Diencephalon Structure & Function

Question 1

Where is the diencephalon located?

Answer 1

• embryologically located:
  
  • between the telencephalon and the mesencephalon
• ​between the cerebral cortex and the brainstem
• medial to the internal capsule
• divided in the midline by the third ventricle

Question 2

DIENCEPHALIC SUBDIVISIONS (5):

Answer 2

1. Epithalamus
2. Dorsal Thalamus (or Thalamus)
3. Ventral Thalamus
4. Subthalamus
5. Hypothalamus

Question 3

Epithalamus:

Answer 3

• Habenula: involved in the limbic pathway
• Pineal gland: synthesizes serotonin and converts it to melatonin
• Posterior commissure: links pretectal and other nuclei of the two sides

Question 4

Dorsal Thalamus or Thalamus:

Answer 4

• Thalamic nuclei:
  
  • provide a strong link to the cerebral cortex
• External medullary lamina:
  
  • a narrow band of myelinated fibers lateral to thalamic nuclei
• Internal medullary lamina:
  
  • a band of myelinated fibers that subdivide thalamic nuclei into anterior, lateral, and medial nuclear groups

Question 5

Ventral Thalamus:

Answer 5

• Reticular Nucleus of the Thalamus:
  
  • between the external medullary lamina and the internal capsule
• Ventral Lateral Geniculate Nucleus (vLGN)

Question 6

Subthalamus:

Answer 6

Located between the hypothalamus and the dorsal thalamus

1. Zona Incerta:
   
   • rostral extension of the brain stem reticular formation
2. Subthalamic Nucleus (of Luys)

• Involved with basal ganglia and extrapyramidal activity

Question 7

Hypothalamus:

Answer 7

Controlling center of the ANS

• Neurobehavioral functions and regulation of hormones released by the hypophysis

1. Hypothalamic nuclei
2. Infundibulum
3. Hypophysis (pituitary gland)
4. Hypophyseal portal system:
   
   • vascular connection between the hypothalamus and the anterior pituatary

Question 8

Blood supply to the thalamus:

Answer 8

Supplied mainly by branches from the Circle of Willis:

1. Anterior communicating artery
2. Posterior communicating artery
3. Anterior cerebral artery (ACA)
4. Posterior cerebral artery (PCA)
5. Internal carotid artery

Question 9

Dorsal Thalamus Proper (Thalamus):

Location

Answer 9

• Medial to the posterior limb of the internal capsule
• Surrounds the third ventricle

Question 10

Dorsal Thalamus Proper (Thalamus):

Major functions

Answer 10

“Gateway to the Cortex”

1. Relays all sensory information to the cerebral cortex
   
   • however, olfactory input to the thalamus is from the piriform cortex
2. Relays information about motor activities to the cerebral cortex
3. Integrates sensory information from different modalities and projects to association cortex
4. Relays emotional and affective information to the cortex
5. It is part of the “Papez circuit” of the Limbic System, projects to the limbic cortex
6. It is intimately involved in the control of alertness, arousal, and sleep
7. Under direct cortical feedback and control:
   
   • reciprocal connections between the thalamus and the cortex

Question 11

How are the specific relay nuclei grouped?

Answer 11

1. Anterior nuclear group
2. Lateral-Ventral tier
3. Lateral-Dorsal tier
4. Medial group

Question 12

• *Specific relay nuclei:**
• *Anterior nuclear group**
• **Afferent Input: **
• Efferent Output:
• Functions:

Answer 12

• Afferent Input: Mammillary body
• Efferent Output: Cingulate gyrus
• **Functions: **Limbic​

Question 13

What specific relay nuclei make up the Lateral-Ventral Tier of the thalamus?

Answer 13

1. Ventral anterior (VA)
2. Ventral lateral (VL)
3. Ventral posterior lateral (VPL)
4. Ventral posterior medial (VPM)
5. Lateral geniculate nucleus (LGN)
6. Medial geniculate nucleus (MGN)

Question 14

Ventral Anterior & Ventral Lateral nuclei:

• Afferent Input:
• Efferent Output:
• Functions:

Answer 14

1. Ventral Anterior (VA)
   
   • Afferent Input: Globus pallidus
   • Efferent Input: Premotor cortex (area 6)
   • Functions: Motor
2. Ventral Lateral (VL)
   
   • Afferent Input: Dentate nucleus of cerebellum
   • Efferent Input: Motor and premotor (areas 4 and 6)
   • Functions: Motor

Question 15

Ventral Posterior Lateral (VPL) & Ventral Posterior Medial (VPM) nuclei:

• Afferent Input:
• Efferent Output:
• ​Functions:

Answer 15

1. Ventral Posterior Lateral (VPL):
   
   • **Afferent Input: **Dorsal column-medial lemniscus & spinothalamic
   • **Efferent Output: **Somatosensory cortex (areas 3,1,2)
   • **Functions: Somatic **sensation (body)
2. Ventral Posterior Medial (VPM):
   
   • Afferent Input: Sensory nuclei of trigeminal nerve
   • Efferent Output: Somatosensory cortex (areas 3,1,2)
   • Functions: Somatic sensation (face)

Question 16

Lateral Geniculate Nuclei (LGN) & Medial Geniculate Nuclei (MGN):

• Afferent Input:
• Efferent Output:
• ​Functions:

Answer 16

1. Lateral Geniculate Nuclei (LGN)
   
   • Afferent Input: Retinal ganglion cells
   • **Efferent Ouput: **Primary visual cortex (area 17)
   • Functions: Vision
2. Medial Geniculate Nuclei (MGN)
   
   • **​​Afferent Input: **Inferior colliculus
   • **Efferent Output: **Primary auditory cortex (areas 41,42)
   • **Functions: **Audition

Question 17

What specific relay nuclei make up the Lateral-Dorsal tier?

Answer 17

1. Lateral doral (LD)
2. Lateral posterior (LP)
3. Pulvinar (Pul)

Question 18

Lateral dorsal (LD), Lateral posterior (LP) and Pulvinar nuclei (Pul):

• Afferent Input:
• Efferent Output:
• Functions:

Answer 18

1. Lateral dorsal (LD)
   
   • Afferent Input: Cingulate gyrus
   • **Efferent Output: **Cingulate gyrus
   • Functions: Emotional expression
2. Lateral posterior (LP)
   
   • Afferent Input: Parietal cortex
   • Efferent Output: Parietal cortex
   • Functions: Sensory integration
3. Pulvinar (Pul)
   
   • Afferent Input: Superior colliculus, parietal, occipital and temporal lobes (POT)
   • Efferent Output: Parietal, occipital and temporal lobes (POT)
   • Functions: Integration of sensory information

Question 19

**Specific relay nuclei: **

Medial group

• Afferent Input:
• Efferent Output:
• Functions:

Answer 19

Medial dorsal (MD)

• **Afferent Input: **Amygdaloid nuclear complex, olfactory, hypothalamus
• Efferent Output: Prefrontal cortex
• Functions: Limbic

Question 20

Name the diffuse-projection nuclei:

Answer 20

1. Midline nuclei
2. Intralaminar nuclei:
   
   • Centro-median (CM)
   • Centro-lateral (CL)
   • Parafascicularis (PF)
3. Reticular nucleus

Question 21

What is the common afferent input for the diffuse-projection nuclei?

Answer 21

reticular formation

Question 22

What is the general function of the diffuse-projection nuclei?

Answer 22

to keep a state of alertness and attention

Question 23

Where do the intralaminar nuclei project to?

Answer 23

Basal ganglia and wide areas of the cortex

Question 24

What would be the single cell response in VPL of human during therapeutic surgery:

Answer 24

bursts of discharge in specific sensory relay nucleus of the VPL when a specific sensory periphery on the contralateral body is stimulated

Question 25

**Thalamic syndrome:**

Answer 25

1. Usually caused by a **vascular lesion or tumor** * relatively rare 2. Usually involves **damage to the lateral group of thalamic nuclei (VPL)** 3. **Initially,** a transitory contralateral hemianalgesia 4. **Soon,** painful sensations appear with noxious stimuli 5. **Later,** pain is provoked by pressure, touch, and vibration 6. **In time,** a state of spontaneous, constant or paroxysmal pain is evoked on the affected side (contralateral to the lesion) without any external stimulus (Dysesthesia) 7. The **threshold** for pain, temperature, and tactile sensation, however, is **usually raised on the affected side** 8. But, once the threshold is reached, **pain has a strong emotional overtone** to it

Question 26

Functional Charactersitics of Non-Specific System (4):

Answer 26

1. Activated by repetitive, low-frequency stimulation 2. Interconnected with each other, and reciprocally with specific thalamic nuclei 3. Repetitive stimulation of the non-specific thalamic nuclei evokes cortical recruitment response that waxes and wanes 4. Controls the level of excitability of neurons over wide areas of cortex