Muscular System Flashcards
Musculoskeletal system
an integrated system of bones, muscles, and joints
myology
scientific study of muscles
orthopedics
the branch of medical science concerned with the prevention or correction of disorders of the musculoskeletal system
overview of muscular tissue
40-50% of total body weight is muscular tissue in an average person (depending on body fat, gender, and exercise regimen)
striations
3 types
skeleal
cardiac
smooth
skeletal
straited; voluntary
cardiac
striated; involuntary
smooth
nonstriated; involuntary
4 functions of the musucular system
producing body movements
stabilizing body positions
storing and moving substances within the body
producing heat
producing body movements
rely on the integrated functioning of skeletal muscles, bones, and
joints
stabilizing body positions
skeletal muscles stabilize joints and help maintain body positions;
postural muscles contract continuously when a person is awake
storing and moving substances within the body
sphincters in digestive and urinary systems;
cardiac muscle contractions; smooth muscle in walls of blood vessels and digestive system; skeletal muscle to return veinous blood to heart
producing heat
heat is produced as muscular tissue contracts; shivering
skeletal muscle tissue
muscle fibers fascicles whole muscle endomysium perimysium epimysium
muscle fibers
muscle cells; elongated shape
fasicicles
bundles of 10-100 or more muscle fibers
whole muscle
hundreds to thousands of muscle fibers
endomysium
connective tissue that wraps each muscle fiber
perimysium
connective tissue that wraps each fasicle
epimysium
connective tissue that wraps whole muscle
fascia
dense sheet or broad band of dense irregular connective tissue that surrounds muscles; allows free movement, carries nerves, blood vessels, and lymphatic vessels; fills spaces between muscles
subcataneous layer ( hypodermis)
separates muscle from skin; composed of areolar connective tissue and adipose tissue; provides pathway for nerves, blood vessels, and lymphatic vessels to enter and exit muscles
tendon
a cord of dense regular connective tissue composed of parallel bundles of collagen fibers; an extension of the epimysium, perimysium, and endomysium beyond the muscle
nerve and blood supply
Well supplied with both which are directly related to contraction
Prolonged muscle action depends on a rich blood supply to deliver nutrients and oxygen and to
remove wastes
Each skeletal muscle fiber also makes contact with the terminal portion of a neuron
Each fiber is connected to one neuron, each neuron may be connected to 10s, 100s, or 1000s of fibers
proprioceptors are located where
throughout the body and inform the brain of the degree of muscle contraction,
the amount of tension on tendons, and the position of joints
muscle spindle cells
a specialized muscle fiber type that detects degree of stretch of a muscle;
activation causes contraction of the muscle to prevent damage to the muscle
golgi tendon organs
cells located in tendons that detect stretch, or tension on the tendon;
activation causes relaxation of the muscle to prevent damage to the tendon
skeletal muscle tissue histology
sacrolemma t tubules multiple nuclei under the sacrolemma sarcoplasm contain many mitchondria to produce ATP consists of thousands of muscle fibers arranged parallel to one another myoglobin myofibrils sarcomeres sacroplasmic reticulum z discs A band h zone i band tropmyosin alternating darker A bands and lighter I bands give the muscle fiber its striated appearance tropomyosin
sarcolemma
plasma membrane covering each muscle fiber
transverse tubules
tunnel in from the surface toward the center of each fiber
sarcoplasm
the muscle fiber’s cytoplasm
myoglobin
reddish pigment; stores oxygen until it is needed by mitochondria to generate ATP of two types of protein filaments
thin/ thick filaments
thin filaments
contain actin, tropomyosin, and troponin; anchored to the Z discs; contains myosin-binding site
thick filaments
contain myosin; project myosin heads
sarcomeres
basic functional units of striated muscle fibers
sarcoplasmic reticulum
a network of fluid-filled membrane-enclosed tubules that stores calcium ions required for muscle contraction
z dics
separate sarcomeres from one another; dense protein material
a band
darker area within each sarcomere, extends the entire length of the thick filaments
h zone
at the center of each A band; narrow; contains only the thick filaments
I band
lighter-colored area to either side of the A band; contains the rest of the thin filaments
but no thick filaments
tropomyosin
protein; covers the myosin-binding sites on actin
troponin
protein; hold tropomyosin in place
When calcium ions bind to troponin, it allows tropomyosin to move off of the myosin binding sites
neuromuscular junction
the synapse formed between the axon terminals of a motor neuron and
the motor end plate of a muscle fiber
muscle action potential motr neuron motor unit axon axon terminals synaptic end bulbs motor end plate synaptic cleft
motor action potential
an electrical signal that stimulates a skeletal muscle fiber to contract
motor neuron
a neuron that delivers the muscle action potential to a muscle fiber
motor unit
a single motor neuron along with all the muscle fibers it stimulates; either all on or
all off; vary greatly in size
axon
long process of a motor neuron
axon terminals
branches of the axon that approach the sarcolemma of a muscle fiber
synaptic end bulbs
the ends of the axon terminals which contain synaptic vesicles filled with a
chemical neurotransmitter
motor end plate
the region of the sarcolemma near the axon terminal
synaptic cleft
the space between the axon terminal and sarcolemma
neuromuscular junction- neurotransmitters
release of acetylcholine
activation of ACh receptors
generation of muscle action potential
breakdown of ACh
release of acetycholine
nerve impulse causes neurotransmitter release from synaptic end bulbs that diffuses across synaptic cleft between the motor neuron and motor end plate
activation of ACh receptor
ACh binds to its receptors in the motor end plate which opens ion channels that allow small cations to flow across the membrane
generation of muscle action potential
the inflow of cations generates a muscle action potential which travels along the sarcolemma and through the T tubules
brakdown of ACh
the effect lasts only briefly because ACh is broken down in the synaptic
cleft by an enzyme called acetylcholinesterase
sliding filament mechanism
the process of muscle contraction by which sarcomeres shorten, causing
the shortening of the muscle fibers
myosin heads of the thick filaments pull on the thin filaments, causing them to overlap and the sarcomere to shorten
length tension relationship
force velocity relationship
length tension relationship
the precise relationship between myofilament
overlap and tension generation
Tension generation in skeletal muscle is a direct function of the magnitude of overlap
between the actin and myosin filaments
Described at a constant length, not in motion
force velocity relationship
describes the force generated by a muscle as a function of velocity under conditions of constant load
The velocity of muscle contraction depends on the force resisting the muscle
Describes force generation of moving muscles
process of muscle contraction
Calcium and ATP are required for muscle contraction
When a fiber is relaxed – low concentration of Ca
When a muscle action potential travels along the sarcolemma into the transverse tubule system,
Ca release channels open, allowing Ca to escape into the sarcoplasm
Ca binds to troponin molecules in the thin filaments, which move the tropomyosin away from the
myosin-binding sites on acting
Cross-bridges are formed with the use of ATP
Power stroke – cross-bridge rotates or swivels
o The cross-bridges remain firmly attached until ATP releases them
muscle relaxation
relaxation is just the absence of contraction
relaxation occurs when
ACh is rapidly broken down to end the generation of muscle action potentials
Ca ions are rapidly transported from the sarcoplasm into the sarcoplasmic reticulum so the tropomyosin slides back over the myosin-binding sites and the filaments slip back to their relaxed positions
muscle tone
when a small number of a muscle’s motor units are involuntarily activated to produce a sustained contraction even when the whole muscle is not contracting
keeps skeletal muscles firm, but does not result in movement
flaccid
flaccid
a state of limpness in which muscle tone is lost (when the motor neurons serving a
skeletal muscle are damaged or cut)
energy for contraction
the ATP present inside muscle fibers is enough to power contraction for only a
few seconds
3 sources for ATP production
creatine phosphate
anaerobic cellular respiration
aerobic cellular respiration
creatine phosphate
about 15 seconds
anaerobic cellular espiration
2 minutes
after creatine phosphate is depleted, glucose is broken down into pyruvic acid (which produces 2 ATPs per glucose molecule), then is converted into lactate; occurs without the presence of oxygen
aerobic cellular respiration
more than 10 minutes
provides energy for activities that last longer than 30 seconds; process that
requires oxygen for ATP to be produced by the mitochondria (produces about 36 ATPs per glucose molecule); occurs with the presence of oxygen
while at rest, muscle produce what?
ATP than they need; some of the excess is used to make creatine
phosphate (stores P’s to add to ADP to form ATP)
muscle fatigue
the inability of a muscle to contract forcefully after prolonged activity
lowered release of calcium ions from sacroplasmic reticulum
depletion of creatine phosphate
insufficient oxygen
depletion of glycogen and other nutrients
buildup of lactate and ADP
failure of nerve impulses in the motor neuron to release enough acetylcholine
Muscle twitch
the contraction that results from a single muscle action potential
control of muscle tension
Total tension that a single muscle fiber can produce depends on the rate at which nerve impulses arrive
The contraction of a whole muscle depends on the number of muscle fibers that are contracting in unison
muscle tension depends on
frequency of stimulation
motor unit recruitment
muscle fiber type
twitch contraction
a brief contraction of all of the muscle fibers in a motor unit in response to a single action potential in its motor neuron
myogram
recording of a muscle contraction
latent period
brief delay between application of the stimulus and the beginning of contraction
contraction period
repetitive power strokes are occurring, generating tension or force of contraction
relaxation period
power strokes cease because the level of Ca in the sarcoplasm is decreasing to the resting level
frequency of stimulation
the number of impulses per second
wave summation
stimuli arriving one after the other before a muscle fiber has completely relaxed causing larger contractions
unfused ( incomplete) tetanus
a sustained but wavering contraction; the muscle can partially relax between stimuli
fused ( complete) tetanus
a sustained contraction in which individual twitches cannot be detected; the muscle does not relax at all between stimuli
motor unit recruitment
the process in which the number of contracting motor units is increased
Asynchronous
Small units give more gradual rise in force for precision
Large units give faster rise in force for strength
Recruited from smallest to largest to avoid fatigue and provide gradual increase in force
muscle fiber types
slow oxidative/ type I
fast oxidative/ glycolytic / type IIa
fast glycolytic /type IIb
slow oxidative/ Type I
red; small; contain a large amount of myoglobin; slow twitch; resistant to fatigue, capable of prolonged, sustained contractions
fast oxidative / glycolytic / type IIa
intermediate size; contain large amount of myoglobin; moderately high resistance to fatigue; contract and relax more quickly than slow oxidative
fast glycolytic/ type IIb
white fibers; largest in diameter; most powerful and rapid contractions; fatigue quickly; intense movements of short duration
how skeletal muscles produce movement
cross at least one joint
When the muscle contracts it draws one bone toward the other
The attachment on the stationary bone is the origin
The attachment on the movable bone is the insertion
The fleshy part of the muscle between the tendons is the belly
skeletal muscle
an organ composed of several types of tissues
skeletal muscle tissue vascular tissue ( blood vessels and blood) nervous tissue ( motor neurons) several types of connective tissues tendons
tendons
connect muscle to boen
type of muscle actions
concentric
eccentric
isometric
concentric
actively shortening muscle
eccentric
actively lengthening muscle
isometric
actively staying the same length
agonist ( prime mover)
a muscle that causes a desired action
antagonist
a muscle that has an effect opposite to that of the prime mover
synergist
a muscle that helps the prime mover function more efficiently by reducing
unnecessary movement
stabilizer ( fixator)
stabilize the origin of the prime mover so that the prime mover can act more
efficiently
skeletal muscle architecture
the arrangement of muscle fibers relative to the axis of force generation
parallel/ longitudinal
pennate
parallel/longitudinal
relatively long with fibers usually going the length of the muscle
flat sphincter fusiform strap triangular
flat
parallel fibers, wide fat tendons; i.e. rhomboids, abdominal muscles
spinchinter
circular muscle to close an opening; i.e. orbicularis oculi
fusiform
wide in the middle, narrow at the ends; i.e. biceps brachii
strap
long and thin, may have an intermediate tendon; i.e. rectus abdominis
triangular
convergent, fan-shaped design often with a spiral; i.e. pectoralis major,
latissimus dorsi, trapezius
pennate
tendon extends most of the length of the muscle with fibers branching off like a bird’s
feather
unipennate
bipennate
multipennate
unipennate
diagonal fibers on one side of the long tendon; i.e. vastus lateralis
bipennate
diagonal fibers branching from both sides of a long tendon; i.e. gastrocnemius
multipennate
multiple bipennate bellies that form one larger muscle; i.e. deltoid
single vs multi joint muscles
The design of a muscle is customized for the functional demands placed on it
Crossing multiple joints creates mechanically complex motion possibilities
A muscle can only act on the joints it crosses
skeletal muscle and satellite cells
In response to muscle inflammation, satellite cells become activated, reproduce, mature, and fuse with damaged muscle fibers to facilitate the remodeling of the damaged muscle fibers
satellite cells
skeletal muscle stem cells that are critical to muscle regeneration following injury
cardiac muscle tissue
makes up most of the heart; striated; involuntary
Fibers are branched, shorter in length, larger in diameter, and have a single centrally located nucleus
Intercalated discs
Has endomysium and perimysium, but no epimysium
Autorhythmicity
Several hormones and neurotransmitters can increase or decrease heart rate by speeding or slowing the heart’s pacemaker
Requires a constant supply of oxygen and nutrients
Mitochondria in cardiac muscle fibers are larger and more numerous than in skeletal muscle and produce most of the needed ATP via aerobic cellular respiration
Can use lactate from skeletal muscle fibers to make more ATP during exercise
Intercalated discs
irregular transverse thickenings of the sarcolemma that interconnect cardiac
muscle fibers
Hold the fibers together and contain gap junctions, which allow muscle action potentials to spread quickly from one cardiac muscle fiber to another
Autorhythmicity
the built-in intrinsic rhythm of heart contractions initiated by specific cardiac
muscle fibers that act as a pacemaker
smooth muscle tissue
Found in many internal organs and blood vessels; involuntary; nonstriated (smooth)
Considerably smaller in length and diameter than skeletal; tapered at both ends
Single, oval, centrally located nucleus
Contain thick, thin, and intermediate filaments with no regular pattern of overlap
Contraction is similar to skeletal muscle fibers, but starts more slowly and lasts much longer
Ca ions enter slowly and move out slowly when excitation declines
Smooth muscle tone
Can both shorten and stretch to a greater extent than other muscle types
dense bodies
functionally similar to Z discs where the thin filaments attach; dispersed
throughout the sarcoplasm and attached to the sarcolemma; attached to bundles of intermediate
filaments
2 kinds of smooth muscle tissue
visveral
multiunit
visceral
more common type; found in sheets that wrap around to form part of the walls
of small arteries and veins and hollow viscera
Fibers are tightly bound together in a continuous network
autorhymthmic
multiunit
consists of individual fibers; in the walls of large arteries, large airways to the lungs, erector pili muscles and internal eye muscles
fibers contract individually
each fiber has its own motor nerve ending
smooth muscle tone
a state of continuous partial contraction because of the prolonged presence
of Ca ions in the cytosol
