Bioenergetics and Metabolic Pathways, part 3, Nervous System, Part 1

Provide energy (especially for the brain and red blood cells), serve as fuel for physical activity, stored as glycogen (~2000 kcal in the body), and contribute to biological structures like glycoproteins and ribose for nucleic acids.

Neuroglia are support cells making up ~90% of CNS cells; they provide nourishment and support, maintain homeostasis, and form myelin sheaths around axons for some neurons.

Carbohydrates can enter anaerobic metabolism via glycolysis or aerobic metabolism via the Krebs cycle, depending on oxygen availability and exercise intensity.

Fat provides ~9 kcal/g, is an efficient energy storage with low water content, serves as primary fuel for organs (heart, kidneys, liver) and for skeletal muscle during low–moderate intensity exercise, and large stored energy (~80,000–100,000 kcal).

Supports cell membrane integrity, satiety, nutrient absorption, inflammation regulation, body temperature maintenance, immune function, organ protection, and facilitates nerve transmission.

Circulating chylomicrons and triglycerides (minor), adipose cell triglycerides, and muscle cell triglycerides; serum free fatty acids (FFA) increase during exercise due to epinephrine stimulation.

About 80% of energy may come from fat, primarily from serum free fatty acids (FFA) released from adipose tissue.

About 32 ATP from glucose and 33 ATP from glycogen when processed aerobically through the Krebs cycle and electron transport chain. [ATP yield differs for fats based on carbon chain length].

ATP yield from fat depends on the carbon chain length; for example, a 16-carbon fatty acid can yield about 106 ATP when fully oxidized.

Aerobic metabolism produces more ATP per substrate without creating acidic conditions in the working cell, can use fats and proteins as substrates, and produces water and CO2 as waste, making it ideal for prolonged low-intensity activities.

The crossover concept describes the shift from lipid-dominant energy use at low–moderate intensities to carbohydrate-dominant use at higher intensities; intensity, training status, and body composition affect the crossover point.

Exercise intensity, endurance training status, and body composition all influence where fat and carbohydrate utilization intersect (the crossover point).

At high intensities, carbohydrates become the dominant fuel; muscle glycogen is the primary source and fatty acid oxidation decreases while carbohydrate oxidation increases.

Increased mitochondrial number and enzymes, increased intramuscular glycogen and triglyceride stores, increased capillary density, improved blood oxygen transport, higher cardiac output, and faster lactate recycling leading to greater reliance on lipid metabolism at submaximal intensities.

Training shifts the lactate threshold to a higher % of VO2max, allowing maintenance of higher intensities before switching to anaerobic metabolism due to improved lipid metabolism and increased mitochondrial and capillary adaptations.

Provides conscious awareness, memory, sensation, thought, perception, subconscious reflexes, initiates movement, maintains homeostasis, detects internal/external disturbances, and coordinates responses via feedback loops.

Understand homeostasis and feedback systems, nervous system organization, neuron structure, CNS/PNS functions, motor units, impulse conduction, size principle, neural adaptations to exercise, and exercise effects on the brain.

Homeostasis is the ability of an organism or cell to maintain internal equilibrium by adjusting physiological processes to keep functions within physiological limits.

Increased body temperature, changes in acid–base balance, hypohydration, changes in blood pressure, and altered blood glucose are common challenges during exercise.

Hypothalamus detects temperature changes → sends signals to effectors: heat triggers sweating and vasodilation to cool, cold triggers vasoconstriction and shivering to generate heat, restoring normal temperature.

An action potential is an electrical impulse initiated and propagated by a neuron when a threshold stimulus is reached; it transmits information along the axon to target cells.

Axon length varies from millimeters to over a meter depending on distance to target cells. Myelination (myelin sheaths) and Nodes of Ranvier enable saltatory conduction, greatly increasing impulse velocity.

Multipolar: many dendrites, one axon (common in CNS); pseudounipolar: single process acting as axon/dendrite (sensory neurons); bipolar: one axon and one dendrite (sensory).

Sensory (afferent) neurons carry information to the CNS; motor (efferent) neurons carry commands from CNS to muscles; interneurons connect sensory and motor pathways within the CNS.

Myelin sheaths increase conduction velocity, enabling faster neural signaling and quicker muscle activation — crucial for rapid, coordinated athletic movements and skill execution.

An action potential arrives at the presynaptic terminal → synaptic vesicles release neurotransmitter into the synaptic cleft → neurotransmitter diffuses and binds receptors on the postsynaptic cell → ion channels open and elicit a response if sufficient binding occurs.

Receptors are proteins that bind specific ligands (e.g., neurotransmitters); each neurotransmitter has specific receptors that open ion channels selective for one ion type, ensuring accurate signaling.

Research examines how exercise affects ANS function, how obesity alters ANS regulation, the impact of ANS dysregulation on conditions like osteoarthritis pain, and how homeostasis is maintained during exercise and environmental stress.