2 - Sept.27&30 - muscles pg. 279-298 & 299-316 Flashcards
myo- or mys-
muscle
sarco-
flesh
muscle fibers
to describe skeletal and smooth muscle cells because they are elongated
skeletal muscles are
the longest muscle cell, striated and voluntary - can be activated by reflexes
what are skeletal muscles responsible for
overall body movement
cardiac muscle constitutes to the —— of the heart walls
bulk
cardiac muscle cells are
striated, not voluntary
where is smooth muscle found
walls of hollow visceral organs like stomach, urinary bladder and respiratory passages
role of smooth muscle
to force fluids and other substances through internal body channels
smooth muscle is
visceral, non-striated and not voluntary - contractions are slow an sustained
special characteristics of muscle
excitability (responsiveness), contractibility, extensibility, elasticity
muscle function
producing movement, maintaining posture & body position, stabilizing joints, generating heat
what are striations
repeating bands of the proteins actin and myosin that are present along the length of myofibrils
what is the skeletal muscle made up of
mainly fibres but also blood vessels, nerve fibres and connective tissue
every skeletal muscle fibres is supplied with what and why
never ending, it controls its activity
what Is the general rule for all muscles in terms of blood supply
one nerve, one artery, one or more vein for each muscle
muscle cells also give away a lot of
metabolic waste
what are the connective sheaths that wrap each individual muscle fibre to keep it intact
epimysium, perimysium & fascicles, endomysium
epimysium
the overcoat on dense irregular cognitive tissue that surrounds the whole muscle - sometimes blends with deep fascia
perimysium and fascicles
each skeletal muscle is grouped into fascicles & surrounding each is a fibrous connective tissue
endomysium
wispy sheath of connective tissue that surrounds each individual muscle fibre and consists of fine areolar connective tissue
muscle attachment can be either
direct or indirect
direct muscle attachment
the epimysium of muscle is fused to the periosteum of a bone or perichondrium of cartilage
indirect muscle attachment
the muscle’s connective tissue wrappings extend beyond the muscle either as a roselike tendon or sheetlike aponeurosis
what is the purpose for the tendon or aponeurosis in indirect muscle attachment
anchors the muscle to the connective tissue covering of a skeletal element (bone or cartilage) or to the fascia of other muscles
what attachments are more common? why?
indirect, because they provide durability and are a small size
what are tendons made up of
tough connective tissue
tendons are more ideal than fleshy muscle because
it’s less fragile, easier to move over a bone and saves space
what does a skeletal muscle look like
long-cylindrical with multiple nuclei located beneath its sarcolemma (plasma membrane)
how is each skeletal muscle made (per fibre)
through the fusion of hundreds of embryonic cells
sarcoplasm
cytoplasm of the muscle cell
what occupies most of the muscle cell volume?
myofibril
A sarcomere is a segment of ?
myofibril
what are the two types of contractile myofilaments
thick & thin
what do thick filaments contain
bundled myosin molecules
what do thin filaments contain
actin molecules plus other proteins
what do elastic filaments provide?
elastic recoil when tension is released and helps maintain organization of myofilaments
how is muscle shortening occur?
the thin filament slides past the thick filaments
what are the connective tissue sheaths of skeletal muscle?
epimysium, perimysium and endomysium
when muscle fibers contract and pull on the sheaths, wha does this cause/create?
a pulling force to the bone to be moved
sarcolemma is the
plasma membrane
the sarcoplasm contains a huge amount of
glycosomes and myoglobin
glycosomes
granules of stored glycogen that provide glucose during muscle cell activity for ATP
Myoglobin
red pigment that stores oxygen
what are the 3 specialized structures in a muscle cell?
myofibrils, sarcoplasmic reticulum and T-tubules
a single muscle fibers contains hundreds to thousands of
myofibrils
myofibrils run —- to the muscle fibre length
parallel
myofibrils are made up of a chain of
sarcomeres linked end to end
sarcomeres contain even smaller rodlike structures called
myofilaments
striations are
repeating series of dark and light bands
where are striations located
along the length of each myofibril
for an undamaged muscle, which bands are light and dark
dark - A bands
light - I bands
each dark A band has a lighter region called ———– located in the ——-
H zone, midsection
Each H zone is ——- vertically by a dark line called ——-
bisected, M line
how is the M line formed
molecules of protein myomesin
each light I band has a midline interruption that is a —— area, called the ——?
Darker, Z disc/line
the region of a myofibril between two successive z discs is called a
sarcomere
a sarcomere is the
smallest contractile unit of a muscle fibre - aka the functional unit of a skeletal muscle
a sarcomere contains an ——- band flanked by half an —— band at each end
A, I
With each myofibril, the sarcomeres
align end to end like boxcars in a train
myofilaments are the muscle equivalents of
the actin-containing microfilaments and myosin motor proteins
what role do the proteins actin and myosin play? Where do these roles reach its highest development?
play a role in motility and shape change in most cells in the body; in the contractile muscle fibers
the central thick filaments extend to? and what are they connected in the middle of the sarcomere?
the entire length of the A band; the M line
where does the more lateral thin filament extend?
across the I band, partway into the A band
What anchors the thin filaments? What is it also known as?
Z disc; a protein sheet
Why does the H zone of the A band appear less dense?
because think filaments do not extend into this region
why is the M line in the centre of the H zone slightly dark?
due to the fine protein strands located there that hold the adjacent thick filaments together
The myofilaments are ——— in alignment at the Z discs and the M lines and are ——– to the sarcolemma at the —— discs
Held; anchored; Z
Muscle contraction depends on what?
myosin- and actin- myofilaments (thick & thin)
what does each myosin molecule consist of (chemically)
6 polypeptide chains: two heavy (aka high-molecular-weight) chains and 4 light chains
What do the heavy chains in a myosin molecule do?
twist together to form the myosin ‘rodlike’ tail
how does each heavy chain in a myosin molecule end and what’s it attached to?
ends in a globular ‘head’; attached to the tail via flexible hinge
what are the globular heads associated with?
each with 2 light chains
The globular heads are the ——- of the myosin?
business end
What happens during contraction with the globular heads?
they link the thick and thin filaments together, form a cross bridge and swivel around the point of attachment to generate force
How does the myosin itself gathers released energy to drive movement?
by splitting into ATP and acts as a ATPase
how many molecules of myosin are in a thick filament
300
what forms the central part of the thick filament?
the tail
the H zone is considered to be —– because it’s made up of the tail of myosin
smooth
Actin has a subunit called
globular actin o G actin
each G actin has a ————- to which the myosin heads attach during contraction
myosin-binding site (active site)
G acting subunits polymerize into long actin filaments called
filamentous or F, actin
what forms the backbone of each thin filament
intertwined G actin and F actin
What are the other regulatory proteins located in thin filaments
polypeptide stands of tropomyosin and troponin
tropomyosin function in a relaxed muscle fiber (assuming it’s successive - end to end of molecule)
block myosin-binding sites on actin so myosin heads on thick filaments don’t bind to the thin filaments
troponin is a globular protein with three polypeptide subunits - what do the 3 subunits do?
- attacks troponin to actin
- brings tropomyosin and helps position it on actin
- binds calcium ions
function of troponin and tropomyosin
help control the myosin-actin interactions involved in muscle contraction
important proteins for the structure of the myofibril
elastic filament and dystrophin
elastic filament is composed of a protein called
titin
where does titin extend from and to?
from the Z dick to the thick filament, then within the thick filament (also forming its core) to attach to the M line
titan forms the core of what filament & does what for the filament?
thick filament; holds it in place, maintaining the A band and helps spring the shape back to normal after stretching
What part of the titin is extensible and unfolding when the muscle stretching and recoils when tension is released?
that spans the I band
how does the titin prevent sarcomeres from pulling apart when stretching
stiffens as it uncoils to help resist excessive stretching
function of dystrophin
links the thin filaments to the integral proteins of the sarcolemma
what are other proteins that bind filaments or sarcomeres together to maintain their alignment
Nebulin, myomesin, C proteins
where do Intermediate (desmin) filaments extend to and it’s function?
extends from the Z disc and connects each myofibril to the next throughout the width of the muscle cell (horizontally)
Duchenne muscular dystrophy (DMD) is caused by
a defective gene for dystrophin
skeletal muscle fibers contain two sets of intracellular tubules that help regulate muscle contraction - what are they called
the sarcoplasmic reticulum and T-tubules
Sarcoplasmic reticulum (SR) is
an elaborate sloth endoplasmic reticulum
endo-
within
Sarcoplasmic reticulum function
regulates intracellular levels of ionic calcium by storing it and releasing it when demanded through stimulation for muscle contraction
What provides the final ‘go’ signal for contraction
calcium
majority of SR tubules run ——– along the myofibril to ——- with each other at the —– zone
longitudinally; communicate; H
terminal cisterns
form larger, perpendicular cross channels at the A band-I band junctions and always in pairs
what is closely associated with SR that is involved in producing energy used during contraction
large numbers of mitochondria and glycogen granules
Cross bridges
the attachment of myosin with actin within a muscle cell
role of ATPase in muscle contraction
energy is released during ATP hydrolysis and changes the angle of myosin head - ready to bind to actin if sites are available
Where is the T-tubule located
at A band - I band junction, just under the sarcolemma - on top f the myofibril
T- tubule stands for
transverse tubule
how does the t-tubule drastically increase the muscle fiber’s surface area
the cavity of the tubule is continuous with extracellular space
how does the increased surface area from the t-tubule benefit the muscle fiber?
allows for changes in membrane potential to rapidly penetrate deep into the muscle fiber
along the length, each t-tubule runs between paired terminal cisterns of the SR to form?
triads
triads are —— groupings of 3 —– structures including ?
successive, membraneous; terminal cistern, t-tubule and terminal cistern
since t-tubules are continuations of the sarcolemma, they can do what with nerve impulses?
conduct impulses to the deepest regions of the muscle cell and every sarcomere
what do the impulses trigger?
the release of calcium from the adjacent terminal cisterns
T-tubule function
rapid communication messaging system that ensures every muscle contraction is synchronous from all fibers
what acts as voltage sensors for contraction
the protruding integral proteins of the t-tubules
what forms gated channels, where the terminal cisterns release calcium
the integral proteins of the SR
contration refers to the
activation of myosin’s cross bridges
when does literal ‘shortening’ occur in muscle contraction
if the cross bridges generate enough tension on the thin filaments to exceed the forces that oppose shortening
where does the thin and thick filaments overlap in a relaxed muscle fiber
end of the A band
during contraction, thin filaments
slide past the thick ones so that the actin and myosin filaments overlap to a greater degree
how does the length of filaments not change during contraction
the cross bridge attachments forms and breaks several times during contraction to generate greater tension and thus propelling thin filaments forward
knowing how filaments do not lengthen during contraction, what is the last piece of the puzzle that creates muscle cell shortening
the event occurs simultaneously in the sarcomere all over the cell
at the microscopic level, what things occur as the muscle cell shortens
- I band shortens
- distance between successive Z discs shortens
- the H zone disappears
- the touching A bands move closer together, without change in length
why are the successive Z discs distance between each other shortens?
due to the thin filaments sliding centrally, the Z discs are pulled towards the M line since thin filaments are attached to Z discs
what is the neurotransmitter that motor neurons use to tell skeletal muscles to contact
acetylcholine
what are the 4 groups of steps in skeletal muscle contraction
- event at the neuromuscular junction
- muscle fiber excitation
- excitation-contraction coupling
- cross bridge cycle
neuromuscular junctions (motor end plates)
specialized chemical synapses formed at the sites where terminal branches of the axon of a motor neuron contact a target muscle cell
how many neuromuscular junctions are in each muscle fiber? where is it located?
one; midway along its length
step one of skeletal muscle contraction - summary
the motor neuron releases ACh that stimulates the muscle fiber causing local depolarization
end plate potential (EPP)
chemically induced change in electric potential of the motor end plate
step two of skeletal muscle contraction - summary
EPP triggers an action potential that travels across the entire sarcolemma
Step 3 of skeletal muscle contraction - summary
the action potential in the sarcolemma propagates along t-tubules causing calcium to release from terminal cisterns of SR - Ca is final trigger for contraction
what does calcium do in the muscle
Ca binds to troponin and causes the myosin-binding sites on actin to be exposed for myosin heads to bind
step 4 skeletal muscle contraction - summary
the muscle contracts as a result of a repeating cycle of steps hat cause myofilaments to slide relative to each other
what are the three steps involved in triggering and then propagating an action potential
- generation of end plate potential
- action potential depolarization
- repolarization
when EPP occurs, EPP spreads to
the adjacent sarcolemma and triggers an AP there
after ACh binds to ACh receptors, its effects are quickly terminated by
acetylcholinesterase
acetylcholinesterase location
synaptic cleft
acetylcholinesterase function
breaks down ACh to its building blocks, acetic acid and choline to prevent continued muscle fiber contraction in absence of addition stimulation
Excitation-contraction (E-C) coupling is
transmission of AP along the sarcolemma that causes myofilaments to slide
E-C coupling occurs when
rapid communication between electrical events occurring in the plasma membrane of skeletal muscle fibres and Ca2+ release from the SR, which leads to contraction.
troponin binds to —— when levels rise and thus allow for the unblocking of myosin-binding sites on actin
calcium
the cross bridge cycle repeats and each repetition causes the myosin head to
take another ‘step’ by attaching to an actin site further along the thin filament
thin filaments continue to slide in cross bridge cycle as long as there’s adequate levels of
calcium and ATP
muscle tension is
the force exerted by a contracting muscle on an object
load
the opposing force exerted on the muscle by the weight of the object to be moved
what are the two facts of muscle mechanics
- principles of contraction of a single muscle fiber and a whole skeletal muscle (many fibers) is pretty much the same
- muscle tension and load definitions
motor unit
single nerve cell that supplies nerves to a group of skeletal muscle
muscle fibers in a single motor unit are not —— ——- but are —— ——— the muscle
clustered together, spread throughout
knowing the position of muscle fibers in a single motor unit, what would be the result of stimulation to a singular motor unit?
a weak but uniform muscle contration
muscle twitch is the
response of a muscle to a single stimulation
what causes muscle twitches to vary in length between different muscle locations
variations in enzymes and metabolic properties of myofibrils
graded muscle contractions
variations in the degree of muscle contraction by changing either the frequency or strength of the stimulus
an increase in frequency of stimulation to muscle causes ——- ——– and the higher the frequency, the ?
temporal summation; greater the strength of contraction of a given motor unit
an increase in strength of stimulation causes —— , the stronger the stimulation the …?
recruitment; more motor units are activated, and the stronger the contraction
in the body, the brain determines the strength of muscle’s contraction by changing what?
(1) rate of firing AP along the axon of its motor neuron (frequency) and (2) the number of neurons activated (strength)
(temporal/wave) summation
accumulation of effect especially for muscular, sensory or mental stimuli
the second contraction of a muscle is stronger causing summation - why is it stronger?
because the muscle was already partially contracted - contraction was added to the previous
unfused tetanus
degree of wave summation where progression to a sustained but quivering contraction
fused tetanus
no muscle relaxation and contraction fuses into a smooth, sustained contraction plateau
sub threshold stimuli
stimuli that produces no observable contraction
threshold stimulus
the stimulus at which the first observable contraction occurs
maximal stimulus
strongest stimulus that increases contractile force - all motor units are recruited
the recruitment process is not ——— , it is dictated by the —– ——–
random; size principle
size principle - in any muscle,
motor units with the smallest muscle fibers are activated first, then the larger muscle fibers which increase contractile strength and then the largest motor units with the largest muscle fibers are activated when the most powerful contraction is needed
prolonging of all muscle contraction due to size principle is important to
prevent and or delay fatigue
muscle tone
when muscles are always slightly contracted to help maintain health and responsiveness to stimuli
what are the two main categories of contractions
isotonic and isometric
isotonic muscle contraction
muscle tension that develops overcomes the load and the muscle shortens in length
isometric muscle contractions
does not always shorten and move a load
what Is measured in isometric muscular contractions
the increasing muscle tension
isometric muscular contractions have no change in —– ——- and a higher amount of ——– and —- —- ——
resting length; resistance; peak tension developed
isotonic muscular contraction has a decrease in —– —- and a lower amount of —– and — — —- compared to isometric muscular contraction
resting length; resistance; peak tension developed
what are the two sub categories of isotonic contractions
concentric and eccentric
concentric contractions
the muscle shortens and does work
eccentric contractions
the muscle generates force as it lengthens
eccentric contractions are still equally important as concentric contractions for
coordination and purposeful movements
which contractions is 50% more forceful than the other
eccentric
when do muscles isometrically contract
when they’re primarily used to maintain upright posture or hold joints stationary while other move
what event in the muscle is identical in both isotonic and isometric contractions but the results are not
the electrochemical and mechanical events
thin filaments in isometric contractions ———- move even through the cross bridges generates force
do not
What is the only energy source directly used for muscle contraction
ATP
what are the three pathways for regenerating ATP during muscle activity
direct phosphorylation, anaerobic pathway and aerobic pathway
what pathway of regenerating ATP during contraction requires oxygen?
aerobic
what is the approximate length of energy from each of the 3 pathways of regenerating ATP?
Direct phos - 15 sec
anaerobic - 40 sec
aerobic - several hours
what is the slowest and fastest ATP regeneration pathway?
aerobic and direct phosphorylation
what is an alternative compound that is a source of energy for muscle tissue
creatine phosphate
muscle cells store 2-3 time more —– than ATP?
creatine phosphate
creatine kinase
enzyme that catalyzes the transfer of phosphate from CP to ADP to create ATP
aerobic endurance
the length of time a muscle can continue to contract using aerobic pathways
anaerobic threshold
the point where the muscle metabolism converts to anaerobic glycolysis
muscle fatigue
physiological inability to contract a muscle even though it’s receiving stimuli
what does muscle fatigue prevent?
complete depletion of ATP in muscle
what chemical changes are involved in muscle fatigue?
ionic imbalances, increased inorganic phosphate and magnesium, decreased ATP and glycogen
what does ionic imbalances in the muscle do to stop muscle contraction?
inhibits action potential which reduces movement to voltage sensitive proteins in T tubules and thus reducing Ca released from SR
excess post exercise oxygen consumption
the volume of oxygen required after exercise to replenish stores of oxygen, ATP, creatine phosphate, glycogen and oxidize the lactic acid that has formed
the force of muscle contraction depends on
the number of myosin cross bridges that are attached to actin
what’s are the four factors that increase the force of skeletal muscle contraction
- high frequency of stimulation
- large number of recruited muscle fibers (=more motor units used)
- large muscle fibers
- muscle & sarcomere being stretched slightly over 100% of resting length
where does muscle generate maximum force between of it’s optimal resting length?
80-120%
what factors influence velocity and duration of skeletal muscle contraction?
muscle fiber type, load and recruitment
two functional characteristics of muscle fiber types
speed of contraction and major pathways for forming ATP
velocity of fiber shortening consists of two groups, slow and fast fibers. What is the general difference between the two reflect?
how fast their myosin ATPases split ATP; pattern of electricity of motor neuron; how fast calcium moves into SR
knowing the two functional criteria for classifying types of muscle fibers- what are the different skeletal muscle cell groups?
slow oxidative fibers, fast oxidative fibers and fast glycolytic fibers
How many types of fiber muscle would all muscle fibers in a particular motor unit have?
one - all the same type
what does a greater load result in? (duration & velocity)
longer latent period, slower shortening and briefer duration of shortening
Aerobic (endurance) exercises result in what changes in the skeletal muscles?
increased number of capillaries and mitochondria in muscle fiber and fibers synthesize more myoglobin
in what type of fiber is aerobic exercise benefits seen the most?
slow oxidative fibers
what type of exercise promotes muscle hypertrophy?
high-intensity resistance especially under anaerobic conditions
what are the two sheets of smooth muscle?
longitudinal layer and circular layer
What are the differences smooth muscle fibers have in contrast to skeletal muscles? (smooth muscle…)
- is small spindle-shaped cells
- lacks the coarse connective tissue sheaths
- has varicosites instead of neuromuscular junctions
4.has less elaborate SR and no T-tubules - usually electrically connected by gap junctions
Varicosities
knoblike swellings of certain autonomic axons containing mitochondria and synaptic vesicles
what do varicosities do for smooth muscle?
form diffuse junctions that sprinkle neurotransmitters in the general area of SM cells
Caveloae description and function
pouch like inholdings containing large numbers of calcium channels; major source of calcium for smooth muscle contraction
no striations in smooth muscle, meaning there’s no?
sarcomeres
how does the proportion and organization of smooth muscle myofilaments differ from skeletal muscle?
- less thick filaments, but myosin heads are along the entire length
- no troponin complex in thin filaments
- contains non contractile intermediate filaments to resist tension
- thick and thin filaments are diagonally
The intermediate filament–dense body network forms a strong, cable-like intracellular cytoskeleton that?
harnesses the pull generated by the sliding of the thick and thin filaments
what do gap junctions connect in smooth muscle?
adjacent fibers
what differentiates smooth muscle in different body organs?
- fiber arrangement and organization
- innervation
- responsiveness to various stimuli
what are the two major types of smooth muscle?
unitary and multi unit
unitary smooth muscle is also called
visceral muscle
location of unitary smooth muscle & commonality
in the walls of all hollow organs except the heart & is far more common
unitary smooth muscle characteristics
- arranged in opposing sheets
- innervated by varicosities of automotive nerve fibers
- exhibit rhythmic spontaneous action potentials
- are electrically coupled by gap junctions and contract as a unit
- respond to various chemical stimuli
multi-unit smooth muscle example locations
large airways to lungs, large arteries, internal eye muscles
what is absent in multi-unit smooth muscle that is present in unitary smooth muscle?
gap junctions and spontaneous depolarizations
like skeletal muscle, multi-unit smooth muscle
- consists of muscle fibers that are structurally independent of one another
- richly supplied with nerve endings which is formed with a motor unit
- responds to neural stimulation with graded contractions that involve recruitment
unitary and multi-unit smooth muscles both served and respond to, that skeletal muscles do not
innervated by autonomic (involuntary) nervous system division and respond to hormones
what are the 2 special features of smooth muscle contraction that differs from skeletal muscles? & explain.
- response to stretch; SM spontaneously contracts when stretched to allow substance movement
- length and tension changes; SM stretches more and generates more tension than skeletal due to irregular filament arrangement and lack of sarcomeres
What is the purpose of smooth muscle stress-relaxation response?
allows a hollow organ to fill or expand slowly to accommodate a greater volume without causing strong contractions that would expel its contents
what does the stress-relaxation response look like in smooth muscle?
when stretched, it contracts but the tension is brief and then the muscle relaxes and adapts to the new length
what are some other unique characteristics of smooth muscle?
smooth muscle tone, slow prolonged contractions and low energy requirements
what are some ways smooth muscle contraction is regulated?
by nerves, hormones or local chemical changes
what does the effect of a specific neurotransmitter on a smooth muscle cell depend on?
type of receptor molecules on the cell’s sarcolemma
Some smooth muscle layers have no nerve supply at all, so how do they respond to chemical factors?
they depolarize spontaneously or in response to chemical stimuli that bind to G protein-linked receptors
what are some chemical factors that cause smooth muscle to contract or relax without action potential by inhibiting or enhancing calcium entry into sarcoplasm?
certain hormones, histamine, excess CO2, low pH and lack of O2
smooth muscle takes —– times longer to contract and relax than skeletal muscle, yet it can maintain the same contractile tension for prolonged periods at less than —% of the energy cost
30; 1
smooth muscle tone
moderate degree of contraction all the time without fatiguing
what is part of the striking energy economy of smooth muscle?
sluggishness of its ATPases and myofilaments may latch together during prolonged contractions (which saves energy)
Smooth muscle contraction responds in unison. What is the synchronization reflecting?
electrical coupling of smooth muscle cells by gap junctions that transmit depolarization to each fiber
purpose of pacemaker cells
once excited, they set the pace of contraction for the entire muscle sheet
what can modify the rate and intensity of smooth muscle contraction
neural and chemical stimuli
what happens to pacemaker cells when there’s an absence of external stimuli?
depolarize spontaneously
smooth muscle contraction is similar to skeletal muscle contraction in what ways?
- calcium ion level is the final trigger for contraction
- actin and myosin interact by the sliding filament mechanism
- ATP energizes the sliding process
calmodulin
a cytoplasmic calcium-binding protein
how does calcium activate myosin in smooth muscle contraction?
by interacting with calmodulin
what does calmodulin do after calcium activates myosin?
interacts with myosin light chain kinase or myosin kinase to phosphorylates the myosin and in turn activiating it
what is part of the process for stopping smooth muscle contraction
calcium detachment from calmodulin; active transport of calcium into SR and extracellular fluid; dephosphorylation of myosin by a phosphate enzyme (reducing myosin ATPase activity)
with rare exceptions from what cell do all three types of muscle tissues develop from?
myoblasts
in skeletal muscle formation, several myoblasts fuse to form?
multinuclear myotubes
how is the number of fast and slow contractile fiber types determined during development?
by the nerves that innervate them
myoblasts producing cardiac and smooth muscle cells do not fuse but instead develop what?
gap junctions early in embryonic stages
satellite cells
myoblast-like cells associated with skeletal muscles, that help retain injured fibers and allow limited regeneration of dead skeletal muscle
how do heart muscles repair?
mainly by scar tissue
smooth muscle blood vessels divide how often?
regularly throughout life
both skeletal muscle and cardiac muscles can retain what ability in a growing child and in adults?
ability to lengthen and thicken in child; hyptertrophy in load response in adults
what hormone is responsible for hypertrophy?
testosterone
what is a preventative and can show disease reversal when done daily to help maintain healthy muscles?
exercise
