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 gustatory-salivary reflex can be modulated (dampened or enhanced) by input from higher centers in the central nervous system. To modulate the salivary response, descending pathways from the brain would most likely synapse onto which part of the reflex arc?

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 gustatory-salivary reflex can be modulated (dampened or enhanced) by input from higher centers in the central nervous system. To modulate the salivary response, descending pathways from the brain would most likely synapse onto which part of the reflex arc?

Quizplus · Accepted Answer

11ecba2d_0fe7_d9c0_a3bf_afa7be44f644_MD0008_00 Reflexes are involuntary responses to stimuli that do not require input from the brain. A reflex arc is the specific neuronal pathway that facilitates the direct muscular or glandular effect associated with a particular reflex. Reflex arcs begin with the stimulation of a sensory neuron, which leads to an electrical impulse that travels toward the spine along a sensory nerve. This impulse enters the spine via the dorsal root ganglia and can be transmitted in one of two ways: Directly to the effector neuron (ie, a monosynaptic reflex arc), or Indirectly through an interneuron that interfaces with the effector neuron (ie, a polysynaptic reflex arc) Subsequently, electrical impulses initiated in the effector neuron leave the spinal cord through the ventral root and travel along the effector neuron's axon to synapse with and stimulate a muscle fiber, gland, or ganglionic neuron. When the effector neuron synapses with a muscle fiber, it is referred to as a motor neuron. Reflexes can be modulated (dampened or enhanced) by input from the brain. Descending signals from higher areas in the central nervous system (CNS) travel along spinal tracts to act on neurons in the reflex arc whose cell bodies lie within the spine. Based on the gustatory-salivary reflex arc depicted in Figure 1, the cell bodies of both the interneuron and the preganglionic neuron lie within the spine. Therefore, descending input could act on either of these two neurons to alter the gustatory-salivary reflex. (Choices A and B) The taste receptor and salivary glands lie outside the spine (the tongue and oral cavity, respectively) and would not receive direct input from higher CNS areas. (Choice D) By definition, a ganglion is a collection of neuron cell bodies outside the CNS. The cell body of the postganglionic neuron lies within this ganglion, not the spine. A nucleus is a collection of neuron cell bodies inside the CNS. Educational objective: A reflex is an involuntary response to a stimulus that does not require input from the brain. Reflexes are mediated by reflex arcs, neuronal pathways that include a sensory neuron, an effector neuron, and possibly an interneuron.

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