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Muscles Locomotion Locomotion Organization of muscles into musculoskeletal systems allows the of translation cellular contraction into animal locomotion. Musculoskeletal system interacts with the nervous system to control position and movement of appendages. Locomotion Invertebrates Most worm-like inverts crawl using overlapping layers of muscle fibers. Hydrostatic skeleton: ◦ Simple muscles work in combination with fluid-filled internal chamber. Nematodes Earthworms Locomotor striated muscles organized into circular longitudinal layers. Segmented = more control ◦ Peristaltic waves of contraction Earthworms Squid One of fastest aquatic invertebrates Circular muscle that surrounds the mantle is composed of 3 layers Squid Jet propulsion: ◦ Water enters mantle ◦ Mantle contracts – ejected thru siphon ◦ Creates flume of water, pushing the squid forward Vertebrates Fish Tetrapods: ◦ ◦ ◦ ◦ Amphibians Reptiles Birds Mammals Fish 2 main types of muscle fibers: White muscle: ◦ glycolytic fiber type, responsible for high intensity, burst swimming Red Muscle: ◦ oxidative fiber type, supports slow steady state cruising activity. Fish White Muscle = ◦ 85% of muscle ◦ 60% of body mass Red Muscle = ◦ Along Lateral Line ◦ Base of Fins Fish Myotome: ◦ Blocks of parallel white muscle fibers connected by thin layers of connective tissue. Fish Each myotome connected to posterior region by tendons. Skin acts as sheath that connects different myotomes: ◦ Integrates force of many contractile units Contraction of a myotome generates a force that is transmitted to the next myotome. Muscle Contraction Oxidative (red) & glycolytic (white) muscles differ in contractile properties and produce different types of movement. Muscle Contraction Fish: ◦ Red muscle = slow swimming ◦ White muscle = higher velocities Pattern of sequential activation of muscle contraction = recruitment Determined by motor neurons, under control of the CNS Fish Tetrapods Build individual muscles using combinations of fiber types. Muscle fiber types are used in different combinations to perform many distinct styles of movement. Tetrapods Limb Movements Flexion: when a limb bends at a joint Extension: limb straightens Induced in response to the contraction of antagonistic muscles. Limb Movement Antagonistic muscles: ◦ muscles which work in opposition Locomotor Module: ◦ all of the muscles responsible for a type of movement. Fiber Types 3 Main Types: ◦ Different species have different types with different mechanical properties matched to their biochemistry and morphology. 1. 2. 3. Slow Oxidative (SO) Fast Oxidative Glycolytic (FOG) Fast Glycolytic (FG) Fiber Types Muscle Description Metabolic Features Slow Oxidative (SO) Red Muscles Endurance Muscles Slow Twitch Marathoners Fast Oxidative Glycolytic (FOG) White – Pink Oxidative based metab. metabolism Fast Glycolytic (FG) White Fatigue Sensitive Fast Twitch Quick Response Mixed Fatigue Resistant Fiber Types Fiber composition varies with: 1. Training 2. Muscle Type 3. Animal species / athlete Fiber Types Animal Sea Otter Dolphin Sea Lion Narwhal %SO 56 43 44 87 %FOG 2 10 18 ? %FG 42 47 39 13 Energy Metabolism & Muscle Types Muscle activity demands a great deal of energy, mainly in the form of ATP. Locomotor activity is supported by some combination of anaerobic glycolysis and mitochondrial aerobic metabolism. Energy Metabolism & Muscle Types These two pathways differ in 5 main respects that determine how they support muscle activity: 1. 2. 3. 4. 5. Metabolic Efficiency Rate of ATP Production Dependence on Oxygen Fuel Diversity Range of Mobilization Metabolic Efficiency Anaerobic Aerobic 2 ATP / Glucose 36 ATP / Glucose Used during fast / explosive movements Used during endurance events Used during rest and recovery periods Rate of ATP Production Anaerobic Aerobic Less Efficient Efficient Much Faster Slower Runs out of fuel fast Sustainable Fatigues Dependence on Oxygen Anaerobic Only option when no oxygen is present Aerobic Needs oxygen During high intensity activity, oxygen cannot be delivered to muscles fast enough to meet ATP demands by oxidative phosphorylation and tissues become functionally hypoxic. Fuel Diversity Anaerobic Aerobic Glycolysis relies exclusively on carbohydrates Able to utilize: ◦ carbohydrates ◦ lipids (fatty acids) ◦ proteins (amino acids) Rate of Mobilization Muscles possess low levels of fuels that can be oxidized immediately (glucose, fatty acids, glycerol, free amino acids). These fuels are consumed rapidly, so animals must be able to mobilize stored fuels to sustain muscle activity. Glycogen stores mobilized much faster than lipid stores Mitochondrial Content Mitochondria are the site of oxidative phosphorylation. Mitochondrial content is an important determinant of aerobic capacity. Mitochondrial Content Mitochondrial content varies widely among muscle types and species. ◦ High [Mitochondria] = slow twitch oxidative ◦ Lower [Mitochondria] = fast twitch glycolytic Fiber Types Slow Oxidative (SO): ◦ Dense with capillaries ◦ Rich in mitochondria and myoglobin Fast Oxidative Glycolytic (FOG): ◦ Less dense in mitrochondria and myoglobin Fast Glycolytic (FG): ◦ Least dense in mitochondria and myoglobin Muscle Recovery High intensity activity is fueled by intramuscular stores of glycogen. As fast twitch muscles undergo glycolysis, lactate is produced. Muscles become exhausted from a combination of energetic shortfalls, ion disturbances, and PH imbalance. Muscle Recovery Muscles must: ◦ Replenish energy stores (glycogen, ATP, PCR) ◦ Reestablish ion gradients (Ca2+ stores and pH) ◦ Remove lactate. Lactate Removal 1. Used in muscle to rebuild glycogen stores. 1. Blood-born lactate can be oxidized by other aerobic tissues (eg. Heart) 2. Export lactate to be processed elsewhere. Cori Cycle Lactate Removal Muscle Recovery Oxygen consumption increase with increasing activity. Oxygen stores must be replenished. Muscles must: ◦ Resynthesize ATP, PCR, and glycogen ◦ Reestablish ion gradients ◦ Repair damaged muscles Restoring Oxygen Levels Energy for these processes is provided by mitochondrial oxidative phosphorylation. Recovering animals often show elevated rates of oxygen consumption long after exercise has ceased = oxygen debt. Muscle Recovery Recovery requires both energy & oxygen. Muscles & Locomotion Metabolic processes must be precisely coordinated to ensure that ATP synthesis matches ATP demand. Hummingbirds Hummingbirds Morning/ first flight - oxidizes fatty acids. ◦ After first nectar it switches to carbohydrate utilization and lipid storage. Actively feeding - dietary carbohydrates ◦ Stores extra surcose as glycogen and lipid. Rest - relies on stores. ◦ Also becomes hypometabolic – lowers body temp to reduce MR. Hummingbirds Salmon Salmon Early Stage of Migration: ◦ large fat stores Mid Migration: ◦ begin breaking down proteins: muscles and intestinal tract Late in migration: ◦ glycogen and glucose support Salmon
