Section 4 - Skeletal muscle contraction Flashcards
Can you name the two types of filament involved in the contraction of skeletal muscles?
Actin and myosin (their binding allows contraction)
True or false? One nerve fiber usually innervates only one muscle fiber
FALSE ( multiple muscle fibers)
What is the definition of skeletal muscles?
Muscles that surround the skeleton + are composed of numerous muscle fibers/cells
What are excitable cells who generate and propagate action potentials + are innervated by nerve fibers to cause muscle contraction?
Muscle fibers
Which disease is characterized by the degeneration of
alpha motoneurons in the spinal cord and brain stem?
A. Multiple sclerosis
B. Parkinson’s disease
C. Muscular dystrophy
D. Alzheimer’s disease
E. Amyotrophic lateral sclerosis)
E. Amyotrophic lateral sclerosis (ice bucket challenge)
What is the name of the nerve fibers that cause muscle contraction?
Motor neurons
Define what is a sarcolemma:
The membrane of the muscle fiber that surrounds myofibrils
Each myofibril is composed of two contractile elements called “myofilaments”, what is the thick one and the thin one called?
Thick = myosin Thin = actin
Where does the contraction of a muscle takes place?
In the sarcomeres
What is the smallest contractile unit of muscle fibers? What separates them?
Sarcomeres are separated by Z discs
T or F : What causes the actin filaments to slide inward
among the myosin filaments is the forces generated by the interaction between the two filaments
TRUE
How do we call the binding of actin and myosin?
Power stroke
T or F : The actin filaments are composed of a body and cross-bridges
False, actin filaments are composed of actin, tropomyosin and troponin
What is the role of the tropomyosin molecule in the actin filament?
Hide/covers the active sites during relaxed state
What molecule moves the tropomyosin from active sites?
Troponin
What does Ca2+ do during a muscle contraction? explain
Ca2+ is released and Ca2+ ions bind on troponin, which makes a change in the molecule to let the tropomyosin move away = uncovering the active sites
What happens to the myosin filaments when the active sites are uncovered?
The myosin cross bridges (heads) are attracted to the active site of the actin (see p.11 image)
Tension developed in responses to one nerve stimulation
Muscle twitch (contraction)
Describe the first summation process : multiple fiber summation
Increasing the number of motor units contracting at the same time
Describe the second summation process : frequency summation
Increasing the frequency of stimulation of one motor unit
T or F : Largest motor units are recruited first for strong stimulation
False, smallest motor units are recruited first for weak stimulation
If the frequency reaches a critical level, the summated twitches fuse together to form one continuous contraction : ???
Tetanization
Ca2+ reaches a max level = no response to further stimulations
Ca2+ ions are maintained in the sarcoplasm, the contractile state of the muscle is sustained (actin and myosin stay attached)
T or F : when the frequency of the signal increases, individual twitches summate and there is no recovery from previous contractions
TRUE