Brainstem (Week 2--Houser) Flashcards Preview

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Flashcards in Brainstem (Week 2--Houser) Deck (65)
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Why is the brainstem so important?

1) Ascending and descending tracts of the spinal cord pass through

2) Cranial nerves located here

3) Centers for regulation of respiration, cardiovascular activity, consciousness, sleep-wake cycle all here


Caudal to rostral organization of brainstem

Continuous with spinal cord caudally

Brainstem begins at foramen magnum

Medulla oblongata, pons, midbrain

Rostrally is diencephalon (thalamus)


Dorsal to ventral organization of the brainstem

Dorsally is tectum, which is the location of the superior and inferior colliculi

Cerebral aqueduct and 4th ventricle

Tegmentum covers entire brainstem (region of cranial nerve nuclei, reticular formation and chemically-identified systems)

Basis is most ventral (region of many ascending and descending tracts)


Caudal medulla

Gray matter surrounds central canal that is continuous with spinal cord

Dorsal columns of spinal cord extend to medulla and fasciculus gracilis continues to nucleus gracilis and fasciculus cuneatus continues to nucleus cuneatus

On ventral surface, have pyraminds (myelinated fibers) and anterior median fissure


Rostral medulla

Central canal expands into 4th ventricle on dorsal surface; lower apex of 4th ventricle where it narrows into central canal is the obex

Area postrema is in walls of ventricle at the obex, and this region has no normal BBB but instead monitors blood for toxins and can trigger vomiting ("vomiting center")

Hypoglossal nucleus and dorsal motor nucleus of the vagus are most medial on floor of 4th ventricle

On ventral side of rostral medulla, have pyramids and olives (more lateral) with inferior olivary nucleus (looks like mini-brain...) that provide major input to cerebellum

Inferior cerebellar peduncles (restiform body) are dorsolateral and extend toward cerebellum

Nucleus ambiguus


Caudal Pons

Transversely oriented mass of fibers on ventral surface in basis pontis

Looks like "bridge" between cerebellar hemispheres but fibers do not connect cerebellar hemispheres, they connect pontine nuclei (within the basis pontis) to the cerebellum

Brachium pontis or middle cerebellar peduncle are large groups of fibers that enter cerebellum

Large 4th ventricle


Superior, middle and inferior cerebellar peduncles

Superior cerebellar peduncle: rostral pons, roof of 4th ventricle

Middle cerebellar peduncle: pons

Inferior cerebellar peduncle: rostral medulla, dorsolaterally


Rostral Pons

Brachium conjunctivum or superior cerebellar peduncle is at roof of 4th ventricle

4th ventricle is closing down


Caudal midbrain

4th ventricle has turned into cerebral aqueduct (aqueduct of Sylvius)

Periaqueductal gray is gray matter around cerebral aqueduct

Cerebral peduncles on ventral surface, contain large groups of (myelinated) fibers descending from cortex to brainstem and spinal cord (corticopontine and corticospinal fibers)

Inferior colliculi are auditory

Superior cerebellar peduncle crossing


Rostral midbrain

Mickey mouse with "o" for mouth!

Cerebral aqueduct

Superior colliculi are visual (not in main visual path but receive visual input in parallel with lateral geniculate nucleus of thalamus and participate in visuomotor control)

Cerebral peduncles on ventral surface, contain large groups of fibers descending from cortex to brainstem and spinal cord (corticopontine and corticospinal fibers)

Interpeduncular fossa between peduncles (oculomotor nerves emerge from interpeduncular fossa)

Substantia nigra is dorsal to axons of cerebral peduncle and divided into pars compacta (dorsal, contains DOPA neurons) and pars reticulata (ventral, contains GABA neurons); all part of basal ganglia system

Red nuclei?


Superior and inferior colliculi

Superior colliculi: visual; dorsal surface of (rostral) midbrain

Inferior colliculi: auditory; dorsal surface of (caudal) midbrain


Substantia nigra

In midbrain

Part of basal ganglia

Lots of cell bodies

Pars compacta: dorsal, contains DOPA neurons

Pars reticulata: ventral, contains GABA neurons (in ventral tegmental area (VTA))


How are brain slices usually oriented?

Dorsal down

Ventral up


Location of cranial nerve nuclei vs. nerves

Nuclei (cell bodies): located dorsally

Nerves exit ventrally or laterally


Idealized (general) view of organization of brainstem nuclei at level of medulla

Motor nuclei medial, sensory nuclei lateral lined along dorsal surface of medulla (adjacent to 4th ventricle)

Separated by sulcus limitans (just as they are in the spinal cord)

This is general plan of cranial nerve nuclei but during development some nuclei shift ventrally and pattern is disrupted


Order of cranial nerves rostrally to caudally

Ascending numerical order rostrally to caudally starting with CN III in midbrain and XII in medulla


CN III (oculomotor)

Somatic motor nucleus and visceral motor (autonomic) nucleus (Edinger-Westphal nucleus)

Motor neurons innervate all extraocular eye muscles (incl LPS) except SO4 and LR6 to move eye up and in

Motor neurons except superior rectus project to ipsilateral eye

Emerges from interpeduncular fossa of midbrain


Damage to CN III (oculumotor)

Damage to CN III causes down and out deviation of the eye due to unopposed action of superior oblique and lateral rectus

Lateral position of eye is called lateral strabismus

Patient will have diplopia (double vision)

Lose innervation of LPS which causes ptosis (drooping of eyelid)

Axons of fibers to extraocular muscles are on the inner surface of the nerve and are sensitive to vascular disease

Usually compressed between medial temporal lobe, cerebral peduncle and edge of tentorium


Edinger Westphal nucleus

Provides autonomic component of CN III

Para pre neurons that form synapses in ciliary ganglia and then postganglionic neurons innervate pupillary constrictor and ciliary muscles

Axons of neurons in E-W nucleus travel with CN III

Normal function is to provide pupillary constriction


Damage to E-W nucleus

Damage to E-W nucleus causes dilation of pupil (mydriasis) on ipsilateral side

Patient will have no pupillary light reflex (because can't constrict pupil!)

Axons of these neurons are on the external surface of the nerve so are damaged first, sensitive to compression, so might see pupil dilation (blown pupils) as first symptom of CN III damage

Note: other eye WILL have reaction to light when light shined in contralateral eye because signal to both E-W nuclei from shining light into just one eye!


Pathway of pupillary light reflex

1) Light into one eye

2) Signal travels bilaterally to pretectum

3) Signal to E-W nucleus

4) Signal to ciliary ganglion

5) Para post to pupillary constrictor to constrict pupils


CN VI (abducens)

Innervates lateral rectus and abducts eye

Smallest and most medially located CN (out of VI, VII, VIII) that leaves the ventral surface of the brainstem along the groove between the basis pontis and medulla--just medial to medial longitudinal fasciculus (MLF)

Normally, CN VI innervates LR on same side and projects through MLF on opposite side to innervate CN III neurons for medial rectus (lateral gaze so both eyes look at the same thing)


Damage to CN VI (abducens)

Damage to CN VI will cause eye on affected side to deviate medially (medial strabismus) and have difficulty moving laterally (abduction)

Also cannot move contralateral eye medially

Together, this is lateral gaze paralysis

Usually compressed over the temporal bone


CN IV (trochlear)

Innervates superior oblique muscle on the contralateral side

Superior oblique moves eye downward and partially in (adducted)

Nerve fibers come out dorsally below inferior colliculus of midbrain and above pons??


Damage to CN IV (trochlear)

Damage to CN IV causes diplopia (vertical) and affected (contralateral) eye appears slightly elevated and has trouble moving down and adducted

Diplopia may be most noticeable when person looking down


CN XII (hypoglossal)

Innervates muscles of the tongue

Nucleus is strung out almost entire way down medulla, dorsal and near 4th ventricle?

Nerve fibers emerge from a sulcus lateral to each pyramid, between pyramid and olive


Damage to XII (hypoglossal)

Damage to CN XII causes tongue deviation to affected/weak side

Possible atrophy of the tongue (so we know this is lower motor neuron damage)


CN VII (facial)

Innervates muscles of facial expression

Nucleus in central pons, ventral?


Damage to CN VII (facial)

Damage to CN VII causes facial paralysis or weakness (generally of both upper and lower face) on ipsilateral side


Ambiguus nucleus

Motor neurons in this nucleus innervate pharynx and larynx and axons are distributed in CN IX and X

Damage to this nucleus causes difficulty swalliwing and laryngeal function (hoarseness)

Located in rostral medulla

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