muscle stimulation & exercise 4-5 november 2014. response to stimulation graded responses...
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Muscle Stimulation & Exercise4-5 November 2014
Response to StimulationMuscles have graded responses – they contract to different
degrees, depending upon the frequency and strength of stimulation
Response to Stimulation If a nerve fires once
(unusual), the muscle contracts and relaxes in a twitch
If the nerve fires rapidly in succession, then the muscle does not relax fully in between impulses – resulting in tetany
(a smooth, prolonged contraction)
Response to Stimulation
Note:
tetanus ≠ tetanus
Tetanus (the type of muscle contraction) is different than tetanus the disease caused by a bacteria (commonly called lockjaw)
Response to Stimulation
The strength of contraction also depends on how many muscle fibers are stimulated.
The more muscle fibers stimulated, the greater the contraction of the muscle.
Quick Review
What vocab word describes the fact that muscles may contract to different degrees?
What two factors determine the extent to which a muscle contracts?
Graded response
Frequency of stimulation and number of cells stimulated
Muscle MetabolismMuscle contraction requires enormous amounts of energy in the form of ATP.
The amount of ATP stored in the cell only lasts for ~5 seconds!
The rest of the ATP must be regenerated, using one of three pathways.
Muscle MetabolismPathway 1: Direct phosphorylation by creatine phosphate
Fast!No O2 required
Quickly used upOnly in muscle
cells
Muscle MetabolismPathway 2: Anaerobic glycolysis and lactic acid formation
Medium speed No O2 required
Less efficient Produces
lactic acid Only in muscle
cells
Muscle MetabolismPathway 2: Anaerobic glycolysis and lactic acid formation
Misconception alert!
Lactic acid build-up
is not responsible for
muscle soreness the
day after exercise
(that’s due to cell
damage).
Muscle MetabolismPathway 2: Anaerobic glycolysis and lactic acid formation
Lactic acid build-up
is responsible for the
burning feeling
during exercise.
Also, lactic acid
build-up increases
muscle fatigue
(inability of muscle to
contract when
stimulated)
Muscle MetabolismPathway 3: Aerobic respiration
Slow Long-lasting All cells Requires O2
Muscle Metabolism
Which energy pathway is better?
CP and anaerobic supply energy at a fast rate (for maximum performance) but for a short term only.
Examples: Sprinting Any sport with bursts of energy & quick changes (e.g. Volleyball, b-ball) Start of exercise
Muscle Metabolism
Which energy pathway is better?
Aerobic can provideenergy for hours withoutfatigue
But, muscles are notworking at peak levels
Examples: cycling, marathon
Muscle Metabolism
Sports & Energy Systems
Muscle Metabolism
Oxygen DebtAll non-aerobic energy use causes changes in the muscle that need to be reversed after the exercise is over
O2, ATP, creatine phosphate, and glycogen reserves need to be replenished
Lactic acid needs be broken down
Oxygen debt is the extra amount of oxygen that must be taken in for these restorative processes.
This is why you breathe deeply for a while after intense exercise.
Think, Pair, Share
Scholar with shorter hair:Name the reactants and products of each energy system.
Which two energy systems are only used in muscles?
Scholar with longer hair:Which two energy systems lead to oxygen debt? Which energy system(s) predominate in the following activities: running for your life, hiking, lifting heavy furniture
Critical Thinking 1The graph below indicates the amount of lactic acid produced by muscle cells as a function of power (energy / time).
1) Describe how lactic acid production varies with power.
2) Explain
the shape of the
graph using
your knowledge
of energy
systems
Critical Thinking 11) Lactic acid increases very slowly from 150 W to 250
W but begins to increase dramatically at about 275 W.
2) At around 275 W, the rate of energy required by the muscle cells is too high, so the body switches from aerobic metabolism
to anaerobic
metabolism. This
point is known as
aerobic threshold.
Exercise & Muscles
Isotonic vs Isometric Contractions Isotonic contractions occur whenever the muscles shorten, causing movement
(e.g. weight lifting, running, swimming, jumping, etc.)
Isometric contractions occur whenever the muscle’s tension increases without actually shortening. This happens when you try to move an immovable object.
(e.g. pushing against a wall; many yoga exercises, etc.)
Exercise & Muscles
Aerobic vs Resistance ExerciseAerobic exercise (aka endurance or cardiovascular) – builds the aerobic endurance of muscles
Examples: jogging, biking Increases blood supply to muscles; # of mitochondria, &
amount of stored oxygen Benefits
Greater resistance to fatigue Better heart and lung function Improved digestion Improved bone density Reduced risk of metabolic disorder Increased immune system function
Exercise & Muscles
Aerobic vs Resistance ExerciseResistance exercise (aka weight training) – focuses on isometric contractions & forcing muscle to contract with as much force as possible
Examples: weights, some yoga exercises, pushups, situps, Increases the number of actin and myosin fibers, resulting in
larger muscles Benefits
Greater strength Greater muscle mass = greater metabolism Increased bone density
Exercise & MusclesExercise recommendations for healthy adults age 18-65 from CDC
Exercise & Muscles
Muscle tone and muscle wasting Muscles quickly deteriorate when not used
Lose 5-10% muscle mass per week with bed rest Lose 20% muscle strength in one week of bed rest Muscle strength plateaus at ~30% original strength after ~6
weeks of bed rest
Our body maintains muscle tone by systematically stimulating and partially contracting muscles around the body
Electrical muscle stimulators can also help prevent muscle atrophy following a stroke, injury, or surgery
Think, Pair, Share
1. Compare and contrast isotonic and isometric exercises, and provide an example of each
2. Compare and contrast resistance and aerobic exercise, and provide an example of each
3. Why is exercise necessary for our muscles?
4. How does exercise help our body function?
ClosureWhat were our objectives today?
What did you learn about these objectives?
How does what we learned today tie to our unit question?
Critical Thinking 2 – Exit TicketThe graph below indicates the amount of lactic acid produced by muscle cells as a function running pace.
1) Describe the data.
2) Explain
the data using
your
knowledge
of energy
systems and
exercise
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