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Interactive Lecture 2.2

The Central Nervous System

The Organization of the Nervous System

How is the nervous system organized?
The nervous system is organized into two parts: the central nervous system (CNS), which consists of the brain and spinal cord, and the peripheral nervous system (PNS), made up of nerves that radiate throughout the body, linking all of the body's parts to the CNS.

Figure 2.5

The Brain

What are the major structures and areas of the brain, and what functions do they serve?
Physically, the brain has three more or less distinct areas: the central core, the limbic system, and the cerebral cortex.

The central core consists of the hindbrain, cerebellum, midbrain, thalamus and hypothalamus, and reticular formation. The hindbrain is made up of the medulla, a narrow structure nearest the spinal cord that controls breathing, heart rate, and blood pressure, and the pons, which produces chemicals that maintain our sleep-wake cycle. The medulla is the point at which many of the nerves from the left part of the body cross to the right side of the brain and vice versa. The cerebellum controls the sense of balance and coordinates the body's actions. The midbrain , which is above the cerebellum, is important for hearing and sight and is one of the places in which pain is registered. The thalamus is a relay station that integrates and shapes incoming sensory signals before transmitting them to the higher levels of the brain. The hypothalamus is important to motivation and emotional behavior. The reticular formation , which is woven through all of these structures, alerts the higher parts of the brain to incoming messages.

The Limbic system , a ring of structures located between the central core and the cerebral hemispheres, is a more recent evolutionary development than the central core. It includes the hippocampus, which is essential to the formation of new memories, and the amygdala, which together with the hippocampus governs emotions related to self-preservation. Other portions of the limbic system heighten the experience of pleasure. In times of stress, the limbic system coordinates and integrates the nervous system's response.

The cerebrum takes up most of the room inside the skull. The outer covering of the cerebral hemispheres is known as the cerebral cortex. They are the most recently evolved portions of the brain, and they regulate the most complex behavior. Each cerebral hemisphere is divided into four lobes, delineated by deep fissures on the surface of the brain. The occipital lobe of the cortex, located at the back of the head, receives and processes visual information. The temporal lobe , located roughly behind the temples, helps us perform complex visual tasks, such as recognizing faces. The parietal lobe , which sits on top of the temporal and occipital lobes, receives sensory information from all over the body and oversees in spatial abilities. Messages from sensory receptors are registered in the primary somatosensory cortex . The frontal lobe receives and coordinates messages from the other lobes and keeps track of past and future body movement. It is primarily responsible for goal-directed behavior and is key to the ability to lead a mature emotional life. The primary motor cortex is responsible for voluntary movement. The association areas-areas that are free to process all kinds of information make up most of the cerebral cortex and enable the brain to produce behaviors requiring the coordination of many brain areas.

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Hemispheric Specialization

How are the left and right hemispheres specialized for different functions?
The two cerebral hemispheres are linked by the corpus callosum , through which they communicate and coordinate their activities. Nevertheless, each hemisphere appears to specialize in certain tasks (although they also have overlapping functions). The right hemisphere excels at visual and spatial tasks, nonverbal imagery, and the perception of emotion, whereas the left hemisphere excels at language and perhaps analytical thinking, too. The right hemisphere controls the left side of the body, and the left hemisphere controls the right side.

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Tools for Studying the Brain

What methods have been developed to study the brain?
An increasingly sophisticated technology exists for investigating the brain. Among the most important tools are microelectrode techniques, macroelectrode techniques (EEG), structural imaging (CT scanning and MRI), and functional imaging (EEG imaging, MEG, and MSI). Two new functional imaging techniques, PET scanning and MRI, allow us to observe not only the structure but also the functioning of parts of the brain. Scientists often combine these techniques to study brain activity in unprecedented detail information that can help in the treatment of medical and psychological disorders.

The Spinal Cord

What does the spinal cord do? How does it work with the brain to sense events and act on them?
The spinal cord is a complex cable of nerves that connects the brain to most of the rest of the body. It is made up of bundles of long nerve fibers and has two basic functions: to permit some reflex movements and to carry messages to and from the brain. A break in the cord disrupts the flow of impulses from the brain below that point, causing paralysis.

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