Skeletal Muscle Flashcards
Cyclically binds with myosin cross-bridges during contraction
Actin
Possess ATPase activity
Myosin
Supplies energy to the myosin cross-bridge, moving it into “cocked” position
ATP
Transmits action potentials to the interior of the muscle fiber
T-tubule
Stores Ca2+ w/in the muscle fiber
Sarcoplasmic reticulum (SR)
Binds troponin, causing the tropomyosin to shift out of its blocking position
Ca2+
Prevents the myosin heads from binding to actin when the muscle fiber is at rest
Tropomyosin
Required for detachment of the myosin heads from the actin filament
ATP
___ are the contraction specialists of the body
Muscles
What are the 3 types of muscle
Skeletal
Smooth
Cardiac
What does contraction of muscle allow?
Purposeful movement of the body in relation to the environment
Manipulation of external objects
Propulsion of contents through hollow organs
Empty the contents of organs to the environment
What is an example of muscles creating purposeful movement of the body in relation to the environment?
Skeletal muscle moves bone
What is an example of muscles propelling contents through hollow organs?
Blood moving through blood vessels
What is an example of muscles emptying an organ’s contents to the environment?
GI tract moving food through and then out
___ comprises the largest group of tissues in the body
Muscle
Muscle is approximately __ of body weight
1/2
Skeletal muscle makes of what percent of body weight in men? women?
40% in men
32% in women
There are approximately __ muscles in the adult human
660
Smooth and cardiac muscle make up __% of body weight
10%
Which muscle(s) are striated (orderl)?
Skeletal
Cardiac
Which muscle(s) are unstriated?
Smooth
Which muscle(s) are voluntary?
Skeletal
Which muscle(s) are involuntary?
Cardiac
Smooth
Voluntary muscle(s) are apart of the __ nervous system
Somatic
Involuntary muslcle(s) are apart of the __ nervous system
Autonomic
__ carry out the orders
Effector organs
The whole muscle is…
an organ
Define: Muscle fiber
a muscle cell
relatively large
multinucleated
Why are muscle fibers multinucleated?
to maintain high protein production of such a large cell
Define: Myofibril
intracellular strucure
80% of muscle fiber
a single filament in the muscle fiber
Define: Sarcomere
Z line to Z line
Functional unit of the muscle
Myofilaments are…
thick and thin filaments
What are the contractile proteins in a muscle?
actin and myosin
Tendons are made from…
connective tissue that extends past the muscle fiber
Define: Thick Filaments
several hundred myosin (heads and tails)
Myosin is made up of…
two identical subunits with heads and tails
The myosin ATPase site on a myosin head…
Binds and hydrolyzies ATP
The actin binding site on a myosin head…
binds actin
What forms the crossbridge?
myosin heads
What does the hinge connecting myosin heads to tails do?
it allows the head to pivot for contraction and relaxation
Define: Thin Filaments
Mostly actin (helix)
Define: G - Actin
Loose actin molecules
Define: F - Actin
Polymerized actin chain
Actin molecules have a binding site for…
attachment with myosin cross bridge head
Do actin and myosin actually contract?
No, the slide by each other
What are the regulatory proteins in thin filaments?
Tropomyosin
Troponin
What is the function of tropomyosin in thin filaments?
It covers the binding site and prevents actin and myosin from binding
prevents contraction
What is the function of troponin in thin filaments?
sits on tropomyosin
Sarcomere: A Band
thick and thin filaments that overlap
size doesn’t change
Where are thick filaments found?
only in the A band of the sarcomere
Sarcomere: Light Band
I Band
Sarcomere: Dark Band
A Band
Sarcomere: I Band
Remaining portion of thin filaments that are not included in A band
only thin filaments
shortens
Which portions of the sarcomere shorten during contraction?
I Band
H Zone
Which portions of the sarcomere remain the same length during contraction?
A Band
Sarcomere: Z Line
middle of I Band
stabilizes thin filament
entire sarcomere
Sarcomere: H Zone
Lighter area in middle of A Band
Thin filaments do not reach
only thick filaments
shortens
Sarcomere: M Line
mid point of sarcomere
stabilizes tick filament
What part of the sarcomere stabilizes thin filaments?
Z Line
What part of the sarcomere stabilizes thick filaments?
M Line
Muscle Sarcomere Mnemonic:
DArk band is A band
LIght band is I Band
Muscle Sarcomere Band order Mnemonic
From Z line working inward
Zee Intelligent Animal Has Muscle
Z Line I Band A Band H Zone M Line
In muscles, excitation leads to…
contraction
What occurs in the muscle during relaxation?
Ca2+ is absent in sarcoplasm
SERCA actively pumps Ca2+ into SR
Troponin and Tropomyosin cover Actin’s Binding Site
Are actin and myosin filaments able to attach during the resting state?
No
What occurs in the muscle cell during excitation?
Influx of Ca2+ into motor neuron
Define: Sarcoplasmic Reticulum (SR)
modified ER
consists of interconnecting tubules surrounding each myofibril like a mesh sleeve
Bring action potentials from surface to center of cell
Define: T-Tubule
invagination of plasma membrane that runs perpendicular to the surface and bring action potentials into the muscle fiber
What occurs when an Action Potential goes down a T-Tubule?
Dihydropyridine Receptors (DHPR) are activated
Normally, DPHR is…
a voltage-gated Ca2+ channel
In skeletal muscle, DHPR function as…
a voltage sensor
What occurs in the muscle cell after DHPR is activated by an Action Potential?
It triggers the Ryanodine Receptor (RyR) to release intracellular Ca2+
How does the RyR release Ca2+?
DHPR activates and causes RyR to shift and open, opening the SR and allowing Ca2+ to move into the sarcoplasm
Does the DHPR or RyR occur first?
DHPR
Steric Block Model: Muscle Relaxation
tropomyosin blocks myosin bindng site on actin
Steric Block Model: Muscle Contraction
Ca2+ binds to troponin subunit C
Binding of Ca2+ causes troponin to change shape
Troponin-tropomyosin complex is pulled aside
Actin’s myosin binding site is uncovered
Myosin binds to actin
What are the 3 subunits of troponin? What do they do?
T - sits on top of tropomyosin
C - binds calcium
I - Inhibits
How does Ca2+ allow the troponin-tropomyosin complex to be physcially pulled aside?
Ca2+ changes the C subunit’s affinity for T and I subunits
results in the filament rolling anf allowing myosin to bind
Before the Myosin Crossbridge links to the actin chain and during relaxation…
ATP is hydrolyzes by myosin ATPase
ADP and P remain attached to myosin
Energy is stored in myosin crossbridge (ready to be fired)
Crossbridge Cycling
ATP is hydrolyzed by myosin ATPase
ADP and P attach to myosin (storing energy)
Ca2+ removes inhibitory influence
Energized myosin crossbridge binds to actin
Contact between actin and myosin causses a power stroke (pulls trigger)
ADP and P are released from crossbridge
Fresh ATP binds and breaks actin-myosin linkage (affinity for actin decreases)
ATP hydrolyzed -> conformational change of head
What occurs if no fresh ATP is available after myosin and actin bind?
The remain contracted
Rigor Mortis
Contracted by no Fresh ATP to break it
3-12 hours after death
How does the muscle return to resting state?
Neural excitation stops
AChase breaks down released ACh
Membrane no longer depolarizes
Muscle excitatin stops
DHPR channels close
Diffusion of Ca2+ out of SR stops
SERCA pumps Ca2+ out (no more Ca2+ is released)
Actin’s binding sites are covered
actin slides back into relaxed position away from center of sarcomere
Black Widow Spider Venom
Alters Release of ACh
toxin can form pores in presynaptic membrane
explosive release of ACh
results in respiratory failure
How does Black Widow Spider Venom cause respiratory failure?
Diaphragm can’t relax due to explosive release of ACh
Clostridium Botulinum Toxin
Blocks release of ACh
interferes with share proteins
can result in respiratory failure
used as medicine
What is Botox used to treat?
Chronic back pain due to muscle spasms
migraines
Curare
Reverisbly binds to ACh receptor, blocking it from activating
antagonist
causes paralyzation and respiratory failure
What are derivatives of curare used for?
to relax skeletal muscles during surgery
Myasthenia Gravis
antibodies inactivate ACh receptor, blocking it
What does the drug neostigmine do?
Short-term anti AChase
prevents ACh from breaking down
type of Myasthenia Gravis
Organophosphates
Irreversibly inhibits AChase, preventing inactivation of ACh
results in respiratory failure
Why do organophoshates resut in respiratory failure?
Diaphragm is unable to repolarize
Which agents/diseases alter the release of ACh?
Black Widow Spider Venom
Clostridium Botulinum Toxin
Which agents/diseases block ACh receptors?
Curare
Myasthenia
Which agents/diseases prevent inactivation of ACh?
Organophosphates (certain pesticides and nerve gases)
Which agents/diseases result in respiratory failure?
Black Widow Spider Venom
Clostridium Botulinum Toxin
Curare
Organophosphates
How are synapses and neuromuscular junctins (NMJ) similar?
2 excitable cells seperated by a narrow cleft that prevents direct transmissionof electrical activity
Axon terminals store NT that are released by Ca2+-induced exocytsis of storae vesicles
Binding of NT with receptor opens membrane channels, permitting ionic movements that change membrane potential
Define: Graded Potential
Resultant change in membrane potential causes by ionic movements through open membrane channels
What prevents direct transmission of electrical activity in synapses and NMJs?
2 excitable cells separated by a narrow cleft
What do axon terminals in synapses and NMJs store?
NTs that are released by Ca2+-induced exocytosis of storage vesicles
What happens in synapses and NMJs when the NT binds with the receptor?
membrane channels open and allow ionic movements that change membrane potential
Define: Synapse
A junction between 2 neurons
Excitatory (EPSP) or inhibitory (IPSP)
Define: Neuromuscular Junction (NMJ)
Exists between a motor neuron and a skeletal muscle fiber
always excitatory (EPP)
What are the 3 energy systems of skeletal muscle?
Oxidative
Nonoxidative
Immediate
Immediate energy system of skeletal muscle
Readily/immeiately available to support muscle contraction
ATPase, CK, or Myokinase
Immediate energy system: ATPase
ATP + H2O -> ADP + Pi
Immediate energy system: CK
CP + ADP -> ATP + Cr
Immediate energy system: Myokinase
ADP + ADP -> ATP + AMP (recycler)
What is the immediate energy system generally used for?
Burst/Power activities
CK in the blood can indicate…
muscle damage
Why is CP good for immediate energy?
CP is 5-6x ATP in resting muscle
Nonoxidative energy system of skeletal muscle
breaks down glucose and glycogen without oxygen for energy utilizing Glycogenolysis and Glycolysis
rapid
oxygen is present but not involved
less efficient (more fuel/ATP needed)
Lactic acid builds up, decreasing performance and muscle pH
How long does Nonoxidative energy last?
30s - 1 min
How long does immediate energy last?
0-30s
How do immediate and non oxidative energy sources compare to oxidative?
Immediate and nonoxidative energy sources combined provide only a fraction of the energy that oxidative metablism can
Oxidative energy system of skeletal muscle
uses carbohydrates, fats, and certain amino acids for energy
slow
requires O2
highly efficient
How long does it take the oxidative energy system to start?
1 min - 1 min 30s
How many ATP are formed from Glycolysis?
Glucose -> 2 ATP
How many ATP are formed from Oxidation of glucose?
Glucose -> 36 ATP
How many ATP are formed from Oxidation of palmitate?
palmitate -> 129 ATP
Which energy source is best for power?
immediate
Which energy source is best for speed?
nonoxidative
Which energy source is best for endurance?
oxidative
Why is oxidative energy best for endurance?
it uses fuel from all over and lasts longer
The speed of contraction is determined by…
the isoform of myosin ATPase
Skeletal muscle fiber types are based on…
speed of contraction (myosin ATPase activity)
type of metabolic pathway -> ATP
What are the 3 muscle fiber classifications?
Type 1 (slow twitch)
Type IIa (Fast Twitch a)
Type IIx (Fast Twitch x)
Slow Twitch fibers
Type 1
Oxidative metabolism
used for walking and posture
fatigue resistant
Fast Twitch a fiber
Type IIa
moderatly high ox capacity
high glycolytic capacity
not as common as Type I and Type IIx
Fast Twitch x fiber
used for power
low oxidative capacity
highest glycolytic capacity
Which fiber type makes up approximately 50% of fibers in the average muscle?
Type 1/Slow Twitch
Which muscle is type 1 in everyone?
Soleus muscle
Which fiber type makes up approximtely 25% of fibers in the average muscle?
Fast Twitch
Type IIa
Type IIx
Which of the following is true about muscle fiber types?
A. the amount of fiber type varies from person to person
B. genetics can indicate fiber types
C. fiber types cannot be changed
D. all of the above
All of the above
Define: Motor Unit
1 motor neuron + all the muscle fibers it innervates
What occurs when a motor neuron is activated?
all of the fibers it supplies are stimulated to contract simultaneously
What happens to motor units when stronger contractions occur?
more motor units are recruited
How does motor unity recruitment alter force production?
different motor unit types will produce different forces
What motor units are used to produce less force?
smaller motor units
Type I
What motor units are used to produce more force
Large motor units
Type II
Muscle with small motor units produce….
Precise, delicate movement
What is an example of a muscle with smaller motor units?
Hand Muscles
a single motor unit can contain a dozen muscle fibers
Muscles with larger motor units produce…
Powerful, coarse movements
What is an example of a muscle with larger motor units?
Legs
A single motor unit contains 1,500 - 2,000 muscle fibers
How does the CNS increase muscle force?
By activating additional motor units in the order of their increasing size, beginning with the smallest
What is the recruitment order of muscle fibers?
Type I, TypeIIa, Type IIx
What occurs first, neural adaptations or changes in muscle size?
neural adapatations
Early gains in strength are due to…
neural factors - which optimize recruitment patterns
Later gains in strength are due to…
increasing cross-sectional area (hypertrophy is important)
What does the force exterted by a single muscle depend on?
what you pick up
less force is required to pick of a piece of paper
more force is required to pick up a 50lb. weight
What factors determine variation of muscle force?
The number of muscle fibers contracting w/in a muscle
The tension developed by each contracting fiber
The number of muscle fibers contracting w/in a muscle is determined by…
Number of motor units recruited
Size of the motor units
The tension developed by each contracting fiber is determined by…
The frequency of stimulation
The length-tension relationshiip
How does the frequency of stimulation effect the tension developed by a contracting fiber?
Reptitive stimulation -> contractions of longer duration and greater tension
Single twitch stimulation
Fiber completely relaxes before next AP
Twitch summation stimulation
Fiber stimulated a 2nd time before it has relaxed -> greater tension
possible because AP = 1-2 ms
Tetanus stimulation
Fiber stimulated so rapidly there is no relaxation
What is the length-tension relationship of a muscle?
The relationship between inital length and tension can be explained by the number of crossbridges that can be formed during the contraction
How do muscle length and tension affect each other?
The length of a muscle before contraction affects the amount of tension the muscle can generate
Length-Tension Relationship: Smallest sarcomere length and Lowest Force
Decreased number of actin sites exposed to crossbridges
Thick filaments forced vs.Z lines
Length-Tension Relationship: Maximal Force
Optimal amount of overlap between thick and thin filaments
Length-Tension Relationship: Force begining to decrease
Actin sites and crossbridges no longer match up
Length-Tension Relationship: Longest Sarcomere length but Lowest Force
Muscle stretched to 70% longer than I0
No crossbridge activity
no contraction
What determines the extent of fatigue of a fiber?
Duration of activity
Amount of asynchronous recruitment of motor units
Type of fiber (fatigue-resistant oxidative vs. fatigue-prone glycolytic)
What determines the thickness of a fiber?
Type of Fiber
Pattern of neural activity
Amount of testosterone
How does fiber type affect fiber thickness?
Type I/oxidative have a smaller diameter than large diameter glycolytic fibers
How does pattern of neural activity affect muscle thickness?
Hypertrophy (w/ stimulation) vs. atrophy (no stimulation)
What are the types of muscle contraction?
Isometric
Isotonic
Define: Isometric (static) contraction
Muscle produces force but does not change length
Joint angle does not change
Myosin cross-bridges for and recycle, no sliding
Define: Isotonic (dynamic) contraction
Muscle produces force and changes length
Joint movement produced
What does it mean if a muscle has static contraction?
It’s length stays the same throughout contraction
What does it mean if a muscle has dynamic contraction?
The muscle length changes but its tension stays the same
What are the two subtypes of Isotonic Contraction?
Concentric Contraction
Eccentric Contraction
Define: Concentric Contraction
Muscle shortens while producing force
most familiar type of contraction
sarcomere shorten, filaments slide toward center
Define: Eccentric Contraction
Muscle lenthens while producing force
Cross-bridges form but sarcomere lengthens
What is an example of eccentric contraction?
lowering a heavy weight
