Question

Which property is characteristic of the sympathetic nervous system? (A) discrete activation of specific organs (B) long preganglionic neurons (C) action terminated by cholinesterase (D) inhibits the enteric nervous system (E) activated by increased arterial blood pressure

Short answer

(D) inhibits the enteric nervous system.

Step-by-step solution

Understand the Sympathetic Nervous System (SNS)

The sympathetic nervous system is part of the autonomic nervous system responsible for the 'fight or flight' response. It prepares the body for stressful or emergency situations by activating various physiological pathways.

Evaluate Each Option

Analyze each option to determine if it aligns with the characteristics of the SNS: - (A) discrete activation: The SNS typically has system-wide effects, not discrete. - (B) long preganglionic neurons: SNS usually has short preganglionic neurons and long postganglionic neurons. - (C) action terminated by cholinesterase: This is more typical of the parasympathetic nervous system. - (D) inhibits the enteric system: SNS can reduce digestive activity, indirectly inhibiting the enteric system. - (E) activated by increased blood pressure: SNS usually raises blood pressure.

Identify Key Sympathetic Actions

Recognize that the SNS typically prepares the body for action by activating multiple systems, including increasing heart rate and blood pressure, dilating airways, and decreasing digestive functions, all fitting the "inhibition of the enteric system."

Consider Options with Known Sympathetic Characteristics

The options containing actions that correlate with the SNS's known physiological effects are considered, such as reducing digestive activity (enteric inhibition), not specifically responding to blood pressure changes or working through cholinesterase pathways.

Select the Best Answer

Given these evaluations, option (D) inhibits the enteric nervous system, correctly describing a common sympathetic action of reducing digestive function.

Key concepts

Autonomic Nervous System

The autonomic nervous system (ANS) is an essential part of our nervous system that controls involuntary bodily functions. It operates below the level of conscious awareness and ensures that critical functions like heartbeat, digestion, and respiratory rate continue smoothly.

The ANS is divided into two main branches:

• Sympathetic Nervous System (SNS)
• Parasympathetic Nervous System (PNS)

Each system plays a vital yet opposite role in maintaining homeostasis. The sympathetic system often stimulates activity, preparing the body for action ('fight or flight'), while the parasympathetic system typically calms the body down ('rest and digest'). These two systems work in tandem to keep our internal environment stable and responsive to changes in our external environment.

Understanding the balance and function of the ANS is crucial, especially when studying physiological responses to stress or relaxation.

Fight or Flight Response

The 'fight or flight response' is a fascinating reaction of the body orchestrated by the sympathetic nervous system. When faced with a perceived threat, the body needs to respond quickly, priming itself for either confrontation or escape.

Here's how this response manifests:

• Increased heart rate and blood pressure to supply muscles with more oxygenated blood
• Dilated pupils to improve vision
• Release of glucose from energy stores in the liver
• Dilated airways to increase oxygen intake

During such stress responses, certain non-essential functions, like digestion, are reduced, enabling more energy for immediate survival needs. This reaction is not only physiological but also psychological, as it increases alertness and readiness for action.

Physiological Pathways

Physiological pathways are the vital routes through which signals travel in the nervous system to elicit responses in the body. In the context of the sympathetic nervous system, these pathways are primarily designed to handle stress and prepare for potential physical demands.

These pathways include:

• Short preganglionic neurons that quickly relay signals from the spinal cord to ganglia.
• Long postganglionic neurons that extend to target organs such as the heart, lungs, and muscles.

The neurotransmitter norepinephrine is commonly released at the end of these pathways, causing changes like increased heart rate or redirected blood flow. Understanding these pathways helps explain how the body manages quick responses to stressors and adjusts various organ functions simultaneously.

Enteric Nervous System

The enteric nervous system (ENS) is often dubbed the 'second brain' of the body, intricately controlling the gastrointestinal system. Unlike other parts of the autonomic nervous system, the ENS can function independently but is still influenced by both the sympathetic and parasympathetic systems.

When the sympathetic nervous system is activated, it can inhibit the ENS. This means a slowdown in digestive processes, which is commonly seen during stressful situations where energy is redirected away from digestion.

Conversely, the parasympathetic system supports the functions of the ENS, promoting digestive activity during restful periods. This balance ensures that the body efficiently manages its resources according to its needs and external challenges.