Muscle Contraction and MovementMusclesContractile apparatusSliding filament theorySliding filament theorySliding filament theoryMotor neurons and muscle contractionMotor neurons and muscle contractionMotor neurons and muscle contractionMuscle Contraction and MovementChapter 30Fig 30.7Muscles• Muscles are attached to bones by tendons• Muscles work in antagonistic pairs– Ex. Biceps and triceps– One muscle contracts while the other relaxesFig 30.8Fig 30.8Contractile apparatus• Skeletal muscle– Muscle cell = muscle fiber (a single cell with one nucleus)– Muscle fibers are made of myofibrils (striated)– Myofibrils are made of units called sarcomeres– Sarcomeres are made of thick and thin filaments– Z line is the end of the sarcomere– Thick and thin filaments slide over one another to shorten the muscle during contractionFig 30.9ASliding filament theory• Links the structure of a sarcomere to its function• During contraction thin filaments slide over thick filaments• Thick filaments= myosin and have “heads”• Thin filaments = actin, these slide• Ca and ATP required for sliding and attachmentFig 30.9AFig 30.9BQuickTime™ and aCinepak decompressorare needed to see this picture.Sliding filament theory• ATP binds to a myosin head, which is released from an actin filament• Hydrolysis of ATP cocks the myosin head• The myosin head attaches to an actinbinding site with the help of Calcium• The power stroke slides the thin filament when ADP and Pi are released from itSliding filament theory• 350 myosin heads per thick filament• Can bind and unbind to thin filament up to 5 times per secondFig 30.10AMotor neurons and muscle contraction• Motor neurons stimulate muscle contraction• Motor neurons are branched and can stimulate more than one muscle fiber• Motor unit = motor unit and all the muscle fibers it controls• Neuromuscular junctions = the synapse between a motor neuron and a muscle fiberFig 30.10AMotor neurons and muscle contraction• The strength of a muscular contraction is controlled by the number of motor units activated. More motor units = stronger contractions• Muscles requiring precise control have one motor neuron per muscle fiberFig 30.10AMotor neurons and muscle contraction• Mechanism of stimulation:– Ap releases acetylcholine into the neuromuscular junction– Ach depolarizes the muscle cell channels inside on the sacroplasmic reticulum release Ca so it can reach the contractile apparatus• Mechanism of relaxation– Motor neuron stops firing– Ca pumped back into the SRFig