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OBJECTIVES

OBJECTIVES

After studying this chapter, you should be able to:

  • Explain the function of the thalamocortical pathway and ascending arousal system in the control of arousal and consciousness.

  • Explain the interplay between brainstem neurons that contain norepinephrine, serotonin, and acetylcholine and diencephalic histaminergic and GABAergic neurons in mediating transitions between sleep and wakefulness.

  • Explain the physiological basis and the main clinical uses of the electroencephalogram (EEG).

  • Describe possible causes of seizure activity and explain the differences between generalized and partial seizures.

  • Identify the primary types of cortical rhythms recorded in an EEG that reflect different states of wakefulness and sleep.

  • Summarize the behavioral and EEG characteristics of rapid eye movement (REM) sleep and the four stages of non-REM sleep.

  • Describe the pattern of normal nighttime sleep in adults and the variations in this pattern from birth to old age.

  • Describe the symptoms of narcolepsy, sleep apnea, and other sleep disorders.

  • Describe the roles of the suprachiasmatic nuclei (SCN) and melatonin in regulation of the circadian rhythm.

INTRODUCTION

Most of the sensory systems introduced in Chapters 8, 9, 10, 11, 12 relay impulses from receptors via multiunit pathways to specific sites in the cerebral cortex. The impulses are responsible for perception and localization of individual sensations; however, they must be processed in the awake brain to be perceived. There is a spectrum of behavioral states ranging from deep sleep through alertness with focused attention. Each distinct state is correlated with a discrete pattern of brain electrical activity. Feedback oscillations within the cerebral cortex and between the thalamus and the cortex produce this activity and are determinants of the behavioral state. Arousal can be produced by sensory stimulation and by impulses ascending from the brainstem to the thalamus and then to the cortex. Some of these activities have rhythmic fluctuations that are approximately 24 h in length (circadian rhythm).

THALAMOCORTICAL PATHWAYS & ASCENDING AROUSAL SYSTEM

THALAMIC NUCLEI

The thalamus within the diencephalon is comprised of groups of nuclei that participate in sensory, motor, and limbic functions. The thalamus is the “gateway to the cerebral cortex” because it processes virtually all information that reaches the cortex. The thalamus also receives input from the cortex.

The thalamus has two major groups of nuclei: those that project diffusely to wide areas of the neocortex (midline and intralaminar nuclei) and those that project to discrete regions of the neocortex and limbic system (specific sensory relay nuclei). The latter group includes the medial and lateral geniculate bodies that relay auditory and visual impulses to the auditory and visual cortices, respectively, and the ventral posterior lateral (VPL) and ventral posteromedial nuclei that relay somatosensory information to the postcentral gyrus. The ventral anterior and ventral lateral nuclei receive input from the basal ganglia and the cerebellum and project to the motor cortex. The anterior nuclei receive ...

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