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Curtin University
School of Physiotherapy

Cortical Connections

Neuroanatomical studies of connections of the motor cortex

The motor cortex projects to the motor neurons of the spinal cord through the corticospinal tract. It receives synaptic inputs from other areas of the cortex and from subcortical loops involving the basal ganglia and cerebellum. The connections from somato-sensory to motor cortex provides sensory feedback from receptors in muscle and skin. Connections of the motor and somato-sensory cortex are studied by the use of neurotracers which are taken up (by endocytosis) by neurons and axon terminals and transported (anterogradely or retrogradely) along the axon.

Figure 1 Figure 1

Horseradish peroxidase is a commonly used neurotracer and the figure 1 shows a small injection of this tracer in the motor cortex (upper panel) and labeled thalamic neurons (lower panel).

Figure 2 Figure 2
Figure 3 Figure 3

Biocytin linked to Dextran (Biotinylated Dextran Amine) is a useful anterograde tracer which labels axons and synaptic terminals and a tracer injection and labeled axons are illustrated in figure 2 and figure 3.

Figure 4 Figure 4
Figure 5 Figure 5

Figure 6 Figure 6

Fluorescent compounds are also used as neurotracers and have the advantage that tracers of different colours can be used simultaneously. Fast Blue fluoresces blue under the microscope (Fig. 4), rhodamine fluoresces red (Fig. 5). Some tracers label only the cell body, others label the nuclei, and some label the cell body and its dendritic processes (Fig. 6).