Passage
Saliva, a secreted fluid with multiple physiologic functions, is composed of water (~99%) , proteins, and electrolytes. Together, these components facilitate nutrient consumption, respiration, and communication. For example, saliva aids in digestion by serving as a lubricant during mastication and by initiating carbohydrate and fat metabolism. In addition, the calcium and phosphate present in saliva promote tooth remineralization, and antimicrobial and chemical buffering agents give saliva protective properties.The gustatory-salivary reflex, the secretion of saliva from the salivary glands in response to gustation (taste) , is primarily mediated by the parasympathetic division of the nervous system. In general, parasympathetic pathways originate from the brain stem or the sacral spinal cord. Fibers originating from nuclei in these regions synapse onto ganglia that lie in close proximity to the target organ. Both preganglionic neurons (those originating from the nuclei) and postganglionic neurons (those originating from the ganglia) release acetylcholine (ACh) .In the gustatory-salivary reflex, activation of taste receptors in the tongue sends impulses to the superior and inferior salivatory nuclei in the brainstem. Local processing within these nuclei activates the parasympathetic pathways that innervate the salivary glands. Ultimately, ACh released from postganglionic neurons acts on the muscarinic acetylcholine receptors (mAChRs) on the secretory cells of the salivary gland to stimulate salivation (Figure 1) .
Figure 1 Parasympathetic regulation of salivary secretionSympathetic stimulation of the salivary glands also promotes salivation but to a lesser degree than parasympathetic stimulation. This may contribute to what is often perceived to be decreased salivation when the sympathetic division is more active than its counterpart. Unlike parasympathetic pathways, sympathetic pathways originate in the thoracic and lumbar spinal segments, and the ganglia lie in close proximity to the spinal cord. Although preganglionic neurons of the sympathetic nervous system release ACh, the postganglionic neurons often release norepinephrine.
-The graph below shows the firing rate of preganglionic neurons within the rat gustatory-salivary reflex arc when the lateral hypothalamic area (LHA) is electrically stimulated at various time intervals before the tongue is stimulated. The results are compared to the preganglionic firing rate following tongue-only stimulation, which was used as a baseline that represented 100% activity. The results of this experiment indicate that at shorter time intervals:

Question

Passage
Saliva, a secreted fluid with multiple physiologic functions, is composed of water (~99%) , proteins, and electrolytes. Together, these components facilitate nutrient consumption, respiration, and communication. For example, saliva aids in digestion by serving as a lubricant during mastication and by initiating carbohydrate and fat metabolism. In addition, the calcium and phosphate present in saliva promote tooth remineralization, and antimicrobial and chemical buffering agents give saliva protective properties.The gustatory-salivary reflex, the secretion of saliva from the salivary glands in response to gustation (taste) , is primarily mediated by the parasympathetic division of the nervous system. In general, parasympathetic pathways originate from the brain stem or the sacral spinal cord. Fibers originating from nuclei in these regions synapse onto ganglia that lie in close proximity to the target organ. Both preganglionic neurons (those originating from the nuclei) and postganglionic neurons (those originating from the ganglia) release acetylcholine (ACh) .In the gustatory-salivary reflex, activation of taste receptors in the tongue sends impulses to the superior and inferior salivatory nuclei in the brainstem. Local processing within these nuclei activates the parasympathetic pathways that innervate the salivary glands. Ultimately, ACh released from postganglionic neurons acts on the muscarinic acetylcholine receptors (mAChRs) on the secretory cells of the salivary gland to stimulate salivation (Figure 1) .

Figure 1 Parasympathetic regulation of salivary secretionSympathetic stimulation of the salivary glands also promotes salivation but to a lesser degree than parasympathetic stimulation. This may contribute to what is often perceived to be decreased salivation when the sympathetic division is more active than its counterpart. Unlike parasympathetic pathways, sympathetic pathways originate in the thoracic and lumbar spinal segments, and the ganglia lie in close proximity to the spinal cord. Although preganglionic neurons of the sympathetic nervous system release ACh, the postganglionic neurons often release norepinephrine.
-The graph below shows the firing rate of preganglionic neurons within the rat gustatory-salivary reflex arc when the lateral hypothalamic area (LHA) is electrically stimulated at various time intervals before the tongue is stimulated. The results are compared to the preganglionic firing rate following tongue-only stimulation, which was used as a baseline that represented 100% activity.

The results of this experiment indicate that at shorter time intervals:

Quizplus · Accepted Answer

11ecba2d_0feb_0e16_a3bf_27af2eed8e40_MD0008_00 In this scenario, researchers are trying to determine whether the lateral hypothalamic area (LHA) of the brain modulates the gustatory-salivary reflex response and, if it does, whether that modulation results in a diminished or enhanced reflex. First, the researchers measured baseline activity in the preganglionic fiber of the gustatory-salivary parasympathetic reflex pathway, which was represented by the firing rate of the preganglionic fiber in response to tongue stimulation alone. The researchers then measured the activity of the fiber in response to sequential stimulation of the LHA and the tongue such that the LHA was stimulated at various time intervals before the tongue. According to the data, the preganglionic fiber responded to this sequential stimulation by exhibiting greater activity at shorter time intervals. This effect was most pronounced when the LHA was stimulated shortly prior to the tongue (<100 msec). The effect weakened as more time elapsed between LHA stimulation and tongue stimulation, and the firing rate of the fiber returned to baseline at a time difference of approximately 200 msec. Therefore, properly timed LHA signaling, which increases the activity of the preganglionic fiber of the gustatory-salivary pathway, would be expected to increase the quantity of salivation due to this reflex pathway. (Choice A) The graph demonstrates a clear relationship between sequential LHA-tongue stimulation and the amount of activity within preganglionic fibers. (Choice C) According to the passage, activation of the gustatory-salivary reflex arc (including the preganglionic fibers that are part of this pathway) results in salivation. Therefore, enhanced activity along this pathway would be expected to increase, not decrease, the magnitude of salivation. (Choice D) The graph indicates that signaling from the LHA affects the gustatory-salivary reflex, which is known to influence the amount of salivation. This suggests that salivation is likely responsive to stimulation of the LHA. Educational objective: Input from higher areas in the central nervous system can modulate the activity of reflexes by either strengthening or weakening the magnitude of the response.

Passage Saliva, a Secreted Fluid with Multiple Physiologic Functions, Is Composed