CNS4
Introduction to the brainstem
Made up of
o Medulla oblongata
o Pons
o Midbrain
Connect spinal cord with forebrain
Function
o Serves as conduit for descending and ascending tracts
o Contains important reflex centers associated with the control of respiration and the
cardiovascular system and with the control of consciousness
o Contains the important nuclei of cranial nerves III-XII
Gross appearance of the medulla oblongata
Connects pons superiorly with spinal cord inferiorly
Junction of medulla and spinal cord
o Origin of the anterior and posterior cervical nerve
o Foramen magnum
Contain central canal of spinal cord in the lower half
o Expand into the 4th ventricle in the upper half
Anterior median fissure
o Located on the anterior surface of medulla
o Continues with the anterior median fissure of the spinal cord
Pyramids
o Swelling on each side of anterior median fissure
o Composed of bundles of nerve fibers, corticospinal fibers
Originate in the precentral gyrus of the cerebral cortex.
Decussation of the pyramids
o Site where majority of the descending fibers cross over to the opposite side
Anterior external arcuate fibers
o Nerve fibers that emerge from the anterior median fissure above the decussation
o Pass laterally to enter the cerebellum
Olives
o Located posterolaterally to the pyramids
o Produced by underlying inferior olivary nuclei
Groove between pyramid and olive
o Rootlets of the hypoglossal nerve emerge
Inferior cerebella peduncles
o Located posterior to olives
o Connect medulla to cerebellum
Groove between olive and inferior cerebellar peduncle
o Roots of the glossopharyngeal and vagus nerves and the cranial roots of the accessory
nerve emerge
Floor of 4th ventricle
o Formed by the posterior surface of the superior half of the medulla (lower part)
Posterior median sulcus
o Located on the posterior surface of the lower half of medulla
Gracile tubercle
o Located on each side of posterior median sulcus
o Produced by underlying gracile nucleus
Cuneate tubercle
o Located lateral to gracile tubercle
o Produced by underlying cuneate nucleus
Gross appearance of the pons
Anterior to the cerebellum
Connects medulla oblongata to midbrain
Form middle cerebellar peduncle
Basilar groove
o Houses basilar artery
Trigeminal nerve
o Emerge from the anterolateral side of the pons
o Consist of small motor root and a large sensory root
Groove between pons and medulla oblongata
o Abducent nerve
o Facial nerve
o Vestibulocochlear nerve
Posterior surface
o Form the upper part of the floor of the 4th ventricle
o Limited laterally by superior cerebellar peduncles
o Divided by median sulcus
o Medial eminence
Lateral to median sulcus
Limited laterally by sulcus limitans
Substantia ferruginea: form the floor of the superior end of sulcus
limitans
Area vestibuli: lateral to sulcus limitans
o Underlying vestibular nuclei
Inferior end expand to facial colliculus
Produced by facial nerve winding around the nucleus of the abducent nerve
Gross appearance of the midbrain
Connect pons and cerebellum with forebrain
Traversed by cerebral aqueduct
Colliculi (Corpora quadrigemina)
o Located on the posterior surface of the midbrain
o Divided into
Superior colliculi
Centers for visual reflexes
Inferior colliculi
Auditory centers
Trochlear nerves
o Emerges in the midline below inferior colliculi
o Wind around the lateral aspect of the midbrain to enter the lateral wall of the cavernous
sinus.
Brachia ascend in an anterolateral direction on the lateral aspect of midbrain
o Superior brachium
Passes from superior colliculus to lateral geniculate body and optic tract
o Inferior brachium
Connects inferior colliculus to the medial geniculate body
Interpeduncular fossa
o Located on the anterior aspect of the midbrain
o Bounded on either side by crus cerebri
o Its floor known as posterior perforated substance
Oculomotor nerve emerges from the medial side of the crus cerebri
o Passes forward in the lateral wall of cavernous sinus
Internal structure of the midbrain
Comprises 2 lateral halves, cerebral peduncles
o Each is divided by substantia nigra into
Anterior part, crus cerebri
Posterior part, tegmentum
Cerebral aqueduct: the narrow cavity of the midbrain
o Connect 3rd with 4th ventricle
Tectum
o Part of midbrain, posterior to the cerebral aqueduct
o Has the 2 superior and 2 inferior colliculi
Gross appearance of the cerebellum
Lies in the posterior cranial fossa
Covered superiorly by the tentorium cerebelli
Largest part of the hindbrain
Lies posterior to the 4th ventricle, pons and medulla oblongata
Consist of 2 cerebellar hemispheres
o Connected by vermis
Connected to the brainstem by
o Superior cerebellar peduncle
Connect the cerebellum to the midbrain
o Middle cerebellar peduncle
Connect the cerebellum to the pons
o Inferior cerebellar peduncle
Connect the cerebellum to the medulla oblongata
Divided into 3 lobes
o Anterior lobe
Seen on the superior surface
Separated from the middle lobe by V-shaped primary fissure
o Middle lobe
Also known as posterior lobe
Largest part of cerebellum
Located between the primary and uvulondular fissures
o Flocculondular lobe
Lies posterior to the uvulondular fissure
Reticular formation
Consist of network of nerve cells and fibers
Extend from the spinal cord through the medulla, pons, midbrain, Subthalamus, hypothalamus
and thalamus.
Divided into 3 longitudinal columns
o Median column
Occupy the median plane
Consist of intermediate size neurons
o Medial column
Contain large neurons
o Lateral column
Contain small neurons
Functions
o Control of skeletal muscle
o Control of somatic and visceral sensation
o Control of the autonomic nervous system
o Control of the endocrine nervous system
o Influence of the biologic clocks
o The reticular activating system
The 12 cranial nerves
Openings in cribriform plate of ethmoid
o Olfactory nerve (CN I)
Sensory
Optic canal
o Optic nerve (CN II)
Sensory
Superior orbital fissure
o Oculomotor nerve (CN III)
Motor
o Trochlear nerve (CN IV)
Motor
o Trigeminal nerve (CN IV)
Ophthalmic division
Sensory
o Abducent nerve (CN VI)
Motor
Foramen rotundum
o Trigeminal nerve (CN IV)
Maxillary division
Sensory
Foramen ovale
o Trigeminal nerve (CN IV)
Mandibular division
Motor
Sensory
Internal acoustic meatus
o Facial nerve (CN VII)
Motor
o Vestibulocochlear nerve (CN VIII)
Vestibular
Sensory
Cochlear
Sensory
Facial canal
o Facial nerve (CN VII)
Sensory
Stylomastoid foramen
o Facial nerve (CN VII)
Secretomotor
Parasympathetic
Jugular foramen
o Glossopharyngeal nerve (CN IX)
Motor
Secretomotor
Parasympathetic
Sensory
o Vagus nerve (CN X)
Motor
Sensory
o Accessory nerve (CN XI)
Cranial root
Motor
Spinal root
Motor
Hypoglossal canal
o Hypoglossal nerve (CN XII)
Motor
Organization of the cranial nerves
Sensory
o Olfactory nerve (CN I)
o Optic nerve (CN II)
o Vestibulocochlear nerve (CN VIII)
Motor
o Oculomotor nerve (CN III)
o Trochlear nerve (CN IV)
o Abducent nerve (CN VI)
o Accessory nerve (CN XI)
o Hypoglossal nerve (CN XII)
Sensory + motor
o Trigeminal nerve (CN V)
o Facial nerve (CN VII)
o Glossopharyngeal nerve (CN IX)
o Vagus nerve (CN X)
Cranial nerves nuclei
Midbrain
o Mesencephalic trigeminal nucleus (CN V)
o Red nucleus
o Trochlear nucleus (IV)
o Oculomotor nucleus (CN III)
o Edinger-Westphal nucleus (CN III)
o Substantia nigra
o Superior colliculus
o Inferior colliculus
Pons
o Cochlear nuclei (CN VIII)
Dorsal cochlear nucleus
Ventral cochlear nucleus
o Vestibular nuclei (CN VIII)
o Salivary nuclei
Inferior salivary nucleus
Superior salivary nucleus
o Facial nucleus (CN VII)
o Abducens nucleus (CN VI)
o Trigeminal motor nucleus (CN V)
o Main trigeminal nucleus (CN V)
o Pontine nuclei
o Trapezoid nuclei
Medulla oblongata
o Hypoglossal nucleus (CN XII)
o Dorsal motor nucleus of vagus nerve (CN X)
o Nucleus ambiguus (CN IX, X, XI)
o Solitary nucleus (CN VII, IX, X)
o Spinal trigeminal nucleus (CN V)
o Inferior olivary nucleus
o Nucleus gracilis
o Nucleus cuneatus
o Accessory nucleus (CN XI)
o Vagal nucleus (CN X)
o Glossopharyngeal nucleus (CN IX)
o Cochlear nucleus
o Lateral vestibular nucleus
o Vestibular nucleus
Fourth ventricle
Lies anterior to the cerebellum
Posterior to the pons and the superior half of the medulla oblongata
Continuous above with the cerebral aqueduct of midbrain
With central canal of medulla oblongata and the spinal cord
Lateral boundaries
Cranial part
o Superior cerebellar peduncle
Caudal part
o Inferior cerebellar peduncle
Roof or posterior wall
Project into cerebellum
Superior part
o Medial borders of 2 superior cerebellar peduncles
Connected by superior medullary velum
Inferior part
o Inferior medullary velum
Devoid of nervous tissue
Formed by ventricular ependyma and pia mater
o Pierced by median aperture or foramen Magendie
Lateral recesses extend laterally and open anteriorly as the lateral openings of the 4th
ventricle or foramina of Luschka
Floor or Rhomboid fossa
Formed by posterior surface of pons and cranial half of medulla oblongata
Divided into 2 halves by median sulcus
o Medial eminence on each side of the sulcus
Bounded laterally by sulcus limitans
Substantia ferruginea
o Lies at the superior end of sulcus limitans
Vestibular area, lateral to sulcus limitans
o Vestibular nuclei lie underneath
Facial colliculus
Inferior end of medial eminence
Produced by fibers of motor nucleus of facial nerve winding around
abducent nucleus
Stria medullaris
o Nerve fibers derived from arcuate nuclei
o Emerge from the median sulcus and pass laterally over the medial eminence and
vestibular area to enter inferior cerebellar peduncle to reach cerebellum
Inferior to stria medullaris
o Hypoglossal trigone
Most medially
Underlying hypoglossal nucleus
o Vagal trigone
Lateral to hypoglossal trigone
Underlying motor nucleus of vagus nerve
Area postrema
o Between vagal trigone and lateral margin of the ventricle
Choroid plexus of 4th ventricle
Suspended from the inferior half of the roof of the ventricle
Supplied by posterior inferior cerebellar arteries
Preolivary sulcus
CN XII
Retroolivary sulcus
IX, X, XI
Bulbopontine sulcus
VI, VII, VIII
Cranial nerves with parasympathetic fibers
Oculomotor nerve CN III
Facial nerve CN VII
Glossopharyngeal nerve CN IX
Vagus nerve CN X
