muscle Flashcards by asw asw

from the largest unit to the smallest unit- list the organization of skeletal muscle

whole muscle

fascicle

muscle fiber (cell)

myofibril

sarcomere

filament

protein

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thin filaments are composed of two intertwined helical chains of what?

actin molecules

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Troponin contains a binding site for _____

calcium ions (Ca2+)

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troponin is comprised of what 3 subunits?

TnC

TnI

TnT

(Remember: Troponin looks like a “TIC” on a tropomyosin strand)

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tropomyosin binds to actin at what sites?

cross-bridge binding sites

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what is meant by “protein isoforms”?

Same protein but slightly different amino acid sequence

eg- myosin heavy and light chians

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a _______ is one functional unit of the contractile apparatus

sarcomere

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what is a sarcomere composed of?

thick filaments, thin filaments and z-lines

does not include any other organelles

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_______ ions play a pivotal role in the activation of skeletal muscle

calcium

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what structure of the muscle cell is responsible for the cytoplasmic uptake and release of calcium ions?

sarcoplasmic reticulum

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t/f: the duration for an AP and for the shortening of a muscle fiber is similar

False- the shortening of a muscle fiber takes place much slower than the action potential

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low cytosolic calcium will lead to a ____ muscle

relaxed

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the energized cross-bridge cannot bind to _____ when Ca2+ is low

actin

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once cyctosolic calcium levels are increased, the _________ are exposed

cross-bridge binding sites

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what is the “sliding filament theory”?

muscle shortens by a relative sliding of thick and thin filaments.

-the filaments do not change length

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when a muscle fiber is shortened, which sections are reduced? which are unchanged?

I band and H zone are reduced in length

A band remains unchanged (length of thick filaments)

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the “cross-bridge theory”

-thick and thin filaments on sarcomeres are not connected at rest

cross-links form between the 2 types of filaments when the Ca2+ levels increase
—-these links are called “cross-bridges”

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how does the cross-bridge theory explain filament sliding?

sliding is due to repetitive cross-bridge cycles

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what is one cycle of cross-bridging?

myosin head attaches to actin
conformational change in myosin
simultaneous sliding of thin filaments relative to thick filaments
detachment of myosin (thick) and actin (thin)

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what is the source of energy for muscle contraction?

ATP

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the concentration of ATP inside muscle cells is buffered by ____________

phosphocreatine (PCr)

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what are the 3 sources of ATP in muscle cells?

Creatine phosphate (1 ATP)
Glycolysis (3 ATP)
Oxidative Phosphorylation (2 ATP)

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what is the basic observation that led to the discovery of the Length-tension relationship?

the amount of tension (force) that a muscle can generate when it is activated depends on its length

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at what percent of muscle length do we see the largest isometric tetanic tension?

100%

anything less than, or greater than, this will cause a decrease in maximum tension

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what does the Load-velocity relationship show?

a muscle can shorten at a higher velocity when moving a lighter load

what are the 2 types of isotonic muscle contractions?

1) constant length isotonic contractions | 2) constant load isotonic contractions

Isometric contractions produced by multiple stimuli can create what types of contraction?

Unfused and fused tetanus

A __________ is the set of muscle fibers innervated by branches of a single motorneuron

single motor unit

T/F: motorneurons innervate one muscle fiber

False- motor neurons can innervate multiple muscle fibers

what is the range of muscle fibers that a single motor neuron can control?

100 fibers (in the fingers) up to 2,000 (in the leg)

Slow muscle fibers, compared to fast fibers, are:

1) smaller in diameter 2) have smaller neuromuscular junctions 3) contain different sarcomere protein isoforms 4) contract more slowly 5) are more fatigue resistant

slow fibers are referred to as ______ fibers

type 1

muscles that are utilized for maintaining posture have a higher proportion of type ___ fibers, where as muscles for rapid tasks involving dexterity use type ___ fibers

posture- type 1 rapid/dexterity movements- type 2

what is the difference between type 1 and type 2 fibers? type 3 fibers?

type 1- slow-oxidative fibers type 2- fast-oxidative fibers type 3- fast-glycolytic fibers

what factors can contribute to skeletal muscle craps?

- dehydration - metabolic- low sodium, magnesium, calcium, glucose, potassium - endocrine- Thyroid, adrenal insufficiency - pregnancy - drugs & toxins

what is the most common form of muscular dystrophy? what population does it effect?

Duchenne muscular dystrophy effects males (x-linked, recessive)

what differentiates a cardiac sarcomere from a skeletal sarcomere?

thin filaments in cardiac sarcomeres are not all the same length

which myosin heavy chain is found in both cardiac and skeletal muscle? which is found only in cardiac muscle?

Beta chain- both cardiac and skeletal | Alpha chain- not normally found in skeletal muscle found in the masseter muscle

_____ is not present in cardiac sarcomeres, which is one striking difference between cardiac and skeletal muscle

Nebulin

while skeletal muscles attach to tendons, cardiac muscle cells are attached how?

end-on-end to each other

what is the physical connection between cardiac muscle cells?

the intercalated disk

________ are found in intercalated disks, which allow the rapid and direct transmission of action potentials between adjacent cells

gap junctions

T/F: gap junctions use neurotransmitters to allow the rapid transmission of AP's between cardiac muscle cells

FALSE- they are "electrical synapses" and do not involve chemical transmitters

what is different about the AP between cardiac and skeletal muscle cells?

the cardiac AP has a "plateau" phase, which increases the refractory period between firing

T/F: the speed of tension development in cardiac and skeletal muscle is roughly the same

FALSE- cardiac muscle cells produce tension much slower than skeletal muscle

what is the purpose of the long refractory period in the Cardiac muscle AP?

it prevents the heart from undergoing a tetanic contraction, which could prevent the heart from functioning

what ion influx is responsible for the "plateau" phase of the cardiac AP?

Calcium -the calcium influx keeps the membrane potential higher, thus leading to the plateau, and the extended AP time

how is Ca2+ removed from a cardiac cell after an action potential has been reached?

Ca-ATPase pump Na/Ca exchanger- moves Na into the cell and Ca out

which mechanism of Ca2+ removal is shared between skeletal and cardiac muscle?

the Calcium-ATPase pump (Ca-ATPase)

T/F: smooth muscle cells are very small, and there is relatively little sarcoplasmic reticulum

True

smooth muscle cells have "_________" which are homologous to the Z lines of sarcomeres in striated muscle

dense bodies

all nerual innervation to smooth muscle is from the ______________, meaning it is normally involuntary

autonomic nervous system

T/F: smooth muscle has a lesser range of cell lengths over which force can be generated (when compared to striated muscle

False- it has a greater range

why is there virtually no fatigue in smooth muscle?

its rate of ATP splitting by myosin is 10-100 times lower than skeletal muscle

what is the role of MLCK? (myosin light chain kinase)

binds to Ca-calmodulin and causes the contraction of myosin phosphorylates myosin in order to contract

_________, that dephosphorylates smooth muscle myosin, is continuously active.

Phosphatase

what does dephosphorylation of myosin prevent?

prevents reattachment of myosin to actin

what are the sources of Calcium ions for the activation of smooth muscle?

1) sarcoplasmic reticulum 2) extracellular fluid Note: the inward positive charge flow during smooth muscle Action Potential is carried by CALCIUM ions (not sodium)

T/F: neurotransmitters are the only mechanism for smooth muscle control

False - pacemaker potential - neurotransmitters - hormones - local factors (pH, oxygen level, nitric oxide, stretch)

how is calcium removed from smooth muscle cells? (hint: 3 mechanisms)

1) Calcium pump in the sarcolemma 2) Na/Ca exchanger 3) Sarcoplasmic reticulum

what are the 2 types of smooth muscle?

- Single-unit | - Multi-unit

which type of smooth muscle is activated by stretch?

single-unit

how wide is the neuromuscular cleft?

400 angstroms | twice the diameter of a synaptic vesicle

what is the aptitude of a motor endplate potential?

Amplitude: 10 mV (remember: AP 130 mV)

what is Nebulin? what is it used for by scientists?

Nebulin = thin filament protein – possibly a molecular ruler, to determine thin filament length.

Ca2+ ions are sequestered (taken up) by the _____________ of the Sarcoplasmic Reticulum to cause relaxation.

fenestrated collar (central portion)

what is a motor unit?

a single motoneuron and all of the of the muscle fibers it innervates

Fast and slow fibers differ with respect to what?

to the relative contribution of the three pathways for ATP production.

which type of muscle fiber, type 2a or 2b, is smaller?

what enzyme is constantly active in smooth muscle, and prevents contraction?

phosphatase

Activation of smooth muscle results when the ______ activity is greater than the _______ activity.

the MLCK activity is greater than the phosphatase activity.

actin in smooth muscle can be dephosphorylated and remain attached in a _____ state with no movement of the cross-bridges. what does this cause?

"rigor" leads to a maintenance of force with very little ATP consumption, very high economy

General characteristics of single-unit smooth muscle:

Electrical synapses (gap junctions) Spontaneously active Stretch-activated Innervation is primarily restricted to pacemaker cells (smooth muscle in intestinal tract, uterus, small diameter blood vessels.)

general characteristics of multi-unit smooth muscle:

Each cell activated independently Not spontaneously activated Gap junctions are rare (smooth muscle in large arteries, large airways.)

Ca2+ ions are released from __________ of the SR to initiate contraction.

lateral sacs (terminal cisterna)