exam 2 muscle contraction Flashcards
first step in muscle contraction
Action potential in motor axon reaches neuromuscular junction and releases ACh to the synaptic cleft
ACh is received by the motor end plate ACh receptors and opens Na+ channels on the muscle fiber
As a result, a new action potential is triggered within muscle fiber
second step in muscle contraction
Action potential is propagated (travels) through muscle fiber through a structure called transverse tubule
Spreading action potential causes calcium to be released from another bag like structure called sacroplasmic reticulum
What is the I-band?
Part of myofibril containing only actin filaments
The I-band appears lighter under a microscope due to the absence of myosin filaments.
What is the A-band?
Part of myofibril containing myosin and actin filaments
The A-band appears darker under a microscope and is essential for muscle contraction.
What is the H zone?
Part of myofibril containing only myosin
The H zone is located within the A-band and decreases in size during muscle contraction.
Sliding-Filament Theory Explained
Muscle contraction is caused by myosin and actin sliding by each other, without changing length.
final steps in muscle contraction
Calcium binds to troponin and allows actin to bind with myosin
Myosin head binds with actin
Actin filament is pulled over myosin filament
Myosin detaches from actin, returns to relaxed position and the cycle repeats
Motor unit:
muscle fibers it innervates
Motor Pool:
many motor units together that innervate one muscle
Motor units respond in an ———- fashion – when the threshold is reached, all muscle fibers in the unit fire
“all-or-none”
Grading of force is reflected in
The number of motor units which are active at one time (more motor units = more force)
The frequency of firing of the motor units (more firing = greater force)
