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Wednesday, July 16, 2014

Vital Signs and the Brain

Vital signs are an important measure of basic bodily functions and are part of most physical examinations. The main vital signs typically reported are body temperature, blood pressure, pulse (heart rate), and respiratory rate (breathing rate). Vital signs fluctuate throughout the day but a significantly high or low deviation from normal indicates the presence of some type of medical problem or situational stressor.

Many times, these medical problems or stressors are relatively mild and can be easily managed or treated. Sometimes, however, abnormal vital signs can indicate a problem with the brain or spinal cord.

Although many people may think that vital signs are solely controlled or influenced by the heart , blood vessels, and lungs, it may surprise you to know the brain plays a major role in regulating vital signs. For example, core body temperature is largely regulated by the preoptic area of the anterior (front) hypothalamus (see picture below). The brain communicates to the rest of the body through the spinal cord and vice versa, which establishes an important and continuous feedback loop.

Another area you will see in the above image and below is the brainstem. The brainstem is an area in the lower part of the brain that connects to the spinal cord. The brainstem consists of three parts: the pons, midbrain, and medulla (from top to bottom).

The brainstem contains structures that regulate arousal and the most basic of life functions such as breathing rate. More specifically, there is an area in the pons and medulla that contains special nerve cells that regulates blood pressure control. This area is known as the lateral tegmental area and is located towards the back of the brainstem. The pons, medulla, and spinal cord also contain nerve cell projections that help regulate breathing rate and temperature control.

But wait, you say, I thought that part of the hypothalamus was involved in temperature control. It is, but there are actually multiple areas within the brain and spine that help regulate vital signs. As another example, there is a group of nerve cell bodies known as the solitary nucleus of the medulla that helps regulate heart rate, breathing rate, and blood pressure by sending messages through other parts of the brainstem and spinal cord.

For this reason, the solitary nucleus is also known as the cardiorespiratory nucleus. This nucleus is a good example of the feedback system that takes place between the brain and spinal cord. That is, in addition to sending out information, the solitary nucleus receives information from special sensory receptors located in major blood vessels that are excited by stretching of blood vessels. The stretching generates a nerve impulse that results in information being communicated to the brain.

This basic tutorial shows the importance of the brain for vital sign functions. The next blog entry on this topic will discuss types of damage to the brain and/or spinal cord that can cause abnormal vital signs.

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