Thalamus Flashcards
What is the general structure of the thalamus?
- It’s a large (4cm long) egg shaped mass of gray matter, composed of two parts (thalami) connected by a structure called thalamic adhesion.
- It’s separated by a vertical sheet of white matter, the internal (medial) medullary lamina into an anterior, middle and a medial and lateral parts each with their own respective nuclei
- It’s covered on the outside by a sheet of white matter called stratum zonale and on its lateral surfaces by the external medullary laminae.
What is the function of the anterior thalamic nucleus?
It’s closely associated with the limbic system which is why it’s thought to be associated with emotional tone and mechanisms of recent memory (episodic emotional memory)
* it’s connected to the limbic system via a special circuit called papez circuit:
Hippocampus -> fornix -> mamillary body -> hypothalamus -> cingulate gyrus -> enterorhinal cortex -> hippocampus
What is the function of the medial part (Dorso-medial nucleus) of the thalamus?
It has a two way connection between the olfactory cortex, amygdala and hypothalamus (inputs) and the prefrontal cortex (output)
It’s associated with the integration of a large variety of sensory information and the relation of those information with one’s emotional and subjective states.
*associated with drive and motivation.
What is the function of the dorsal group of the lateral aspect of the thalamus?
This tier includes: lateral dorsal, lateral posterior and pulvinar nuclei.
They have interconnections with other thalamic nuclei, and with the parietal lobe, cingulate gyrus, and occipital & temporal lobes
associated with processing of vision
What is the function of the ventral tier of the lateral thalamic nuclei?
- Ventral anterior nucleus:
- associated with the reticular formation & the direct, indirect and substantial-striatal pathway; which is why it is thought to influence (initiate) motor activities - Ventral lateral nucleus:
- it has similar associations as the ventral anterior nucleus
- also associated with the cerebellum majorly (dentate nucleus) and the red nucleus minorly
- functions in coordination of movement and modulation (planning and initiation) of movements - Ventral posterior nucleus:
A. VPL:
Associated with important ascending sensory tracts; the medial and spinal lemnisci
* functions in proprioception, vibration, fine touch
B. VPM:
Associated with the trigeminal and gustatory pathways
*functions in gustation, and facial sensation
- both of the aforementioned thalamocortical projections run through the posterior limb of the internal capsule & corona radiata to the primary sensory cortex in the postcentral gyrus
What is the function of the intralaminar nuclei?
It is thought to influence the level of consciousness and alertness in an individual
What is the function of the midline nuclei?
They receive afferent fibers from the reticular formation but their precise function is unknown
What is the function of the medial geniculate body?
- It forms part of the auditory pathway
- It receives afferent fibers from the inferior colliculi which from a dilation called the inferior brachium.
- It receives sensory information from both ears, but predominately from the contra lateral ear.
- The efferent fibers form what is known as the auditory radiation which travels to the auditory center in the superior temporal gyrus.
What is the function of the lateral geniculate body?
- It forms part of the visual pathway.
- It consists of 6 layers of neurons.
- It receives axons from the ganglionic cells of the retina of the way in the following manner:
A. It receives the temporal fibers of the ipsilateral eye
B. It receives the nasal fibers of the contralateral eye, the fibers on either side cross in the midline forming the optic chiasma - The efferent fibers leave the lateral geniculate body to form the visual radiation, which passes to the visual cortex of the occipital lobe
