Nolte Chapter 23 – Drives and Emotions: The Hypothalamus and Limbic System

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Nolte Chapter 23 – Drives and Emotions: The Hypothalamus and Limbic System

Limbic system is interposed between the hypothalamus and the neocrotex, so limbic structures serve as birdges between autonomic and voluntary responses to changes in the environment.

the hypothalamus is concerned with autonomic, endocrine, emotional, and somatic functions that maintain our internal environment(homeostasis).

Three components: intereconnections with the limbic system, outputs that influence the pituitary, and interconnection with various visceral and somatic nuclei.

Hypothalamic Divisions

  • The inferior surface of the hypothalamus, excluding the mammillary bodies is the tuber cinereum

    • the median eminence protrudes from the ventral surface of this and is continuous with the infundibular stalk, which is then continuous with the posterior pituitary.

      • taken together (infundibular stalk and posterior pituitary) is known as the neurohypophysis

  • the medial surface of the hypothalamus extends anteriorly to the lamina terminalis.

  • the hypothalamus can be subdivided from anterior to posterior as anterior, tuberal, and posterior regions.

    • the anterior is above the optic chiasm

    • tuberal region is above and including the tuber cinereum

    • posterior region is right above the including the mammillary bodies

  • longitudinally it can be subdivided into the

    • perventricular (wall of the third ventricle) which is a rostral continuation of the periaqueductal gray

      • the dorsal longitudinal fasciculus is a bundle of hypothalamic afferents and efferents

      • suprachiasmatic nucleus

        • a master clock that gets direct projections from the retina and releases melatonin in conjunction with the pineal

      • arcuate nucleus

        • feeding behavior

    • the lateral zone (lateral to the fornix) which is a rostral continuation of the reticular formation

      • has the medial forebrain bundle

      • anteriorly it has the lateral preoptic nucleus that is a sleep-promoting area

      • caudally it is continusous with the reticular formation

      • also contains the lateral tuberal nuclei and the tuberomammillary nucleus which is the source of histaminergic fibers that project widely to the cerebral cortex to participate in the sleep-wake cycle.

    • the medial zone

      • has neurosecretory cells

        • supraoptic and paraventricular

inputs to the hypothalamus include the forebrain (particularly the limbic system) and the brainstem and spinal cord.

Brainstem conveys visceral and somatic sensory information and limbic structures convey information relevant to the role of the hypothalamus in mediating many of the autonomic and somatic aspects of affective states.

Major forebrain afferents include the septal nuclei, hippocampus, amygdala, insula, and the retina.

Septal nuclei project fibers to the hypothalamus in the medial forebrain bundle.

The major output of the hippocampus is the fornix

the amygdala projects to the hypothalamus via the stria terminalis, which accompanies the caudate nucleus. Or they pass under the lenticular directly to the hypothalamus.

There are direct projections from the cerebral cortex to the hypothalamus that mainly arise in orbital and medial prefrontal cortex and in the insula and join the medial forebrain bundle. There are also contributions from the cingulate.

Afferents travel in the medial forebrain bundle. Others are contained in the dorsal longitudinal fasciculus. VTA also projects to the hypothalamus.

Some cells in the hypothalamus are sensitive to the temperature of the hypothalamus itself and the blood osmolality or the concentration of glucose or certain hormones.

Outputs from the hypothalamus largely reciprocate inputs

Their efferents blanket the cortex. Histaminergic fibers from the tuberomammillary nucleus and orexinergic fibers from the tuberal and posterior hypothalamis do this.

mammilothalamic tract foes to the anterior nucleus of the thalamus.

There are branches to the midbrain reticular formation by way of the mammilotegmental tract.

Hypothalmic Control of the Pituitary Gland

  • efferents of the hypothalamus control the hypophysis (pituitary gland)

  • The pituitary has an two lobes

  • the pituitary has an upward extension around the infundibular stalk and constitutes the adenohypophysis that is anterior to the neurohypohosis

  • Supraoptic and paraventricular propduce two peptide hormones

    • vasopressin which increases reabsorption of water in the kidney and decreases the production of urine

    • oxytocin which causes contraction of uterine and mammary smooth muscle and is important in parturition and milk ejection.

    • these hormones travel down the axons of their parent cell bodys by axoplasmic flow in what is called the supraopticohypophyseal tract

  • the hypophyseal support system is a vascular connection between the hypothalamus and the adenohypophosis via the superior hypophyseal artery (a branch of the carotid)

    • it breaks up into a capillary bed in the prximal part of the infundibular stalk then sends vessels down the infundibular stalk to a second capillary bed in the adenohypophysis

      • small peoptides called hypothalamic releasing hormones and inhibiting hormones get released by the arcuate into this bloodstream.

  • the nuecleus of the solitary tract, the parabrachial nuclei, the reticular formation, and periaqueductal gray all work together with the thalamus.

    • nucleus of solitary tract is the principal viscery nucleus with primary afferent nerves in VII, IX, and X conveying info about taste and internal organs.

    • parabrachial have a more general role in visceral sensation and give the general sensation of general well-ornotsowell-being since it receives inputs from the solitary tract nucleus and deals with spinothalamic inputs of pain and temperature

    • central pattern generators in the reticular formation help with cardiovascular, respitory, and micruition.

    • periaqueductal gray helps descending control of pain.

The hypothalamus has a maintained value at a set point that it likes to be. deviation of that creates an error signal that then activates mechanisms to decrease that error signal.

medial preoptic nuclei are directly warm-sensitive, firing faster as their temperature increases

body water can also be regulated by the medial preoptic neurons. decreased water volume causes a decrease in blood volume and an increase in its osmality. this stimulates receptors in an near the heart which is transmitted via the flossopharyngeal and vagus nerves to the nucleus of the solitary tract and then sent to preoptic neurons. medial preoptic can also get signals from the kidney and project to ADH secreting neurons in the supraoptic and pareventricular nuclei which leads to increased reabsorption of water by the kidnesy and signals to the cerebral cortex that say “I’m thirsty”.

arcuate nucleus is related to feeding behavior and receives projection from the nucleus of the solitary about stomach contents and glucose content. Ghrelin is secreted by the stomach at rates that increase with time since the last meal. it binds to arcuate neurons and stimulates feeding behavior. Leptin id produces by adipocytes and cause the opposite effect.

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