Skeletal Muscle - Questions - High Yield Flashcards
Muscle cells are specialized for…
contraction
What are the 3 types of muscle?
skeletal
cardiac
smooth
Why is skeletal muscle striated?
due to the orderly arrangement of filaments
What type of control does skeletal muscle have?
voluntary
Which system is skeletal muscle innervated by?
somatic nervous system
Skeletal muscle contracts ___ and fatigues ___
quickly
quickly
Skeletal muscle has ___, depending on…
myosin ATPase activity
fast or slow fiber type
Is smooth unstriated or striated?
unstriated
What type of control does smooth muscle have?
involuntary
Which system is smooth muscle innervated by?
autonomic nervous system
Where is smooth muscle found?
walls of tubular organs (intestines, blood vessels)
What is the major concern of smooth muscle?
movement of materials through tubular organs
Smooth muscle contracts ___ and fatigues ___.
Slowly
Slowly
Smooth musle has ___ myosin ATPase activity
very slow
Is cardiac muscle striated or unstriated?
striated
What kind of control does cardiac muscle have?
involuntary
Which system innervates cardiac muscle?
the autonomic nervous system
What does it mean that cardiac muscle is myogenic?
it contracts spontaenously
Cardiac muscle has ___ myosin ATPase activity and is highly ___ resistant
slow
fatigue
What is the composition of skeletal muscles?
long, cylindrical, multinucleated muscle cells (muscle fibers) bundled in connective tissue
Define: Muscle Fibers
long, cylindrical, multinucleated muscle cells
Muscle fibers are packed with…
myofibrils
Within each myofibril is…
a sarcomere
Define: Saromere
an ordered arrangement of thick and thin filaments
Thick filaments are composed mostly of…
myosin
Thin filaments are composed of
actin
tropomyosin
troponin
What are cross-bridges composed of?
myosin heads
How do cross bridges cause contraction?
cross-bridges project from thick filaments and bind with actin to bring about contraction
Define: Neurogenic
only contracts when externally stimulated by a nerve
Is skeletal muscle neurogenic or myogenic?
neurogenic
How does a skeletal muscle contract?
Excitation by its motor neuron brings about contractin through a series of events that results in the thin filaments sliding closer together between the thick filaments
Where is ACh released in skeletal muscles?
from the terminal of the motor neuron
What effect does ACh have on skeletal muscles?
it initiates an action potential in the muscle cell that is propagated over the entire surface of the sarcolemma
How does electrical activity travel deep into skeletal muscle?
by T tubules
What happens when the t tubule depolarizes?
movement of the voltage sensor in the dihydropyridine receptors
What is the voltage sensor in the dihydropyridine receptors mechanically linked to?
the opening of the ryanodine receptor Ca2+ release channels in the SR
What effect does Ca2+ have on skeletal muscls when it is released from the SR?
it binds to troponin, pulling the troponin-tropomyosin complex aside, and uncovers actin’s cross-bridge binding sites
What occurs in the muscle when actin binding sites are opened?
exposed actin sites bind with myosin cross bridges
How are the myosin cross-bridges energized before binding with actin?
by the hydrolysis of ATP into ADP+ Pi by the myosin ATPase ite on the cross bridges
Binding of actin and myosin at a cross bridge causes…
the crossbridge head to roate 45 degrees as Pi is released
What happens when the crossbridge head rotates?
it produces a power stroke that pulls the thin filament inward
How does the myosin crossbridge detach from the actin binding sites?
dissociation of ADP and binding of ATP after the power stroke
How does the cycle continue after the cross-bridge detaches?
splitting of fresh ATP molecule by myosin energies the crossbridge again
What occurs in the muscle if Ca2+ is still present after the contraction cycle is finished?
the toponin-tropomyosin complex remains pulled aside and the crossbridges go through another cycle of binding and bending, pulling the thin filament even further
How does contraction end?
When excitation stops and Ca2+ has been actively returned to its storage site, the troponin-tropomyosin complex slips back into its blocking position, actin and myosin no longe bind at the cross-bbridges, and the thin filaments slide back to their resting position as relaxation takes place
How is Ca2+ returned to its storage site?
via SERCA
Define: steric inhibition
troponin-tropomyosin complex slips back into its blocking position
Define: Motor unit
a single α motor neuron and all of the skeletal muscles it innervates
How does skeletal muscle generate force during contraction?
by shortening, lengthening or allowing the length to remain unchanged
Define: Isotonic Contraction
the muscle shortens or lengthens while generating a constant amount of force
Define: Isometric Contraction
the muscle generates force at a constant length
T or F: most contractions are part isometric and part isotonic
TRUE
Define: Sliding filament mechanism
the relationship between the length of the muscle and the tension it can develop
Define: Optimal Length
active force generated is maximal
Where is the optimal length in muscle?
where overlap between thick and thin filaments is maximal
When does active tension decline?
at lengths both shorter and longer than optimal length
Why does active tension decline?
because fewer crossbridges form
How does the muscle obtain the ATP needed for contraction?
- immediate in the form of high energy phosphates from stored creatine phosphate
- non-oxidative pathways such as glycogenolysis and glycolysis which synthesize ATP w/o O2 and uses glycogen stores and generates lactic acid
- oxidative phosphorylation, which efficiently extracts large amounts of ATP from nutrient molecules but requires suffiecent O2
Define: Immediate ATP pathway for contraction
high energy phosphates from stored creatine phosphate
Define: Non-oxidative pathways muscles obtain ATP for contraction
synthesize ATP w/o O2 and uses glycogen stores and generates lactic acid
ex: glycogenolysis and glycolysis
Define: Oxidative phosphorylation pathway muscles use to obtain ATP for contraction
efficiently extracts large amounts of ATP from nutrient molecules but requires suffiecent O2
What are the 3 major skeletal muscle fiber types?
1 slow twitch and 2 fast twitch
What is the difference between the 2 fast twitch muscle fibers?
they rely on different metabolic pathways for ATP synthesis
Gradation of whole muscle contractioncan be accomplished by…
- varying the. number of muscle fibers contracting within the muscle
- varying the tension developed by each contracting fiber
The number of muscle fibers contracting depends on….
- the size of the muscle (number of muscle fibers present)
- the extent of motor unit recruitment (how many motor neurons supplying the muscles are active)
- the size of each motor unit (how many muscle fibers are activated simultaneously by a single motor neuron)
How is the size of a motor unit defined?
how many muscle fibers are activated simultaneously by a single motor neuron
How is the ectent of motor unit recruiment determined?
by how many motor neurons suppllying the muscles are active
How is the size of the muscle determined?
by the number of muscle fibers present
The greater tthe tension developed by each contracting fiber….
the stronger the contraction of the whole muscle
What are the two readibly variable factors relating to contraction tension?
- the frequency of stimulation
- the length of the fiber before onset of contraction
What does the frequency of stimulation of a muscle contraction determine?
the extent of twitch summation
Which of the following is the light band of the sarcomere?
A. A Band
B. H Zone
C. I Band
D. Z Line
I Band
Which of the following remains the same width during contraction?
A. A Band
B. H Zone
C. I Band
A Band
Which of the following describes a sarcomere?
A. 1 whole A Band and 1/2 of each I Band located on either side
B. 1 Z line to the next Z Line
C. The functional unit of skeletal muscle
D. All of the above
All of the above
What is responsible for removing the steric inhibition for the act of contraction?
Ca2+
What is responsible for detachment?
ATP
All of the following result in muscle relaxation except:
A. reuptake of Ca2+ by the SR
B. No more ATP
C. no more AP
D. Removal of ACh at the end plate by AChase
E. Filaments sliding back to their restign position
B. No more ATP
What is the purpose of immediate and nonoxidative pathways?
power -? ATP/min
Immediate and nonoxidative energy sources activate ___ and produce energy at a ___ rate
Rapidly
high
Oxidative energy sources activate __ and produce energy at a __ rate.
Slowly
Low
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
