Major Functions of the Nervous System

Three main functions of the nervous system are sensation, response, and integration.^[1]

Sensation

The first major function of the nervous system is sensation (i.e., receiving information about what is happening within or outside the body). Our five senses receive sensations from the outside world, and various receptors within the body receive internal sensations.^[2]

Paresthesia (par-es-THĒ-zh(ē-)ă) refers to an abnormal sensation in the extremities (i.e., numbness, tingling, and pain), and anesthesia (an-ĕs-THĒ-zhă) refers to a lack of feeling or sensation.

Response

The nervous system produces a response based on sensations received. For example, if our hand accidentally touches a hot stove, the nervous system automatically and quickly moves the hand away. Responses can be classified as voluntary (such as contraction of skeletal muscle) and involuntary (such as contraction of smooth muscles, regulation of cardiac muscle, and activation of endocrine glands).^[3]

Voluntary responses are governed by the somatic nervous system, and involuntary responses are governed by the autonomic nervous system. The somatic nervous system is responsible for conscious perception, senses, and voluntary motor responses. An example of the somatic nervous system is when a person purposefully takes deep breaths to quell feelings of anxiety.^[4]

The autonomic nervous system (ANS) is responsible for involuntary regulation of body processes to maintain homeostasis. For example, sweat glands are controlled by the autonomic nervous system. When a person receives the sensation of feeling hot, the ANS system processes this information and automatically creates a response of sweating to help cool down the body.^[5]

The autonomic nervous system is further divided into the sympathetic nervous system and the parasympathetic nervous system. The sympathetic nervous system is responsible for “fight or flight” responses, and the parasympathetic nervous system controls rest and digestive functions.^[6]

Integration

Stimuli are interpreted and acted upon by the brain during a process referred to as integration. The brain analyzes stimuli with other perceived stimuli, memories of previous stimuli, or the person’s emotional state and generates a specific response. For example, a person may receive an internal sensation from the bladder for the need to urinate. However, the brain analyzes that stimulus and integrates it with the awareness of being in a public area and postpones the response to urinate until there is time to locate a nearby restroom.^[7]

Higher Mental Functions

The cerebral cortex performs higher mental functions referred to as cognitive abilities. The responsibilities for these cognitive abilities are distributed across regions of the cortex, and specific locations can be said to be responsible for particular functions. For this reason, if a particular area of the brain becomes injured or diseased, specific cognitive abilities are affected.^[8]

Cognitive abilities can be classified by four areas: orientation and memory, language and speech, sensorium, and judgment and abstract reasoning^[9]:

• Orientation and Memory: Orientation (or-ē-ĕn-TĀ-shŏn) is the patient’s awareness of their immediate circumstances. In the medical field, this is typically referred to as “being oriented to person, place, and time.” An adult with normal cognitive functioning is aware of their name, where they are and why, and the date. This function occurs in the prefrontal cortex, and it can be temporarily or permanently affected by many medical conditions. Memory (MĔM-ŏ-rē) refers to how the brain stores and remembers information. It is a function of the temporal lobe.
• Language (LĂNG-gwij) and Speech (spēch): Wernicke’s area and Broca’s area are involved in speech and language. See Figure 16.7^[10] for an illustration of the location of Wernicke’s area and Broca’s area in the brain. Both areas are found in a person’s dominant hemisphere, which for most people is the left side of the brain. Aphasia (ă-FĀ-zh-ē-ă) is the inability to speak. Aphasia associated with Broca’s area is known as an expressive aphasia (eks-PRĒS-ĭv ă-FĀ-zh-ē-ă), which means that speech production is compromised, leading to broken, slow, or hesitant speech. Receptive aphasia (rĭ-SEP-tĭv ă-FĀ-zh-ē-ă) is associated with Wernicke’s area, which is a loss of understanding of speech content.

• Sensorium (sĕn-SAWR-ē-ŭm): Sensorium refers to interpretation of sensory stimuli, as previously discussed in this section. The cerebral cortex has several regions responsible for sensory perception.
• Abstract reasoning (ăb-străkt RĒ-zŏn-ĭng) and judgment (JŬJ-mĕnt): Abstract reasoning and judgment refer to making sense of concepts and making appropriate decisions. For example, when your alarm goes off in the morning, you must decide whether to hit the snooze button or jump out of bed. You use judgement and abstract reasoning to decide if the ten extra minutes of sleep is worth rushing through your morning routine or risking being late. The decision you make can potentially impact the rest of your day. The prefrontal cortex is responsible for these functions of planning and making decisions.^[11]