15: The Organization of the Central Nervous System

Introduction

• The Central Nervous System Consists of the Spinal Cord and the Brain

• The Major Functional Systems Are Similarly Organized

  • Information Is Transformed at Each Synaptic Relay

  • Neurons at Each Synaptic Relay Are Organized into a Neural Map of the Body

  • Each Functional System Is Hierarchically Organized

  • Functional Systems on One Side of the Brain Control the Other Side of the Body

• The Cerebral Cortex Is Concerned with Cognition

  • Neurons in the Cerebral Cortex Are Organized in Layers and Columns

  • The Cerebral Cortex Has a Large Variety of Neurons

• Subcortical Regions of the Brain Are Functionally Organized into Nuclei

• Modulatory Systems in the Brain Influence Motivation, Emotion, and Memory

• The Peripheral Nervous System Is Anatomically Distinct from the Central Nervous System

• An Overall View

In the earlier chapters of this book we emphasized that modern neuroscience is based importantly on two tenets. First, the brain is organized into functionally specific areas, and second, neurons in different parts of the vertebrate nervous system, indeed in all nervous systems, are quite similar. What distinguishes one functionally distinct brain region from another, and one brain from the next, are the number and types of neurons in each and how they are interconnected through development. The specific patterns of interconnection and the resulting functional organization of neural circuits in distinct brain regions underlie the individuation of behavior.

All behavior, from simple reflex responses to complex mental acts, is the product of signaling between appropriately interconnected neurons. Consider the simple act of hitting a tennis ball (Figure 15–1). Visual information about the motion of the approaching ball is analyzed in the visual system. This information is combined with proprioceptive information about the position of the arms, legs, and trunk to calculate the movement necessary to intercept the ball. Once the swing is initiated, many minor adjustments of the motor program are made based on a steady stream of sensory information about the trajectory of the approaching ball. Finally, this entire act is accessible to consciousness, and thus may elicit memories and emotions. Of course, as the swing is being executed, the brain is also engaged in maintaining the player's heart rate, respiration, and other autonomic functions that are typically outside the awareness of the player.