Lecture 2 - Thalamus, Internal Capsule, Cerebral Cortex

What is the thalamus often called?

The thalamus is called the "gateway to the cerebral cortex" because nearly all sensory information reaching the cortex passes through it.

From which embryologic brain vesicle does the thalamus develop?

The thalamus develops from the diencephalon, which is derived from the prosencephalon (forebrain).

Into what two structures does the prosencephalon divide during the 5th week of development?

The prosencephalon divides into the telencephalon (cerebrum) and diencephalon (thalamus).

What percentage of the diencephalon is formed by the thalamus?

Approximately 80%.

What is the thalamus composed of?

A large mass of gray matter.

What structure forms the lateral wall of the third ventricle?

The thalamus.

What structure separates the thalamus from the hypothalamus?

The hypothalamic sulcus.

What is the massa intermedia?

The interthalamic adhesion that may connect the two thalami.

Is the diencephalon paired or unpaired?

Paired.

Where is the diencephalon located?

Between the brainstem and cerebral hemispheres.

With which part of the brain is the diencephalon continuous?

The rostral part of the midbrain.

What wall of the third ventricle is formed by the diencephalon?

The lateral wall.

What divides the diencephalon into dorsal and ventral parts?

The hypothalamic sulcus.

What structures form the dorsal part of the diencephalon?

The thalamus and epithalamus.

What structures form the ventral part of the diencephalon?

The hypothalamus and subthalamus.

What are the four major functional roles of the thalamus?

Sensory, motor, emotion/memory, and vegetative functions.

Which sensory modality does NOT relay through the thalamus before reaching the cortex?

Olfaction.

How is the thalamus involved in motor function?

It relays motor outputs from the basal ganglia and cerebellum to the cerebral cortex.

Which limbic circuit includes the thalamus?

The Papez circuit.

What emotional and memory-related cortical area receives thalamic input through the Papez circuit?

The cingulate gyrus.

Which thalamic function is associated with alertness and arousal?

Vegetative function.

Disorders of consciousness may result from damage to which thalamic function?

The vegetative/arousal function.

What is the anterior pole of the thalamus called?

The tubercle of the thalamus.

What boundary is formed by the tubercle of the thalamus?

The posterior boundary of the interventricular foramen.

What is the posterior pole of the thalamus called?

The pulvinar.

Which midbrain structure is overhung by the pulvinar?

The superior colliculus.

What connects the superior colliculus to the lateral geniculate body?

The superior quadrigeminal brachium.

What is medial to the thalamus?

The third ventricle.

What is dorsal to the thalamus?

The lateral ventricle.

What is ventral to the thalamus?

The subthalamus and hypothalamus.

What is lateral to the thalamus?

The internal capsule.

What is caudal to the thalamus?

The midbrain.

What is anterior to the thalamus?

The interventricular foramen.

How many surfaces does the thalamus have?

Four.

What are the four surfaces of the thalamus?

Superior, inferior, medial, and lateral.

What covers the superior surface of the thalamus?

The stratum zonale.

Which structures bound the superior surface laterally?

The caudate nucleus, thalamostriate vein, and stria terminalis.

Which ventricle floor is formed partly by the superior surface of the thalamus?

The lateral ventricle.

What covers the lateral part of the superior surface?

Ependyma.

To what is the medial part of the superior surface related?

The choroid plexus of the third ventricle.

What is related to the lateral surface of the thalamus?

The internal capsule.

On what does the inferior surface of the thalamus rest?

The subthalamus and hypothalamus.

What fiber tract runs along the dorsomedial margin of the medial surface?

The stria medullaris thalami.

What part of the third ventricle wall is formed by the medial surface?

The upper part of the lateral wall.

What white matter structure separates the reticular nucleus from the rest of the thalamus?

The external medullary lamina.

What fibers are found in the external medullary lamina?

Thalamocortical and corticothalamic fibers.

What shape is the internal medullary lamina?

Y-shaped.

Into what groups does the internal medullary lamina divide the thalamus?

Anterior, medial, and lateral nuclear groups.

What nuclei are found within the internal medullary lamina?

Intralaminar nuclei.

Which nucleus forms the anterior division of the thalamus?

The anterior nucleus.

Which nucleus forms the medial division?

The dorsomedial (mediodorsal) nucleus.

What nuclei compose the dorsal tier of the lateral division?

Lateral dorsal, lateral posterior, and pulvinar nuclei.

What nuclei compose the ventral tier of the lateral division?

VA, VL, VPL, and VPM nuclei.

What does VPL stand for?

Ventral posterolateral nucleus.

What does VPM stand for?

Ventral posteromedial nucleus.

What are the two geniculate nuclei of the thalamus?

Lateral geniculate nucleus (LGN) and medial geniculate nucleus (MGN).

What are the two major intralaminar nuclei?

Centromedian and parafascicular nuclei.

What is the role of relay nuclei?

To relay specific information from a particular tract or modality.

Do relay nuclei simply pass information unchanged?

No, they condense and process incoming information.

What cortical regions are supported by association nuclei?

Prefrontal cortex and parietal-occipital-temporal association cortex.

What is the major function of association cortex?

Higher cognitive functions.

What inputs do intralaminar nuclei receive?

Cortex, basal ganglia, cerebellum, reticular formation, and spinothalamic tract.

Where do intralaminar nuclei project?

Widespread cortex and basal ganglia.

What is the overall effect of intralaminar nuclei on the cortex?

General changes in cortical function.

What is the major characteristic of specific thalamic nuclei?

Highly organized point-to-point sensory and motor connections.

Where are specific nuclei located?

In the ventral group of the lateral nuclear group.

What is the major characteristic of nonspecific nuclei?

Broad cortical projections and less functionally distinct input.

Which nuclear groups are considered nonspecific?

Dorsal tier nuclei plus the anterior and medial groups.

What are the three subdivisions of the anterior nuclear group?

Anteroventral, anteromedial, and anterodorsal nuclei.

What major hypothalamic structure projects to the anterior nucleus?

The mammillary body.

Through what tract do mammillary body fibers reach the anterior nucleus?

The mammillothalamic tract.

To which cortical area does the anterior nucleus project?

The cingulate gyrus.

What system is the anterior nucleus functionally part of?

The limbic system.

What are major functions of the anterior nucleus?

Alertness, attention, and memory acquisition.

What are the 5 Fs of the limbic system?

Feeding, Forgetting/Memory, Fighting/Fleeing, Family, and Fornicating.

What is the major function of the mediodorsal nucleus?

Integration of emotion, thought, and judgment.

What are major inputs to the mediodorsal nucleus?

Hypothalamus, amygdala, other thalamic nuclei, and prefrontal cortex.

What are major outputs of the mediodorsal nucleus?

Prefrontal cortex, posterior parietal cortex, and limbic structures.

What is the main function of the VA nucleus?

Influencing motor activity.

What are the major inputs to VA?

Ipsilateral globus pallidus and substantia nigra.

What are the major outputs of VA?

Premotor cortex and frontal eye fields.

What are major functions of the anterior nucleus?

Alertness, attention, and memory acquisition.

What is the internal capsule?

A compact bundle of projection fibers located between the thalamus and caudate nucleus medially and the lentiform nucleus laterally.

What structures are medial to the internal capsule?

The head of the caudate nucleus and the thalamus.

What structure is lateral to the internal capsule?

The lentiform nucleus (putamen and globus pallidus).

What does the internal capsule become superiorly?

The corona radiata.

What does the internal capsule become inferiorly?

The crus cerebri of the midbrain.

What are the five parts of the internal capsule?

Anterior limb, genu, posterior limb, retrolentiform part, and sublentiform part.

Where is the anterior limb of the internal capsule located?

Between the head of the caudate nucleus medially and the anterior part of the lentiform nucleus laterally.

Where is the posterior limb of the internal capsule located?

Between the thalamus medially and the posterior part of the lentiform nucleus laterally.

What is the genu of the internal capsule?

The bend between the anterior and posterior limbs with its concavity facing laterally.

Where is the retrolentiform part located?

Posterior to the lentiform nucleus.

Where is the sublentiform part located?

Inferior to the lentiform nucleus.

What types of fibers pass through the internal capsule?

Motor fibers and sensory fibers.

What motor fibers pass through the internal capsule?

Corticopontine fibers, pyramidal fibers, and extrapyramidal fibers.

What sensory fibers pass through the internal capsule?

Thalamocortical fibers.

What are thalamocortical fibers?

Sensory projection fibers connecting the thalamus and cerebral cortex.

What are the four divisions of the thalamic radiation?

Anterior, superior, posterior, and inferior thalamic radiations.

What does the anterior thalamic radiation connect?

The thalamus to the frontal lobe cortex.

What does the superior thalamic radiation connect?

The thalamus with the frontal and parietal lobes.