Thalamus, metathalamus and epithalamus Flashcards
(31 cards)
What is the diencephalon?
The diencephalon is the part of the brain located between the cerebral hemispheres above and the midbrain below. It includes the thalamus, epithalamus, metathalamus, subthalamus, and hypothalamus, and forms the boundaries of the third ventricle.
What are the two main divisions of the diencephalon, and what structures do they include?
Pars dorsalis diencephalon: Thalamus, epithalamus, metathalamus (medial and lateral geniculate bodies).
Pars ventralis diencephalon: Subthalamus (ventral thalamus) and hypothalamus.
What is the function of the medial geniculate body?
It acts as a relay station in the auditory pathway, with tonotopic organization in its ventral nucleus (projects to primary auditory cortex) and non-tonotopic dorsal nucleus (projects to secondary auditory cortex).
What are the afferent and efferent connections of the lateral geniculate body?
Afferent: Optic tract (receives input from both retinae; contralateral retina projects to laminae 1,4,6; ipsilateral to 2,3,5).
Efferent: Optic radiation to the visual cortex.
What is the function of the pineal gland?
It secretes melatonin, regulates circadian rhythms, and influences reproductive activity and secondary sexual characteristics.
What structures make up the epithalamus?
Pineal gland, habenular nuclei, posterior commissure, stria medullaris thalami, and habenular commissure.
Describe the habenular nuclei’s role and connections.
Function: Integrates olfactory, visceral, and somatic pathways; may regulate sleep and temperature.
Connections: Afferents from amygdala, hippocampus, and hypothalamus; efferents to medial thalamus and reticular formation via habenulo-peduncular tract.
What are the external features of the thalamus?
Poles: Anterior (near interventricular foramen) and posterior (pulvinar, above superior colliculus).
Surfaces: Medial (third ventricle), dorsal (caudate nucleus/fornix), lateral (internal capsule), and ventral (hypothalamus/subthalamus).
How is the thalamus internally organized?
Divided by the Y-shaped internal medullary lamina into anterior, medial, and lateral nuclear groups.
What are the functions of the anterior thalamic nucleus?
Recent memory, emotional behavior, and autonomic regulation (hormonal, homeostatic, and visceral control).
What are the connections of the ventral posterolateral (VPL) nucleus?
Afferents: Medial and spinal lemnisci (somatotopic input from spinal cord).
Efferents: Postcentral gyrus (sensory cortex for pain, touch, temperature, proprioception).
What is the role of intralaminar thalamic nuclei?
They regulate consciousness and alertness, with connections to the reticular formation, cerebral cortex, and corpus striatum.
Which arteries supply the thalamus?
Primary: Posterior cerebral and posterior communicating arteries.
Contributors: Anterior/posterior choroidal, thalamoperforating, and thalamogeniculate arteries.
What clinical problems arise from thalamic lesions?
Sensory deficits (e.g., contralateral loss of touch/pain), motor dysfunction, memory impairment, and thalamic pain syndrome (Dejerine-Roussy syndrome).
What is the pulvinar’s function?
Integrates visual (inferior pulvinar) and somatosensory input, projecting to parietal, occipital, and temporal cortices for sensory-motor coordination.
How do the medial and lateral geniculate bodies differ in organization?
Medial (auditory): Tonotopic in ventral nucleus (frequency mapping).
Lateral (visual): Laminated (6 layers); contralateral retina → laminae 1,4,6.
Exam tip: “Tonotopic vs. laminated” is a common comparison.
What is the only sensory modality that does NOT relay in the thalamus?
Olfaction (bypasses thalamus, projects directly to cortex via limbic system).
Why it’s tested: Classic “exception” question.
A patient has contralateral hemianesthesia (loss of touch/pain) but intact proprioception. Which thalamic nucleus is likely affected?
VPL (Ventral Posterolateral) – processes spinothalamic (pain/touch) but not dorsal column (proprioception) inputs.
Why: VPL lesions spare proprioception (relayed via cerebellum → VL nucleus).
What connects the habenular nuclei to the midbrain’s reticular formation?
Habenulo-peduncular tract (efferent pathway).
Key point: Often overlooked but tested as a “connection” question.
Why does the pineal gland calcify with age, and what imaging finding does this cause?
Physiologic calcification (post-puberty) → visible as “brain sand” on CT/X-ray.
Clinical relevance: Mistaken for pathology if unaware of normal aging.
Which artery supplies the VPM/VPL nuclei, and what stroke syndrome results from its occlusion?
Thalamogeniculate artery (branch of PCA) → Dejerine-Roussy syndrome (contralateral sensory loss + later burning pain).
Why: High-yield for vascular anatomy + clinical syndromes.
What is the role of intralaminar nuclei (e.g., centromedian)?
Regulate consciousness/alertness via connections to reticular formation and cortex.
Tie to clinical: Lesions cause drowsiness or coma.
Which thalamic nucleus is part of the Papez circuit (limbic memory loop)?
Anterior nucleus (connects mammillary bodies → cingulate gyrus).
Why: Classic neuroanatomy pathway.
How is the subthalamus functionally distinct from the thalamus?
Subthalamus includes motor regulators (e.g., subthalamic nucleus, part of basal ganglia).
Exam trap: Often confused with thalamic nuclei.
