Module 9: Diencephalon- Thalamus

which structure is one of the main structures comprising the diencephalon?

thalamus

what are the boundaries of the thalamus?

• anterior end forms the posterior boundary of the intraventricular foramen

• posterior end overhands the superior colliculus of the midbrain

• inferior surface is continuous with the tegmentum of the midbrain

• medial surface forms the lateral wall of the 3rd ventricle

what connects the two thalamic hemispheres?

the interthalamic connection

what is the functional role of the thalamus?

is considered the relay station to the cerebral cortex, relays sensory info (VPL, VPM) motor info (VA, VL), and plays a role in memory and emotional functions of motor control through connections with the limbic system

what is the vascular supply of the thalamus?

originates from posterior circulation, the medial, lateral and posterior thalamic regions are supplied primarily by branches of the posterior cerebral artery and posterior communicating arteries

what is the primary neurotransmitter of the thalamus?

glutamate, which has excitatory influences on structures within the CNS

the thalamus receives direct input from every sensory system except which one?

the olfactory sense

which thalamic nuclei receive motor signals (including from the basal ganglia and cerebellum)?

the ventral anterior (VA) and ventral lateral (VL) nuclei

how is the thalamus subdivided by location?

divided into three major groups of nuclei: anterior, medial, and lateral groups

what is the role of the anteiror group?

receives info from the limbic system structures so has a role in attention, alertness, and memory acquisition

what is the role of the medial group?

integrates sensory, motor, visceral, and olfactory information and relates it to the person’s emotional state, functions similar to the pre-frontal cortex- affect and foresight

what is the role of the lateral group?

receives sensory and motor information

how is the thalamus subdivided by function?

three general functional groups:

• relay nuclei (majority of thalamus)

• association nuclei

• nonspecific nuclei

what is the role of the association nuclei (pulvinar, anterior nucleus, and dorsal-medial nucleus)?

receive inputs from and transmit information back to the sensory and motor association areas of the cerebral cortex

what is the role of the nonspecific nuclei?

believed to be involved in general functions of consciousness and attention, limbic pathways and memory, and help our nervous system decide what to focus on amongst all signals being received

what is the primary function of the pulvinar nucleus?

processes visual information

what are the characteristics of the pulvinar nucleus?

largest and pillow shaped nuclei comprising of the posterior thalamus, receives input from the superior colliculus, hippocampus, and mammillary bodies, projects tot he visual cortex and visual association areas, and areas of temporal, parietal, and frontal lobes associated with visual function and eye movements

what group do the most clinically relevant nuclei fall into?

lateral nuclear group, these include VA, VL (for motor) and VPM, VPL, and lateral and medial geniculate nuclei for sensory

what information do the VPM and VPL relay?

somatic sensation, VPM receives somatosensory from the face via the trigeminal nerve, and VPL from the rest of the body

where are the medial and lateral geniculate nuclei located?

posterior portion of the thalamus

what is the function of the medial geniculate?

processes auditory information (input from inferior colliculus and outputs to the auditory portion of temporal lobe)

what is the function of the lateral geniculate?

processes visual information (input from superior colliculus and outputs to occipital lobe)

what is the role of the ventral lateral nucleus (VL)?

relaying motor feedback from the cerebellum to motor areas (important for coordination, timing, scaling of movement), and believed to be responsible for mild motor weakness and ataxic movements with thalamic strokes (L = cerebeLLum)

what are the inputs and outputs of the VL nucleus?

inputs from the cerebellum (dentate nucleus) and outputs to M1, PMA, SMA

what is the role of the ventral anterior nucleus (VA)?

modulates and relay signals between the BG and the PMA, plays a role in planning and initiating movement (ABG- asian baby girl)