ANEQ305 Week 6 Notes
ANEQ305 Week 6 Notes ANEQ305
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This 8 page Class Notes was uploaded by Andrew Everitt on Saturday October 1, 2016. The Class Notes belongs to ANEQ305 at Colorado State University taught by Dr. Hyungchul Han in Fall 2016. Since its upload, it has received 15 views. For similar materials see Functional Large Animal Anatomy/Physiology in Animal Science at Colorado State University.
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Date Created: 10/01/16
ANEQ305 9-26-16 Quiz Friday 9-30-16 Chapter 8.2 Skeletal Muscle Basis of striations in skeletal muscle - Alternating dark bands (A bands) and light bands (I bands) - A band consists of a stacked set of thick filaments and portions of thin filaments that overlap them - H zone (lighter area in middle of A band) has only thick filaments with no overlapping thin filaments - M line (in center of A band) holds thick filaments together - I band consists of thin filaments where they do not overlap with thick filaments - Z line (in center of I band) is a flat cytoskeletal disc where thin filaments connect - Sarcomere is the area between 2 Z lines o Functional unit of skeletal muscle Sliding filament mechanism of muscle contraction - During contraction, thin filaments slide toward center of the A band, resulting in shortening of the sarcomere - Neither thick nor thin filaments change length - Mechanism applies to both vertebrate and non-vertebrate striated muscle Cross-bridge cycling - Occurs during muscle contraction when Ca2+ binds to troponin, troponin changes shape and binding sites on actin are uncovered - Myosin globular heads (cross-bridges) bind to actin - Cross-bridge bends 45 degrees inward, pulling thin filament with it (power stroke) - Myosin detaches from actin and returns to its original conformation, attaching to a new site on actin - Complete shortening is accomplished by repeated cross-bridge cycles Ca2+ is the link between excitation and contraction - Skeletal muscles are stimulated to contract by release of Acetylcholine (ACTH) at neuromuscular junctions - Resulting action potential is conducted along the muscle cell membrane - Surface membrane dips deeply into the muscle fiber to form a transverse tubule (T tubule) o Action potential enters the interior of the muscle fiber along the T tubules o Induces permeability changes in the adjacent sarcoplasmic reticulum - Ca 2+ is stored in the lateral sacs of the sarcoplasmic reticulum - Action potential in T tubule triggers release of Ca2+ from sarcoplasmic reticulum into the cytosol - Elevated cytosolic Ca2+ results in increased binding of Ca2+ to troponin, initiating contraction - During relaxation, Ca2+ is pumped back into the sarcoplasmic reticulum by Ca2+ - ATPase pumps, reducing cytosolic Ca2+ levels Three things ATP is used for - Power stroke - Detachment between myosin and actin - Send calcium back to Sarcoplasmic reticulum through active transport for relaxation ATP powers cross-bridge cycling - Myosin ATPase on thick filaments splits ATP to form adenosine diphosphate (ADP) and inorganic phosphate - ADP and P remain attached to myosin, energizing it - During and after the subsequent power stroke, Pi and ADP are released - Myosin ATPase site attaches a new ATP molecule - Attachment of new ATP permits detachment of the cross bridge, setting up for another power stroke Contractile activity outlasts the action potential that created it - A single action potential lasts 1-2 msec - Produces a muscle contraction (twitch) after a short latent period - Contraction time averages 50 msec o Contraction continues until completion of Ca2+ release - Relaxation time is slightly longer o Relaxation occurs as Ca2+ is pumped back into the sarcoplasmic reticulum - Total twitch time is about 100 msec Myoglobin makes muscle red Muscle Structure - In vertebrates, tendons attach muscle to bones - In arthropods, muscles attach to ridges that project from the inner face of the exoskeleton (apodemes) - Muscles are arranged in antagonistic pairs o Flexors bend a limb o Extensors straighten the limb Motor Units - A single action potential in a muscle fiber produces an all-or-none contraction - Each vertebrate muscle fiber is supplied by only 1 motor neuron - Each motor neuron branches and innervates many muscle fibers - All of the muscle fibers innervated by 1 motor neuron will contract simultaneously, forming a motor unit - To produce stronger muscle contractions, more motor units are stimulated to contract ( motor unit recruitment) - Muscle that provide precise, delicate movements have few muscle fibers per motor unit - Muscles used for powerful, coarsely controlled movement have many muscle fibers per motor unit - Asynchronous recruitment of motor units is coordinated by the brain to prevent fatigue Repetitive stimulation of muscle fibers - If a muscle fiber is stimulated before it relaxes from a previous stimulus, the second contraction is added to the first (twitch summation) o This happens because the duration of the muscle contraction is much longer than the duration of the action potential - Factors contributing to twitch summation o Sustained elevation to cytosolic Ca2+ o More time to stretch the series-elastic component allows a stronger recoil Repetitive stimulation of muscle fibers - If a muscle fiber is stimulated so rapidly that is has no chance to relax at all between stimuli, a smooth sustained contraction occurs (tetanus) - Graded muscle contractions are produced by controlling the number of motor units stimulated and the frequency of their stimulation - Tetanic contraction and asynchronous motor unit recruitment are used in normal physiological motor control Energy Sources for Skeletal Muscle - Phosphagens o ATP is required for muscle contraction, but storage of ATP is limited o Creatine phosphate (vertebrates) and arginine phosphate (non- vertebrates) are the first energy storehouse tapped at the onset of contractile activity o Phosphagens contain a high-energy phosphate group that can be quickly donated to ADP o Vertebrate muscle contains 5x as muscle creatine phosphate as ATP - Oxidative Phosphorylation o Takes place in muscle mitochondria o Requires oxygen o Fueled by fatty acids or glucose o Rich yield (about 30 ATP per glucose) o Used during light to moderate (aerobic) activity o Myoglobin stores oxygen in muscle fibers - Glycolysis o Takes place in muscle cytoplasm o Can form ATP in the absence of oxygen o Fueled by glucose Insects also use trehalose, a non-reducing sugar o Low yield (2 ATP per glucose) o Proceeds more rapidly than oxidative phosphorylation o Used during high-intensity (anaerobic) activity o Produces lactate and accompanying acidosis Fatigue - Decreased contractile response of exercising muscle to stimulation - Causes of fatigue o Local increase in ADP and inorganic Phosphate o Accumulation of lactate o Accumulation of extracellular K+ o Depletion of glycogen energy reserves - Central fatigue involves a decrease in CNS stimulation of motor neurons Oxygen Deficit - An animal must continue to breather deeply and rapidly after exhaustive activity - Oxygen is needed for recovery of energy systems through oxidative phosphorylation o Replenishment of creatine phosphate o Conversion of lactate into pyruvic acid and pyruvic acid into glucose o Replenishment of glycogen stores Sugar/glucose is stored in liver and thigh muscle Thinnest blood vessel that carries blood – Capillaries Skeletal Muscle fiber types - Slow-oxidative fibers (type 1) o 60 -100 msecs to peak tension o Lower myosin-ATPase activity o High resistance to fatigue o Lots of mitochondria o Many capillaries o High quantity of myoglobin o Red in color - Fast-oxidative fibers (type 2a) o 20-40msec to peak tension o Higher myosin-ATPase activity o Intermediate resistance to fatigue o Better for endurance o Lots of mitochondria o Many capillaries o High quantity of myoglobin o Red in color - Fast – glycolytic fibers (type 2b, 2d, or 2x) o Similar to fast-oxidative fibers in speed and myosin-ATPase activity o Low resistance to fatigue o Desirable for short distances o Few capillaries o Low quantities of myoglobin o White in color Adaption of Muscle Fibers - Skeletal muscle has a high degree of plasticity - Regular endurance activities improve oxidative capacity o Increase in number of mitochondria o Increase in number of capillaries - Regular high-intensity activity stimulates hypertrophy (increased diameter) of fast-glycolytic fibers o Increased synthesis of myosin and actin filaments o Increased muscle strength o Growth in size of muscle - Hormones influence muscle size and strength o Testosterone and growth hormone/IGF-I promote synthesis of myosin and actin filaments o Myostatin is a negative regulator of muscle growth - Interconversion between fast-glycolytic and fast-oxidative fibers takes place with specific forms of regular exercise - Unused muscle loses mass and strength - Limited repair is possible due to ability to form new myoblasts if muscle is damaged Smooth muscle - Mostly in walls of hollow organs and tubes - Fibers are smaller than skeletal muscle fibers and spindle-shaped, with a single nucleus - Fibers are arranged in sheets - 3 types of filaments o Thick myosin filaments o Thin actin filaments anchored at dense bodies o Intermediate filaments form a scaffold for dense bodies - No striations – diagonal arrangement of filaments Mechanism of smooth muscle contraction - During excitation, cytosolic Ca2+ is increased - Ca2+ binds with calmodulin - Ca2+-calmodulin complex binds to and activates myosin light chain kinase (MLC kinase) - MLC kinase phosphorylates myosin light chains - Allows myosin heads to interact with actin and cross-bridge cycling begins Classification of Smooth Muscle - Phasic vs Tonic o Phasic smooth muscle contracts in bursts triggered by action potentials that cause increased cytosolic Ca2+ o Tonic smooth muscle is partially contracted at all times; varies its contraction according to cytosolic Ca2+ Multiunit vs single-unit smooth muscle - Multiple units must be separately stimulated by nerves to contract o Contractile activity is neurogenic and phasic o Can be initiated by the autonomic nervous system - Single-unit muscle fibers are self-excitable and contract as a single unit o Gap junctions electrically link neighboring cells (functional syncytium) o Contractile activity is myogenic and may be phasic (pacemaker potentials) or tonic (slow-wave potentials) o Modified by autonomic nervous system Neurogenic – from the neuron Myogenic – generates own potential Chapter 7- Endocrine Systems Endocrinology is the study of the evolution and physiological function of hormones - The endocrine system regulates and coordinates distant organs through the secretion of hormones - Hormones are signal molecules delivered by circulatory fluids - In contrast to the nervous system, the endocrine system controls activities that require duration rather than speed - Hormone – chemical messenger Chemical classes of hormones - Peptides and protein hormones o few chains of amino acids o hydrophilic - Protein – long chain of amino acids - Amines o come from tyrosine o Catecholamines are hydrophilic o Thyroid hormones are lipophilic - Steroids o come from cholesterol o Lipophilic Hormone synthesis and secretion - Peptide hormones o Synthesized as large precursor proteins, preprohormones o Portions are cleaved and peptide hormone is packaged into secretory vesicles o Released from cell by exocytosis - Steroid hormones o Cholesterol is synthesized or obtained from diet o Chemically modified by a series of enzymatic reactions o Once synthesized, steroid hormones immediately diffuse across the plasma membrane - Both good and bad cholesterol - Steroids diffuse in blood Progesterone is the key for maintaining pregnancy Mechanism of hormone action - Hormones are widely distributed, but only target cells have receptors to respond to each hormone - Peptide and catecholamines bind with membrane receptors o Alter the conformation of adjacent ion channels, or o Activate second-messenger systems - Steroid and thyroid hormones pass through the plasma membrane and bind with internal receptors o Receptors inside the cell are transcription factors that regulate specific genes o Hormone receptor complex binds with hormone response element (HRE) on nuclear DNA o Turns on synthesis of a specific protein - Hydrophilic bind with membrane receptors - Hydrophobic bind inside the cell Regulation of plasma concentration of hormones - Negative Feedback control o When plasma hormone levels fall, hormone secretion is stimulated - Neuroendocrine reflexes o Produce a sudden increase in hormone secretion in response to a specific stimulus - Biological rhythms o Secretion of most hormones rhythmically fluctuates as a function of time (biological clocks) o Readjustment of set points by CNS - Diurnal rhythm – hormone levels change with cycle of the day - Growth hormone goes up at night Endocrine Disorders - Hyposecretion – inadequate secretion of a hormone o Primary hyposecretion – abnormality within the gland o Secondary hyposecretion – deficiency of tropic hormones - Hypersecretion – excessive secretion of a hormone o Primary or Secondary - Endocrine-disrupting chemicals (EDCs) o Human-made substances released into the environment that mimic or oppose the actions of hormones - Pituitary gland produces 6 hormones - More than 1 hormone can be produced from 1 organ - Hormones may have more than 1 target organ or cell - Vasopressin (kidney, atrioler smooth muscle) and oxytocin - Neurohormone – released from neuron and supposed to be neurotransmitter but is released into blood and acts as hormone Steroid Hormones - Produced when needed - Not stored in vesicles like other hormones Peptide and Amine Hormones - Produced from tyrosine Preprohormone – precursor to prohormone which is precursor to hormone Exam Friday 10-7-16 Key Highlighted = extra lecture information Underlined = important info Bold= slide header Bold and underlined = chapter title