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Diencephalon

Last updated: July 16, 2021

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The diencephalon is the caudal part of the forebrain (prosencephalon), located between the midbrain (mesencephalon) and the cerebrum (telencephalon). It consists of the thalamus, hypothalamus, epithalamus, and subthalamus. The thalamus is the relay center for sensory information. The hypothalamus regulates autonomic function and the endocrine system. The epithalamus, which comprises the pineal gland, habenula, habenular commissure, and stria medullaris, regulates the sleep-wake cycle. The subthalamus, which contains the subthalamic nucleus, is part of the indirect basal ganglia circuit and is involved in the inhibition of involuntary movements. The limbic system consists of the amygdala, hypothalamus, anterior thalamus, hippocampus, mammillary bodies, cingulate cortex, and entorhinal cortex. These structures are involved in memory formation, regulation of appetite and satiety, attention, emotional responses, and sexual arousal.

Characteristics

Thalamic nuclei

Overview of thalamic nuclei
Components Input Projects to Function
Anterior nuclear group
Anterior thalamic nuclei
Lateral nuclear group

Dorsal subgroup

Lateral dorsal thalamic nucleus
Posterior subgroup Pulvinar
  • Contribute to visual perception and regulation of visual attention
Lateral posterior thalamic nucleus

Ventral subgroup

Ventral anterior thalamic nucleus
  • Planning of movement
Ventral lateral thalamic nucleus
  • Coordination of movement
Ventral posterior thalamic nucleus Ventral posterolateral thalamic nucleus (VPL)
  • Proprioception and fine touch
  • Sensation of
    • Pain
    • Pressure
    • Crude touch
    • Temperature
    • Vibration
Ventral posteromedial thalamic nucleus (VPM)
Medial nuclear group
Dorsomedial thalamic nucleus
  • Expression of affect, behavior, emotions (part of the limbic system)
Metathalamus
Lateral geniculate thalamic nucleus
Medial geniculate thalamic nucleus
Intralaminar nuclear group
Intralaminar thalamic nuclei
  • Awareness
  • Arousal

Thalamic stroke causes contralateral hemiparesis and hemisensory loss, miotic and unreactive pupils, and upgaze palsy with gaze deviation away from the side of the lesion (a phenomenon known as wrong-way eyes).

Olfaction is the only sensory modality that is not relayed through the thalamus.

VPL: receives sensory information from the Limbs. VPM: receives sensory information from your Mug (face).

The Lateral geniculate body processes Light (part of the visual pathway); the Medial geniculate body processes Music (part of the hearing pathway).

Blood supply [1]

Characteristics

Hypothalamic nuclei

Overview of hypothalamic nuclei
Nucleus Function Clinical significance of injury
Supraoptic (anterior) nuclear group
Anterior hypothalamic nucleus
Suprachiasmatic nucleus

Supraoptic nucleus

Paraventricular nucleus
Preoptic nucleus
Tuberal (middle) nuclear group
Dorsomedial hypothalamic nucleus
  • Regulation of:
    • Thirst and appetite (body-weight regulation)
    • Cardiovascular response to stress (↑ blood pressure and heart rate)
    • Circadian rhythm
  • Hypophagia
  • Hypodipsia
Ventromedial hypothalamic nucleus
  • Satiety: stimulated by leptin
Arcuate hypothalamic nucleus
  • Neuroendocrine dysregulation
Mammillary (posterior) nuclear group
Posterior hypothalamic nucleus
Mammillary body
Preoptic (anterior-posterior) nuclear group
Lateral nucleus

Hypothalamic functions (Thirst and water balance; Adenohypophysis produces releasing hormones that act on the anterior pituitary, Neurohypophysis produces ADH and oxytocin for the posterior pituitary; Hunger; Anger; Temperature; Sexual functions): TAN HATS

Injury to the Lateral nucleus makes you Lean (due to the absence of hunger), and injury to the VentroMedial nucleus makes you Very Massive (due to the absence of satiety).

Function of suprachiasmatic nucleus (SCN): Sun Censing Nucleus

Functions of hypothalamic nuclei (Supraoptic nucleus releases, ADH release, Paraventricular nucleus release, OXytocin): SAD POX

The MaMmillary bOdY is important for MeMOrY.

Blood supply

Epithalamus

Overview of the epithalamus
Structure Characteristics Function Clinical significance
Pineal gland
  • An endocrine gland named after its resemblance to a pine cone
  • Contains specialized neurons (pinealocytes) with endocrine functions
  • Receives input from the suprachiasmatic nucleus
  • Circadian secretion of melatonin (derived from tryptophan)
  • Regulation of the sleep-wake cycle
Habenula
  • Modulation of:
    • Nociception
    • Behavioral response to pain or stress
    • Sleep-wake cycle
    • Mood
    • Reproductive behavior
Habenular commissure
  • Calcification is common
Stria medullaris
  • -

Subthalamus

Characteristics

Components of the limbic system

Overview of the limbic system
Structure Location Input Projects to Function/Characteristics
Hippocampus
Dentate gyrus
Entorhinal cortex
Mammillary bodies
Amygdala
  • Relays emotional reactions, especially to fear, aggression, and anxiety
  • Involved in decision-making
  • Regulates the activity of the autonomic nervous and endocrine systems
  • Recognition of emotional facial expressions
Cingulate gyrus
  • Superior to the corpus callosum bilaterally
  • On the medial surface of the frontal and parietal lobe
Anterior thalamic nuclei

Papez circuit

The limbic system is responsible for the famous 5 F's: Feeding, Fleeing, Fighting, Feeling, and … Sex.

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