Neuroendocrine Regulation of Exercise - Notes

Nervous System Overview

• Structural Organization:
  • Central Nervous System (CNS): Brain and spinal cord.
    • Source of thoughts, emotions, and memories.
    • Neurons facilitate signal communication.
  • Peripheral Nervous System (PNS): Outside the CNS.
    • Somatic Nervous System: Sensory (touch, sight, taste, sound) and motor (voluntary muscle movement).
    • Autonomic Nervous System: Internal organs (stomach, lungs, heart); involuntary control; responds to changes in temperature, pressure, and chemical imbalances; motor neurons control smooth/cardiac muscle and hormone release.
    • Enteric Nervous System: Gastrointestinal (GI) tract; regulates contractions, secretions, and endocrine cells within the GI tract.

Key Functions of the Nervous System

• Sensing: Detects internal and external changes (stimuli).
• Integration: Processes information to determine an appropriate response.
• Motor Response: Sends information to effector organs.
• Neurotransmitters: Chemicals facilitating neuron communication
  • Examples:
    • Acetylcholine: Neuromuscular junction.
    • Nitric Oxide: Vasodilator.
    • Serotonin: Mood.
    • Epinephrine: Fight or flight.
    • Endorphins: Pain relief.

Exercise Related Neurotransmitters

• Nitric Oxide: Vasodilator, regulates blood pressure and flow.
• Serotonin: Mood elevation.
• Acetylcholine: Muscle contraction.
• Epinephrine: Fight or flight response.
• Dopamine: Pleasure, feel-good sensation.
• Endorphins: Pain mitigation.

Autonomic Motor Neurons

• 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).

Autonomic Nervous System Neurotransmitters

• 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.

Control of Autonomic Functions

• 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.

Endocrine System

• 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.

Anterior Pituitary Hormones

• Human Growth Hormone.
• Thyroid Stimulating Hormone.
• Follicle Stimulating Hormone.
• Luteinizing Hormone.
• Prolactin.
• Adrenocorticotropic Hormone.
• Melanocyte Stimulating Hormone.

Posterior Pituitary Hormones

• Oxytocin
• Antidiuretic Hormone.

Thyroid Gland

• 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.

Parathyroid Gland

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

Adrenal Glands

• Located above the kidneys.
  • Adrenal Cortex:
    • Mineralocorticoids: Maintain mineral balance (e.g., aldosterone).
    • Glucocorticoids: Regulate glucose homeostasis (e.g., cortisol).
    • Androgens: Steroid hormones (e.g., DHEA).
  • Adrenal Medulla:
    • Epinephrine and Norepinephrine: Augment fight or flight response; increase cardiovascular output, blood pressure, blood flow, and glucose/free fatty acid mobilization.

Pancreas

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

Nervous vs. Endocrine System

• 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 Interactions and Control

• 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.

Neuroendocrine Regulation of Exercise

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

Autonomic Nervous System Stimulation of Organs

• 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.

Endocrine System and Exercise - Metabolic Goals

• Ensure Sufficient ATP Synthesis.
• Maintain Blood Glucose for CNS Function.

Endocrine System and Exercise

• 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).

Hormonal Responses to Exercise

• 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.

Adaptations to Training

• 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.