BIOL 1911 Chapter 49.1: 49.1 – Nervous systems consist of circuits of neurons and supporting cells
29 Apr 2018
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49.1 – Nervous systems consist of circuits of neurons
and supporting cells
• Scientists have begun to sort out the cellular mechanisms for information processing in the brain, thus revealing the
processes that underlie thought and emotion
• Development of powerful imaging techniques reveal activity in the working brain, which allows researchers to analyze
data to determine if there is a correlation between a particular task and activity in specific brain areas
• Use of brainbow technology to develop detailed maps of the connections that transfer information between particular
regions of the brain
o Brainbow = method for expressing random combinations of colored proteins in brain cells; highlights neurons
in the brain of a mouse
• Ability to sense and react originated in prokaryotes, enhancing survival and reproductive success in changing
environments
• Modification of simple recognition and response processes provided a basis for communication between cells in an
animal body, later in evolution
• Specialized nervous system had appeared that enable animals to sense their surroundings and respond rapidly, by the
time of the Cambrian explosion (more than 500 mya)
• Hydras, jellies, and other cnidarians are the simplest animals with nervous systems
o Interconnected neurons form a diffuse nerve net in most cnidarians, which controls the contraction and
expansion of the gastrovascular cavity
• Nerves – bundles of axons of multiple neurons – in more complex animals
o Fibrous structures channel information flow along specific routes through the nervous system
o Ex: sea stars have a set of radial nerves connecting to a central nerve ring; the radial nerve within each arm of
sea star is linked to a nerve net from which it receives input and to which it sends signals that control muscle
contraction
• Cephalization – an evolutionary trend toward a clustering of sensory neurons and interneurons at the anterior end of the
body
o In animals with elongated, bilaterally symmetrical bodies
o Nerves that extend towards the posterior end enable these anterior neurons to communicate with cells
elsewhere in the body
• In many animals, neurons that carry out integration form a central nervous system and neurons that carry information
into and out of the CNS form a peripheral nervous system
o Ex: in nonsegmented worms such as the planarian, a small brain and longitudinal nerve cords constitute the
simplest clearly defined CNS
o In certain nonsegmented worms, the entire nervous system is constructed from only a small number of cells
(only 302 neurons in C. elegans!)
• More complicated invertebrates, such as segmented worms and arthropods, have many more neurons
o Their behavior is regulated by more complicated brains and by ventral nerve cords containing ganglia,
segmentally arranged clusters of neurons that act as relay points in transmitting information
• Nervous system organization often correlates with lifestyle within an animal group
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