UNIT 6 THE MUSCULAR SYSTEM I. Functions of Muscular System A. Produces Movement Internal vs. External «locomotion & manipulation «circulate blood & maintain blood pressure «move fluids, food, baby B. Maintaining Posture C. Stabilizing Joints tendons span across joint D. Generation of Heat ATP ADP + P + Energy 1
II. Types of Muscle (Review) *Muscle cells are also called muscle fibers myomyssarco- SHAPE Elongated cylinder shape Spindle shape NUCLEUS Multi nucleated Single Single APPEARANCE CONTROL CONTRACTION Key Words: SKELETAL SMOOTH CARDIAC Striated, nonbranching Voluntary (reflex also), by nervous system Slow Rapid, Great force, Tire easily Cylinder shape w/ branching ends, intercalated disks Non striated, Striated, Branched arranged in sheets/ ends layers Involuntary, nervous system, hormones Slow sustained contractions Involuntary, nervous system, hormones Sustained steady rate, can increase 2
III. Gross Anatomy: Skeletal Muscle A. Connective Tissue Protection Muscle fibers are fragile Protected by... «Surrounded by connective tissue «Bundled together B. Organization Endomysium: Delicate connective tissue sheath around individual muscle fibers Perimysium: Coarser membrane wrapped around several fibers (Fasicle) «Fasicle: Bundle of fibers Epimysium: Very tough layer surrounding many fasicles making up entire muscle «Blends together at end to form» Tendons: cordlike» Aponeuroses: sheetlike *Tendons & Aponeuroses attach muscle to bones, cartilage, or other connective tissue III. Gross Anatomy: Skeletal Muscle cont'd > Origin: site of attachment on a fixed bone > Insertion: site of attachment on a bone that moves > Action: function ex. 3
IV. Microscopic Anatomy: Skeletal Muscle A. Sarcolemma: plasma membrane of muscle fiber B. Myofibril: organelles that fill up muscle fiber that are made up of smaller units called myofilaments C. Myofilaments: protein filaments that are responsible for the contraction (shortening) of muscle fiber/cell «Myosin: thick filament w/ projections «Actin: thin filament 4
IV. Microscopic Anatomy: Skeletal Muscle cont'd D. Sarcoplasmic Reticulum: smooth ER that surrounds myofibril stores & releases Ca 2+ on demand E. T Tubules: extensions of sarcolemma that penetrate into cell passes by each myofibril, conducts impulse ensures each myofibril contracts at same time 5
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IV. Microscopic Anatomy: Skeletal Muscle cont'd MYOFIBRIL F. Sarcomere: tiny contractile unit linked together making up myofibril one sarcomere goes from z line to z line gives muscle banded appearance «A Band: appear dark because thick Myosin filaments overlap with thin Actin filaments» except for small space in middle (H Zone) «I Band: appear light because only thin actin REVIEW: 7
Sliding Filament Model: Actin slides past myosin causing shortening of muscle fiber Contracted Sarcomere: > I bands shorten > Z lines move closer together > H zone disappears > Successive A bands move closer together > A bands stay same length 8
V. Muscle Stimulation & Contraction A. Terms: > Neurotransmitter: chemical released from axonal terminals > Acetylcholine (ACh): neurotransmitter for muscle contractions > Action Potential: electrical current caused by changes in ion concentration across a membrane > Contractility: ability to shorten/contract > Irritability: ability to receive and respond to a stimulus > Neuron: nerve cell > Motor Unit: motor neuron & all cells it stimulates > Neuromuscular Junction: nerve muscle junction > Synaptic Cleft: gap between axonal terminal and sarcolemma Leave space (~1/3 to 1/2 page) to draw a motor unit Motor Unit > Motor neuron and all muscle fibers it stimulates Neuromuscular Junction 9
Motor Unit > Motor neuron and all muscle fibers it stimulates Neuromuscular Junction V. Muscle Stimulation & Contraction cont'd B. Contraction Intro: POLARIZED MUSCLE FIBER (will add to...) RESTING MEMBRANE POTENTIAL 10
V. Muscle Stimulation & Contraction cont'd B. Contraction Intro: POLARIZED MUSCLE FIBER RESTING MEMBRANE POTENTIAL NEUROMUSCULAR JUNCTION 11
V. Muscle Stimulation & Contraction B. Contraction: > Nerve impulse AP reaches axon terminal Ca 2+ voltage gated channels open & Ca 2+ diffuses in > Acetylcholine is released from axonal terminal & diffuses across synaptic cleft Attaches to sarcolemma (receptors on chemically gated ion channels) > Sarcolemma becomes permeable to Na + ( leads to change in membrane voltage) As Na + diffuses into the cell, local depolarization occurs «Opening Na + voltage gated channels along sarcolemma Depolarization can lead to an ACTION POTENTIAL «Membrane voltage must reach threshold to generate an AP (Depolarization Action Potential) K + diffuses out, repolarization wave occurs (Repolarization) «Due to a certain change in membrane potential» Na+ voltage gated channels close» K+ voltage gated channels open «Repolarization only restores electrical conditions DEPOLARIZATION VS REPOLARIZATION 12
DEPOLARIZATION VS REPOLARIZATION Effects of Membrane Potential Changes 13
V. Muscle Stimulation & Contraction cont'd B. Contraction cont'd: > As AP travels along sarcolemma & T tubules: Calcium ions are released from the sarcoplasmic reticulum > Ca 2+ allows myosin heads to attach to actin filaments (forming cross bridges) Sliding Filament Model Role of: > Ca 2+ > ATP RELAXED SARCOMERE CONTRACTED SARCOMERE > When action potential ends: ACh broken down by Acetylcholinesterase Ca 2+ reabsorbed by SR (via active transport) Na + /K + pump restores ion concentrations Muscle cell relaxes and returns to original length REVIEW: 14
Action Potential: Generation & Propagation Depolarization Action Potential Local Depolarization Repolarization 15
Cross Bridge Cycle 16