BRAINSTEM
BRAINSTEM
In general, the brainstem is made up of a
mixture of long fiber pathways, wellorganized nuclei, and a network of cells
which forms the brainstem reticular
formation. Most of the nuclei are related
directly either to cranial nerve functions or
to motor control pathways.
 10 of 12 cranial nerves enter and leave
through the brainstem.

Brainstem Components
Medulla
 Pons
 Midbrain

Medulla Ascending Tracts
Medial lemniscus
 Spinothalamic tract
 Spinoreticular tract
 Spinocerebellar tract
 Cuneocerebellar tract

Medulla Descending Tracts
Corticospinal
 Spinal tract V
 Medial longitudinal fasciculus
 Tectospinal
 Rubrospinal

Medulla Components

Cranial nerve nuclei:
VIII – XII

Inferior cerebellar peduncle
Medullary Pyramids (Anterior)
Location of lateral corticospinal tracts.
 85 percent of fibers decussate in the
pyramidal decussation at the inferior
border of the medulla.
 Fibers then enter lateral columns of spinal
cord.
 These tracts help with initiating and
modulating movement.

Medullary Olives (Anterior)
Inferior olivary nuclei receive input from
most motor areas of the brain and spinal
cord.
 Axons project to the contralateral
cerebellar hemisphere via the
olivocerebellar tract.
 These axons signal the cerebellum when a
movement deviates from the planned
movement.

Medullary Olives (Anterior)

Inferior olivary nuclei:
Balance
Coordination
Sound impulse modulation
Medulla


Sends many fibers to the cerebellum via the
inferior cerebellar peduncles:
Spinocerebellar
Olivocerebellar
Vestibulocerebellar
Reticulocerebellar
Cerebellovestibular tract:
Sends information from cerebellum to
medulla
Medullary Nuclei

Cranial nerve nuclei:
VIII, IX, X, XI, XII

Vestibular nuclear complex
Medullary Vital Reflex Centers

Cardiac center:
Inhibitory via CN X.
Excitatory via T1-T5.
Medullary rhythmicity center.
 Vasomotor center.
 Coordination of head movement and
swallowing.

Nonvital Reflex Centers
Swallowing
 Vomiting
 Coughing
 Sneezing
 Hiccupping

Dorsal Medullary Nuclei

Nucleus cuneatus:
Point of synapse for ascending fibers of the
fasciculus cuneatus.

Nucleus gracilis:
Point of synapse for ascending fibers of the
fasciculus gracilis.

Portions of reticular formation:
Associated with consciousness and arousal.
Medullary Roof
Cranial portion = superior medullary
velum.
 Caudal portion = inferior medullary velum.

Very thin.
Foramen (aperture) of Magendie.

Posterior choroid plexus.
Lateral Medullary Syndrome

Wallenberg’s syndrome effects:
Spinothalamic tract
Spinal trigeminal tract and nucleus
Fibers and nuclei of the glossopharyngeal
nerve, vagus nerve, and part of the
reticular formation.
Portions of the vestibular nuclei and/or
Portions of the inferior cerebellar peduncle.
Lateral Medullary Syndrome

Results in:
Loss of pain and temperature on the contralateral
side (spinothalamic tract)
Loss of pain and temperature on the same side of
the face and nasal and oral cavities
(uncrossed spinal trigeminal tract)
Difficulty swallowing and a hoarse, weak voice.
Due to damage to nucleus ambiguus
Loss of gag reflex on the same side and absence of
sensation of the same side due to damage to
Glossopharyngeal nerve
Pons Fiber Tracts

Transverse:
Travel through middle cerebellar peduncles.
Connect pons to cerebellum.

Longitudinal:
Both sensory and motor.
Connect spinal cord to upper brain stem:
Most pass through pons without synapsing
Pons Fiber Tracts

Two longitudinal tracts synapse in pons:
Corticopontine tracts synapse on pontine
nuclei.
Corticobulbar tracts (some) synapse with
neurons in the trigeminal (CN V) motor
nucleus and the facial (CN VII)
nucleus.
Nuclei in the Pons

Cranial nerve nuclei:
V, VI, VII, VIII (part)

Pontine:
Relay information from cerebrum to
cerebellum.

Other centers:
Sleep
Respiratory
Pneumotaxic
Apneustic
Lesions in the Pons

Lesion to lateral half of the pons would
affect:
Trigeminal nerve, resulting in:
Loss of general sensation to the face on the
same side.
Paralysis to the muscles of mastication – with
the chin deviating to the side of the lesion.
Medial lemniscus
Resulting in a loss of position, muscle, and
joint sense on the opposite side
Lesions in the Pons

Lesion to lateral half of the pons would
affect:
Pontocerebellar fibers, resulting in:
Hypotonia
Coarse intention tremor
Tendency to fall to the same side as the
lesion.
Lesions in the Pons

Damage to the midpons:
Extensive bilateral lesions involving the pons
and the midbrain reticular formation are
associated with “COMA”:
State of sustained unconsciousness and
unresponsiveness.
Lesions in the Pons

Bilateral lesions to the ventral pons:
Caused by occlusion to the basilar artery that
spares the reticular formation.
Interrupts the corticospinal and some
corticobulbar tracts.
Results in a patient who is quadriplegic and
unable to speak or have tongue or
facial movements.
Lesions in the Pons

Bilateral lesions to the ventral pons:
Patients are conscious.
Patients can communicate with eye
movements if the corticobulbar fibers to
the oculomotor nuclei are intact.
Midbrain Nuclei
CN nuclei III and IV.
 Red nucleus (nucleus ruber):

Involved in unconscious regulation and
coordination of motor activities.
Midbrain Tectum

Superior colliculi:
Visual reflexes.
Receive input from eyes, inferior colliculi,
skin, cerebrum.
Fibers project to cranial nerve nuclei and to
superior cervical portion of spinal cord.
Stimulate motor neurons involved in
turning eyes and head.
Involved in visual tracking of moving objects.
Midbrain Tectum

Inferior colliculi:
Auditory and olfactory reflexes.
Midbrain Tegmentum
Tracts
 Red nucleus:

Receives information from the cerebellum
and cerebral cortex.
Projects to the cerebellum, spinal cord, and
reticular formation:
Rubrospinal tract:
Neurons contribute to upper limb
flexion.
Midbrain Tegmentum
Cerebral peduncles
 Interpeduncular fossa
 Substantia nigra:

Interconnected with basal ganglia.
Involved in coordinating movement and in
muscle tone.
Midbrain Tegmentum

Oculomotor complex:
Nucleus of CN III
Edinger-Westphal nucleus:
Parasympathetic control of pupillary sphincter
and ciliary muscle.

Nucleus of CN IV
Periaquaductal Gray of Midbrain
Gray matter surrounding the cerebral
aquaduct.
 Involved in pain suppression.
 Coordinates somatic and autonomic
reactions to pain, threats, and emotions.
 Activity results in flight-or-flight reactions
and in vocalization during laughing and
crying.

Decerebrate rigidity
Transection of the midbrain at the
midcollicular level causes decerebration
(disconnection) of cerebral control.
 Vestibular system drives the rigidity which
is released from control by higher centers.
 Patient is comatose.

Decerebrate Rigidity

Characteristics:
Opisthotonus (arched back)
Upper extremity extension
Forearm pronation
Flexed wrists
Lower extremity extension
Plantar flexion