Skeletal Muscle Objectives

15. Place the events of muscle contraction-relaxation in correct order and under the appropriate period of objective 14.

*steps 1-3 are events that are necessary to prepare for latent period to occur LATENT PERIOD: (red arrow) steps 4-8 4. Acetylcholine opens sodium channels in sarcolemma 5. Sarcolemma and T-tubules depolarize. 6. Calcium released from SR into sarcomeres 7. Calcium binds to troponin on actin filiment 8. tropomyosin moves, exposing sites on actin filiment to which myosin cross- bridge binds CONTRACTION PERIOD: 9. Myosin cross-bridge slides actin filiment toward the center of the sacromere, sacromere shortens RELAXATION PERIOD: 10.Calcium is transported back to SR 11. new ATP molecule is added to mysoin cross-bridge

11. Describe the steps of a single myosin cross-bridge cycle

1. (top) Myosin cross bridge attaches to the actin myofilament 2. (going right) working stroke- the myosin head pivots and bends it as it pulls on the actin filament, sliding it towards the M-line (the point of the sacromere in the center where the the actin filiment crosses) hydrolized ATP (ADP and inorganic phosphate) released. 3.(bottom) New ATP attaches to the myosin head which causes it to move into a low energy state and detach from the cross bridge 4.( left): As ATP is split into ADP and P1 (by hydrolysis), cocking of the myosin head occurs (into a high energy state)

13. List the steps of skeletal muscle fiber contraction starting with an action potential in a motor neuron and proceeding through a contraction-relaxation cycle of the muscle fiber.

1. Action potential in motor neuron 2. Influx of calcium into neuron 3. Neurotransmitter (acetylcholine) released into synaptic cleft 4. Acetylcholine opens sodium channels in sarcolemma 5. Sarcolemma and T-tubules depolarize 6. Calcium released from SR into sarcomeres 7. Calcium binds to troponin on actin filament 8. Tropomyosin moves, exposing sites on actin to which myosin cross-bridge binds 9. Myosin cross-bridge slides actin filament toward center of sarcomere 10. Calcium is transported back to SR 11. New ATP molecule is added to myosin cross-bridge

12. Describe excitation-contraction coupling as it takes place at a neuromuscular junction using these terms: synaptic vesicles, calcium ions, acetylcholine, acetylcholinesterase, sarcolemma, sodium ion channels and depolarization.

1. action potential arrives at axon terminal of pre-synaptic motor neuron which causes Ca2+ ions to flow into the axon terminal. 2. influx of Ca2+ ions cause synaptic vesicles to fuse to the binding sites of the axon terminals membrane, where it empties ACh (neruotransmitter) into the neuromuscular junction 3. ACh binds to receptor sites on the sarcolemma of post-synaptic neuron. Na+/K+ pumps open. sodium ion channels allow influx of Na+ ions, which make the interior of the sarcolemma less negative. Depolarization occurs and action potential is generated. 4. enzyme, acetylcholinesterase, terminates the effects of ACh by degregrading it and sending it back into the neuromuscular junction to be recycled.

9. Describe how energy is derived from any molecule.

Breaking apart chemical bonds within a molecule releases the energetic force holding the chemicals within the molecule together. Once that energy is released is can be used elsewhere.

21. Describe the three ways (energy systems) by which skeletal muscle fibers generate ATP: creatine phosphate, anaerobic respiration (glycolysis) and aerobic respiration (Krebs cycle).

CREATINE PHOSPHATE: CP, a unique high energy molecule stored in muscles is tapped to regenerate ATP. This occurs by coupling CP w/ADP, and adding the enzyme, creatine kinase, to catalyze the reaction. Once catalyzed, the energy released from breaking the high energy bonds between the CP and it's phosphate group result in: creatine + ATP, which can then be used for muscle fibers. ANAEROBIC RESPIRATION (GLYCOLYSIS): ATP is generated by breaking down glucose obtained for the blood or from glycogen stored in muscle by glyclosis (sugar splitting). If blood flow and oxygen delivery is compromised, which is the case when muscle reaches fatigue, the pyruvic acid gets converted into lactic acid (anaerobic glycolysis - no O2)) which cells can use for an energy source. Build up of lactic acid is whats responsible for muscle soreness after exercise AEROBIC RESPIRATION (KREBS CYCLE): In aerobic respiration, glycolysis, glucose is broken down into two pyruvic acid molecules, which enter mitochondria in the cells and react with oxygen to produce ATP aerobically. This glycolysis process completely breaks the glucose down and its final products are water, carbon dioxide, and large amounts of ATP. During the first 30 min or so of exercise, muscle glycogen is used to provide most of the food for glycolysis, but once those stores are used, fatty and amino acids begin to be used as the primary fuel for ATP generation.

18. Define wave summation, draw it on a graph, and tell the importance of this concept in understanding skeletal muscle graded response to varying loads.

Delivering stimuli of increasing frequency with a constant stimulus intensity. When loads vary in graded potential, the brain sends stimuli in slowly increasing frequencies; increasing amounts of motor units are activated until the amount of contraction nesesscary is reached.

20. Describe the two main types of skeletal muscle contraction: isometric and isotonic contraction, and the two subtypes of isotonic contractions, concentric and eccentric.

ISOTONIC CONTRACTIONS: muscle changes length as it does work 1. concentric: the muscle shortens and does work 2. eccentric: the muscle generates force as it lengthens ISOMETRIC CONTRACTIONS: the muscle stays the same length as it does work, myosin cross-bridges are "spinning their wheels"

14. Describe the events associated with the three periods of a muscle contraction-relaxation cycle; latent period, contraction period, and relaxation period.

LATENT PERIOD: the first few milliseconds following stimulation when excitation-contraction coupling is occuring. During this period, cross bridges begin to cycle but muscle tension is not yet measurable CONTRACTION PERIOD: cross bridge cycle in motion, and tension development occurs. If the tension becomes great enough, sarcomere shortens RELAXATION PERIOD: Ca2+ ions enter SR which stimulate this phase. Force causing contraction declines and muscle tension decreases to zero. If the muscle shortened during contraction then it now returns to its original length. These three phases combined if called a "muscle twitch"

16. Define motor unit and tell the importance of this concept in understanding skeletal muscle graded response to varying loads.

MOTOR UNIT: A motor neuron and all of the muscle fibers that it innervates, or contract when an action potential is fired in the motor neuron. *motor units can be small or large: small: muscles that exert fine control (fingers, and eyes...) Motor units will innervate fewer fibers Large: large weight bearing muscles with less precise movements. Motor units will innervate many fibers. GRADED POTENTIAL RESPONSES: Varying contractions of muscle contraction smoothness, by either the frequency of stimulation or the strength of stimulation. In a smooth contraction, small motor units are activated first, and feedback is sent to the brain relaying that more fibers are needed to contract the muscle. This feedback will continue, and larger motor units will be activated until contraction has meet the resistance of the load. (the size principle.) This gradual increase in contraction strength creates smooth movement

Define: Tendon, origin and insertion of a skeletal muscle.

Tendon: Point where muscle attaches to bone at insertion at insertion and origin points Origin: tendon attachment where muscle stems, little action Insertion: point of tendon attachment where muscle action takes place

17. Define treppe and draw contractions on a graph that demonstrate this phenomenon.

The contraction of muscle by Delivering stimuli of the same intensity but allowing the muscle to relax between stimuli: "warming up"

19. Describe the size principle as it applies to skeletal muscle contraction and tell the importance of this concept in understanding skeletal muscle graded response to varying loads

When only a small amount of contraction is needed (only a few motor units activated), then the brain will only only excite a few axon terminals to generate action potentials. As load increases, the brain will recruit more axons to fire, resulting in increasing contraction until contraction reaches threshold (the point in the nerve where all of its axons are being activated).

10. Draw the hydrolysis of ATP and describe how this reaction provides energy for cross bridge activation

When we add H2O (through the addition of ATPase, an enzyme that hydrolyizes ATP) to ATP, we break down one of the phosphate groups on the molecule ATP which are held together by high energy bonds. this results in the molecule ADP, a Phosphate, and a water molecule. The energy from breaking that bond is what puts the myosin heads into a high energy state where they then bind to sites on the G-actin molicules.

CREATINE PHOSPHATE a. Reactants and products b. Number of ATP molecules per glucose generated c. Role of oxygen d. Length of time each system can produce ATP e. Time necessary for each system to recover

a. reactants: CP, phosphate, ADP products: creatine + ATP b. 1 ATP per CP c. none d. 15 sec energy provided e. a few minutes to recover

ANAEROBIC RESPIRATION (GLYCOLYSIS) a. Reactants and products b. Number of ATP molecules per glucose generated c. Role of oxygen d. Length of time each system can produce ATP e. Time necessary for each system to recover

a. reactants: glucose, b. products: 2 ATP per glucose, lactic acid. c. none d. energy provided for 30-40 seconds e. 30-60 min to recover

AEROBIC RESPIRATION (KREB'S CYCLE) a. Reactants and products b. Number of ATP molecules per glucose generated c. Role of oxygen d. Length of time each system can produce ATP e. Time necessary for each system to recover

a. reactants: glucose, pyruvic acid, fatty acids, amino acids b. products: 32 ATP per glucose, CO2, H2O c. required d. energy provided for hours e. 1-2 days to recover

define muscle fiber and fasicle

muscle fiber: individual muscle cell fasicle: groups of muscle fibers

Define myofibril

one of several fibrils packed into a muscle cell lengthwise

24. Explain the role of resting muscle (sarcomere) length in determining the strength of a skeletal muscle fiber contraction.

sarcomere length of resting muscle is 100% efficient at its full relaxed. This means that the strength or force of the muscle fiber contraction will be the most efficient. When muscle contraction occurs, and sarcomere is not in its fully relaxed state (either slightly contracted, or hyper-relaxed) percentage of muscle contraction force potential is greatly reduced.

The Size Principle

skinny motor neurons, serve skinny muscle fibers. motor neuron thickness matches muscle fiber thickness.