D13 Movement and Muscle Tissue PDF

D13 - Movement and Muscle Tissue Functions of Skeletal Muscles 1. Support body Contraction of skeletal muscle opposes force of gravity and enables us to remain upright...

D13 - Movement and Muscle Tissue Functions of Skeletal Muscles 1. Support body Contraction of skeletal muscle opposes force of gravity and enables us to remain upright 2. Make bones move Muscle contraction accounts for movement of arms, legs, eyes, face, and breathing 3. Maintain constant body temperature Causes ATP to break down, releasing heat which is distributed around body 4. Protect organs and stabilize joints Pads bones that protect organs Has tendons that help hold bones together at joints Cooperation of Skeletal Muscles All skeletal muscles pull - can’t push Work of muscles is done during contraction To move parts of the body, muscles work in pairs ○ Ex. To bend elbow, biceps contract ○ Ex. To return arm to straightened state, triceps contract Diagram - Composition of Muscle Mechanism of Muscle Fibre Contractions Muscle contractions rely on action between two types of myofilaments (actin and myosin) Actin: Pair of protein strands woven together that resembles a string of beads (thin) ○ Ex. Myosin: Consists of protein molecules wound together, but is 10x longer than actin and has different shape (thick) ○ Ex. Contraction 1. Myosin head is attached to actin filament. 2. Myosin head then flexes, moving actin filament. 3. Myosin head then releases and unflexes, powered by ATP. 4. Myosin head reattaches to actin filament in new location. Sliding Filament Model Actin “slides” past myosin - movement known as sliding filament model Actin is anchored to position within striated muscle, known as Z-line When muscle contracts, actin moves and Z-line moves along with it These Z-lines are attached to membranes of other cells in tissue, causing contraction of entire muscle Calcium Ions and Contraction When a muscle is relaxed, myosin heads are ready to bind to actin, but can’t ○ Because protein (tropomyosin) physically prevents their binding Tropomyosin can be moved by another protein, called troponin, which is activated when Ca2+ ion from sarcoplasm is bonded to it When muscles contract, Ca2+ ion diffuse into myofibrils and attaches to troponin, allowing myosin heads to bind with actin Energy for Muscle Contraction ATP provides energy for muscles However, the method through which this ATP is produced can vary Three methods our body can use to produce ATP: 1. Creatine phosphate 2. Aerobic cellular respiration 3. Fermentation 1. Creatine Phosphate Anaerobic process: Does not require oxygen ○ Occurs before oxygen enters the mitochondria This molecule builds up when muscle is at rest When muscle starts contracting, stored creatine phosphate gets broken down → generates ATP Provides enough energy for about 8 seconds of intense activity 2. Aerobic Cellular Respiration Takes place in mitochondria Provides most of the muscle’s ATP Myoglobin, an oxygen containing molecule, is synthesized in muscle cells ○ Has higher affinity (strong hold) for oxygen than hemoglobin ○ Temporarily stores oxygen and makes it available to mitochondria when cellular respiration begins 3. Fermentation Supplies ATP in the absence of oxygen Occurs if exercise is so vigorous that oxygen can’t be delivered to muscles fast enough ○ Glucose is broken down to produce lactate ○ Accumulation of lactate causes sarcoplasm to become acidic, eventually cramping and fatigue occur Oxygen Deficit An oxygen deficit occurs when we use fermentation to supply our energy ○ Muscle cells can do this, but brain cells can’t Athletes have an increased number of mitochondria in their muscles - they don’t need to use fermentation ○ Blood pH remains more steady and there is less of an oxygen deficit To get rid of oxygen deficit, we need to replenish creatine phosphate and dispose of lactate