1. Dendrite Soma (body) Axon receives and integrates information Motor Neurons transmits information

2. Motor Unit A motor unit is composed of a motor neuron and all of the muscle fibers it innervates It is the smallest functional unit of muscular shortening

3. Motor Unit (cont) each muscle has many motor units (m.u.) # of fibers in a m.u. is dependent on the precision of movement required of that muscle (average: 100-200 fibers per m.u.) –more precision is obtained with more neurons –100 to 2000 motor neurons per muscle # of m.u.’s in a muscle decreases in the elderly

4. Precision of 2 Muscles 1st muscle2nd muscle10,000 fibers 100 motor neurons200 motor neurons 100 motor units200 motor units 100 fibers/mu50 fibers/mu less precisionmore precision

5. MuscleNumber of Muscle Fibers Number of MU’s Mean Number of Fibers Per MU Platysma27,1001,10025 Brachioradialias>129,200330>410 FirstLumbrical10,000100110 Tibialias Anterior 250,000450600 Gastrocnemius (medial head) 1,120,0005802,000

6. Neuromuscular Control a motor nerve action potential stimulates the release of acetylcholine (ACh) from the nerve ending ACh binds to the muscle fiber which causes depolarization and results in the release of calcium ions from the sarcoplasmic reticulum (5 ms) the calcium ions permit the actin-myosin interaction, which produces force the contraction stops when the calcium ions are removed by a pumping action (100 ms)

7. EMG

8. Electromechanical Delay electromechanical delay - stimulation begins before force is developed –it is thought that this is the time necessary to “take up the slack in the SEC”

9. Control of Tension excitation of each motor unit is an all-or- nothing event increased tension can be accomplished by: –increasing the # of stimulated motor units (recruitment) –increasing the stimulation rate of the active motor units (rate coding)

10. Stimulation vs Activation Voltage threshold ALLNOTHING

11. Recruitment each motor unit has a stimulation threshold at which it will begin to produce force small motor units have a lower threshold than large motor unit, therefore they are recruited first (size principle)

12. Rate Coding summation (B) - the overall effect of added stimuli tetanus (C) - sustained maximal tension due to high frequency stimulation

13. Sensory Receptors Sensory neurons provide feedback on the characteristics of the muscle or other tissues. 2 neuromuscular proprioceptors: MUSCLE SPINDLES & GOLGI TENDON ORGANS

14. Muscle Spindles location: –interspersed throughout muscle belly responds to: –muscle length –muscle velocity causes: –autogenic facilitation –reciprocal inhibition

15. Stretch Reflex The muscle spindle is responsible for the stretch reflex. As a muscle is rapidly stretched, the muscle spindle responds by facilitation of the same muscle and inhibition of the antagonistic muscle. This reflex can be seen in the patellar tendon tap.

16. Golgi Tendon Organ location: –near the muscle-tendon junction responds to: –muscle tension causes: –autogenic inhibition –antagonistic facilitation tendon Muscle Fibers GTO

17. GOLGI TENDON ORGAN

18. “My Little GTO” possibly the critical determinant to maximal lifting levels in weight training may also be responsible for uncoordinated responses in untrained individuals response is adapted through training

19. STATIC BALLISTIC activate muscle spindles which elicits a stretch reflex may result in tearing a muscle if static position achieved slowly then can minimize muscle spindle response if held for sufficiently long period (~30s) then can elicit GTO response STATIC BETTER THAN BALLISTIC

20. ACTIVE STRETCH Spindle response: minimal if performed slowly GTO response: active stretch of hip extensors causes GTO to relax hip extensors and to activate the hip flexors motive force: actions of the hip flexors consequences: no negatives -- limited ROM limits possibility of injury and exercise antagonists

21. PASSIVE STRETCH Spindle response: minimal if performed slowly GTO response: passive stretch of hip extensors causes GTO to relax hip extensors motive force: external force consequences: no direct control of ROM thus may exceed physiological limits and induce muscle damage

22. Stretching Proprioceptive Neuromuscular Facilitation PNF –alternating contraction - relaxation of agonist & antagonist muscles –takes advantage of the response of the proprioceptors –e.g. hamstrings passive static stretch of hams - relax active maximal concentric action of hams - relax repeat

23. Plyometric Training Plyometric training consists of exercises that rapidly stretch a muscle followed immediately by a contraction. They improve power output in the muscle by: Neurological Influences: rapidly stretching of the muscle, which excites the motoneurons via the stretch reflex. Structural Influences: involving elastic energy from the stretch-shortening cycle.