Week 3 Tuesday Neuroanatomy: Diencephalon and Internal Capsule

30 flashcards covering diencephalon anatomy, boundaries, thalamic nuclei and pathways, hypothalamus functions and connections, epithalamus, and the internal capsule with its fiber tracts and blood supply.

What are the three primary components of the diencephalon?

The thalamus, the hypothalamus, and the epithalamus.

Which two smaller structures are described as part of the diencephalon and sit around it?

The subthalamus and the retina/optic nerve (outgrowth from the diencephalon).

What is the massa intermedia?

A bridge of gray matter joining the two halves of the thalamus, often cut in midline views.

Where is the infundibular stalk located and why is it significant?

On the ventral surface, connecting the hypothalamus to the pituitary gland; the pituitary is not part of the diencephalon but is attached to it.

What is the tuber cinereum?

A gray matter patch between the mammillary bodies and the infundibular stalk on the ventral surface.

What marks the caudal boundary of the diencephalon?

The posterior commissure.

What marks the dorsal (superior) boundary of the diencephalon?

The fornix and septum pellucidum, with the corpus callosum forming part of the boundary.

What marks the lateral boundary of the diencephalon in a coronal section?

The internal capsule (projection fibers separating diencephalon from basal ganglia).

Which sensory pathway does not pass through the thalamus?

Olfaction (smell) — it goes from the nose to the entorhinal cortex bypassing the thalamus.

Where does the visual pathway terminate in the thalamus and what is its nucleus?

In the lateral geniculate body (LGN); the LGN relays visual information to the visual cortex.

Where does the auditory pathway terminate in the thalamus and what is its nucleus?

In the medial geniculate body (MGN); the MGN relays auditory information to the auditory cortex.

What thalamic nucleus receives general somatic sensation from the body?

Ventrolateral Posterior (VPL) nucleus.

What thalamic nucleus receives general somatic sensation from the head and face?

Ventral Posteromedial (VPM) nucleus.

Which thalamic nuclei relay information back to the motor cortex from the basal ganglia and cerebellum?

The ventral anterior (VA) and ventral lateral (VL) nuclei.

Which nuclei comprise the dorsal tear of the lateral division, and what are their roles?

Lateral dorsal nucleus, lateral posterior nucleus, and pulvinar; involved in emotion, memory, and integration of sensory information.

Which nuclei comprise the ventral tear of the lateral division?

Ventral anterior (VA), ventral lateral (VL), ventral posterior (VPL and VPN).

What are the intralaminar nuclei and where are they located?

Nuclei within the internal medullary lamina; involved in pain perception and arousal, connecting with brainstem, cerebellum, basal ganglia, and cortex.

What is the role of the reticular nucleus of the thalamus?

An outermost nucleus that provides inhibitory modulation to other thalamic nuclei.

What is the anterior nucleus of the thalamus known for connecting?

Connects the hypothalamus to the limbic system and is involved in emotion, memory, and alertness.

What is the dorsomedial (dorsomedial) nucleus known to connect?

Cortex to limbic system; involved in memory, learning, cognition, and awareness.

What is the midline nucleus and where is it located?

A thalamic nucleus near the massa intermedia, involved in memory and olfaction (limbic connections).

What nuclei are part of the periventricular region and what is their general role?

Preoptic, supraoptic, paraventricular, anterior hypothalamic, and suprachiasmatic nuclei; they regulate hormones, thermoregulation, circadian rhythms, and autonomic functions.

What is the suprachiasmatic nucleus responsible for?

Regulating day-night (circadian) cycles in response to light input from the eyes.

What is the habenula and where is it located?

A small habenular nucleus area located beside the pineal gland; part of the epithalamus involved in reward processing and cognitive aspects of sleep and spatial learning.

What are the major components of the epithalamus?

The pineal gland and the habenula (with the stria medullaris thalami linking them to the thalamus).

What hormone does the pineal gland secrete and what is its role?

Melatonin; promotes sleepiness and helps regulate circadian rhythms, especially in darkness.

What tract connects the habenula to the thalamus and basal ganglia inputs?

The stria medullaris thalami.

Where is the hypothalamus located relative to the third ventricle and what is its general role?

Around the third ventricle; it is the master regulator of homeostasis, controlling autonomic and endocrine functions.

What are the two main output modes of the hypothalamus?

Humoral (hormonal) output via releasing/inhibiting hormones to the anterior pituitary and autonomic output via the hypothalamo-spinal pathways.

What is the hypothalamic-pituitary portal system and how does it function?

Hypothalamic releasing/inhibiting hormones are released into the primary capillary plexus, travel via the hypophyseal portal vein to the secondary capillary plexus in the anterior pituitary, and regulate pituitary hormone secretion.

Which hormones are released by the posterior pituitary (neurohypophysis) and how are they delivered?

Oxytocin and antidiuretic hormone (ADH); they are produced by hypothalamic neurosecretory neurons and travel down the hypothalamo-hypophyseal tract to be released from the posterior pituitary.

What is the functional difference between prolactin and oxytocin in lactation?

Prolactin stimulates milk synthesis; oxytocin stimulates milk ejection (let-down) and uterine contractions.

What nuclei are in the preoptic region and what are their functions?

Medial and lateral preoptic nuclei; medial preoptic participates in gonadotropin release hormone production and thermoregulation; lateral preoptic is involved in thirst and hunger.

What is the role of the arcuate nucleus in the tuberal region of the hypothalamus?

Involved in eating patterns (hunger and satiety) and also secretes growth hormone release hormone and prolactin-inhibitory hormone.

What nucleus regulates blood pressure, heart rate, and gastrointestinal function within the hypothalamus?

Dorsomedial nucleus (influences autonomic output and GIT function; helps regulate blood pressure and heart rate).

What function does the mammillary region of the hypothalamus mainly contribute to?

Memory; mammillary bodies are key components of memory circuits in the limbic system.

What is the posterior hypothalamic nucleus associated with?

Sympathetic functions such as pupil dilation and influencing blood pressure.

How is projection fiber tract anatomy of the internal capsule described in simple terms?

A sheet of white matter carrying descending cortical motor fibers and ascending thalamocortical sensory fibers, with an anterior limb, genu, posterior limb, and retrolenticular part as it courses laterally to medially.