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64 Cards in this Set

  • Front
  • Back
What are the 3 types of muscle tissue:
skeletal, cardiac, smooth
What are the 3 prefixes describing muscle:
myo, mys, sarco
What is special about skeletal muscle and smooth muscles cells?
They are elongated and are called muscle fibers
What is the name given for the muscle cell membrane?
What is the name given to muscle cell cytoplasm?
Actin and myosin
What are the two myofilaments responsible for muscle contraction?
Actin and myosin
Describe the function, location, structure, and means of activation of skeletal muscle Tissue:
-Tissue is found packed in skeletal muscles attached to the bony skeleton.
-Cells are elongated and are called muscle fibers.
-Function is mobility and manipulation of environment.
-Muscle fibers are striated.
-Muscle is voluntary.
-Muscle contracts rapidly and tires easily.
-Muscle is extremely adaptable. Can exert fractions of ounce to hundreds of pounds in force.
Describe the function, location, structure and means of activation for cardiac muscle tissue:
-muscle is located only in the walls of the heart
-muscle is striated but cells are NOT elongated
-muscle is involuntary
-neural controls respond to changes in bodily needs (short term)
-muscle contracts constantly, rhythmically, controlled by the heart’s pacemaker
What are the functional characteristics of muscle tissue?
-excitability – muscle can receive and respond to stimuli, both internal and external
-extensibility – muscle can be extended and stretched
-elasticity – muscle can recoil and regain it’s original at rest length
-contractility – muscle can forcibly shorten
What makes muscle tissue unique from other tissues of the body?
it’s contractility – ability to forcibly shorten
What are the functions of muscle tissue?
-mobility of body, manipulation of environment

-forces liquids and other substances through the body

-courses (pumps) blood through the veins

-generates heat, posture, helps control blood pressure
Skeletal Muscle has associated connective tissue. Name the 3 types of skeletal muscle tissue, where they are located, and their composition:
endomysium: thin connective tissue sheath wrapping every single muscle fiber, composed of reticular fibers

perimysium: fibrous connective tissue sheath surrounding bundles of muscle fibers called fascicles

epimysium: dense irregular connective tissue fiber that surrounds the entire muscle
Each skeletal muscle is a discrete organ, containing:
-it’s own blood supply (1 artery and 1 or more veins)

-a single nerve

-muscle tissue and connective tissue
Skeletal muscles are attached in how many places?
2 or more, and typically span joints
Skeletal muscle tissue attach one of two ways, what are they?
directly – epimysium to periosteum

indirectly – connective tissue extends beyond the muscle as in tendons or aponeurosis
When muscle contracts the moveable bone, the muscle’s ___________
Moves toward the immovable bone, the muscle’s ___________
1. insertion
2. origin
Describe skeletal muscle fiber:
Elongated, thin in diameter
cells go through mitosis but do not divide, rather, the embryonic cells fuse to form syncytium
contain the usual organelles
contain sarcoplasmic reticulum
contain sugar filled vesicles called glycosomes
contain atypical (special) oxygen binding proteins called myoglobin
contain t tubules
contain myofibrils (contractile elements)
These organelles are unique to skeletal cells.
The term used to describe skeletal muscle fibers whose cells fuse and are multinucleate
The reticulum of skeletal muscle is called what?
sarcoplasmic reticulum
The reticulum of skeletal muscle is smooth T/F
These vesicles are common organelles in skeletal tissue.
These rod-shaped bodies make up most of the muscle cell.
The arrangements of _________ in a skeletal muscle cell are such that there are repeating light I and dark A bands.
Describe the arrangement of myofibrils in a skeletal muscle fiber
myofibrils make up the majority of the skeletal muscle cell’s volume

myofibrils are tightly packed, rod-like contractile elements
These are the smallest contractile units of a skeletal muscle
What is the space between 2 successive z discs called?
a sarcomere
What is the composition of a sarcomere?
This protein is responsible for the dark color found in M lines of a myofibril.
z disc
This elastic filament anchors myosin myofilaments to a z disk
titin, and is shaped like a pigs tail, in a spiral (could be an extra credit question)
M lines are darker due to the presence of what protein
elastic filament that anchors myosin to Z discs
Describe each myosin molecule:
-a myosin molecule is composed of a rod like tail and two globular heads

-the tail is a rod-like and constructed of two heavy interwoven polypeptide chains

-the heads are constructed of two lighter, smaller polypeptide chains called cross bridges

-the heads have binding sites for ATP actin subunits G Actin
Describe the structure of an actin molecule:
-pair of twisted fibrous strands F Actin
-each subunit is G Actin
-the regulatory subunits are Troponin and Tropomyosin
When calcium is released by terminal cisternae what happens?
calcium its binds to troponin and pulls tropomyosin away from the F Actin globular heads
Describe the arrangement of myofilaments within a sarcomere.
they run longitudinally, along the length of a muscle fiber
Describe the SR of a muscle fiber
-runs mostly longitudinally
-is elaborate, smooth
-surrounds each myofibril
-forms perpendicular pairs of terminal cisternae
-terminal cisternae associate with 1 t tubule to form triads
-functions in the regulation of intracellular calcium
What are T tubules and found where?
T tubules are elongated tubes that run perpendicular to the myofibril, penetrating deep within the cell at the junction of light I and Dark A bands
What do t tubules do?
T tubules are associated with paired terminal cisternae, forming a triad.

T tubules have protein voltage sensors that detect action potential and
signal the terminal cisternae to release calcium

T tubules penetrate deep into muscle tissue, conducting impulses that signal release of calcium from terminal cisternae
What is a cross bridge?
a cross bridge is the connection of myosin heads to actin subunits protein G Actin.
What does the name for the action of a myosin head as it pulls actin towards the center of the sarcomere?
it is called a power stroke
What is a contraction?
a contraction is a generation of force

a contraction does not constitute a shortening

a shorten will occur only with the tension from the cross bridges (of myosin/actin) is strong enough to overcome forces opposing shortening
What is the action called when thin filaments are pulled towards the center of the sarcomere?
Describe the sliding mechanism in the sliding filament model
Myosin heads (about ½) attach to actin and then perform a power stroke, pulling actin towards the center of the sarcomere. Meanwhile, just after the power stroke, ATP binds to myosin heads and trigger release from myosin. Meanwhile, the other ½ of the myosin heads are binding to actin. Those myosin heads perform the power stroke (rinse, repeat). This action continues until the thin filament actin is propelled to the center of the sarcomere.
It is important to note that neither actin nor myosin change length in this process. Rather, the thin filament actin is pulled past the thick filament myosin.
This process continues throughout the sarcomeres of the muscle during contraction.
What must happen in order for a muscle to contract? From beginning to end.
an action potential must be sent from a motor neuron of the somatic nervous system down a nerve (bundle of axons)
the action potential enters the terminal end of the axon, stimulating voltage controlled channels to open and allow calcium to enter the terminal end of the axon. The calcium triggers nearby synaptic vesicles containing ACh to fuse to the axonal ending and exocytose ACh into the synaptic cleft (a gel like substance of glycoproteins and collagen fibers).
ACh migrates across the synaptic cleft and binds with chemically controlled gates on an invaginated portion of the sarcolemma called the motor end plate. The gates open and allow the inflow of Sodium and the outflow of potassium.
This chemical exchange causes a localized depolarization of the sarcolemma and the generation of an end plate potential. End plate potential ignites an action potential across the entire sarcolemma.
This potential starts a chain reaction (like the ripples in water when a stone is dropped in) across the entire sarcolemma signaling adjacent sodium channels to open and sodium to enter each local area until it obtains a certain membrane voltage, referred to as threshold. This generates and action potential that is spread to other adjacent sodium channels. The process repeats until it has covered the entire cell.
Action potential moves from the sarcolemma down t tubules, triggering protein voltage sensors. The T tubule signals the adjacent terminal cisternae to release calcium into sarcomere.
And Finally (wow) Calcium binds to troponin, pulls tropomyosin away from F actin strands, allowing myosin heads to bind to actin (forming cross bridges). About ½ of myosin heads become active at a time (by hydrolyzed ATP – now ADP and Pi). Cross bridges form, connected heads perform a power stroke, moving thin filament actin past fixed myosin myofibrils, towards the center of the sarcomere. ADP and Pi combine back to ATP, bind with the myosin heads, heads release. At the same time release begins, the other ½ of myosin heads form cross bridges and the process repeats until such time as calcium is no longer released from terminal cisternae. Then reverse, troponin aligns tropomyosin back across the helical, globular heads of protein G Actin.
By the way, I know that ACh is quickly broken down into Acetic acid and choline. Without further action potential from motor neurons, the ACh receptive ligand gates close, and muscle contraction ceases. The end. And I hope this is right!!!
What happens in cells when there is low calcium concentrations vs. at higher calcium concentrations?
At lower concentrations of intercellular calcium, troponin continues to hold tropomyosin over thin actin fibrous strands, blocking binding sites. No binding takes place, no contraction occurs.

At higher concentrations of intercellular calcium, troponin is pulled away from fibrous protein strands of actin, exposing binding sites. Cross bridges are formed and can now cycle, permitting contraction/
What causes the “cocking” of myosin heads?
ATP hydrolysis to ADP + Pi, puts head into high energy state
Cross bridging is the activation of myosin heads. What is this known as?
It is a contraction. The activation of myosin heads is a contraction.
When myosin heads cross bridge, what is this called?
When does a shortening occur? Is this considered a contraction?
A shortening occurs when the tension of cross bridges overcomes forces opposing contraction

A shortening, is a contraction.
What is a contraction?
Simply, it is the binding of myosin heads to actin which creates tension or force. Maybe it becomes shortening.
This is a contraction where force is generated by no shortening of muscle fiber.
isometric contraction
What type of contraction does not result in a shortening of the muscle fiber?
isometric contraction
This is a type of contraction where shortening takes place?
isotonic contraction
Describe and isometric contraction versus an isotonic contraction.
In an isometric contraction, myosin heads bind with actin but no shortening of muscle occurs.

In an isotonic contraction, myosin heads bind with actin and the muscle shortens.
What is the variation of muscle fibers controlled by a motor unit?
from four to several hundred
What is a muscle twitch?
a muscle twitch is the muscle’s response to a single, brief, threshold stimulus
What are the 3 phases of a muscle twitch?
latency, contraction, and relaxation
This is the phase of muscle twitch where Calcium is reabsorbed.
relaxation period
This is the phase of muscle twitch where, just milliseconds after stimulus, EC coupling begins to take place.
Latency Period
This is the phase of muscle twitch where the cross bridges form and shortening takes place
Healthy muscle contractions are relatively smooth and vary in strength as different demands are placed on them. What helps maintain smooth muscle contractions?
graded muscle responses.
How is a muscle response graded?
either by changing the strength of the muscle stimulation or the frequency of muscle stimulation.
This is the stimulus strength at which the first observable muscle contraction occurs
the threshold stimulus