Muscle Structure and Function Flashcards
muscle tissue
consist of muscle cells (fibres)
all muscle characteristics
excitability
contractibility
extensibility
elasticity
3 major muscle types
smooth
cardiac
skeletal
smooth muscle
has spindle-shaped non-striated uninucleated fibres
occurs in walls of internal organs
vessel, digestive tract
-is involuntary
Muscle types differentiated by
fibre shape
location of nuclei
appearance - striated, smooth
nature of control- voluntary or involuntary- hybrid
cardiac muscle
has striated, branched, uninucleated fibres
occurs in walls of heart
is voluntary
skeletal muscle
has striated, tubular, multinucleate fibres
is usually attached to skeleton
is voluntary
Epimysium
surrounds all the muscle fibre bundles (fasciculi) to form the entire muscle
Perimysium
surrounds several muscle fibres and forms bindles called fasciculi
Fassiculus
bundle of up to 150 muscle fibres
endomysium
wraps each muscle fibre
by weight, a single muscle fibre is made up of primarily
water
single muscle fibre (cell, weight consists of)
75% water
20% protein
5% other
-minerals (K+, Na+, CI-) fats, CHO, amino acids, enzymes, ATP, lactate ect.
Microstructure of muscle: sarcolemma
muscle cell membrane surrounding muscle fibre
Microstructure of muscle: satellite cells
located within the sarcolemma (between the plasma and basement and membrane)
-help regenerative cell growth (myogenic stem cells)
-play a role in hypertrophy
Microstructure of muscle: sarcoplasm
protoplasm (enzymes, fat, glycogen)
nuclei
sarcoplasmic reticulum (SR)
network of tubules and vesicles (triads)
located around myofibrils
provides structural integrity and spreads depolarization
role: stores, releases and reabsorbs Ca2+
each sarcomere contains ____ triads
two
triad system
2 large sacs (vesicles)
-terminal cistern of the SR
small central sac
-T tubule
Muscle microstructure
within the single muscle fibre there are myofibrils
-myofibrils =1/1000mm in diameter
up to 8000 myofibrils
myofibrils contain myofilaments
Myofilaments are _______ that make up sarcomere units
proteins
myofilaments
-functional unit of muscle fibre
-runs from z-line to z-line
order from whole muscle
-myofilament
-myofibril
-muscle fibre
-muscle fasiculi
whole muscle
muscle fasiculi
muscle fiber
myofibril
myofilament
at what level would we find a bundle of muscle fibres?
fascicle
Myofibril proteins (aka myofilaments) making up the sarcomere include:
myosin (thick filament)
actin (thin filament)
Actin and myosin are _______ proteins
contractile
within the actin filament
troponin (thin filament)
tropomyosin (thin filament)
Both troponin and tropomyosin are _______ proteins
regulatory
12-15 other proteins are present; however, myosin and actin make up _________
85% of myofibrillar complex
I band
light, actin only
A band
dark, actin and myosin overlap
sarcomere:
an arrangement of actins and myosins, bordered by z-discs
actin
a thin myofilament which is parallel to and slides past myosin, a thick, myofilament, resulting in muscle contraction
z discs
thick structures that are perpendicular to and anchor the actin
I-band: a _____ area that contains only ____
light, actin
A-band: a ______ area that contains _____
dark, myosin and actin
H-zone: a _____ area that contains only _____
light, myosin
which is considered a “light” zone
H zone and I band
Actin contains which contractile proteins
G-actin
F-actin
tropomyosin
troponin
3 subunits (I, C and T)
regulatory proteins: tropomyosin
lies along actin like a cord
-inhibits actin-myosin interaction
regulatory proteins: troponin
embedded at regular intervals along actin
-interacts with Ca2+
-removes inhibition
muscle contractile proteins
myosin
-cross bridges (actin and myosin overlap)
globular heads
-actin binding site
-ATP binding site
-Heavy and light chains
myosin has ____ heads
each head has ____ “heavy chain”
2, 1
ATPase activity will determine speed of contraction
Myosin is composed of _________
heavy chains and light chains
type of heavy chains determines the ATPase activity
3 predominant types of MHCs:
Type 1 MHC: slowest contracting
Type 2 MHC: moderately fast contracting
Type 3 MHC: fast contracting
Type IIB= very fast contracting
functions of skeletal muscle
-stabilize body
-moment of joints
-locomotion
- movement of limbs = improve circulation
-thermogenesis (shivering) capillirization
-body posture
venous return
skeletal muscle has a rich vascular network
-flow is rhythmic
-vessels compress during contraction phase
-vessels open during relaxation phase
muscle action contraction and relaxation: 2 components
mechanical: sliding filament model
chemical: energy - via ATP hydrolysis
mechanical component: sliding filament theory
-contraction occurs as myosin and actin slide past one another
-myosin pulls actin, actin slides past myosin
sliding filament model
-myosin bridges attach to actin filament
-cross bridges rotate
-cross bridges detach
repeat
-only about 50% of cross bridges attached at any one time
which shortens during a contraction
the sarcomere
rearrangement of actin and myosin at rest and surfing muscle ______
shortening
during contraction (concentric)
-the length if the thick and thin filament do not change
-the length of the sarcomere decreases as actin is pulled over myosin
which filament has moved as the sarcomere contracted ?
actin
chemical component of sliding filament theory
-main molecule used for energy in muscle contraction is from ATP hydrolysis
-adenosine triphosphate
ATP is broken down to ADP+Pi + energy
ADP= adenosine triphosphate
Pi= inorganic phosphate
sliding filament theory - chemical
ATP – ADP + Pi +energy
globular head of myosin contains (actin activated) myosin ATPase
sliding filament model review
-ATP bound to myosin
-ATP hydrolysis, energy stored in myosin head
-loose binding between myosin and actin
-Pi is released- tightens binding
-conformational change of myosin head (repositions angle of attachment of myosin to actin)
-elecits pulling of actin towards M-line (cross bridge movement)
-myosin drops ADP as it moves
-New ATP binds to myosin
-release of myosin head from actin (cross bridge dissociates)
Sliding filament theory: 1. Relaxed state: detached
myosin globular head
-ATP attached to binding site on globular head
-ACTIN binding site empty
ACTIN
-myosin binding site on actin covered by troponin and tropomyosin
Sliding Filament theory: 2. Actomyosin complex
-if binding site is available. loose binding- myosin and actin
-ADP+Pi both still attached to the globular head
ATP hydrolysis, energy stored in globular head
Sliding filament theory: 3. Power stroke
-Pi released = tightens binding
-myosin head-conformation change
-reposition angle of attachment
-myosin pulls actin towards M-line
sliding filament theory: end
myosin releases ADP as it moves
-new ATP
-myosin head released from actin
repeat cycle
cycle of mechanical action
-For continued muscle contraction we need repeated myosin cross bridges to combine, deteach and recombine with active actin site
-detachment of myosin from actin occurs when a new ATP joins the actomyosin complex (combined actin and myosin) this completes the sliding motion, cross bridges dissociate
-myosin then returns to original state and is ready to reattach to new active site
what are considered regulatory proteins
troponin and tropomyosin
inhibitory action of regulatory proteins =
steric blocking (tropomyosin sits on binding sites)
7 steps of the sliding filament model
1.Mysoin head bound to ATP
2. ATP hydrolysis, energy stored in globular head
3. Myosin loosely interacts with actin
4.Pi releases, myosin and actin bond tightens
5. Myosin cross bridge movement starts to create sliding motion (generate muscle tension)
6.ADP released
7. Myosin binds with new ATP, actomyosin complex disassociation
Excitation-Contraction coupling
Physiological mechanism
-electrical discharge at muscle initiates chemical events at cell surface
-Cell (sarcoplasmic reticulum) releases intracellular Ca2+
-Ca2+ combines to troponin-tropomyosin in actin filament
-Troponin pulls tropomyosin off actin active sites (removes inhibitory action)
-Allows actin to combine with myosin
relaxation of muscle
-Ca2+ is actively pumped out and back into SR (SR ATPase)
-Removal of Ca2+ restores the inhibitory action of troponin-tropomyosin
-troponin allows tropomyosin to interfere with actin-myosin interaction
if a muscle fibre has greater SR ATPase what characteristic would it demonstrate?
it would relax faster
EC Coupling order
- Electrical discharge at muscle initiates chemical events at cell surface
- Cell (sarcoplasmic reticulum) releases intracellular Ca2+
- Ca2+ combines to troponin-tropomyosin
- troponin pulls tropomyosin off actin active sites (removes inhibitory action)
- allows actin to combine with myosin
- removal of Ca2+ restores the inhibitory action of troponin-tropomyosin
possible effects of caffeine
-enhances motoneuronal excitability
-increases calcium release from sarcoplasmic reticulum
-improves performance, msucular endurance, NOT as much support for improve anaerobic performance
Macro level structure
epimysium = around entire muscle
perimysium= around bundles of fibres
endomysium = around individual fibre
muscle - fascicles - fibers - myofibrils - myofilaments
Summary sequence of events (sequence of muscle action events)
step 3
depolarization of T-tubules system causes Ca2+ to release from lateral sacs of sarcoplasmic reticulum
Summary sequence of events (sequence of muscle action events)
step 4
Ca2+ binds to troponin-tropomyosin in actin filaments, releasing the inhibition that prevented actin from combing with myosin
Summary sequence of events (sequence of muscle action events)
step 5
-actin combines with myosin
-stored energy produces myosin and actin cross bridge movement and creates tension
Summary sequence of events (sequence of muscle action events)
step 6
-ATP binds to myosin cross bridge which breaks actin-myosin bond, allowing actin dissociation from crossbridge
-thick and thin filaments complete the slide past each other and muscle shortens
Summary sequence of events (sequence of muscle action events)
step 8
-when muscle stimulation ceases, intracellular Ca2+ concentration rapidly decreases as Ca2+ moves back into lateral sacs of sarcoplasmic reticulum thorough active transport; requires ATP hydrolysis
Summary sequence of events (sequence of muscle action events)
step 9
Ca2+ removal restores inhibitory action of troponin-tropomyosin
-in presence of ATP, actin and myosin remain in dissociated, relaxed state
two major fibre types in humans: Type I
slow
-Type I and type Ic
two major fibre types in humans: Type II
fast
subdivisions
-type IIc, Type Iliac, type IIa, Type IIax, type Iix
in animals there are even more
Muscle fibre classifications: primary means of differentiation/classification based on
- Myosin heavy chains (Myosin ATPase activity) isoforms
- type of motore neuron innervation - twitch properties
- biochemical pathways used to produce energy “ metabolic properties”
fibre type: classification based on myosin heavy chains (ATPase activity)
type I
low myosin ATPase activity
fibre type: classification based on myosin heavy chains (ATPase activity)
type IIa
high myosin ATPase activity
fibre type: classification based on myosin heavy chains (ATPase activity)
type IIx
myosin ATPase activity, may see denoted as type IIb is more accurate for humans
fibre type: classification based on myosin heavy chains (ATPase activity)
type IIb
highest myosin ATPase activity
fibre type: contraction speed (slowest to fastest)
type I
type IIA
type IIx (type IIb)
type IIb
fibre type based on “twitch” properties
slow or slow twitch
fast fatigue or fast twitch a (FTa)
fast fatiguable or fast twitch x (Fix)
fibre type
classification based on metabolic properties
-slow oxidative / aerobic metabolism
-fast oxidative glycolytic /anaerobic metabolism
-fast glycolytic/ anaerobic metabolism
glycolytic enzymes in cytoplasm
typically a fast-twitch or type IIb muscle fibre
carbohydrates = (fast) a small amount of energy
uses glycogen
by product lactic acid
oxidative enzymes (in the mitochondria)
typically a slow twitch or type 1 muscle fibre
carbohydrates, proteins, fat
= (slow) much energy
by product - a low amount of lactic acid
muscle fibre classification
1) classification based on “twitch” properties
-slow or slow twitch
-fast-fatigue resistant or fast twitch a (FTa)
-fast-fatiguable or fast twitch b
muscle fiber classification
2) based on myosin heavy chains (ATPase activity)
-Type I, IIa, IIx, IIb
muscle fiber classification
3) based on metabolic properties
slow oxidative
fast oxidative
fast glycolytic
type 1: slow twitch fibers (slow oxidative- SO)
-low myosin
-less extensive SR
-slower Ca2+ releases and uptake
-slowest contracting, least fatiguable
-aerobic metabolism (highest # oxidative enzymes)
-large and numerous # of mitochondria
-high in myoglobin
type II: fast twitch fibers (glycolytic)
-high myosin ATPase activity
-extensive SR network
-rapid Ca2+ release and uptake by SR
-high rate of cross bridge turnover
-fats contractions
-capable of high force generation
-fatigue quickly
-rely on anaerobic metabolism (glycolytic enzymes)
-low in myoglobin
fast twitch subdivisions
IIa (fast oxidative-glycolytic)
-fast shortening speed
-moderalty well developed capacity for both anaerobic and aerobic energy production
Iix fibers- middle (fast-glycolytic)
IIb fibers (“true” fast-glycolytic)
-most rapid
-rely most heavily on anaerobic energy production
myoglobin
is a protein in your muscle responsible for transporting oxygen from th muscle membrane-capillary interface to the mitochondria
-myoglobin gives the muscle a red pigmentation
which muscle fibers (light vs. dark) are most likely type I
Dark ones are more likely to be type I (they will appear red), they have more myoglobin
histochemical staining for muscle fiber types
-muscle cross section (on a cover slip, place in history jar)
-based on the sensitivity of the muscle fiber’s myosin ATPase to different pH environments
FT fibers- when exposed to an acid environment myosin ATPase becomes inactive (light)
ST fibers- when exposed to an alkaline environment myosin ATPase becomes inactive (light)
another way to measure muscle fibre types
fatigue index
-significantly less invasive
-mathematical equation
-uses characteristics of muscle fiber types, specifically fatigue to determine distribution
(lab 1)
Alteration of fiber type by training (adaptation)
-fiber percentage and distribution is most likely explained by genetics ; however, exercise training may induce modification
endurance and resistance training
-cannot convert fast fibers to slow fibers
-cna result in shift b/w type IIx fibers
towards more oxidative properties
what happens to type II fibers when the muscle undergoes strength training
increase in size
hypertrophy
Muscle fiber types transitions
In general understanding there seems to be confusion with interpretation of the literature
current research does not strongly support the notion of training induced conversion between Type I and type II muscle fibers
other non-training scenarios may induce muscle fiber type conversion:
-by applying chronic low frequency electrical stimulation auto a type IIx muscle it can be converted to a type I muscle
-by applying phasic high frequency electrical stimulation to a type I muscle it can be converted to a faster muscle (type IIa or type Iix)
-the above are experimental , unnatural situations
-other non-training, but natural induced conversion: space flight, casting, paralysis, bed rest (tends to then behave more like a fast twitch muscle) you lose a lot of type I muscle fibres
fiber type distribution
average person
45-55% ST fibres (arm/leg)
-FT distribution approximately equal across IIa and IIb
-Larger inter-individual variation
elite athletes tend to demonstrate the greatest differences between distribution and link with performance
fiber types and performance
power athletes
such as sprinters
-high percentage of fast twitch/ type II fibres
fibre types and performance
endurance athletes
such as endurance runners
-high percentages of slow twitch/type I fibers
-some as high as 90-95% in gastroc
why do we see this to be truer as level fo completion increases?
-more specific training for that sport
-genetics
why in children do we see a child who excels at both sprinting and cross-county running
there is no specialization, they are doing a lot of sports (exposure to different movements)
-different rates of growth
fibres have not differentiated
distribution of fibre types
Males and females
no statistical difference between males and females; however may see sex difference in fiber area
Muscle fiber alignment overview
long axis of a muscle
fusiform and pennate muscle fiber
long axis of a muscle -determines fiber arrangement
-Fusiform: long fiber, high FL:ML ratio
-hamstring dorsiflexor
-spindle like long and narrow (decrease PCSA)
pennate: short fibers, low FL:ML ratio
-Quad, plantar flexors
-fan like fascicles (increase PCSA)
more muscle cross-sectional area= can generate more force
alignment and force
the more fibers packed into the PCSA the greater the force
what is the difference between anatomical CSA and PCSA ?
-Anatomical CSA parallel
-PCSA is perpendicular to its fibers
physiological cross sectional area is the area of the cross section of a muscle perpendicular to its fibers, generally at its largest point
does a fusiform or pennate muscle have greater PCSA? why?
pennate
because it is stacking of fibers
short fibres create a ____
greater force
the greater the force, the lower the velocity thus long fibres create greater velocity
quadriceps is a ______- muscle
pennate
hamstring is a _________ muscle
fusiform
_______- muscle is fan like
pennate
____________ muscle is spindle like
fusiform
___________ muscle has a higher force
pennate
_______ muscle has a greater ROM
fusiform
fiber arrangement influences
force generating capacity
-fusiform : longer working range, lower max force
Pennate: about 2x force of fusiform
range of motion
fusiform muscle also exhibits increased ROM as compared to pennate muscle
at what stage is the push up or bench press most challenging (starting with the bar in your chest or chest on floor for push-up) ?
start
pectoralis, tricep. Anterior deltoid
start is the hardest because all these muscles are in a lengthened position (weak point for generating force)
force-muscle length relationship
-muscle force varies with the length of the muscle
-this variation in force is due to variation in actin-myosin overlap
graphs for muscle lengths
the nautilus “cam” system
Becuase you can generate different amount of forces for different ROM
-as it roataed it didn’t rotate in a circle, provided les resistance at the start and more in the middle
how do you think the ability to create velocity changes with increased force of contraction ?
decrease
how do you think ability to generate muscular force changes as velocity contraction increases?
what do you think is happening with actin and myosin to cause this force-velocity relationship?
it would decrease as velocity increases
if you move a rapid speed the ability to form cross bridges is impaired
at any absolute force the _____ of the movement is grater in muscles with higher percent of fast twitch fibers
speed
the maximum velocity of shortening is greatest at the lowest force
True for both slow and fast twitch fibers
influence of velocity of contraction (concentric) on muscle fore
force declines
isometric
no change in length
concentric
muscle shortening
eccentric
muscle lengthening
force velocity is dependent on muscle action
isometric
0 velocity
force velocity is dependent on muscle action
concentric
as velocity increases, max force decreases
force velocity is dependent on muscle action
eccentric
as velocity increases, max force increases
endomysium vs. sarcolemma
endomysium is connective tissue that surrounds muscle fibers and occupies space between muscle fibers
sarcolemma is the muscle fiber cell membrane (plasma membrane) surround the fiber
ATPase as a protein
ATP is the energy containing molecule, which is hydrolyzed as an enzyme. ATPase is an enzyme and a protien
ATP is the energy molecule
