Which of the following organs is part of the nervous system?

The brain is a central organ of the nervous system and plays a crucial role in processing sensory information, coordinating bodily functions, and regulating behavior. It is responsible for cognitive functions such as thinking, memory, and decision-making, as well as controlling voluntary muscle movements and managing involuntary processes, such as heart rate and respiration.

Understanding the brain's role underscores its significance in maintaining homeostasis and responding to environmental stimuli. The brain is part of a complex network that includes the spinal cord and peripheral nerves, which work together to transmit signals throughout the body. This integration ensures that the body can react appropriately to various stimuli and maintain its overall function.

The other options listed do not belong to the nervous system. The heart is part of the cardiovascular system, the liver is part of the digestive system, and the lungs are associated with the respiratory system. Each of these organs has distinct functions that do not include the processing and transmitting of information, which is the primary role of the nervous system.