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Neuroanatomy > Diencephalon > Flashcards

Diencephalon Flashcards

1
Q

Where is the diencephalon located?

A
  • it sits on top of the brainstem and connects it to the cerebral hemispheres
  • it is obscured by the cerebral hemispheres
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2
Q

What are the 4 divisions of the diencephalon?

A
  1. thalamus
  2. epithalamus
  3. hypothalamus
  4. subthalamus
  • both “hypo-“ and “sub-“ mean below
  • the hypothalamus is located immediately below the thalamus and the subthalamus is located below and lateral to the thalamus
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3
Q

What type information are the LGN and MGN of the thalamus important for?

A

Lateral geniculate nucleus (LGN):

  • important structure in the relay of visual information
  • connected to superior colliculus via the superior brachium

Medial geniculate nucleus (MGN):

  • important structure in the relay of auditory information
  • connected to inferior colliculus via the inferior brachium
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4
Q

Label the following structures

A
  • the mammillary bodies and infundibulum (pituitary stalk) are part of the hypothalamus
  • the pineal gland is part of the epithalamus
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5
Q

Which structures does the septum pellucidum run between?

What structures are located superior and inferior to the diencephalon?

A
  • septum pellucidum is the wall between the corpus callosum and the fornix
  • the diencephalon is wedged between the fornix superiorly and the midbrain inferiorly
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6
Q

What are the following structures?

What is marked by the dotted line and ?

A
  • ? is the roof of the thalamus, which is formed by the choroid plexus of IIIrd ventricle
  • dotted line is the hypothalamic sulcus, which separates the thalamus from the hypothalamus
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7
Q

What is located superior, anterior and inferior to the thalamus?

What is the interthalamic adhesion?

A
  • the body of the fornix is located superior to the thalamus
  • the choroid plexus of the IIIrd ventricle forms the roof of the thalamus
  • the interventricular foramen and column of the fornix are located anterior to the thalamus
  • the midbrain forms the inferior border of the diencephalon
  • the inter-thalamic adhesion is a small bundle of fibres that connects the 2 thalami to each other
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8
Q

What separates the thalamus from the hypothalamus?

What are the borders of the hypothalamus?

A
  • the hypothalamic sulcus separates the thalamus from the hypothalamus
  • the anterior border of the hypothalamus is formed by the lamina terminalis** and the **anterior commissure
  • the infundibulum is located ventrally and is connected to the pituitary gland
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9
Q

What is indicated by the *

A
  • recesses of the IIIrd ventricle found in the space bounded by the hypothalamus on both sides
  1. supraoptic recess
  2. infundibular recess
  • these are spaces within the IIIrd ventricle
  • if there is an expanded IIIrd ventricle, these recesses can balloon out and compress structures surrounding them
    • e.g. optic chiasm, infundibulum
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10
Q

What are the 2 components of the epithalamus?

A

habenula + pineal gland

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11
Q

Label the structures and nuclei of the thalamus

A
  • the thalamus is not one homogenous mass, but it is composed of many nuclear complexes
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12
Q

What forms the medial and lateral borders of the thalamus?

A
  • the medial border is the IIIrd ventricle
    • the thalamus has a free border medially
  • the lateral border is the internal capsule
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13
Q

Label the coronal section

What is located medial, lateral and anterior to the thalamus?

A
  • the medial border of the thalamus is a “free border” formed by the IIIrd ventricle
  • the lateral border is formed by the internal capsule
    • this is continuous with the cerebral peduncles at the level of the midbrain
  • the body of the fornix and choroid plexus are located superiorly
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14
Q

What are the borders of the diencephalon?

A
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15
Q

What is the massa intermedia?

A
  • another name for the interthalamic adhesion that connects the thalami to each other
  • the thalami are bilateral egg-shaped masses of grey matter that sit on top of the brainstem
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16
Q

Why are the thalami referred to as the “receptionist of the brain”?

A
  • they receive information, process it and pass it to the appropriate location in the brain
  • they are relay nuclei to the cerebral cortex that are involved in processing sensory impulses
  • it is also involved in motor processing through its connection with the basal ganglia and cerebellum
    • ​they do not directly connect to the corticospinal tract
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17
Q

What is the only sense not processed by the thalamus?

A

olfaction

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18
Q

What are the fibres that travel between the thalamus and the cortex?

A
  • thalamocortical fibres travel from the thalamus to the cerebral cortex
  • corticothalamic projections travel from the cortex to the thalamus
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19
Q

What is the internal medullary lamina and how does it segregate the thalamus?

A
  • it is a Y-shaped layer of myelinated fibres
  • it divides most of the thalamus into nuclear groups
  1. anterior nuclear group
  2. medial nuclear group
  3. lateral nuclear group (further subdivided)
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20
Q

What are the thalamic nuclei that are only visible in coronal section?

A

midline thalamic nuclei (MTN):

  • these are adjacent to the IIIrd ventricle

intralaminar nuclei:

  • these are embedded within the internal medullary lamina

reticular nucleus:

  • this is located lateral to the external medullary lamina
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21
Q

What does the anterior nuclear group communicate with?

Where is it located and what does it form the posterior boundary of?

A
  • the anterior nuclear group communicates with the limbic system
  • it relays information related to emotion, memory and learning
  • it is located in the more narrow end of the thalamus and forms the posterior boundary of the interventricular foramen
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22
Q

What is the role of the medial nuclear group?

A
  • the medial group contains the medial dorsal nucleus
  • it receives and relays information related to emotional behaviour
23
Q

What are the roles of the ventral anterior (VA) and ventral lateral (VL) nuclei of the lateral nuclear group?

A
  • they are important for motor relay
  • they communicate with motor structures such as the supplementary motor area, premotor area, cerebellum and basal ganglia
24
Q

What are the roles of the ventral posterior medial (VPM) and ventral posterior lateral (VPL) nuclei of the lateral nuclear group?

A
  • they both have a role in sensory relay
  • VPM receives sensory information from the face
  • VPL receives sensory information from the body via the dorsal column pathway and spinothalamic tract
25
Q

What is the role of the lateral posterior (LP) and pulvinar nuclei of the lateral nuclear group?

A
  • they both have an integrative function

Lateral posterior (LP):

  • receives information from multiple parts of the brain and puts it together

Pulvinar nucleus:

  • receives information from all the association areas and relays it to different parts of the thalamus and brain
  • has a role in cognitive function associated with visual and auditory stimuli
  • forms the wide end of the thalamus
26
Q

Where are the reticular nuclei of the thalamus found?

What is significant about the communications of these nuclei?

A
  • they are located between the external medullary lamina and the internal capsule
  • they are the only thalamic nuclei that DO NOT connect with the cerebral cortex
  • they still communicate with the cerebral cortex, but there are no thalamocortical fibres projecting directly to the cortex
27
Q

What type of neurones are found within the reticular nucleus?

What are the 2 main roles of this nucleus?

A
  • it contains a thin sheet of inhibitory neurones that project deep into the rest of the thalamus
  • the reticular nucleus has a role in:
  1. dampening down ascending sensory pathways during sleep
  2. modulating the state of alertness
28
Q

How is the reticular nucleus able to dampen down ascending sensory pathways during sleep?

A
  • if someone touches your arm whilst sleeping, this information still travels to the thalamus via the dorsal column pathway
  • usually, thalamocortical fibres project from the thalamus to the somatosensory cortex to make us aware of touch information
  • when asleep, corticothalamic fibres travel to the thalamus to make it aware that sleep is occurring
  • the corticothalamic fibres connect to inhibitory interneurones in the reticular nucleus
  • the inhibitory interneurones increase their activity to dampen down sensory information and stop it from coming into awareness
29
Q

what are the 3 surgical approaches to the thalamus?

A
  1. interhemispheric transcallosal
  2. transcortical transventricular
  3. pterional transylvanian transinsular
30
Q

What is involved in the transcortical transventricular approach to the thalamus?

Why is this approach less preferable?

A
  • involves cutting through the cortex to reach the ventricles to approach tumours in this vicinity
  • as it involves cutting through the cortex, there will be side effects (depending on which part of the cortex has been cut - usually seizures)
  • as a lot of white matter is cut through to reach the ventricles, it is associated with a higher rate of complications
31
Q

What is involved in the pterional transylvanian-transinsular approach to the thalamus and when might this be used?

What is the associated risk?

A
  • used to treat more lateral tumours located close to the insula
  • a window is made by cutting through the pterion, dura and meninges
  • the lateral fissure is opened up and a cut is made through the insula to reach the tumour
  • risk of disturbing the fibres of the internal capsule
32
Q

What is involved in the interhemispheric transcallosal approach to the thalamus?

When can this be used and why is it a preferred approach?

A
  • the hemispheres are pushed apart and a cut is made through the corpus callosum** to reach the **lateral ventricles superiorly
  • the IIIrd ventricle and thalamus can be reached via connecting channels from the lateral ventricles
  • no cutting through the cortex so less risk of complications
  • only suitable for tumours that can be reached through the ventricles
    • these are tumours located more medially within the thalamus
33
Q

What are the 3 most common complications of thalamic surgery and what injury causes them?

A

contralateral motor dysfunction:

  • due to injury to the adjacent internal capsule

visual field defects:

  • due to injury to the optic pathways related to the posterior thalamus (pulvinar & LGN)

aphasia:

  • can occur during left thalamic tumour resection
34
Q

What are the following borders of the thalamus?

A
35
Q

Where is the “critical surface” of the thalamus and why is it important?

What are the 3 “free” surfaces of the thalamus?

A
  • the critical surface is the ventrolateral border of the thalamus, which has relationships with the internal capsule and subthalamic structures
  • surgeons must take extra care when operating in this area
  • the anterior, posterior and medial surfaces of the thalamus are “free” borders
36
Q

Where is the subthalamus located?

What does it lie medial to?

A
  • it is inferior to the thalamus** and **lateral to the hypothalamus
  • it is located medial to the internal capsule and cerebral peduncles
37
Q

What is the role of the subthalamus?

Why is its functional grouping different to its anatomical grouping?

A
  • it has roles in initiating and coordinating smooth and controlled movements
  • it is anatomically grouped with the diencephalon, but functionally grouped with the basal ganglia
38
Q

What is the main component of the subthalamus?

A

subthalamic nucleus

  • this is associated with the motor functions of the basal ganglia and has roles in initiating smooth, controlled and coordinated movements
39
Q

What are the following structures and which component of the diencephalon are they part of?

A
  • the habenula and pineal gland** make up the **epithalamus
  • the stria medullaris thalami is a bundle of fibres that arches over the thalamus to connect to the habenula
40
Q

Where are the habenulas located?

What underlies this structure?

A
  • they are located on the dorsomedial surface of the posterior thalamus
  • underlying each habenula are the habenular nuclei
  • the habenular nuclei are a centre for the integration of smell
    • they are involved in the link between smell and memory / emotions
41
Q
A
42
Q

Where does the stria medullaris thalami run to and from?

What information is received by the habenula and what is its role?

A
  • the septal (paraolfactory) area is located on the medial aspect of the hemispheres and receives information about smell after processing by the primary olfactory cortex
  • the septal area is also part of the limbic system
  • the stria medullaris thalami runs from the septal area to the habenula
  • the habenula receives information about smell, emotions and memory and projects to specific areas of the brainstem
43
Q

What nuclei can the habenula connect to to induce an autonomic response?

A
  • the habenula integrates smell, memory and emotions and connects to the superior** and **inferior salivatory nuclei
  • these send GVE fibres to the salivatory glands to stimulate salivation
  • salivation occurs in response to smell / the memory of a certain smell
44
Q

Where is the pineal gland located?

What does it form the posterior aspect of?

A
  • located above the tectum of the midbrain (superior colliculus)
  • located below the splenium of the corpus callosum
  • it forms the posterior aspect of the IIIrd ventricle
45
Q

What is the role of the pineal gland?

A
  • it is an endocrine gland that releases melatonin** in response to **levels of light
  • it has no direct connection to the CNS
46
Q

Describe the indirect pathway from the retina involving the pineal gland

A
  • retina sends some information about the levels of light to the suprachiasmatic nucleus (SCN) of the hypothalamus
  • hypothalamus sends descending fibres through the thoracic spinal cord via the intermediolateral cell column (T1 - L2)
  • fibres pass into the sympathetic chain and ascend to reach the superior cervical ganglion
  • fibres pass from superior cervical ganglion into the nervus conarii**, which travels to the **pineal gland
  • the pineal gland decides how to regulate levels of melatonin in response to levels of light
47
Q

Why is the pathway from the retina to the pineal gland called the “indirect” pathway?

Why is melatonin production important?

A
  • it is an indirect pathway as the pineal gland does not have any direct connections to the CNS
  • melatonin production is important for the regulation of circadian rhythms (sleep-wake cycle)
48
Q

What are the boundaries of the hypothalamus?

A
49
Q

What is the role of the hypothalamus?

A
  • it has a role in regulating the internal environment and maintaining homeostasis
50
Q

How is the hypothalamus involved in temperature regulation?

Which part of the hypothalamus coordinates this?

A
  • if there is an increase in blood temperature, the hypothalamus responds by initiating heat loss mechanisms (e.g. sweating)
  • this is performed by the anterior hypothalamus
  • if there is a decrease in blood temperature, the hypothalamus responds by initiating heat maintenance mechanisms (e.g. shivering)
  • this is performed by the posterior hypothalamus
51
Q

What is the result of a lesion to the anterior hypothalamus?

A

hyperthermia

  • the person feels warm all the time as they are unable to initiate heat loss mechanisms
52
Q

What are the 2 parasympathetic and 2 sympathetic nuclei of the hypothalamus?

Other than autonomic events, what are the other roles of the hypothalamus?

A

Parasympathetic nuclei:

  • preoptic nucleus
  • anterior nucleus

Sympathetic nuclei:

  • posterior nucleus
  • lateral nucleus

Other functions:

  • also has roles in sexual and eating behaviour
53
Q

How can the thalamus be divided into zones?

A
  • the column of the fornix descends through the hypothalamus to reach the mamillary bodies
  • this divides the hypothalamus into a medial and lateral zone

Neuroanatomy (16 decks)

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