MODULE 15B - [Anatomy 3.0] BRAINSTEM ONLY (NO CN)

The brainstem, together with the cerebellum, are structures that occupy the _____

posterior cranial fossa

The brainstem is located _____ to the cerebellum

anterior

The Brainstem is continuous with the diencephalon _____, and the spinal cord ____

• continuous to the diencephalon superiorly

• continuous to the spinal cord inferiorly

Enumerate the segments of the Brainstem (SUPERIOR TO INFERIOR)

• Midbrain

• Pons

• Medulla Oblongata

The brainstem receives sensory information coming from the cranial structures and through the _____ controls the muscles of the ____

cranial nerves; head

The function of the brainstem is comparable to what the spinal cord is doing in relation to the _____ and _____.

trunk and extremities

• Embedded in the brain stem

• Give rise to CN III - CN XII

CRANIAL NUCLEI

• Various divisions of the brainstem subserve specific functions that _____ and ______.

control blood pressure and respiratory regulatory mechanisms

Long fiber tracts that enter and exit the brain via the brainstem

ASCENDING AND DESCENDING PATHWAYS

Carry sensory information coming from the trunk and extremities that will be processed in the cerebrum, where we appreciate sensations like pain, light touch, pressure

Ascending Pathway

Carry motor fibers that control the skeletal muscles of the trunk and extremities, thereby allowing an individual to move

Descending Pathway

In the sagittal section of the brainstem, cavitation can be appreciated on its posterior region. This is the part of the ventricular system that will contain ____.

cerebrospinal fluid

• The cavity traversing the midbrain

• becomes continuous with the triangular cavity of the 4th ventricle, which can be appreciated at the levels of pons and upper medulla.

Cerebral Aqueduct of Sylvius

• The connection of the brainstem to the cerebellum

  posteriorly

  • It serves as the pathway through which the cerebellum connects to other parts of the central nervous system, such as the brain and spinal cord

• Since there are 3 segments of the brain stem, therefore, there are also 3 separate cerebellar peduncles

CEREBELLAR PEDUNCLES

Enumerate the 3 separate cerebellar peduncles and their other terms:

• Superior Cerebellar Peduncles - Brachium Conjunctivum

• Middle Cerebellar Peduncles - Brachium Pontis

• Inferior Cerebellar Peduncles - Restiform Body

In the actual cadaveric specimen, the adult brainstem is around ____ in length and its diameter is about the size of a pinky finger.

2.5 centimeters

Signs and symptoms that points to brainstem affectation unless proven otherwise

• affectation of motor and sensory of the head

• involvement of the cranial nerves

• alteration of the sensorium

• association with cardiorespiratory abnormalities

• long tract signs

external structures of the Midbrain

• ANTERIOR SURFACE OF THE MIDBRAIN

• POSTERIOR SURFACE OF THE MIDBRAIN

The Anterior surface of the Midbrain contains the

• Crus cerebri of cerebral peduncles

• Interpeduncular fossa

Two pillar-like structures that emerge from the pons

Crus cerebri of cerebral peduncles

• A hollow groove or depression in between the two

  crus cerebri

Interpeduncular fossa

From the interpeduncular fossa, this is where the _____ can be appreciated.

oculomotor nerve (CN III) can be appreciated in the interpeduncular fossa

Enumerate the structures in the posterior surface of the midbrain

• Corpora quadrigemina

• superior colliculi

• inferior colliculi

Two pairs of swelling on the posterior side of the midbrain

Corpora quadrigemina or Tectum

superior paired swellings in the posterior surface of the midbrain

superior colliculi

inferior paired swellings in the posterior surface of the midbrain

inferior colliculi

Just inferior to the inferior colliculi in the midline is where the _____ will emerge from the brainstem, coursing its way to the lateral side of the crus cerebri.

trochlear nerve (CN IV) will emerge inferior to the inferior colliculi

Enumerate the two levels of the midbrain internal stucture

• Level of the superior colliculus

• Level of the inferior colliculus

In the Level of Superior Colliculus an imaginary line can be placed in the middle to designate the midline, dividing the midbrain into left and right side

• Posteriorly is the ______

• Anteriorly is the _____

• Posteriorly is the superior colliculus

• Posteriorly is the superior colliculus

Colliculus for visual reflex

Superior colliculus

Colliculus for auditory pathway

Inferior colliculus

What are the structures found in the level of the superior colliculus of the midbrain

• Substantia Nigra

• Cerebral Aqueduct

• Tectum

• Motor Nucleus of CN III and Edinger-Westphal Nucleus

• Pretectal Nucleus

• Medial Longitudinal Fasciculus

• Mesencephalic Nucleus of CN V

• Ascending Tracts

• Ascending Tracts

• Red Nucleus

• A dark pigmented region that plays an important role in movement and reward function.

• Part of the Superior Colliculus Level

Substantia Nigra

• In the midline of the midbrain

  • This is surrounded by an area called the periaqueductal grey mater

• Part of the Superior Colliculus Level

cavity of the cerebral aqueduct of Sylvius

• In the area of the periaqueductal grey mater, lies the

  motor nucleus of cranial nerve III and its accessory

  nucleus, called the _____

• This accessory nucleus also carries the parasympathetic function of cranial nerve III

Edinger–Westphal nucleus

Midbrain area posterior to the periaqueductal grey mater and also contains the colliculi.

Tectum

The Tectum contains the nucleus of the ______, which is important in the control of visual reflexes

superior colliculus

The presence of substantia nigra further subdivides the midbrain into the _____ anteriorly and the rest of the area into the _____

• crus cerebri (anteriorly)

• tegmentum (rest of the area)

Fibers of the motor nucleus of the oculomotor and Edinger-Westphal nucleus will give rise to CN III that exits at the ____

interpeduncular fossa

• Controls the Edinger-Westphal on both sides

• Plays a role in the pupillary light reflex reaction

Pretectal Nucleus

• Bundle of white mater in the middle region of the tegmentum

• Links the three cranial nerves that control the eyeball

  ○ CN III - Oculomotor

  ○ CN IV - Trochlear

  ○ CN VI - Abducens

Medial Longitudinal Fasciculus

• Present in the midbrain

• One of the sensory nuclei of the trigeminal nerve

Mesencephalic Nucleus of CN V

• Long tracts will pass through the brainstem in order to connect the spinal cord to the cerebrum and vice versa.

• These fibers originating from the spinal cord will form a bundle of white mater on the lateral side of the tegmentum.

Ascending Tracts

What are the ascending tracts that originate from the spinal cord and forms a bundle of white mater on the lateral side of the tegmentun

• Spinothalamic Tract

• Medial Lemniscus.

• Descending motor pathways are organized in the

  crus cerebri

Descending Tracts

Enumerate the descending tracts that organize in the crus cerebri

• corticospinal tract

• corticobulbar tract

• are pale pink structures present in the area which is usually involved in motor coordination.

• The fibers of CN III traverses this structure

  • Patients with affectation of the red nucleus may also involve the third cranial nerve.

Red Nucleus

What are the structures found at the level of the inferior colliculus of the midbrain

• Trochlear Nerve (CN IV)

• Motor of the Nucleus of CN IV

• CN III is absent in this level

• Sometimes, the red nucleus can no longer be appreciated in the lower level

• The inferior colliculus is present at this level, rather than the superior colliculus

• These nuclei will be part of the auditory pathway

• Main highlight: presence of the motor nucleus of CN IV

Inferior colliculus of the midbrain

• The longest cranial nerve intracranially

• The ONLY cranial nerve that exits at the posterior side of the brainstem

• The ONLY crossed cranial nerve

• Origin: motor nucleus

• Innervates: superior oblique muscles (one of the extraocular muscles of the eye)

• Arises from: behind the midbrain

• Exits: posteriorly and prior to its exit the fibers crosses the midline

Trochlear Nerve (CN IV) (Midbrain)

Enumerate the external structures of Pons

• PONTINEPROTUBERANCE

• BASILAR GROOVE

• CN V or TRIGEMINAL NERVE

• PONTO-MEDULLARY JUNCTION

• Large bulging structures at the anterior brainstem

• Identifying feature of the pons

PONTINEPROTUBERANCE

• At the middle of the pontine protuberance

• Central depression/groove

• Occupied by the basilar artery, which is one of the main arteries of the brainstem

BASILAR GROOVE

• Found at the lateral sides of the pontine protuberance

CN V or TRIGEMINAL NERVE (Pons)

• Junction between the pons and medulla

• A sulcus where several cranial nerves emerge from the brainstem:

  • Abducens nerve (CN VI)

  • Facial Nerve (CN VII)

  • Vestibulocochlear Nerve (CN VIII)

PONTO-MEDULLARY JUNCTION

Enumerate the structures found ant the posterior surface of Pons

• Upper Half of the floor of the 4th Ventricle

• Facial colliculus

• Forms the upper half of the floor of the 4th ventricle.

  • Triangular in shape

  • The 4th ventricle cavity can be clearly seen if the cerebellum is removed.

POSTERIOR SURFACE OF THE PONS

• Prominent swelling

• Produced by the root of the Facial nerve (CN VII) winding around the nucleus of the Abducens nerve (CN VI)

Facial colliculus

To study the internal structure of Pons we would need to transect at the level of ____ and ____

• level of the Trigeminal nerve (CN V)

• level of the Facial colliculus

Enumerate the two (2) regions of the internal surface of the Pons

• Basis ponti (anteriorly)

• Tegmentum (posteriorly)

Region that is the continuation of the crus cerebri (found in the midbrain) in the internal structure of the Pons

Basis Ponti

Enumerate the structures found in the Basis Ponti

• Pontine Nuclei

• Pontocerebellar /Pontine fibers

• Middle Cerebellar Peduncle

• Corticospinal and Corticobulbar Tract

• Scattered at the middle of the basis ponti

Pontine Nuclei

• Horizontally arranged

• Arise from the pontine nuclei

• Externally, horizontally arranged fibers can be appreciated as it courses laterally and forming the middle cerebellar peduncle

Pontocerebellar/Pontine fibers

• Input pathway that connects the pons’ pontocerebellar/pontine fibers to the cerebellum

Middle Cerebellar Peduncle

• Interspersed within the basis ponti are bundles of descending motor tracts coming from the crus cerebri of the midbrain

• Organized in crus cerebri, and continues to descend in the pons, inserting in bundles of fascicles among fibers of pontine nucleus until it reaches the medulla oblongata

Corticospinal and Corticobulbar Tract

• Continuation of the tegmentum of the midbrain

• Contains ascending pathways that originated from the

  spinal cord

• This contains the fibers of:

  • Medial lemniscus

  • Spinothalamic tract

Tegmentum

Enumerate the Internal structures of the pons in the tegmentum at the level of CN V

• Medial Lemniscus and Spinothalamic Tract

• Medial Longitudinal Fasciculus

• Motor Nucleus and Main Sensory Nucleus of CN V

Located in the most anterior part of the tegmentum

Medial Lemniscus and Spinothalamic Tract

Organized on the medial region of the tegmentum

Medial Longitudinal Fasciculus

Main motor and sensory nucleus of CN V

• Give rise to the Trigeminal Nerve (CN V)

Motor Nucleus and Main Sensory Nucleus of CN V

Represented by a bump at the posterior wall of pons

Facial colliculus

Enumerate the strucutres found at the level of Facial Colliculus

• Spinal Nucleus of Trigeminal Nerve (CN V)

• Motor Nucleus of Abducens Nerve (CN VI)

• Motor Nucleus of Facial Nerve (CN VII)

• Located at the lower regions of the pons and will extend until the medulla oblongata

Spinal Nucleus of Trigeminal Nerve (CN V)

• Main highlight of this level

• Will give rise to the Abducens Nerve (CN VI)

Motor Nucleus of Abducens Nerve (CN VI)

• Will give rise to the Facial Nerve (CN VII)

  • Fibers of Facial nerve winds around motor nucleus of abducens, which creates a bump or swelling at posterior wall of pons (Facial colliculus)

Motor Nucleus of Facial Nerve (CN VII)

Enumerate the structures associated with motor nucleus of CN Vii

• SUPERIOR SALIVATORY NUCLEUS

• NUCLEUS TRACTUS SOLITARIUS

• Parasympathetic nucleus of Facial Nerve (CN VII)

• Responsible for controlling the secretion of certain salivary glands

SUPERIOR SALIVATORY NUCLEUS

• Sensory nucleus of the Facial Nerve (CN VII)

• Relay station for the taste sensation, originating from the taste receptors of the tongue and the pharyngeal mucosa

NUCLEUS TRACTUS SOLITARIUS

• Last segment and most inferior region of the brainstem

• Is divided into two segments

  • Open Medulla

  • Closed Medulla

MEDULLA OBLONGATA

Upper half of the medulla that coincides with the lower region of the 4th ventricle.

Open Medulla

• Lower half of medulla; the central canal can be seen in its cross section

Closed Medulla

From the midline of the Medulla, the first bump seen is ____

Pyramid

In the Medulla, lateral to the pyramid is another swelling which is called

Olive

Enumerate the cranial nerves that emerges from the anterior surface of the medulla

• CN IX Glossopharyngeal Nerve

• CN X Vagus Nerve

• CN XI Spinal Accessory Nerve

• CN XII Hypoglossal Nerve

In the posterior of medulla, a series of bumps and swellings can also be appreciated from the Midline

Gracile Tubercle

In the posterior of medulla, a series of bumps and swellings can also be appreciated Lateral to the Gracile

Cuneate Tubercle

Enumerate the division of the Dorsal column

• Fasciculus gracilis

• Fasciculus cuneatus

Matches with the gracile tubercle in the medulla

Fasciculus gracilis (medial)

Enumerate the levels at which the medulla is divided

• Level of the olives

• The great sensory decussation

• The great motor decussation (inferiormost level)

Attaches the medulla to the cerebellum.

Inferior Cerebellar Peduncle

Enumerate the structures at the level of Olives

• Inferior Olivary Nucleus

• Motor Nucleus of CN XII/Hypoglossal

• Vestibular Nucleus and Cochlear Nucleus

• Dorsal Motor Nucleus

• Nucleus Tractus Solitarius

• Nucleus Ambiguus

• Vagus Nerve

• Spinal Trigeminal Nucleus

• Medial Longitudinal Fasciculus

• Medial Lemniscus and Lateral Spinothalamic Tract

• Corticospinal Tract/Pyramidal Tract

• Seen in the Internal Medulla at the levels of Olives

• Most prominent with a crumpled U-shape nucleus.

  • Forms a projected swelling in the lateral surface of the medulla.

  • Coordinates movements and is associated with learning

Inferior Olivary Nucleus

• Seen in the Internal Medulla at the levels of Olives

• Located as the posterior wall of the medulla.

  Give rise to Hypoglossal nerve CN (XII).

Motor Nucleus of CN XII/Hypoglossal

• Seen in the Internal Medulla at the levels of Olives

• Near the area of cerebellar peduncle; made up of 4 individual nuclei.

• Give rise to the vestibulocochlear nerve CN (VIII); will exit at the anterolateral pontomedullary junction.

Vestibular Nucleus and Cochlear Nucleus

• Seen in the Internal Medulla at the levels of Olives

• Adjacent to the hypoglossal nucleus

• The parasympathetic component of the vagus nerve.

Dorsal Motor Nucleus

• Seen in the Internal Medulla at the levels of Olives

• Process taste sensation coming from the tongue and oropharynx.

Nucleus Tractus Solitarius

• Seen in the Internal Medulla at the levels of Olives

• Shared by several cranial nerves.

• The motor nucleus that supplies the muscles of deglutition.

Nucleus Ambiguus

• Seen in the Internal Medulla at the levels of Olives

• Contributes nerve fibers for the formation of CN X.

  • Dorsal Motor Nucleus

  • Nucleus Tractus Solitarius

  • Nucleus Ambiguus

Vagus Nerve (Medulla)

• Seen in the Internal Medulla at the levels of Olives

• Spinal Trigeminal Nucleus

Picture of Spinal Trigeminal Nucleus