Thalamus and hypothalamus Flashcards
Describe the anatomy of the thalamus
It is part of the diencephalon (thalamus, hypothalamus, sub thalamic nucleus). It is divided into left and right by the third ventricle each being a collection of individual nuclei. They have separate functions and connections with ipsilateral forebrain structures.
How is the thalamus separated from the caudate nucleus?
by the internal capsule
What are the functions of the thalamus?
- Relay centre between the cerebral cortex and other parts of the CNS
- Integrates/modulates information en route
- Involved in all functions except olfaction
- Some nuclei form part of the Reticular Activating System.
How are the nuclei in the thalamus classed? (according to the connection of the nuclei to the cortex)
Specific – connected to primary cortical areas.
Association – connected to association cortex.
Intralaminar – connected to all cortical areas.
Reticular – not connected to the cortex.
Where is the thalamus located?
In the middle of the brain under the posterior half of the corpus callosum
What divides the thalamus?
the 3rd ventricle
What sense isn’t the thalamus involved in?
olfaction
How are nuclei named?
According to the position e.g. ventral lateral
Which nuclei link to the motor cortices (primary, premotor and supplementary)?
ALL ALONGSIDE EACHOTHER
Ventral lateral and ventral anterior
Which nuclei link to the somatosensory head cortex?
ventral posteromedial
Which nuclei link to the somatosensory body cortex?
ventral posterolateral
Which nuclei link to the visual cortex?
lateral geniculate
Which nuclei link to the auditory cortex?
medial geniculate
How can the association cortices be divided into 3 areas?
According to thalamic function:
Prefrontal Cortex - most of the frontal lobe except for the primary motor cortex and some other motor cortical areas
Parieto-tempero-occipital Cortex - consists of all of the cortex in the parietal, temporal and occipital lobes except for the primary cortical areas
Cingulate Cortex - it follows the line of the corpus callosum
Where do the association nuclei project?
The mammillary bodies, the hypothalamus, the cingulate and prefrontal cortices.
Where do the anterior, lateral dorsal and dorsomedial association nuclei project?
mamillary body, hypothalamus, cingulate and prefrontal crotex
Where does the lateral posterior association nuclei project?
parieto temporo occipital
Where does the pulvinar association nuclei project?
prefrontal cortex
What is the intralaminar and reticular nuclei part of?
the reticular activating system
What does the reticular activating system do?
involved in consciousness
Where does the intralaminar nucleus project?
Where does the reticular nuclei receive projections from?
Where do they both get inputs from?
Where does the RAS project from?
The intralaminar nucleus is involved with the RAS, which projects up from the brainstem
The intralaminar nuclei project to the whole cortex
The reticular nuclei receive projections from within the thalamus
Both receive inputs from the reticular formation
What is the reticular formation?
A core of grey matter through the brainstem. It projects up to the thalamus (to the intralaminar nuclei). Then, the intralaminar nuclei, because of their connections to all areas of the cortex, modulate the activity of the cortex.
If there is more activity going through the reticular formation to the thalamus, what happens to the cortex?
It is more activated hence more conscious/aware
What happens if the information flow through the reticular formation is interrupted?
unconsciousness and coma
Why are the intralaminar nuclei so important?
they have connections to all parts of the cortex so they can modulate its activity
What is thalamic syndrome?
Develops after a thalamic stroke. The exact pattern of symptoms depends on which part of the thalamus has been affected.
What is the most likely thing to happen in thalamic syndrome?
A change in sensation due to disturbance of the nuclei that relay somatosensory information from the body to the primary somatosensory cortex
What is a common cause of thalamic syndrome?
strokes in the posterior region (e.g. posterior cerebral artery stroke)
What are some symptoms of thalamic syndrome?
- Pain (central, non-localised pain)
- Emotional disturbance
- Derjerine-Roussy syndrome (pain syndrome)
How is traumatic brain injury different to strokes?
There is widespread brain damage rather than localised - due to diffuse axonal injury
What happens when there is brain damage from traumatic brain injury?
inflammation occurs through microglial inflammation hence inflammation is seen in the thalamus years after
How would thalamic inflammation appear in the PET scan?
the more red, the more microglial acitvation
What divides the hypothalamus into 2?
the 3rd ventricle
Describe structures that are near the hypothalamus?
behind the optic chiasm and in front of the mamillary bodies, seperated from pituitary by infundibular stalk, anterior commisure at the front
What is the anterior commissure?
A bundle of nerved fibres connecting the two temporal lobes
What does the hypothalamus contain?
A large number of nuclei that have seperate functions. Each side has ipsilateral connection with forebrain and brainstem
How do each nuclei vary?
Have different neuropeptides and project to different places and do different things
Give examples of hypothalamic nuclei
paraventricular, suproptic, suprachiasmatic
What are the functions of the thalamus?
Involved in homeostasis - coordinates:
- Autonomic Nervous System
- Endocrine System
- Behaviour
What are some structures that the thalamus is closely connected to?
olfactory system limbic system (hippocampus, amygdala, cingulate cortex and septal nuclei), also to brainstem
How is behaviour controlled by the hypothalamus?
- Eating and drinking (in hunger, the nucleus involved in appetite regulation becomes more active)
- Expression of emotion (the limbic system
- Sexual behaviour
- Circadian rhythm (SCN)
- Memory (there are hypothalamic structures that help to consolidate memory)
How are we rewarded for goals by the limbic system?
There is a pleasure centre within the limbic system; activity of the pleasure centre increases when you achieve a goal. This motivational system reinforced beneficial behaviour, but can go wrong e.g. in addiction
What are some conditions causing hypothalamic structural damage?
MOST COMMONLY BY TUMOURS:
- Craniopharyngioma (more common in children/younger adults) - Other tumours e.g. glioma, meningioma (usually benign)
- Chronic inflammatory conditions (e.g. sarcoidosis)
How may hypothalamic damage present?
- Anterior pituitary hormone deficiencies
- Diabetes insipidus (polydipsia, polyuria)
- Labile emotions, rage (prefrontal cortex/ventromedial nucleus plays a role in inhibition of aggression)
- Inappropriate sexual behaviour
- Memory lapses (suprachiasmatic nucleus mammillary bodies involved in memory)
- Temperature fluctuation (preoptic area damage)
- Hyperphagia (loss of food regulation -> infundibular and paraventricular nuclei damage)
