Table Of Contents
Connections
- Physiological division Basa Ganglia-
- Corpus Striatum
- Anatomically–
- Caudate nucleus
- Lenticular nucleus-
- Outer Putamen
- Inner Globus Pallidus.
- Phylogenetically/Functionally-
- Neostriatum/Striatum-
- Caudate Nucleus
- Outer Putamen
- Paleostriatum/Pallidum/Globus Pallidus-
- Dorsal pallidum
- Ventral pallidum
- Neostriatum/Striatum-
- Anatomically–
- Subthalamic Nucleus/Body of Luys
- Substantia Nigra
- Corpus Striatum
- Connections of Basal ganglia are of 3 types-
- Afferents/Inputs to Striatum
- Projections from Striatum
- Efferent/Output from Globus Pallidus
- Afferents/Inputs to striatum-
- Basal ganglia does not receive direct sensory input from the peripheral structures, spinal cord or sensory nucleus in brain stem.
- Most afferent information enters basal ganglia through Neostriatum
- Corticostriate projections-
- Glutamatergic fibers
- Originate from all parts of cerebral cortex
- Terminate in striatum
- Putamen receives mainly from sensory motor cortex
- Caudate nucleus receives from remainder of cortex
- Thalamostriate Projection-
- Originate from centromedian nucleus of thalamus
- Terminate in striatum
- Raphe striate projections-
- Serotoninergic fibres
- From dorsal raphe nucleus in the reticular formation of brain stem.
- Terminate in striatum
- Pedunculostriate projections-
- From Pedunculopontine nucleus of brain stem
- Projects to basal ganglia
- Locus coeruleus striate fibres-
- Noradrenergic fibres
- From locus coeruleus
- Terminate in striatum
- Projections from Striatum-
- Robust GABAergic inhibitory projections to both segments of Globus Pallidus
- GABAergic inhibitory impulses to pars reticulata of substantia nigra.
- Efferents/Output from Globus Pallidus-
- Principal output nucleus is Internal Segment of Globus Pallidus
- Efferents to thalamus-
- Called thalamic fasciculus or Ansa fascicularis
- Inhibitory and originate from Internal segment of Globus pallidus (GP1)
- Terminate in Ventrolateral, Ventroanterior and centromedian nuclei of thalamus.
- From thalamus fibres project on to prefrontal and premotor cortex as excitatory outputs.
- Efferents/Output to Substantia Nigra-
- Directly to SN
- First to subthalamic nigra then to SN
- Via pedunculopontine nucleus
- Substantia Nigra further projects to-
- Substantia nigra brain stem reticular formation-reticulo-spinal tract pathway.
- Substantia nigra superior colliculus-tectospinal tract pathway.
- Substantia nigra-habenula.
- Efferents to red nucleus. This pathway includes fibres from globus pallidus-red nucleus-rubrospinal tract pathway
- This completes the motor loop:- cerebral cortex -> Striatum -> Internal Segment of Globus Pallidus -> Thalamus -> Cerebral Cortex.
Functions
- Control of Voluntary Motor Activities-
- Cognitive control of motor activity-
- Planning and programming of movement
- Caudate loop is primarily involved
- Neural discharge in basal ganglia occurs before the movement begins
- Timing and scaling of intensity of movements-
- Timing- how rapidly the movement should be performed
- Scaling- how large the movement should be
- Important coordinating center of extrapyramidal system
- Subconscious execution of trained motor activities-
- Swinging of arms while walking
- Crude movement of facial expression accompanying expression
- Movements of limb while swimming
- Control of clutch and brake while driving
- This relieves cortex from routine acts so that it can focus on planning of actions
- Pathway is by Putamen feedback circuit
- Cognitive control of motor activity-
- Control of Reflex Muscular Activity-
- Inhibitory effect on spinal reflex
- Regulation of activity of posture maintaining muscles
- Coordination and integration of visual and labyrinthine reflexes important for maintaining posture
- Control of Muscle tone-
- Substantia nigra of BG controls the muscle spindle and gamma motor neurons which are responsible for maintaining tone of muscle.
- Basal ganglia decrease the muscle tone by inhibiting gamma motor neurons through descending inhibitory reticular system in brainstem.
- Pathway: Projection from cortical inhibitory area-striatum-pallidum-substantia nigra-reticular formation-spinal cord
- Proof- lead pipe rigidity in Parkinson’s due to lesion of basal ganglia
- Role in arousal mechanism-
- Through Globus pallidus and red nucleus because of their association with reticular formation.
- Lesion of GP – Drowsiness leading to sleep.
- Release of neurotransmitters-
- Inhibitory-
- Dopamine- Fibres from substantia nigra to corpus striatum
- GABA – Intrinsic fibres of corpus striatum and substantia nigra
- Excitatory-
- Ach- Fibers from cerebral cortex to caudate nucleus and putamen
- Substance P- Fibers from globus pallidus reaching substantia nigra
- Enkephalins- Fibers from globus pallidus reaching substantia nigra
- Noradrenaline- Fibers between basal ganglia and reticular formation
- Glutamic acid- Fibers from subthalamic nucleus to globus pallidus and substantia nigra
- Inhibitory-