= Solution
\b[The <nervous system> regulates visceral movement, <glandular secretion>, <blood flow> and coordinated bodily responses, while also influencing <nutrition> indirectly through those functions.] Organic or vegetative life here means activities maintaining the body, such as <blood circulation>, <digestion>, <pulmonary ventilation>, secretion and excretion. It does not designate an independent form of living substance.
One influence is directly motor. <Autonomic nerves> alter the rate and force of the <heart>, contract or relax <smooth muscle> in the <intestine>, <urinary bladder>, airways and <blood vessels>, and coordinate movement with the opening and closure of sphincters. Their effect need not be excitatory: an active <vagus nerve> can slow the <heart>, while other pathways accelerate it. In the modern account, <sympathetic> and <parasympathetic> effects depend on the target and its <receptors>; they are not respectively universal accelerator and brake systems. Some organs receive both divisions, while others do not have a simple balanced double supply.<Anatomy and Physiology 2e by J. Gordon Betts and others/15.1 Divisions of the Autonomic Nervous System>[Opening comparison; Sympathetic Division; Parasympathetic Division; target-specific actions]{ref}
A second influence is secretomotor. Activity in appropriate <nerves> can increase <salivary secretion>, alter <gastric acid secretion> and promote <sweating>. This is distinguishable from moving a duct or changing its calibre. A convincing experiment collects a secretion from a cannulated duct while a <nerve> is stimulated, rather than inferring secretion from a change of colour or organ size. For example, stimulation of the <chorda tympani> can evoke fluid from the <submandibular gland>. The response depends on functioning secretory <biological cells>; the <nerve> communicates a command rather than supplying the material constituents of saliva.
A third influence is vasomotor. Changing the calibre of <arterioles> changes local <vascular resistance> and <perfusion>. The classic comparison of an ear before and after interruption of its cervical <sympathetic> supply illustrates loss of vasoconstrictor tone: the vessels dilate and the ear becomes warmer because more warm <blood> reaches it. Stimulation of the peripheral cut pathway can produce the converse vascular effect. Warmth therefore need not mean that the local <nerves> themselves generate more <heat>. Vascular control also changes the delivery of <oxygen> and <nutrients> to a <gland> or <tissue>, so it can modify function indirectly.
These outputs are organized by sensory feedback and <reflexes>. Distension of the <intestine> can evoke coordinated movement; changes in <blood pressure> or blood-gas composition influence <heart rate> and <breathing>. Local circuits in the <enteric nervous system> permit some digestive activity without an intact connection to the <brain>, while longer <reflexes> involve the <spinal cord> or <brainstem>. Central states also matter: the sight or expectation of food can initiate preparatory digestive responses, and fear can alter <heart rate>, <sweating> and visceral movement.<Anatomy and Physiology 2e by J. Gordon Betts and others/15.2 Autonomic Reflexes and Homeostasis>[Long and Short Reflexes; control of cardiovascular and digestive functions]{ref}
Somatic motor activity also supports vegetative functions. <Breathing> uses the <respiratory diaphragm> and other <skeletal muscles>; swallowing and continence use coordinated <skeletal muscle> as well as <smooth muscle>. Thus organic function cannot be identified solely with the anatomical distribution of the <sympathetic nervous system>.
The historical idea of a direct trophic influence requires discrimination. A <denervation> region may change through loss of movement, altered <perfusion>, loss of protective sensation or changed secretion. Those observations alone do not establish a special nutritive fluid flowing down the <nerve>. Modern biology recognizes molecular signalling between <nerves> and their targets, as well as <neuroendocrine signalling> pathways: the <hypothalamus> can influence <hormone> release, and <sympathetic> input can evoke <adrenal medulla> secretion. These are mechanisms added to, rather than evidence for an undefined historical nutritive force. A useful experimental design measures the motor, vascular and secretory consequences separately before assigning a residual effect to direct trophic action.
Back to article page
