Lecture 4 - Muscular system org. Flashcards
what are the 6 functions of muscular system?
- MOVEMENT: muscles contract and pull on bones to produce voluntary movement
- POSTURE AND STABILITY: muscles are constantly contracting to keep body upright
- HEAT PRODUCTION: muscle contractions generate heat, thermogenesis (muscles = most metabolically active tissue in body)
- CIRCULATION: cardiac muscles (and skeletal muscles) in heart pump blood throughout body
- RESPIRATION: muscles like diaphragm and intercostal muscles are crucial for breathing
- DIGESTION AND PERISTALSIS: smooth muscles in GI tract help move food through digestive system
what are the 3 types of muscles?
- skeletal muscle
- cardiac muscle
- smooth muscle
SKELETAL MUSCLE: what percent:
- water
- protein
- salts and other substances including (7)
*what is the most abundant and largest muscle protein in body? function?
- 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
explain the hierarchical structure of skeletal muscle. 6 layers ish
- muscle (organ), covered by epimysium (structural support role, helps sliding) –> contains lots of fascicles
*also tendon and deep fascia - fascicles (bundle of muscle fibers) –> each covered by perimysium
- muscle fibers (cells): surrounded by endomysium
- myofibrils (within muscle fibers): contain contractile elements/protein (actin and myosin)
- sarcomeres (within myofibrils): functional units of contraction
- myofilaments (within sarcomeres): actin and myosin filaments responsible for contraction
describe
SARCOLEMMA
- what
- 3 fcts
SARCOPLASM
- what
- 2 fcts
SARCOPLASMIC RETICULUM
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
what is thick vs thin filament?
- describe
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
what is tropomyosin?
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
what is troponin? + 3 subunits
- 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
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
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
- a-band: what? length during contraction?
- i-band: what? length during contraction?
- h-zone: what? length during contraction?
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
what are 3 ways to look at if a muscle is damaged?
- indirect look: creatine kinase content in the muscle –> proxy, increase [CK] if damage
- direct: muscle biopsy: damage or disruption of Z-lines –> disrupted structural component = less efficient contraction
- in the gym: do 1RM, then workout, then 1RM again –> if muscle is damaged, force production will decrease
what is Z-line streaming?
- occurs when?
- consequence?
- 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
what is the role of ATP in cross-bridge cycling?
repeated interaction btw myosin (motor protein) and actin (structural protein) for muscle contraction)
explain the 4 steps of the cross-bridge cycle
- 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
- Pi is released = strengthens bond btw actin and myosin –> myosin head pulls actin filament inward = power stroke
- 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
- 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
explain the 11 steps of the cross-bridge cycle
- action potential arrives at neuromuscular junction = nerve impulse
- acetylcholine is released into synaptic cleft
- Ach binds to receptor on muscle fiber membrane (sarcolemma) and opens sodium ion channels/change membrane permeability –> leading to an action potential in sarcolemma
- action potential travels along the transverse-tubules/penetrates muscle fibers
- calcium is released from sarcoplasm reticulum into muscle fiber
- Ca2+ binds to troponin and tropomyosin –> conformational change
- myosin-binding site on actin filament is exposed
- actin and myosin bind together = cross-bridge
- power stroke: ATP is hydrolyzed = provide E to undergo power stroke –> sliding of actin past myosin, causing sarcomere to shorten and phosphate to release
- calcium is resorbed, beginning relaxation cycle, ATP is required. re-establish low calcium concentration in cytoplasm
- termination of contraction bc binding site is locked by troponin/tropomyosin (bc no more calcium)
what are t-tubules?
- typically aligned with what?
- allow for what?
- 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
when does muscle contraction cease? (2)
when nerve impulses stop and calcium is actively pumped back into sarcoplasmic reticulum
Does calcium only return into the SR once the muscle contraction is over?
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!
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)
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
which type of fiber would have a larger power drop in 3 wingate tests?
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
what are the 3 type of muscle contractions?
- what
- example
- force production
- E req
- ISOMETRIC:
- muscle generates force without changing its length (no mvt)
- ie holding plank OR wall sit
- moderate force production
- low to moderate E req - 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 - 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
why do eccentric contractions generally generate most force? (4)
- 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 - eccentric contractions are more energy-efficient –> muscle can sustain greater force with less E expenditure
- strain on myosin heads during lengthening makes it harder to detach from actin –> contributes to overall output
if muscle is in static position during an isometric contraction, is cross-bridge cycling still taking place?
yes! bc generating force! moving myosin heads, still binding and release, still power stroke BUT myosin and actin don’t slide!
why do eccentric contractions have lower E reqs than concentric if more cross-bridges during eccentric?
- myosin heads are more attached to actin (less detachment) bc of external force (gravity) –> less ATP required for detachment of myosin heads
- rate of bridges cycles (detach attach) is slower vs concentric –> need less ATP over time
- a portion of force is generated by passive elements like titin = don’t require ATP –> part of force is generated without needing additional E
what is a motor unit?
_____A_____ + _____B_______ ish
- when ____A______ sends signal, which ______B______ are stimulated?
- number of _____B____ stimulated depend on what?
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
what is the Henneman’s size principle of motor unit requirement?
- are small or larger motor units recruited first? low or high preceision?
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
compare slow vs fast motor units?
- characteristics?
- examples of activities
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
explain the force-velocity curve
- high vs low force
- 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
describe if increase or decrease force production at high vs low velocity for
CONCENTRIC
ECCENTRIC
ISOMETRIC
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
Why do high velocity eccentric contractions increase force production and why do low velocity eccentric contractions decrease force production?
- 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 - 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 - 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
what is the length-tension curve?
- only for which contractions?
- represents the relationship btw length of a muscle/sarcomeres and amount of force it can generate
- only for isometric contractions!
explain effect of shortened muscle vs extended muscle vs optimal length on force production
- what is optimal length?
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
what is the muscle cross-sectional area?
- how is is related to force production?
- affected by (2)
- 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
how to increase Muscle CSA? (2)
- strength training (total amount of load you can lift): promotes hypertrophy and increases CSA, leading to overall force production
- power training (speed component); focuses on type 2 fibers to enhance force prod and explosive strength
what is muscle fatigue?
2 types
temporary decrease in ability of a muscle/muscle group to generate force
- central vs peripheral fatigue
describe central (what + 2 causes) vs peripheral fatigue (what + 3 causes)
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)
what factors contribute to fatigue during exercise (4)
- intensity and duration
- training status (trained vs untrained)
- nutrition and hydration (electrolyte imbalance, nerve excitability)
- environmental conditions (heat, humidity, cold, altitude training)
can you determine who is the strongest athlete by just looking at their muscle size?
no! although muscle size is a good indicator of force production, there is also skill, nerve excitability, technique, specialization to take into consideration
