Muscle Tissue Flashcards
Like nervous tissue, muscles are excitable or ___
“irritable”
Unlike nerves, however, muscles are also:
Contractible (they can shorten in length)
Extensible (they can extend or stretch)
Elastic (they can return to their original shape)
Skeletal muscle type appearance
striated
multi-nucleated (eccentric)
parallel fibers
cardiac appearance
striated, one central nucleus
Smooth (visceral) muscle appearance
no striations
one nucleus
Myofiber & myofibril are different
cool
Myofiber is a single ____
cell
a bundle of muscle fibers (Muscle cells)
fascicle
An organelle in a muscle fiber composed of filament
myofibril
Fibrous protein molecules within myofibrils (the thick/thin filaments that are contractile proteins)
filaments
surrounds a fiber
Endomysium
surrounds a fascicle
Perimysium
surrounds the entire muscle
epimysium
Epimysium, perimysium, and endomysium all blend together and tie into a tendon ( a broad, flat tendon is a ____)
aponeurosis
A nerve cell called a ____ supplies a group of muscle fibers. This comprises a ____
somatic motor neuron
motor unit
Each muscle fiber is supplied by ___ neuron
only one
the site where the neuron contacts the muscle fiber
Neuromuscular junction
During embryonic development, a number of ___ fuse to form one skeletal muscle fiber
myoblasts
This is why skeletal muscle fibers are multinucleate
Muscle fibers don’t undergo mitosis
Beneath the connective tissue endomysium is found the plasma membrane (called the ___) of an individual skeletal muscle fiber
sarcolemma
The cytoplasm (sarcoplasm) of skeletal muscle fibers is chocked full of contractile proteins arranged in _____
myofibrils
kind of like a cul-de-sac opening from the outside of the fiber toward the interior of the fiber
T-tubule
Openings that invaginate from the sarcolemma, and extend toward the interior of the cell
T-tubule
Important in propagation of muscle action potentials
Open to the outside of the fiber, so they are filled with interstitial fluid
T-tubule
Smooth endoplasmic reticulum of a muscle fiber
Sarcoplasmic reticulum
Stores calcium ions, and releases them when the muscle fiber is stimulated
Sarcoplasmic reticulum
is a calcium-binding protein inside the sarcoplasmic reticulum, thereby enabling the Ca++ concentration in a relaxed muscle to be 10,000 times higher than in the cytosol
Calsequestrin
dilated regions that flank the T-tubules
Terminal cisterns
Two terminal cisterns flanking one T-tubule is called a
triad
The basic functional unit of skeletal muscle fibers is the
sarcomere
An arrangement of thick and thin filaments sandwiched between two Z discs
sarcomere
Myofibrils are made of smaller structures called filaments called
actin (thin)
myosin (thick)
contractile protein
Actin (thin)
Myosin (thick)
regulatory protein
Troponin
tropomyosin
Overall, there are __ thin filaments for every thick filament
two
Sarcomeres are the basic functional units of a myofibril (a long chain of sarcomeres is a _____)
myofibril
Sarcomeres connect at
z-disc
Thick and thin filaments overlap to a varying degree, depending on the ___ state of the muscle
contraction
The thick and thin filaments create the ___ that are seen both in single myofibrils and in whole muscle fibers
striations
The pattern of overlap gives rise to a number of zones and bands
A band I band Z line H zone M line
where adjacent sarcomeres abut; center of an I band
Z discs
darker zone, which comprises the length of the thick filaments and a varying overlap of thin filaments
A band
only thin filaments; consist of parts of 2 adjacent sarcomeres
I band
center of an A band; only thick filaments
H zone
midline of a sarcomere
M line
The thick filament is composed of
myosin molecules
About half point toward one Z disc of a sarcomere; the other half point toward the opposite Z disc
myosin molecules
The ___ of the myosin molecules are bound together to form the thick filament
tails
Bind and hydrolyze ATP; also bind the products of ATP hydrolysis (ADP and phosphate)
Change shape (move toward or away from an M line)
Bind reversibly to actin
myosin heads
Block the myosin binding sites (on actin)
The regulatory proteins troponin and tropomyosin
Movement of the troponin-tropomyosin complex allows __ to begin
contraction
Movement is triggered by ___ binding to troponin
calcium
Titin
Myomesin
Dystrophin
Sarcolemmal proteins
Other structural proteins
each molecule spans half a sarcomere, from a Z disc to an M line, and attaches thick filaments to Z discs and M lines; very elastic and probably helps sarcomere return to its resting length
Titin
links the thin filaments of the sarcomeres to integral membrane proteins in the sarcolemma, transmitting the tensive forces of the sarcomeres
Dystrophin
The muscle action potential travels along the entire ___ and down the T tubules to the interior of the fiber
sarcolemma
A neuromuscular junction (NMJ) is the synapse between a ___ and a skeletal muscle fiber
somatic motor neuron
Synaptic end bulbs at the tips of axon terminals contain synaptic vesicles filled with ___, which carries the impulse across the synaptic cleft
acetylcholine (ACh)
The ___ is the region of the sarcolemma opposite the synaptic end bulb. It comprises the muscle fiber part of the NMJ
motor end plate
Acetylcholine receptors in the sarcolemma bind to ACh. Millions of these transmembrane proteins are in deep grooves in the motor end plate called
junctional folds
Binding of two molecules of ACh opens an ion channel in the ACh receptor allowing ___, most importantly ___, to flow across the membrane
cations, Na+
Inflow of ___ makes the inside of the muscle fiber more positively charged, triggering an action potential
Na+
The bacterium Clostridium botulinum produces a botulinum toxin that blocks ___of synaptic vesicles at the NMJ
exocytosis
- Muscle AP arrives at T-tubules
- Ca channels open in ___. Active transporter continuously pump Ca into sarcoplasmic reticulum. Concentration of Ca in the ____ is very low when muscle relaxed.
- Calcium flows out of the terminal cisterns into the ____.
- Calcium binds with ___
Terminal cistern
cytosol
cytosol
troponin
The troponin-tropomyosin complex moves aside, uncovering myosin-binding sites on the actin molecules after the binding of ___ to troponin, allowing contraction to begin
Ca
With exposure of the myosin binding sites on actin (the thin filaments)—in the presence of Ca2+ and ATP—the ____ “slide” on one another and the sarcomere is shortened
thick and thin filaments
myosin crossbridges detach only when ___ binds to the myosin heads
ATP
The H zone and I band
change in length
decrease
The A band width
change in length
remains the same
Sarcomere length
change in length
decreases
The thick and thin filaments do not change length.
aight
Muscular hypertrophy is an increase in the ___ of muscle fibers.
diameter
Organelles increase in number: myofibrils, mitochondria, sarcoplasmic reticulum, etc.
Achieved by forceful, repetitive muscular activity
Hypertrophied muscles are capable of more forceful contractions because they contain more ___
myofibrils
increase in size of tissues and organs due to an increase in the number of cells
Hyperplasia
decrease in the size of a cell, tissue, organ, or entire body; it is accompanied by diminished function
Atrophy
The dramatic muscle growth that occurs after birth is due to ___
hypertrophy
unable to undergo mitosis
A red-colored protein
Found only in muscle
Similar to hemoglobin in both structure, chemical composition, and function
Binds ___ in muscle cells and releases it when needed by the mitochondria during high levels of aerobic respiration
Myoglobin
oxygen
Uses for ATP in muscle contraction are . . .
Na+-K+ pumps: active transport; maintain concentration gradients across the sarcolemma; necessary for producing action potentials
Calcium ion pumping: active transport; necessary to terminate contraction
Energize the myosin head in preparation for the power strokeATP must be made at the same rate that is it used
ATP must be made at the same rate that is it used because
cells don’t store much
Need __ grams of creatine/day
two
One nerve impulse in a motor neuron causes one action potential in all the muscle fibers of that ____
motor unit
Although action potentials in neurons and muscles are always the same ___ once initiated, the contraction resulting from a single muscle action potential is much smaller than the maximum force the fibers of that motor unit can produce
magnitude
The force that a single fiber can produce is primarily dependent on the ____ at which it is stimulated (which normally is by nerve impulses arriving at the neuromuscular junction)
rate
The number of impulses per unit time (typically, per second) is the ____ of stimulation
frequency
A brief contraction of all the muscle fibers in a motor unit is a ___
twitch, or twitch contraction
The ___ is a device used to measure the force generated by a contracting muscle
myograph
an example of a transducer, which is something that converts one form of energy into another
Myogram is a record of a muscle contraction, initiated by direct electrical stimulation of either a ____ or its muscle fibers
motor neuron
Duration of periods is associated with ___ movement, stretching, and elasticity
(myogram process, slide ~60)
Ca++
the refractory period is the period of time after the ___ stimulus when response to a second stimulus is not possible (applies to both muscles and nerves)
first
The ____ period begins upon stimulation and commonly lasts into the early part of the contraction period, although the duration varies
refractory
Latent period: the muscle action potential sweeps over the sarcolemma, and Ca++ are ___ from the ____
(myogram events)
released
sarcoplasmic reticulum
Contraction period: Ca++ binds to ____ resulting in exposure of myosin binding sites on actin, crossbridges form; peak tension develops in the muscle fiber
troponin
Relaxation period: Ca++ is actively transported back into the sarcoplasmic reticulum, myosin binding sites are covered by tropomyosin, myosin heads detach from actin; tension in the muscle fiber ____
decreases
_____ is the process whereby the number of active motor units is increased according to need
Motor unit recruitment
The more neurons that are activated (in the spinal cord), the more motor units will be stimulated, the more ____ will be produced
muscle tension
the second wave is “added” to the first, called ____
More Ca++ is released from the sarcoplasmic reticulum
wave summation
Not all motor units are recruited ____
simultaneously
Only the number of motor units ____ are recruited
needed
The ____ motor units are recruited first
smallest, weakest
_____ motor units are recruited if required by the task
Larger, stronger
Much of the initial apparent gain in strength that occurs after starting a program of weight lifting or vigorous exercise is due to ____ rather than increased contractile force capability (hypertrophy) of muscle fibers
more efficient motor recruitment
In response to a single AP, CARDIAC muscle contracts 10-15 times ___ than skeletal muscle, and must continue to do so, without rest, for the life of the individual
longer
To meet this constant demand, cardiac muscle generally uses the rich supply of O2 delivered by the extensive coronary circulation to generate ATP through ____
aerobic respiration
To meet this constant demand, cardiac muscle generally uses the rich supply of O2 delivered by the extensive coronary circulation to generate ATP through ____
aerobic respiration
Muscle fibers of cardiac muscle exhibit ____
Interconnectedness of fibers results in synchronous contraction, normal contraction rate is about 75 times per minute, Altered by autonomic nervous system and endocrine system
autorhythmicity
___ larger and more numerous in cardiac than skeletal muscle in accordance with a greater dependency on aerobic respiration to generate ATP
Mitochondria
___ larger and more numerous in cardiac than skeletal muscle in accordance with a greater dependency on aerobic respiration to generate ATP
Mitochondria
Like cardiac muscle, ___ (in your deep organs) is autorhythmic and is not under voluntary control (your heart beats and your stomach digests without you thinking about it).
smooth muscle
Unlike cardiac (and skeletal muscle) however, smooth muscle has a ___ capacity for generating ATP and does so only through anaerobic respiration (glycolysis)
low
In addition to the thick and thin filaments, ___ filaments are present
(smooth muscle)
intermediate
Intermediate filaments attach to dense bodies, which are functionally similar to __ found in striated muscle and found in both the sarcoplasm and the sarcolemma
(smooth muscle)
Z discs
Intermediate filaments attach to dense bodies, which are functionally similar to __ found in striated muscle and found in both the sarcoplasm and the sarcolemma
(smooth muscle)
Z discs
Contraction of the thick and thin filaments generates tension on the ___ filaments, which pulls the dense bodies and causes shortening of the muscle fiber
(smooth muscle)
intermediate
Distinguishing feature between the two types of smooth muscle is primarily the ___ that comprise a motor unit, but there are other factors
number of fibers
___ smooth muscle fibers connect to one another by gap junctions and contract as a single unit
____ lack gap junctions and contract independently
Visceral (single-unit)
Multiunit smooth muscle fibers
___ smooth muscle fibers connect to one another by gap junctions and contract as a single unit
____ lack gap junctions and contract independently
Visceral (single-unit)
Multiunit smooth muscle fibers
Electron microscopy has shown that intense exercise can cause damage, including torn ___, damaged myofibrils, and disrupted Z discs
sarcolemmas
Chemical analysis after exercise has also shown increases in blood levels of ____, both of which are normally confined within muscle
myoglobin and creatine kinase
Apparently delayed onset muscle soreness (DOMS) that follows strenuous exercise by some ___ hours has microscopic muscle damage as a major factor, although not all contributors to DOMS are known
12 to 48
Muscle fatigue is the inability of a muscle to maintain force of contraction after prolonged activity.
It results mainly from changes within muscle fibers including inadequate release of ____, depletion of ____, insufficient oxygen, depletion of glycogen and other nutrients, buildup of ___ and ADP, and failure of action potentials in the motor neuron to release enough acetylcholine
calcium ions
creatine phosphate
lactic acid
Even before actual muscle fatigue, a response called ____ causes feelings of tiredness and desire to cease activity, which may be a protective mechanism to stop the exercise before muscles become damaged. The exact mechanism of central fatigue is not known
central fatigue
Muscle tone is the small amount of ___ or contraction that a muscle exhibits even at rest
It is caused by weak, ____ contractions of motor units
tension
involuntary
Muscle tone is established by neurons in the ___
brain and spinal cord
Muscle tone keeps skeletal muscles firm, but does not cause a force strong enough to produce ____
movement
Muscle tone is necessary and important , for example in maintaining posture, keeping steady pressure on the contents of digestive organs, maintaining blood pressure
neat
When motor neurons to skeletal muscles are severed they become ___, which is a state of limpness in which muscle tone is lost
flaccid
Abnormalities of skeletal muscle function may be due to disease or damage of any of the components of a motor unit:
Somatic motor neuron
Neuromuscular junctions
Muscle fibers
The term neuromuscular disease encompasses problems at all three sites:
Somatic motor neuron
Neuromuscular junctions
Muscle fibers
___ is an autoimmune disease that causes chronic, progressive damage of the neuromuscular junction by producing antibodies that bind to and block acetylcholine receptors
Myasthenia gravis
This decreases the number of functional ACh receptors at the motor end plates of skeletal muscles, causing weakness and fatigue, and may eventually result in loss of muscle function
a sudden involuntary contraction of a single muscle that is part of a large group of muscles
spasm
a painful spasmodic contraction. Cramps may be caused by inadequate blood flow to muscles, overuse of a muscle, dehydration, holding a position for an extended period of time, or low levels of electrolytes
cramp
spasmodic twitching made involuntarily by muscles that are ordinarily under voluntary control
tic
rhythmic, involuntary, purposeless contraction that produces a quivering or shaking movement
tremor
an involuntary, brief twitch of an entire motor unit that is visible under the skin; it occurs irregularly and is not associated with movement of the affected muscle
fasiculation
a spontaneous contraction of a single muscle fiber that is not visible under the skin but can be recorded by electromyography. Fibrillations may signal destruction of motor neurons
fibrillation
a disease or disorder of skeletal muscle tissue
myopathy
forceful stretching or tearing of muscle fibers, this often occurs in contact sports where it frequently affects the quadriceps femoris muscle
muscle strain
pain in or associated with muscles
myalgia
a tumor consisting of muscle tissue
myoma
inflammation of muscle fibers
myositis
slow relaxation, or decreased ability to relax muscles after voluntary contraction, may be accompanied by increased muscular excitability and contractility
myotonia
pathological softening of muscle tissue
Myomalacia
