17.7
神经调节
消化开始于头部阶段，准备消化系统接受食物。当我们的大脑处理有关食物的视觉或嗅觉信息时，它会在支配唾液腺和胃的颅神经中触发脉冲来准备食物。
头相是对熟悉食物的条件反应或习得反应。我们对某种食物的胃口或欲望会改变大脑的准备反应。个人可能会产生更多的唾液，胃隆隆作响期待着苹果派而不是西兰花。食欲和欲望是下…
During the first part of digestion, the cephalic phase, the brain responds to related stimuli such as the visual or olfactory information about food before it even enters the mouth.
Such condition control is designed to prepare the digestive system by triggering neural impulses in the cranial nerves that innovates salivary glands to produce more saliva. The vagus nerve is also activated and increases the production of gastric juices in the stomach.
Once food is swallowed, digestion becomes an unconditioned reflex governed by a branch of the autonomic nervous system called the enteric nervous system or ENS, which governs smooth muscle movements that churn and propel food along the digestive track, from the esophagus to the anus.
The arrival of food in the stomach during the gastric phase stretches the walls and the distention is detected by mechanoreceptors in the ENS. Other sensory receptors, chemoreceptors, detect changes in pH in the stomach as the food is turned into chyme, a liquid mixture of food and gastric juices.
During the intestinal phase, when chyme moves into the duodenum, the beginning of the small intestine, similar receptors are activated. In both gastric and intestinal phases, activation of ENS receptors is connected to the secretion of digestive hormones, establishing a neuroendocrine relationship in digestion.
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Q1: What happens during the cephalic phase of digestion?
During the cephalic phase, the brain responds to visual or olfactory information about food before it enters the mouth. This triggers neural impulses in cranial nerves that stimulate salivary glands to produce more saliva and activate the vagus nerve to increase gastric juice production in the stomach. The cephalic phase is a conditioned response modified by appetite and desire, which are controlled by the hypothalamus and amygdala.
Q2: How does the enteric nervous system control digestion after food is swallowed?
Once food is swallowed, the enteric nervous system (ENS) governs digestion as an unconditioned reflex. The ENS directs smooth muscle movements that churn and propel food along the digestive tract through monogastric digestion and peristalsis. Unlike the cephalic phase, this process occurs automatically regardless of food type and does not require conscious learning or brain involvement.
Q3: What role do mechanoreceptors and chemoreceptors play in the gastric and intestinal phases?
Mechanoreceptors detect stretching and distension of the stomach and duodenum walls when food arrives. Chemoreceptors detect changes in pH and chemical composition of chyme, the liquid mixture of food and gastric juices. This sensory information from both receptor types is used to coordinate digestive steps and signal the release of digestive hormones through a neuroendocrine relationship.
Q4: Why is the enteric nervous system sometimes called the little brain?
The enteric nervous system contains 200-600 million neurons and uses many of the same neurotransmitters as the central nervous system and brain. Because of these similarities, ENS neurons are susceptible to the same neurological insults as brain neurons, creating links between gut disorders and neurological disorders like Parkinson's disease.
Q5: How does the enteric nervous system communicate with the brain?
The enteric nervous system functions mostly independent of the brain, with approximately 90% of communication flowing from the ENS to the brain rather than the reverse. These messages provide the brain with information about satiety, nausea, bloating, and other digestive states, establishing a bidirectional gut-brain axis that influences overall digestive regulation.
Q6: What is the difference between conscious and unconscious digestive processes?
The brain directs skeletal muscles for conscious processes like swallowing and defecation. The enteric nervous system, however, directs smooth muscle movements and sensory detection throughout the digestive tract automatically. This division allows voluntary control over entry and exit of food while the ENS handles involuntary propulsion and chemical processing.
Q7: How does appetite influence the cephalic phase of digestion?
Appetite and desire, controlled by the hypothalamus and amygdala, modify preparatory responses during the cephalic phase. Individuals produce more saliva and experience stomach rumblings in anticipation of preferred foods like apple pie compared to less desirable foods like broccoli. This learned response demonstrates how emotional and visceral brain areas personalize digestive preparation.