Ganong's Review of Medical Physiology, 23rd Edition

Amygdaloid
nucleus
Caudate nucleus
Globus
pallidus
Caudate nucleus
Lateral view
Putamen
Thalamus
Putamen and
globus pallidus
Horizontal section
Thalamus
Tail of
caudate nucleus
The main feature of the connections of the basal ganglia is
that the cerebral cortex projects to the striatum, the striatum
to GPi, GPi to the thalamus, and the thalamus back to the cortex,
completing a loop. The output from GPi to the thalamus
is inhibitory, whereas the output from the thalamus to the
cerebral cortex is excitatory.
CHAPTER 16 Control of Posture & Movement 251
Substantia
nigra
Amygdala
FIGURE 16–9 The basal ganglia. The basal ganglia are composed of the caudate nucleus, putamen, and globus pallidus and the functionally
related subthalamic nucleus and substantia nigra. The frontal (coronal) section shows the location of the basal ganglia in relation to surrounding
structures.
Globus
pallidus, ES
GABA
Glu
Subthalamic
nucleus
Brain stem
and
spinal cord
Glu
GABA
Internal capsule
GABA
Cerebral
cortex
Glu
Striatum
(acetylcholine)
Globus
pallidus, IS
GABA
GABA GABA GABA
PPN
Thalamus
Thalamus
Internal
capsule
FIGURE 16–10 Diagrammatic representation of the principal
connections of the basal ganglia. Solid lines indicate excitatory pathways,
dashed lines inhibitory pathways. The transmitters are indicated
in the pathways, where they are known. Glu, glutamate; DA, dopamine.
Acetylcholine is the transmitter produced by interneurons in the striatum.
SNPR, substantia nigra, pars reticulata; SNPC, substantia nigra, pars
compacta; ES, external segment; IS, internal segment; PPN, pedunculopontine
nuclei. The subthalamic nucleus also projects to the pars compacta
of the substantia nigra; this pathway has been omitted for clarity.
DA
SNPR SNPC
Frontal section
The striatum is made up of two parts that differ histologically:
a unique mosaic of patches or striosomes (an area with
little acetylcholinesterase) and a matrix (an area high in acetylcholinesterase).
The neurons of the corticostriate projection
that originate in the deep portion of layer V of the cortex
terminate in the patches, whereas the neurons that originate
in layers II and III and the superficial part of layer V end primarily
in the matrix. Neurons with their cell bodies in patches
project in large part to dopaminergic neurons in the substantia
nigra pars compacta, whereas many of the neurons with
their cell bodies in the matrix project to GABAergic neurons
in the substantia nigra pars reticulata.
FUNCTION
Lateral ventricle
Caudate nucleus
Putamen
Globus pallidus:
External segment
Internal segment
Subthalamic
nucleus
Neurons in the basal ganglia, like those in the lateral portions
of the cerebellar hemispheres, discharge before movements
begin. This observation, plus careful analysis of the effects of
diseases of the basal ganglion in humans and the effects of
drugs that destroy dopaminergic neurons in animals, have led
to the idea that the basal ganglia are involved in the planning
and programming of movement or, more broadly, in the processes
by which an abstract thought is converted into voluntary
action (Figure 16–1). They influence the motor cortex via
the thalamus, and the corticospinal pathways provide the final
common pathway to motor neurons. In addition, GPi projects
to nuclei in the brain stem, and from there to motor neurons
in the brain stem and spinal cord. The basal ganglia, particularly