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synergy · 2
Tyrosine competes with the branched-chain amino acids and tryptophan for the same transporter (LAT1) into the brain; the enzyme that makes dopamine and norepinephrine is normally close to saturated, so extra tyrosine only helps refill them when these neurotransmitters are being used up heavily, as during short bursts of intense stress.
During exercise, muscle releases signaling molecules, and brain-derived neurotrophic factor (BDNF) in the brain rises briefly; in animals, these changes promote neural plasticity. They are candidate explanations for how exercise improves mood and thinking, but whether they are the main reason in people has not been shown.
cofactor · 2
Vitamin B12 deficiency damages the myelin sheath that wraps nerve fibers, and the spinal cord pathways for position sense and movement are hit first; this is called subacute combined degeneration. The sooner B12 is replaced, the better the chance the nerves recover; left too long, the damage can become permanent. Methylmalonic acid (MMA) in the blood is a very sensitive marker for catching deficiency early.
The semicircular canals sense rotation, not straight-line movement. When you turn your head, the fluid inside lags behind by inertia, bends a gel-like flap called the cupula, and with it the hair cells' bundles, which fire signals down the nerve at once. In an elevator going straight up or down, they stay quiet.
regulates · 11
The gut and brain talk in both directions. The gut has its own large nerve network (the enteric nervous system), through which, along with the vagus nerve, the brain adjusts gut movement; in animal studies, the short-chain fatty acids made when gut bacteria ferment fiber can influence the brain through routes such as the vagus nerve. Most of the body's serotonin is made in the gut, but it cannot enter the brain and acts mainly in the gut.
The hypothalamus connects the nervous system to the endocrine system: the three hormone axes for the stress response (cortisol), the thyroid and reproduction all take their orders from here. So long-term stress may pull on several hormone axes at once through the hypothalamus.
Motor neurons send their commands across the neuromuscular junction, and only then does the muscle contract. A muscle that loses its nerve supply wastes visibly within weeks. Magnesium affects how excitable nerves and muscles are, and very low blood magnesium can cause muscle twitching and spasms.
The autonomic nerves (sympathetic and vagal) directly adjust heart rate and how tight blood vessels are, and heart rate variability (HRV) is a simple, non-invasive measure of this regulation. Heart attacks happen more often in the morning (Muller 1985), which is thought to be linked with the morning surge in sympathetic activity; long-term stress keeps the sympathetic system switched on and is also thought to raise cardiovascular risk.
The current model of migraine: the trigeminal nerve and the blood vessels of the brain's coverings are activated and release calcitonin gene-related peptide (CGRP), which carries pain signals inward and makes the central nervous system more sensitive. Monoclonal antibodies against CGRP or its receptor, and small-molecule drugs called gepants, have reached the market since 2018 and changed both prevention and acute treatment of migraine.
Breathing shapes the brainstem's control of the autonomic nerves through the carbon dioxide and acidity of the blood, sensed by chemoreceptors, and through stretch receptors in the lungs. Long-term carbon dioxide retention (as in severe chronic lung disease) may affect attention and mood; overbreathing causes dizziness, tingling hands and a racing heart and is easily mistaken for a panic attack.
During infection or inflammation, inflammatory signals such as IL-6, IL-1β and TNF reach the brain and make people listless, sleepy, off their food and withdrawn; this is called sickness behavior. Some people with depression show similar signs of inflammation, which is thought to involve this pathway; gut bacteria shaping the immune system, which in turn shapes the brain, is one possible route of the gut-brain axis.
Caffeine is shaped like adenosine: it occupies the adenosine receptors on neurons without switching them on, keeping the time-to-sleep signal locked out. It does not give you energy; it only mutes the fatigue signal for a while.
After long static stretching of a muscle, that muscle's maximal strength drops briefly and slightly (about 5% in the studies pooled by Simic 2013) and recovers within minutes. There are two reasons: the nervous system's drive to the muscle is temporarily turned down, and the tendon is left slacker, so force is passed on more slowly; the muscle is not injured. With less than 60 seconds per muscle followed by a dynamic warm-up, whole-body performance such as jumping and sprinting is largely unaffected.
When the signal from one frequency band of the cochlea thins out, auditory structures closer to the brain become more active rather than less (central gain enhancement): in animal studies, inhibitory signaling weakens, neurons become more excitable, and spontaneous firing increases. Tinnitus mostly arises along this pathway rather than from the ear itself ringing.
Lion's mane has a respectable mechanistic starting point: in a dish, several of its small molecules make cells produce more nerve growth factor (NGF), which prompts neurons to grow new branches. The chain breaks between the dish and the brain: NGF itself cannot cross the blood-brain barrier, and there is no human evidence on how much of these small molecules reaches the brain after you swallow them, or whether they boost NGF signaling there.
contrast · 1
Ketones are the brain's backup fuel and enter it through transporters such as MCT1; astrocytes making lactate on the spot and handing it to neurons is a separate route (a mechanism that comes mainly from cell studies). Drinking exogenous ketone esters cannot replace this local supply system.