Lecture 12Electromyography.ppt

Lecture 12Electromyography EXS 587 Dr. Moran Outline Finish Lecture 11 (Muscle Moment – Moment Arm) Review of Muscle Contraction Physiology Physiological Basis and Concepts of EMG (Alwin Luttmann) Methods of EMG Collection Electromyograhy in Ergonomics (Shrawan Kumar) Limitations Uses Journal of Electromyography and Kinesiology (full-text in ScienceDirect) Physiological Basis Muscle contraction due to a change in the relative sliding of thread-like molecules or filaments Actin and Myosin Filament sliding triggered by electrical phenomenon (ACTION POTENTIAL, AP) The recording of muscle APs is called electromyography The record is known as an electromyogram What can be learned from an EMG? Time course of muscle contraction Contraction force Coordination of several muscles in a movement sequence These parameters are DERIVED from the amplitude, frequency, and change of these over time of the EMG signal Field of Ergonomics: from the EMG conclusions about muscle strain and the occurrence of muscular fatigue can be derived as well Excitable Membranes Cell membrane separates intracellular from extracellular space Diffusion barrier which restricts ION flow Cell Membrane Structure Double layer of phospholipids (both surfaces covered in proteins) Hydrophyllic Head Hydrophobic Tail Role of Proteins Transport “carrier molecules” Receptor Transfer information Fluid Distribution Concentration of ions different inside vs. outside of cell membrane This results in an electrical potential difference known as a MEMBRANE POTENTIAL Typical magnitude of membrane potential is -60 and -90 mV (interior of cell is negatively charged) This potential can change within fractions of seconds to +20 to +50 mV This rapid change is called an ACTION POTENTIAL Ion Concentration Intracellular Fluid High concentration of Potassium cations (K+) and Protein anions (A-) Extracellular Space High concentrations of Sodium cations (Na+) and chloride anions (Cl-) Nernst Equation Used to determine re