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Exercise physiology > Lecture 4 - Muscular system org. > Flashcards

Lecture 4 - Muscular system org. Flashcards

1
Q

what are the 6 functions of muscular system?

A
  1. MOVEMENT: muscles contract and pull on bones to produce voluntary movement
  2. POSTURE AND STABILITY: muscles are constantly contracting to keep body upright
  3. HEAT PRODUCTION: muscle contractions generate heat, thermogenesis (muscles = most metabolically active tissue in body)
  4. CIRCULATION: cardiac muscles (and skeletal muscles) in heart pump blood throughout body
  5. RESPIRATION: muscles like diaphragm and intercostal muscles are crucial for breathing
  6. DIGESTION AND PERISTALSIS: smooth muscles in GI tract help move food through digestive system
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2
Q

what are the 3 types of muscles?

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

SKELETAL MUSCLE: what percent:
- water
- protein
- salts and other substances including (7)
*what is the most abundant and largest muscle protein in body? function?

A
  • 75% water
  • 20% protein
  • 5% salts and –> high E phosphates, urea, lactate, minerals, amino acids, fats, carbs
    *titin! 27 000 aa –> 10% of muscle mass –> holds sarcomere together: binds sarcomere to Z-line
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4
Q

explain the hierarchical structure of skeletal muscle. 6 layers ish

A
  1. muscle (organ), covered by epimysium (structural support role, helps sliding) –> contains lots of fascicles
    *also tendon and deep fascia
  2. fascicles (bundle of muscle fibers) –> each covered by perimysium
  3. muscle fibers (cells): surrounded by endomysium
  4. myofibrils (within muscle fibers): contain contractile elements/protein (actin and myosin)
  5. sarcomeres (within myofibrils): functional units of contraction
  6. myofilaments (within sarcomeres): actin and myosin filaments responsible for contraction
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5
Q

describe
SARCOLEMMA
- what
- 3 fcts
SARCOPLASM
- what
- 2 fcts
SARCOPLASMIC RETICULUM

A

SARCOLEMMA
- plasma membrane of muscle fiber
- provides structure and protection + shape
- transmits electrical signals
- excitation-contraction coupling (depolarization)
SARCOPLASM
- cytoplasm of muscle fiber (contains normal stuff: mitochondria, lysosomes…)
- houses myofibrils, which are made up of repeating units called sarcomere
- stores glycogen for E and myoglobin (O2 binding protein)
SARCOPLASMIC RETICULUM
- specialized form of smooth ER found in muscle cells
- regulates Ca ions within muscle fiber: releases Ca into sarcoplasm OR pumps Ca back into storage

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6
Q

what is thick vs thin filament?
- describe

A

thick = MYOSIN filament
- composed of hundreds of myosin molecules: each myosin molecule has long tail and globular heads
- myosin heads: extend outward from thick filaments and are essential for forming cross-bridges with actin –> has actin-binding site + ATPase activity (enzymatic fct: hydrolyze ATP to release E for muscle contraction)
- role = generate force by attaching to actin

thin = ACTIN filament:
- composed of globular actin (G-actin) monomers that polymerize to form long, helical filaments (F-actin)
- contains tropomyosin and troponin

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7
Q

what is tropomyosin?

A

long, rope like protein that winds around the actin filament
- in relaxed muscle, tropomyosin covers the myosin-binding sites on actin, preventing interaction btw actin and myosin

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8
Q

what is troponin? + 3 subunits

A
  • regulatory protein complex attached to tropomyosin
    1. troponin C –> binds to calcium ions
    2. troponin I: inhibits actin-myosin interaction by maintaining tropomyosin’s position over actin’s myosin binding sites –> keeps locked position
    3. troponin T: binds the troponin complex to tropomyosin
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9
Q

Sacromere structure:
- actin: extend from where to where?
- myosin: extend from where to where?
- z-disc/z-line: what? moves where during contraction
- m-line: what? moves where during contraction

A

ACTIN: extend from z-disc toward center of sarcomere (M-line)
MYOSIN: extend from M-line towards Z-disc
Z-DISC: located at boundaries of each sarcomere, anchoring actin filaments –> moves closer together during contraction
M-LINE: center of sarcomere, where thick myosin are anchored –> remains centered during contraction

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10
Q
  • a-band: what? length during contraction?
  • i-band: what? length during contraction?
  • h-zone: what? length during contraction?
A

A-BAND: contains full length of myosin filaments overlapping actin filaments (dark?) –> length remains constant during contraction
I-BAND: contains only actin filaments and shortens during contraction
H-ZONE: middle region of the a-band: no overlap btw actin and myosin: becomes narrower or may disappear during contraction

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11
Q

what are 3 ways to look at if a muscle is damaged?

A
  1. indirect look: creatine kinase content in the muscle –> proxy, increase [CK] if damage
  2. direct: muscle biopsy: damage or disruption of Z-lines –> disrupted structural component = less efficient contraction
  3. in the gym: do 1RM, then workout, then 1RM again –> if muscle is damaged, force production will decrease
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12
Q

what is Z-line streaming?
- occurs when?
- consequence?

A
  • refers to damage or disruption of Z-discs (Z-lines)
  • occurs due to injury or excessive muscle stress
  • integrity of sarcomere is compromised –> misalignment of actin filaments anchored at the Z-disc
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13
Q

what is the role of ATP in cross-bridge cycling?

A

repeated interaction btw myosin (motor protein) and actin (structural protein) for muscle contraction)

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14
Q

explain the 4 steps of the cross-bridge cycle

A
  1. ATP binds to myosin head and undergoes hydrolysis (into ADP + Pi + E) –> head is cocked into high-E position –> myosin head attaches to actin to form cross bridge
  2. Pi is released = strengthens bond btw actin and myosin –> myosin head pulls actin filament inward = power stroke
  3. ADP is released from myosin head, myosin still bound to actin in low E state –> new ATP binds to myosin = breaks the crossbridge = relaxes sarcomere
  4. ATP hydrolysis: ATP is split into ADP and Pi –> myosin head is recocked and is returned to high-E position, ready for another cross-bridge
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15
Q

explain the 11 steps of the cross-bridge cycle

A
  1. action potential arrives at neuromuscular junction = nerve impulse
  2. acetylcholine is released into synaptic cleft
  3. Ach binds to receptor on muscle fiber membrane (sarcolemma) and opens sodium ion channels/change membrane permeability –> leading to an action potential in sarcolemma
  4. action potential travels along the transverse-tubules/penetrates muscle fibers
  5. calcium is released from sarcoplasm reticulum into muscle fiber
  6. Ca2+ binds to troponin and tropomyosin –> conformational change
  7. myosin-binding site on actin filament is exposed
  8. actin and myosin bind together = cross-bridge
  9. power stroke: ATP is hydrolyzed = provide E to undergo power stroke –> sliding of actin past myosin, causing sarcomere to shorten and phosphate to release
  10. calcium is resorbed, beginning relaxation cycle, ATP is required. re-establish low calcium concentration in cytoplasm
  11. termination of contraction bc binding site is locked by troponin/tropomyosin (bc no more calcium)
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16
Q

what are t-tubules?
- typically aligned with what?
- allow for what?

A
  • invaginations of sarcolemma that penetrate muscle fiber
  • typically aligned with z-disc of sarcomere
  • allow action potential to reach all parts of muscle fiber quickly
17
Q

when does muscle contraction cease? (2)

A

when nerve impulses stop and calcium is actively pumped back into sarcoplasmic reticulum

18
Q

Does calcium only return into the SR once the muscle contraction is over?

A

Calcium is always being actively transported back into the sarcoplasmic reticulum, even during muscle contraction, but the rate of calcium release and reuptake differs at the various stages of contraction.
- during contraction: calcium release > calcium reuptake
- after contraction: no more calcium release bc no nerve impulse to calcium reuptake dominates!

19
Q

type I vs type II fibers
- well suite for what activity?
- high or low: mit density, capillary density, myoglobin
- graph shape of power (I vs 2a vs 2x)

A

TYPE I:
- well suited for endurance running
- HIGH of all 3
- low power but can maintain! not that much decrease in power
TYPE II:
- well suited for power and short bursts of high-intensity activity
- LOW of all 3
- 2a: medium power, short lived, decrease rapidly
- 2x: very high power, very short lived, decrease very fast

20
Q

which type of fiber would have a larger power drop in 3 wingate tests?

A

fast-twitch/type 2 had larger power drop –> not as efficient to recover + more fatiguing –> not recovered after 5 hours
VS slow-twitch: recovered after 20min to baseline

21
Q

what are the 3 type of muscle contractions?
- what
- example
- force production
- E req

A
  1. ISOMETRIC:
    - muscle generates force without changing its length (no mvt)
    - ie holding plank OR wall sit
    - moderate force production
    - low to moderate E req
  2. CONCENTRIC:
    - muscle shortens while generating force, causing movement of joint
    - ie pushing off ground during a vertical jump
    - moderate to low force prod
    - high E req
  3. ECCENTRIC:
    - muscle lengthens while generating force often controlling movement as it returns to starting position
    - ie lowering phase of bicep curl or running downhill
    - highest force production
    - moderate E req
22
Q

why do eccentric contractions generally generate most force? (4)

A
  1. elastic components (ie titin + connective tissues) add passive force to force from contractile protein that increases overall force production
    2; bc filaments are being pulled apart, less detachment of cross-bridges –> allows for more cross-bridges to be engaged = increase force
  2. eccentric contractions are more energy-efficient –> muscle can sustain greater force with less E expenditure
  3. strain on myosin heads during lengthening makes it harder to detach from actin –> contributes to overall output
23
Q

if muscle is in static position during an isometric contraction, is cross-bridge cycling still taking place?

A

yes! bc generating force! moving myosin heads, still binding and release, still power stroke BUT myosin and actin don’t slide!

24
Q

why do eccentric contractions have lower E reqs than concentric if more cross-bridges during eccentric?

A
  1. myosin heads are more attached to actin (less detachment) bc of external force (gravity) –> less ATP required for detachment of myosin heads
  2. rate of bridges cycles (detach attach) is slower vs concentric –> need less ATP over time
  3. a portion of force is generated by passive elements like titin = don’t require ATP –> part of force is generated without needing additional E
25
Q

what is a motor unit?
_____A_____ + _____B_______ ish
- when ____A______ sends signal, which ______B______ are stimulated?
- number of _____B____ stimulated depend on what?

A

single motor neuron and all the muscle fibers it innervates
- when a motor neuron sends a signal, all muscle fibers in that motor unit contract simultaneously
- number of muscle fibers per motor unit varies depending on precision of mvt required

26
Q

what is the Henneman’s size principle of motor unit requirement?
- are small or larger motor units recruited first? low or high preceision?

A

motor units are recruited in an orderly fashion based on size of motor neuron
SMALLER motor units (with smaller motor neurons) are recruited first –> these motor unis generate less force but allow for fine control = high precision but low-force activity (ie eyes)
LARGER motor units are recruited as more force is required = low precision + high force activities
- ie squat, picking smtg off floor
- ie 1RM bypass small motor units and activate large motor units first

27
Q

compare slow vs fast motor units?
- characteristics?
- examples of activities

A

SLOW (type 1):
- small motor neurons, fewer muscle fibers, slow conduction speed, generate less force
- highly resistant to fatigue
- used in low-intensity, endurance activities like posture maintenant or long-distance running
FAST (type 2):
- larger motor neurons, more muscle fibers, fast conduction speed, generate more force, fatigue quickly
- used in high-intensity, short duration activities, like sprinting and weightlifting

28
Q

explain the force-velocity curve
- high vs low force

A
  • relationship btw the force a muscle can generate and the velocity at which it can shorten and lengthen
  • high force = low velocity: muscles produce a greater force at a lower contraction velocity
  • low force = high velocity: muscles generate less force at higher contraction velocity
29
Q

describe if increase or decrease force production at high vs low velocity for
CONCENTRIC
ECCENTRIC
ISOMETRIC

A

CONCENTRIC
- high velocity: decrease force prod
- low velocity: increase force prod
ECCENTRIC
- high velocity: increase force prod
- low velocity: decrease force prod
ISOMETRIC
- velocity: no change in muscle lengths so force is maintained without influence of velocity

30
Q

Why do high velocity eccentric contractions increase force production and why do low velocity eccentric contractions decrease force production?

A
  1. cross-bridge dynamics:
    - high velocity: for ecc, rapid stretch pulls apart cross-bridges rapidly –> leads to higher proportion of engaged cross-bridges = more force generated bc muscle is trying to prevent rapid lengthening
    - low velocity: fewer cross-bridges are resisting lengthening –> muscles don’t resist as much = lower force
  2. elastic-component:
    - high velocity: elastic components like titin are stretched more abruptly –> rapid stretch stores more E, which is released as tension, increasing overall force output
    - low velocity: contribution of elastic components is reduced = lower force output
  3. force-velocity relationship:
    - high velocity: eccentric contractions allow muscle to generate more force due to mechanical resistance against rapid stretching
    - low velocity: lower force bc muscle fibers are not being stretched quickly enough to engage cross-bridges and elastic components fully
31
Q

what is the length-tension curve?
- only for which contractions?

A
  • represents the relationship btw length of a muscle/sarcomeres and amount of force it can generate
  • only for isometric contractions!
32
Q

explain effect of shortened muscle vs extended muscle vs optimal length on force production
- what is optimal length?

A

SHORTENED:
- if muscle is too short, overlap of actin and myosin reduces # of cross-bridges that can be formed = decrease force production
EXTENDED:
- if muscle is too stretched, fewer cross-bridges can form due to increased distance btw actin and myosin filaments = decrease force prod
OPTIMAL LENGTH:
- ideal overlap btw actin and myosin allowing for maximum amount of cross-bridge formation to generate force = increase force produ
- optimal sarcomere length for maximum force production is around 2.0-2.2 micrometers
- ie going down a squat, optimal point to generate force to come up

33
Q

what is the muscle cross-sectional area?
- how is is related to force production?
- affected by (2)

A
  • area of a muscle’s cross-section perpendicular to its length
  • force production is directly proportional: the larger the CSA, the more contractiles proteins and neurons, the greater the force production
  • CSA affected by hypertrophy and fiber recruitment
34
Q

how to increase Muscle CSA? (2)

A
  1. strength training (total amount of load you can lift): promotes hypertrophy and increases CSA, leading to overall force production
  2. power training (speed component); focuses on type 2 fibers to enhance force prod and explosive strength
35
Q

what is muscle fatigue?
2 types

A

temporary decrease in ability of a muscle/muscle group to generate force
- central vs peripheral fatigue

36
Q

describe central (what + 2 causes) vs peripheral fatigue (what + 3 causes)

A

CENTRAL:
- fatigue originating from CNS affecting ability to initiate and sustain voluntary muscle contractions
1. reduced neural drive: decreased motor neurons firing rates
2. cognitive factors: psychological factors such as motivation and perception of effort (prevents you from pushing more: brain will fatigue before muscle)
PERIPHERAL:
- fatigue occurring at or beyond neuromuscular junction involving muscle fibers themselves
1. metabolic changes: depletion of ATP and glycogen and the accumulation of metabolic byproducts (lactate)
2. ion imbalance: disruption in calcium, potassium and sodium balance
3. muscle damage: structural damage to muscle fibers and membranes (Z-line streaming)

37
Q

what factors contribute to fatigue during exercise (4)

A
  1. intensity and duration
  2. training status (trained vs untrained)
  3. nutrition and hydration (electrolyte imbalance, nerve excitability)
  4. environmental conditions (heat, humidity, cold, altitude training)
38
Q

can you determine who is the strongest athlete by just looking at their muscle size?

A

no! although muscle size is a good indicator of force production, there is also skill, nerve excitability, technique, specialization to take into consideration

Exercise physiology (14 decks)

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