KIN 365 Applied Biomechanics Exam Two 2 12 Connective tissues Endomysium surrounds individual muscle fiber Sarcolemma cell membrane complicated lipid bilayer Sarcoplasm fluid in cell compare to cytoplasm Muscle cell fiber can develop tension like no other cell in the body Perimysium surrounds a group of muscle fibers Fasciculi group of muscle fibers number of fibers varies Epimysium surrounds entire muscle o All fuse at end to make the tendon muscle to bone Myofibrils make up a single muscle fiber myofilaments make up a myofibril Protein myosin and actin actin is thin filament myosin is thick filament Myosin has cross bridges the cross bridges spiral as myosin comes Actin thin filament has three proteins tropomyosin troponin actin Actin doesn t meet it just overlaps myosin cross bridge actin myosin z band Sliding Filament Theory 1 Rest ATP is on the tip of the myosin cross bridge Ca hasn t attached to troponin Knock off a phosphate energy and turns to ADP ATP energy currency 2 Excitation coupling Ca attaches to troponin excitation Myosin cross bridge interacts with attaches to actin coupling 3 Contraction ATP is broken down knock off phosphate and energy is released Energy is then used for the cross bridge to change shape which pulls attached actin Z bands moved closer together 4 Recharging New ATP is placed on the head of the cross bridge Allows cross bridge to detach from the actin Now set up to do contraction phase again 2 15 Function of skeletal muscle Motor unit motor nerve and all the muscle fibers it innervates communicates with through the moto endplates neuromuscular junctions Size of motor unit is dictated by the precision accuracy and coordination of movement More precise small motor unit Motor endplates don t actually touch the fibers synapse gap Strength gradations 1 Multiple motor unit summation Sum up the effect pick up something light and you need a few motor units versus picking up something heavy and you need more stimulated motor units 2 Wave summation Increase in frequency in which a muscle is stimulated increases contraction strength Tetanus such rapid stimulation of a muscle fiber that it doesn t get the chance to relax b w stimuli and it produces a smooth sustained contraction tetanus fatigue Tension or strength Unfused tetanus Peak tension Twitch response to single stimulus Response to two consecutive stimuli relaxing Time sec All or nothing either you hit minimum threshold or you get nothing 0 tension doesn t produce the tension and 10x doesn t produce 10x the tension Two consecutive stimuli stimulate again before it has a chance to relax that s how you get more tension strength Nervous physiology Myelin sheath covers axon but not where hot dogs hook together node of Ranvier Fatty substance Insulation speeds up nervous transitions 2 17 Three basic functions of nervous system 1 Excitability 2 Conduction of signals conduct an action potential 3 Integration and regulation in CNS Noci receptor sensitive to pain Noci excites afferent sensory nerve fiber Information conducted into spinal cord CNS Myelin sheath covering axon needs fast reaction Results in action by efferent motor nerve fiber Myelinated as well Action potential Happens on axon At rest inside is negative 70 mV POLARIZED Depolarization becomes more positive less negative the ion Na leaks in 20 mV Repolarization goes back to negative close Na gates and K gates open Hyperpolarization occur across cell body or dendrites Cl ions coming in becomes more negative 70mV 90 mV WAVE OF DEPOLARIZATION 70mV 20mV Na charge diffuses 70mV 40mV Open at 40mV Na influx K Na gates shut first Voltage regulated gates 2 19 Hyperpolarization make more polar Make axon more negative using Cl Purpose is to keep the muscle from contracting Neuromuscular junction synapse b w motor nerve and muscle Neurotransmitter released and goes across synapse Acetylcholine Always lets in Na Broken down fast so the gates can close acetylcholinesterase breaks down Ach Inhibits a muscle from contraction Allows sodium gates to close Excitatory transmitter substances Acetylcholine Ach Opens gates for Na Causes depolarization Inhibitory transmitter substances GABA glycine Opens gates to let in Cl Causes hyperpolarization 2 22 Spatial and temporal summation Over the space of a membrane Over time Three people bang on a door in three different spots at the same time spatial summation Added Na ions 1x 2x then 3x temporal summation multiple times summed up Specialized sense organs in neuromuscular system 1 Muscle spindle Found in muscle Afferent sensory nerve fibers coming from it going to CNS Sensitive to the degree or amount and the rate of muscle stretch Not just how much but also how fast it stretches Excited by stretch and excites sensory nerves DEPOLARIZATION Sensory neuron goes to CNS with information from the stretched muscle CNS says that it doesn t want the muscle stretched so it sends out a motor nerve to that muscle which leads to contraction of the muscle Agonist where the reflex originates stimulation antagonist is inhibited 2 Golgi tendon organ Found in tendon Golgi responsible for finding these Sensitive to tension in the tendon due primarily to muscle contraction Sensory nerve comes to CNS and says did you know it was this much tension CNS says that it doesn t want the muscle contracted and hyperpolarizes muscle Every nerve only has ONE neurotransmitter Inhibit agonist at the same time you stimulate the antagonist 2 24 Best way to describe motion Axes and planes of motion Axes of rotation 1 Mediolateral ex flexion and extension of knee o From medial middle to lateral side o Sagittal plane of motion 2 Anteroposterio ex moving trunk torso from right to left 3 Longitudinal o From anterior to posterior o Frontal plane of motion o Runs the length of a bone o Transverse plane of motion Anthropometrics Measurement of size shape and proportions of human body and its segments ex height weight Biomechanical advantage weight of football player height of basketball player center of gravity Ponderal index 103 3 weight height Weigh a lot higher PI stocky and short Very tall lower PI tall and thin Somatotype based on simple measures of the body Ectomorph lean not much adipose or muscle ex marathon runner Mesomorph high degree of muscle ex running back Endomorph high degree of adipose tissue 2 26 Neuromuscular aspects of movement Muscle properties Irritability can conduct a wave of depolarization action potential Contractibility can develop