November 14, 2014

BASAL GANGLIA & CEREBELLUMTwo CNS areas that regulate skeletal motor activity, not by influencing lower motor neurons directly but, rather, by regulating activity of upper motor neurons.

Voluntary MovementCortex and brainstem contain motor centers that control voluntary movement, viaDescending pathwaysMotor neuronsSkeletal muscles

Cortex fine voluntary movementsBrainstem maintenance of posture, orienting movements, stereotypical movementschewing, swallowing, locomotion

Movement ModifiersBasal ganglia -- choose WHICH movements occur; can only do one, or a few, things at a timeCerebellum ensures that movements we make are those we intend to make; learns from past motor experiences to ensure accurate movement execution

Basal GangliaEach action below easy enough by itselfWalk and chew gumPat head and rub stomach need to practicePat head, rub stomach, wiggle left foot back and forth, count up by sevens probably notThe brain chooses to perform only one, or very few, (related) actions at a time, while simultaneously suppressing others

ReceptorsMuscle actionCerebral CortexUMNsUMNsUMNsDCML / ALS

Do NOT contact lower motor neurons.

Regulate activity of UMNs.

Involved in loop-like circuitrythrough the dorsal thalamus andmotor areas of the cerebral cortex.

Input from all cortical areas exceptprimary visual and primary auditoryareas.

Output to motor areas of cortex.

Does NOT contact lower motor neurons.

Regulates activity of UMNs.

Involved in loop-like circuitry throughdorsal thalamus and motor areas of the cerebral cortex.

Input from primarily motor areas ofcortex.

Input ALSO from vestibular apparatus and unconscious proprioception from spinal cord Output directed to motor areas of cortex, the tectum, the red nucleus, the vestibular nuclei, and the reticular formation all sources of descending pathways that regulate motor neurons in the spinal cord.COMPARISONS

Basal Ganglia Cerebellum

What are the basal ganglia?Where are the basal ganglia?Not ganglia, actually; they are nuclei. Most are located in the telencephalon.

TELENCEPHALON

Cortex White matter Nuclei

DIENCEPHALON (dorsal thalamus- also nuclei)INTERNAL CAPSULE

DIENCEPHALON (dorsal thalamus)INTERNAL CAPSULELentiform nucleus part of BG

INTERNAL CAPSULELentiform nucleus part of BGDIENCEPHALON (dorsal thalamus)Caudate shaped like a tail; is curved, therefore can be cut twiceCaudate nucleus part of BG

Lateral ventricleA c-shaped structure LATERAL VENTRICLE inLEFT HEMISPHERE

Caudate Nucleusa c-shaped structure CAUDATE NUCLEUS one of the basal ganglia

in left hemisphere

Lateral Ventricle c-shaped structure LATERAL VENTRICLE CAUDATE NUCLEUS

LEFT HEMISPHERECaudate Nucleusa c-shaped structure

Lateral VentricleCoronal section through brainPlane of section INT CAPSULECaudate NucleusLentiform Nucleus

Coronal section through brainPlane of section INT CAPSULEDIENCEPHALON (dorsal thalamus)Lateral VentricleCaudate NucleusLentiform Nucleus

LateralVentricle

Lateral ventricleCoronal section through forebrainPlane of section Caudate Nucleusa c-shaped structureINT CAPSULEDIENCEPHALON (dorsal thalamus)Temporal lobeLateral Ventricle

Lateralventricle

Caudate nucleusCaudate nucleus

Lateral ventricleCoronal section through forebrainPlane of section Caudate Nucleusa c-shaped structureINT CAPSULEDIENCEPHALON (dorsal thalamus)Temporal lobeLateral Ventricle

Lateral VentricleLateralventricleLateral ventricleCoronal section through brainthalamusLENTIFORM NUCLEUSTemporal lobeINT CAPSULECaudate Nucleusa c-shaped structureCaudate nucleusCaudate nucleus

thalamusCaudate nucleus = C = shaped like a tailCC Lentiform = shaped like a lensTemporal lobeINT CAPSULELentiformnucleus

thalamus Caudate nucleus = CCCLentiform nucleus =PUTAMEN = L. = a husk, a shell

GLOBUS PALLIDUS = L. pale globePUTAMENGLOBUS PALLIDUS+INT CAPSULE

thalamusCaudate nucleus = CCCLentiform nucleus =

PUTAMEN

GLOBUS PALLIDUS Striatum =CAUDATE+PUTAMEN

explanation- STRIATUM: Cell bridges between CAUDATE and PUTAMEN across anterior limb of internal capsule = striated appearance, hence, CORPUS STRIATUM.lateral ventricle

CAUDATE NUCLEUS

anterior limb, internal capsule

PUTAMEN

Anterior, middle cerebral arteries

Optic chiasm

thalamusCaudate nucleus = CCC Striatum =

PUTAMEN + CAUDATE

thalamusCaudate nucleus = CCC Striatum =

PUTAMEN + CAUDATEEXTINT GLOBUS PALLIDUS

EXTERNAL SEGMENT (EXT) & INTERNAL SEGMENT (INT)

The lateral ventricle and theCAUDATE and LENTIFORM NUCLEIof the left cerebral hemisphere.Of course, the globus pallidus cannot be seen,because it lies medial to the putamen.) Lentiform nucleusLateral Medial< -- > LateralLateral VentricleCaudate NucleusPutamen

BASAL GANGLIA in telencephalonCAUDATE NUCLEUSPUTAMENGLOBUS PALLIDUSLENTIFORM NUCLEUSSTRIATUM

BASAL GANGLIA CAUDATE

PUTAMEN

GLOBUS PALLIDUS

Below are critical accessories

SUBSTANTIA NIGRA

SUBTHALAMIC NUCLEUS

What are the basal ganglia?Where are the basal ganglia?Not ganglia, actually; they are nuclei. Most are located in the telencephalon.TWO more structures: Substantia nigra is in the midbrain and the subthalamic nucleus is in the diencephalon specifically, in the ventral thalamus.

TELENCEPHALON

DIENCEPHALON (dorsal thalamus)INTERNAL CAPSULE

TELENCEPHALON

DIENCEPHALON (dorsal thalamus)MIDBRAININTERNAL CAPSULE

TELENCEPHALON

DIENCEPHALON (dorsal thalamus)MIDBRAININTERNAL CAPSULEPONS

TELENCEPHALON

DIENCEPHALON (dorsal thalamus)MIDBRAININTERNAL CAPSULE Subthalamic nucleusSubstantia nigra

INTERNAL CAPSULE Subthalamic nucleusSubstantia nigraCEREBRAL PEDUNCLE??

INTERNAL CAPSULE Subthalamic nucleusSubstantia nigraCEREBRAL PEDUNCLERed nucleus

INTERNAL CAPSULE Subthalamic nucleusSubstantia nigraCEREBRAL PEDUNCLEMIDBRAINTectum

Red nucleus

Substantia nigraRed nucleus

INTERNAL CAPSULE Subthalamic nucleusSubstantia nigraCEREBRAL PEDUNCLE Caudate nucleusPutamenGlobuspallidus Caudate nucleus ALL OF THEBASAL GANGLIA

CAUDATE

PUTAMEN

GLOBUS PALLIDUS

SUBSTANTIA NIGRA

SUBTHALAMIC NUCLEUS

What are the basal ganglia?Where are the basal ganglia?Not ganglia, actually; they are nuclei. Most are located in the telencephalon.In addition, substantia nigra is in the midbrain and the subthalamic nucleus is in the diencephalon specifically, in the ventral thalamus.Provide supervisory control over CORTICAL upper motor neurons (think corticospinal and corticonuclear tracts)

PURVES et al., Neuroscience

INPUTS TO BASAL GANGLIA are received by STRIATUM

Widespread cortical areas (except auditory and visual)

via corticostriate pathways, travel through internal capsule

Substantia nigra, pars compacta, sends dopamine

Inputs to striatum (from all sources) terminatedirectly on dendrites of medium spiny neurons;this neuron makes up 90% of the striatum.

Substantia nigra, pars compacta, sends dopamine

GP neuron

All medium spiny neurons employ the inhibitory neurotransmitter GABA on their targets, neuronsin the globus pallidus.

GP neuron

Neurons in the globus pallidus (here, GP internal) alsoemploy GABA and project to a nucleus (nuclei) in the dorsal thalamusnucleus ventralis anterior and nucleus ventralis lateralis (NVA/NVL).GP neuron

GP neuronNVA/NVL projects back to the cerebral cortex.Neurons in the globus pallidus (here, GP internal) alsoemploy GABA and project to a nucleus (nuclei) in the dorsal thalamusnucleus ventralis anterior and nucleus ventralis lateralis (NVA/NVL).

Subthalamic nucleusSubstantia nigra Caudate nucleusPutamenGlobuspallidus Caudate nucleus+++--+pars compacta

Basal ganglia: interconnectionsModel of basal ganglia function Attempts to explain normal and abnormal function derived from anatomic and physiologic observationsIs (!) oversimplified2 major divisionsDIRECT PATHWAYINDIRECT PATHWAY

Basal ganglia: interconnectionsDIRECT PATHWAY:Striatal output to GPi directly, from which output is to thalamus, and then to motor cortex.Activity in this pathway excites UMNs in cerebral cortex

++--

RELEASES tonic inhibition (by Gpi) of thethalamic neurons that drive the motorcortex. NET = facilitation initiation ofwilled movements.

Basal ganglia: interconnectionsIndirect pathway:Striatal output to GPe, then STN, then to GPi and through the rest of the loopActivity in this pathway excites fewer UMNs in cerebral cortexProbably fewer striatal projection neurons involved in this pathway

++---+-INDIRECT PATHWAYDopamine!

Subthalamic nucleusSubstantia nigra Caudate nucleusPutamenGlobuspallidus Caudate nucleus++---+Dopamine!pars compacta

Basal ganglia: interconnectionsGlutamate neurons (excitatory)Cerebral cortexVA/VL thalamusSTN (subthalamic nucleus)

GABA neurons (inhibitory)Striatal medium spiny neuronsGPe (globus pallidus externa)GPi (globus pallidus interna)Dopaminergic neuronsSNc (substantia nigra pars compacta)++--

Basal ganglia: interconnectionsParallel pathways concept.Topographic organization of projections in each of these segments (striatum, pallidum, STN, SNr, VA/VL).For motor control, this means that signals related to a particular limb or body region may travel together.This applies to nonmotor circuits as well Our understanding of the (motor and nonmotor) function of the basal ganglia is incomplete.System appears to be involved in motor planning.Electrophysiologic recording from striatum demonstrates firing just before an impending movement.

The INDIRECT Pathway Cortex

Striatum Thalamus Gpe

Subthalamic GPi nucleus Net result of = .RELEASES tonic inhibition of thethalamic neurons (by GPi) that drive themotor cortex. NET = facilitation initiation ofwilled movements.INCREASES tonic inhibition of thethalamic neurons (by GPi) that drive themotor cortex. NET = counter-act direct Pathway B U T T T---dopamine inhibits theStriatal neurons in this pathway. This is a good thingDopamine excites the striatal neurons in this pathway.

The INDIRECT Pathway Cortex

Striatum Thalamus Gpe

Subthalamic GPi nucleus Net result of = .RELEASES tonic inhibition of thethalamic neurons (by GPi) that drive themotor cortex. NET = facilitation initiation ofwilled movements.Dopamine excites the striatal neurons in this pathway.

INCREASES tonic inhibition of thethalamic neurons (by GPi) that drive themotor cortex. NET = counter-act direct pathway There are probably fewerstriatal neurons involved in this pathway. Dopamine inhibits the striatal neurons in this pathway.

DOPAMINE facilitates normal motor activity:

DOPAMINE facilitates transmission of signals through the direct path, and, therefore, excitation of the motor and premotor cortices by the NVA & NVL. Dopamine is excitatory at D1 receptors of neurons in the striatum; neurons expressing D1 receptors are the ones that project to Gpi DIRECT PATHWAY

At the same time, DOPAMINE reduces transmission of signals through the indirect path; net result is still excitation of motor and premotor cortices by NVA and NVL Dopamine is inhibitory at D2 receptors; striatal neurons expressing D2 receptors are the ones that project to Gpe INDIRECT PATHWAY

Normal movement appears to be a result of a balance of activity between the direct and indirect pathways.

The tonic effect that GPi has on the NVA, NVL nuclei of the dorsal thalamus is an inhibitory one, ultimately keeping areas 4 and 6 in check.

Activity in the direct pathway releases the brake that GPi applies to NVA/NVL; the direct pathway may be activated when a specific motor programis to be executed.

Activity in the indrect pathway increases the braking effect;the indirect pathway may be activated to prevent execution of competing or interfering motor programs.

Basal ganglia: interconnectionsRecap Input to striatumOutput mainly to VA/VL thalamusInternally, complex mix of direct and indirect pathways whose functions are thought to modulate each other.DOPAMINE !

Do not contact lower motor neurons.

Involved in loop-like circuitrythrough the dorsal thalamus andmotor areas of the cerebral cortex.

Input from all cortical areas exceptprimary visual and primary auditoryareas.

Output to motor areas of cortex--corticospinal and corticobulbar tracts. and to superior colliculus, for UMNs to cranial nerve nuclei that innervate extraocular muscles *

*Not same part of tectum that gives rise to TECTOSPINAL TRACT

The Basal Ganglia

BASAL GANGLIA concerned with selection and initiation of willed movementsand timing (starting, stopping) and velocity of movements.

Basal ganglia dysfunction = Difficulty in initiating movement, in continuing or stopping ongoing movement, abnormalities of muscle tone (rigidity), developmentof involuntary tremors.

Motor control difficulties are among the key signs of basal ganglia disease,ranging from the tremor and rigidity of Parkinsons Disease to the Involuntary writhing movements of Huntingtons disease or the bizarre tics of Tourette syndrome.

It appears that the basal ganglia are also involved in circuitry with the cerebral cortex that has to do with other than strictly motor functions. Discoveries are being made that suggest that parts of the basal ganglia are involved in certain aspects of memory and cognitive function. Basal ganglia disease can also impair cognitive function dementia and emotional function.

The basal ganglia and related circuitry are actually very complex and a poorly understood part of the brain.

The Central Nervous System Structure & Function, 3rd ed Per BrodalC5T1distalC5

T1

proximalORGANIZATION OFVENTRAL HORN NEURONS

The Central Nervous System Structure & Function, 3rd ed Per BrodalC5T1distalC5

T1

proximalORGANIZATION OFVENTRAL HORN NEURONSFLEXORSEXTENSORS

ABCDEFGG

ABCDEFGGSPINOCEREBELLAR TRACTS unconscious proprioception

ABCDEFGGSPINOCEREBELLAR TRACTS unconscious proprioception Lamina VIII = pools of interneurons that servemotor neurons in lamina IX

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