Exam 2: Tension Production Energy use and Muscular Activity Flashcards
Tension “Pulling Strength”
Tension “Pulling Strength”
- Sliding of actin and myosin filaments causes sarcomere shortening
- In a muscle cell, all sarcomeres shorten causinf muscle cell shorten
- Tension in a muscle depends on:
- Tension that develops in individual muscle cells during contraction
- Numer of muscle cell that contract
- Amount of shortening depends in resistance
Fiber Shortening
Fiber Shortening
- As sarcomeres shorten, muscle cell shortens, producing tension
- Pulls on connective tissue and bone to which it is attached
Tension
Tension
Tension produced in individual muscle fibers (Muscle cells) can vary due to:
* Length-tension relationship
* Frequency of stimulation by motor neuron
Tension produced by entire muscle can vary due to:
* Number of muscle cells receving nerve stimulation, commanding them to contract
* Muscle cells are grouped in motor units
Tension production by muscle fibers: Length-Tension relationship
Tension production by muscle fibers: Length-Tension relationship
Amount of tension depends on number of cross bridges formed
* Depends on degree of overlap of actin and myosin filaments
Skeletal muscle contracts most forecully over a narrow range of resting lengths
Tension Production by Muscle Fibers: Frequency of Stimualtion
Tension Production by Muscle Fibers: Frequency of Stimualtion
Twitch
* Cycle of contraction, relaxation produced by a single action potential in a muscle cell
* not typical of most normal skeletal muscle activity
Latent Phase - Action potential occurs
* No contraction until Ca2+ is released from SR
Contraction Phase - Tension rises to Peak
* Ca2+ moves tropomyosin off actin active sites
* Myosin cross bridges form, actin is pulled
Relaxation phase - Tension falls to resting levels
* Ca2+ is pumped back into Sr
* Actin sites coverd by tropomyosin
* No cross bridges remain
Tension Production by Muscle Fibers: Frequency of Stimulation
Tension Production by Muscle Fibers: Frequency of Stimulation
Most muscular activities invlove sustained musclular contraction
* Produced by high frequency of action potentials in muscle cell
* Produced in response to high frequency of action potentials in motor neuron (high frequency of stimulation)
* Summation of tension produces greater tension
Tension Production by Muscle Fibers: Frequency of Stimulation
Tension Production by Muscle Fibers: Frequency of Stimulation
Most muscular activities invlove sustained musclular contraction
* Produced by high frequency of action potentials in muscle cell
* Produced in response to high frequency of action potentials in motor neuron (high frequency of stimulation)
* Summation of tension produces greater tension
Summation
Summation
Repeated stimulation produced before relaxation phase has been completed
* Summation of tension caused by build up of calcium ions in sarcoplasm
Complete tetanus
* Mamximum tension production in a muscle cell - maximum cross bridge formation
Tetanus “disease”
* caused by clostridium tetani bacteria
* Bacterial toxin causes high frequency of action potentials in motor neurons
Summation
Summation
Repeated stimulation produced before relaxation phase has been completed
* Summation of tension caused by build up of calcium ions in sarcoplasm
Complete tetanus
* Mamximum tension production in a muscle cell - maximum cross bridge formation
Tetanus “disease”
* caused by clostridium tetani bacteria
* Bacterial toxin causes high frequency of action potentials in motor neurons
Treppe vs. Wave Summation
Treppe vs. Wave Summation
incomplete vs. Complete Tetanus
incomplete vs. Complete Tetanus
Tension
Tension
Tension produced in individual muscle fibers (cells) can vary due to:
* Length-Tension relationship
* Frequency of stimulation
Tension Produced by entire muscle can vary even more due to:
* Number of muscle cells reciving nerve stimulation, comanding them to contract
* Muscle cells are grouped in motor units
Tension Production by Skeletal muscls Number of active motor units
Tension Production by Skeletal muscls Number of active motor units
Motor Units:
* All the muscle fibers (cells) innervated by one motor neuron
* ammount of tension produced in a muscle determined by number of motor units activated
* Asynchronous Motor unit summation for sustained contractions
Tension Production by Skeletal muscls Number of active motor units
Tension Production by Skeletal muscls Number of active motor units
Differences in number and size of motor units in different muscles determines precision of control of movements
Small motor unit - precise control
* One motor neuron innervates a small number of muscle fibers
Large Motor Unit - Gross movement control
* One motor neuron innervates a large number of muscle fibers
Muscle Tone
Muscle Tone
- Restin tension in a skeletal muscle
- In any muscle, some motor units are always active: tense and firm the muscle
- Which motor units are active is constantly changing, muscle tone is not produced by a specific subset of motor units
- Stabalizes bones and joints
- Greater resting muscle tone causes higher resting rate of metabolism
Contractions: Isotonic and Isometric
Contractions: Isotonic and Isometric
Isotonic - tension rises, length of muscle changes
* Concentric - muscle tension exceeds resistance and muscle shortens
* Eccentric - peak tension developed is less than the resistance, muscle elongates
Contractions: Isotonic and Isometric
Contractions: Isotonic and Isometric
Isometric - tension rises, length of muscle remains constant
* Tension produced never exceeeds resistance
* Muscle as a whole does not shorten but individual muscle fibers shorten until internal connective tissues and tendons are taut
* Cannot shorten further because tension does not exceed resistance
Lengthening a Muscle
Lengthening a Muscle
No active mechanism for a muscle fiber elongation
* A muscle cell does not cause itself to lengthen after contraction process ends
Returns to resting length due to:
* Recoil in elastic components in connective tissue
* Contraction of opposing muscle groups
* Gravity
Energy use and muscle contraction
Energy use and muscle contraction
- Muscle contraction requires large amounts of ATP
- Muscle cells stores only enough high energy molecules to sustain contraction until additional ATP can be generated
- ATP and Creatine Phopshate (CP) reserve last about 15 seconds once contraction begins
- Muscle cell must genertae ATP at approx the same rate as it is used for remainder of contraction
Energy use and muscle contraction
Energy use and muscle contraction
- Muscle contraction requires large amounts of ATP
- Muscle cells stores only enough high energy molecules to sustain contraction until additional ATP can be generated
- ATP and Creatine Phopshate (CP) reserve last about 15 seconds once contraction begins
- Muscle cell must genertae ATP at approx the same rate as it is used for remainder of contraction
Creatine Phosphate and ATP
Creatine Phosphate and ATP
Creatine Phosphate (CP) reserves
* Adenosine Triphosphate (ATP) not used for long term storage of energy
* At rest, muscle cell makes more ATP than needed, extra ATP transfers high energy phosphate to creatine for storage
* CP reserves releases stored energy to convert ADP to ATP when ATP is needed at start of contraction
* Start of exercise CP+ADP <–> C + ATP
* At RestC+ATP <–> CP + ADP
Cellular Respiration
Cellular Respiration
ATP Generation
* Aerobic cellular resp: most ATP used for resting muscle and for moderate levels of muscle activity
* Aerobic and Anerobic glycolosis pathways needed to generate additonal ATP for Peal Performance
Aerobic Metabolism
Aerobic Metabolism
Aerboic Metabolism
* Uses O2 and releases Co2
Occurs in mitochondria
* Citric acid cycle
* CO2 is produces
Electron transport Chain
* ATP synthesis
* O is used as the final electron acceptor
Muscle cell ATP Generation
Muscle cell ATP Generation
Resting muscle fibers rely on aerobic metabolism of Fatty Acids to generate ATP
* FA absorbed from ciruclation
* Broken down to 2-carbon units of acetyl CoA which enter directly into the Citric Acid Cycle
* Excess ATP used to store gluclose into glycogen, and create creatine phosphate . Also pumps ions and recycles waste products
Muscle cell ATP Generation
Muscle cell ATP Generation
Resting muscle fibers rely on aerobic metabolism of Fatty Acids to generate ATP
* FA absorbed from ciruclation
* Broken down to 2-carbon units of acetyl CoA which enter directly into the Citric Acid Cycle
* Excess ATP used to store gluclose into glycogen, and create creatine phosphate . Also pumps ions and recycles waste products
Muscle Cell ATP Generation
Muscle Cell ATP Generation
Contracting Muscle Fibers rely on aerobic and anaerobic metabolism of glucose
* Ammount of aerobic vs. anerobic metabolism depends on intensity of muscle contraction (Moderate vs. Peak)
* Glucose comes from circulation and breakdown of glycogen reserves within muscle cell
Gluclose Metabolism in Muscle Cells
Gluclose Metabolism in Muscle Cells
Pyruvate Metabolism - anaerobic
* If oxygen supply to cells is too slow to allow all of pyruvate to be metabolized aerobically by cellular resp, rest of pyruvate converted to Lactic acid
* Conversion of pyruvate to lactic acid recycles cofactors needed by glycolysis enzymes
At peak performace
* 1/3 Aerobic (mito)
* 2/3 Anerobic glucose->pyruvate->lactic acid
Anaerobic Metabolism
Anaerobic Metabolism
Anerobic Metabolism
* Produces ATP rapidly
* Allows muscle cell to generate additional ATP whem mitochondiral cellular rep pathway is unable to meet cells energy demands
Disadvantages
* Inneficient use of glucose
* Lactc acid lowers intracellular PH
Recover Period
Recover Period
Begin immediatley after activity ends
Oxygen Debt (excess post-exercise oxygen consumption)
* Ammount of oxygen required during resting period to make enough ATP to restore muscle to normal conditions
* Rebuild ATP and Creatine Phosphate leveles
* Recycle lactic acid to make pyruvate
* Revuild Glycogen reserves
Muscle Fatigue
Muscle Fatigue
Fatigued Muscle - a muscle that can no longer perform at required level of activity
Possible causes of fatigue:
* Exhaustion of energy resources
* Build up of lactic acid and lowering of PH
* Psychological Fatigue if lactic acid eneters the blood stream
