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StatPearls . Treasure Island (FL): StatPearls Publishing; 2021 Jan-.



The brainstem is the structure that connect the cerebrum the the brain to the spinal cord and also cerebellum. The is composed of four sections in to decrease order: the diencephalon, midbrain, pons, and also medulla oblongata. It is responsible because that many critical functions the life, such as breathing, consciousness, blood pressure, love rate, and sleep. The brainstem contains many an important collections of white and grey matter. The grey matter within the brainstem consists of nerve cell bodies and kind many crucial brainstem nuclei. The white matter tracts that the brainstem encompass axons of nerves traversing their course to different structures; the axons originate from cabinet bodies located elsewhere within the main nervous system (CNS). Some of the white matter tract cell bodies are situated within the brainstem together well. These tracts take trip both come the mind (afferent) and also from the brain (efferent) such as the somatosensory pathways and also the corticospinal tracts, respectively. Ten that the twelve cranial nerves to happen from their cranial nerve nuclei in the brainstem. Clinicians deserve to localize lesions the the brainstem through a thorough understanding of brainstem anatomy and also functions. The following activity addresses the nuclei, tracts, and functions that the brainstem.

Structure and Function

The brainstem includes many various nuclei and tracts. This section overviews the significant structures situated in every area the the brainstem, adhered to by a review of the course of the major pathways v the brainstem.


The diencephalon is the many superior section of the brainstem and also connects come the midbrain inferiorly. This structure includes the third ventricle, i beg your pardon connects the interventricular foramen of the lateral ventricles to the cerebral aqueduct. The diencephalon is composed of four significant portions: the epithalamus, subthalamus, hypothalamus, and thalamus.<1> Some resources state the subthalamus is among the four components of the diencephalon when others refer to the pretectum in place of the subthalamus; however, both terms refer to the inferior section of the diencephalon that is consistent with the midbrain.<1><2> The epithalamus is situated in the posterior diencephalon and also is created of the pineal gland, habenular commissure, and also posterior commissure.<2> The subthalamus is the upward continuation of the tegmentum of the midbrain and forms the greater part of the inferior portion of the 3rd ventricle. The substantia nigra and also red nucleus extend upward native the midbrain into the worse subthalamus. The acetylcholine-producing neurons that the cell core of Meynert are situated within the subthalamus. The lose of neurons of the nucleus of Meynert wake up in numerous pathologies that result in dementia.<3> The subthalamus likewise contains the subthalamic nucleus in ~ the base of the cerebral peduncle. The subthalamic cell nucleus participates in the regulation of movement with the basal ganglia. The hypothalamus is located in the anterior inferior part of the diencephalon and also includes the infundibulum, mammillary bodies, hypophysis, and also many hypothalamic nuclei. The posterior thalamus protrudes and overlaps the exceptional colliculus that the midbrain, the medial part of this is the pulvinar. The pulvinar extend laterally come the lateral geniculate bodies which beat a role in vision. The medial geniculate body are located inferior to the pulvinar and also play a function in the listening pathway.

The thalamus is the most substantial part of the diencephalon, writing its remainder as two big oval masses flanking the 3rd ventricle. The thalamus serves as a relay allude for all sensory intake tracts. The thalamus divides into several materials composed of different thalamic nuclei and tracts. The anterior thalamus consists of the anterior thalamic nuclei the receive interaction from the mammillary nuclei via the mammillothalamic tract and play a role in the limbic system. The medial thalamus contains the dorsomedial nucleus and also has connections with hypothalamic nuclei and the prefrontal cortex. The medial thalamus integrates an enormous amount the sensory data. The lateral thalamus subdivides right into dorsal and also ventral components. The dorsal portion includes the lateral dorsal nucleus, pulvinar, and also the lateral posterior nucleus. The ventral portion contains the ventral anterior and lateral nuclei; these nuclei affect activities of the motor cortex since they have actually connections come the reticular formation, substantia nigra, and corpus striatum. The ventral section also contains the ventral posterior medial nuclei which have connections through the ascending trigeminal tracts, and also the ventral posterior lateral nuclei which serve as the primary sensory relay terminal for input indigenous the body. The major nuclei have actually been addressed in this section, however some researches divide the thalamus into 14 major nuclei, and also those deserve to be subdivided further into plenty of subnuclei.<4>


The midbrain serves together the connection in between the pons and also the diencephalon. It additionally connects posteriorly come the cerebellum via the premium cerebellar peduncles. The anterior component of the midbrain contains the crus cerebri with the interpeduncular fossa located in between them. The crus cerebri bring motor cortical spinal fibers, corticonuclear fibers, and pontine fiber tracts. The midbrain consists of the cerebral aqueduct centrally which connects the 3rd ventricle superiorly with the fourth ventricle inferiorly. The periaqueductal grey surrounds the cerebral aqueduct. The midbrain is separated relative to the cerebral aqueduct through the posterior portion being the tectum (floor) and also anterior come the aqueduct serving as the tegmentum (roof). The posterior surface of the midbrain includes the corpora quadrigemina which room composed that bilateral premium colliculi and bilateral inferior colliculi. The exceptional colliculi are affiliated in intuitive reflexes such as saccadic eye movements. Each superior colliculus sends out fibers to the corresponding lateral geniculate body and optic tract with the remarkable brachium. The inferior colliculi are connected in hear processing and also connect come their corresponding medial geniculate nuclei v the inferior brachium. Just inferior to the inferior colliculi in ~ the posterior midline that the brainstem cranial nerve IV, the trochlear nerve, emerges. The trochlear nerve is unique among cranial nerves together it is the just one to emerge from the posterior surface ar of the brainstem. The various other cranial nerve that arises from the midbrain is cranial nerve III, the oculomotor nerve. The oculomotor nerve arises from the midbrain in the oculomotor sulcus top top the medial surface of the crus cerebri, within the interpeduncular cistern.

The midbrain additionally includes plenty of other essential nuclei including yet not limited to the substantia nigra in ~ the base of the midbrain, the red cell nucleus anterior medially at the level of the remarkable colliculus, and the dorsal raphe nucleus. The largest of the raphe nuclei are in the anterior midline of the periaqueductal grey, and the ar of the ventral tegmental area is near the midline medial come the red nucleus. The substantia nigra consists of dopaminergic neurons that assist to regulate movement associated with the basal ganglia. The ventral tegmental area also contains dopaminergic neurons and also plays a function in reward pathways.<5> The raphe nuclei save serotonergic neurons and project widely throughout the brain. The periaqueductal grey is assumed to play a role in pain suppression.<6> The red cell nucleus is affiliated with movement and contains numerous connections v the cerebellum.<7> The medial longitudinal fasciculus lies anterior come the periaqueductal grey and also plays a duty in coordinating eye movements.


The pons associate the medulla oblongata inferiorly come the midbrain superiorly. The anterior section of the pons is convex and can be conveniently seen together a visible distention as soon as viewing the brainstem anteriorly. The surface of the anterior distention contains the basilar groove, which is where the basilar artery rests. The posterior pons is connected to the cerebellum by the center cerebellar peduncles which space the biggest of the cerebellar peduncles. The posterior part of the pons develops the superior portion of the floor of the 4th ventricle. A groove is created inferiorly whereby the pons meets the medulla from which cranial nerves VI, VII, and also VIII emerge medially come laterally. Cranial nerve V, the biggest cranial nerve, exits from the superior anterior lateral pons. Essential nuclei the the pons include the cranial nerve nuclei spanned in the nerves section, the locus coeruleus, and pontine nuclei. The neurons that the locus coeruleus produce norepinephrine and also have projections that spread out widely transparent the CNS. The locus coeruleus is located in the posterior lateral pons at the lateral border that the periaqueductal grey and also is involved in the reticular activating system. The locus coeruleus also suffers damage in Alzheimer disease.<8><8> The pontine nuclei room a collection of pontine motor nuclei in the anterior pons that have many connections with the cerebellum via the center cerebellar peduncle and also assist with coordinating activity and help to modulate breathing.<9>

Medulla Oblongata

The most inferior part of the midbrain is the medulla oblongata, i beg your pardon connects the pons to the spinal cord. The meets the spinal cord in ~ the level of the foramen magnum. The anterior section of the medulla oblongata contains the pyramids. The pyramids carry motor fibers from the precentral gyrus, or engine cortex, come the grey matter of the spinal cord wherein they synapse and also continue come the muscle of the body through the peripheral concerned system. The pyramids save on computer a decussation caudally in i m sorry the majority of the motor fibers consisted of cross to the contralateral side of the body. The fibers that decussate end up being the lateral corticospinal street in the spinal cord, the fibers that do not decussate come to be the medial corticospinal street in the anterior section of the spinal cord. The pyramids lie on either next of the anterior mean fissure, a midline groove that continues caudally follow me the anterior part of the spinal cord. Lateral come the pyramids are the olivary bodies that are component of the olivocerebellar system. The hypoglossal nerve, cranial nerve XII, emerges from the anterior surface ar of the medulla indigenous the sulcus in between the olivary bodies and the pyramids. Posterior to the olivary body is the postolivary groove. Cranial nerves IX (glossopharyngeal), X (vagus), and XI (accessory) emerge from the postolivary groove in superior to worse order. Posterior to the postolivary grooves space the worse cerebellar peduncles that connect the medulla to the cerebellum. The posterior part of the medulla oblongata inferiorly connects come the spinal cord. The posterior average sulcus is situated in the midline top top the posterior element of the worse medulla and also continues caudally follow me the posterior spinal cord.  The posterior typical sulcus in the posterior midline that the spinal cord is flanked by clearly shows localized prominences referred to as the gracile tubercles. On every side, the gracile tubercle includes the gracile nucleus. Comparable bilateral localized prominences referred to as the cuneate tubercles (containing the cuneate cell core on every side) are just lateral to every of the gracile tubercles ~ above the posterior facet of the spinal cord. The gracile and cuneate tubercles lug second-order neurons of the dorsal column-medial lemniscus system. The gracile cell core carries fibers for the lower extremities and also trunk, and the cuneate cell nucleus carries fibers for the upper body over T6 except for the face and also ears. The remarkable area that the posterior medulla oblongata creates a part of the floor that the fourth ventricle.<1>

Major Brainstem Tracts

The Reticular Formation

The reticular formation is discovered in the anterior portion of the brainstem and is written of lot of tracts that have a huge number the connections. The reticular development extends indigenous the spinal cord v the brainstem come the diencephalon. It receives intake from assorted tracts including, spinothalamic tracts, spinoreticular tracts, the dorsal column-medial lemniscus pathway, intuitive pathways, hear pathways, vestibular pathways, and cerebelloreticular pathways. The reticular development sends efferent yarn to the thalamic nuclei, cerebellum, red nucleus, corpus striatum, substantia nigra, hypothalamus, and also subthalamic nucleus.<1> The huge connections of the reticular formation enable it come modulate numerous different functions; few of these include movement coordination, autonomic regulation that blood pressure, heart rate, and respiratory rate, postural reflexes, neuro-vegetative reflexes, and taste.<1> It also plays a function in wakefulness and sleep.<10>

The engine Tracts

Corticospinal Tracts

The bulk of the upper motor neurons of the engine tracts originate in the precentral gyrus. The corticospinal fibers descend v the posterior body of the internal capsule to the crus cerebri and also then under the anterior pons to the pyramids that the medulla. At the pyramids, the majority of the corticospinal fibers decussate and descend the spinal cord together the lateral corticospinal tract and also eventually proceed to supply engine innervation come the limbs and digits. The majority of corticospinal yarn that do not cross end at the medullary pyramids end up being the medial corticospinal tracts, located anteriorly in the spinal cord, and provide innervation to the muscle of the trunk.<11>

Corticobulbar Tracts

The corticobulbar tracts descend v the genu the the interior capsule and down v a similar course together the corticospinal fibers; however, the corticobulbar fibers leave this course and also synapse in ~ the proper cranial nerve nuclei in ~ their respective levels. The majority of corticospinal fibers decussate while only some of the corticobulbar yarn decussate as described in the nerves ar of this article. The corticobulbar tracts also contain relations with many of the sensory nuclei that the brainstem.<1>

The Sensory Tracts

Spinothalamic street or Anterolateral System

The spinothalamic street is responsible because that conveying pain and temperature info from the human body to the brain. Peripheral neurons bring sensory details to the posterior shaft of the spinal cord. After ~ synapsing in the spinal cord, the axons ascend two to 3 levels before decussating. ~ decussating, the yarn ascend together the lateral and also anterior spinothalamic tracts in the anterior and also lateral sections of the spinal cord. When the tracts ascend v the medulla, they merge to form the spinothalamic tract and also course along the lateral part of the medulla. The tract proceeds up the lateral section of the anterior pons and also midbrain come the ventral posterior lateral thalamus whereby the axons synapse and also continue up through the posterior body of the internal capsule to go into the post-central gyrus that the cortex.<12>

Dorsal Column-Medial Lemniscus

The dorsal column-medial lemniscus tract is responsible for moving afferent proprioception, well touch, two-point discrimination, and vibration to the cortex native the body. Peripheral neurons bring sensory details to the posterior pillar of the spinal cord and also ascend in the posterior parts of the spinal cord together the gracile fasciculus and also cuneate fasciculus. The neurons in this fasciculi will certainly synapse of the gracile nucleus and also cuneate nucleus in ~ the level of the worse medulla respectively. The second order neurons will decussate in ~ the level that the medulla and also become the medial lemniscus. The medial lemniscus maintains a medial position within the brainstem as it ascends come the ventral posterior lateral thalamus. After ~ synapsing in the thalamus, the fibers proceed through the posterior body of the inner capsule come the post-central gyrus the the cortex.<13>

Trigeminal Lemniscus and also Spinotrigeminal Tract

Pain and also temperature sensory input from the challenge enters the brainstem via cranial nerve V. The yarn that carry this information go into the brainstem and also descend parallel come the spinal trigeminal nucleus before synapsing in it. Your descent creates the spinotrigeminal tract. After these fibers synapse, lock decussate come the contralateral side and ascend together a component of the trigeminal lemniscus.<1>

The trigeminal lemniscus dead sensory axons native the second-order neurons of the major sensory cell core of the trigeminal nerve, i beg your pardon contain discriminative touch and oral cavity proprioception. These neurons carry out not descend prior to synapsing ~ entering the brainstem. Many of this fibers decussate come the contralateral next on their course come the ventral posterior medial thalamus and then proceed to the post-central gyrus that the cortex. The fibers of the trigeminal lemniscus ascend the pons and midbrain posterior to the medial lemniscus.

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Lateral Lemniscus

The lateral lemniscus carries auditory information from the cochlear nuclei in ~ the level the the worse pons superiorly come the remarkable olivary complex, nuclei the the lateral lemniscus, inferior colliculi, and also eventually to the medial geniculate human body which sends the auditory information to the temporal lobes of the cerebral cortex. Several of the fibers of the lateral lemniscus decussate when others carry out not. The lateral lemniscus travels up the posterior lateral part of the pons and is crucial for sensory input to the brain.<14>