Human Physiology - William F. Ganong 2002

Functions of the Nervous System
Anxiety States, Sleep, and Electrical Activity of the Brain
Thalamus and Cerebral Cortex

Thalamic nuclei

Considering the development and Topography of the thalamus, it can be divided into three parts: the epithalamus, dorsal thalamus, and ventral thalamus. The epithalamus is connected with the olfactory system. The projections and Functions of the ventral thalamus remain not fully defined. Within the dorsal thalamus, there are nuclei with diffuse projections to the entire neocortex, as well as nuclei projecting to specific, discrete Regions of the neocortex and the limbic system. Projections to all PARTS OF THE neocortex originate from the medial and intralaminar nuclei.

The nuclei of the dorsal thalamus that project to specific areas include specific sensory Relay nuclei and nuclei involved in efferent regulatory mechanisms. The specific sensory relay nuclei comprise the medial and lateral geniculate bodies, which transmit auditory and visual impulses to the auditory and visual cortex, respectively, as well as the ventrobasal nuclear group, which relays somatosensory information to the postcentral gyrus. The nuclei involved in efferent (regulatory) mechanisms encompass A number of nuclei responsible for motor function. They receive signals from the Basal Ganglia and Cerebellum and transmit them to the motor cortex. This group also includes the anterior nuclei, which receive afferent signals from the mamillary bodies and project them to the limbic cortex.

Structure OF THE cortex

The neocortex typically consists of six layers (Fig. 11-1). The Neurons are predominantly pyramidal Cells with elongated vertical dendritic structures (Figs. 11-1, 11-2) that can reach all the way to the cortical surface. The axons of these cells typically give off recurrent collaterals that turn back to form synapses on the superficial portions of the dendritic structures.

Afferent impulses from specific thalamic nuclei terminate primarily in cortical layer 4, whereas nonspecific afferents are distributed across layers 1–4.