116 Lecture 14.S10

116 Lecture 14.S10 - CBNS 116 Lecture 14 The Thalamus and...

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CBNS 116 Lecture 14 - The Thalamus and internal Capsule: Getting to and from cerebral cortex Lecture notes by Todd Fiacco ASSIGNMENT: Read Nolte Chapter 16: “The thalamus and internal capsule: Getting to and from the cerebral cortex”. FOR NEXT LECTURE: Read Nolte Chapter 19: “Basal Ganglia”. TODAY'S LECTURE: The big picture: The thalamus (from the Greek meaning “inner chamber”), is a large, egg- shaped nuclear mass sitting atop the midbrain that makes up about 80% of the diencephalon. Many of the thalamic nuclei you have already been introduced to - mainly the thalamic relay nuclei , which receive input from a specific pathway before passing this information on to the appropriate cortical area. You have already become aware of specific inputs to the thalamus from sensory systems (e.g. somatosensory, vision, auditory) as well as from the limbic system (amygdala and hippocampus), basal ganglia, and cerebellum. But the thalamus does more than simply act as a pipeline through which information flows to the cerebral cortex. If this is all it did, then why should it exist at all? As the title of the chapter indicates, the thalamus is the gateway to cerebral cortex, and a gate can either be open or closed. Thus, the thalamus is the site where decisions are made about which information should reach the cerebral cortex accurately for further processing . This is reflected in the physiological properties of thalamic neurons, which exist primarily in one of two states. In the first state the gate is open, and information about specific inputs can be passed accurately and faithfully to cerebral cortex. In the second state the gate is “closed”, and information from specific inputs is not transmitted accurately to cerebral cortex (and therefore we are not consciously aware of it). Neurons in the closed state are vigilant , however, waiting for the right inputs to signal them to change to a physiologically “open” state. Whether a given thalamic neuron is in the open or closed state is governed by regulatory inputs from cerebral cortex, reticular neurons, and the diffuse brainstem modulatory neurotransmitter systems. I. Anatomical organization and function of the thalamic nuclei [slides 48-51]. The thalamus is divided into anterior , medial , and lateral zones by a thin sheet of myelinated fibers called the internal medullary lamina .
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A. Anteriorly, the internal medullary lamina splits to enclose the anterior nucleus , an important relay nucleus of Papez’z circuit . The anterior nucleus receives information from the hippocampus by way of the fornix and mammilothalamic tract , and projects to cingulate cortex. B. The medial “group” contains a single large nucleus, the dorsomedial (or mediodorsal) nucleus . This is the primary relay nucleus from the amygdala to prefrontal association areas of cortex (via the anterior cingulate gyrus) providing awareness of emotions and influencing decisions we make by providing an emotional context. As we learned in the first limbic system lecture, the dorsomedial nucleus is also involved
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116 Lecture 14.S10 - CBNS 116 Lecture 14 The Thalamus and...

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