Alpha motoneuron

AN ACTION POTENTIAL

Neuromuscular Junction

Skeletal Muscle Macrostructure

Sarcoplasmic Reticulum and T-Tubule System

Skeletal Muscle Microstructure

ARRANGEMENT OF FILAMENTS IN A SARCOMERE

AN ACTIN FILAMENT Filamentous actin-entire strand Globular actin- each globule Tropomyosin situated in a groove along the actin Troponin situated each seventh G-actin

EVENTS LEADING TO MUSCLE ACTION

CONTRACTING MUSCLE FIBER

Each crossbridge moves independently of the other crossbridges At any given moment during contraction, typically 50% of myosin is attached to actin

Architectural Factors and Force Development Muscle fibers in series mean increased velocity w/ lower force Pennate arrangement means increased maximal force due to increased x sectional area w/ decreased max velocity

FORCE-VELOCITY RELATIONSHIP The less force applied, the quicker the shortening when stimulated until there is no movement (maximal isometric tension). More and more force is required to increase the velocity of eccentric contraction, as a greater amount of force is necessary to detach cross-bridges during muscle lengthening.

Motor Unit Recruitment Patterns Number (AND SIZE‚ of motor units stimulated affects force production Patterns are additive, not sequential

Proprioceptors

Muscle Spindles Parallel to muscle fibers Larger concentration in muscles involving complex movements Important for maintaining posture Respond to stretch by initiating reflexive contraction (stretch reflex) Example: Patellar tendon stretch

Golgi Tendon Organs High threshold Function to protect the muscle and connective tissue from injury Are stimulated with excessive tension during muscle shortening or when the muscle is stretched passively Cause a reflex inhibition of the muscle