Neuroendocrine Regulation of Exercise - Notes

Nervous System Overview

Preganglionic: Cell bodies in CNS, myelinated, release acetylcholine.
Postganglionic: Extend from autonomic ganglion, unmyelinated.
- Sympathetic: Release epinephrine and norepinephrine (increase heart rate and contraction).
- Parasympathetic: Release acetylcholine (slow heart rate, vasodilation, lower contraction force).

Cholinogenic or Adrenogenic: Stored in synaptic vessels and released via exocytosis.
Sympathetic Nervous System: Neural pathways to various organs.
Parasympathetic Nervous System: Efferent pathways from the brainstem and sacral plexus.

Sympathetic Nervous System: Fight or flight; increases alertness and metabolism; longer lasting and widespread effects; triggers hormonal responses (epinephrine, norepinephrine).
Parasympathetic Nervous System: Rest and digest; slows bodily responses; short-lived and isolated effects.
Autonomic Tone: Balance between systems, regulated by the hypothalamus.
Sympathetic vs. Parasympathetic:
- Sympathetic: Widespread, longer-lasting due to hormonal release; no direct innervation.
- Parasympathetic: Short-lived, direct innervation for targeted effects.

Hormone response system that works with the nervous system to maintain homeostasis.
Hypothalamus: Links the nervous and endocrine systems.
Pituitary Gland: Master endocrine gland.
- Two Lobes: Anterior and posterior, influence hormone release.

Located on the trachea, regulates metabolism.
- Hormones: T3 (triadothyronine) and T4 (thyroxine).
  - Increase metabolic rate and stimulate cellular oxygen use.
  - Stimulate sodium-potassium pump and increase protein synthesis.
- Calcitonin: Regulates calcium levels and opposes parathyroid hormone.

Located behind the thyroid gland; regulates blood calcium and magnesium levels resulting in regulation of osteoclast/blast activity.

Key hormones: Glucagon and insulin.
- Glucagon: Increases blood glucose levels.
- Insulin: Decreases blood glucose levels.

Work together to coordinate body systems.
- Nervous: Local neurotransmitter release, acts quickly and is more fine tuned.
- Endocrine: Slower hormone release via blood, longer lasting, more broad.

Hormone Responsiveness: Influenced by hormone concentration, receptor amount, and other hormones.
- Permissive: Enhance outcome (e.g., epinephrine and T3/T4 for lipolysis).
- Synergistic: Ensure normal function (e.g., follicle stimulating hormone and estrogens).
- Antagonistic: Oppose each other (e.g., insulin and glucagon).
Hormone Secretion Control: Short bursts regulated by nervous system signals, blood chemistry changes, and other hormones.
- Regulation via Negative and Positive Feedback.

Neural Role in Exercise:
- Brain controls skeletal muscle contraction, cardiovascular, and respiratory systems; coordinates with endocrine system.

Heart: Sympathetic increases rate and force; parasympathetic decreases rate.
Liver: Sympathetic increases lipolysis, glycogenolysis, and gluconeogenesis.
Fluid Balance: Sympathetic increases sweating, renin secretion, and ADH secretion; parasympathetic has minimal effect.

Cardiovascular: Enhances cardiac function (epinephrine, norepinephrine), directs blood to active tissue, and maintains blood pressure (ADH).
Muscle and Bone: Muscle repair and growth (estrogen, progesterone, testosterone, growth hormone, insulin-like growth factor 1).
Adipose Tissue: Regulates hormone balance (leptins) and produces hormones (adiponectin, interleukin 6, tumor necrosis factor, resistin).

Over Time:
- Insulin and Glucagon: Antagonistic hormones; glucagon increases, insulin decreases at exercise onset to mobilize glucose.
- Cortisol: Intensity dependent; increases during high intensity to facilitate gluconeogenesis and act as an anti-inflammatory; decreases during low intensity.
- Growth Hormone: Stimulates lipolysis and tissue repair.
Intensity:
- Glucagon: Increases with intensity, stimulating glycogen breakdown.
- Insulin: Decreases at lower intensities to limit glucose uptake in non-working tissue; increases at maximal intensity for recovery.
- Growth Hormone: Minimal change at lower intensities; increases near maximal intensity to stimulate lipolysis and protein synthesis.
- Cortisol: Decreases at lower intensity; increases above 50% max capacity to mobilize glucose and free fatty acids.
- Antidiuretic Hormone (ADH): Increases with intensity above 50% maximum to minimize water loss.

Epinephrine and Norepinephrine:
- Trained individuals: Lower response due to higher turnover at submaximal intensities;
- Greater capacity to release more at maximal intensities.
Higher turnover leads to faster recovery.
Training leads to a higher turnover, which can lead to a faster recovery.
Metabolic (Insulin and Glucagon):
- Trained individuals: More stable insulin to glucagon ratio, efficient glycolysis.
- Untrained individuals: Unstable ratio, inefficient glycolysis.
- Training leads to a higher insulin to norepinephrine ratio, enhanced lipolysis.
Growth Hormone:
- Trained individuals: Lower and shorter response, less need to mobilize free fatty acids.
- Untrained individuals: Bigger and longer rising response; diminish returns to exercise.
Cortisol:
- Trained individuals: More controlled and lower response due to exercise being less stressful.
- Untrained individuals: Higher, more pronounced, less controlled response.