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Chapter 26 Notes
* Most Animals Have a
Nervous System That Allows Responses to Stimuli
* 26.1 Invertebrates reflect an evolutionary trend toward bilateral symmetry
and cephalization
* Invertebrate Nervous Organization
* In simple animals, such as sponges, the most common observable response is closure of the osculum (central opening)
* Hydras (cnidarians) have a nerve net that is composed of neurons
* Planarians, (flatworms) have a ladderlike nervous system
* In annelids (earthworm), arthropods (crab), and molluscs (squid) the nervous system shows further advances
* Cephalization - concentration of ganglia and sensory receptors in a head region
* Ganglion (pl. ganglia) - cluster of neurons
*
Figure 26.1A Evolution of the nervous system
Figure 26.1A Evolution of the nervous system (Cont.)
* Vertebrate Nervous Organization
* Cephalization, and bilateral symmetry, results in paired sensory receptors to gather information about environment
* Eyes, ears, and olfactory structures
* Central nervous system (CNS)
* Spinal cord and brain and develops from an embryonic dorsal neural tube
* Ascending tracts carry sensory information to the brain, and descending tracts carry motor commands to the neurons in the spinal cord that control the muscles
* Vertebrate brain divided into three parts
* Hindbrain - most ancient part and regulates motor activity below the level of consciousness
* Midbrain - optic lobes are part of the midbrain and was a center for coordinating reflexes involving the eyes and ears
* Forebrain - originally dealt mainly with smell. Later, the thalamus evolved to receive sensory input from the midbrain and the hindbrain and to pass it on to cerebrum
* Cerebrum integrates sensory and motor input and is particularly associated with higher mental capabilities
* Figure 26.1B Organization of the vertebrate brain
* 26.2 Humans...