Muscle Physiology Flashcards
Events at the NEUROMUSCULAR JUCTION: Part one - In the SYNANPTIC KNOB of SOMATIC MOTOR NEURON
- AP opens voltage-gated Ca2+ channels
- Ca2+ influx triggers exocytosis of SYNAPTIC VESICLES
- Ach diffuses across SYNAPTIC CLEFT
Events at the NEUROMUSCULAR JUNCTION: Part two - At the motor end plate of SKELETAL MUSCLE FIBER
- Ach binds ligand-gated channels
- Na+ influx depol. MUSCLE FIBER to threshold
- AP generated along SARCOLEMMA
- AchE removes Ach and stops signal
What does the āEā is AchE stand for?
AcetylcholinESTERASE
After travelling along the SARCOLEMMA, where does AP go?
Down the TRANSVERSE TUBULES
What kind of channels does AP open in the TERMINAL CISTERNAE of SR?
Voltage-gated Ca2+ channels
Where is Ca2+ released into?
The CYTOSOL
What does Ca2+ bind to?
TROPONIN
When TROPONIN changes shape, what effect does it have on TROPOMYOSIN?
It moves TROPOMYOSIN to expose the MYOSIN binding sites on ACTIN
How does Ca2+ get back into the SR?
A PUMP
What would happen if Ca2+ pumps stop working?
Ca2+ will build up and the MUSCLE will stay contracted, no relaxation
What is it called when MYOSIN HEADS bind to ACTIN?
The CROSS BRIDGE
What happens during a POWERSTROKE?
MYOSIN pulls ACTIN, shortening the SARCOMERE and causing CONTRACTION
What releases MYOSIN from ACTIN?
ATP
What provides energy for the MYOSIN HEAD to re-cock for another POWERSTROKE?
ATP splitting
How many times does the CROSS BRIDGE CYCLE repeat?
Many times
ISOTONIC, CONCENTRIC CONTRACTION = ?
Muscle shortens e.g. lift object
ISOTONIC, ECCENTRIC CONTRACTION = ?
MUSCLE lengthens e.g put down object
ISOMETRIC CONTRACTION = ?
MUSCLE stays the same length e.g. holding object, maintaining body position
CONTRACTION of many SACROMERES leads to
CONTRACTION of many MYOFIBRILS
CONTRACTION of many MYOFIBRILS leads to
CONTRACTION of MUSCLE FIBERS + pull on ENDOMYSIUM
CONTRACTION of MUSCLE FIBERS leads to
CONTRACTION of MUSCLE FASCICLE + pull on PERIMYSIUM
CONTRACTION of MUSCLE FASCICLE leads to
CONTRACTION of whole MUSCLE + pull on EPIMYSIUM
CONTRACTION of whole MUSCLE pulls on TENDON which pulls on
PERIOSTEUM/BONE
T or F: Do MUSCLES push
F, they pull
How many MUSCLE groups are required for action?
At least 2
What are the 4 functional MUSCLE groups?
1) PRIME MOVERS
2) ANTAGONISTS
3) SYNERGISTS
4) FIXATORS
PRIME MOVER =
a force for specific movement, aka AGONIST e.g. BRACHIALIS for arm FLEXION
ANTAGONIST =
Reverse, slow, stop movement e.g. TRICEPS BRACHII for arm FLEXION
SYNERGISTS =
Stabilize joints, aids PRIME MOVER movement e.g. BICEPS BRACHII
FIXATORS =
Holds BONES in place e.g. rotator cuff MUSCLES
How long does AP last?
1-2 msec
How long does CONTRACTION last?
7-100 msec
What leads to TETANUS
Many consecutive APs
1 MOTOR UNIT =
1 MOTOR NEURON + all MUSCLE FIBERS it innervates
What factors effect CONTRACTION?
1) Freq. of STIM.
2) Number of MUSCLE FIBERS contracting
3) Type of MUSCLE FIBER
How many MUSCLE FIBERS/MOTOR UNITS for precise movement?
About 10
How many MUSCLE FIBERS/MOTOR UNITS for powerful movement?
About 1000
What is the benefit of MOTOR UNITS recruited in shifts?
Allows sustained CONTRACTION without fatigue
An immediate source of energy:
One step transfer of E and PHOSPHATE from CREATINE PHOSPHATE (CREATINE PHOSPHATE + ADP = CREATINE + ATP)
Sustained E sources:
AEROBIC and ANAEROBIC RESPIRATION
AEROBIC RESP. =
Requires O2, makes 32 ATP/GLUCOSE, many steps = slooow
ANAEROBIC RESP. =
No O2, makes 2 ATP/GLUCOSE, few steps, makes LACTIC ACID = changes pH
Slow-oxidative fibers =
Slow to contract/fatigue, uses AEROBIC, mitochondria, many caps, hi myoglobin, appear red
e.g. MUSCLES of leg, back, marathon, endurance
Intermediate fibers =
intermediate resistance to fatigue, AEROBIC, some mitochondria, some caps, lo myoglobin, appears pink
Fast-glycolytic =
fast to contract/fatigue, fast/powerful, but not for long, ANAEROBIC, more MYOSIN, ACTIN = larger diameter fibers, appears white
MUSCLE fatigue is caused by
1) Dec. E reserves
2) Damage to MUSCLE FIBER
3) Dec. pH leading to dec. Ca2+ binding to TROPONIN
4) Central fatigue: mental, pain, dec. motor recruitment
O2 debt =
Amount of O2 required to restore levels of ATP, CREATINE PHOSPHATE, GLYCOGEN, remove lactic acid, power sweat gland activity
