Unit V: Movement Muscle Contraction - Part II Chapter 9 – pg 293-307.
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Transcript of Unit V: Movement Muscle Contraction - Part II Chapter 9 – pg 293-307.
Unit V: MovementMuscle Contraction - Part II
Chapter 9 – pg 293-307
Review
1. What are the four stages of muscular activity?
2. Before a muscle fiber can contract, ATP must bind to: a.) a Z disc, b.) the myosin head, c.) sarcomere, d.) motor end plate
3. Before a muscle fiber can contract, Ca2+ must bind to: a.) calsequestrin, b.) the myosin head, c.) tropomysin, d.) troponin, e.) G-actin
4. The __________ portion of the thin filament houses the active site to make muscles contract.
5. Whereas the ______________ is the portion of the thin filament that changes shape and allows the muscles to relax.
Neural Control
Muscle Activity
A skeletal muscle fiber contracts when stimulated by a motor neuron
The action potential causes the release of ACh which leads to the production of an action potential in the sarcolemma.
Release of calcium ions from thesarcoplasmic reticulum.
Contraction cycle begins.
The sarcomeres shorten, pulling the ends of the muscle fiber closer together.
Skeletal muscle produces tension on the tendons at either end.
Tensionproduction
Muscle fibercontraction
leads to
Thick-thinfilament interaction
triggers
Calciumrelease
Excitation
Muscle Twitch in Frogs
• Threshold =
– Twitch: cycle of contraction and relaxation at threshold (lasting less than 1/10 second)
• Phases of a twitch contraction
– latent period (2 msec delay)
– contraction phase
– relaxation phase
• Myogram
Contraction Strength of Twitches
Intensity:
• Multiple motor unit summation (recruitment)
– lift a glass of milk versus a whole gallon of milk
Varies with:•Muscle temperature•Muscle pH•Hydration•Concentration of Ca+
•Stretch of muscle•Intensity•Frequency
Contraction Strength of Twitches
Frequency:
• Higher frequency = stronger contractions
– sustained fluttering contractions
• Maximum frequency stimulation (40-50 stimuli/second)
– Tetanus
Twitch
Muscle twitches
Stimuli(a)
High Highest-Tetanus
LowComplete tetanus
Fatigue
Tension in tendon
Motor unit 1
Motor unit 2
Motor unit 3
Ten
sion
Time
Asynchronous motor unit summation during a sustained contraction
Contraction Strength
Decrease in the resting sarcomere length reducestension.
Optimal range = optimal tension
Increase in sarcomere length, reduced tension
When overlap equals zero, fibers cannot produce tension.Normal
range
Decreased length Increased sarcomere length
Optimal resting length:75 to 130% of the optimal length.
With complete overlap, tension equals zero.
Ten
sion
(%
of
max
imu
m)
Sarcomere Length vs. Tension
Isometric and Isotonic Contractions
• Isometric muscle contraction– prelude to muscle movement
• Isotonic muscle contraction– Concentric
– Eccentric
6 kg 6 kg
6 kg
6 kg
Tendon
2 kg2 kg
Muscle Contraction Phases
Immediate Energy Needs
• Phosphagen system– myokinase– creatine kinase
• Short, intense exercise (100 m dash)
• Result is power enough for 1 minute brisk walk or 6 seconds of sprinting
Energy NeedsShort-term
• Glycogen-lactic acid system
– produces ATP for 30-40 seconds of maximum activity
• playing basketball or running around baseball diamonds Long-term
• Aerobic respiration
–Produces 36 ATPs/glucose molecule
Aerobic respirationusing oxygen frommyoglobin
Glycogen–lactic acidSystem (anaerobicfermentation)
Phosphagensystem
Duration of exercise
0 10 seconds 40 seconds
Aerobic respirationsupported bycardiopulmonaryfunction
Repayment ofoxygen debt
Mode of ATP synthesis
Muscle Fatigue
• Progressive weakness from use– ATP synthesis declines– Na+ and K+ pumps slow– lactic acid inhibits enzyme function– accumulation of extracellular K+– motor nerve fibers use up their ACh
Oxygen Debt
• Difference between resting rate of O2 consumption and elevated rate following exercise.
• Purposes for extra oxygen– replace oxygen reserves– replenishing the phosphagen system– oxidizing lactic acid– serving the elevated metabolic rate
Slow- and Fast-Twitch Fibers
• Slow oxidative, slow-twitch fibers, red
– adapted for aerobic respiration and resistant to fatigue
– postural muscles of the back (100msec/twitch)
• Fast glycolytic, fast-twitch fibers, white
– adapted for anaerobic fermentation
– sarcoplasmic reticulum releases calcium quickly so contractions are quicker (7.5 msec/twitch)
– extrinsic eye muscles, gastrocnemius and biceps brachii
• Proportions genetically determined
Cardiac Muscle
• Autorhythmic due to pacemaker cells
• aerobic respiration
– resistant to fatigue
– very vulnerable to interruptions in oxygen supply
Types of Smooth Muscle
Functional categories:
• Multiunit smooth muscle
– terminal nerve branches synapse on myocytes
– large arteries, iris, arrector pili muscles
– independent contraction
• Single-unit smooth muscle
– blood vessel walls, digestive, respiratory, urinary, and reproductive tracts
– coupled by gap junctions
– large number of cells contract as a unit
Synapses
Autonomicnerve fibers
(a) Multiunit smooth muscle
Gap junctions
Autonomicnerve fibers
Smooth Muscle Contraction
• Ca2+ binds to calmodulin
• activates myosin light-chain kinase
• which activates myosin ATPase
• power stroke occurs
• Thin filaments pull on plasma membrane
– shortens the entire cell in a twisting fashion
Repsonses to Stretch
• Ex. – esophagus distended by food brings on peristalsis
• Stress-relaxation response
– Ex. - urinary bladder
The process of peristalsis
Foodbolus
Towardanus
Longitudinalmuscle
Circular muscle
Circular musclescontract behindbolus.
Bolus of foodarrives indigestivesystem.
Longitudinalmuscles aheadof boluscontract.
Contraction incircular musclelayer forcesbolus forward.