The series of events linking the electrical signal to muscle contraction
Extracellular space between the neuron terminal and the muscle cell membrane (sarcolemma)
The period during repolarizaton when the cell is insensitive to further stimulation
An action potential, once initiated, ultimately results in full contraction of the muscle cell
An enzyme located on the sarcolemma in the neuromuscular junction which degrades acetylcholine
lower motor neuron that comes from the spinal cord and muscle fibers it stimulates. They can be small or large.
the protein that is pulled toward the center of the sarcomere by the myosin during contraction
contains myosin heads that stick out in six different directions to pull thin filaments.
Step 1a - active site exposure
impulse from CNS, ACh released, diffuses across cleft, stimulates fiber/cell
Step 1c This movement exposes the binding site actin
Ca+2 diffuses out of sarcoplasmic reticulum, binds to troponin, alters its shape and position of tropomyosin
Step 3 "ratchetting"
"power stroke" myosin cross brindge bends, pulling thin filaments toward center of sarcomere + contraction/muscle fibers shorten
Step 5a Myosin reactivation
ATPase (enzyme in myosin) breaks down ATP, energy is released (catabolism), myosin uses energy to straighten its cross-bridge
Myosin cross-bridge can now combine with another binding site further down the actin filament and pull again
No more ACh = no stiumlation to sarcolemma = SR pumps Ca+2 back inside = no Ca+2 meansactin binding sites are covered
Ca+2 floods ICF from sarcoplasmic reticulum AND extracellular fluid, actin & myosin are binding but no ATP to break the myosin/actin bond
a quick way to get more ATP, used to convert ADP to ATP. provide ATP before aerobic metabolism only last 15 sec
Tropomyosin & troponin
proteins attached to actin that help control the myosin-actin interactions involved in muscle contraction
converted into lactic acid
What happens to pyruvic acid when there is a lack of oxygen in the muscle?
composed of the protein titin. Extends from the z disk to the thin filament and runs with it to attach to the m line
smooth ER that surround each myofibril. Mitochondria and glycogen granules produce energy during contraction
positioned on either side of the sarcomere and are pulled toward the center of the sarcomere during contraction
warm up effect
Single cell- can experience treppe effect where subsequent twitches can generate more force
Recruitment of motor unit
Whole muscle you have many motor units with different thresholds. Recruit more motor units for stronger whole muscle contraction.
Crossbridge step 1
1. Energized thick filament (give ATP and phosphorus.) Myosin heads in a cocked back position.
Crossbridge step 2 stimulus
2. Stimulus- causes binding sites on actin to be uncovered. Myosin heads bind to actin binding site.
Crossbridge step 3 powerstroke
"ratchetting" of myosin heads---thin filaments are pulled torward the center of the sarcomere. During the powerstroke the ADP & phosphorus leave the myosin head.
Crossbridge step 4
4. Myosin head detaches from the actin thin filament . This occurs when ATP binds to the myosin head.
Crossbridge step 5
5. ATP is hydrolyzed to ADP and inorganic phosphate to energize the myosin head and cock it back again.
"same-length" muscle generates the same force through whole muscle during contraction.
Intero sensory receptor
detect muscle stretch and contraction (shortening) Protects from overstretching
larger diameter, pailer color (less 02 carrier mypglobin,) faster contracting, less mitochondria, more anaerobic metabolism, can generate more power. Power lifting fatigues fast.
darker= myoglobin that carries the 02 to mitochondria for aerobic metabolism. High endurance but fairly low power.
when does crossbridge formation occur?
When myosin heads bind to actin molecules located on the thin filaments.