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Motor cortex - Inputs, Outputs and functions in briefPresentation Transcript
Thalamic connections of the primary motor cortex (M1) of owl monkeysIwona Stepniewska, Todd M. Preuss, Jon H. Kaas Ph.D.*• Fluorescent tracers and wheatgerm agglutinin/horseradish peroxidase conjugate (WGA-HRP).• The strongest connections of M1 are with subdivisions of the ventral lateral thalamus (VL);other connections are mainly with intralaminar nuclei (the central lateral, paracentral, and centermedian nuclei) and the reticular nucleus.• Most projections are reciprocal and topographically organized. M1 is strongly connected withthe principal (VLp), medial (VLx), and anterior (VLa) subdivisions of the VL complex but has atmost weak connections with the dorsal division (VLd).•The connections are somatotopically organized such that the M1 hindlimb representation isconnected with a band of cells in the lateral and anterior portions of the VL complex (spanningVLa and VLp), whereas the trunk, forelimb, and face representations are connected withsuccessively more medially and posteriorly situated cell bands (spanning VLa, VLp, and VLx).RostralCaudalVL thalamusMedialLateral
• There is some degree of overlap between the somatotopic territories within VL,although the absence of double-labeled cells in cases with injections of adjacentsomatotopic divisions of M1 suggests that individual thalamic neurons project tosingle somatotopic regions.• In addition to somatotopic differences, the connections of the caudal and rostralsubdivisions of M1 differ to some extent. Caudal M1 is connected most strongly withVLp, a target of cerebellar projections, but it is also connected with VLa, whichreceives pallidal inputs.• In complementary fashion, rostral M1 is most strongly connected with VLa, but it isalso connected with VLp. VLx, a target of cerebellar projections, has significantconnections with both caudal and rostral M1.Thalamic connections of the primary motor cortex (M1) of owl monkeysIwona Stepniewska, Todd M. Preuss, Jon H. Kaas Ph.D.*
http://www.neuroanatomy.wisc.edu/coursebook/thalamus.pdfALS – Anterolateral system (Painfrom periphery)TTT – Trigeminal thalamocorticaltract (Pain from face, neck etc)STT – Spino-thalamic tract (type ofALS)
Nigrostriatal pathway• DOPAMINE is produced by cells in the pars compacta of the substantia nigra(SNc).• Dopamine has an EXCITATORY effect upon cells in the striatum that are part ofthe Direct Pathway. This is via D1receptors.• Dopamine has an INHIBITORY effect upon striatal cells associated with theIndirect Pathway. This is via D2 receptors.•In other words, the direct pathway (which turns up motor activity) is excited bydopamine while the indirect pathway (which turns down motor activity) isinhibited.•Both of these effects lead to increased motor activity.
Chollinergic interneurons -striatum• There is a population of cholinergic(ACh) neurons in the striatum whoseaxons do not leave the striatum (called interneurons or local circuit neurons).• These cholinergic interneurons synapse on the GABAergic striatal neuronsthat project to GP(internal) AND on the striatal neurons that project toGP(external).• The cholinergic actions INHIBIT striatal cells of the Direct pathway andEXCITE striatal cells of the Indirect pathway.• Thus the effects of ACh are OPPOSITE the effects of dopamine on the directand indirect pathways so the ACh effects on motor activity are opposite thoseof dopamine.
SMASMA proper:Inputs - basal ganglia via the VA thalamus,from the parietal andpremotor cortices, and from thecontralateral SMAOutputs - premotor cortex, bilaterally to themotor cortex, and to the basal ganglia, tothalamic nuclei and the brain stem andspinal cord.Pre-SMA:Inputs - from the basal ganglia and non-motorareas of the cortex (prefrontal andtemporal)Outputs – dorsolateral prefrontal cortex andbasal ganglia
SMA – proposed functions:Four main hypotheses have been proposed for the function of SMA:• the control of postural stability during stance or walking,• coordinating temporal sequences of actions,• bimanual coordination and• the initiation of internally generated as opposed to stimulus drivenmovement.• The data, however, tend not to support an exclusive role of SMA in any one ofthese functions. Indeed, SMA is demonstrably active during non-sequential,unimanual, and stimulus-cued movements.http://en.wikipedia.org/wiki/Supplementary_motor_area
Extra Reading:PMDc (F2)PMDc is often studied with respect to its role in guiding reaching. Neurons in PMDc are active during reaching.When monkeys are trained to reach from a central location to a set of target locations, neurons in PMDc are activeduring the preparation for the reach and also during the reach itself. They are broadly tuned, responding best toone direction of reach and less well to different directions. Electrical stimulation of the PMDc on a behavioral timescale was reported to evoke a complex movement of the shoulder, arm, and hand that resembles reaching withthe hand opened in preparation to grasp.PMDr(F7)PMDr may participate in learning to associate arbitrary sensory stimuli with specific movements or learningarbitrary response rules. In this sense it may resemble the prefrontal cortex more than other motor cortex fields. Itmay also have some relation to eye movement. Electrical stimulation in the PMDr can evoke eye movements andneuronal activity in the PMDr can be modulated by eye movement.PMVc(F4)PMVc or F4 is often studied with respect to its role in the sensory guidance of movement. Neurons here areresponsive to tactile stimuli, visual stimuli, and auditory stimuli. These neurons are especially sensitive to objectsin the space immediately surrounding the body, in so-called peripersonal space. Electrical stimulation of theseneurons causes an apparent defensive movement as if protecting the body surface. This premotor region may bepart of a larger circuit for maintaining a margin of safety around the body and guiding movement with respect tonearby objects.PMVr(F5)PMVr or F5 is often studied with respect to its role in shaping the hand during grasping and in interactionsbetween the hand and the mouth. Electrical stimulation of at least some parts of F5, when the stimulation isapplied on a behavioral time scale, evokes a complex movement in which the hand moves to the mouth, closes ina grip, orients such that the grip faces the mouth, the neck turns to align the mouth to the hand, and the mouthopens.
CerebellumMedial Cerebellum – Vestibular andpropriospinal inputs-> Mainly controls postureLateral Cerebellum – inputs fromcerebral cortex via basilar pontine nucleithrough mossy fibers.Mossy fibers from red nucleusAlso climbing fibers from inferior olivecomplex