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BIOL 319: EXAM 2
functions of muscle (4) |
heat generation
posture
movement
stabilizing joints |
characteristics of muscle cells (4) |
excitability
contractibility
extensibility
elasticity |
connective tissue of skeletal muscle (3) |
1. epimysium - dense irregular CT
2. perimysium - fibrous CT
3. endomysium - reticular CT |
direct attachment (skeletal muscle) |
epimysium fused with periosteum (bone) |
indirect attachment (skeletal muscle) |
epimysium connected to bone by tendon or aponeurosis (dense CT) |
specialized components of sarcoplasm (2)
|
glycosomes - store glycogen
myoglobin - oxygen storing pigment (red) |
H-zone |
central light zone of dark A band (thick filaments only) |
M-line |
biseects H-zone of dark A band |
Z-disc |
bisects light I-bands; connects sarcomeres together |
thick filaments |
bundles of myosin
tails=2 interwoven heavy meromysin chains
heads=2 connected light meromysins |
thin filaments (of skeletal muscle) |
backbone of actin molecules
tropomyosin - spirals around backbone
tropinin - acts as hinge (ITC) |
tropomyosin |
spirals around actin core of thin filaments |
tropinin |
"hinge" of thin filaments
TnI - binds to actin (inhibitory)
TnT - binds to tropomyosin
TnC - binds to calcium |
terminal cisternae |
ends of SR; release Ca when stimulated by impulses from T-tubules |
T-tubules |
form triads with terminal cisternae; conduct impulses that signal release of Ca from TC |
sliding filament hypothesis |
contraction due to filaments sliding past each other
dark a band widens, h-zone disappears |
Phase 1 - muscle fiber stimulation by motor neuron (5) |
1. AP arrives at axon terminal of neuromuscular junction
2. ACh released
3. Ion permeability of sarcolemma changes
4. local change in membrane voltage (depolarization)
5. AP ignited in sarcolemma |
Phase 2 - E-C coupling (4) |
1. AP travels across sarcolemma
2. AP travels along T-tubules down into sarcomere
3. Ca binds to troponin, active sites of actin exposed
4. myosin heads bind to actin; contractions begin |
cross bridge cycle (4) |
1. cross bridge formation
2. power stroke (ADP released)
3. cross bridge detachment
4. cocking of myosin head (ATP hydrolyzed) |
Requirements to maintain muscle contraction (2) |
1. high sarcoplasmic [Ca]
2. constant supply of ATP |
phases of muscle twitch (3) |
latent period
period of contraction
period of relaxation |
wave summation |
graded muscle responses to changes in stimulus FREQUENCY
muscle still partially contracted when next stimulus arrives |
tetanus |
sustained contraction of summated twitches
unfused and fused |
Recruitment (or multiple motor unit summation) |
higher intensity = more unitis activated
helps prevent fatigue |
asychronous activation |
recruitment; some motor units rest while others contract |
isotonic contraction |
tension>load
tension constant, length decreases
thin filaments sliding
1. concentric (shortening)
2. eccentric (lengthening) |
concentric isotonic contraction |
muscle shortens as it produces tension
ex-picking up heavy object |
eccentric isotonic contraction |
muscle lengthens as it produces tension
ex-setting down heavy object
more force than conceaerntric |
isometric contraction |
tension<load
tension increases, length constant
cross bridges generating force but not moving thin filaments
ex-muscle tone |
atp generation-aerobic metabolism |
low intensity, long (unlimited) duration
32 ATP/glucose
dependent on O2 from blood |
factors affecting muscle fatigue (3) |
depletion of fuels/CP
ionic imbalances
lactic acid build up (if anaerobic) |
cotractures |
state of continuous contraction
result of complete ATP depletion
crossbridges unable to detach |
brain regulation of metabolism 34) |
1. monitors chemical changes in blood
2. monitors degree of muscle stretch
3. monitors body temp |
steps to restoring cellular metabolic environment (5) |
1. decrease temp
2. restore glycogen stores
3. restore CP (via ox)
4. restore Oxygen stores
5. detoxify lactic acid in liver (Cori Cycle) |
ability of muscle to do work depends on... (3) |
force
velocity
duration |
factors affecting force (4) |
# muscle fibers
size of muscle fibers
frequency of stimulation
degree of muscle stretch |
hypertrophy |
increases sacromere size, adds myofilaments
from hormones, androgens, or exercise |
internal tension |
generated by sarcomeres (contractile units); force generated by cross bridges |
external tension |
CT (noncontractile units) stretch and exert tension from sarcomeres to load |
length-tension relationship |
amt of force depends on length of resting muscle
produce max force when stimulated at 100% resting length |
fascicle arrangements of muscle (5) |
circular sphincters (eye)
parallel (sartorius)
convergent
fusiformpenate (feather)
uni-, bi-, and multipennate |
smooth muscle contraction |
1. Ca enters cytosol from ECF
2. Ca binds to calmodulin
3. act calmodulin activates MLCKE
4. MLCKE phosphorylates myosin (ATP-->ADP)
5. activated myosin forms cross bridges with actin |
regulation of smooth muscle contraction (3) |
spontaneous depolarization
mechanical stimulation
hormonal factors |
stress-release response |
smooth muscle; allows hollow organ to expand and fill (mech. stimulation) |
diffuse junctions |
junctions where neurotransmitters from viscosities diffuse to smooth muscle |
single unit smooth muscle |
linked by electrical gap junctions; entire sheet contracts together
contraction initiated by stretch/hormonal factors (intestine/uterus) |
multiunit smooth muscle |
not electrically linked; independent contraction; initiated by stretch/hormonal factors (BVs, airway, eye muscles) |