Chapter 15 - Section 15.2 - Study Guide - Assess Your Learning Outcomes - Page 575: 4

The sympathetic nervous system has several pathways by which nerve fibers can leave the sympathetic chain ganglia to reach their target organs and tissues. These pathways include the spinal nerve route, sympathetic nerve route, and splanchnic nerve route. Here are the key differences between these routes: 1. **Spinal Nerve Route**: - **Description**: In the spinal nerve route, postganglionic sympathetic nerve fibers rejoin the spinal nerves directly after leaving the sympathetic chain ganglia. - **Location**: This route is primarily associated with spinal nerves in the thoracic and upper lumbar regions (T1 to L2) because these are the regions where white rami communicantes carry preganglionic fibers into the sympathetic chain ganglia. - **Function**: The spinal nerve route allows for the distribution of sympathetic signals to structures in the body regions served by the thoracic and upper lumbar spinal nerves. It includes targets such as sweat glands and blood vessels in the skin, as well as skeletal muscles. 2. **Sympathetic Nerve Route**: - **Description**: In the sympathetic nerve route, postganglionic sympathetic nerve fibers may bypass the spinal nerves and form sympathetic nerves that travel directly to target organs or tissues. - **Location**: This route can involve sympathetic nerves formed at various levels along the entire sympathetic chain ganglia, not just in the thoracic and upper lumbar regions. - **Function**: The sympathetic nerve route allows for the direct innervation of specific target organs or tissues without traveling through spinal nerves. This is especially important for structures like the heart, lungs, and digestive organs. 3. **Splanchnic Nerve Route**: - **Description**: The splanchnic nerve route involves preganglionic sympathetic fibers bypassing the sympathetic chain ganglia and forming splanchnic nerves that synapse in prevertebral ganglia located in the abdominal cavity. - **Location**: The splanchnic nerve route primarily applies to preganglionic fibers originating in the lower thoracic and upper lumbar regions (T5 to L2). - **Function**: Preganglionic fibers in the splanchnic nerve route synapse in prevertebral ganglia located near target organs in the abdominal cavity. This allows for precise control of digestive and abdominal organ functions, including digestion, blood flow regulation, and secretion. In summary, the differences between these routes lie in their locations, functions, and the specific nerve fibers they involve. The spinal nerve route primarily serves regions associated with the thoracic and upper lumbar spinal nerves, the sympathetic nerve route bypasses spinal nerves for direct innervation of certain targets, and the splanchnic nerve route involves preganglionic fibers bypassing the sympathetic chain for innervation of abdominal organs through prevertebral ganglia. These routes collectively enable the sympathetic nervous system to exert control over a wide range of physiological functions throughout the body.

The sympathetic nervous system has several pathways by which nerve fibers can leave the sympathetic chain ganglia to reach their target organs and tissues. These pathways include the spinal nerve route, sympathetic nerve route, and splanchnic nerve route. Here are the key differences between these routes: 1. **Spinal Nerve Route**: - **Description**: In the spinal nerve route, postganglionic sympathetic nerve fibers rejoin the spinal nerves directly after leaving the sympathetic chain ganglia. - **Location**: This route is primarily associated with spinal nerves in the thoracic and upper lumbar regions (T1 to L2) because these are the regions where white rami communicantes carry preganglionic fibers into the sympathetic chain ganglia. - **Function**: The spinal nerve route allows for the distribution of sympathetic signals to structures in the body regions served by the thoracic and upper lumbar spinal nerves. It includes targets such as sweat glands and blood vessels in the skin, as well as skeletal muscles. 2. **Sympathetic Nerve Route**: - **Description**: In the sympathetic nerve route, postganglionic sympathetic nerve fibers may bypass the spinal nerves and form sympathetic nerves that travel directly to target organs or tissues. - **Location**: This route can involve sympathetic nerves formed at various levels along the entire sympathetic chain ganglia, not just in the thoracic and upper lumbar regions. - **Function**: The sympathetic nerve route allows for the direct innervation of specific target organs or tissues without traveling through spinal nerves. This is especially important for structures like the heart, lungs, and digestive organs. 3. **Splanchnic Nerve Route**: - **Description**: The splanchnic nerve route involves preganglionic sympathetic fibers bypassing the sympathetic chain ganglia and forming splanchnic nerves that synapse in prevertebral ganglia located in the abdominal cavity. - **Location**: The splanchnic nerve route primarily applies to preganglionic fibers originating in the lower thoracic and upper lumbar regions (T5 to L2). - **Function**: Preganglionic fibers in the splanchnic nerve route synapse in prevertebral ganglia located near target organs in the abdominal cavity. This allows for precise control of digestive and abdominal organ functions, including digestion, blood flow regulation, and secretion. In summary, the differences between these routes lie in their locations, functions, and the specific nerve fibers they involve. The spinal nerve route primarily serves regions associated with the thoracic and upper lumbar spinal nerves, the sympathetic nerve route bypasses spinal nerves for direct innervation of certain targets, and the splanchnic nerve route involves preganglionic fibers bypassing the sympathetic chain for innervation of abdominal organs through prevertebral ganglia. These routes collectively enable the sympathetic nervous system to exert control over a wide range of physiological functions throughout the body.