Jlpascual Brainstem Version 2

THE BRAINSTEM

J. Leonard Pascual MD FPNA Associate Professor, Department of Anatomy, College of Medicine, UP Manila Department of Neurosciences, Philippine General Hospital

OBJECTIVES FORM: identify the different structures in the brainstem External anatomy Subdivisions (diencephalon, midbrain, pons, medulla) Fissures and sulci Cranial nerves Peduncles Relationships to surrounding structures and cisterns

Cross-sectional anatomy Subdivisions (tectum, tegmentum) Grey matter (cranial nerve nuclei, other nuclei) White matter (fiber tracts)

FUNCTION: know the significance of each structure of the brainstem in the normal human being

Neuroanatomy at a Glance

Neuroanatomy at a Glance

Neuroanatomy at a Glance

The diencephalon is actually the most rostral end of the brainstem

Subdivisions of the Brainstem Diencephalon Midbrain Pons Medulla

Hypothalamus

Infundibulum

Mammillary body

Internal capsule

Internal capsule Basal ganglia

Internal capsule Basal ganglia Optic nerve

Internal capsule Basal ganglia Optic nerve Optic chiasm

Internal capsule Basal ganglia Optic nerve Optic chiasm Optic tract

Mammillary body

Hypothalamus

Third ventricle

Putamen

Putamen Nucleus accumbens

Anterior limb, internal capsule Putamen Nucleus accumbens

Posterior limb, internal capsule Anterior limb, internal capsule Putamen Nucleus accumbens

Hypothalamus

Thalamus

Pineal body

Habenula

Third ventricle

Internal capsule

Internal capsule Caudate nucleus

Internal capsule Putamen

Caudate nucleus

Third ventricle

Thalamus

Subthalamus

Infundibulum

Hypothalamus

Anterior commissure

Posterior commissure

Third ventricle

Mammillary body

Thalamus

Thalamus

Hypothalamus

Third ventricle

Interthalamic adhesion

Thalamus

The thalami are paired symmetrical bulb-shaped masses obliquely and lateral to the 3rd ventricle

Thalamus

The thalami are paired symmetrical bulb-shaped masses located obliquely and lateral to the 3rd ventricle

Thalamus

Lies medial to the posterior limb of the internal capsule

Thalamus

Between 70-80% of humans will have an interthalamic adhesion (massa intermedia) connecting both thalami

Neuroanatomy at a Glance

Neuroanatomy at a Glance

Neuroanatomy at a Glance

Subdivisions of the Brainstem Diencephalon Midbrain Pons Medulla

Subdivisions of the Brainstem Diencephalon Midbrain Pons Medulla

Subdivisions of the Brainstem Diencephalon Midbrain Pons Medulla

Subdivisions of the Brainstem (lateral view)

Subdivisions of the Brainstem (dorsal view)

Subdivisions of the Brainstem (ventral view)

Midbrain (cerebral peduncles)

Pons (basis pontis)

Medulla oblongata

Interpeduncular fossa

Cerebellopontine angle

Pontomedullary sulcus

Anterior median sulcus

Anterolateral sulcus

Pyramid

Olive

Pontomedullary sulcus

Anterior median sulcus

Anteriorolateral sulcus

Posterolateral sulcus

Pyramid

Pyramid

CP angle

Medulla

Pons

Midbrain

Thalamus

Posterior commissure

Cerebral peduncle

Superior cerebellar peduncle

Superior colliculus

Inferior colliculus

Middle cerebellar peduncle

Middle cerebellar peduncle

Pons

Latin for “bridge” (ventral pons appears like a bridge between cerebellar hemispheres) Cerebellar peduncles Superior cerebellar peduncle Middle cerebellar peduncle

(brachium conjunctivum) (brachium pontis)

Floor of the 4th ventricle

*

Obex

Open medulla

*

Obex Closed medulla

Open medulla

*

Obex Closed medulla

Inferior cerebellar peduncle

*

The Cranial Nerves

Olfactory nerve

Optic nerve, chiasm, and tract

Interpeduncular fossa

Midbrain

The oculomotor nerve exits from the ventral surface of the midbrain into the space between the two cerebral peduncles (interpeduncular fossa)

Oculomotor nerve

Oculomotor nerve

Uncus

Midbrain

The trochlear nerve exits dorsally at the junction between the caudal midbrain and pons

Trochlear nerve

Neuroanatomy at a Glance

Trochlear nerve

Trochlear nerve

Parahippocampal gyrus

Pons

The trigeminal nerve enters the brainstem at mid-pons Tri – Gemini (3 twins): ophthalmic, maxillary, and mandibular nerves

Trigeminal nerve

Trigeminal nerve

Middle cerebellar peduncle

Pons

3 other cranial nerves enter / leave along groove between pons and medulla (pontomedullary sulcus)

Pons

The abducens nerve is the smallest and most medial of the 3 cranial nerves that enter / leave at the pontomedullary junction

Pons

The facial nerve is further lateral Consists of a larger medial root and a smaller sensory root (nervus intermedius)

Pons

The vestibulocochlear nerve is slightly lateral to the facial nerve Consists of a vestibular division and a more lateral cochlear division

Abducens nerve

Abducens nerve

Pontomedullary sulcus

Facial nerve

Vestibulocochlear nerve

Vagus nerve

Vagus nerve

Olive

Hypoglossal nerve

Hypoglossal nerve

Pyramid

Abducens nerve

Facial nerve

Vestibulocochlear nerve

Posterolateral sulcus

Glossopharyngeal nerve

Vagus nerve

Anterolateral sulcus

Hypoglossal nerve

Spinal accessory nerve

Spinal accessory nerve

The Brain “Stem”: Nuclei

Organizational Set-Up of the Nervous System

ROSTRAL

CAUDAL

Organizational Set-Up of the Nervous System

DORSAL

VENTRAL

Organizational Set-Up of the Nervous System

DORSAL

VENTRAL Neurons specialized for receiving information (SENSORY) from the environment and their axons are located dorsally

Organizational Set-Up of the Nervous System

DORSAL

VENTRAL Neurons specialized for receiving information (SENSORY) from the environment and their axons are located dorsally Neurons that control movements (MOTOR) are located ventrally

Organizational Set-Up of the Nervous System

Organizational Set-Up of the Nervous System

Organizational Set-Up of the Nervous System Curling of the neural tube results in rotation of structures in the telencephalon Ventral structures come to lie anteriorly (MOTOR) Dorsal structures come to lie posteriorly (SENSORY) dorsal

anterior

ventral

dorsal

posterior

anterior

posterior

ventral

Organizational Set-Up of the Nervous System The dorsal:sensory / ventral:motor orientation remains the same within the brainstem and spinal cord

dorsal

anterior

ventral

dorsal

posterior

anterior

posterior

ventral

Embryology and the Architecture of the Brainstem

4th Ventricle Somatic afferent column Sensory inputs Located dorsally and laterally

Embryology and the Architecture of the Brainstem

4th Ventricle Somatic afferent column Sensory inputs Located dorsally and laterally

Somatic efferent column Motor output for muscles Located ventrally and medially

Embryology and the Architecture of the Brainstem

4th Ventricle SENSORY Sulcus limitans MOTOR

Embryology and the Architecture of the Brainstem

Somatic afferent column 4th Ventricle

Somatic afferents Visceral afferents

Somatic efferent column Somatic efferent Visceral efferent

Unlike the spinal cord which innervates only skeletal muscles (somites), the brainstem also innervates muscles in the face derived from the branchial arches

Embryology and the Architecture of the Brainstem Somatic afferent column

4th Ventricle

Somatic afferents GSA SSA Visceral afferents GVA SVA

Somatic efferent column Somatic efferent GSE Visceral efferent GVE SVE

Additional components in cranial nerves are innervations for special functions

Embryology and the Architecture of the Brainstem Somatic afferent column Somatic afferents GSA SSA Visceral afferents GVA

Vision

Somatic efferent column

Hearing and balance

SSA: afferents to the special senses

Somatic efferent GSE Visceral efferent GVE

Embryology and the Architecture of the Brainstem Somatic afferent column

Olfaction

Taste

Somatic afferents GSA SSA Visceral afferents GVA SVA

Somatic efferent column

Choking

Somatic efferent GSE Visceral efferent GVE

SVA's are sensory nerves that develop in association with the gastrointestinal system

Embryology and the Architecture of the Brainstem Somatic afferent column

Smiling and facial movements Chewing

Somatic afferents GSA SSA Visceral afferents GVA SVA

Somatic efferent column

Swallowing and digesting

Somatic efferent GSE Visceral efferent GVE SVE

SVE's innervate muscles derived from the branchial arches (branchiomotor nerves)

Embryology and the Architecture of the Brainstem

4th Ventricle Somatic afferent column SSA GSA GVA SVA

Embryology and the Architecture of the Brainstem

4th Ventricle Somatic afferent column

Somatic efferent column GVE SVE GSE

Somatic afferent column Somatic afferents GSA SSA Visceral afferents GVA SVA

Somatic efferent column Somatic efferent GSE Visceral efferent GVE SVE

Columnar arrangement of cranial nerve nuclei

Cranial nerve fibers will proceed to / arise from cranial nerve nuclei

Cranial Nerve Nuclei in the Midbrain

III

Oculomotor nerve nuclei complex

Cranial Nerve Nuclei in the Midbrain

III

Oculomotor nerve nuclei complex Edinger-Westphal nucleus

EW

Cranial Nerve Nuclei in the Midbrain

III

IV

Oculomotor nerve nuclei complex Edinger-Westphal nucleus Trochlear nerve nucleus

EW

Cranial Nerve Nuclei in the Midbrain

III

IV

Oculomotor nerve nuclei complex Edinger-Westphal nucleus Trochlear nerve nucleus Mesencephalic nucleus of CN V

EW V

Cranial Nerve Nuclei in the Midbrain

III

EW V

IV

Oculomotor nerve nuclei complex Edinger-Westphal nucleus Trochlear nerve nucleus Mesencephalic nucleus of CN V

B M 5 34

Cranial Nerve Nuclei in the Pons

V

Motor nucleus of CN V

Cranial Nerve Nuclei in the Pons

V VI

Motor nucleus of CN V Abducens nucleus

Cranial Nerve Nuclei in the Pons

V VI VII

Motor nucleus of CN V Abducens nucleus Facial nucleus

Cranial Nerve Nuclei in the Pons

V VI VII X

Motor nucleus of CN V Abducens nucleus Facial nucleus Superior salivatory nucleus (CN X)

Cranial Nerve Nuclei in the Pons

V V VI VII X

Main sensory nucleus of CN V

Cranial Nerve Nuclei in the Pons

V V VI VII

V X

Main sensory nucleus of CN V Spinal nucleus of CN V

Cranial Nerve Nuclei in the Pons

V V VI

VII VII

V X

Main sensory nucleus of CN V Spinal nucleus of CN V Vestibular nucleus (CN VIII)

Cranial Nerve Nuclei in the Pons

V V VI

VIII VII

V X

Main sensory nucleus of CN V Spinal nucleus of CN V Vestibular nucleus (CN VIII) Cochlear nucleus (CN VIII)

VIII

Cranial Nerve Nuclei in the Pons

Motor nuclei

V V

VI

VIII VII

V X

VIII

Cranial Nerve Nuclei in the Pons

Motor nuclei

Sensory nuclei

V

V

VI

VIII VII

V X

VIII

Cranial Nerve Nuclei in the Rostral Medulla

XII

Hypoglossal nucleus

Cranial Nerve Nuclei in the Rostral Medulla IX

XII

X

Hypoglossal nucleus Ambiguous nucleus (CN's IX and X)

Cranial Nerve Nuclei in the Rostral Medulla IX IX

XII

X

Hypoglossal nucleus Ambiguous nucleus (CN's IX and X) Inferior salivatory nucleus (CN IX)

Cranial Nerve Nuclei in the Rostral Medulla IX IX X XII

X

Hypoglossal nucleus Ambiguous nucleus (CN's IX and X) Inferior salivatory nucleus (CN IX) Dorsal motor nucleus of CN X

Cranial Nerve Nuclei in the Rostral Medulla IX IX X X XII

Solitary nucleus (CN X)

X

Cranial Nerve Nuclei in the Rostral Medulla IX IX X X XII

X

Solitary nucleus (CN X) Continuation of Spinal nucleus of CN V

V

Cranial Nerve Nuclei in the Rostral Medulla IX VIII

IX X X XII

X

Solitary nucleus (CN X) Continuation of Spinal nucleus of CN V Continuation of Vestibular nucleus

V

Cranial Nerve Nuclei in the Caudal Medulla

XI

Accessory nucleus

Cranial Nerve Nuclei in the Caudal Medulla

V XI

Accessory nucleus Spinal nucleus of CN V (continuation)

The Brain “Stem”: Long Tracts

Organizational Set-Up of the Nervous System

DESCENDING

ASCENDING

Organizational Set-Up of the Nervous System

DECUSSATION

Organizational Set-Up of the Nervous System

LAMINATION

The Brainstem and its contents Grey matter on the inside White matter on the outside

The Brainstem and its contents Grey matter on the inside Cranial nerve nuclei Reticular formation Pontine nuclei

White matter on the outside

The Brainstem and its contents Grey matter on the inside Cranial nerve nuclei Reticular formation Pontine nuclei

White matter on the outside Ascending Descending Mixed ascending and descending

The Brainstem and its contents Grey matter on the inside Cranial nerve nuclei Reticular formation Pontine nuclei

White matter on the outside Ascending Reticular activating system Spinothalamic tract Spinocerebellar tract Medial lemniscal – dorsal column pathway Auditory pathway Gustatory pathway

Descending Mixed ascending and descending

ASCENDING RETICULAR ACTIVATING SYSTEM

ASCENDING RETICULAR ACTIVATING SYSTEM Portion of the reticular formation concerned with arousal Ensures that thalamocortical impulses are fired to “awaken” the cerebral hemispheres Damage leads to coma Affected by psychotropic drugs and anesthetics Overactivity (imbalance of norepinephrine) has been linked to ADHD (attention deficit hyperactivity disorder)

The Brainstem and its contents Grey matter on the inside Cranial nerve nuclei Reticular formation Pontine nuclei

White matter on the outside Ascending Descending Corticospinal tract Corticobulbar tract

Mixed ascending and descending

The Brainstem and its contents Grey matter on the inside Cranial nerve nuclei Reticular formation Pontine nuclei

White matter on the outside Ascending Descending Mixed ascending and descending Medial longitudinal fasciculus

Corticospinal tract

Spinothalamic tract

Medial longitudinal fasciculus

Cross-sectional Anatomy of the Brainstem

Organizational Set-Up of the Nervous System

EXTRA-AXIAL

INTRA-AXIAL

Organizational Set-Up of the Nervous System

EXTRAMEDULLARY

MEDULLARY

Architecture of the Brainstem General morphology of the brainstem: Tectum: roof of ventricular cavity Tegmentum: floor of ventricular cavity: Dorsolateral: sensory fibers / nuclei Ventromedial: motor cranial nuclei In between: reticular formation

Base: mainly motor fibers

Neuroanatomy at a Glance

Neuroanatomy at a Glance

Cerebral aqueduct

Neuroanatomy at a Glance

Cerebral peduncle

Midbrain

Large cerebral peduncles on its anterior surface

Neuroanatomy at a Glance

Substantia nigra

Neuroanatomy at a Glance

Neuroanatomy at a Glance

Neuroanatomy at a Glance

Thalamus

Neuroanatomy at a Glance

3rd ventricle Thalamus

Neuroanatomy at a Glance

Red nucleus

Neuroanatomy at a Glance

Pinkish color is attributed to iron content Red nucleus

Neuroanatomy at a Glance

Pinkish color is attributed to iron content Red nucleus

Mainly responsible for movement in animals without corticospinal tracts (controls large muscle groups)

Neuroanatomy at a Glance

Red nucleus

Crawling of babies and arm swing is controlled by this nucleus

Midbrain (Internal Structure)

Rostral midbrain: contains the superior colliculi Extends from the intercollicular groove to the posterior commissure

Rostral Midbrain

Superior colliculus: paired bumps in the midbrain tectum Its neurons respond to visual, auditory, and somatosensory stimuli Together with the inferior colliculus = corpora quadrigemina

Rostral Midbrain

Superior colliculus: involved in saccades (fast eye movements) Helps orient the head and the eyes towards something seen or heard

Rostral Midbrain

Substantia nigra: pale on myelin-stained brain tissue, dark on unstained brain tissue produces dopamine Receives and sends fibers to the putamen (striatum) and caudate nucleus

Rostral Midbrain

Ventral tegmental area of the midbrain

Ventral tegmental area: lies close to the substantia nigra and red nucleus Provides dopaminergic innervation to the frontal cortex and limbic system Activities that elicit pleasure activates this area (including psychostimulants like cocaine) Reward / addiction Fear / avoidance behavior

Rostral Midbrain

Oculomotor nucleus: in the floor of the cerebral aqueduct Actually a complex of 2 groups of smaller subnuclei that innervate individual muscles

Rostral Midbrain

Oculomotor nuclei complex: the subnucleus for the levator palpebrae superioris (upper eyelid) is shared by both oculomotor nuclei

Rostral Midbrain

SR

Oculomotor nuclei complex: the nucleus for the superior rectus (SR) muscle travels in the contralateral oculomotor nerve (similar to CN IV) to innervate the contralateral muscle.

Rostral Midbrain

MR

IO

IR

Oculomotor nuclei complex: the nucleus for the medial rectus (MR), inferior oblique (IO), and inferior rectus (IR) muscles travel in the ipsilateral CN III to the eyeball

Rostral Midbrain

Edinger-Westphal nucleus: Lies in close proximity to CN III nucleus Sends GVE's to the ipsilateral ciliary ganglion Ciliary ganglion innervates the sphincter pupillae (iris) and ciliary muscle

Midbrain (Internal Structure)

Caudal midbrain: contains the inferior colliculi Extends from where the trochlear nerve emerges to the intercollicular groove

Caudal midbrain Cerebral aqueduct Periaqueductal gray

The 4th ventricle has narrowed into the cerebral aqueduct The periaqueductal gray matter encircles the aqueduct

Caudal midbrain Periaqueductal gray: Role in defensive behavior in animals (freezing, jumping, rapid heart beat, high blood pressure) Role in female copulatory behavior (lordosis behavior) via pathway from the hypothalamus Excited by endorphins and by opiate analgesics

Caudal midbrain

Inferior colliculus

The inferior colliculus: principal nucleus of the auditory pathway in the midbrain Relays auditory input from the contralateral ear to the thalamus (medial geniculate body)

Caudal midbrain

MLF

The MLF continues its course in the midline below the floor of the cerebral aqueduct

Caudal midbrain

Trochlear nucleus

Caudal midbrain Superior medullary velum

Trochlear nucleus: fibers decussate in the superior medullary velum of the tectum and exit dorsally.

Caudal midbrain

Trochlear nucleus: innervates the contralateral superior oblique muscle of the eyeball

Neuroanatomy at a Glance

Pons (Internal Structure)

Rostral pons: from the point of attachment of the trigeminal nerve to the beginning of the cerebral aqueduct / at the point of emergence of the trochlear nerve

Rostral Pons

The median longitudinal fasciculus (MLF) lies near the midline beneath the 4th ventricle

Rostral Pons

The superior cerebellar peduncle appears in the lateral walls of the 4th ventricle Major outflow from the cerebellum (efferent) to the thalamus

Rostral Pons

Locus ceruleus: contains norepinephrine, innervates virtually the entire CNS, from spinal cord to cerebral cortex Increased firing rate of neurons during arousal, decreases with drowsiness, and abolished during sleep Receives afferents from hypothalamus, cingulate cortex, and amygdala Activated during stress, neurons seen to be depleted in posttraumatic stress disorder patients

Pons (Internal Structure)

Caudal pons: bottom half of the pons from the point of attachment of CN V to the lateral wall of the 4th ventricle

Caudal Pons

Caudal pons: bottom half of the pons from the point of attachment of CN V to the lateral wall of the 4th ventricle

Caudal Pons

The pyramidal tract is broken up by pontine nuclei and their decussating fibers, which form the middle cerebellar peduncle

Cranial Nerve Nuclei in the Pons

V VI VII X

Motor nucleus of CN V Abducens nucleus Facial nucleus Superior salivatory nucleus (CN X)

Cranial Nerve Nuclei in the Pons

V V VI

VIII VII

V X

Main sensory nucleus of CN V Spinal nucleus of CN V Vestibular nucleus (CN VIII) Cochlear nucleus (CN VIII)

VIII

Caudal Pons

CN VI

CN VII

The facial colliculus is formed by fascicles from the facial nucleus which loop around the abducens nucleus which lies on the floor of the 4th ventricle

Caudal Pons

CN VI

CN VII

The facial colliculus is formed by fascicles from the facial nucleus which loop around the abducens nucleus which lies on the floor of the 4th ventricle

Caudal Pons

The abducens innervates the lateral rectus muscle of the eyeball (GSE) Due to the long distance it travels en route to the eyeball, it is most frequently compressed / stretched by space-occupying lesions in the cranial cavity Usually stretched / compressed against the clivus

Caudal Pons

The abducens lies in close proximity to the parapontine reticular formation (PPRF) which is the horizontal gaze center in the pons

Caudal Pons

The MLF is nearby (yokes / synchronizes the movements of the eyeballs) Connects the abducens to the contralateral oculomotor nucleus in the midbrain

Neuroanatomy at a Glance

Neuroanatomy at a Glance

Neuroanatomy at a Glance

Neuroanatomy at a Glance

Medulla (Internal Structure)

Rostral medulla: from the obex to the lateral recess where the inferior cerebellar peduncle enters the cerebellum

Rostral Medulla

The rostral medulla no longer looks like the spinal cord due to the presence of the 4th ventricle dorsally

Rostral Medulla

The inferior olivary nucleus is a prominent feature of the rostral medulla, forms the swelling called the olive. Fibers from each nucleus arch across the midline to enter the contralateral inferior cerebellar peduncle

Cranial Nerve Nuclei in the Rostral Medulla IX IX X XII

X

Hypoglossal nucleus Ambiguous nucleus (CN's IX and X) Inferior salivatory nucleus (CN IX) Dorsal motor nucleus of CN X

Cranial Nerve Nuclei in the Rostral Medulla IX VIII

IX X X XII

X

Solitary nucleus (CN X) Continuation of Spinal nucleus of CN V Continuation of Vestibular nucleus

V

Rostral Medulla

Fascicles of the hypoglossal nerve exit between the pyramid and the inferior olivary nucleus

Rostral Medulla

Fascicles of the hypoglossal nerve exit between the pyramid and the inferior olivary nucleus Innervates the muscles of the tongue (general visceral efferent)

Rostral Medulla

A pair of medial longitudinal fasciculi (MLF) lie beneath the floor of the 4th ventricle posterior to the medial lemniscus, can be traced all the way to the midbrain involved in yoking eye movements as well as vestibular functions

Rostral Medulla

The dorsal motor nucleus of the vagus lies in the floor of the 4th ventricle, dorsolateral to the hypoglossal nucleus Main parasympathetic nucleus Sends GVE to the thoracic and abdominal viscera

Rostral Medulla

The solitary tract and nucleus of the vagus lies in the floor of the 4th ventricle, lateral to the dorsal nucleus of X Taste impulses from the CN VII, IX, X, and XI (gustatory / rostral half of the solitary nucleus)

Rostral Medulla

The solitary tract and nucleus of the vagus: The caudal half of the solitary nucleus receives cranial afferent inputs related to cardiovascular, respiratory, and gastrointestinal receptors

Rostral Medulla

The solitary tract and nucleus of the vagus: Mediates the cough reflex, baroceptor reflex, gag reflex, baroceptor and chemoreceptor reflexes, among others

Rostral Medulla

The solitary tract and nucleus of the vagus: Projects efferent output to the hypothalamus, cingulate gyrus, and other brainstem nuclei (heart beat, breathing)

Rostral Medulla

Nucleus ambiguus

The ambiguous nucleus: Cannot be distinguished in myelin stained brain tissue Located dorsal to the inferior olivary nucleus, within the ventrolateral tegmentum, embedded within the reticular formation

Rostral Medulla

The ambiguous nucleus: Gives rise to SVE's that travel within the glossopharyngeal nerve to innervate the stylopharyngeus muscle, and within the vagus nerve to innervate the rest of the pharyngeal muscles (swallowing)

Rostral Medulla

The vestibular and cochlear nuclei are found dorsolaterally

The Pontomedullary Junction

The vestibular and cochlear nuclei occupy the ventricular floor at the pontomedullary junction

Neuroanatomy at a Glance

Medulla (Ventral aspect)

Pyramids contain the descending fibers of the corticospinal tract Crossing over of the fibers to the other side (decussation)

Medulla (Dorsal aspect)

The dorsal columns of the spinal cord continue into the medulla The cuneate fasciculus ends in a swelling called the cuneate tubercle (overlying the nucleus cuneatus)

Medulla (Dorsal aspect)

The dorsal columns of the spinal cord continue into the medulla The fasciculus gracilis near the midline ends in a similar small bump called the gracile tubercle (or clava) overlying the nucleus gracilis.

Medulla (Internal Structure)

Caudal medulla: from pyramidal decussation to the obex Similar appearance to the spinal cord

Caudal Medulla

The pyramids of the corticospinal tract lie most anteriorly Fibers will decussate and travel to the contralateral anterior horn of the spinal cord

External Relationships of the Brainstem

External Anatomical Relationships of the Brainstem

The ventral brainstem is bathed in cerebrospinal fluid within the subarachnoid space Contains blood vessels and cranial nerves

External Anatomical Relationships of the Brainstem

Interpeduncular cistern = the space between (and around) the two cerebral peduncles in the midbrain

External Anatomical Relationships of the Brainstem

Interpeduncular cistern = the space between (and around) the two cerebral peduncles in the midbrain

External Anatomical Relationships of the Brainstem

The basilar artery runs across the midline of the pons within the pontine cistern

External Anatomical Relationships of the Brainstem

Medullary cistern

External Anatomical Relationships of the Brainstem

The cerebral peduncles of the midbrain must pass through the incisura of the tentorium cerebelli

External Anatomical Relationships of the Brainstem

Clivus is a sloping shallow depression of the sphenoid bone of the base of the skull which supports the pons

External Anatomical Relationships of the Brainstem

The sphenoid sinus is one of the paranasal sinuses that lies beneath the sella turcica (where the pituitary gland sits) and anterior to the clivus

External Anatomical Relationships of the Brainstem

CN V CN VII

CN VIII

Pontocerebellar cistern over the cerebellopontine angle The facial and vestibulocochlear nerves as well as the trigeminal nerve lie close to the cerebellum

External Anatomical Relationships of the Brainstem

Foramen magnum is the largest opening of the skull through which the medulla passes to become the spinal cord

Pons (Dorsal Aspect)

Cerebellar peduncles The superior cerebellar peduncles form the roof of diamondshaped cavity of the 4th ventricle