Motor Neuronsreceives and integrates informationtransmits information

Motor UnitA motor unit is composed of a motor neuron and all of the muscle fibers it innervatesIt is the smallest functional unit of muscular shortening

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 neurons100 to 2000 motor neurons per muscle# of m.u.s in a muscle decreases in the elderly

Precision of 2 Muscles1st muscle2nd muscle10,000 fibers10,000 fibers100 motor neurons200 motor neurons 100 motor units200 motor units100 fibers/mu50 fibers/mu

less precisionmore precision

Neuromuscular Controla motor nerve action potential stimulates the release of acetylcholine (ACh) from the nerve endingACh 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 forcethe contraction stops when the calcium ions are removed by a pumping action (100 ms)

EMG

Electromechanical Delayelectromechanical delay - stimulation begins before force is developedit is thought that this is the time necessary to take up the slack in the SEC

Control of Tensionexcitation of each motor unit is an all-or-nothing eventincreased tension can be accomplished by:increasing the # of stimulated motor units (recruitment)increasing the stimulation rate of the active motor units (rate coding)

Stimulation vs ActivationVoltageVoltagethresholdALLNOTHING

Recruitmenteach motor unit has a stimulation threshold at which it will begin to produce forcesmall motor units have a lower threshold than large motor unit, therefore they are recruited first (size principle)

Rate Codingsummation (B) - the overall effect of added stimulitetanus (C) - sustained maximal tension due to high frequency stimulation

Sensory ReceptorsSensory neurons provide feedback on the characteristics of the muscle or other tissues.

2 neuromuscular proprioceptors:MUSCLE SPINDLES & GOLGI TENDON ORGANS

Muscle Spindleslocation:interspersed throughout muscle bellyresponds to:muscle lengthmuscle velocitycauses:autogenic facilitation reciprocal inhibition

Stretch ReflexThe 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.

Golgi Tendon Organlocation:near the muscle-tendon junctionresponds to:muscle tensioncauses:autogenic inhibitionantagonistic facilitationtendonMuscle FibersGTO

GOLGI TENDON ORGAN

My Little GTOpossibly 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

STATICBALLISTICactivate musclespindles whichelicits a stretch reflexmay result intearing a muscleif static positionachieved slowly thencan minimize musclespindle response

if held for sufficientlylong period (~30s) then can elicit GTO responseSTATIC BETTER THAN BALLISTIC

Spindle response: minimal if performed slowly

GTO response: active stretch of hip extensorscauses GTO to relax hip extensors and toactivate the hip flexors

motive force: actions of the hip flexors

consequences: no negatives -- limited ROMlimits possibility of injury and exerciseantagonists

Spindle response: minimal if performed slowly

GTO response: passive stretch of hip extensorscauses GTO to relax hip extensors

motive force: external force

consequences: no direct control of ROM thusmay exceed physiological limits and inducemuscle damage

StretchingProprioceptive Neuromuscular FacilitationPNFalternating contraction - relaxation of agonist & antagonist musclestakes advantage of the response of the proprioceptorse.g. hamstringspassive static stretch of hams - relaxactive maximal concentric action of hams - relaxrepeat

Plyometric TrainingPlyometric 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.