Thalamus and Hypothalamus Flashcards
What three structures make up the diencephalon?
Thalamus
Subthalamus
Hypothalamus
Where is the thalamus found within the brain?
It is right in the middle the brain just under the posterior half of the corpus callosum
What separates the two halves of the thalamus?
3rd ventricle
Some people have a bridge connecting the two halves (inter-thalamic connection)
Describe the connections of the thalamus with the forebrain
Each half of the thalamus has ipsilateral connections with the forebrain (originating from thalamic nuclei)
What is the main function of the thalamus?
It is a relay centre for both motor and sensory fibres between the cerebral cortex and the rest of the CNS; Enhances or restricts signals
What is the only sensory system that doesn’t involve the thalamus?
Olfaction
Describe the organisation of the thalamic nuclei
A thin sheet of white matter called the internal medullary lamina runs longitudinally through the thalamus (Y shaped) and splits the thalamus into three main areas - anterior, medial and lateral.
Each of the three parts of the thalamus has discrete nuclei that are reciprocally connected to the cerebral cortex
Classify the different types of thalamic nuclei
Relay/specific nuclei - have reciprocal connections with a primary cortical area (ie. with a clearly defined function)
Association nuclei - have more diffuse reciprocal connections with association cortex (to regulate the integration and interpretation of the sensory information)
Non-specific nuclei - (such as the intra-laminar nuclei and reticular nuclei) show diffuse projections to many parts of the brain
Outline the organisation of thalamic nuclei
Anterior part = anteroventral, anteromedial and anterodorsal nuclei
Middle part = dorsomedial nucleus (subdivided into anteromedial magnocellular and posterolateral parvocellular)
Lateral part = Dorsal group (lateral dorsal nucleus, lateral posterior nucleus and pulvinar) and Ventral group (ventral anterior, ventral lateral and ventral posterior nuclei); Middle and lateral geniculate nucleus located on the posterior surface of the ventrolateral surface of the thalamus underneath the pulvinar
What do the anterior, lateral dorsal and dorsomedial nuclei connect with?
Prefrontal and Cingulate Cortex (part of the limbic system)
What do the lateral posterior and pulvinar nuclei connect with?
The association cortex at the junction of the parietal, temporal and occipital lobes, and the prefrontal cortex
The Intralaminar nuclei receive inputs form which part of the brainstem and project where?
They receive inputs from the Reticular Formation of the brainstem and project diffusely to all cortical areas, including medial temporal lobe structures (e.g. amygdala, hippocampus and basal ganglia)
Intralaminar neurones are mostly of what type? What is the clinical significance of a loss of these neurones?
Mostly glutamatergic neurons (i.e. excitatory)
Loss of neurons in this region is associated with Progressive Supranuclear Palsy (rare brain disorder causing problems with walking and balance) and Parkinson’s disease
The reticular nucleus receives inputs from which part of the brainstem and project where?
Receives inputs from the Reticular Formation, cerebral cortex and dorsal thalamic nuclei (most input comes from collaterals of fibres passing through the thalamic reticular nucleus). Efferent fibres project to the other thalamic nuclei only, regulating the flow of information through these to the cortex (modulates thalamic activity)
The majority of neurones raising form the reticular nucleus are of what type?
Majority of neurons are GABAergic (e.g. inhibitory)
