L13, 14 & 15: Muscle Physiology Flashcards
three types of muscle?
skeletal, cardiac, smooth
skeletal properties?
multinucleate, unbranched, voluntary activity
cardiac properties?
1 or 2 nuclei, branched, non-voluntary
smooth
single nucleus, unbranched, non-voluntary
skeletal muscles are connected
to at least two bones
an exception of the two-bone rule
biceps
muscles are connected to bones with
tendons, connective elastic tissue
muscle bodies are covered by
epimysium
muscle bodies are divided into
fascicles
fascicles are covered by
perimysium
fascicles contain
muscle fibers
muscle fibers are covered by
endomysium
a muscle fiber semifluid cytoplasm
sarcoplasm
contractile machinery in sarcoplasm
myofibrils
plasma membrane of a musle fiber
sarcolemma
surrounds each myofibril
sarcoplasmic reticulum
fundamental unit of myofibril
sarcomere
sarcomere elements
a band, i band, z line, m line, h zone
z line
end of sarcomere, links thin filaments
m line
middle of sarcomere, links thick filaments
i band
thin filaments only
h zone
thick filaments only
a band
thick filaments + overlap
which band is dark?
a band
which band is light?
i band
myosin parts
head, neck, tail
myosin types
myosin I inside the cell, myosin II in muscles
muscle contracts by
a sliding filament mechanism
cross-bridge steps
cross-bridge formation, power stroke, cross-bridge detachment, reactivation of myosin
cross-bridge formation?
activated myosin head with ADP and Pi binds to actin site, then Pi is released, the bond becomes stronger
power stroke?
ADP is released, sliding microfilament due to pivoting of the head
cross-bridge detachment?
ATP binds the head, the actin-myosin bond weakens, myosin head detaches
you got this!
you got this!
reactivation of myosin?
ATP is hydrolyzed to ADP and Pi, the energy activates the head, moves to the cocked position
does the H zone length change due contraction?
yes
does the Z distance change due to the contraction?
yes
does the A band length changes due to the contraction?
no
does the I band length change due to contraction?
yes
tropomyosin is
a rod-shaped protein, overlaps 7 actin monomers, covering myosin-binding sites
troponin is
a 3 subunit protein with TnC subunit doing Ca2+ binding
what causes uncovering of myosin-binding sites?
Ca2+ to TnC of troponin results in a conformational change of tropomyosin
what works together to coordinate contraction
transverse (t-)tubules and sarcoplasmic reticulum
what carries electrical information in muscle fibers?
by T-tubules
what releases calcium?
sarcoplasmic reticulum
muscle contraction step 1
action potential stimulates the muscle
muscle contraction step 2
muscle action potential goes to the T-tubule
muscle contraction step 3
t-tubules make SER release Ca2+
muscle contraction step 4
ATP and Ca2+ are required for thick-thin filament
muscle contraction step 5
electrical potential returns to normal, Ca2+ is pumped back to SER by Ca2+ pump proteins
what releases Ca2+ ions into the cytoplasm from SER
ryanodine receptors
what activates ryanodine receptors
voltage-gated protein, dihydropyridine (DHP) receptor in the T-tubule membrane
what triggers the DHP receptor?
muscle action potential
the only mechanism to stimulate an action potential
activation of motor neuron
motor neurons are located in
ventral horn
motor neuron axons are
myelinated and largest diameter
do motor neurons have a delay?
no
motor unit
motor neuron plus all muscle fiber it innervates
neuromuscular junction
junction of an axon terminal with the muscle fiber plasma membrane
the first major difference between interneuronal synapses and NMJs
a single depolarization of motor endplate is much larger
why is the depolarization of NMJ is larger than of interneuronal synapse?
larger area, more N-AChRs
second major difference between interneuronal synapses and NMJs
no inhibitory potentials in NMJs
tubocurarine
nondepolarizing neuromuscular blocking agent, antagonists, relaxes muscles
nicotine
N-ACh-R agonist
muscarine
M-ACh-R agonist
atropine
M-ACh-R antagonist
isometric contraction
no shortening, static
isotonic contraction
change of length, dynamic
concentratic contraction
tension > load, result
eccentric contraction
load > tension, no result
latent period
onset of contraction, few msec
contraction phase
tension increasing, 10-100 msec, calcium levels increases, release exceeds reuptake
relaxation phase
tension decreasing, long, cytosolic calcium levels decrease, reuptake exceeds release
types of isotonic contraction
concentric, eccentric
as load increases, plateau times
decreases
as load increases, latent period
increases
eventually, isotonic movement becomes
isometric
summation
increase in muscle tension from successive action potentials
unfused tetanus
at low stimulation frequencies, the tension may oscillate as the fiber partially relaxes between stimuli
fused tetanus
at higher stimulation frequencies tension does not oscillate, it becomes 3-5 times greater than isotonic twitch
twitch
same tension over a period of time
during tetanus, Ca2+ concentration
persistently elevated
the magnitude of active tension depends on
muscle fiber length
shorter than optimum length
thin filaments overlap, causing a decline in tension
beyond optimum length
decreased overlap between thin and thick filaments, no binding of myosin heads to actin
ATP is used in the skeletal muscle to… reason 1
dissociate myosin heads from actin
ATP is used in the skeletal muscle to… reason 2
energize the myosin heads when hydrolyzed
ATP is used in the skeletal muscle to… reason 3
lower cytosolic Ca2+ levels via Ca2+ pump in the SER
ATP is used in the skeletal muscle to… reason 4
restore ions that cross the cell membrane to their original compartment the Na+ K+ ATPase
three ways of ATP formation
phophorylation of ADP by creatine phosphate, glycolysis, oxidative phosphorylation
fatigue
muscle is no longer able to generate or sustain the expected power output
fatigue depends on
intensity and duration of activity, metabolism, muscle composition, fitness level
two types of fatigue
central and peripheral
_ fatigue comes before physiological fatigue
phychological
central fatigue
changes proximal to motor neuron, motivation, recruitment
peripheral fatigue
motor unit itself, exhaustion of muscle energy supplies
high-frequency fatigue
fast fatigue, fast rest period
low-frequency
long duration, long rest period
extended submaximal exertion
depletion of glycogen stores, decreased Ca2+ release
short-duration maximal exertion
increased level of inorganic phosphate, altered power stroke
maximal exercise
K+ rise in the t-tubule ECF, altering the muscle fiber membrane potential
muscle fibers are classified on the basis of
maximal velocities of shortening and the major pathway used to form ATP
high ATPase activity
fast and type II fibers
low ATPase activity
slow and type I fibers
major pathways to form ATP
oxidative and glycolytic
oxidate fibers have lots of
myoglobin
myoglobin
oxygen-binding protein, gives fibers dark red color
fiber with glycolytic enzymes
white muscle fibers
three principal types of skeletal muscle fibers
slow-oxidative (type I), fast-oxidative glycolytic fibers (type IIa), fast-glycolytic fibers (type IIb)
type I fibers description
low myosin ATPase activity, high oxidative capacity
type IIa fibers description
high myosin ATPase activity, high oxidative capacity, intermediate glycolytic capacity
type IIb fibers description
high myosin ATPase activity with high glycolytic capacity
type I fatigue?
resistant to fatigue, maintain long periods of contractile activity
type IIa fatigue?
intermediate capacity to resist fatigue
type IIb
fatigue rapidly
singe motor unit is composed of
single fiber type
recruitment order
first type IIb, then type IIa, then type I
