HESI A2 Science Practice Test 2025 - Free Practice Questions and Study Guide

The brain is a critical component of the nervous system, which is responsible for controlling and coordinating bodily functions, processing sensory information, and facilitating communication between different parts of the body. This system includes not only the brain but also the spinal cord and a network of nerves that extend throughout the body. The nervous system plays a vital role in responding to external stimuli and maintaining homeostasis.

In contrast, the respiratory system is primarily involved in gas exchange, facilitating inhalation and exhalation for oxygen uptake and carbon dioxide removal. The digestive system focuses on the breakdown and absorption of nutrients from food, while the endocrine system regulates various bodily functions through hormones. Thus, the brain is correctly classified as part of the nervous system, which encompasses all aspects of perception, thought, and motor control.