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 Fast 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 Muscle tension 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 A bands: thick and thin I bands: only thin 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 Trigger: 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_A8A

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.