Search databaseBooksAll DatabasesAssemblyBiocollectionsBioProjectBioSampleBioSystemsBooksClinVarConserved DomainsdbGaPdbVarGeneGenomeGEO DataSetsGEO ProfilesGTRHomoloGeneIdentical Protein GroupsMedGenMeSHaramuseum.org net Sitearamuseum.org CatalogNucleotideOMIMPMCPopSetProteinProtein ClustersProtein family members ModelsPubChem BioAssayPubChem CompoundPubChem SubstancePubMedSNPSRAStructureTaxonomyToolKitToolKitAllToolKitBookgh

aramuseum.org Bookshelf. A organization of the national Library the Medicine, nationwide Institutes the Health.

You are watching: Important synapse site for afferent fibers

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


*

Introduction

The brainstem is the structure that connect the cerebrum of the brain to the spinal cord and also cerebellum. The is written of four sections in to decrease order: the diencephalon, midbrain, pons, and also medulla oblongata. The is responsible for many crucial functions of life, such together breathing, consciousness, blood pressure, love rate, and also sleep. The brainstem contains many an important collections that white and grey matter. The grey matter within the brainstem is composed of nerve cabinet bodies and form many essential brainstem nuclei. The white issue tracts that the brainstem incorporate axons that nerves traversing your course to various structures; the axons originate from cell bodies located somewhere else within the central nervous mechanism (CNS). Few of the white issue tract cell bodies are situated within the brainstem as well. These tracts travel both come the brain (afferent) and from the mind (efferent) such as the somatosensory pathways and the corticospinal tracts, respectively. Ten of the twelve cranial nerves happen from their cranial nerve nuclei in the brainstem. Clinicians have the right to localize lesions of the brainstem through a thorough understanding of brainstem anatomy and functions. The following activity addresses the nuclei, tracts, and also functions the the brainstem.


Structure and also Function

The brainstem consists of many various nuclei and also tracts. This section overviews the significant structures located in every area the the brainstem, complied with by a summary of the course of the major pathways v the brainstem.

Diencephalon

The diencephalon is the most superior portion of the brainstem and also connects come the midbrain inferiorly. This structure encompasses the third ventricle, which connects the interventricular foramen that the lateral ventricles come the cerebral aqueduct. The diencephalon is composed of four major portions: the epithalamus, subthalamus, hypothalamus, and also thalamus.<1> Some sources state the subthalamus is just one of the four components of the diencephalon when others describe the pretectum in place of the subthalamus; however, both terms describe the inferior part of the diencephalon that is constant with the midbrain.<1><2> The epithalamus is located in the posterior diencephalon and also is written of the pineal gland, habenular commissure, and posterior commissure.<2> The subthalamus is the upward continuation of the tegmentum that the midbrain and forms the greater part of the inferior portion of the third ventricle. The substantia nigra and also red nucleus prolong upward indigenous the midbrain into the inferior subthalamus. The acetylcholine-producing neurons that the cell core of Meynert are located within the subthalamus. The ns of neurons of the nucleus of Meynert wake up in several pathologies that result in dementia.<3> The subthalamus likewise contains the subthalamic nucleus in ~ the basic of the cerebral peduncle. The subthalamic cell nucleus participates in the regulation of motion with the basal ganglia. The hypothalamus is located in the anterior inferior portion of the diencephalon and also includes the infundibulum, mammillary bodies, hypophysis, and many hypothalamic nuclei. The posterior thalamus protrudes and overlaps the exceptional colliculus of the midbrain, the medial portion of this is the pulvinar. The pulvinar extend laterally come the lateral geniculate bodies which pat a role in vision. The medial geniculate body are located inferior to the pulvinar and play a duty in the listening pathway.

The thalamus is the many substantial portion of the diencephalon, creating its remainder as two huge oval masses flanking the 3rd ventricle. The thalamus serves as a relay suggest for every sensory intake tracts. The thalamus divides into several materials composed of different thalamic nuclei and also tracts. The anterior thalamus includes the anterior thalamic nuclei the receive interaction from the mammillary nuclei via the mammillothalamic tract and also play a duty in the limbic system. The medial thalamus includes the dorsomedial nucleus and also has relations with hypothalamic nuclei and the prefrontal cortex. The medial thalamus integrates an tremendous amount of sensory data. The lateral thalamus subdivides into dorsal and ventral components. The dorsal part includes the lateral dorsal nucleus, pulvinar, and the lateral posterior nucleus. The ventral section contains the ventral anterior and lateral nuclei; this nuclei affect tasks of the engine cortex because they have connections come the reticular formation, substantia nigra, and also corpus striatum. The ventral section also consists of the ventral posterior medial nuclei which have actually connections with the ascending trigeminal tracts, and also the ventral posterior lateral nuclei which serve as the main sensory relay terminal for input indigenous the body. The significant nuclei have actually been addressed in this section, but some research studies divide the thalamus right into 14 major nuclei, and those have the right to be subdivided additional into countless subnuclei.<4>

Midbrain

The midbrain serves as the connection in between the pons and the diencephalon. It also connects posteriorly to the cerebellum via the exceptional cerebellar peduncles. The anterior component of the midbrain consists of the crus cerebri with the interpeduncular fossa located in between them. The crus cerebri lug motor cortical spinal fibers, corticonuclear fibers, and also pontine fiber tracts. The midbrain contains the cerebral aqueduct centrally which connects the 3rd ventricle superiorly with the 4th ventricle inferiorly. The periaqueductal grey surrounds the cerebral aqueduct. The midbrain is separated family member to the cerebral aqueduct v the posterior part being the tectum (floor) and also anterior to the aqueduct serving together the tegmentum (roof). The posterior surface of the midbrain includes the corpora quadrigemina which room composed the bilateral remarkable colliculi and also bilateral worse colliculi. The premium colliculi are affiliated in intuitive reflexes such as saccadic eye movements. Each superior colliculus sends fibers come the equivalent lateral geniculate body and optic tract through the remarkable brachium. The inferior colliculi are associated in hear processing and connect to their matching medial geniculate nuclei v the worse brachium. Simply inferior to the inferior colliculi in ~ the posterior midline the the brainstem cranial nerve IV, the trochlear nerve, emerges. The trochlear nerve is unique amongst cranial nerves together it is the only one to emerge from the posterior surface of the brainstem. The various other cranial nerve the arises indigenous the midbrain is cranial nerve III, the oculomotor nerve. The oculomotor nerve arises from the midbrain in the oculomotor sulcus on the medial surface of the crus cerebri, within the interpeduncular cistern.

The midbrain also includes plenty of other crucial nuclei including however not minimal to the substantia nigra at the basic of the midbrain, the red nucleus anterior medially at the level the the premium colliculus, and the dorsal raphe nucleus. The largest of the raphe nuclei are in the anterior midline the the periaqueductal grey, and the ar of the ventral tegmental area is near the midline medial come the red nucleus. The substantia nigra includes dopaminergic neurons that assist to manage movement associated with the basal ganglia. The ventral tegmental area additionally contains dopaminergic neurons and also plays a duty in prize pathways.<5> The raphe nuclei save serotonergic neurons and also project commonly throughout the brain. The periaqueductal grey is assumed to beat a duty in ache suppression.<6> The red cell core is affiliated with movement and also contains countless connections through the cerebellum.<7> The medial longitudinal fasciculus lies anterior come the periaqueductal grey and also plays a role in coordinating eye movements.

Pons

The pons connect the medulla oblongata inferiorly come the midbrain superiorly. The anterior section of the pons is convex and can be easily seen together a visible distention as soon as viewing the brainstem anteriorly. The surface ar of the anterior distention includes the basilar groove, i beg your pardon is where the basilar artery rests. The posterior pons is linked to the cerebellum by the center cerebellar peduncles which are the biggest of the cerebellar peduncles. The posterior portion of the pons creates the superior part of the floor that the 4th ventricle. A groove is formed inferiorly whereby the pons meets the medulla from which cranial nerves VI, VII, and VIII emerge medially to laterally. Cranial nerve V, the largest cranial nerve, exits from the remarkable anterior lateral pons. Vital nuclei that the pons incorporate the cranial nerve nuclei extended in the nerves section, the locus coeruleus, and also pontine nuclei. The neurons that the locus coeruleus develop norepinephrine and also have projections that spread out widely throughout the CNS. The locus coeruleus is situated in the posterior lateral pons in ~ the lateral border of the periaqueductal grey and also is affiliated in the reticular activating system. The locus coeruleus additionally suffers weaken in Alzheimer disease.<8><8> The pontine nuclei space a collection of pontine motor nuclei in the anterior pons the have many connections through the cerebellum via the center cerebellar peduncle and also assist through coordinating movement and help to modulate breathing.<9>

Medulla Oblongata

The many inferior section of the midbrain is the medulla oblongata, i m sorry connects the pons to the spinal cord. The meets the spinal cord in ~ the level the the foramen magnum. The anterior part of the medulla oblongata consists of the pyramids. The pyramids bring motor fibers from the precentral gyrus, or motor cortex, come the grey issue of the spinal cord where they synapse and continue to the muscles of the body v the peripheral nervous system. The pyramids save a decussation caudally in i beg your pardon the majority of the motor fibers contained cross come the contralateral side of the body. The fibers that decussate come to be the lateral corticospinal tract in the spinal cord, the fibers that perform not decussate come to be the medial corticospinal street in the anterior section of the spinal cord. The pyramids lied on either next of the anterior median fissure, a midline groove that proceeds caudally along the anterior section of the spinal cord. Lateral come the pyramids are the olivary bodies the are component of the olivocerebellar system. The hypoglossal nerve, cranial nerve XII, increase from the anterior surface of the medulla from the sulcus in between the olivary bodies and also the pyramids. Posterior come the olivary body is the postolivary groove. Cranial nerves IX (glossopharyngeal), X (vagus), and XI (accessory) arise from the postolivary groove in exceptional to inferior order. Posterior come the postolivary grooves are the worse cerebellar peduncles that affix the medulla come the cerebellum. The posterior section of the medulla oblongata inferiorly connects come the spinal cord. The posterior median sulcus is situated in the midline on the posterior aspect of the worse medulla and continues caudally follow me the posterior spinal cord.  The posterior mean sulcus in the posterior midline the the spinal cord is flanked by clearly shows localized prominences called the gracile tubercles. On every side, the gracile tubercle includes the gracile nucleus. Comparable bilateral localized prominences dubbed the cuneate tubercles (containing the cuneate cell nucleus on every side) are simply lateral to each of the gracile tubercles on the posterior aspect of the spinal cord. The gracile and also cuneate tubercles bring second-order neurons of the dorsal column-medial lemniscus system. The gracile cell nucleus carries fibers for the lower extremities and trunk, and also the cuneate cell nucleus carries fibers because that the top body over T6 except for the face and also ears. The exceptional area of the posterior medulla oblongata forms a section of the floor that the fourth ventricle.<1>

Major Brainstem Tracts

The Reticular Formation

The reticular development is discovered in the anterior part of the brainstem and also is composed of many tracts that have a huge number of connections. The reticular development extends native the spinal cord with the brainstem to the diencephalon. It receives intake from miscellaneous tracts including, spinothalamic tracts, spinoreticular tracts, the dorsal column-medial lemniscus pathway, intuitive pathways, listening pathways, vestibular pathways, and also cerebelloreticular pathways. The reticular formation sends efferent fibers to the thalamic nuclei, cerebellum, red nucleus, body striatum, substantia nigra, hypothalamus, and subthalamic nucleus.<1> The large connections the the reticular formation enable it to modulate numerous different functions; several of these encompass movement coordination, autonomic regulation the blood pressure, heart rate, and respiratory rate, postural reflexes, neuro-vegetative reflexes, and also taste.<1> It additionally plays a role in wakefulness and also sleep.<10>

The engine Tracts

Corticospinal Tracts

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

Corticobulbar Tracts

The corticobulbar tracts descend v the genu that the inner capsule and also down with a comparable course together the corticospinal fibers; however, the corticobulbar fibers leave this course and also synapse in ~ the proper cranial nerve nuclei in ~ their particular levels. The bulk of corticospinal yarn decussate while just some of the corticobulbar yarn decussate as defined in the nerves ar of this article. The corticobulbar tracts additionally contain relationships with numerous of the sensory nuclei of the brainstem.<1>

The Sensory Tracts

Spinothalamic street or Anterolateral System

The spinothalamic street is responsible because that conveying pain and also temperature details from the human body to the brain. Peripheral neurons carry sensory info to the posterior column 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 lateral sections of the spinal cord. Once the tracts ascend through the medulla, they merge to form the spinothalamic tract and also course follow me the lateral section of the medulla. The tract proceeds up the lateral part of the anterior pons and also midbrain come the ventral posterior lateral thalamus wherein the axons synapse and also continue up with the posterior limb of the internal capsule to get in the post-central gyrus that the cortex.<12>

Dorsal Column-Medial Lemniscus

The dorsal column-medial lemniscus tract is responsible for moving afferent proprioception, fine touch, two-point discrimination, and also vibration come the cortex native the body. Peripheral neurons bring sensory details to the posterior column of the spinal cord and also ascend in the posterior portions of the spinal cord together the gracile fasciculus and cuneate fasciculus. The neurons in this fasciculi will synapse that the gracile nucleus and cuneate nucleus in ~ the level of the worse medulla respectively. The 2nd order neurons will certainly decussate at the level the the medulla and also become the medial lemniscus. The medial lemniscus maintains a medial place within the brainstem as it ascends come the ventral posterior lateral thalamus. After ~ synapsing in the thalamus, the fibers continue through the posterior limb of the internal capsule come the post-central gyrus that the cortex.<13>

Trigeminal Lemniscus and also Spinotrigeminal Tract

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

The trigeminal lemniscus dead sensory axons indigenous the second-order neurons of the major sensory cell nucleus of the trigeminal nerve, which contain discriminative touch and also oral cavity proprioception. This neurons carry out not descend before synapsing ~ entering the brainstem. Most of these fibers decussate come the contralateral side on your course come the ventral posterior medial thalamus and also then proceed to the post-central gyrus of the cortex. The fibers of the trigeminal lemniscus ascend the pons and midbrain posterior come the medial lemniscus.

See more: Is Air A Homogeneous Mixture Or A Heterogeneous Mixture ? Describe How Air Is A Homogeneous Mixture

Lateral Lemniscus

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