1. NOTES: The Muscular System (Ch 8, part 3)
Muscular Responses

2. MUSCULAR RESPONSES
THRESHOLD STIMULUS: the minimal stimulus required to cause a muscular contraction

3. MUSCULAR RESPONSES
If a muscle is stimulated to threshold potential a TWITCH CONTRACTION (single contraction) will occur
SUMMATION:
-A rapid series of stimuli may produce summation of TWITCHES (short contractions)
-Forceful, sustained contraction without relaxation is a tetanic contraction (TETANUS)
*NOT to be confused with
the disease caused by a
Bacteria (aka “lockjaw”)!

5. MUSCULAR RESPONSES
Even when a muscle appears to be at rest, its fibers remain partially contracted…this is known as “muscle tone,” or TONUS

6. Isotonic (same tension) Contraction
Types of Contraction:
Isotonic (same tension) Contraction
Occurs when the tone or tension in a muscle stays the same, but the length of a muscle changes
Ex: lifting exercises, doing a sit up,
swinging a bat 
Isometric (same length) Contraction
The muscle length remains the same, but the tension increases
Does not produce movement
Ex: attempting to lift an immovable object, holding a weight at arm’s length; maintaining your posture

7. ISOTONIC
ISOMETRIC

8. MUSCULAR RESPONSES ALL-OR-NONE RESPONSE:
-If a skeletal muscle fiber contracts at
all, it will contract completely
*Conditions may affect the force of the
cell’s contraction
i.e. temperature
-Motor unit:1 motor neuron & all the muscle fibers it gives a message to, will also respond in an all-or-none manner
All muscle fibers of a motor unit contract together
One motor neuron may stimulate a few muscle fibers or hundreds at a time
The fewer the # of fibers supplied, the more precise the movements will be (ex. Hand)

10. Graded Strength Principle
Skeletal muscles as a whole do not contract with the all-or-none principal like individual muscle cells
Muscles contract with varying degrees of strength at different times
Engage more motor units to generate more strength
Different muscles can also generate different degrees of strength so we can match the force of movement to specific demands

11. Oxygen Supply and Cellular Respiration
● Aerobic respiration requires oxygen
● Cellular Respiration Equation:
glucose CO2 + H20 + ATP/Heat!!!

12. Oxygen Supply and Cellular Respiration
● Red blood cells carry oxygen to body cells (oxygen binds to HEMOGLOBIN proteins inside RBCs)
● MYOGLOBIN : protein in muscle cells that temporarily binds & stores oxygen
When the O2 supply in a cell decreases rapidly, as during exercise, it can be quickly resupplied by myoglobin
Similar to hemoglobin (also contains iron, gives muscle a reddish color)
Cells with a lot of myoglobin, called red fibers (“red meat”)
White fibers have less myoglobin (“white meat”)

13. **the metabolic capacity of a muscle may change with training!**
Oxygen Debt
● During rest or moderate exercise, muscles receive enough oxygen to respire aerobically
● During strenuous exercise, oxygen deficiency may cause LACTIC ACID to accumulate within the cells (IMMEDIATE BURN!)
● OXYGEN DEBT is the amount of oxygen required to convert accumulated lactic acid back to glucose and to restore supplies of ATP
**the metabolic capacity of a muscle may change with training!**

15. No O2
With oxygen: Glucose  Pyruvate  ATP + CO2 +H2O
Without oxygen: Glucose  Pyruvate  Lactic Acid

16. Muscle Fatigue: ● A fatigued muscle loses its ability to contract
● Muscle fatigue is usually due to accumulated lactic acid

17. Fiber Types
The ability of a muscle to contract and to continue to contract without fatigue depends on fiber types
Our muscle fibers can be classified as slow twitch fibers or fast twitch fibers

18. Slow twitch Contracts more slowly than a fast twitch fiber
More mitochondria
More efficient at using oxygen to generate ATP over a long period of time
Used in endurance sports

19. Fast twitch Generates short bursts of strength and speed
Fatigues more quickly
Uses stored glycogen instead of blood delivered glucose
Has fewer mitochondria & less myoglobin than slow twitch

20. Genetics may affect the amount of slow and fast twitch fibers you have

21. Muscle Adaptations to Exercise
With exercise, muscle will increase in size and strength as well as efficiency
Effects of Aerobic (Endurance) Exercise
Increased #’s of capillaries in and around muscles
Increased #’s of mitochondria
More myoglobin
Effects of Resistance Exercise
Hypertrophy (increase in size) and hyperplasia ?? (increase in # of cells)
More mitochondria
More myofilaments and myofibrils
More glycogen stored in muscles
More connective tissue between muscles