Ch. 11 - Musculoskeletal System Flashcards
What are the 3 kinda of muscle fibers?
Skeletal muscle
Smooth muscle
Cardiac muscle
Skeletal muscle:
1) Responsible for ___?
2) Innervated by ___?
3) sarcomere
4) Nucleation of skeletal muscle?
5) Red Fibers
6) White Fibers
1) voluntary movement
2) Somatic nervous system
3) repeating unit of actin and myosin
4) multinucleated because skeletal muscle consists of many fused individual cells
5) slow twitch fibers, high myoglobin content and high mitochondria content because derive energy aerobically
6) fast twitch fibers contain much less myoglobin, contract rapidly but fatigue quickly
Smooth Muscle:
1) Responsible for ___?
2) Innervated by ___?
3) Nucleation?
4) Made up of ___ and ___?
1) involuntary action
2) Autonomic nervous system
3) Have a single nucleus in center of cell
4) actin and myosin, but much less organized arrangement than skeletal muscle so no striation
Myogenic activity
Contraction without nervous system input, happens in smooth muscle and cardiac muscle
Cardiac Muscle:
1) Characteristics of ___ and ___?
2) Nucleation? striation?
3) Contraction is ___?
4) How do cardiac muscle cells communicate?
1) smooth and skeletal muscle
2) Cells are not usually nucleated, but the muscle does appear striated
3) Involuntary, Innervated by autonomic NS
4) connected by intercalated discs that contain gap junctions which allow for flow of ions directly between the cytoplasm of the cells allowing for rapid and coordinated depolarization and thus contraction
What do all muscle cells require for contraction?
Calcium
What is a thick filament?
Myosin
What is a thin filament?
Actin
Think: “acthin”
What 3 molecules are associated with the thin filament actin and what is their function?
Troponin + tropomyosin = regulate interaction between actin and myosin
Titin = anchors actin and myosin together to prevent excessive stretching
THINK: “all these compounds start with t and actin has a t in it while myosin does not”
To remember the parts of the sarcomere:
Z is the end of the alphabet so the Z line is___
M is the middle of the ___?
I is a thin letter so it represents ___?
H is a thick letter so it represents___?
All of the thick filament is contained in the ___?
The end of the sarcomere
Myosin filaments (thick filaments)
The part of the sarcomere that is thin filaments only
The part of the sarcomere that is thick filaments only
A band
Sarcoplasmic Reticulum
Modified endoplasmic reticulum that contains a high concentration of Ca2+
Sarcolemma and T - tubules
Sarcolemma is cell membrane of myocyte and is capable of propagating action potential and can distribute it across all sarcomeres In muscle using t tubules that are perpendicular to myofibrils
What are the 3 steps of muscle contraction?
Initiation
Contraction (shortening of sarcomere)
Relaxation
Explain the initiation of muscle contraction.
At the neuromuscular junction, motor neurons synapse with muscle cells (myocytes) and release acetylcholine into synapse, which binds to receptors on sarcolemma which causes depolarization. This triggers an action potential which spreads down the sarcolemma to the t-tubules, which are in contact with sarcoplasmic reticulum. Action potential reaching the SR promotes release of Ca2+, which binds to troponin. Troponin is bound to tropomyosin so when Ca2+ binds it causes a conformational change in tropomyosin, which exposes myosin binding sites on actin.
Explain the shortening of the sarcomere.
Once myosin binding sites exposes in actin, myosin heads carrying ADP + Pi can bind to actin forming cross bridges. This prompts the ADP + Pi to release from the myosin head and it is this DISSOCIATION that provides the energy for the power stroke that results in the myosin head sliding the actin filament over the myosin filament. Once that occurs, ATP binds to the myosin head, which releases it from actin. The bound ATP is hydrolysis to ADP + Pi which recocks the myosin head for another cycle.
