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Musculoskeletal System
Consists of muscles and skeletons--the effectors that produce movement. TERM 2
What are the three types of vertebrate
muscle?
DEFINITION 2 Skeletal : Voluntary movement, breathing. Cardiac : Beating of the heart. Smooth : Involuntary, movement of internal organs. TERM 3
Skeletal Muscle ("Striated")
DEFINITION 3 Cells are called muscle fibers. They are extremely large, multinucleate cells. Form by fusion of embryonic myoblasts. One muscle consists of many muscle fibers bundled together by connective tissue. TERM 4
Myofibrils
DEFINITION 4 Highly ordered assemblages of thick myosin and thin actin filaments. Numerous myofibrils make up each muscle fiber. Consists of repeating units: sarcomeres. TERM 5
What are the two contractile proteins found in
myofibrils?
DEFINITION 5 Actin : Thin filaments. Myosin : Thick filaments.
Sarcomere
Overlapping actin and myosin filaments. TERM 7
Titin
DEFINITION 7 A protein that holds bundles of myosin filaments in place. Titin is the largest protein in the body. TERM 8
Describe the sliding filament mechanism of
muscle contraction.
DEFINITION 8 Myosin heads can bind specific sites on actin molecules to form bridges. Myosin changes conformation, causes actin filament to slide 5-10 nm. TERM 9
What are the three components of actin?
DEFINITION 9 Actin monomer Tropomyosin Troponin TERM 10
What are the functions of the three subunits
of Troponin?
DEFINITION 10 Binds Actin Bind Tropomyosin Binds Ca2+
Action potentials travel deep within muscle
fibers via ______.
T tubules; T tubules (transverse tubules) descend into the sarcoplasm (muscle fiber cytoplasm). TERM 17
Give a description of the muscle contraction
process.
DEFINITION 17 An action potential arrives at the motor neuron terminal and vesicles of Ach are released. The neuromuscular synapse generates an action potential that spreads down T tubules, which causes the release of Ca2+ stored in the sarcoplasmic reticulum. Released Ca2+ diffuses in the sarcoplasm, stimulating muscle contraction. Ca2+ is taken up by the sarcoplasmic reticulum, terminating muscle contraction. TERM 18
The _________ is a closed compartment that
surround every myofibril.
DEFINITION 18 sarcoplasmic reticulum; the sarcoplasmic reticulum is a fancy name for the endoplasmic reticulum of muscle cells. Has Ca2+ pumps. At rest there is a high concentration of Ca2+ in the lumen of the sarcoplasmic reticulum. An action potential will open the Ca2+ channels, Ca2+ flows out of the sarcoplasmic reticulum and triggers interaction of actin and myosin. TERM 19
At rest, ______ blocks the binding sites on
actin.
DEFINITION 19 tropomyosin TERM 20
What are the chain of events that occur after
the release of Ca2+ from the sarcoplasmic
reticulum?
DEFINITION 20 Ca2+ is the sarcoplasm binds troponin and exposes myosin- binding sites on the actin filaments. Myosin heads bind to actin; release of Pi initiates power stroke. In the power stroke, the myosin head changes conformation; filaments slide past one another. ADP is released; ATP binds to myosin, causing it to release actin. ATP is hydrolyzed, and the myosin head returns to its extended conformation.
Cardiac Muscle
Striated. Cells are smaller than skeletal muscle cells. Cells have one nucleus. Cardiac muscle cells also branch and interdigitate: can withstand high pressures. TERM 22
______ and ______ initiate and coordinate heart
contractions.
DEFINITION 22 Pacemaker; conducting cells The heartbeat is myogenic --generated by the heart muscle itself. The autonomic nervous system modifies the rate of pacemaker cells, but is not necessary for their function. This makes heart transplantations possible. TERM 23
Cardiac and smooth muscle cells are
arranged in ______.
DEFINITION 23 sheets TERM 24
Cells in the smooth muscle sheets are in
electrical contact via _______.
DEFINITION 24 gap junctions; An action potential in one cell can spread to all others in the sheet. This allows for synchronized contractions. TERM 25
Gap Junctions
DEFINITION 25 Connect the cytoplasm of two neighboring cells. Allows direct electrical communication between cells. Allows passage of molecules smaller than ~1, Daltons. Allow cardiac and smooth muscle cells to contract simultaneously.
Immediate System
Muscles contain creatine phosphate (CP) which stores energy in a phosphate bond that can transfer to ADP. Immediate system = ATP + CP. This system is exhausted within seconds. TERM 32
Glycolytic System
DEFINITION 32 Enzymes are in the cytoplasm (sarcoplasm). ATP generated is directly available to myosin (fast). Anaerobic. Not very efficient (low ATP yield). Lactic acid accumulates. TERM 33
Immediate and glycolytic systems provide
energy for ______.
DEFINITION 33 less than one minute TERM 34
Oxidative Phosphorylation
DEFINITION 34 Produces large amounts of ATP. Aerobic. Occurs in mitochondria. ATP must diffuse from mitochondria to the myosin in the cytoplasm ( slower than the other two systems) TERM 35
What are the two main types of skeletal
muscle fibers?
DEFINITION 35 Slow-twitch Fast-twitch
Slow-Twitch Muscle Fibers
"Oxidative" or "red" muscle. Contain myoglobin : oxygen binding protein. Contain many mitochondria. Are well-supplied with blood vessels. Maximum tension develops slowly, but is highly resistant to fatigue. Have reserves of glycogen and fat; can produce ATP as long as oxygen is available. Muscles with high proportion of slow-twitch fibers are good for aerobic work (e.g., long distance running, cycling, swimming). TERM 37
Fast-Twitch Fibers
DEFINITION 37 " Glycolytic " or " white " muscle. Fewer mitochondria, fewer blood vessels, little or no myoglobin. Develop greater maximum tension faster, but fatigue more quickly. Can't replenish ATP for prolonged contraction.. TERM 38
What determines muscle strength and
endurance?
DEFINITION 38 The proportion of fast- and slow-twitch fibers in skeletal muscles is determined mostly by genetic heritage. Training can alter muscle properties to a certain extent. TERM 39
______ activities increase muscle strength;
new actin and myosin filaments form, muscle
gets larger.
DEFINITION 39 Anaerobic TERM 40
______ activities increase endurance:
oxidative capacity is enhanced by increasing
number of mitochondria, blood vessels,
myoglobin, and enzymes.
DEFINITION 40 Aerobic
