parallel to eachother and are not attached end-to-end within a muscle
do NOT contain Z lines within their A bands
are multinucleated
characteristic that is shared by all types of the muscle tissues
every type contains tropomyosin
the functional unit of skeletal muscle is the
sarcomere = the area btwn the Z lines
troponin
binds with calcium to allow sarcomere shortening
the smallest unit of contraction with a skeletal muscle is a
sarcomere
the function of tropomyosin
prevent myosin cross bridges from attaching to the thin filaments
troponin
3 polypeptide sequence
inhibitory subunit that binds to actin
binds to tropomysosin and helps bing to actin
3 binds to calcium
sliding filament mechanism
this filaments slide inward toward the center of the A band
during contraction thin filaments slide past the thick ones so that the actin and myosin overlap to a greater degree
1. when the nervous system stimulates muscle fibers, the myosin heads on the thick filaments latch on to the myosin-binding sites on the actin thin filaments and the sliding begins
2. the cross bridge attachments formnd break several times during contraction, acting like tiny ratchets to generate tension and propel the thin filaments toward the center of the sarcomere
3. this event occurs simultaneously in sarcomeres through out the cell and the muscle cell shortens
4. the Z discs (attached to thin filaments) pull toward the M line
the muscle cell shortens: I bands shorten, the distance between sucessive Z discs shorten, the H zones disappear and A bands move closer together but their length does not change
during contraction of the skeletal muscle fibers...
thin filaments slide inward to the A band center and as a result of cycles of cross-bridges binding and bending
molecules involved in regulation of the cross bridge attachment
calsium ions
troponin
myosin
the H zone
the area within the middle of the A band where the thin filaments do not reach
shortens or disappears during contraction
contains only thick filaments
during muscle contraction
changes in band pattern that occur during muscle relaxation
I bands get wider
H zones become wider
thick filaments remain the same length
during contraction, asynchronous cycling of crossbridges
prevents thin filaments from slipping backwards
during exciation - contraction coupling
the AP travels down the T tubules
Ca2+ is released form the sarcoplasmic reticulum
the T tubules
provide a mean of rapidly tansmitting the AP from the surfaces into the central portions of the muscle fiber
runs perpendicularly betwen the myofibrils
sarcomere
stores Ca2+
sequences of events that are involved in muscle contraction
impulse reaches the axon's synaptic knob
synaptic vesicles fuse with neurons membrane and release ACh via exocytosis
ACh bings to receptors on the muscle cell membrane
sodium channels open and soidum flows in
if enough sodium moves into the muscle cell, an impulse (AP) develops
motor end plate
provide attachment sites for ACh
An action potential rapidly spreads to the central portions of a muscle cell by the means of
T tubules
binding of _____ to myosin permits the cross-bridge to _____
bindig of ATP
detach from actin
the sarcoplasmic reticulum stores ______ when a muslce is relaxed and releases it for binding to ______ during contraction
SR stores Ca2+
binds with troponin
one of the steps excitation-contraction occurs in the begining
sodium channels open in the fiber's membranes
characteristic of cross-bridges
they are comprised of myosin
they have an actin binding site
they have an ATPase binding site
they provide power stroking
globular myosin heads that protrude from the thick filaments
they bend during muscle contraction
they detach from actin during muscle contraction
they are not found in the I band
foot proteins
span the gap between a lateral sac of the SR and the adjacent T tubule
are are believed to serve as Ca2+ channels
during a cross-bridge cycle in skeletal muscle
cross bridge is energized when it hydrolyzes ATP
cross-bridge interaction btwn actin and myosin in skeletal muscle is directly blocked by
tropomyosin
the energy for cross bridge cycling during muscle contraction is provided by
ATP
relaxation of muscle
initaited by re-entry Ca2+ into the SR
contraction force is declining
muscle tension decrease
muscle returns to its initial length
detachment of actin from tropomyosin
troponin-tropomyosin complex is slipping back into its blocking position
Acetylcholinesterase destroys ACh to allow muscle membrane to return to resting potential
Ca2+ is actively taken up by the lateral sacs of the SR when there is no longer a AP
lack of ATP in skeletal muscle cell would most likely cause
and increase in tension and inability to relax
whole muscle tension depends on
number of muscle fibers contracting
tension produced by each cortracting fiber
extent of motor-unit recruitment
frequency of stimulation
motor unit refer to
a single motor neuron plus all of the muscle fibers it innervate
twitch summation
the muscle fiber is stimulated again before the filaments have completely returned to their resting positions and strong muscle contractions occur but stronger AP do not occur
is means by which gradation of muscle contraction may be accomplished results from the additional release of Ca2+ within the cystol of muscle fibers
results from increasing the frequency at which motor units are firing with a muscle
to pick up something heavier than your pencil, your nervous system could
stimulate larger motor units
based on the length-tension relationship
a resting muscle that is shorter or longer than its 1o will generate less tesion at the onset of contraction
picking up a book at a constant speed requires that
the muscle preform a concentric contraction
muscle tension
is created during muscle contraction as the tension generated by the contractile elements is transmitted via the connective tissue and tendons to the bones
the origin of a muscle is its
stationary end of attchment
during an isotonic contraction
the muscle's tension remains constant
with eccentric muscle contractions
muscle lengthens while contraction
submaximal isometric contractions are important for
maintaining postitions
in a muscle fiber undergoing maximal tetanic stimulation the velocity of shortening ________ as the load ______
decreases, increases
if the load on a muscle is increased, eventually a load will be reached at which the veloity of shortening becomes zero. At this point, the muscle contraction is referred to as
isometric
energy sources available to form ATP in muscle fibers in the absence of oxygen include
creatine, phosphate and glycolysis
the first means by which ATP is produced at the onset of contractile activity is
transfer of energy and phosphate from creatine phosphate to ADP
during aerobic exercise, the primary means for ATP production in muscle fibers involves
oxidative phosphorylation
myoglobin
can store small amounts of O2 and increases the rate of O2 transfer from the blood into muscle fibers
summation of simple twitches
the twitches resulting from seperate AP added together
different types of muscle fiber
the higher the ATPase activity, the faster the spped of contraction
muscles with high ATP-synthesizing ability are more resistant to fatigue
oxidative types of muscle fibers contain myoglobin
muscle fibers containing large amounts of myoglobin have a dark red color in comparison to the paler fibers, which have little myoglobin
fast-glycolytic (type IIx) muscle fibers
have high myosin-ATPase activity
can carry out oxidative phosphorylation
fatigue rapidly
contain myoglobin
fast-oxidative (type IIa) fibers
can be converted into fast-glycolytic fibers by regular resistance activities and are most abundant in muscles specialized for maintaining low-intensity contractions for long periods of time without fatigue
muscle cells of a marathon runner's lefs would exhibit
high resistance fatigue
low glycogen content
many mitochondria
slow speed of contraction
slow oxidative type I
fatigue is the failure of a muscle fiber to maintain ______ as a result of previous contractile activity
in the body's lever system, the fulcrums are represented by the
joints
bones= levers
joints= fulcrums
muscle= applied force
with the type of lever system exemplified by flexion of the elbow joint , whan an object is held in the hand
the power arm of the lever is the distance btwn the elbow joint and the insertion of the biceps muscle
load arm of the lever is the distance btwn the elbow joint and the hand
velocity and distance moved by the hand is amplified at the expense of the biceps muscle having to exert considerably greater force than the actual lad that is moved
characteristic of most of the body's lever system
they work at a mechanical disadvantage '
muscles must exert greater forces than the load
enlargement of muscle due to weight lifting is primarily a result of
hypertropht and increased production of actin and myosin
corticospinal system
consists of fiber that originate within the primary motor cortex and terminate on motor neurons
conscious initiation of muscle contraction is controlled by
the cerebral cortex
spastic paralysis occurs when
excitatory inputs to motor neruons are unopposed bc of disruption of an inhibitory system in the brain stem
during coactivation
the gamma motor neuron and the alpha motor neuron systems to a skeletal muscle are activated simultaneously
intrafusal muscle fibers
are found within muscle spindles and contain sensory nerver endings that are activated by stretch
extrafusal muscle fibers
supplied by alpha motor neurons
the stretch receptors in the central portion of the muscle spindle can be activated by
a passive strech of the whole muscle, including stretch of the muscle spindles
contraction of the end proportions of the muscle spindle
gamma motor neuron stimulation of the muscle spindle
calium turns on cross bridges by physically repositioning the troporin-tropomyosin complex to uncover the actin cross-bridge binding sites in
skeletal and cardiac muscle
characteristics of SM
its contractionis initiated neurogenically only
cells are spindle shaped
can develop less tension per unit cross-sectional area compared to skeletal muscle
can maintain tension with comparatively less ATP consumption than skeletal muscle
the range of lenths over which SM is able to develop near maximal tension is much greater than skeletal muscle
a hollow organ enclosed by SM accomodates variable volumes with little change in pressure exerted on the contents
cardiac muscle tissue
has gap junctions
has a moderatley developed SR
has slow myosin ATPase activity
stors calcium in the SR
the reglation of smooth muscle contraction is mediated by the phosphorylation of _______ and response of calcium binding to ______
myosin is phosphorylated
calcium binds to calmodulin
______ is not required for contraction of SM
troponin
calcium that enters the cell during SM excitation binds with
calmodulin
types of muscles that are myogenic
cardiac muscle
single-unit SM
multi-unit SM
neurogenically activated
under ANS control
found in the iris of the eye
single-unit SM
contains an abundance of gap junctions and forms functional syncytia
self-excitable
found in the walls of the digestive, reproductive and urnary tracts and small blood vessels
a functional syncytium
can be excited to contract as a unit bc AP can be conducted from one cell to adjacent cells through gap junctions
what is responsible for initiating contraction of SM
stimulation of the autonomic nervous system
repaying the oxygen deficit after strenuous exercise involves
removes lactate in the muscle cells
replenishing stores of creatine phosphate
replenishing store of glycogen
pacemaker activity
refers to spontaneously depolarizations of the membrane resulting from shifts in passive ionic fluxes accompanying automatic changes in channel permeability
a functional syncytium of cardiac muscle cells means that they
work as a unit mechanically and electrically
cardiac muscle
contains tropomyosin
contains gap junctions
found only in the heart
is self-excitable
straited with intercalted disks
True or False : muscle cells are the only cell types that contain intracellular contractile proteins
true
True or False: all skeletal muscles are attached to the skeleton
FALSE
True or False:skeletal fibers are formed during embryonic development by the fusion of many smaller cells
TRUE
True or False a single muscle cell is know as a myofibril
FALSE : muscle fiber
True or False: The H zone of the sarcomere consists of myosin but does not contain actin
TRUE
True or False: The M line is formed by a flattened disc-like cytoskeletal protein that connects the thin filaments of two adjoining sarcomeres
FALSE
Z-line
True or False: thin and thick filaments in a sarcomere contain cross bridges
TRUE
True or False: myosin is considered to be a regulatory protein because it plays an important role in regulation of muscle contraction
FALSE
tropomyosin and troponin
True or False: the thick filaments overlap in the A band
TRUE
True or False: tropomyosin covers the cross bridge binding sites on the thick filaments when the a sacomere is not contracting
FALSE
thin
True or False: the thick filaments in a sarcomere contains cross bridges
TRUE
True or False: all cross bridges within a sarcomere stroke in unison when pulling the actin filaments
FALSE
True or False the functional unit of skeletal muscle is the myofibril
FLASE
during isometric contraction
the muscle maintains constant length
True or False: Foot proteins link the actin molecules together within a thin filament
FALSE
True or False: according to the sliding filament mechanism of muscle contraction, the thick filaments slide in closer together to shorten the sarcomere
false
True or False: the T tubule is line with muscle cell's membrane
false
True or False : according to the sliding filament mechanism of muscle contraction, the muscle fibers of one motor unit slide in closer together between the muscle fibers of adjacent motor units
FALSE
True or False: the thick filaments within a myofibril have ATPase activity
TRUE
True or False: cross-bridges have actin binding sites that are normally covered by troponin and tropomyosin except during the excitation-contraction coupling
FALSE
True or False during muscle contraction the A band becomes shorter
FALSE
True or False: muscle relaxation does not take place until all of the ATP is used up
FALSE
True or False: in order for relaxation to occur, ACh must be removed from the muscle cell's receptors
TRUE
True or False: acetylcholinesterase removes ACh from receptors
TRUE
True or False: the contraction phase of a muscle cell lasts longer than the refractory period
FALSE
True or False: rigor mortis occurs when Ca2+links actin and the myosin globular head together in a rigor complex
FALSE
True or False: Muscle cells require ATP in order to relax, following a contraction
True
True or False: more tension is developed during twitch summation than during a single twitch bc the duration of elevated cytosolic Ca2+ concentration increases during summation, thus increasing the availability of cross-bridge binding sites
TRUE
True or False: gradation of muscle contraction can be accomplished by stimulating variable portions of each muscle fiber
FALSE
True or False: Summation events result om increasing amounts of cytoplasmic calcium levels
TRUE
True or False: a motor unit is a single muscle plus all of the motor neurons that innervate it
FALSE
True or False: Muscles that have a fine degress of control have small motor units
TRUE
True or False: the larger motor units within a muscle, the more precisely controlled the gradations of contraction
FALSE
True or False: increasing the number of recruited motor units in a muscle increases its force or strength of contraction
TRUE
True or False: with twitch summation, the muscle fiber is stimulated so rapidly that it does not have an opportunity to returnto resting potential between stimuli
FALSE
True or False: tetnus occurs when a muscle fiber is stimulated so rapidly that it is not allowed to relax btwn stimulations, resulting in a smooth, sustained contraction
TRUE
True or False: the shorter a muscle fiber is before the onset of a contraction, the greater the force that can be developed upon the subsequent contraction bc the thin filaments are already partially slid inward
FALSE
True or False: the metabolic capability of a muscle fiber can affect the degree of tension it can develop
TRUE
True or False: denervated muscle fibers become progressively smaller and their content of actin and myosin decreases
TRU
True or False: a skeletal muscle produces motion by pulling the origin toward its insertion
FALSE
True or False: bones serve as fulcrums for muscle action
FALSE
joints
True or False: the muscle-lever systems work at a mechanical disadvantage
TRUE
True or False: muscle tension does not change in isometric contractions
FALSE
True or False: the skeletal muscle shortens during concentric, isotonic contraction
TRUE
True or False: in an isotonic contraction, about 50% of the energy is consumed is realized as external work and the remainig50% is converted to hear
FALSE
True or False:the work performed by a muscle is the force it develops divided by distance
FALSE
True or False: oxidative phosphorylation occurs within the mitochondria of the muscle cells
TRUE
True or False: repaying the oxygen deficit involves the formatino of lactate in fatigues muscle cells
FALSE
True or False: anaerobic exercise is endurance-type exercise
FALSE
True or False:central fatigue of a muscle directly results from the accumulation of lactic acid in the muscle
FALSE
True or False: slow-oxidative muscle fibers have a high resistance to fatigue
TRUE
True or False: fast-oxidative muscle fibers have a high concentration of mitochondria
TRUE
True or False: fast-glycolytic muscle fibers do not require as much oxygen use as slow-oxidative fibers
TRUE
True or False: slow-oxidative muscles fibers would be found in high density in the leg muscles of an olympic sprinter
FALSE
True or False: a skeletal muscle undergoes hypertrophy mainly by producing many more muscle fibers
FALSE
True or False: atrophy can develop in a muscle by either denervation or disuse
TRUE
True or False: skeletal muscles are capable of limited repair after injury
TRUE
True or False: single-unit SM has no innervation
FALSE
True or False: the corticospinal system controls fine, descrete, voluntary body movements
true
True or False: the 2 types of fast twitch fibers are interconvertible depending on the type of conditioning they recieve
TRUE
True or False: single unit SM and cardiac muscle are both self-excitable
TRUE
True or False: both multi-unit SM and single unit SM are under motor control from the autonomic nervous system
TRUE
True or False: all smooth muscle is myogenic
FALSE
True or False: the strengthe and the rate of contraction of the heart can be influenced by the ANS
TRUE
True or False: the heart initiates its own AP without any external stimulation
