BRAINSTEMBRAINSTEM

BRAINSTEMBRAINSTEM

In general, the brainstem is made up of a In general, the brainstem is made up of a mixture of long fiber pathways, well-mixture of long fiber pathways, well-organized nuclei, and a network of cells organized nuclei, and a network of cells which forms the brainstem reticular which forms the brainstem reticular formation. Most of the nuclei are related formation. Most of the nuclei are related directly either to cranial nerve functions or directly either to cranial nerve functions or to motor control pathways.to motor control pathways.

10 of 12 cranial nerves enter and leave 10 of 12 cranial nerves enter and leave through the brainstem.through the brainstem.

Brainstem ComponentsBrainstem Components

MedullaMedullaPonsPonsMidbrainMidbrain

Medulla Ascending TractsMedulla Ascending Tracts

Medial lemniscusMedial lemniscusSpinothalamic tractSpinothalamic tractSpinoreticular tractSpinoreticular tractSpinocerebellar tractSpinocerebellar tractCuneocerebellar tractCuneocerebellar tract

Medulla Descending TractsMedulla Descending Tracts

CorticospinalCorticospinalSpinal tract VSpinal tract VMedial longitudinal fasciculusMedial longitudinal fasciculusTectospinalTectospinalRubrospinalRubrospinal

Medulla ComponentsMedulla Components

Cranial nerve nuclei:Cranial nerve nuclei:VIII – XIIVIII – XII

Inferior cerebellar peduncleInferior cerebellar peduncle

Medullary Pyramids (Anterior)Medullary Pyramids (Anterior)

Location of lateral corticospinal tracts.Location of lateral corticospinal tracts.85 percent of fibers decussate in the 85 percent of fibers decussate in the

pyramidal decussation at the inferior pyramidal decussation at the inferior border of the medulla.border of the medulla.

Fibers then enter lateral columns of spinal Fibers then enter lateral columns of spinal cord.cord.

These tracts help with initiating and These tracts help with initiating and modulating movement.modulating movement.

Medullary Olives (Anterior)Medullary Olives (Anterior)

Inferior olivary nuclei receive input from Inferior olivary nuclei receive input from most motor areas of the brain and spinal most motor areas of the brain and spinal cord.cord.

Axons project to the contralateral Axons project to the contralateral cerebellar hemisphere via the cerebellar hemisphere via the olivocerebellar tract.olivocerebellar tract.

These axons signal the cerebellum when a These axons signal the cerebellum when a movement deviates from the planned movement deviates from the planned movement.movement.

Medullary Olives (Anterior)Medullary Olives (Anterior)

Inferior olivary nuclei:Inferior olivary nuclei:

BalanceBalance

CoordinationCoordination

Sound impulse modulationSound impulse modulation

MedullaMedulla

Sends many fibers to the cerebellum via the Sends many fibers to the cerebellum via the inferior cerebellar peduncles:inferior cerebellar peduncles:

SpinocerebellarSpinocerebellar

OlivocerebellarOlivocerebellar

VestibulocerebellarVestibulocerebellar

ReticulocerebellarReticulocerebellar Cerebellovestibular tract:Cerebellovestibular tract:

Sends information from cerebellum to Sends information from cerebellum to medullamedulla

Medullary NucleiMedullary Nuclei

Cranial nerve nuclei:Cranial nerve nuclei:VIII, IX, X, XI, XIIVIII, IX, X, XI, XII

Vestibular nuclear complexVestibular nuclear complex

Medullary Vital Reflex CentersMedullary Vital Reflex Centers

Cardiac center:Cardiac center:

Inhibitory via CN X.Inhibitory via CN X.

Excitatory via T1-T5.Excitatory via T1-T5.Medullary rhythmicity center.Medullary rhythmicity center.Vasomotor center.Vasomotor center.Coordination of head movement and Coordination of head movement and

swallowing.swallowing.

Nonvital Reflex CentersNonvital Reflex Centers

SwallowingSwallowingVomitingVomitingCoughingCoughingSneezingSneezingHiccupping Hiccupping

Dorsal Medullary NucleiDorsal Medullary Nuclei

Nucleus cuneatus:Nucleus cuneatus:Point of synapse for ascending fibers of Point of synapse for ascending fibers of

the the fasciculus cuneatus.fasciculus cuneatus.Nucleus gracilis:Nucleus gracilis:

Point of synapse for ascending fibers of Point of synapse for ascending fibers of the the fasciculus gracilis.fasciculus gracilis.

Portions of reticular formation:Portions of reticular formation:Associated with consciousness and Associated with consciousness and

arousal.arousal.

Medullary RoofMedullary Roof

Cranial portion = superior medullary Cranial portion = superior medullary velum.velum.

Caudal portion = inferior medullary velum.Caudal portion = inferior medullary velum.

Very thin.Very thin.

Foramen (aperture) of Magendie.Foramen (aperture) of Magendie.Posterior choroid plexus.Posterior choroid plexus.

Lateral Medullary SyndromeLateral Medullary Syndrome

Wallenberg’s syndrome effects:Wallenberg’s syndrome effects:Spinothalamic tractSpinothalamic tract

Spinal trigeminal tract and nucleusSpinal trigeminal tract and nucleus

Fibers and nuclei of the glossopharyngeal Fibers and nuclei of the glossopharyngeal nerve, vagus nerve, and part of the nerve, vagus nerve, and part of the reticular formation.reticular formation.

Portions of the vestibular nuclei and/orPortions of the vestibular nuclei and/or

Portions of the inferior cerebellar Portions of the inferior cerebellar peduncle.peduncle.

Lateral Medullary SyndromeLateral Medullary Syndrome

Results in:Results in:Loss of pain and temperature on the contralateral Loss of pain and temperature on the contralateral

side (spinothalamic tract)side (spinothalamic tract)Loss of pain and temperature on the same side of Loss of pain and temperature on the same side of

the face and nasal and oral cavities the face and nasal and oral cavities (uncrossed spinal trigeminal tract)(uncrossed spinal trigeminal tract)

Difficulty swallowing and a hoarse, weak voice.Difficulty swallowing and a hoarse, weak voice.Due to damage to nucleus ambiguusDue to damage to nucleus ambiguus

Loss of gag reflex on the same side and absence Loss of gag reflex on the same side and absence of of sensation of the same side due to damage sensation of the same side due to damage to to Glossopharyngeal nerveGlossopharyngeal nerve

Pons Fiber TractsPons Fiber Tracts

Transverse:Transverse:Travel through middle cerebellar Travel through middle cerebellar

peduncles.peduncles.

Connect pons to cerebellum.Connect pons to cerebellum.Longitudinal:Longitudinal:

Both sensory and motor.Both sensory and motor.

Connect spinal cord to upper brain stem:Connect spinal cord to upper brain stem:

Most pass through pons without synapsingMost pass through pons without synapsing

Pons Fiber TractsPons Fiber Tracts

Two longitudinal tracts synapse in pons:Two longitudinal tracts synapse in pons:

Corticopontine tracts synapse on pontine Corticopontine tracts synapse on pontine nuclei.nuclei.

Corticobulbar tracts (some) synapse with Corticobulbar tracts (some) synapse with neurons in the trigeminal (CN V) neurons in the trigeminal (CN V)

motor motor nucleus and the facial (CN VII) nucleus and the facial (CN VII) nucleus.nucleus.

Nuclei in the PonsNuclei in the Pons

Cranial nerve nuclei:Cranial nerve nuclei:V, VI, VII, VIII (part)V, VI, VII, VIII (part)

Pontine:Pontine:Relay information from cerebrum to Relay information from cerebrum to

cerebellum.cerebellum.Other centers:Other centers:

SleepSleepRespiratoryRespiratory

PneumotaxicPneumotaxicApneustic Apneustic

Lesions in the PonsLesions in the Pons

Lesion to lateral half of the pons would Lesion to lateral half of the pons would affect:affect:

Trigeminal nerve, resulting in:Trigeminal nerve, resulting in:LLoss of general sensation to the face on oss of general sensation to the face on

the the same side.same side.Paralysis to the muscles of mastication – Paralysis to the muscles of mastication –

with with the chin deviating to the side of the lesion.the chin deviating to the side of the lesion.

Medial lemniscusMedial lemniscusResulting in a loss of position, muscle, and Resulting in a loss of position, muscle, and joint sense on the opposite sidejoint sense on the opposite side

Lesions in the PonsLesions in the Pons

Lesion to lateral half of the pons would Lesion to lateral half of the pons would affect:affect:

Pontocerebellar fibers, resulting in:Pontocerebellar fibers, resulting in:HypotoniaHypotonia

Coarse intention tremorCoarse intention tremor

Tendency to fall to the same side as the Tendency to fall to the same side as the lesion.lesion.

Lesions in the PonsLesions in the Pons

Damage to the midpons:Damage to the midpons:

Extensive bilateral lesions involving the Extensive bilateral lesions involving the pons pons and the midbrain reticular formation are and the midbrain reticular formation are associated with “COMA”:associated with “COMA”:

State of sustained unconsciousness and State of sustained unconsciousness and unresponsiveness.unresponsiveness.

Lesions in the PonsLesions in the Pons

Bilateral lesions to the ventral pons:Bilateral lesions to the ventral pons:

Caused by occlusion to the basilar artery Caused by occlusion to the basilar artery that that spares the reticular formation.spares the reticular formation.

Interrupts the corticospinal and some Interrupts the corticospinal and some corticobulbar tracts.corticobulbar tracts.

Results in a patient who is quadriplegic Results in a patient who is quadriplegic and and unable to speak or have tongue or unable to speak or have tongue or

facial movements.facial movements.

Lesions in the PonsLesions in the Pons

Bilateral lesions to the ventral pons:Bilateral lesions to the ventral pons:

Patients are conscious.Patients are conscious.

Patients can communicate with eye Patients can communicate with eye movements if the corticobulbar fibers movements if the corticobulbar fibers

to to the oculomotor nuclei are intact.the oculomotor nuclei are intact.

Midbrain NucleiMidbrain Nuclei

CN nuclei III and IV.CN nuclei III and IV.Red nucleus (nucleus ruber):Red nucleus (nucleus ruber):

Involved in unconscious regulation and Involved in unconscious regulation and coordination of motor activities.coordination of motor activities.

Midbrain TectumMidbrain Tectum

Superior colliculi:Superior colliculi:Visual reflexes.Visual reflexes.

Receive input from eyes, inferior colliculi, Receive input from eyes, inferior colliculi, skin, cerebrum.skin, cerebrum.

Fibers project to cranial nerve nuclei and to Fibers project to cranial nerve nuclei and to superior cervical portion of spinal cord.superior cervical portion of spinal cord.

Stimulate motor neurons involved in Stimulate motor neurons involved in turning eyes and head.turning eyes and head.

Involved in visual tracking of moving objects.Involved in visual tracking of moving objects.

Midbrain TectumMidbrain Tectum

Inferior colliculi:Inferior colliculi:Auditory and olfactory reflexes.Auditory and olfactory reflexes.

Midbrain TegmentumMidbrain Tegmentum

Tracts Tracts Red nucleus:Red nucleus:

Receives information from the cerebellum Receives information from the cerebellum and cerebral cortex.and cerebral cortex.Projects to the cerebellum, spinal cord, Projects to the cerebellum, spinal cord,

and and reticular formation:reticular formation:Rubrospinal tract:Rubrospinal tract:

Neurons contribute to upper limb Neurons contribute to upper limb flexion.flexion.

Midbrain TegmentumMidbrain Tegmentum

Cerebral pedunclesCerebral peduncles Interpeduncular fossaInterpeduncular fossaSubstantia nigra:Substantia nigra:

Interconnected with basal ganglia.Interconnected with basal ganglia.

Involved in coordinating movement and in Involved in coordinating movement and in muscle tone.muscle tone.

Midbrain TegmentumMidbrain Tegmentum

Oculomotor complex:Oculomotor complex:

Nucleus of CN IIINucleus of CN III

Edinger-Westphal nucleus:Edinger-Westphal nucleus:Parasympathetic control of pupillary Parasympathetic control of pupillary

sphincter sphincter and ciliary muscle.and ciliary muscle.

Nucleus of CN IVNucleus of CN IV

Periaquaductal Gray of MidbrainPeriaquaductal Gray of Midbrain

Gray matter surrounding the cerebral Gray matter surrounding the cerebral aquaduct.aquaduct.

Involved in pain suppression.Involved in pain suppression.Coordinates somatic and autonomic Coordinates somatic and autonomic

reactions to pain, threats, and emotions.reactions to pain, threats, and emotions.Activity results in flight-or-flight reactions Activity results in flight-or-flight reactions

and in vocalization during laughing and and in vocalization during laughing and crying.crying.

Decerebrate rigidityDecerebrate rigidity

Transection of the midbrain at the Transection of the midbrain at the midcollicular level causes decerebration midcollicular level causes decerebration (disconnection) of cerebral control.(disconnection) of cerebral control.

Vestibular system drives the rigidity which Vestibular system drives the rigidity which is released from control by higher centers.is released from control by higher centers.

Patient is comatose.Patient is comatose.

Decerebrate RigidityDecerebrate Rigidity

Characteristics:Characteristics:

Opisthotonus (arched back)Opisthotonus (arched back)

Upper extremity extensionUpper extremity extension

Forearm pronationForearm pronation

Flexed wristsFlexed wrists

Lower extremity extensionLower extremity extension

Plantar flexionPlantar flexion