle and calcium is released from sarcoplasmic reticulum

33
Q

what happens during (frequency) summation?

A

frequent and prolonged stimulation –> insufficient time to relax –> contractions combine, becoming stronger and more prolonged

34
Q

what is tetanus, the physiological phenomenon?

A

when contractions become so frequent that muscles cannot relax

35
Q

what is oxygen debt?

A

= the difference between amount of oxygen needed by muscles and the amount of oxygen available
= the amount of oxygen needed to convert lactic acid back into pyruvate

36
Q

what are two supplemental energy reserves in muscles in addition to oxidative phosphorylation in mitochondria of red/slow-twich fibers?

A
  1. creatine phosphate + ADP –> ATP + creatine

2. glycolysis + fermentation to make ATP

37
Q

How does creatine phosphate help with energy production in muscles?

A

during rest, ATP transfers a phosphate group to creatine to produce creatine phosphate and ADP. when needed, this reaction is reversed to generate ATP from ADP.

38
Q

when does muscle fatigue occur?

A

insuffient oxygen supply –> anaerobic metabolism: glycolysis+fermentation –> lactic acid
this occurs during times of high exercise or prolonged tetanus

Kaplan MCAT Biology (14 decks)

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