6. Thalamus and hypothalamus Flashcards
What divides the thalamus and hypothalamus into two halves?
3rd ventricle
What is the function of the thalamus?
- Relay station between the cerebral cortex and the rest of the CNS
- Transmission and integration of information
- Involved in all functional systems within the cortex - not olfaction
How are thalamic nuclei classified?
Classified based on the connection with the cortex:
• Specific - primary cortical areas
• Association - association cortex
• Reticular - not connected to the cortex directly - connected to the brainstem
• Intralaminar - all cortical areas
What do the following nuclei link: • ventral lateral/anterior • ventral posterolateral • ventral posteromedial • lateral geniculate • medial geniculate
- ventral lateral/anterior - motor cortices
- ventral posterolateral - somatosensory (below the neck)
- ventral posteromedial - somatosensory (head)
- lateral geniculate - retina to the primary visual cortex
- medial geniculate - inner ear to primary auditory cortex
How can the association cortex be divided?
- Prefrontal cortex - most of the frontal lobe, except for the primary motor cortex and some other motor cortical areas
- Parieto-tempero-occipital cortex - all of the cortex in the 3 lobes except the primary cortical areas
- Cingulate cortex - follows the line of the corpus callosum
Where do the association nuclei project?
Mammillary bodies, hypothalamus, cingulate and prefrontal cortices
Which nuclei are part of the reticular activating system (RAS) and what does this mean?
• Intralaminar and reticular nuclei
• Involved in consciousness and arousal
• RAS is a core of grey matter, the activity of which determines stimulation of cortex and consciousness
• RAS projects up from the brainstem - projections activate both nuclei
• Intralaminar nuclei project to the whole cortex
• Reticular nuclei:
- no direct connections with the cortex
- intrathalamic connections with all other nuclei, increasing their activity
What happens if the reticular activating system (RAS) is damaged?
Unconscious => coma
What is thalamic syndrome?
- Develops after a thalamic stroke - usually PCA
- Change in sensation - disturbance of nuclei that relay somatosensory information from body to primary somatosensory cortex
- Pain can be altered
- Emotional disturbance - association with limbic system
- Derjerine-Roussy syndrome
How does damage in traumatic brain injury affect the thalamus?
• Widespread damage - shearing forces => diffuse axonal injury
• Connections between different parts of the brain severed
• PET scans - more red, more microglial activation
• Connections all lead to the thalamus
• Neuroinflammation in the thalamus years after injury
- higher microglial activation in thalamo-cortical tract
- greater damage in white matter tract
Where is the hypothalamus located?
- Behind the optic chiasma and anterior commissure
- In front of the mammillary bodies
- Separated from pituitary gland below by infundibular stalk
What is the anterior commissure?
- Anterior boundary of hypothalamus
* Bundle of nerve fibres connecting the 2 temporal lobes, across the midline
What is the function of the hypothalamus?
- Involved in homeostasis
* Coordinates the ANS, endocrine system and behaviour
Which structures in the forebrain does the hypothalamus have close connections with?
- Olfactory system
* Limbic system - hyppocampus, amygdala, cingulate cortex, septal nuclei
What behaviours does the hypothalamus control?
- Eating and drinking
- Expression of emotion
- Sexual behaviour
- Circadian rhythm
- Memory
- Motivational process (addiction if it goes wrong)
