CH 1 Flashcards
smooth muscle
involuntary, hollow organs like bronchioles, GI tract, blood vessels
not striated
cardiac muscle
involuntary, heart
skeletal muscle
voluntary, needs neural stimulation
mysium
connective sheaths that transfer force production
epimysium
surrounds the entire muscle
perimysium
surrounds singular fasciculus
fasciculus
bundle of muscle fibers
endomysium
surrounds individual muscle fiber
tendon
connects muscle to bone
sarcolemma
the plasma membrane of a muscle fiber
transverse tubules
enfolding of the sarcolemma
sarcoplasmic reticulum
wrap completely around the fiber, stores Ca+2
myofibrils
column containing myofilaments
mitochondria
ATP production
sarcomere
the functional unit of a myofibril, Z-line to Z-line
myofilaments
contractile filaments of a sarcomere (actin and myosin)
actin
thin contains myosin-binding sites
myosin
thick contains head to form cross-bridge
tropomyosin
lies within the groove of actin
troponin complex
protein bound to tropomyosin, Ca+2 binds
alpha-motor neurons
innervate muscle fibers
motor unit
single alpha-motor neuron and all its fibers it innervates
more motor units = more force
neuromuscular junction
site of communication between neuron and muscle
ligand-gate channel
opens in response to binding of a chemical messenger (neurotransmitter)
voltage-gated channel
opens by changes in electrical membrane potential near the channel (depolarization)
skeletal muscle charge at rest
-90mV
action potential
occur in response to depolarization (becomes more +)
ion responsible for depolarization
Na+
ion responsible for repolarization
K+
voltage-gate Ca+2 channel
allows Ca+2 to enter when depolarized
ACh
neurotransmitter released within the synaptic cleft
motor endplate
part of the muscle at the NMJ
steps of an action potential
1) motor neuron AP travels to the synaptic terminal
2) AP opens Ca+2 channels
3) Ca+2 enters synaptic terminal, release ACh, ACh binds to Na+ ligand channels
4) Na+ enters, motor endplate depolarizes
5) Na+ enters muscle fiber, sarcolemma depolarizes (more+)
6) depolarization spreads across the sarcolemma
7) depolarization continues down t-tubules, depolarization of t-tubules
8)opens Ca+2 channels in SR, released from SR into the
cytosol
9) Ca+2 binds to troponin causing conformational change to tropomyosin, exposes cross-bridge binding sites on actin
cross-bridge formation
1) cross-bridge binds to actin, depolarization, Ca+2 binds to troponin, cross-bridge site exposed, myosin heads energized, binds to actin
2) ADP + Pi released from cross-bridge, results in Powerstroke of cross-bridge, sarcomere shortens
3) ATP binds to myosin cross-bridge, detach actin
4) hydrolysis of ATP energizes cross-bridge, myosin reenergized
sliding filament theory
always begins with depolarization
1) Ca+2 released from SR
2) Ca+2 binds to troponin, conformational change to tropomyosin
3) cross-bridge binding sites on actin become exposed
4) energized myosin heads bind actin
5) ADP + Pi release from cross-bridge, Powerstroke
6) sarcomere shortens
7) ATP binds to myosin cross-bridge
8) cross-bridge release from actin
9) myosin ATPase breaks down ATP, release energy captured by the myosin head
9) myosin head reenergized
a-band
length of myosin molecule, unchanged with length, contain both actin and myosin
I-bands
contain only actin, length reduced
H-zone
contains only myosin, length reduced
Z-lines
borders of the sarcomere
type I muscle fiber
slow-twitch, response to single AP, slow oxidative, high fatigue, high oxidative capacity,
type II
fast-twitch, larger
type IIa
fast oxidative/glycolytic (FOG), small cell body,
type IIx
fast glycolytic (FG)
type I during exercise
high aerobic endurance, maintain exercise for long times, requires oxygen, recruited during low intensity, daily activities, uses fat for ATP
type IIa during exercise
fatigue quickly, faster, short, high-intensity endurance events
type IIx during exercise
short, explosive activities
fiber type determinants
genetics
training factors
aging
recruitment order
type I, type IIa, type IIx
size principle
as force requirements increase, there is orderly recruitment of progressively larger motor units directly related to the size of alpha-motor neuron
static (isometric) contraction
muscle produces force but doesn’t change length, attempts Powerstroke but doesn’t occur
joint angle doesn’t change
myosin cross-bridge form and recycle, no sliding
dynamic contraction
muscle produces force and length, joint movement
concentric contraction
muscle shortens while producing force
eccentric contraction
muscle lengthens while producing force
two factors of generation of force
1) motor unit recruitment
2) frequency of stimulation
length-tension relationship
optimal sarcomere length = optimal overlap
too short or too stretched = little or no force
speed-force relationship
“force-velocity relationship”
max force development decreases at higher speeds during concentric muscle actions
