Chapter 6 The Muscular System

Chapter 6: THE MUSCULAR SYSTEM Three types of muscular tissue: 1. Skeletal (voluntary)- movement of body  Origin: joins to a bone that remains relatively stationary  Insertion: attaches to another bone across a joint ***the insertion is pulled toward the origin 2. Cardiac (involuntary)- pumping of blood 3. Smooth (involuntary)- control blood vessel diameter/movement in hollow organs SONG: 1. Sarcolemma, sarcolemma, sarcolemma 2. WOOSH 3. T tubule 4. BANG Calcium 5. Calcium comes in 6. Binds to troponin 7. Troponin binds to tropomyosin----SHIFTS-----open myosin binding site 8. Myosin binds 9. Filaments slide 10. Cells get short 11. Contraction is performed Myofibrils: long cylindrical structures that contain protein (myosin/actin) Sarcomere: contractile unit Myosin: forms thick filaments Actin: forms thin filaments Motor neurons: nerve cells that are stimulated to contract (secrete acetylcholine) Neurotransmitter: (acetylcholine) chemical released by nerve cells that has either an excitatory or inhibitory effect on another excitable cell Neuromuscular junction: junction between a motor neuron and skeletal muscle cell Sarcoplasmic reticulum: membrane-bound chambers (“flesh” or “muscle”) Sliding filament mechanism: when the thick/thin filaments slide past each other (sarcomeres shorten) ***once you kill a muscle cell it does NOT grow back Muscle energy/activity: ***ATP is required for both contraction and relaxation  Isotonic contractions: muscles shorten, maintaining a constant force, movement occurs (“same” + “strength” or “tone”)  Isometric contractions: Force is generated, nothing shortens/moves (“same” + “length”) Motor unit: smallest functional unit of muscle contraction Muscle tension: mechanical force muscles generate when they contract Depends on—1. Number of muscle cells in each motor unit 2. The number of motor units active at any one time 3. The frequency of stimulation of individual motor units All-or-nothing principle: muscles are completely under the control of their motor neuron Muscle tone: intermediate level of force (b/w contraction and relaxation) Recruitment: increasing tone (or force) by activation more motor units The relationship between neural stimuli and muscle force: 1. Latent Period 2. Contraction 3. Relaxation 4. Summation: increasing muscle cell force by increasing the rate of nerve cell stimulation 5. Tetanus (maximum contraction-cannot relax) ***can be observed using a myogram SLOW TWITCH o Slowly o Make ATP as needed by aerobic metabolism o Many mitochondria o Well-supplied with blood vessels o Store little glycogen o “Red” muscle o endurance activities FAST TWITCH o Quickly o Rapidly break down ATP o Few mitochondria o Little to no o Lots of glycogen o “White” muscle o Brief high-intensity activity Exercise: -Strength training: short/intense (weight lifting, free weights, machines) -Aerobic training: increases oxygen intake (jogging, walking, biking, swimming) ***with aerobic…blood capillaries, mitochondria, and myoglobin increase…muscle fibers DO NOT Cardiac/Smooth muscles: -involuntary (can contract on own in absence of nerve stimulation) -cardiac joined by intercalated discs (have gap junctions allowing cells to electrically stimulate the next time) -smooth muscle cells join by gap junctions, allowing cells to activate each other -cardiac/smooth muscle cells respond to stimulation from autonomic nervous system which can modify the degree of contraction ***sarcomeres are the smallest contractile unit of a muscle fiber ***there is no difference between a muscle fiber/muscle cell Diseases/disorders:  Muscular dystrophy: “abnormal growth”  Tetanus (caused by bacterial infection… “maximal contraction”)  Muscle cramps  Pulled muscles  Fasciitis (inflammation of the connective tissue sheath, or fascia, that surrounds a muscle)