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Download Exercise, Muscle, Motor Neuron, and Anxiety
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Exercise, Muscle, Motor Neuron, and Anxiety Yufeng Zhang Outlines • Exercise physiology (Mainly muscle physiology) • Exercise and neural control/function • Exercise and anxiety Exercise physiology • Exercise – Muscle contration • Excitable (like nerves) • Only pull, not push – Straited muscle and Smooth muscle – Voluntary and Involuntary muscle – Muslce fiber • Multicellular (multinucleate), merging of cells • Parallel to each other Muscle fiber type • Slow twitched fibers – Slow-oxidative • Fast twitched fibers – Fast-glycolytic fibers (muscle hypertrophy) • Fast-oxidative glycolytic • Interconversion between fast muscle-fiber types • Slow and fast fibers are not interconverible. • Proportions can change Overall strength • Muscle fibers employed – Activation of total number of motor neurons – Frequency of AP • Muscle tension – AP in muscle fiber set up sliding interaction • Isometric (same length) • Isotonic (shorten) Muscle fiber • Myofibrils – Myosin, thick – Actin thin – A and I bands • A bands—dark • I bands—light • A bands: thick and thin • I bands: only thin Muscle contraction • Cross-bridge – – – – – – Two filament types sliding over and past each other ATP Myosin heads attaching and detaching Filament overlap Total force : the number of cross- bridges Molecular sequence • Dissociate myosin and actin • Use ATP faster when actin-myosin bonding. Molecular basis • Sliding-filament mechanism – Neither thick nor thin filaments decrease in length – Thin filaments sliding closer of thick filaments • Trigger: – Sarcoplasmic reticulum (SR) wrap around A and I bands – Release of Calcium from SR – Removal of Calcium to muscle relaxation • https://www.youtube.com/watch?v=Ct8AbZn_A8 A Motor Unit • Muscle and nerves working together – Motor neurons leave spinal cord via ventral roots – One muscle fiber – one neuron (motor unit) – Use acetylcholine as transmitter – APs and twitch 1:1 relationship Recruitment of motor neurons • Size principle – Motor units with small number of muscle fiber first – Larger units later Synapses • AP in terminal buttons open Voltage-gated Ca2+ channels • Ca2+ release acetylcholine of the vesicles • Acetylcholine binds receptor on muscle membrane • Chemically gated cation channels: Na+ in K+ out • End-plate potential- local current- open Na+ channels • Na+ initiate AP throughout muscle fiber Exercise and HPA • Exercise – Decreased heart rate – Enhanced oxidative capacity – Decreased blood pressure – Spatial learning – Memory tasks – Neurogenesis – Improved coping with stress For birds • Migration • Over-winter residences Results Results Results • Thymus and adrenal -HPA axis Results • Figure 4. Changes in the size of the left and right adrenal gland in exercising (4 wk) and control mice • higher impact of sympathoadrenomedullary input in the right medulla. Results Results • Adrenocorticotropic hormone (ACTH) • Driving and negative feedback mechanisms may be playing a role Results • Anticipatory and adaptive to support metabolism for the upcoming physical activity Results • CBG: corticosterone-binding globulin Results Results • GR: lucocorticoid receptor MR: mineralocorticoid receptor • MR levels can bedown-regulated by glucocorticoid hormones Discussion • long-term voluntary exercise→ complex changes of the HPA axis →hormonal responses → physical vs. psychological challenges • intensified right-sided sympathoadrenomedullary input • Difference between voluntary and forced exercise Discussion • Nor-adrenaline suppress MR mRNA levels • Exercising mice can produce a normal ACTH response to such potentially life-threatening situations • Exercised mice respond to stressors comprising a strong physical component • Exposure to novelty has lower impact in exercise animals → reduced anxiety Discussion • Exercise training has been shown to exert anxiolytic and antidepressant effects • Parallels with the mechanism of action of antidepressant drugs Exercise and Anxiety • Dentate gyrus contribute to new memories, exploration of novel environment • Exercise ↓ anxiety • Exercise ↑ ventral hippocampus, ↑ anxious behavior. • local inhibitory of GABAA receptors expression Disscussion • Hippocampus of runners may be fine-tuned to respond to different environments optimally. • brain can be extremely adaptive and tailor its own processes to an organism's lifestyle. • Function of new neurons need to be determined.
