Jan 31st Content Flashcards
Muscle classifications
skeletal, smooth, cardiac
Characteristics of skeletal muscle
multinucleated, has mitochondria, transverse tubules (t-tubules), myofibrils, sarcomeres, intracellular structures (sarcolemma, sarcoplasm, sarcoplasmic reticulum)
Sarcolemma =
plasma membrane
Sarcoplasm =
cytoplasm
Sarcoplasmic reticulum =
smooth ER
What transfers force to the tendon then force to bone resulting in movement?
connective tissue
Force produced at the level of the
sarcomere
Epimysium
surrounds entire muscle
Perimysium
middle; surround bundles of muscle fibers
Endomysium
surrounds individual muscle fibers
Satellite cells
myogenic stem cells located within the sarcolemma
Satellite cells help with
regenerative cell growth
Satellite cells may play a role in
hypertrophy
Through donation of what do muscle fibers continue to grow
nuclei
Structures that give skeletal and cardiac muscle their striated appearance
myofibrils
Myofibrils consist of orderly arrangements of
actin (thin) & myosin (thick)
Structure of the sarcomere
I-band (Z-line, titin), A-band (thin filament, m-line, thick filament), I-band (titin, z-line)
Myofibrils lead to
sarcomeres
Tropomyosin is locked onto
actin
Troponin is the lock that attaches to
tropomyosin
Troponin pulls away when
calcium attaches to it
A molecule spring that provides tension
Titin
Myofibrils inside
endomysium
Myosin filaments are oriented with their trials pointed
toward the center of the sarcomere
Proportion of actin to myosin in myofibril =
density
Myosin is
thick
Actin is
thin
Actin consists of
tropomyosin and troponin
Skeletal Muscle Mass
75% water, 20% protein, 5% other
Arteries and veins lie parallel to
individual muscle fibers
Extensive branching of blood vessels ensures each muscle fiber an
adequate oxygenated blood supply from the arterial and rapid removal of CO2 in venous circulation
Trained muscle increased capillary to muscle fibers ratio helps explain
improved exercise capacity with endurance training
Enhanced capillary microcirculation expedites removal of
heat and metabolic byproducts from active tissues in addition to facilitating delivery of oxygen, nutrients, and hormones
Enhanced vascularization at capillary levels proves beneficial during activities that require
high level steady-rate aerobic metabolism
Vascular stretch and shear stress on the vessel walls from increased blood flow during exercise stimulates _____________ __________ with ____________ __________ ___________
capillary development; intense aerobic training
Capillary to fiber ratio
fibers grow more than added capillaries; ratio decreases
Motor units are made up of
a motor neuron and the skeletal muscle fibers innervated by the motor neuron’s axon terminals
Groups of motor units work together to
coordinate contractions of a single muscle
All motor units within a muscle are considered a
motor pool
What moves down the axon arriving at the nerve terminak?
action potential
Action potential ________ the nerve terminal
depolarizes
Depolarization of the nerve terminal activates
voltage-gated calcium channels
Calcium enters the synaptic terminal and increases
cytosolic calcium concentration
Increased cytosolic calcium causes release of
neurotransmitter from vesicles
Neurotransmitter enters into __________ _________ through ____________
synaptic cleft; exocytosis
Neurotransmitter dissociates from receptor and is removed from synpase by (3)
metabolism, reuptake into nerve terminal, or diffusion away from synapse
Neurotransmitter =
Acetylcholine
Postsynaptic receptor
nicotinic-cholinergic receptor (NAChR)
What is nicotinic-cholinergic receptor (NAChR)?
a ligand-gated channel
Nicotinic-cholinergic receptor (NAChR) is selective for
sodium and potassium
Activation of nicotinic-cholinergic receptor (NAChR) allows
diffusion of sodium into the cell and potassium out of the cell
Acetylcholine esterase (AChE) is localized in
folds of the endplate
Acetylcholine esterase (AChE) hydrolyses the Ach to
choline and acetate
What is taken back into the nerve terminal by sodium dependent co-transporter
choline
Choline taken back into the nerve terminal is used to
synthesize new Ach
What diffuses away from the synaptic cleft
acetate
Acetate is taken up by _______ and enters __________ ___________
cells; metabolic pathways
Duration of synaptic transmission
1 ms
Only channels present at endplate
nicotinic-cholinergic receptor (NAChR)
Endplate is/is not electrically excitable
is not
The membrane surrounding the endplate is/is not electrically excitable
is
Membrane surrounding the endplate contains
voltage-gated sodium and potassium channels
Current produced by EPP spread to surrounding muscle membrane and ________ it to _________
depolarized; threshold
Current activates ________________ __________ __________ and produces an
voltage-gated sodium channels; action potential
Ratio correspondence of motor neuron action potentials and action potentials in muscle
1:1
Voltage-dependent calcium channels (DHP receptors) located in
t-tubules
Activation of what channels allows calcium to flow out of the SR into cytoplasm
calcium release channels
What is in the SR membrane that pumps cytosolic calcium into the SR
calcium ATPase
Action potentials travel down sarcolemma from endplate into the ____________ and activate ___________ __________ ____________
t-tubules; voltage-gated calcium channels
Activation of voltage gated calcium channels activates
calcium release channels
Activation of calcium release channels causes release of
calcium from lateral sacs of SR
Calcium binds to
troponin
Troponin removes blocking action of
tropomyosin
Myosin cross-bridge bind to
actin
Sequestration of calcium into the SR decrease
cytosolic calcium concentrations
Calcium dissociates from
troponin
Once calcium dissociates from troponin, what ceases
cross-bridge cycling
One cross-bridge cycling ceases, the sarcomere
extends to resting length
Force generation produces shortening of skeletal muscle fiber, overlapping of filaments in each sarcomere, propelled by movements of cross-bridges
Sliding filament theory
Ability of muscle fiber to generate force and movement depends on
interaction of contractile proteins actin and myosin
Cross-Bridge Cycle
- energized cross-bridge binds to actin
- phosphate release from myosin for power stroke pulli actin towards center of sarcomere
- ATP binds to myosin head causes detach
- ATP hydrolyzed into ADP + Pi for new cross-bridge
If no ATP available for cross-bridge, it remains
attached to actin producing rigor mortis
Rigor mortis peaks
12 hours after death
rigor mortis disappears
48-60 hours after death due to breakdown of muscle
Regulator proteins
tropomyosin and troponin
Protein that intertwines with actin and covers myosin binding sites on actin
tropomyosin
protein binds to tropomyosin and holds it over myosin binding site
troponin
Subunits of troponin
inhibitory, calcium-binding, tropomyosin-binding
Calcium-binding sites are on
troponin
Binding of calcium to calcium-binding sites causes
change of troponin to move tropomyosin and expose myosin binding sites on actin
Endoplasmic reticulum-like organelles that store calcium in skeletal muscle (and cardiac) muscle fibers
sarcoplasmic reticulum (SR)
The SR surrounds the
myofibrils
Enlargements at the end of SR and is associated with the transverse tubule
lateral sacs
Invaginations of the muscle plasma membrane (sarcolemma)
transverse tubules (t-tubules)
Activation of motor neuron cell body leads to
an action potnetial
Action potential at nerve terminal of motor neurons causes release of
acetylcholine at neuromuscular junction
Acetylcholine activates
nicotinic receptors in endplate
Activation of nicotinic receptors produces a
end-plate potential
End-plate potential depolarizes the ____________ ___________ ___________ and produces an _________ ______________
surrounding muscle membrane; action potential
Action potential propagates to the
end of the muscle fiber
Action potential enters t-tubule and activates
voltage-gated calcium channels (DHP receptors)
Calcium is released from sarcoplasmic reticulum via
calcium release channels
Calcium binds to
troponin
Tropomyosin moves to uncover
myosin binding sites on actin
Once myosin binding sites are uncovered
cross bridge cycling begins
Calcium ATPase pumps calcium back into
sarcoplasmic reticulum
Once calcium ATPase pumps calcium back to the SR, calcium dissociates from
troponin
Once calcium dissociates from troponin, tropomyosin
covers myosin binding sites and cross bridge cycling ends
The plateau and descending limb of the isometric/concentric force-length relationship are well predicted and explained by the amount of
overlap between actin and myosin filaments
When muscle is stretched while activated and held at a final length long enough for force transients to cease, steady force achieved is higher than steady force developed when muscle is activated while already held isometrically at same final length
Residual Force Enhancement
Force enhancement after active muscle stretching was maintained when muscles were deactivated
Passive Force Enhancement
Force enhancement has a passive component and part of that passive components originates in the
molecular spring titin
Hypothesized that titin is a molecular spring whose stiffness can be regulated by
activation and/or force production
Titin extends from
sarcomere’s z-disc to m-band
Titin runs freely in the
I-band
Titin’s extensibility provdes sarcomeres with
passive force
Passive force from titin is thought to
maintain thick filaments during contraction and provide stability and uniformity to adjacent sarcomeres
Structural arrangement of serially aligned spring elements indicates titin’s stiffness can be
regulated
Skeletal muscles are activated by release of
calcium from SR
Stretching myofibrils within physiological limits results in
higher passive forces in presence of physiological levels of calcium
Deactivation of actively stretched myofibrils at an average sarcomere length of 5.0 um resulted in
no change in force
Passive structures of muscles are ________ and ________ when passively stretched out and become _________ and ___________ during active stretching
soft and compliant; hard and stiff
Titin forces increase when actin-myosin force
decrease
When titin is eliminated, all passive and active force transmission across sarcomeres is
lost
The long axis of a muscle determines the
arrangement of individual fibers
Differences in sarcomere alignment and length strongly affect a muscle’s
force and power generating capacity
Fibers run parallel to muscle’s long axis and taper at tendinous attachment
fusiform
Fan-shaped fiber’s fasciculi lie obliquely
pennate
Fusiform’s fiber length and fiber force generation transmits directly to
tendon
Fusiform fiber arrangement facilitates
rapid muscle shortening
In fusiform, what are equal
physiological and anatomical
In pennate, anatomical misses
some fibers
In pennate, physiological contains
all fibers
Total cross-sectional areas of all fibers within a particular muscle
Physiologic Cross Sectional Area
How do pennate differ from fusiform?
contain shorter fibers, possess more individual fibers, exhibit less range of motion
Muscles with greater pennation are slower in _______ _________, and generate greater _________ and __________
contractile velocity; force and power
Series-fibered muscle features
individual fibers that run parallel to muscle’s line of pull
Complex parallel arrangement features
muscle fibers that terminate in muscle’s midbelly and taper to interact with connective tissue matrix or adjacent fibers
Arrangement enables parallel packing of
short fibers within a long muscle
Force exerted by muscle on object
tension
Force exerted by object on muscle
Load
Contraction under conditions in which it develops tension but does not change length
isometric
Contraction in which muscle changes length while load on muscle remains constant
isotonic
When tension is greater than load, muscle shortens
concentric
Load is greater than tension on an unsupported muscle
eccentric
Contraction of muscle fiber in response to a single action potential
twitch
Keep length constant and measure tension
isometric twitch
Keep load constant and measure muscle length
isotonic twitch
Following action potential, an interval of a few ms known as latent period before tension of muscle fiber begins to increase
latency
Time interval from beginning of tension development at the end of the latent period to peak tension
contraction time
The latent period is longer in which twitch
isotonic twitch
Isometric twitch experiment, twitch tension begins to rise as soon as
first cross-bridge attaches
Isotonic twitch experiment, the latent period includes both time for ________________________ and extra time to accumulate enough _______________ _________________
excitation-contraction coupling; attached cross-bridges
Characteristics of isotonic twitch depend upon magnitude of
load being lifted
At heavier loads
latent period is longer, velocity of shortening is slower, duration of twitch is shorter, distance shortened is less
Maximum velocity with
zero load
Zero velocity at
maximum load
Unloaded shortening velocity is determined by rate at which
individual cross-bridges undergo cyclical activity
One ATP splits during each cross-bridge cycle, the rate of ATP splitting determines
shortening velocity
Increasing the load on a cross-bridge slows its forward movement during
power stroke
If interval between stimuli is long enough for tension to return to baseline, the amplitude of the second twitch will be
similar to the first
Increases tension due to second stimulus occurring before the tension returns to baseline
summation
Unfused Tetanus
oscillating summated tension
Fused Tetanus
sustained summated tension
Maximal tetanic tension is about _______ the tension of a single twitch
5x
Tension developed is dependent on
overlap of thick and thin filaments
Maximal tension occurs when
all of the myosin cross bridges can bind to actin
As muscle fiber is stretched, fewer cross bridges can bind to actin until no cross bridges can bind, meaning
no tension is developed
As muscle fiber shortened, thin filaments on one side will interfere with cross bridge formation on opposite side and this will
reduce tension developed
At very short lengths, the z-lines collide with ends of relatively rigid thick filaments, creating an
internal resistance to sarcomere shortening
Initial length that produces maximal active tension
optimal length
Muscles normally operate at plus/minus what % of optimal muscle length
30%
