Muscular System Part II PDF

# Muscular System Part II ## EXS 115 ## Activation of Muscles - All-or-None Principle: - Each action potential results in a short period of activation of the muscle fibers within the motor unit - A = single twitch - B = force resulting from summations of two twitches - C = unfused tetan...

# Muscular System Part II ## EXS 115 ## Activation of Muscles - All-or-None Principle: - Each action potential results in a short period of activation of the muscle fibers within the motor unit - A = single twitch - B = force resulting from summations of two twitches - C = unfused tetanus - D = fused tetanus - A graph shows force on the y-axis and frequency on the x-axis. - The graph portrays a single twitch (a), two twitches summed (b), unfused tetanus (c), and fused tetanus (d). ## Muscle Fiber Types | Characteristic | Type I | Type IIa | Type IIx | |---|---|---|---| | Motor neuron size | Small | Large | Large | | Recruitment threshold | Low | Intermediate/High | High | | Nerve conduction velocity | Slow | Fast | Fast | | Contraction speed | Slow | Fast | Fast | | Relaxation speed | Slow | Fast | Fast | | Fatigue resistance | High | Intermediate/Low | Low | | Endurance | High | Intermediate/Low | Low | | Force production | Low | Intermediate | High | | Power output | Low | Intermediate/High | High | | Aerobic enzyme content | High | Intermediate/Low | Low | | Anaerobic enzyme content | Low | High | High | | Sarcoplasmic reticulum complexity | Low | Intermediate/High | High | | Capillary density | High | Intermediate | Low | | Myoglobin content | High | Low | Low | | Mitochondrial size, density | High | Intermediate | Low | | Fiber diameter | Small | Intermediate | Large | | Color | Red | White/Red | White | ## Increasing Force Output - **Recruitment** - Increase in number of activated motor units - Requires higher intensity of stimulation - **Muscle tone** - Based on nervous connection - Disrupt nerve connection = muscle fibers shrink = ATROPHY - **Frequency of Stimulation** - A graph shows the relationship between force and action potentials. - The graph portrays a twitch, incomplete tetanus, and complete tetanus. - **↑** number of motor units firing = **↑** Force - **↑** motor unit size = **↑** Force - **↑** rate of stimulation = **↑** Force ## Factors Affecting Force - Muscle Fiber Recruitment - **Henneman's Size Principle:** - A graph shows recruitment threshold on the y-axis and force production on the x-axis. - The graph portrays a cluster of circles representing endurance exercises, and then a larger cluster of circles representing strength power exercises. - **Why is this beneficial?** - 1) - 2) ## Muscle (sarcomere)Length - Muscle can generate maximal force at resting length - Number of actin and myosin cross bridges is maximal - Stretched muscle - Number of cross bridges decreases, decreasing the ability to generate force - Shortened muscle - Overlap of actin filaments - Fewer cross-bridging sites available, decreasing force capability - A diagram shows a muscle in three states: too short, just right, and too long. - A graph shows contraction strength on the y-axis and sacromere length on the x-axis. - Maximal contraction strength occurs at the optimal sarcomere length. ## Exception to the Rule... - A graph shows the relationship between active muscle fibers and exercise intensity (percent of maximal). - Slow-twitch (Type I) fibers are active at lower exercise intensities - Fast-twitch (Type IIa) fibers are active at moderate exercise intensities - Fast-twitch (Type IIx) fibers are active at high exercise intensities ## Muscle Actions - **Agonist** (Prime Mover) - **Antagonist** - **Synergist** - **Example:** - A diagram shows a runner with the quads acting as the agonist and the hamstrings acting as the antagonist. ### Agonist (Prime Mover) | Antagonist ---|---| | Biceps | Triceps | | Deltoids | Latissimus Dorsi | | Pectoralis Major | Trapezius/Rhomboids | | Rectus Abdominis | Erector Spinae | | Iliopsoas | Gluteus Maximus | | Quadriceps | Hamstrings | | Hip Adductor | Gluteus Medius | | Tibialis Anterior | Gastrocnemius | ## Contraction Types - **Isometric** - **Isotonic** - **Concentric** - **Eccentric** - **Isokinetics** - Speed is constant - Resistance changes throughout the ROM - Three diagrams show: 1) an isometric contraction, 2) a concentric isotonic contraction, and 3) an eccentric isotonic contraction. - **Isometric Contraction:** Muscle length doesn't change - **Concentric Contraction:** Muscle shortens - **Eccentric Contraction:** Muscle lengthens