Biology

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...