Muscle Tissue Chapter # 4 6/13/ Muscular System
Muscles “muscle” = myo- or mys- sarco- = “flesh” - also refers to muscles 6/13/ Muscular System
Main Functions of Muscles 1.Produce movement 2.Maintain posture & body position 3.Stabilize joints 4.Generate heat Additional: protect organs, valves, dilate pupils, raise hairs 6/13/ Muscular System
Types of Muscle Tissue Skeletal : voluntary, striated, multinucleated Cardiac : (heart) striated, involuntary Smooth : visceral (lines hollow organs), nonstriated, involuntary 6/13/ Muscular System
Special Characteristics Excitability – can receive and respond to stimuli Contractility – can shorten forcibly Extensibility – can be stretched or extended Elasticity – can recoil and resume resting length after being stretched 6/13/ Muscular System
Gross Anatomy of Skeletal Muscle 1 muscle = 1 organ Each muscle served by a nerve, artery, & vein (1+) Rich blood supply – need energy & O 2 Connective tissue sheaths: wraps each cell and reinforce whole muscle Attachment : (1) directly to bone, (2) by tendons or aponeuroses to bone, cartilage, or other muscles 6/13/ Muscular System
Muscle Muscle cells + blood vessels + nerve fibers Covered by epimysium (connective tissue) Fascicle Bundle of muscle cells Surrounded by perimysium Muscle fiber (cell) Surrounded by endomysium Myofibril Complex organelle Sarcomere Contractile unit Organization of Skeletal Muscle 6/13/ Muscular System
6/13/ Muscular System
Anatomy of Muscle Fiber Multinucleate cell Up to 30 cm long Sarcolemma (plasma membrane) Sarcoplasm (cytoplasm) Myofibril = rodlike organelle Contains contractile element ( sarcomeres ) Alternating light (I) and dark (A) bands 6/13/ Muscular System
Sarcomere Smallest contractile unit of muscle fiber Region between 2 successive Z discs 6/13/ Muscular System
Sarcomere Protein myofilaments : Thick filaments = myosin protein Thin filaments = actin protein 6/13/ Muscular System
Myofilaments Thick Filaments Myosin head: forms cross bridges with thin filaments to contract muscle cell Thin Filaments Tropomyosin: protein strand stabilizes actin Troponin: bound to actin, affected by Ca 2+ 6/13/ Muscular System
Sarcoplasmic Reticulum (SR): specialized smooth ER, surrounds each myofibril Stores and releases calcium T Tubule : part of sarcolemma, conduct nerve impulses to every sarcomere Triggers release of calcium from SR 6/13/ Muscular System
Sliding Filament Model During contractions : thin filaments slide past thick ones so they overlap more 6/13/ Muscular System
Sliding Filament Model cross-bridge Myosin heads latch onto active sites on actin to form a cross-bridge Attachments made to propel thin filaments to center of sarcomere 6/13/ Muscular System
Basic Muscle Contraction 1.Stimulation by nerve impulse action potential 2.Generate and send electrical current (action potential) along sarcolemma 3.Rise in calcium ion levels to trigger contraction 6/13/ Muscular System
Nerve Impulse motor neuron 1 nerve cell (motor neuron) stimulates a few or hundreds of muscle cells Motor unit = 1 neuron + muscle cells stimulated Axon: extension of neuron Axon terminal: end of axon Neuromuscular junction (NMJ): where axon terminal meets muscle fiber Synpatic cleft: space between neuron & muscle fiber Acetylcholine (ACh): neurotransmitter 6/13/ Muscular System
Excitation of Muscle Cell 1.Action potential travels down axon and arrives at neuromuscular junction acetylcholine (ACh) 2.Release of acetylcholine (ACh) into synaptic cleft 3.ACh diffuses across cleft & attaches to ACh receptors on sarcolemma of muscle fiber sodium (Na + ) 4.Rush of sodium (Na + ) into sarcoplasm produces action potential in sarcolemma 5.ACh broken down 6/13/ Muscular System
6/13/ Muscular System
6/13/ Muscular System
6/13/ Muscular System
6/13/ Muscular System
6/13/ Muscular System
6/13/ Muscular System
Contraction of Muscle Cell 1.Action potential travels down sarcolemma along T- Tubules 2.Calcium is released from SR 3.Calcium binds to troponin changes shape myosin binding sites exposed on actin 4.Myosin cross-bridge forms with actin 5.Myosin head pivots and pulls actin filament toward M line 6.ATP attaches to myosin and cross-bridge detaches 7.Myosin can be reactivated 6/13/ Muscular System
6/13/ Muscular System
Homeostatic Imbalances Myasthenia gravis Myasthenia gravis: loss of ACh receptors in sarcolemma by immune system attack progressive muscular paralysis Botulism Botulism: from bacterial toxin; prevents release of ACh at synaptic terminals muscular paralysis Rigor mortis Rigor mortis: “death stiffness” = no ATP production, myosin cross-bridges “stuck” until proteins break down (peak: 12 hrs, fades: hrs later) 6/13/ Muscular System
Muscle Responses Twitches Twitches (single, brief, jerky contractions) = problem, Healthy muscle shows smooth contraction Graded muscle responses Graded muscle responses: different degrees of muscle shortening Greater force by : frequency 1.Increase frequency of muscle stimulation complete tetanus Contractions are summed (max tension = complete tetanus) number of muscle cells 2.Increase number of muscle cells being stimulated 6/13/ Muscular System
Muscle response to changes in stimulation frequency 6/13/ Muscular System
Increasing stimulus Increasing muscle tension 6/13/ Muscular System
Energy ATP ATP = only energy source for muscles Regenerated by: 1.Creatine phosphate (CP) 1.Creatine phosphate (CP): transfers energy to ATP 2.Aerobic respiration 2.Aerobic respiration: complete glucose breakdown with O 2 present 3.Lactic acid fermentation 3.Lactic acid fermentation: glucose breakdown without O 2 Muscle fatigue Muscle fatigue: lack of O 2, ATP supply low, lactic acid accumulates, soreness muscle contracts more weakly until it stops 6/13/ Muscular System
Types of Contractions Isotonic “same tension” Muscle length changes Concentric: shortens Eccentric: lengthens Eg. bicep curl, bend knee, smiling Isometric “same length” Muscle length stays same Tension increases Moving against heavy load or immovable object Eg. lifting heavy weights 6/13/ Muscular System
Isotonic Contractions 6/13/ Muscular System
Sequence the events for Muscle Contraction: Put the following events in order: A.Calcium binds to troponin changes shape myosin binding sites exposed on actin B.Myosin head pivots and pulls actin filament toward M line C.ATP attaches to myosin and cross-bridge detaches D.Action potential travels down sarcolemma along T- Tubules E.Myosin cross-bridge forms with actin F.Calcium is released from sarcoplasmic reticulum (SR) 6/13/ Muscular System