neuroanatomy Neuroanatomy is the study of the structure and organization of the nervous system. In contrast to animals with radial symmetry, whose nervous system consists of a distributed network of cells, animals with bilateral symmetry have segregated, defi ...

, the corticobulbar (or corticonuclear) tract is a two-neuron

white matter White matter refers to areas of the central nervous system (CNS) that are mainly made up of myelinated axons, also called tracts. Long thought to be passive tissue, white matter affects learning and brain functions, modulating the distributi ...

motor pathway connecting the

motor cortex The motor cortex is the region of the cerebral cortex believed to be involved in the planning, control, and execution of voluntary movements. The motor cortex is an area of the frontal lobe located in the posterior precentral gyrus immediately ...

in the

cerebral cortex The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consistin ...

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's medulla oblongata (also called "bulbar") region, and are primarily involved in carrying the

motor function Motor control is the regulation of movement in organisms that possess a nervous system. Motor control includes reflexes as well as directed movement. To control movement, the nervous system must integrate multimodal sensory information (both ...

of the non-oculomotor cranial nerves. The corticobulbar tract is one of the

pyramidal tracts The pyramidal tracts include both the corticobulbar tract and the corticospinal tract. These are aggregations of efferent nerve fibers from the upper motor neurons that travel from the cerebral cortex and terminate either in the brainstem (''cort ...

, the other being the

corticospinal tract The corticospinal tract is a white matter motor pathway starting at the cerebral cortex that terminates on lower motor neurons and interneurons in the spinal cord, controlling movements of the limbs and trunk. There are more than one million neur ...

Structure

The corticobulbar tract originates in the primary

of the

frontal lobe The frontal lobe is the largest of the four major lobes of the brain in mammals, and is located at the front of each cerebral hemisphere (in front of the parietal lobe and the temporal lobe). It is parted from the parietal lobe by a groove be ...

, just superior to the

lateral fissure In neuroanatomy, the lateral sulcus (also called Sylvian fissure, after Franciscus Sylvius, or lateral fissure) is one of the most prominent features of the human brain. The lateral sulcus is a deep fissure in each hemisphere that separates the ...

and rostral to the central sulcus in the

precentral gyrus The precentral gyrus is a prominent gyrus on the surface of the posterior frontal lobe of the brain. It is the site of the primary motor cortex that in humans is cytoarchitecturally defined as Brodmann area 4. Structure The precentral gyrus l ...

(

Brodmann area 4 Brodmann area 4 refers to the primary motor cortex of the human brain. It is located in the posterior portion of the frontal lobe. Brodmann area 4 is part of the precentral gyrus. The borders of this area are: the precentral sulcus in front (an ...

). The tract descends through the

corona radiata In neuroanatomy, the corona radiata is a white matter sheet that continues inferiorly as the internal capsule and superiorly as the centrum semiovale. This sheet of both ascending and descending axons carries most of the neural traffic from and ...

and genu of the

internal capsule The internal capsule is a white matter structure situated in the inferomedial part of each cerebral hemisphere of the brain. It carries information past the basal ganglia, separating the caudate nucleus and the thalamus from the putamen and the ...

with a few fibers in the posterior limb of the

, as it passes from the cortex down to the

midbrain The midbrain or mesencephalon is the forward-most portion of the brainstem and is associated with vision, hearing, motor control, sleep and wakefulness, arousal (alertness), and temperature regulation. The name comes from the Greek ''mesos'', " ...

. In the midbrain, the internal capsule becomes the

cerebral peduncles The cerebral peduncles are the two stalks that attach the cerebrum to the brainstem. They are structures at the front of the midbrain which arise from the ventral pons and contain the large ascending (sensory) and descending (motor) nerve tract ...

. The white matter is located in the ventral portion of the cerebral peduncles, called the

crus cerebri The cerebral crus (crus cerebri) is the anterior portion of the cerebral peduncle which contains the motor tracts, travelling from the cerebral cortex to the pons and spine. The plural of which is cerebral crura. In some older texts this is calle ...

. 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,

cuneate 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 ...

solitary nucleus In the human brainstem, the solitary nucleus, also called nucleus of the solitary tract, nucleus solitarius, and nucleus tractus solitarii, (SN or NTS) is a series of purely sensory nuclei (clusters of nerve cell bodies) forming a vertical column ...

, and all trigeminal nuclei. Only 50% of the corticobulbar fibers decussate, in contrast to those of the

where most decussate.

Functions

The corticobulbar tract is composed of the upper motor neurons of the

cranial nerves Cranial nerves are the nerves that emerge directly from the brain (including the brainstem), of which there are conventionally considered twelve pairs. Cranial nerves relay information between the brain and parts of the body, primarily to and f ...

. The muscles of the face, head and neck are controlled by the corticobulbar system, which terminates on motor neurons within brainstem motor nuclei. This is in contrast to the

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 V,

VII VII or vii may refer to: the Roman numeral 7 Art and entertainment * The Vii, a video game console * vii, leading-tone triad, see diminished triad * ''VII'' (Blitzen Trapper album) * ''VII'' (Just-Ice album) * ''VII'' (Teyana Taylor album) * ...

, IX, and XII. The corticobulbar tract also contributes to the motor regions of cranial nerve X in the

nucleus ambiguus The nucleus ambiguus ("ambiguous nucleus" in English) is a group of large motor neurons, situated deep in the medullary reticular formation named by Jacob Clarke. The nucleus ambiguus contains the cell bodies of neurons that innervate the muscle ...

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