VPHY3100: Week of 9/28
VPHY3100: Week of 9/28 VPHY 3100
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This 7 page Class Notes was uploaded by Lorin Crear on Friday October 2, 2015. The Class Notes belongs to VPHY 3100 at University of Georgia taught by Dr. Li, Dr. Wells, Dr. Brown in Summer 2015. Since its upload, it has received 169 views. For similar materials see Elements of Physiology in Animal Science and Zoology at University of Georgia.
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Date Created: 10/02/15
Chapter 11 Endocrinology o Thyroid gland o Consists of spherical hollow sacs called follicles I Follicles are lined by follicular cells I Sac filled with uid known as colloid 0 Also has parafollicular cells 0 Thyroid hormones I T4 amp T3 0 Secreted by follicular cells 0 Regulate body metabolism growth and development 0 Production 0 Hypothalamus secretes TRH anterior pituitary secretes TSH thyroid gland secretes T3ampT4 o 4 and 3 refer to number of iodides attached to molecule I Iodides in colloid obtained from blood by follicular cells I Iodine attached to tyrosine amino acid within thyroglobulin protein to create MIT one I39 or DIT two Iquot 0 T3 MIT DIT 0 T4 DIT DIT 0 Following presence of TSH thyroglobulin molecules to which T4 amp T3 are still attached is taken from the colloid to follicular cells and hydrolyzed to free T4 amp T3 from protein 0 T4 most commonly circulates but T3 is the active form 0 TBG thyroxinebinding globulin is carrier protein that transports hydrophobic T4 in blood 0 Target tissues 0 Liver promotes gluconeogenesis o Skeletal amp cardiac muscle bones brain promotes normal growth and development I Calcitonin 0 Secreted by parafollicular cells 0 Regulate blood calcium levels I Thyroid Hormones vs Steroid Hormones 0 Steroid hormones form HOMOdimers in nucleus in order to promote transcription thyroid hormones form HETEROdimers 0 Steroid hormones formed from cholesterol thyroid hormones formed from tyrosine 0 Steroid hormone receptor proteins reside in cytosol and shuttle to nucleus When bound to hormone in order to promote transcription thyroid hormone receptor proteins reside permanently in nucleus 0 Hypothalamopituitarythyroid axis negative feedback control I Increased concentrations of blood T4 decrease responsiveness of anterior pituitary to TRH and inhibit secretion of TRH by hypothalamus I Thyroid disease 0 Goiter abnormal growth of thyroid gland o Iodine insufficiency endemic goiter o HYPOthyroid condition 0 Low levels of I 9 Low levels of T4 production 9 low levels of circulating T4 9 no negative feedback to anterior pituitary 9 elevated TSH levels 9 increased trophic effects to thyroid gland 9 goiter o Graves disease toxic goiter autoimmune disease 0 HYPERthyroid condition 0 Antibodies mimic effects of TSH at thyroid gland 9 excessive T4 circulation in blood but antibodies not affected by negative feedback loop 9 goiter Chapter 12 Muscle Physiology 0 Muscle Cells 0 Contraction occurs by slidingoverlapping of actin and myosin filaments causes cells to physically shrink Excitationconcentration coupling relies on increase in intracellular calcium 0 Skeletal Muscle I Sarcomere is smallest contractile unit striated striped appearance 0 Stripes due to overlapping of thin and thick filaments I Controlled by somatic motor neurons 0 Cardiac Muscle I Sarcomere is smallest contractile unit striated striped appearance I Pacemaker cells automatic rhythmic action potentials amp contractions I Autonomic motor neurons regulate strength and frequency of contraction 0 Smooth Muscle I No sarcomeres no striated appearance I Controlled by autonomic motor neurons 0 Skeletal Muscle 0 Organization of muscle tissue I Sarcomere smallest unit of muscle cell 0 Center of sarcomere tends to have greatest overlapping of filaments I Myofibril rod of repeating sarcomeres I Muscle fiber aka myofiber muscle cell bundle of myofibrils 0 Sarcolemma plasma membrane of muscle cell 0 Sarcoplasm cytoplasm of muscle cell 0 Sarcoplasmic reticulum specialized endoplasmic reticulum of muscle cells 0 Multiple nuclei in single cell 0 Tend to be very long I Fasciculus bundle of muscle fibers I Muscle bundle of fasciculi o The motor unit I Comprised of single motor neuron and all muscle fibers cells it innervates 0 Typical motor neuron innervates 100 to 1000 muscle cells Depends on Whether it controls fine or gross motor movement 0 But one muscle cell is only innervated by a single motor neuron o All muscle fibers in same motor unit Will be same type of skeletal muscle cell I One muscle comprised of multiple motor units 0 Neuromuscular junction I Specialized synapse between somatic motor neuron s nerve terminal and motor end plate of skeletal muscle cell I Nerve terminals release acetylcholine and interact With nicotinic receptors on motor end plate 9 EPSP o ExcitationContraction Coupling I Transformation of electrical signal action potential in muscle cell into contraction of sarcomeres I Anatomy of a myofiber 0 Sarcoplasmic reticulum SR Surrounds myofibrils as a network of interconnected tubules Terminal cistemae enlarged areas of SR surrounding Ttransverse tubules o Ttubules Continuous With sarcolemma 5 6 Wrap around myofibrils at regular intervals Binding of acetylcholine to nicotinic receptors on motor end plate sparks action potential Sodium channels carry action potential across sarcolemma and through T tubules Action potentials activate voltage gated dihydropyridine receptors DHPRs on Ttubules DHPRs force open ryanodine receptors RyRs they re physically attached to on terminal cisternae of SR RyRs open and allow Ca2 to pass into sarcoplasm Ca2 stimulates contraction of sarcomeres o Sliding filament model of contraction Anatomy of sarcomere 0 Thin filaments actin Two intertwining chains of Gactin Gactin spheres with myosin binding sites Myosin binding sites blocked in relaxed muscle by tropomyosin protein Tropomyosin long strand intertwined with Gactin chains Troponin proteins sit on tropomyosin 0 Thick filament myosin Composed of long rods with head groups Head groups I Each have one ATPbinding site and one actin binding site I Exist in either cocked or exed position relative to actin 0 Only binds to actin in cocked position I Only bind to actin in presence of Ca2 o Zones H zone I Middle of sarcomere I Just thick filaments with no overlap I Gets shorter during contraction A band I Defined by length of thick filament I Does not change size during contractionrelaxation I M line protein filaments that join thick filaments together in middle I band I Ends of sarcomere I Just thin filaments with no overlap I Gets shorter during contraction Z disc I Center of each I band I Mark the ends of each sarcomere I Springlike titin proteins bound here I Contraction Z discs moving closer together 9 shortening of myofibrils 9 shortening of muscle cells I Crossbridge cycle 1 Myosin head in cocked position bound to ADP and Pi inorganic phosphate that was previously hydrolyzed for energy Ca2 circulating in sarcoplasm binds to Troponin C subunit of troponin protein Troponin goes through conformational change which causes conformational change of tropomyosin Tropomyosin moves to uncover myosinbinding sites on Gactin Myosin head binds to actin Pi is released causing myosin head to change from cocked to exed position Conformational change causes power stroke slide of actin filaments ADP is released and replaced by ATP ATP binding causes myosin head to detach from actin ATP is hydrolyzed and myosin head returns to cocked position Multiple power moves cause contraction of muscles Myosin head movements are not synchronized separate power strokes occur at different times 0 Muscle Contraction I Twitch smallest unit of contraction response of muscle to one action potential I Muscle responses Summation Unfused incomplete tetanus Fused complete tetanus Individual twitches cannot be distinguished Not a natural physiological state I Different motor units are not activated in synch I Contraction strength increases With increase in motor unit activation 0 Muscles amp Energy I Production of ATP in muscles 0 Aerobic respiration oxidative phosphorylation in mitochondria o Anaerobic respiration glycolysis and fermentation to lactate For bursts of heavy activity 0 Phosphocreatine For bursts of heavy activity I Use of ATP in muscles 0 Myosin ATPases create contraction 0 Ca2ATPases create relaxation I Fatigue 0 Causes Depletion of muscle glycogen stores Lactic acid accumulation from anaerobic respiration Impaired EC coupling decreased release of Ca2 0 Effects Decreased force production Reduced rate of rise of force Longer time to relax 0 Motor Unit Types I Slow Type I 0 Red bers Slow high oxidative capacity Smaller diameter amp less myosin 9 less forceful contractions o Fatigueresistant I Fast FatigueResistant Type IIA 0 Red bers 0 Fast high oxidative capacity 0 Medium diameter amp more myosin 9 intermediate forcefulness I Fast Fatigable Type IIX White bers 0 Fast low oxidative capacity relies more on anaerobic respiration 0 Large diameter amp more myosin 9 greatest force 0 Fatigue quickly 0 Neural control of skeletal muscle I Proprioceptors in musculature 0 Muscle spindle apparatus Sensory receptor Located on intrafusal muscle fibers specialized fibers that detect amount and rate of change in muscle length Muscle stretch 9 spindle stretch 9 stimulation of sensory neurons Increased length of muscle 9 increased action potential frequency 0 Golgi tendon organs Spinal interneurons Lower motor neurons 0 0tmotoneurons innervate extrafusal type that engage in contraction muscle fibers 0 ymotoneurons innervate intrafusal muscle fibers Corticospinal pyramidal tract 0 Motor cortex 0 Spinal cord Extrapyramidal tract 0 Cerebral cortex 0 Thalamusbasal gangliacerebellum 0 Brain stem 0 Spinal cord 0 Knee jerk re ex monosynaptic stretch re ex 1 2 3 4 Striking of patellar ligament stretches tendon and quadriceps femoris muscle Spindle is stretched activating sensory neuron Sensory neuron activates amotoneuron amotoneuron stimulates extrafusal muscle fibers to contract knee jerk o Reciprocal innervation agonistantagonist muscle 1 2 3 Agonist and antagonist muscle work against each other like quadriceps and hamstring Muscle stretch activates spindle apparatus Agonist muscle quad contracts in stretch re ex Antagonist muscle hamstring relaxes 0 Double reciprocal innervation crossedextensor re ex 1 When walking Flexor of right hamstring contracts extensor of right quad relaxes to lift foot Extensor of left quad contracts exor of left hamstring relaxes to support weight