Transcript Brainstem Nuclei and Tracts

Brain stem: Nuclei and tracts
Medulla
• Transitional zone between spinal cord and the medulla.
• Dorsal expansions of gray matter at the level of pyramids
decussation, form the gracile and cuneate nuclei.
• Ventral gray horn includes first cervical, spinal root of
accessory nerve. Bundles of fibers traversed that pass
from the pyramids to the lateral corticospinal (CS) tracts.
• The dorsal gray horns of the spinal cord are replaced by
spinal trigeminal nuclei.
• Above the pyramidal decussation (DP), the medulla has
entirely different structures than that in spinal cord.
Fig 7-2
Fig 7-3
Medial lemniscus system
• Gracile fasciculus: touch, proprioception from lower limb
(ipsilateral) ends in gracile nucleus. Cuneate fasciculus
from upper limb and terminates in cuneate nucleus.
There is a point to point projection of the fibers, which
served as the anatomical basis for reorganization of the
source of a stimulus.
• Axons from gracile nucleus and cuneate nucleus form
the internal arcuate fibers (IA), cross the midline in the
decussation of the medial lemniscus then becomes
medial lemniscus. It then runs to the ipsilateral ventral
posterior nucleus of thalamus, from there then project to
the primary somesthetic cortex of the parietal lobe.
Fig 7-4
Fig 7-5
Fig 7-6
Fig 7-7
Spinothalamic & Spinotectal Tracts
• Spinothalamic tract conveys pain, temperature,
from the contralateral side of the body
• Spinotectal: same as spinothalamic, conveys
somesthetic information to superior colliculus
and reticular formation of the midbrain.
• The two tracts merge to form spinal lemniscus.
Spinal thalamic fibers continue to the ventral
posterior nucleus of the thalamus (see previous
slides)
Spinoreticular fibers
• conveys sensory data from skin and internal organs
• It has different route from spinal cord up to thalamus and
cerebral cortex.
• 1).medial lemniscus system
– to ventral posterior thalamic nuclei then somatosensory area of
the cerebral cortex.
• 2). neospinothalamic system
– prominent in mammals, from lamina I, IV-VI (tract cells) in the
dorsal horn. It has no collateral fibers to the reticular formation. It
ends in ventral posteriolateral division of ventral posterior
nucleus of thalamus.
• 3). Paleospinothalamic
– prominent in all vertibrates. It sends collateral branches to
reticular formation, diversed projections.
Spinocerebellar Tracts
• Carry proprioceptive signals, dorsal (uncrossed),
ventral (crossed).
• Dorsal spinocerebellar fibers (L3 above, ) enter
the inferior cerebellar peduncle and the ventral
spinocerebellar (lumbarsacral region, L-S)
continues through pons and enters the
cerebellum by superior cerebellar peduncle.
Both carry unconscious proprioception to
cerebellum (see previous slides).
Fig 7-2
Fig 7-3
Fig 7-4
Fig 7-5
Fig 7-6
Fig 7-7
Fig 7-8
Accessory (external) cuneate nucleus
• Lateral to cuneate nucleus, fibers form
these nuclei, cuneocerebellar fibers, enter
cerebellum via inferior cerebellar
peduncle. Served as supplemental
pathway for proprioceptive information
from upper limbs.
Fig 7-5
Inferior olivary complex
• Several groups of neurons receive afferent
information from different sources and
then project them to cerebellum. These
neurons are called precerebellar nuclei,
which include components of inferior
olivary complex. Inferior olivary nucleus is
the largest component.
Fig 7-5
Fig 7-6
Fig 7-7
Components
• Inferior olivary complex includes
– 1). inferior olivary nucleus
– 2). medial accessory olivary nucleus
– 3). dorsal accessory olivary nucleus
Olivocerebellar fibers
• originate from inferior olivary complex,
cross in the midline, enter the inferior
cerebellar peduncle. Their function is to
maintain equilibrium and the stereotyped
movements of postural changes and
locomotion
DESCENDING TRACTS
• Corticospinal tract:
• Originate from frontal and parietal lobes,
fibers that cross over in the decussation of
pyramids (lateral corticospinal tract).
Uncrossed fibers (15%, Ventral
corticospinal tract), cross at spinal cord
level. Major function: motor control
Tracts originate from midbrain
• 1). Central tegmental tract:
– arises from ipsilateral red nucleus, terminates in
inferior olivary complex, relay signals
• 2). Axons from contralateral red nucleus
(rubrospinal tract)
– terminates C2 in human
• 3). tectospinal tract:
– originates in superior colliculus, cross the midline
• 4). tectobulbar fibers:
– from superior colliculus, ends in reticular formation of
pons and medulla, involves eye movements.
Nuclei of Cranial Nerves
• Hypoglossal nucleus
– Innervate tongue muscles
• Nucleus ambiguus
– Of vagus nerve, innervate muscles of soft
palate, pharynx, larynx, upper esophagus
• Dorsal nucleus
– Vagus’ largest parasympathetic nucleus
Fig 7-6
Fig 7-7
Dorsal Pons (Tegmentum)
• Pons can be divided into:
– Ventral (Basal)
– Tegmental (dorsal)
Acsending tracts
• Medial lemniscus
– Twisted when it leaves medullar and enters
pons. So the sequence is neck, arm, trunk,
and leg from medial to lateral.
• Spinal lemniscus
– Lateral to the medial lemniscus
• Ventral spinocerebellar tract: most lateral,
enters cerebellum through the superior
cerebellar peduncle
Fig 7-9
Fig 7-11
Cerebellar peduncles
• Inferior cerebellar peduncle
– Inferior cerebellar peduncles enter the
cerebellum from the caudal part of the pons.
superior cerebellar
• superior cerebellar peduncle and its decussation
• Superior cerebellar peduncles (mainly cerebellar efferent
fibers) enter the brain stem caudal to the inferior colliculi
of the midbrain. The fibers cross the midline in the
decussation of the superior cerebellar peduncles. Then
most of the fibers continue to the ventral lateral nucleus
of the thalamus, from there, project to motor area of the
cortex in the frontal lobe. Rest of the fibers end in red
nucleus and in the reticular formation. Ascending fibers
of superior cerebellar peduncles include ventral
spinocerebellar tract as well as fibers from the red
nucleus and the mensencephalic trigeminal nucleus.
Fig 7-11
Fig 7-12
Fig 7-13
Nuclei of Cranial Nerves
• Trapezoid body from dorsal and ventral
cochlear nuclei
• Such fibers above end in superior olivary
nucleus
• Fibers from dorsal cochlear nucleus and
superior olivary nucleus form lateral
lemniscus
Fig 7-8
Fig 7-12
MLF
• Medial longitudinal fasciculus
– From superior vestibular nucleus, terminates
in abducens. Trochlear and oculomotor
nerves
– Coordinate movements of eyes with the rest
of the head
Fig 7-8
Nuclei of Cranial Nerves
•
•
•
•
Facial motor nucleus
Abducens nucleus
Spinal Trigeminal Tract and Nucleus
See previous slide
(Ventral) Basal Pons
• Corticospinal fibers pass through pons
• Corticopontine fibers:
– originate from cerebral cortex, end in ipsilateral
pontine nuclei. Axons from these nuclei cross the
midline forming the pontocerebellar fibers and enter
the cerebellum through the middle cerebellar
peduncle. The information from cerebral cortex could
then be transmitted to cerebellum by the relay of
pontine nuclei. Precision and efficiency of voluntary
movements.
Fig 7-9
Fig 7-10
Midbrain
• subdivided into:
• 1. tectum: consists of superior (Fig 14, 15) and
inferior colliculi (Fig 12, 13)
• 2. basis pedunculi: mass of descending fibers
• 3. substantia nigra: zone of gray matter dorsal to
the basis of pedunculi
• 4. Remaining of the midbrain is called
tegmentum, which includes red nucleus,
periaqueductal gray matter
• Cerebral peduncle: structure on either side of
the midbrain except tectum (superior and inferior
colliculi)
Fig 7-12
Fig 7-13
Fig 7-14
Fig 7-15
Tectum and associated tracts
• inferior colliculus:
• fibers from lateral lemniscus enter inferior
colliculus, then fibers from inferior colliculus
traverse via inferior brachium to the medial
geniculate body of the thalamus. Fibers from
medial geniculate then project into temporal
lobe. Commissural fibers between inferior
colluculi, accounting in part for the bilateral
cortical projection from each ear.
• Some fibers from inferior colliculus pass forward
to superior colliculus, which provides a reflex
turning of head, ear in response toward
unexpected sound.
Superior colliculus
• Afferent fibers to the superior colliculus are coming from occipital
lobe. Corticotectal fibers come from visual cortex of occipital lobe
and an area in front lobe, called frontal eye field, make up the most
of superior brachium ipsilaterally.
• Efferent fibers from superior colliculus are then distributed to the
spinal cord and nuclei of the brain stem. The fibers destined for the
spinal cord cross to the opposite side in the dorsal tegmental
decussation and continue as tectospinal fibers. Efferent fibers for
brain stem are called tectobulbar fibers directed bilaterally. They
distribute fibers to the pretectal area, to the accessory oculomotor
nuclei and to the paramedian pontine reticular formation. From
there, these neuclei project to the nuclei of oculomotor, trochlear,
and abducens nervers. Other efferent fibers terminate in the reticular
formation near motor nuclei of facial nerve providing reflex pathway
for protective closure of eyelids when there is a sudden visual
stimulus.
• The pair of superior colliculi is interconnected by the commissure of
the superior colliculi.
Superior colliculus
• Corticotectal fibers reach superior colliculus via
superior brachium, they provide a connection
between cortex and the superior colliculus,
which is responsible for voluntary and
involuntary movements of eyes and head, as
when rapidly shifting the direction of gaze
(saccadic movement) or when following objects
passing across the visual field (smooth pursuit
movement). Corticotectal fibers originated from
occipital lobe are also responsible for
accommodation reflex.
Pretectal area
• consists of four small nuclei rostral to the
lateral edge of the superior colliculus.
They receive fibers from the retina via
optic tract and the superior brachium,
which are collateral branches destined for
the lateral geniculate body of the
thalamus. Efferent fibers travel to EdingerWestphal nuclei (Oculomotor). Participate
the pupillary light response.
Tegmentum
• Medial and spinal leminiscus passing by
feed the thalamus.
Red nucleus and associated tracts
• Afferent fibers:
– from contralateral cerebellum by superior cerebellar
peduncle and its decussation and from the ipsilateral
cerebral motor area via corticorubral fibers.
• Efferent fibers:
– axons crossing the midline in the ventral tegmental
decussation and continue through the brain stem into
the lateral funiculus of the spinal cord as rubrospinal
tract. Uncrossed fibers travel to the ipsilateral side
terminate in the inferior olivary complex as
rubroolivary fibers in the central tegmental tract. The
axons from inferior olivary nucleus cross the midline
as olivocerebellar fibers enter the inferior cerebellar
peduncle, to the cerebellum.
Substantia Nigra
Large nucleus between the tegmentum
and the basis pedunculi. The black color of
the nuclei is due to the dopaminergic
neurons of the pars compacta, area
adjacent to the tegmentum. These
neurons have neuromelanin pigments.
The major afferent source to pars
compacta is the striatum (associated with
Parkinson’s disease, more later) and
efferent fibers go back to the striatum.
Fig 7-13
Fig 7-14
Fig 7-15
Parkinson's Disease
• Muscular rigidity, slow tremor,
bradykinesia, or lack of movement (mask
face, loss uncessary involuntary muscle
movements, like swing arms while
walking). Caused by degeneration of
melanin-containing cells in substantia
nigra. Treatment: Dopamine like L-Dopa ,
surgical removal, and transplant of adrenal
cells, or fetal cells.
Ventral tegmental area
• Basis pedunculi
• Corticospinal fibers: middle three-fifths of the basis
pedunculi
• Corticobulbar (corticonuclear) fibers are between
corticospinal and frontpontine tract, which occupies
medial one fifth of the basis pedunculi. Most fibers
terminate in reticular formation. Others end in motor
nuclei of cranial nerves. The function of those
corticobulbar fibers is to modify sensory transmission
and control movement.
• Corticopontine fibers (two parts)
• Front pontine tract is part of the corticopontine fibers.
The other part is called parietotemporopontine tract,
mainly from parietal lobe.
Fig 7-14
Visceral Pathways in the brain stem
• The ascending visceral pathway in the spinal
cord are in the ventral and ventrolateral funiculi.
They can be considered as part of the
spinothalamic, and spinoreticular tracts. Data
from these tracts reach reticular formation,
thalamus and hypothalamus.
• Visceral information can also be transmitted by
vagus and glossopharyngeal nerves to solitary
nucleus. Then to hypothalamus by central
tegmental tract.
Clinical consideration
• Medial Medullary Syndrome
– Branches of vertebral and anterior spinal
arteries.
– Structures affected: pyramidal tract, medial
lemniscus, nucleus CN XII
– Contralateral arm or leg weakness
– Contralateral decreased
proprioception/vibration sense
– Ipsilateral tongue weakness
Medulla Vascular Territories
Medial Medullary Syndrome
• Crossed paralysis: neck down affected by
opposite side but muscles innervated by
cranial nerve are affected on the same
side. Be aware that hypoglossal nerve
here is the lower motor neuron, which
innervates the same side of the tongue
muscle. Different from upper motor neuron
damage.
Lateral medullary syndrome
(Wallenberg’s Syndrome)
• occlusion of medullary branch of posterior
inferior cerebellar artery
• Areas affected:
• Spinal trigeminal tract and nucleus:
– Ipsilateral loss of pain, temperature sensation in the
area of trigeminal nerve
• Affected spinal lemniscus:
– Contralateral loss of pain and temperature sensation
below neck (affected spinothalamic tract)
• Destruction of ambiguus nuclei:
– Paralysis of the muscles of the soft palate, pharynx,
and the larynx on the same side, difficulty swallowing
and phonation (efferent fiber of glossopharyngeal N)
Wallenberg’s Syndrome
• Pathway to intermediolateral cell column
of the spinal cord is usually also affected:
• (Sympathetic fibers affected, so
parasympathetic innervation dominant )
• Horner’s syndrome:
• Small pupil, drooping upper eyelids
(ptosis), warm, dry skin on same side of
the lesion
Lesion of basal portion of pons or midbrain
• Occlusion of pontine artery off basilar
artery. Corticospinal fibers affected,
contralateral paralysis, abducens nerve
affected, ipsilateral lateral rectus
paralyzed, medial strabismus.
Millard Gübler Syndrome
• Damage:
– Corticospinal tract (contralateral
hemiparelysis)
– Motor nuclei of facial nerve (ipsilateral facial
paralysis, lower motor damage)
Foville’s Syndrome
• Damage:
– Corticospinal tract partially (contralateral
hemiparelysis)
– Motor nuclei abducens (ipsilateral lateral
rectus paralyzed)
– Motor nuclei of facial (facial muscle paralysis)
– medial rectus paralysis caused by destruction
of crossed fiber that innervate such muscle)
Weber’s syndrome
• Occlusion of branch of posterior cerebral
artery
• Damage:
– Corticospinal tract
– Motor nucleus of oculomotor nerve (inability to
raise upper eyelid, lateral strabismus,
paralysis of all eye muscles except lateral
rectus and superior oblique, pupil dilation
because of interruption of parasympathetic
fibers)