Chapter 49 (1)

During an __, the subject lies with his or her head in the center of a large, doughnut-shaped magnet. When the brain is scanned with electromagnetic waves, changes in blood oxygen where the brain is active generate a signal that can be recorded.

True or False:
The ability to sense and react originated billions of years ago with prok that could detect changes in their environment and respond in ways that enhanced their survival and reproductive success.
- Later, modification of simple recognition and response processes provided multicellular organisms with a mechanism for communication between cells of the body.
True False

In most animals with nervous systems, clusters of neurons perform specialized functions. However, such clustering is absent in the __, the simplest animals with NSs.
- Hydras, jellies, and other cnidarians have radially symmetrical bodies organized around a __. In most cnidarians, a series of interconnected nerve cells form a diffuse __, which controls the contraction and expansion of the __.

In more complex animals, the axons of multiple nerve cells are often bundled together, forming __. These fibrous structures channel and organize info flow along specific routes through the NS.

Animals with elongated, bilaterally symmetrical bodies have even more specialized NSs.
- Such animals exhibit __, an evolutionary trend toward a clustering of sensory neurons and interneurons at hte anterior (front) end. One or more nerve cords extending toward the posterior (back) end connect these structures with nerves elsewhere in the body.

In nonsegmented worms, a small brain and longitudinal nerve cords constitue the simplest clearly defined __. In some such animals, the entire NS is constructed from only a small number of cells.
- More complex invertebrates and arthropods have many more neurons. The behavior of such animals is regulated by more complicated brains and by ventral nerve cords containing __, segmentally arranged clusters of neurons.

Within an animal group, NS organization often correlates with lifestyle.
- In vertebrates, the brain and spinal cord form the __; the nerves and ganglia comprise the __. Regional specialization is a hallmark of both systems.

The brain and spinal cord of the vertebrate CNS are tightly coordinated. The brain provides the integrative power that underlies the complex behavior of vertebrates. The spinal cord, which runs lengthise inside the vertebral column (__), conveys info to and from the brain and generates basic patterns of locomtion. The spinal cord also acts independelty of the brain as part of the simple nerve circuits that produce __, the body's automatic responses to certain stimuli.

A __ protects the body by triggering rapid, involuntary response toa particular stimulus.

Unlike the __ of many invertebrates, the spinal cord of vertebrates runs along the dorsal side of the body. Although the vertebrate spinal cord does not contain segmental __, such __ are present just outside the spinal cord. Furthermore, an underlying segmental organization is apparent in the arrangement of neurons within the spinal cord.

The brain and spinal cord of vertebrates are derived from the __, which is hollow- a hallmark of chordates. During development, the hollow cavity of the embryonic nerve cord is transformed into the narrow __ of the spinal cord and the __ of the brain.

Both the central canal and the four ventricles are filled with __, which is formed by filtration of arterial blood in the brain. The __ circulates slowly through the central canal and ventricles and then drains into the veins, supplying different parts of hte brain with nutrients and hormones and carrying away wastes.

The __ circulates slowly through the central canal and ventricles and hten drains into the veins, supplying idfferent parts of the brain with nutrients and hormones and carrying away wastes. In mammals, the __ also cushions the brain adn spinal cord by circulating between layers of connective tissue that surround hte CNS.

In addition to these fluid-filled spacess, the brain and the spinal cord contain __ and __.

__ consists mainly of neuron cell bodies, dendrites and unmyelinated axons.

In contrast, __ consists of bundled axosns that have myelin sheaths, which give the axons a whitish appearance. __ in the spinal cord lies on the outside, consistent with its function in linking the CNS to sensory and motor neurons of the PNS. __ in the brain is instead predominantly on the inside, reflecting hte role of signaling between neurons of the brain in learning, feeling emotions, processing sensory info, and generating commands.

The __ present throughout the vertebrate brain and spinal cord fall into a number of different categories. __ cells line the ventricles and have __ that promote circulation of the __. __ protect teh nervous system from invadin gmicroorganisms. __ function in __, a critical ativity in the vertebrate nervous system. (__ perform this function in the PNS.)

Among the different types of glia, __ appear to have the most diverse set of functions. They provide structural support for neurons adn regulat ethe extracellular concentrations of ions and neurotransmitters. __ can respond to activity in neighboring neurons by facilitating information transfer at synapses and in some instancfes releasing neurotransmitters.

__ adjacent to active neurons cause nearby blood vesseles to dilate, increasing blood flow to the area and enabling the neurons to obtain oxygen and glucose more quickly. During development, __ induce cells taht line the capillaries in the CNS to form tight junctions. The result is the __, which restricts the passage of most substances into the CNS. The existence of the extracellular chemical environment of the brain and spinal cord.

__ play a critical role in development of the NS. In an embryo, __ form tracks along which newly formed neurons migrate from the neural tube, the structure that gives rise to the CNS.

Both __ and __ can also act as stem cells, generating neurons and additional glia. Researchers view these multpotent precursors as a potential way to replace neurons and glia that are lost to injury or disease.

The PNS trasmits info to and from the CNS and plays a large role in regulating an animal's movement and internal environment. Sensory information reaches the CNS along PNS neurons designated as __.

Following information processing within the CNS, instructrions then travel to muscles, glands, and endocrine cells along PNS neurons designated as __.

Structurally, the vertebrate PNS consists of left-right pairs of cranial and spinal nerves and their associated __.
- The __ connect he brain with locations mostly in organs of the head and upper body.
- The __ run between the spinal cord and parts of the body below the head.

Most of the __ and all of the __ contain both afferent and efferent neurons. A few __ are afferent only.

The efferent branch of the PNS consists of two functional components: __ and the __.
- The __ consists of neurons that carry signals to skeletal muscles, mainly in response to external stimuli. Although the motor system is often considered voluntary because it is subject to conscious control, much skeletal muscle activity is actually controlled by the brainstem or by reflexes mediated by the spinal cord.

The __ regulates the internal environment by controlling smooth and cardiac muscles and the organs of the digestive, cardiovascular, excretory, and endocrine systems. This control is generally inoluntary. Three dvisons- __, __ and __- together make up the __.

The __ and __ divisios of the autonomic nervous system have largely antagonistic functions in regulating organ function. Activation of the __ corresponds to arousal and energy generation.
Activation of the __ generally causes opposite responses that promote calming and a return to self-maintainence functions.
-

In regulating reproductive activity, the __ complements rather than antagonizes the __. The overall functions of the __ and __ are reflected int he location of neurons i each division and the neurotransmitters that these neurons release.

The __ of the PNS consists of networks of neurons in the digestive tract, pancreas and gallbladder. Within these organs, nbeurons of the __ control secretion and they also control the smooth muscles that produce peristalsis. Although the __ can function independently, it is normally regulated by the __ and __ divisions.

The __ and __ nervous systems often cooperate in maintaining homeostasis.