Lecture Week 11 Flashcards
Sliding Filament of Skeletal Muscle Contraction (thin)
Proteins involved
1. Thin myofilaments
—actin forms two chains slightly wound together
—tripomyosin binds to each actin chain, blocking actin/myosin binding sites
—troponin binds to tropomyosin
—when calcium binds to troponin, tropomyosin moves and actin/myosin binding sites are exposed
Sliding Filament of Skeletal Muscle Contraction (thick)
- Thick myofilaments
—each myosin has a tail and a head
—tails form the core of the myofilament and heads stick out (lean toward end they are closest ot)
—myosin heads bind to thin myofilaments at the actin/myosin binding sites
Sliding Filament Model of Skeletal Muscle Contraction (ATP)
ATP is involved
1. ATP binds to myosin head and causes it to detach from thin myofilament
2. ATP breaks down to ADP and P which allows myosin head to cock
3. head binds to actin binding site forming a crossbridge
4. ADP and P are released from the head and it reverts to original shape (fires)
5. repeat
Stimulus for Contraction
-ACh released from synaptic vesicles of a motor neuron binds to chemical gated sodium channels on the muscle fibers motor end plate
-threshold depolarization -> action potential -> muscle impulse
-impulse travels along the sarcolemma and intro transverse tubules
-SR releases CA2+ into sarcoplasm
-Ca2+ binds to troponin and actin/myosin binding sites are exposed
The Sarcomere During Contraction
Sarcomere shortens, I bands shorten, H zones disappear, A bands stay the same
After Neural Stimulation Stops
-ACh degraded by acetylocholinesterase in the synaptic cleft
-CA2+ is returned to the SR by calcium pumps performing active transport
-crossbridges break
-tropomyosin covers actin/myosin binding sites
-sarcomere returns to original length
What is a myogram?
Recording of a muscle contraction
What is a twitch?
Contraction resulting from a single threshold stimulus
-latent period, contraction period, relaxation period
What is atrophy?
Decrease in muscle size due to lack of use (ex. bedridden)
-cells lose filaments but muscle does not lose cells
What is hypertrophy?
Increase in muscle size due to use (ex. weight training)
-cells gain filaments or myofibrils but muscle does not gain cells
Treppe (Staircase Effect)
-Occurs when a muscle fiber that has not recently contracted is subjected to repeated stimulation (provided complete relaxation between contractions)
-first few contractions will show increasing contraction strength
Wave Summation
-Occurs when a muscle is subjected to repeated stimulation (without complete relaxation between contractions)
-Strength of sustained contraction increases to maximum level called tetanus
Muscle Tone
State of partial sustained contraction that assists in posture and keeps muscles tight
Recruitment
-Contraction strength of a skeletal muscle is a result of the number of motor units that are being stimulated
-recruiting more motor units increases strength of contraction
-during sustained contraction, motor units contract on a rotating basis called asynchronous motor unit summation (take turns to synthesize ATP)
ATP Sources for Contraction
- Stored ATP - use first to supply energy
- ATP generated from creatine phosphate
–creatine phosphate contains high energy bond like ATP
–generated from ATP when ATP is plentiful
–many time more abundant than ATP in muscle fiber - ATP generated from glucose
–glucose is stored in the fiber as glycogen –glucose linked together
–aerobic if oxen is available (38/glucose)
–> oxygen delivered to fibers by hemoglobin and stored in fibers by myoglobin
–anaerobic if oxygen is not available (2/glucose)
–> lactate accumulates
–> liver requires oxygen to convert lactate to glucose
–> amount of oxygen required for this is called oxygen debt
