Basal Ganglia 14

7/28/2019 Basal Ganglia 14

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The Basal Ganglia


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I. Functional anatomy

A. Input and output components

cerebral cortex BG thalamus (VA) frontal lobe.

B. Parallel circuits

C. Neurotransmitters

D. Intrinsic circuitry of the basal ganglia and movement

without.

II. Regional anatomy

A. Internal capsule and striatumB. Series of coronal sections revealing anatomy and

relationships of the nuclei.

C. Midbrain sections showing substantia nigra.


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I. Functional anatomy

Introduction: Basal ganglia are subcortical

structures that are part of cerebralhemispheres. They receive input from and

send regulatory signals back to the cortex

(frontal lobes).Regulation of movement, cognitive,

motivation, and emotion.


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A. Input and Output Components of the Basal Ganglia

VL

Know this figure!!


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The Striatum shown in relation to ventricles

Note that caudate n. and putamen are connected by cell bridges

(spanning internal capsule)


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B. Parallel circuitsanatomical loops

subserve the various functions.

Input-output nuclei specifically assigned to

these jobs are outlined and specific frontal

cortical projection areas are illustrated in

Fig. 14-3.


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Parallel circuits Fig. 14-3

Skeletomotor loop:

Control of skel muscle

Oculomotor loop:

Control of extraocular muscles

Association loop:

Role in cognition

Limbic loop:

Maturation/emotions


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Fig. 14-3 - Loops


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C. BG Neurotransmittersused in the various BG

circuits and outlined (Fig. 14-4)

Glu/Asp: excitatory

GABA: inhibitory (major neurotransmitter of the BG)Important neuromodulators:

dopamine (from SN pc to striatum)

acetylcholine (connect within striatum)

enkephalin, substance P (out of striatum direct + indirect pathways


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D. Intrinsic circuitry of the basal gangliaandmovement disorders.

Refer to Box 14-1.

Direct and indirect striatal output pathways:

direct excitatory to thalamus (VA)

indirect inhibitory to thalamic target neurons.

Direct path: what happens when you inhibit an

inhibitory signal (disinhibition = doublenegative)?

Indirect path: opposite effect on thalamus (-) (and

ultimately, cerebral cortex.


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Double negative (disinhibition) excites the

output of the STN, which will drive

inhibitory output from Gpi

SNr Thalamus

{Internal segment of globus pallidus and SN pc}Therefore, the inhibition is increased inhibitory output.

This model helps us understand the mechanism of

hypokinetic disorders (e.g.,Parkinsons Disease) and

hyperkinetic disorders (e.g., Huntingtons Disease andhemiballism).


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Parkinsons Disease: decreased dopamine fromSN decreased inhibition of the inhibition

excessive inhibitory output classic signs of PD(hypokinesia, bradykinesia)via decreased

thalamic signals to cortex decreased

corticospinal outflow.

Huntingtons Disease: decreased striatal(enkephalin) output and decreased inhibition of

Gpo enhanced excitatory effects of indirect path

decreased inhibition via direct path

hyperkinesis.

Hemiballism: similar mechanism (subthalamic n.lesion).


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Parkinsons: increased indirect


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Most modern therapies for PD have

involved lesions without the circuit in an

effect to re-established the balance (e.g.,STN lesion)


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Hyperkinesis: increased direct


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II. Regional Anatomy

A. Internal capsule and striatumrecall how the

striatum is divided into caudate n. and putamen

by the anterior limb of the internal capsule and

that cellular bridges (visible in horizontal

section) exist between these (Fig. 14-6).

Note also that internal and external segments of

globus pallidus, posterior limb, and the thalamic

nuclei below (Fig. 14-8).

B. Series of coronal sections revealing anatomy ofthe nuclei and their spatial relationships.


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Horizontal Section Through Basal Ganglia (Fig. 14-6)


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Anterior section (Fig. 14-8)

Note: head of caudate, nucleus accumbens, and

cell bridges are prominent here.

The head of caudate is often used as a radioligand landmarknormally

buldges into anterior horn of lateral ventricles.


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Head of caudate = radiological landmark (Fig. 14-10)


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Fig. 14-11

The globus pallidus and ventral pallidum are beneath the anterior

commissure.


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Subthalamic nucleus (Fig. 14-14)


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Mid-section


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Midbrain through the substantia nigra (Fig. 14-16).


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Basal Ganglia 14

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