THALAMUS AND BASAL GANGLIA
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THALAMUS AND BASAL
GANGLIA
THALAMUS
A group of nuclei in the wall of 3rd ventricle
Largest structure in the diencephalon
Bounderies
-medial: third ventricle
-lateral: posterior limb of internal capsule
-dorsolateral: terminal sulcus
-inferior: hypothalamic sulcus
Cont’d
Internal medullary lamina divides thalamus
into ant., medial and lateral areas
-ant. area: anterior nuclear group
-medial area: dorsomedial and medline nuclei
-lateral nuclei: dorsal and ventral tier
Cont’d
Ventral tier
Dorsal tier
-vent. Anterior
-dorsolateral
-vent. Lateral
-lateral posterior
-vent. Posterior
-pulvinar
Others:
-intralaminar nuclei
-reticular nuclei
Four regions from diagnostic
standpoint
1.The midline, intralaminar, reticular nuclei
-nonspecific thalamic nuclei
-mediate general cortical alerting responses
-projections from midbrain RF, fibers from
spinothalamic tract
-project to midbrain and specific thalamic nuc
-bilateral lesions cause impairment of
conciousness
Cont’d
2.The medial﴾ dorsomedial ﴿ and ant. thalamic n.
-important role in memory and emotions
-connected with hyypoth. and the “limbic lobe”
-lesions associated with memory and executive
function loss
3.The dorsolateral and post. nuclear groups
-modulates occipito-temporo-parietal cortical
attention
-facilitates visual attention and the cortical attention needed for language
related sensory tasks in the L. hemisphere and visuospatial tasks in the R..
cont’d
4.ventral lateral and basal nuclear groups
-for processing and relay to the cortex of
sensory information and sensorimotor control
-ventral posterior nuclear group
-medial geniculate body
-lateral geniculate body
VASCULAR SUPPLY
From posterior cerebral and post.
Communicating arteries
Polar arteries
Paramedian thalamomesencephalic arteries
Thalamogeniculate pedicle
Posteromedial choroidal arteries
Posterolateral choroidal arteries
LOCALISATION OF ISCHEMIC
THALAMIC LESIONS
Paramedian territory
-due to embolic occlusion of top of basilar a. Or
local atheroma
-clinical triad of somnolent apathy , memory loss and
abnormalities of vertical gaze
Thalamogeniculate territory
-ischemia around VP,VL nuc., subthalamic n.
-hemianesthesia, transient slight hemiparesis
,hemiataxia, choreoathetoid mov’ts, paroxyxmal
pain,homonymous hemianpopia
Cont’d
Tuberothalamic territory
-due to thalamopolar a. lesions
results in neuropsychological dysfunction
Posterior choroidal a. territory
-homonymous quadrantanopsia
-hemisensory loss with mild hemiparesis
-transcortical aphasia
Thalamic hemorrhages
One of the common sites of hypertensive h’ge
Prominent sensory deficits
Contralat. Hemiplegia or hemiparesis
Aphasia after h’ge into dominant thalamus
Homonymous visual field defects
Ocular dysfunction
Dejerine-Roussy syndrome
Prognosis depends on amount and site of bleeding
-ant. and dorsal types: usually benign
-posteromed. and posterolat. types: poor prognosis
BASAL GANGLIA
COMPONENTS
No generally accepted defination
Considered to include
1.corpus striatum﴾ neostriatum﴿
-putamen and caudate nucleus
2.claustrum
3.substantia nigra: pars compacta and pars reticularis
4.globus pallides
5. subthalamic nucleus
Cont’d
Play a major role in the control of posture and
movement
Straitum- receptive component
Globus pallidus – its internal seg’t, output str.
Subthalamic – input from cer. cortex and reciprocal
connection with G.P
Substantia nigra- pars compacta: contain dopamine
-pars reticulata :continuation of
internal segment of globus pallidus
connections
Striatum receives three main inputs
-excitatory input from cerebral cortex
-excitatory input from intralaminar thalamic
nuclei
-modulatory input from substantia nigra PC.
Striatal efferents
-inhibitory GABAergic cells that project to
the G.p and substantia nigra
Cont’d
Internal segment of G.P
-project to three main targets
-to thalamus
-tosuperior colliculus
-pedenculopontine nuclei of reticular form
Output of B.G affects both corticospinal and
brainstem motor pathways
Lesions of B.G
Subthalamic nuc.- contralat. Hemiballismuss
Caudate nucleus- contralat. Choreoathetosis
Globus pallidus-unilat.: contralat.hemidystonia ,hemiparkin.
or tremor
-bilat.:dystonia ,parkisonism abulia, akinesia
Substantia nigra -parkinsonism
Cont’d
Two main types of disorders of B.G
·hyperkinetic﴾ dyskinetic ﴿ disorders
-when dopaminergic mechs.exagerated
·hypokinetic ﴾akinetic ﴿disorders
-when dopaminergic mechs. impaired
Dyskinesias
Chorea
Tardive and orofacial dyskinesias
Ballismus
Athetosis, dystonia, torticollis
Myoclonus
Tics
tremor
Hypokinetic disorders
Parkinsonism
Corticobasal degeneration
Progressive supranuclear palsy
Multiple systems atrophy