unit 3: skeletal muscles Flashcards
both ends of a muscle are attached
to bone by
tough tendons
what happens when a muscle contracts
it shortens
when a muscle contracts, what happens to tendons
places tension on tendons connecting it to a bone
The bone that moves is attached at
muscle insertion
The bone that does not move is attached at
muscle origin
movt is towards
muscle origin
Different movements depend on
the joint and how the muscles are attached
flexor muscles
decrease angle btwn 2 bones at a joint
extensor muscles
increase angle btwn 2 bones at joint
main muscle responsible for movement in a
given direction is
agonist
Flexors and extensors that act on the same joint
to produce opposite actions
antagonist
cross 1 joint and 1 movt. example brachialis (cross elbow joint)
single joint muscle
moveable attachment of muscle to bone. usually distal from body center and moves when muscle contracts.
insertion
example of insertion
biceps brachii inserts into radius bone of forearm
fixed attachment point of muscle to bone. typically proximal to body center and not move during contraction.
origin
example of origin
biceps brachii muscle originates at scapula
relax/stretch to allow smooth movt. provide stabilization and control by preventing overextension.
antagonist
example of antagonist
during elbow flexion, the triceps brachii is antagonist
example of agonist
during elbow flexion, the biceps brachii are agonist
Moves insertion downward
depressor
moves insertion upwards
levator
circular muscle that surrounds and controls the opening/ closing of a passage in the body
contract=close
relax=opens
sphincter
example of sphincter
orbicularis oculi= eyelids
orbicularis oris= lips
connective tissue components of skeletal muscles
epimysium, perimysium, and endomysium
skeletal muscles are surrounded by —
protects the muscles from friction with nearby structures. Provides structural support and maintains shape. connects to tendons
epimysium
subdivides the muscle into fascicles. surrounds bundles of muscle fibers (fascicles). provide pathways for nerves and BV to reach individual muscle fibers. contributes to muscle elasticity and strength
perimysium
each fascicle is subdivided into muscle fibers (myofibers) surrounded by—
provides support and insulation to each muscle fiber. electric insulator
endomysium
what are skeletal muscle cells known as
muscle fibers (myofibers)
muscle fibers have many— found in other cells like..
organelles; mitochondria, ribosomes, ER, nuclei
muscle fiber have plasma memb called
sarcolemma
muscle fibers are multinucleated and form
syncytium
multinucleated cell/tissue formed by fushion of multiple cells or incomplete cell division. behaves as a single functional unit, sharing cytoplasm and coordinating activity
syncytium
what causes striations
I bands, A bands, Z lines (discs)
what is a motor unit
single motor neuron and all the
muscle fibers it innervates
all the muscle fibers
in a motor unit contract
at once
varied contraction strength
due to different numbers of motor units being
stimulated
graded contractions
dont need to contract the entire muscle. produce smooth and controlled movts and prevent muscle fatigue by recruiting motor units progressively
graded contractions
site where a
motor neuron stimulates a muscle fiber
neuromuscular junction
when nerve reaches NMJ, what happens
ACh released, ACh binds to receptors and trigger AP, muscle contracts
area of the muscle fiber
sarcolemma where a motor neuron stimulates it
using the neurotransmitter, acetylcholine
motor end plate
transmits neural signals to muscle. initiates/ controld muscle contractions
motor end plate
Contraction strength comes
motor unit recruitment
activating more motor units in a muscle to increase force of contraction. allows gradual and controlled force production
motor unit recruitment
Finer muscle control requires
smaller
motor units (fewer muscle fibers)
eye muscles may have
23 muscle
fibers/motor units
Larger, stronger muscles may have motor
units with
thousands of muscle fibers
finer muscle control requires
control and strength trade-offs
muscles with greater control have less strength (small motor units). muscles with greater strength have less control (large motor units)
trade off
ensures efficient force production and precise movement in tasks
trade off
accounts for half of the
more than 30 genetically different muscular dystrophies and is
the most severe form. This disease is caused by mutations in
a recessive X-linked gene
Duchenne muscular dystrophy (DMD)
gene codes for a protein called
dystrophin
dystrophin protein is located just under the
sarcolemma
provides support by bridging the cytoskeleton and
myofibrils in the muscle fiber with the extracellular matrix
dystrophin protein
Mutations result in activity-induced damage to the — that cannot be replaced by satallite cells
sarcolemma
what does no repair by satallite cells cause
causes muscle fiber necrosis and replacement
by fibrous connective and fatty tissue
muscle fiber necrosis
death of muscle cells (fibers) due to cellular damage or inflammation
each muscle fiber has densely packed subunits called
myofibrils
how are myofibrils stacked any why are they stacked that way
Stacked in register so that the dark and light
bands align
muscle fibers are composed of
thick and thin myofilaments
individual and elongated muscle cells that make up skeletal, cardiac, and smooth muscle tissue
muscle fibers
how are skeletal muscle fibers formed
fushion of myoblasts
extensions of sarcolemma that penetrate muscl fiber. transmit action potentials deep into fiber
t tubules
how are striation produced
thick and thin fil
contain only thin filaments, primarily of the
protein, actin
i bands
contain all of the thick filament with some
thin filament overlap; the thick filament is the
protein, myosin
a bands
the center of the A band with no thin
filament overlap.
h bands
found in the center of each I
band.
z discs (lines)
basic subunit of striated muscle
contraction
sarcomere
area of one z disc to the next
sarcomere
protein in sarcomere that runs from the Z disc to the M
line and allows elastic recoil
titin
found in the center of each A band
and help hold down thick filaments
m lines
In three dimension, the sarcomere forms
hexagonal pattern
When a muscle contracts
sacromeres shorten
A bands do not shorten, but
move closer tgthr
I bands do shorten, but
thin fil do not
Thin filaments slide toward
the H bond
what happens to h band during sliding filament theory
shortens or disappears
during sliding fil theory, what happens to A muscle fiber, together with all its myofibrils
shortens by movement of the
insertion toward the origin of the muscle
Shortening of the myofibrils is caused by
shortening of sacromeres- distance btwn z lines are reduced
Shortening of the sarcomeres is accomplished by
sliding of the
myofilaments—the length of each filament remains the same during
contraction
Sliding of the filaments is produced by
asynchronous power strokes of
myosin cross bridges, which pull the thin filaments (actin) over the thick
filaments (myosin
The A bands remain the same length during contraction, but are
pulled
toward the origin of the muscle.
Adjacent A bands are pulled closer together as
the I bands between them
shorten
The H bands shorten during contraction as
the thin filaments on the sides
of the sarcomeres are pulled toward the middle.
change in sarcomere during contraction
sliding fil theory
connections between thick and thin fil during muscle contract. force generation, muscle tension, and atp dependent
cross bridge
composed of the protein myosin
a) Each protein has two globular heads with actin-binding
sites and ATP-binding sites
thick fil
composed of the protein actin
a) Have proteins called tropomyosin and troponin that
prevent myosin binding at rest.
thin fil
cover myosin site to prevent contract
tropomyosin
binds calcium during contraction
troponin
is produced by several cross bridges
that form between myosin and actin
sliding
The myosin head serves as a
myosin ATPase
enzyme, splitting ATP into ADP + P i
what does sliding allow
allows the head to bind to actin when the
muscle is stimulated
Release of P i upon binding cocks the myosin
head, producing a
power stroke that pulls the
thin filament toward the center
After the power stroke, what is released and binds
adp is released and a new atp binds
what makes the myosin release actin and atp is split
after the power stroke and release of adp
myosin head straightens out and
rebinds to
actin farther back
sliding continues until
sarcomere has shortened
F-actin is made of 300-400 G-actin
subunits, arranged in a
double row and
twisted to form a helix
what physically blocks cross
bridges
tropomyosin
troponin complex
Troponin I, troponin t, troponin c
Troponin I inhibits
binding of myosin.
Troponin T binds to
tropomyosin
troponin c binds to
calcium
When muscle cells are stimulated, Ca 2+ is
released inside the muscle fiber
Some attaches to troponin C, causing a
conformational change in troponin and
tropomyosin
Myosin is allowed access to form
cross bridges with actin
SR is modified endoplasmic reticulum that
stores Ca 2+ when muscle is at rest
invagination in striated muscle that are vital for contraction. functions in electrical signal from surface to interior, enables release of calcium for contraction
T-tubules
large sac like located at A-I bands that store and release calcium
terminal cisternae
When a muscle fiber is stimulated, Ca 2+
diffuses out of calcium release channels
(ryanodine receptors)
At the end of a contraction, Ca 2+ is
actively
pumped back into the SR.
Narrow membranous tunnels formed from
the sarcolemma
transverse tubules
Open to the extracellular environment
tranverse tubules
able to conduct AP bc their memb contain high conc of ion channels, transporters, and pumps
ttubules
Closely situated next to terminal cisternae
ttubules
Acetylcholine is released from
motor neuron
when muscle fiber is stim, what potentials are produced
-end plate potentials
-AP
during stim muscle fiber, what do VG calcium channels do
Voltage-gated calcium channels in transverse
tubules change shape and cause calcium
channels in SR to open
what happens to calcium during stim muscle fiber
calcium is released and can bind to troponin c
during muscle relaxation, what happens
-AP cease
-Calcium release channels close
during muscle relax, what does ca atpase do
Ca 2+ -ATPase pumps move Ca 2+ back into
SR (active transport) and no more calcium us able to bind to troponin c
during muscle relax, what does tropomyosin do
Tropomyosin moves to block the myosin
heads from binding to actin
when a muscle quickly contracts
and relaxes after a single electrical shock
of sufficient voltage
twitch
Increasing the voltage increases the
strength
of the twitch up to a maximum
When a second shock is applied immediately
after the first, a second twitch will partially
piggyback the first. This is called
summation
time between the
stimulus and the contraction
(excitation-contraction coupling to the
attachment of myosin cross bridges to
actin)
latent period
stronger
contractions result in recruitment of more
fibers, until all fibers are contracting
graded contractions
For muscles to contract, they must generate force
that is greater than the
opposing forces
the greater the force,
slower the contraction
types of muscle contractions
isotonic (concentric and eccentric) and isometric
Muscle fibers shorten
when the tension produced is just greater than
the load
isotonic
change in muscle length while maintaining constant tension
isotonic
example of isotonic
squats, curls, bridges (needing constant tension and pressure while length changes)
muscle fiber shortens
when force is greater than load
concentric
example of concentric
bicep curl and lifting up a weight
muscle may actually
lengthen, despite contraction, if the load is too
great.
eccentric
allows you to lower a weight gently after full concentric contraction
eccentric
Muscles can’t shorten because the load is
too great
isometric
muscles contract without changing length; pressure changes while length stays the same
isometric
what must be pulled tight when muscles contract
noncontractile parts of muscle
what are elastic, resist distension, and snap back to resting length
tendons
what absorb some of the tension as
muscles contract
tendons
how is muscle strength determined
-number of fibers recruited to contract
-frequency of stimulation
-thickness of each muscle fiber (thicker is stronger)
-initial length of fiber at rest
why is thicker muscle fiber stronger
more cross bridges and interactions
a really stretched out and/or condensed muscle are
weak
Tension is maximal when sarcomeres are at
normal resting length
Increasing sarcomere length decreases
muscle tension
Increasing sarcomere length decreases muscle tension. why?
-fewer interactions btwn myosin and actin
-at a certain point, no tension can be generated
Decreasing sarcomere length decreases
muscle tension because
the fiber gets shorter and thicker (contractile proteins cant work efficiently)
Decreasing sarcomere length decreases
muscle tension because the fiber gets
shorter and thicker. this causes ?
-increased fluid pressure
-increased distance between actin and myosin
why do muscles buldge as they contract
the physical mass has to go somewhere. the cells also buldge and creates pressure
increase overlap of thin and thick fil are weaker because
theres fluid pressure that makes it harder for those proteins to interact
