Brainstem

The brainstem (or brain stem) is the posterior part of the brain, continuous with the spinal cord. In the human brain the brainstem includes the midbrain, and the pons and medulla oblongata of the hindbrain. Sometimes the diencephalon, the caudal part of the forebrain, is included.[1]

The brainstem provides the main motor and sensory nerve supply to the face and neck via the cranial nerves. Of the thirteen pairs of cranial nerves, ten pairs (or twelve, if the diencephalon is included in the brainstem) come from the brainstem. The brainstem is an extremely important part of the brain as the nerve connections of the motor and sensory systems from the main part of the brain to the rest of the body pass through the brainstem. This includes the corticospinal tract (motor), the dorsal column-medial lemniscus pathway (fine touch, vibration sensation, and proprioception), and the spinothalamic tract (pain, temperature, itch, and crude touch).

The brainstem also plays an important role in the regulation of cardiac and respiratory function. It also regulates the central nervous system, and is pivotal in maintaining consciousness and regulating the sleep cycle. The brainstem has many basic functions including heart rate, breathing, sleeping, and eating.

Brainstem
1311 Brain Stem
The three distinct parts of the brainstem are colored in this sagittal section of a human brain.
Details
Part ofBrain
PartsMedulla, Pons, Midbrain
Identifiers
Latintruncus encephali
MeSHD001933
NeuroNames2052, 236
NeuroLex IDbirnlex_1565
TAA14.1.03.009
FMA79876
Anatomical terms of neuroanatomy

Structure

Parts

Midbrain

The midbrain is divided into three parts: tectum, tegmentum, and the ventral tegmentum. The tectum (Latin:roof), which forms the ceiling. The tectum comprises the paired structure of the superior and inferior colliculi and is the dorsal covering of the cerebral aqueduct. The inferior colliculus, is the principal midbrain nucleus of the auditory pathway and receives input from several peripheral brainstem nuclei, as well as inputs from the auditory cortex. Its inferior brachium (arm-like process) reaches to the medial geniculate nucleus of the diencephalon. Superior to the inferior colliculus, the superior colliculus marks the rostral midbrain. It is involved in the special sense of vision and sends its superior brachium to the lateral geniculate body of the diencephalon.

The tegmentum which forms the floor of the midbrain, is ventral to the cerebral aqueduct. Several nuclei, tracts, and the reticular formation are contained here.

The ventral tegmental area (VTA) is composed of paired cerebral peduncles. These transmit axons of upper motor neurons.

The midbrain consists of:

Midbrain - superior colliculus

Cross-section of the midbrain at the level of the superior colliculus.

Midbrain - inferior colliculus

Cross-section of the midbrain at the level of the inferior colliculus.

Pons

The pons lies between the medulla oblongata and the midbrain. It contains tracts that carry signals from the cerebrum to the medulla and to the cerebellum and also tracts that carry sensory signals to the thalamus. The pons is connected to the cerebellum by the cerebellar peduncles. The pons houses the respiratory pneumotaxic center and apneustic center that make up the pontine respiratory group in the respiratory center. The pons co-ordinates activities of the cerebellar hemispheres.

The pons and medulla oblongata are parts of the hindbrain that form much of the brainstem.

Pons - Middle

Cross-section of the middle pons (at the level of cranial nerve V).

Pons - Inferior

Cross-section of the inferior pons (at the level of the facial genu).

Medulla oblongata

The medulla oblongata often just referred to as the medulla, is the lower half of the brainstem continuous with the spinal cord. Its upper part is continuous with the pons.[2] The medulla contains the cardiac, dorsal and ventral respiratory groups, and vasomotor centres, dealing with heart rate, breathing and blood pressure. Another important medullary structure is the area postrema whose functions include the control of vomiting.

Medulla - Rostral level cross section

Cross-section of the rostral (superior) medulla.

Medulla - Middle level cross section

Cross-section of the middle medulla.

Medulla - Inferior level cross section

Cross-section of the inferior medulla.

Appearance

From the front
Slide2RAFA
The appearance of a cadaveric brainstem from the front, with major parts labelled.

In the medial part of the medulla is the anterior median fissure. Moving laterally on each side are the medullary pyramids. The pyramids contain the fibers of the corticospinal tract (also called the pyramidal tract), or the upper motor neuronal axons as they head inferiorly to synapse on lower motor neuronal cell bodies within the anterior grey column of the spinal cord.

The anterolateral sulcus is lateral to the pyramids. Emerging from the anterolateral sulci are the CN XII (hypoglossal nerve) rootlets. Lateral to these rootlets and the anterolateral sulci are the olives. The olives are swellings in the medulla containing underlying inferior nucleary nuclei (containing various nuclei and afferent fibers). Lateral (and dorsal) to the olives are the rootlets for CN IX (glossopharyngeal), CN X (vagus) and CN XI (accessory nerve). The pyramids end at the pontine medulla junction, noted most obviously by the large basal pons. From this junction, CN VI (abducens nerve), CN VII (facial nerve) and CN VIII (vestibulocochlear nerve) emerge. At the level of the midpons, CN V (the trigeminal nerve) emerges. Cranial nerve III (the oculomotor nerve) emerges ventrally from the midbrain, while the CN IV (the trochlear nerve) emerges out from the dorsal aspect of the midbrain.

Between the two pyramids can be seen a decussation of fibers which marks the transition from the medulla to the spinal cord. The medulla is above the decussation and the spinal cord below.

From behind
Slide4RAFA
The appearance of a cadaveric brainstem from behind, with major parts labelled.

The most medial part of the medulla is the posterior median sulcus. Moving laterally on each side is the fasciculus gracilis, and lateral to that is the fasciculus cuneatus. Superior to each of these, and directly inferior to the obex, are the gracile and cuneate tubercles, respectively. Underlying these are their respective nuclei. The obex marks the end of the fourth ventricle and the beginning of the central canal. The posterior intermediate sulcus separates the fasciculus gracilis from the fasciculus cuneatus. Lateral to the fasciculus cuneatus is the lateral funiculus.

Superior to the obex is the floor of the fourth ventricle. In the floor of the fourth ventricle, various nuclei can be visualized by the small bumps that they make in the overlying tissue. In the midline and directly superior to the obex is the vagal trigone and superior to that it the hypoglossal trigone. Underlying each of these are motor nuclei for the respective cranial nerves. Superior to these trigones are fibers running laterally in both directions. These fibers are known collectively as the striae medullares. Continuing in a rostral direction, the large bumps are called the facial colliculi. Each facial colliculus, contrary to their names, do not contain the facial nerve nuclei. Instead, they have facial nerve axons traversing superficial to underlying abducens (CN VI) nuclei. Lateral to all these bumps previously discussed is an indented line, or sulcus that runs rostrally, and is known as the sulcus limitans. This separates the medial motor neurons from the lateral sensory neurons. Lateral to the sulcus limitans is the area of the vestibular system, which is involved in special sensation. Moving rostrally, the inferior, middle, and superior cerebellar peduncles are found connecting the midbrain to the cerebellum. Directly rostral to the superior cerebellar peduncle, there is the superior medullary velum and then the two trochlear nerves. This marks the end of the pons as the inferior colliculus is directly rostral and marks the caudal midbrain. Middle cerebellar peduncle is located inferior and lateral to the superior cerebellar peduncle, connecting pons to the cerebellum. Likewise, inferior cerebellar peduncle is found connecting the medulla oblongata to the cerebellum.

Blood supply

Blausen 0114 BrainstemAnatomy
The brainstem receives blood via the vertebral arteries, shown here.

The main supply of blood to the brainstem is provided by the basilar arteries and the vertebral arteries.[3]

Development

The adult human brainstem emerges from two of the three primary vesicles formed of the neural tube. The mesencephalon is the second of the three primary vesicles, and does not further differentiate into a secondary vesicle. This will become the midbrain. The third primary vesicle, the rhombencephalon (hindbrain) will further differentiate into two secondary vesicles, the metencephalon and the myelencephalon. The metencephalon will become the cerebellum and the pons. The more caudal myelencephalon will become the medulla.

Function

There are three main functions of the brainstem:

  1. The brainstem plays a role in conduction. That is, all information relayed from the body to the cerebrum and cerebellum and vice versa must traverse the brainstem. The ascending pathways coming from the body to the brain are the sensory pathways and include the spinothalamic tract for pain and temperature sensation and the dorsal column-medial lemniscus pathway (DCML) including the gracile fasciculus and the cuneate fasciculus for touch, proprioception, and pressure sensation. The facial sensations have similar pathways and will travel in the spinothalamic tract and the DCML. Descending tracts are the axons of upper motor neurons destined to synapse on lower motor neurons in the ventral horn and posterior horn. In addition, there are upper motor neurons that originate in the brainstem's vestibular, red, tectal, and reticular nuclei, which also descend and synapse in the spinal cord.
  2. The cranial nerves III-XII emerge from the brainstem.[4] These cranial nerves supply the face, head, and viscera. (The first two pairs of cranial nerves arise from the cerebrum).
  3. The brainstem has integrative functions being involved in cardiovascular system control, respiratory control, pain sensitivity control, alertness, awareness, and consciousness. Thus, brainstem damage is a very serious and often life-threatening problem.

Cranial nerves

Brain stem sagittal section
A cross-section of the brainstem showing the multiple nuclei of the ten pairs of cranial nerves that emerge from it.

Ten of the twelve pairs of cranial nerves either target or are sourced from the brainstem.[5] The nuclei of the oculomotor nerve (III) and trochlear nerve (IV) are located in the midbrain. The nuclei of the trigeminal nerve (V), abducens nerve (VI), facial nerve (VII) and vestibulocochlear nerve (VIII) are located in the pons. The nuclei of the glossopharyngeal nerve (IX), vagus nerve (X), accessory nerve (XI) and hypoglossal nerve (XII) are located in the medulla. The fibers of these cranial nerves exit the brainstem from these nuclei.[6]

Clinical significance

Diseases of the brainstem can result in abnormalities in the function of cranial nerves that may lead to visual disturbances, pupil abnormalities, changes in sensation, muscle weakness, hearing problems, vertigo, swallowing and speech difficulty, voice change, and co-ordination problems. Localizing neurological lesions in the brainstem may be very precise, although it relies on a clear understanding on the functions of brainstem anatomical structures and how to test them.

Brainstem stroke syndrome can cause a range of impairments including locked-in syndrome.

Duret haemorrhages are areas of bleeding in the midbrain and upper pons due to a downward traumatic displacement of the brainstem.[7]

Cysts known as syrinxes can affect the brainstem, in a condition, called syringobulbia. These fluid-filled cavities can be congenital, acquired or the result of a tumor.

Criteria for claiming brainstem death in the UK have developed in order to make the decision of when to stop ventilation of somebody who could not otherwise sustain life. These determining factors are that the patient is irreversibly unconscious and incapable of breathing unaided. All other possible causes must be ruled out that might otherwise indicate a temporary condition. The state of irreversible brain damage has to be unequivocal. There are brainstem reflexes that are checked for by two senior doctors so that imaging technology is unnecessary. The absence of the cough and gag reflexes, of the corneal reflex and the vestibulo–ocular reflex need to be established; the pupils of the eyes must be fixed and dilated; there must be an absence of motor response to stimulation and an absence of breathing marked by concentrations of carbon dioxide in the arterial blood. All of these tests must be repeated after a certain time before death can be declared.[8]

Additional images

Human brain frontal (coronal) section description

The midbrain, pons, and medulla oblongata are labelled on this coronal section of the human brain.

See also

References

  1. ^ Alberts, Daniel (2012). Dorland's illustrated medical dictionary (32nd ed.). Philadelphia, PA: Saunders/Elsevier. p. 248. ISBN 978-1-4160-6257-8.
  2. ^ Dorland's (2012). Dorland's Illustrated Medical Dictionary (32nd ed.). Elsevier Saunders. p. 1121. ISBN 978-1-4160-6257-8.
  3. ^ Purves, Dale (2011). Neuroscience (5. ed.). Sunderland, Mass.: Sinauer. p. 740. ISBN 978-0-87893-695-3.
  4. ^ "Archived copy" (PDF). Archived (PDF) from the original on 2013-04-18. Retrieved 2012-11-10.CS1 maint: Archived copy as title (link)
  5. ^ Purves, Dale (2011). Neuroscience (5. ed.). Sunderland, Mass.: Sinauer. p. 725. ISBN 978-0-87893-695-3.
  6. ^ Vilensky, Joel; Robertson, Wendy; Suarez-Quian, Carlos (2015). The Clinical Anatomy of the Cranial Nerves: The Nerves of "On Olympus Towering Top". Ames, Iowa: Wiley-Blackwell. ISBN 978-1-118-49201-7.
  7. ^ Dorland's (2012). Dorland's Illustrated Medical Dictionary (32nd ed.). Elsevier. p. 842. ISBN 978-1-4160-6257-8.
  8. ^ Black's Medical Dictionary 39th edition 1999

External links

Alpha motor neuron

Alpha (α) motor neurons (also called alpha motoneurons), are large, multipolar lower motor neurons of the brainstem and spinal cord. They innervate extrafusal muscle fibers of skeletal muscle and are directly responsible for initiating their contraction. Alpha motor neurons are distinct from gamma motor neurons, which innervate intrafusal muscle fibers of muscle spindles.

While their cell bodies are found in the central nervous system (CNS), α motor neurons are also considered part of the somatic nervous system—a branch of the peripheral nervous system (PNS)—because their axons extend into the periphery to innervate skeletal muscles.

An alpha motor neuron and the muscle fibers it innervates is a motor unit. A motor neuron pool contains the cell bodies of all the alpha motor neurons involved in contracting a single muscle.

Auditory brainstem response

The auditory brainstem response (ABR) is an auditory evoked potential extracted from ongoing electrical activity in the brain and recorded via electrodes placed on the scalp. The measured recording is a series of six to seven vertex positive waves of which I through V are evaluated. These waves, labeled with Roman numerals in Jewett and Williston convention, occur in the first 10 milliseconds after onset of an auditory stimulus. The ABR is considered an exogenous response because it is dependent upon external factors.The auditory structures that generate the auditory brainstem response are believed to be as follows:

Wave I through III – generated by the auditory branch of cranial nerve VIII and lower

Wave IV and V – generated by the upper brainstem

More in depth location – wave I originates from the dendrites of the auditory nerve fibers, wave II from the cochlear nucleus, III showing activity in the superior olivary complex, and wave IV–V associated with the lateral lemniscus.

Brain death

Brain death is the complete loss of brain function (including involuntary activity necessary to sustain life). It differs from persistent vegetative state, in which the person is alive and some autonomic functions remain. It is also distinct from an ordinary coma, whether induced medically or caused by injury and/or illness, even if it is very deep, as long as some brain and bodily activity and function remains; and it is also not the same as the condition known as locked-in syndrome. A differential diagnosis can medically distinguish these differing conditions.

Brain death is used as an indicator of legal death in many jurisdictions, but it is defined inconsistently and often confused by the lay public. Various parts of the brain may keep functioning when others do not anymore, and the term "brain death" has been used to refer to various combinations. For example, although one major medical dictionary considers "brain death" to be synonymous with "cerebral death" (death of the cerebrum), the US National Library of Medicine Medical Subject Headings (MeSH) system defines brain death as including the brainstem. The distinctions are medically significant because, for example, in someone with a dead cerebrum but a living brainstem, the heartbeat and ventilation can continue unaided, whereas in whole-brain death (which includes brainstem death), only life support equipment would keep those functions going. Patients classified as brain-dead can have their organs surgically removed for organ donation.

Brainstem death

Brainstem death is a clinical syndrome defined by the absence of reflexes with pathways through the brainstem—the "stalk" of the brain, which connects the spinal cord to the mid-brain, cerebellum and cerebral hemispheres—in a deeply comatose, ventilator-dependent patient.

Identification of this state carries a very grave prognosis for survival; cessation of heartbeat often occurs within a few days although it may continue for weeks if intensive support is maintained.In the United Kingdom, the formal diagnosis of brainstem death by the procedure laid down in the official Code of Practice permits the diagnosis and certification of death on the premise that a person is dead when consciousness and the ability to breathe are permanently lost, regardless of continuing life in the body and parts of the brain, and that death of the brainstem alone is sufficient to produce this state.This concept of brainstem death is also accepted as grounds for pronouncing death for legal purposes in India and Trinidad & Tobago. Elsewhere in the world the concept upon which the certification of death on neurological grounds is based is that of permanent cessation of all function in all parts of the brain—whole brain death—with which the British concept should not be confused. The United States' President's Council on Bioethics made it clear, for example, in its White Paper of December 2008, that the British concept and clinical criteria are not considered sufficient for the diagnosis of death in the United States of America.

Brainstem stroke syndrome

A brainstem stroke syndrome falls under the broader category of stroke syndromes, or specific symptoms caused by vascular injury to an area of brain (for example, the lacunar syndromes). As the brainstem contains numerous cranial nuclei and white matter tracts, a stroke in this area can have a number of unique symptoms depending on the particular blood vessel that was injured and the group of cranial nerves and tracts that are no longer perfused. Symptoms of a brainstem stroke frequently include sudden vertigo and ataxia, with or without weakness. Brainstem stroke can also cause diplopia, slurred speech and decreased level of consciousness. A more serious outcome is locked-in syndrome.

Coma

A coma is a deep state of prolonged unconsciousness in which a person cannot be awakened; fails to respond normally to painful stimuli, light, or sound; lacks a normal wake-sleep cycle; and does not initiate voluntary actions. Coma patients exhibit a complete absence of wakefulness and are unable to consciously feel, speak or move. Comas can be derived by natural causes, or can be medically induced.

Clinically, a coma can be defined as the inability to consistently follow a one-step command. It can also be defined as a score of ≤ 8 on the Glasgow Coma Scale (GCS) lasting ≥ 6 hours. For a patient to maintain consciousness, the components of wakefulness and awareness must be maintained. Wakefulness describes the quantitative degree of consciousness, whereas awareness relates to the qualitative aspects of the functions mediated by the cortex, including cognitive abilities such as attention, sensory perception, explicit memory, language, the execution of tasks, temporal and spatial orientation and reality judgment. From a neurological perspective, consciousness is maintained by the activation of the cerebral cortex—the gray matter that forms the outer layer of the brain and by the reticular activating system (RAS), a structure located within the brainstem.

Cranial nerves

Cranial nerves are the nerves that emerge directly from the brain (including the brainstem), in contrast to spinal nerves (which emerge from segments of the spinal cord). 10 of the cranial nerves originate in the brainstem. Cranial nerves relay information between the brain and parts of the body, primarily to and from regions of the head and neck.Spinal nerves emerge sequentially from the spinal cord with the spinal nerve closest to the head (C1) emerging in the space above the first cervical vertebra. The cranial nerves, however, emerge from the central nervous system above this level. Each cranial nerve is paired and is present on both sides. Depending on definition in humans there are twelve or thirteen cranial nerves pairs, which are assigned Roman numerals I–XII, sometimes also including cranial nerve zero. The numbering of the cranial nerves is based on the order in which they emerge from the brain, front to back (brainstem).The terminal nerves (0), olfactory nerves (I) and optic nerves (II) emerge from the cerebrum or forebrain, and the remaining ten pairs arise from the brainstem, which is the lower part of the brain.The cranial nerves are considered components of the peripheral nervous system (PNS), although on a structural level the olfactory (I), optic (II), and trigeminal (V) nerves are more accurately considered part of the central nervous system (CNS).

Dorsal column nuclei

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 junction between the spinal cord and the medulla oblongata. Both nuclei contain second-order neurons of the dorsal column-medial lemniscus pathway, which carries fine touch and proprioceptive information from the body to the brain. Each nucleus has an associated nerve tract, the gracile fasciculus and the cuneate fasciculus.

Dorsal longitudinal fasciculus

The dorsal longitudinal fasciculus (DLF) (not to be confused with the medial longitudinal fasciculus, nor the superior longitudinal fasciculus) is a white matter fiber tract located within the brain stem, specifically in the dorsal brainstem tegmentum. The DLF travels through the periaqueductal gray matter. The tract is composed of a diffuse brainstem pathway located in the periventricular gray matter comprising ascending visceral sensory axons and descending hypothalamic axons.

As with all white matter tracts, the DLF consists of myelinated axons carrying information between neurons. The DLF, carries both ascending and descending fibers, and conveys visceral motor and sensory signals.

Lateral lemniscus

The lateral lemniscus is a tract of axons in the brainstem that carries information about sound from the cochlear nucleus to various brainstem nuclei and ultimately the contralateral inferior colliculus of the midbrain. Three distinct, primarily inhibitory, cellular groups are located interspersed within these fibers, and are thus named the nuclei of the lateral lemniscus.

Lenticular fasciculus

The lenticular fasciculus is a tract connecting the globus pallidus to the thalamic fasciculus. It is synonymous with field H2 of Forel. The thalamic fasciculus is (composed of the lenticular fasciculus and ansa lenticularis) runs into the thalamus.

It connects the globus pallidus to the thalamus.

Medial lemniscus

The medial lemniscus, also known as Reil's band or Reil's ribbon, is a large ascending bundle of heavily myelinated axons that decussate in the brainstem, specifically in the medulla oblongata. The medial lemniscus is formed by the crossings of the internal arcuate fibers. The internal arcuate fibers are composed of axons of nucleus gracilis and nucleus cuneatus. The axons of the nucleus gracilis and nucleus cuneatus in the medial lemniscus have cell bodies that lie contralaterally.

The medial lemniscus is part of the dorsal column–medial lemniscus pathway, which ascends from the skin to the thalamus, which is important for somatosensation from the skin and joints, therefore, lesion of the medial lemnisci causes an impairment of vibratory and touch-pressure sense.

Medial longitudinal fasciculus

The medial longitudinal fasciculus (MLF) is one of a pair of crossed over tracts, on each side of the brainstem. These bundles of axons are situated near the midline of the brainstem and are made up of both ascending and descending fibers that arise from a number of sources and terminate in different areas. The MLF is the main central connection for the oculomotor nerve, trochlear nerve, and abducens nerve. The vertical gaze center is at the rostral interstitial nucleus (riMLF).

The MLF ascends to the interstitial nucleus of Cajal, which lies in the lateral wall of the third ventricle, just above the cerebral aqueduct.

Medullary pyramids (brainstem)

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 of the pyramids is marked when the fibers cross (decussate).

Olivary body

In anatomy, the olivary bodies or simply olives (Latin oliva and olivae, singular and plural, respectively) are a pair of prominent oval structures in the medulla oblongata, the lower portion of the brainstem. They contain the olivary nuclei.

Pons

The pons (Latin for "bridge") is part of the brainstem, and in humans and other bipeds lies inferior to the midbrain, superior to the medulla oblongata and anterior to the cerebellum.

The pons is also called the pons Varolii ("bridge of Varolius"), after the Italian anatomist and surgeon Costanzo Varolio (1543–75). This region of the brainstem includes neural pathways and tracts that conduct signals from the brain down to the cerebellum and medulla, and tracts that carry the sensory signals up into the thalamus.

Syringobulbia

Syringobulbia is a medical condition in which syrinxes, or fluid-filled cavities, affect the brainstem. This defect normally results from congenital abnormality, trauma or tumor growth.

It mostly occurs within the lower brainstem as a slit-like gap. This may affect one or more cranial nerves, resulting in various kinds of facial palsies. Sensory and motor nerve pathways may be affected by interruption or compression of nerves. This disorder is associated with syringomyelia, a syrinx limited to the spinal cord.

Trochlear nerve

The trochlear nerve, also called the fourth cranial nerve or CN IV, is a motor nerve (a somatic efferent nerve) that innervates only a single muscle: the superior oblique muscle of the eye, which operates through the pulley-like trochlea.

The trochlear nerve is unique among the cranial nerves in several respects:

It is the smallest nerve in terms of the number of axons it contains.

It has the greatest intracranial length.

It is the only cranial nerve that exits from the dorsal (rear) aspect of the brainstem.

It innervates a muscle, the superior oblique muscle, on the opposite side (contralateral) from its nucleus. The trochlear nerve decussates within the brainstem before emerging on the contralateral side of the brainstem (at the level of the inferior colliculus). An injury to the trochlear nucleus in the brainstem will result in an contralateral superior oblique muscle palsy, whereas an injury to the trochlear nerve (after it has emerged from the brainstem) results in an ipsilateral superior oblique muscle palsy.Homologous trochlear nerves are found in all jawed vertebrates. The unique features of the trochlear nerve, including its dorsal exit from the brainstem and its contralateral innervation, are seen in the primitive brains of sharks.The human trochlear nerve is derived from the basal plate of the embryonic midbrain. The words trochlea and trochlear (, ) come from Ancient Greek τροχιλέα trokhiléa, “pulley; block-and-tackle equipment”.

Vestibulocerebellar tract

The vestibulocerebellar tract is a tract in the pontine tegmentum which connects the vestibular nerve and the cerebellar cortex. It terminates in the Archicerebellum.

Central nervous system
Peripheral nervous system
Anatomy of the medulla
Grey matter
White matter
Surface
Grey
Anatomy of the pons
Dorsal/
(tegmentum)
Ventral/
(base)
Other grey: Raphe/
reticular
Anatomy of the midbrain
Tectum
(Dorsal)
Peduncle
(Ventral)

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