Transcript Exercise, Muscle, Motor Neuron, and Anxiety

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
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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.