Download Thalamus and basal ganglia

Thalamus and basal ganglia
Eunice Abrams
PGY4 Neurology
U of Michigan
• Diencephalon:
• Thalamus
• Hypothalamus
• epithalamus
Thalamus(Greek:inner chamber)
• Relay center
• Sensory
• Cerebellum, basal ganglia
• Limbic inputs
• Modulatory inputs for behavioral and sleep-wake cycles.
Thalamic nuclei and function
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lateral geniculate nucleus (LGN): thalamic nucleus for vision
medial geniculate nucleus (MGN): thalamic nucleus for hearing
pulvinar: association thalamic nucleus
ventral posterolateral (VPL) nucleus: nucleus for processing somatosensory
information from the body
• ventral posteromedial (VPM) nucleus: nucleus for processing somatosensory
information from the face; contains a medial parvocellular part for taste
• internal medullary lamina: partition between groups of thalamic nuclei; consists of
bundles of axons for intrathalamic communication
• centromedian nucleus: an intralaminar nucleus embedded in the internal medullary
lamina
• related to the basal ganglia
• receives input from the ascending reticular activating system (ARAS) & projects
impulses to widespread areas of the cerebral cortex for arousal.
Thalamic nuclei and function
• internal medullary lamina: axonal partition between thalamic nuclei
• external medullary lamina: outer capsule of thalamus; consists of
fibers traveling to & from thalamic nuclei
• reticular nucleus: scattered cells in the external medullary lamina
• - receives impulses from & projects impulses to other thalamic
nuclei
• - inhibits other thalamocortical circuits (attention)
• dorsomedial nucleus: component of the limbic system
• anterior nucleus: part of the limbic system; involved in declarative
memory storage.
Thalamic nuclei
• Thalamic nuclei <------> CORTEX
• Corticothalamic projections > thalamocortical projections.
Main noncortical inputs
to the different thalamic
nuclei
Major
reciprocal
connections
between
thalamus
and cortex
Vascular supply
Thalamic infarction
• Paramedian territory(off basilar comm a.)
• Clinical triad: somnolent apathy, memory loss, and abnormalities of vertical gaze.
• Thalamogeniculate a.: VPN, VL, subthalamic
• Contralateral-Hemianesthesia, slight hemiparesis, hemiataxia-hypesthesia,
disequilibrium, choreoathetoid movements, athetoid posture, paroxysmal pain
syndrome, homonymous hemianopia.
• Tuberothalamic/polar a.:
• Facial paresis for emotional movement, hemiparesis, visual field defects, dysphasia
with left sided lesions, hemineglect, impaired visuo-spatial processing(right sided
lesions).
• Bilat polar a: abulia, apathy, frontal lobe deficits, lethargy, impaired memory.
• Post choroidal a.: lat geniculate body
• Contralateral Partial hemianopsia, assymetric optokinetic visual fields.
Question
1.Which vessels provide the main blood supply of the thalamus?
2.The amygdala sends fibers to which part of the thalamus?
3.Which thalamic nucleus only projects to other thalamic nuclei?
Basal ganglia
• Neostriatum: Caudate and putamen
• Substantia Nigra
• Globus pallidus
• Subthalamic nucleus
• Nucleus accumbens
Function
• Control posture and movement.
• Execution of learned motor plans(subconscious)
• Anticipating rewards(nucleus accumbens)-involved in addiction.
Information processing
• Motor channel: cortex-putamen; Globus pallidus internal, substantia
nigra-thalamus(VL, VA)-supplementary motor, premotor cortex,
primary motor cortex.
• Oculomotor channel-higher control of eye movements:
• body of caudate nucleus-frontal eyefields, supplementary eyefields(frontal
lobes).
• Prefrontal channel-cognition involving frontal lobe.
• Head of caudate-prefrontal cortex.
• Limbic channel(regulation of emotions, and motivational drives)
• Limbic system-nucleus accumbens, ventral striatum
• Ventral pallidum-thalamic mediodorsal and ventral anterior nuclei.
Inputs to striatum
• Cortical efferent fibers to caudate and
putamen(corticostriate)ipsilateral-topographic pattern
• Cortex to substantia nigra
• Thalamostriatal: intralaminar nuclei/centrum mediumstriatum
• Nigrostriatal projections: substantia nigrastriatum, globus pallidum.
• Brain stem raphe nucleiascending fibers to striatum.
• Orbitofrontal cortex, and limbic systemNucleus accumbens
Striatal efferents
• Striatumglobus pallidus(internal, and external segments)
• Striatumsubstantia nigra
Pallidal afferents
• Substantia nigraGlobus pallidus
• SubthalamusGlobus pallidus(medial or internal)
• Striatuminternal and external globus pallidus
Pallidal efferents
• Globus pallidus(internal)→Thalamus(VA, VL)premotor, motor
cortex/influence motor system
• Globus pallidus(int)Thalamus(centrum
medianum)putamen(closed circuit)
• Globus pallidus(int)lateral habernacular nucleus
• Globus pallidus(external)internal pallidum, subthalamic
nucleusGpi, Gpe(closed circuit)
• Globus pallidussubstantia nigra, red nucleus, mesencephalic
reticular formation
Nigral afferents and efferents
• Cerebral cortex
• Globus pallidus
Pars reticularis Substantia nigra
• Subthalamic nucleus
• Striatum
• Pars reticularisVA, VL, reticular formation and superior colliculus.
• Pars compacta(dopaminergic fibers)caudate, putamen
• Excitatory direct pathway
• Inhibitory-indirect pathway
Direct and indirect pathway
• Direct pathway:
• Pars compacta(SN)excitatorycaudate & putamen inhibitory(GABA+P) GPi, and pars
reticularis(SN)inhibitorythalamus(ventral nucleus)cortical excitation
• Indirect pathway:
• Pars compacta(SN)(-) caudate & putamen(-)(GABA+E)GPe()subthalmus(+)GPi(-) thalamus(ventral nucleus)cortical inhibition
Lesions of the basal ganglia
• Subthalamic nucleus: contralateral hemiballismus
• Caudate(anteroventral): choreoathetosis
• Caudate and putamen degeneration: Huntington disease
• Bilateral pallidal lesions: akinesia
• Substantia nigra: parkinsonism
• Unilateral basal ganglia(pallidal-putaminal)
• Falling to contralateral side, slow tilting movements
• Substantia nigra pars compacta degeneration: Parkinson’s disease
Questions
• 1. True or false: Globus pallidus externa is part of the direct pathway.
• 2. Which of these sensor modalities bypass the thalamus: Gustatory,
auditory, visual, nociception, olfactory.