The Thalamus and White Matter Structures Flashcards
What is the shape and size of the thalamus?
Large, egg-shaped gray matter; 4x1.5x1.5 cm. Forms major part of the
diencephalon
How many thalami are there, and where are they located?
Two thalami, one on each side of the third ventricle.
Describe the anterior and posterior ends of the thalamus.
Anterior end: Narrow and rounded.
Posterior end: Expanded to form the pulvinar.
What are the superior and inferior relations of the thalamus?
Superior: Lateral to medial - Caudate nucleus, stria terminalis, thalamostriate vein, fornix.
Inferior: Tegmentum of the midbrain.
Describe the medial and Lateral relations of the Thalamus
Medial:
* forms part of the lateral wall of the third ventricle
* connected to the opposite thalamus by a band of gray matter - interthalamic adhesion
Lateral: Internal capsule
What structure divides the thalamus into medial and lateral halves?
The internal medullary lamina (a vertical sheet of white matter).
The internal medullary lamina splits,
resembling a Y shape.
What are the three main parts of the thalamus based on the internal medullary lamina?
Anterior part.
Medial part.
Lateral part
How is the thalamus subdivided, and what additional nuclear groups exist?
Three main parts by the internal medullary lamina:
Anterior part.
Medial part.
Lateral part.
Smaller nuclear groups:
Located within the internal medullary lamina.
Found on the medial and lateral surfaces of the thalamus.
What are the key features of the anterior part of the thalamus?
Contains the anterior thalamic nuclei.
Afferent connections:
Mammillothalamic tract.
Reciprocal connections:
Cingulate gyrus.
Hypothalamus.
Function:
Regulates emotional tone.
Plays a role in recent memory.
Why is a reciprocal relationship crucial for the anterior part of the thalamus?
Reciprocal relations refer to two-way communication between structures. For the anterior part of the thalamus, this means:
It receives inputs (afferents) from structures like the cingulate gyrus and the hypothalamus, and it also sends outputs (efferents) back to them.
This two-way communication forms a feedback loop, allowing constant interaction and regulation between these regions.
What is the main nucleus in the medial part of the thalamus?
The medial part contains the dorsomedial nucleus.
What are the dorsomedial nuceus’ afferent and reciprocal connections?
Afferents: Amygdaloid complex.
Reciprocal connections:
Prefrontal cortex (higher cognitive functions).
Hypothalamic nuclei (autonomic and emotional regulation).
Interconnected with all other thalamic nuclei.
What is the function of the dorsomedial nucleus in the medial part of the thalamus?
Integrates sensory information, including somatic, visceral, and olfactory inputs.
Relates this information to emotion and subjective states for emotional regulation and response.
What are the nuclei in the dorsal tier of the lateral part of the thalamus?
Lateral dorsal nucleus
Lateral posterior nucleus
Pulvinar
What are the interconnections of the dorsal tier nuclei in the lateral part of the thalamus?
The nuclei are interconnected with:
Other thalamic nuclei
Parietal lobe (sensory integration)
Cingulate gyrus (emotional and attentional processing)
Occipital lobe (visual processing)
Temporal lobe (auditory and memory functions)
What are the nuclei in the ventral tier of the thalamus listed in craniocaudal sequence?
Ventral anterior nucleus
Ventral lateral nucleus
Ventral posterior nucleus
What are the afferents of the ventral anterior (VA) and ventral lateral (VL) nuclei?
Substantia nigra
Globus pallidus
Dentate nucleus (specific to VL)
What are the efferents of the ventral anterior (VA) and ventral lateral (VL) nuclei?
Premotor cortex (Area 4 and Area 6) Pre central gyri
What is the function of the VA and VL nuclei?
Influence the activities of the motor cortex.
What are the subdivisions of the ventral posterior nucleus?
Ventral Posterolateral (VPL) nucleus
Ventral Posteromedial (VPM) nucleus
What are the afferents of the VPL nucleus?
Medial lemniscus
Spinal lemniscus
What are the efferents of the VPL nucleus?
Parietal lobe (postcentral gyrus)
What is the function of the VPL nucleus?
Relay station for:
Touch, pain, temperature, and proprioceptive sensations from the contralateral body (excluding the face).
What are the afferents of the VPM nucleus?
Trigeminal lemniscus - A somatosensory tract containing second-order neuron fibers of the trigeminal system. It consists of the ventral and dorsal trigeminal tracts.
Solitary nucleus - Afferents of the SN mediate the gag reflex, the carotid sinus reflex, the aortic reflex, the cough reflex, the baroreflex and chemoreceptor reflexes, several respiratory reflexes and reflexes within the gastrointestinal tract
What are the efferents of the VPM nucleus?
Parietal lobe (postcentral gyrus) via superior thalamic radiation
What is the function of the VPM nucleus?
Relay station for:
Touch, pain, temperature, and proprioception from the contralateral face.
Taste sensations.
What are the geniculate bodies?
The medial and lateral geniculate bodies are small oval collections of grey matter situated below the posterior part of the thalamus, lateral to the colliculi of the midbrain
Where is the Medial Geniculate Body (MGB) located, and what is its primary function?
The MGB is located on the posterior surface of the thalamus beneath the pulvinar. Its primary function is to relay auditory information as part of the auditory pathway.
What are the afferent and efferent connections of the Medial Geniculate Body (MGB)?
Afferent: Inferior brachium from the inferior colliculus.
Efferent: Auditory radiation to the auditory cortex in the superior temporal gyrus (areas 41 and 42).
What happens if the Medial Geniculate Body (MGB) is damaged?
Damage to the MGB can result in auditory processing deficits, especially with complex sounds, due to disruption in the relay of auditory information to the auditory cortex. “GB antheM”
Where is the Lateral Geniculate Body (LGB) located, and what is its function?
The LGB is located on the undersurface of the pulvinar of the thalamus. It is a relay station for visual information in the visual pathway. “See The Rainbow”
How many layers of nerve cells does the Lateral Geniculate Body (LGB) have, and what is their role?
The LGB contains 6 layers of nerve cells, which help segregate and process visual information from each eye.
What are the afferent and efferent connections of the Lateral Geniculate Body (LGB)?
Afferent: The optic tract carries visual signals from the retina. (Arrives)
Efferent: The optic radiation projects visual information to the visual cortex in the occipital lobe. (Exits)
What could happen if the Lateral Geniculate Body (LGB) is damaged?
Lesions in the LGB can lead to visual deficits, such as contralateral homonymous hemianopia, where a person loses vision in the same part of both visual fields of the eyes.
What is the blood supply to the geniculate bodies?
The geniculate bodies are supplied by branches from the:
Posterior communicating arteries
Basilar artery
Posterior cerebral arteries
What could happen if there is ischemia in the blood vessels supplying the geniculate bodies?
Ischemia in the blood supply can result in sensory deficits related to the auditory or visual pathways, depending on whether the MGB or LGB is affected.
Why are thalamic lesions less likely to produce highly specific effects?
Thalamic nuclei are small, so lesions tend to produce less specific and more widespread effects.
What additional symptoms often accompany thalamic lesions?
Thalamic lesions frequently affect structures that are closely related, such as the internal capsule, caudate nucleus, and lentiform nucleus, leading to additional symptoms.
What is contralateral hemianesthesia, and which thalamic nuclei are typically involved?
Contralateral hemianesthesia is the loss of sensation on one side of the body.
It is typically due to damage to the VPL (ventral posterolateral) and VPM (ventral posteromedial) nuclei of the thalamus, affecting all somatic sensory modalities, including light touch, conscious proprioception, 2-point discrimination, vibration, pain, and temperature.
What is hyperalgesia or causalgia, and when is it observed in thalamic lesions?
Hyperalgesia or causalgia refers to spontaneous pain with no apparent stimulus. It is observed after a period of recovery from damage to the VPL and VPM nuclei, typically within days to months. The pain can become severe and intractable.
What visual disturbance is associated with damage to the lateral geniculate body (LGB)?
Damage to the LGB (lateral geniculate body) causes contralateral homonymous hemianopia, where vision loss occurs in the same field of vision in both eyes (e.g., loss of vision in the right or left half of the visual field).
How can damage to the VA and VL thalamic nuclei affect movement?
Damage to the VA (ventral anterior) and VL (ventral lateral) nuclei can lead to movement disorders, including motor disturbances, because these nuclei are involved in the cerebellum and basal ganglia pathways. The movement disorder would occur contralateral to the side of the lesion.
Which arteries provide blood supply to the thalamus?
The thalamus is primarily supplied by branches of the posterior communicating arteries, basilar artery, and posterior cerebral arteries.
What are the three main types of white matter fibers in the cerebrum?
- Commissural fibers: Connect corresponding gyri of the two hemispheres.
- Association fibers: Connect different regions within the same hemisphere.
- Projection fibers: Connect the cerebrum to lower parts of the brain and spinal cord.
What is the function of commissural fibers?
Commissural fibers interconnect corresponding areas of the two cerebral hemispheres, facilitating communication between them.
Name the major commissural fibers in the cerebrum.
The major commissural fibers include:
1. Corpus callosum: The largest commissural tract connecting the two hemispheres.
2. Anterior commissure: Connects the temporal lobes and parts of the olfactory system.
3. Posterior commissure: Involved in the pupillary light reflex.
4. Commissure of the fornix: Connects the hippocampi of both hemispheres.
5. Habenular commissure: Connects the habenular nuclei, involved in the limbic system. “Habenaro’s make me cry”
What are association fibers, and what is their function?
Association fibers connect different regions within the same cerebral hemisphere, facilitating communication between various cortical areas.
What are projection fibers, and what is their function?
Projection fibers connect the cerebrum to lower parts of the brain and spinal cord, transmitting motor and sensory information.
Describe the internal capsule and its components.
The internal capsule is a white matter structure that contains projection fibers. It is divided into:
- Anterior limb: Contains fibers connecting the thalamus to the frontal lobe.
- Genu: Contains corticobulbar fibers, which connect the cerebral cortex to the brainstem.
- Posterior limb: Contains corticospinal fibers, which connect the cerebral cortex to the spinal cord.
- Retrolenticular part: Contains optic radiation fibers, which transmit visual information from the thalamus to the occipital lobe.
- Sublenticular part: Contains auditory radiation fibers, which transmit auditory information from the thalamus to the temporal lobe.
What is the corona radiata?
The corona radiata is a fan-shaped mass of white matter fibers that radiate from the internal capsule to the cerebral cortex, carrying motor and sensory information.
What are the thalamic radiations?
Thalamic radiations are projection fibers that connect the thalamus to various cortical areas.
They include:
Anterior thalamic radiation: Connects the anterior thalamic nuclei to the cingulate gyrus.
Superior thalamic radiation: Connects the lateral geniculate body to the visual cortex.
Posterior thalamic radiation: Connects the pulvinar to the parietal, occipital, and temporal lobes.
What is the role of the corpus callosum?
The corpus callosum is the largest commissural tract, connecting the left and right cerebral hemispheres, allowing for communication between them.
How do projection fibers influence motor control?
Projection fibers, such as corticospinal fibers, transmit motor commands from the cerebral cortex to the spinal cord, facilitating voluntary movement.
What is the significance of the anterior commissure?
The anterior commissure connects the temporal lobes and parts of the olfactory system, playing a role in the sense of smell and emotional responses.
How do association fibers contribute to cognitive functions?
Association fibers connect different regions within the same hemisphere, enabling integration of information across various cortical areas, which is essential for complex cognitive functions.
What is the function of the posterior commissure?
The posterior commissure is involved in the pupillary light reflex, coordinating the constriction of both pupils in response to light.
Describe the role of the habenular commissure.
The habenular commissure connects the habenular nuclei, which are involved in the limbic system, playing a role in emotional and behavioral responses.
What is the relationship between the internal capsule and the basal ganglia?
The internal capsule passes between the caudate nucleus and the lentiform nucleus (putamen and globus pallidus), serving as a major pathway for projection fibers connecting the cerebral cortex to subcortical structures.
How do projection fibers contribute to sensory perception?
Projection fibers, such as thalamocortical fibers, transmit sensory information from the thalamus to the cerebral cortex, enabling perception of sensory stimuli.
What is the function of the corona radiata?
The corona radiata is a fan-shaped mass of white matter fibers that radiate from the internal capsule to the cerebral cortex, carrying motor and sensory information.
How do thalamic radiations facilitate sensory processing?
Thalamic radiations transmit sensory information from the thalamus to specific cortical areas, such as the visual cortex for visual information and the somatosensory cortex for tactile information.
What is the role of the sublenticular part of the internal capsule?
The sublenticular part of the internal capsule contains auditory radiation fibers, transmitting auditory information from the medial geniculate body of the thalamus to the auditory cortex in the temporal lobe.
How do thalamic radiations facilitate sensory processing?
Thalamic radiations are projection fibers that connect the thalamus to various cortical areas, enabling the transmission of sensory information. For example, the superior thalamic radiation connects the lateral geniculate body to the visual cortex, facilitating visual perception
What is the function of the anterior thalamic radiation?
The anterior thalamic radiation connects the anterior thalamic nuclei to the cingulate gyrus, playing a role in emotional processing and memory formation.
How do projection fibers influence motor control?
Projection fibers, such as corticospinal fibers, transmit motor commands from the cerebral cortex to the spinal cord, facilitating voluntary movement. Damage to these fibers can result in motor deficits
What is the significance of the posterior thalamic radiation?
The posterior thalamic radiation connects the pulvinar to the parietal, occipital, and temporal lobes, integrating sensory information and contributing to spatial awareness and attention.
What is the role of the posterior commissure?
The posterior commissure is involved in the pupillary light reflex, coordinating the constriction of both pupils in response to light. It also plays a role in the coordination of eye movements.
Describe the role of the habenular commissure.
The habenular commissure connects the habenular nuclei, which are involved in the limbic system, playing a role in emotional and behavioral responses. It is also involved in the regulation of dopamine release.
What is the relationship between the internal capsule and the basal ganglia?
The internal capsule passes between the caudate nucleus and the lentiform nucleus (putamen and globus pallidus), serving as a major pathway for projection fibers connecting the cerebral cortex to subcortical structures, including the basal ganglia. Damage to the internal capsule can result in motor and sensory deficits.
