In neuroanatomy, the corticobulbar (or corticonuclear) tract is a two-neuron white matter motor pathway connecting the motor cortex in the cerebral cortex to the

medullary pyramids In neuroanatomy, the medullary pyramids are paired white matter structures of the brainstem's medulla oblongata that contain motor fibers of the corticospinal and corticobulbar tracts – known together as the pyramidal tracts. The lower limit ...

, which are part of the

brainstem The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is cont ...

medulla oblongata The medulla oblongata or simply medulla is a long stem-like structure which makes up the lower part of the brainstem. It is anterior and partially inferior to the cerebellum. It is a cone-shaped neuronal mass responsible for autonomic (involun ...

(also called "bulbar") region, and are primarily involved in carrying the motor function of the non-oculomotor cranial nerves. The corticobulbar tract is one of the pyramidal tracts, the other being the corticospinal tract.

Structure

The corticobulbar tract originates in the primary motor cortex of the frontal lobe, just superior to the lateral fissure and

rostral Rostral may refer to: Anatomy * Rostral (anatomical term), situated toward the oral or nasal region * Rostral bone, in ceratopsian dinosaurs * Rostral organ, of certain fish * Rostral scale, in snakes and scaled reptiles Other uses * Rostral colu ...

to the

central sulcus In neuroanatomy, the central sulcus (also central fissure, fissure of Rolando, or Rolandic fissure, after Luigi Rolando) is a sulcus, or groove, in the cerebral cortex in the brains of vertebrates. It is sometimes confused with the longitudinal ...

in the precentral gyrus ( Brodmann area 4). The tract descends through the corona radiata and

genu Genu, a Latin word for "knee," may refer to: * Genu of internal capsule * Genu of the corpus callosum * Genu recurvatum * Genu valgum * Genu varum Genu varum (also called bow-leggedness, bandiness, bandy-leg, and tibia vara) is a varus deform ...

of the internal capsule with a few fibers in the posterior limb of the internal capsule, as it passes from the cortex down to the midbrain. In the midbrain, the internal capsule becomes the cerebral peduncles. The white matter is located in the ventral portion of the cerebral peduncles, called the crus cerebri. The middle third of the crus cerebri contains the corticobulbar and corticospinal fibers. The corticobulbar fibers exit at the appropriate level of the brainstem to synapse on the lower motor neurons of the cranial nerves. In addition to endings in these motor neurons, fibers of the corticobulbar tract also end in the sensory nuclei of the brainstem including

gracile nucleus In neuroanatomy, the dorsal column nuclei are a pair of nuclei in the dorsal columns in the brainstem. The name refers collectively to the cuneate nucleus and gracile nucleus, which are present at the bottom of the medulla oblongata. Both nucl ...

, cuneate nucleus, solitary nucleus, and all trigeminal nuclei. Only 50% of the corticobulbar fibers decussate, in contrast to those of the corticospinal tract where most decussate.

Functions

The corticobulbar tract is composed of the upper motor neurons of the cranial nerves. The muscles of the face, head and neck are controlled by the corticobulbar system, which terminates on

motor neuron A motor neuron (or motoneuron or efferent neuron) is a neuron whose cell body is located in the motor cortex, brainstem or the spinal cord, and whose axon (fiber) projects to the spinal cord or outside of the spinal cord to directly or indirectl ...

s within brainstem motor cranial nerve nuclei, nuclei. This is in contrast to the corticospinal tract in which the cerebral cortex connects to spinal motor neurons, and thereby controls movement of the torso, upper and lower limbs. Fibers that end in the sensory nuclei of the brainstem are thought to enhance or inhibit sensory transmission across various sensory nuclei. This allows for the selective attention or inattention towards various stimuli. The corticobulbar tract innervates cranial motor nuclei bilaterally with the exception of the lower facial nuclei (which innervates facial muscles below the eyes) and the genioglossus muscle, which are innervated only unilaterally by the contralateral cortex. Among those nuclei that are bilaterally innervated a slightly stronger connection contralaterally than ipsilaterally is observed. The corticobulbar tract directly innervates the nuclei for cranial nerves trigeminal nerve, V, facial nerve, VII, glossopharyngeal nerve, IX, and hypoglossal nerve, XII. The corticobulbar tract also contributes to the motor regions of cranial nerve vagus nerve, X in the nucleus ambiguus.

References

External links

* * http://thebrain.mcgill.ca/flash/i/i_06/i_06_cl/i_06_cl_mou/i_06_cl_mou.html * http://pathology.mc.duke.edu/neuropath/nawr/motor-systems.html {{Neural tracts Central nervous system pathways Motor system Frontal lobe

Structure

Functions

See also

References

External links