Muscle Physiology Chapter 11

• Produce movement
• Maintain body posture/position
• Support soft tissues
• Guard entrances and exits
• Maintain body teperature

• Concentric and eccentric isotonic contractions
• Flexion
• extension 
• abduction (towards body)
• addutction (away from body)

helps maintain body posture and body position

• Shivering (warm up)
• Vasodilation (cool down)

• body
• fascicles
• fibers
• myofibrils
• sacromeres

• made from sacromeres in series
• from 2 proteins
• myosin and actin

myosin backbone

actin backbone

actin

myosin

• sliding of myosin and actin
• z lines move closer

• made of proteins
• looks like 2 golf clubs twisted together
• actin binding site
• ATP site
• hinge
• High engery (big angle)
• Low engery (small angle)

• looks like 2 strands of pearls twisted together
• Tropomyosin (thread-like protein)
• Troponin (found in intervals)
• G-actin (myosin binding sites)

Ca++ released from sarcoplasmic reticulum

Ca++ binds to troponin complex

Tropomyosin moves off the myosin binding sites of the actin filament

Myosin binding sites are covered by tropomyosin

• Binding site of actin is exposed due to Ca++ released from S.R. and shifting tropomyosin off  
• g actin

• 1. Ca++ released from S.R., binds to troponin, causes active sites on actin to be exposed
• 2. ATP binds to myosin head
• 3. ATP hydrolyzed to ADP and Pi (still bound by myosin)
• 4. Myosin head goes into high energy state ("cocked")
• 5. Myosin head attaches to active site of actin molecule
• 6. Pi is released from myosin head
• 7. Myosin head goes to low energy state, producing "power stroke"
• 8. Myosin and actin in rigor state and ADP is released from myosin head
• 9. New ATP binds to myosin head and detaches from actin filament (rigor state ends)
• 10. Repeats from #2

• 1. Action potential down motor neuron
• 2. Acetylcholine (ACh) is released by neuron
• 3. ACh binds to nicotinic receptors Na+ influx & K+ efflux (net depolarization of cell)
• 4. New action potential propagates along muscle fiber
• 5. Action potential enters fiber via transverse tubules
• 6. Ca++ channels open in S.R. releasing Ca++ into cytosol
• 7. Ca++ binds to troponin, causing tropomyosin to slide off active sites on actin filaments
• 8. Molecular mechanism of actin and myosin movement occurs

• 1. Latent phase
• 2. Contraction phase
• 3. Relaxation phase

• 1. action potential travels along muscle fiber and into the t-tubules
• 2. Ca++ channels in SR open
• 3. Ca++ floods into cytosol
• 4. Ca++ binds to troponin
• 5. Tropomyosin moves off of myosin binding sites on actin

• 1. Myosin head attach to the actin and do the "power stroke"
• 2. Myosin heads bind a new ATP, release from the actin, recock, reattach, and perform another "power stroke"
• 3. Repeats a few times

Increase in tension, depending on muscle fiber can last 50 ms

• 1. Ca++ is pumpled back into SR
• 2. tropomyosin covers up the myosin binding sites on actin
• 3. myosin is no longer able to bind to actin

Decreases in tension and depending on muscle fiber can last 50 ms

Can't see where action potentials are because they are so close together

you can see on the graph where a bump is, is where and action potential has occured

a sustain contraction, action potentials keep occuring and keep seeing bumps as tension increases

• Lifting weights (same tension)
• 1. straining (concentric)
• 2. Tension (plateau)
• 3. Shortening length (eccentric)

• Strain against load
• muscle fibers never shorten
• Never enough tension to lift load

TRUE

A group of muscle fibers that are all controlled by the same motor neuron.

• Extraocular muscles (fine dexterity)
•     few muscle fibers per motor unit

• Gastrocnemius (leg)
•    thousands of muscle fibers per motor unit

the turning on of more then one motor unit to complete an action

small motor units recruit first then larger ones

the switching or changing of motor units to prevent muscle fatique

Use small first the progressively larger are recruited.

Motor neurons that control certain muscles are controlled by interneurons in CNS 

Interneurons begin to fire, and motor neurons with smaller cell bodies will reach -55 mV (threshold) before (few EPSPs) motor neurons with larger (more EPSPs) cell bodies

small motor units are innervated by smaller neurons with smaller cell bodies, thus fire first in sequence

the more load we put on muscles the shorter the shortening velocity

remember velocity is the change in distance over the change in time

• 1. phosphagen system
• 2. Glycogen-lactate system (anaerobic)
• 3. Aerobic system

• ATP & phosphocreatine (PC)
•    creatine-PO4 + ADP -> Creatine + ATP

Rate of energy release: 4 moles of ATP per min

Size about 10 s (3 s of ATP and 6 s of PC)

Glycolysis & fermentation

sugar -> pyruvate -> lactate

Rate of energyy release: 2.5 moles

Size about 90 s

Doing all the steps of cellular respiration

Glycolysis, pyruvate decarboxylation, citric acid cycle, and the electron transport chain

O2 + Sugar -> CO2 + Water

Rate of energy release: 1 mole of ATP/min

unlimited duration, as long as nutrients last

Type 1 (slow-oxidative)

Type 2a (fast-oxidative)

Type 2x (fast-glycolytic)

likes using oxygen and aerobic reserviors

• Slow myosin ATPase
• Slow contraction
• Longer time to fatique
• High use oxygen
• Low use glycolysis
• Many mitochondria
• Many capillaries
• Lots of myoglobin
• Red color
• Low glycogen content

• Fast myosin ATPase
• Fast contraction
• intermediate time to fatigue
• high oxygen use
• intermediate glycolysis
• many mitochondria
• many capillaries
• alot of myoglobin
• red in color
• intermediate glycogin content

• Fast myosin ATPase
• fast contraction
• short time to fatique
• low oxygen use
• high glycolysis use
• few mitochondria
• few capillaries
• less myoglobin
• white in color
• high glycogen

• Oxidative fibers
•   glycogen depletion and increased temperature

• Fatigue of glycolytic fibers
•   Possible accumulation of lactate, mechanical injury to muscle fiber, lack of blood supply and increased temperature

• True neuromuscular fatique
•    depletion of ACh from motor neuron termini, and only occurs in artificially stimulated neurons and muscle fibers.

Produced by a load around a joint is equal to the torque produced by the muscle around the same joint.

Is equal to the force on a lever multiplied by the length of the lever arm.

T = ( r X F)

FALSE, skeletal muscles have a mechanical distadvantage and must produce a force in  excess of the actual force that gravity is directly producing on the load.

The mechanical disadvantage permits a small (and slow) shortening of the muscle to result in the long (and fast) movement of a load.

• (Autonomic Nervous System)
• digestive tract
• blood vessels
• bronchioles of lungs
• eye (iris and ciliary body)
• reproductive and urinary tract

• Found in hollow organs and tubes
• a cell has a single nucleus
• shorter than skeletal muscles
• develops tension slowly and relaxes slowly, resulting in longer contractile response (twitch)
• Not striated (actin/myosin not arranged)
• actin filaments radiate out of "dense bodies"

• regulated by Ca++
• No troponin 
• instead uses calmodulin to control muscle contraction (movement is not predictable)

• 1. Ca++ enters cytosol from extracellular fluid and from SR
• 2. Ca++ binds to calmodulin in cytosol
• 3. Ca-calmodulin activates myosin light chain kinase 
• 4. Myosin heads are activated (phosphorylated) by MLCK
• 5. Phosphorylated myosin attaches to actin filaments and completes the "power stroke"

Takes time to turn on/off because of enzymes