1. Exercise, Muscle, Motor Neuron, and Anxiety
Yufeng Zhang

2. Outlines Exercise physiology (Mainly muscle physiology)
Exercise and neural control/function
Exercise and anxiety

3. 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

4. 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

6. 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)

7. 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

9. 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.

10. 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

12. 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

13. Recruitment of motor neurons
Size principle
Motor units with small number of muscle fiber first
Larger units later

14. 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

17. Exercise and HPA Exercise Decreased heart rate
Enhanced oxidative capacity
Decreased blood pressure
Spatial learning
Memory tasks
Neurogenesis
Improved coping with stress

18. For birds
Migration
Over-winter residences

19. Results

20. Results

21. Results
Thymus and adrenal --HPA axis

22. 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.

23. Results

24. Results Adrenocorticotropic hormone (ACTH)
Driving and negative feedback mechanisms may be playing a role

25. Results
Anticipatory and adaptive to support metabolism for the upcoming physical activity

26. Results
CBG: corticosterone-binding globulin

27. Results

28. Results

29. GR: lucocorticoid receptor MR: mineralocorticoid receptor
MR levels can bedown-regulated by glucocorticoid hormones

30. 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

31. 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

32. Discussion
Exercise training has been shown to exert anxiolytic and antidepressant effects
Parallels with the mechanism of action of antidepressant drugs

33. 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

37. 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.