3Major Functions of the Muscular System Produce MovementHeat productionMaintain Posture
4Skeletal Muscle-Voluntary Muscle Threadlike cells that have multiple nucleiMany cross striations (stripes)Attached to bones to produce body movement or facial expressionsSmooth Muscle-Involuntary Muscle Elongated narrow cells with single nucleusNo cross striationsFound in the walls of hollow organs to propel food through them by peristalsisCardiac Muscle-Also involuntaryFound only in the heartBranching cells joined by intercalated disks with gap junctions that allow ions to pass freely from cell to cell=rapid conduction of electrical impulse.
10Physiology of Muscles contraction What Happens and Why? 1. A nerve impulse reaches the end of a motor neuron – releases acetylcholineAcetylcholine diffuses across the gap of the neuromuscular junction and binds to receptors on the motor endplate of the muscle fiber.Impulse travels along the sarcolemma, to the T tubules to sacs of the SR.
11THEN What HAPPENS?Ca++ is released from the SR into the sarcoplasm, where it binds to troponin mlcs in the thin myofilaments.5. Tropomyosin mlcs in the myofilaments shift, exposing actin’s active sites.Energized myosin cross bridges of the thick myofilaments bind to actin and pull the thin myofilaments together.Muscles Shortens.
17Types of Muscle contractions Isotonic –muscle shortens and movement occurs.Isometric- muscle does not shorten but tension increases.
18Twitch contractionThreshold stimulus – electrical stimulus of sufficient intensity must be applied to the muscle.A single brief threshold stimulus produces a quick jerk of the muscle.2msec25msec15msec
19Treppe: A Staircase phenomenon A gradual step-like increase in the strength of contraction that can be observed in a series of twitch contractions that occur about 1 second apart.Muscle Fatigue -Repeated stimulation of muscle in time lessens itsexcitability and contractility.
20Tetanus Smooth sustained contractions Stimuli comes in rapid succession the muscle does not have time to relax completely before the next contraction.Normal skeletal muscles exhibit this most of the time.Rapid repeated Twitch contractionsLooks like one continuous contraction
21Muscle Tone --tonic contractions A continual partial contraction. Maintaining posture – sitting or standingWhen you pass out/faint muscle tone is lostMuscles with Less tone are flaccid.Muscles with More tone are spastic.Tone is maintained by a negative feedback mechanisms centered in the nervous system (in spinal cord)
22Muscle ProblemsCramps-painful muscle spasms (involuntary twitches) caused by any irritation or ion and water imbalanceConvulsions-uncoordinated tetanic contractions of varying groups of muscles.May result from a disturbance in the brain or seizure. AP along motor nerve increases and becomes disorganized
23Fibrillation – abnormal contraction in which individual fibers contract outof sync.(asynchronously)instead of at the same time.
24Muscular Disorders Sprains – Joint and ligament damage Myalgia – Muscle painContusions – bruises – localized bleedingPoliomyelitis – Viral infection of the nerves that control skeletal muscles.Muscular Dystrophy – A group of GeneticDisease characterized by atrophy of skeletal muscle tissues. Some forms Fatal
25Myasthenia Gravis – Autoimmune disease in which the immune system attacks muscle cells at the neuromuscular junctionSo nerve impulses are unable to fully stimulate the affected muscle.Hernias – Weakness of abdominal muscles can lead to protrusion of an abdominal organ.Strangulated Hernia – Cuts off blood supply to an organ which can lead to gangrene – death of the organ or individual – Requires emergency surgery.