Question

Which of the following is not a response to activation of the sympathetic division of the autonomic nervous system? a. increased breathing rate b. decreased heart rate c. increased blood flow to the skeletal muscles d. increased blood glucose levels e. inhibition of digestion

Short answer

The correct answer is 'b. decreased heart rate' as this is not a proper response to sympathetic activation.

Step-by-step solution

Identify the Functions of Sympathetic Division

The sympathetic division of the autonomic nervous system is responsible for the 'fight or flight' response of the body. During its activation, it accelerates the heart rate, dilates the bronchioles to increase air passage into the lungs (which increases breathing rate), prepares the muscles for exertion (which increases blood flow to the skeletal muscles), and promotes glucose release from the liver to provide energy (this increases blood glucose levels). It also redirects energy from non-emergency bodily processes, such as digestion, which is inhibited.

Review the options

From the understanding of sympathetic activation, one can now look into the five options (a-e), each one suggesting a possible response to sympathetic activation.

Select the correct answer

In response to sympathetic activation, the heart rate doesn't decrease but rather increases to prepare the body for fight or flight. Therefore, the correct answer is 'b. decreased heart rate' as it does not correctly represent a response of sympathetic activation.

Key concepts

Autonomic Nervous System

The autonomic nervous system (ANS) is a critical part of our involuntary nervous functions. Unlike the voluntary nervous system, which handles conscious movements, the ANS operates without conscious control. The ANS manages key involuntary functions that keep us alive, such as heart rate, digestion, respiratory rate, and more.
It consists of two main divisions: the sympathetic nervous system and the parasympathetic nervous system.

• **Sympathetic nervous system:** Often described as the body's arousal system, it prepares the body for physical activity.
• **Parasympathetic nervous system:** Known for its role in relaxation, it conserves energy and promotes restful states.

The balance between these systems helps maintain homeostasis—a stable condition needed for health. Each division supports the other, ensuring the body reacts correctly in diverse situations.

Fight or Flight Response

The 'fight or flight' response is a fundamental reaction to perceived threats. It describes how animals, including humans, instinctively react to danger by preparing either to confront it (fight) or escape (flight). This response is governed by the sympathetic nervous system, a division of the autonomic nervous system.
When the fight or flight response is triggered, several changes occur:

• The heart rate escalates to pump more blood to muscles.
• Breathing quickens to increase oxygen supply.
• Glucose is released from stores to provide immediate energy.
• Non-essential systems like digestion slow down to conserve energy.

These physiological changes enable quick action, improving the chance of survival in critical situations. While beneficial short-term, chronic activation—such as from prolonged stress—can lead to health issues.

Sympathetic Division Functions

The sympathetic division of the autonomic nervous system plays a pivotal role in preparing the body to respond to high-stress situations. Its functions are geared towards enhancing survival by enabling rapid responses.
Here's how it functions:

• **Cardiovascular adjustments:** Increases heart rate and blood pressure to ensure sufficient blood delivery to vital organs and muscles.
• **Respiratory changes:** Dilates bronchioles in the lungs to increase airflow, securing more oxygen for bodily tissues.
• **Metabolic effects:** Raises blood glucose levels by stimulating the liver to release glucose, providing crucial energy especially to muscles.
• **Digestive inhibition:** Diverts blood away from digestive processes, effectively slowing or halting digestion.

These changes align with the body's need to prioritize immediate physical capabilities over other functions during a crisis or stress.

Physiological Responses to Stress

Stress triggers a cascade of physiological changes, many of which involve the sympathetic nervous system. These responses prepare the body to face challenges and can have both immediate and long-lasting effects on health.
Key physiological changes include:

• **Adrenaline secretion:** Released from the adrenal glands, it amplifies the fight or flight response.
• **Heart and respiratory rate increase:** Provides more oxygen and nutrients to muscles quickly.
• **Blood flow adjustment:** Redirects blood toward essential organs and muscles, while away from non-critical functions.

While stress responses are beneficial for immediate survival, chronic stress—keeping the body in a state of prolonged sympathetic activation—can lead to health issues like hypertension, impaired immune function, and digestive problems. Managing stress through relaxation techniques and lifestyle changes can mitigate these adverse effects.