Download Brainstem

Brainstem (I)
李立仁 副教授
解剖學暨細胞生物學科
[email protected]
Brainstem
General Arrangement
Brainstem (I)
Three major functions
Conduit function :
Ascending/descending fibers and numerous relay
nuclei are present in the brainstem.
Cranial nerve function :
All cranial nerves except the olfactory (I) and optic (II)
nerves emerge from the brainstem.
Integration function :
Sensory, motor information and some visceral
activities are regulated in the brainstem.
#These functions are not mutually exclusive#
Brainstem
Brainstem (I)
General Arrangement
Three major components
Nuclear groups :
Nuclei of cranial nerves
Relay nuclei
Long fiber tracts:
Sensory (ascending) and motor (descending) fibers
Reticular formation :
Loosely organized clusters of cells
#These structures are somewhat interwoven#
General Arrangement
Brainstem (I)
Three major structures
Medulla oblongata (myelencephalon) :
Caudal limit : the level of foramen magnum
Rostral limit : inferior to the bulge of pons
Pons (metencephalon) :
Broad budge
Rostral limit : inferior to the
corpora quadrigemina
Midbrain (mesencephalon) :
Caudal limit : superior to the
bulge of pons
Rostral limit : inferior to the
pineal body (dorsal) and
mammillary body (ventral)
General Arrangement
Brainstem (I)
Three major structures
Medulla oblongata :
consists ascending/descending fibers, relay nuclei to
cerebellum, nuclei of cranial nerves VIII – XII and reticular
formation.
Pons :
consists ascending/descending fibers, relay nuclei to
cerebellum, nuclei of cranial nerves V – VII and reticular
formation.
Midbrain :
consists ascending/descending fibers, superior and
inferior colliculi (visual and auditory reflexes), red nucleus
and substantia nigra (motor functions), periaquductal gray
(pain control) and nuclei of cranial nerve III and IV.
Brainstem (I)
General Arrangement
Three major areas
Tectum (posterior to the ventricular space, midbrain only)
consists superior and inferior colliculi (corpora
quadrigemina)
Tegmentum (anterior to the ventricular space)
consists reticular formation, cranial nerve nuclei and
tracts, ascending and some descending pathways
Appended structures (appended to the anterior surface)
consists descending fibers from the cerebral cortex:
cerebral peduncles, basal pons and pyramids of the medulla.
Brainstem (I)
Medulla Oblongata
Ventral surface of medulla oblongata
Anterior medium sulcus
Medullary pyramids
- bounded by the anterolateral sulcus
- descending fibers from the cerebral cortex to lateral
(crossing at pyramidal decussation) and anterior (crossing
before teminatation) corticospinal tracts
- descending corticobulbar fibers to cranial nerve nuclei
Brainstem (I)
Medulla Oblongata
Ventral surface of medulla oblongata
Olive : at level of middle medulla
- lateral to anterolateral sulcus
- roolets of hypoglossal (XII) nerve exit
between pyramids and olives in
the anterolateral sulcus
- rootlets of accessory (XI), vagus (X),
glossopharyngeal (IX) nerves exit
lateral to the olives
Brainstem (I)
Medulla Oblongata
Dorsal surface of medulla oblongata
Sulci : posterior median sulcus and posterolateral sulcus
Fasciculi : fasciculi gracilis and cuneatus
Protuberances :
Clava (nuclei gracilis), cuneate tubercles (nuclei cuneatus)
Tuberculum cinereum (spinal nucleus of trigeminial nerve)
Brainstem (I)
Medulla Oblongata
Fourth ventricle :
Floor (rhomboid fossa) :
- obex ( )
- posterior median sulcus
- hypoglossal trigone
- vagal trigone
- area postrema (
) : rostral to
the obex, lacking BBB
- stria medulares : surface mark of
arcuatocerebellar bundle running
from the arcuate nucleus to
cerebellum
Brainstem (I)
Medulla Oblongata
Fourth ventricle :
Roof :
- anterior medullary velum
- cerebellum
- tela choroidea (posterior medullary velum covered by a
mesodermal pia meter)
anterior medullary velum
cerebellum
tela choroidea
post. medullary velum
choroid plexus
Brainstem (I)
Medulla Oblongata
Fourth ventricle :
Lateral boundaries :
- brachium conjunctivum (sup. cerebellar peduncle) :
connects the cerebellum and the midbrain
- restiform body (inf. cerebellar peduncle) : connects the
cerebellum and medulla
- clava and cuneate tubercles
Medulla Oblongata
Brainstem (I)
Fourth ventricle :
Openings :
- lateral apertures (foramen of Luschka)
- median aperture (foramen of Magendie)
foramen of Luschka
foramen of Magendie
Brainstem (I)
Medulla Oblongata
Internal structures of medulla oblongata
Weigert stain for myelin : myelin stained deep blue
Brainstem (I)
Medulla Oblongata
level of pyramidal decussation
pyramids
pyramidal decussation
Brainstem (I)
Medulla Oblongata
level of pyramidal decussation
pyramids and pyramidal decussation (motor)
- pyramids contain corticospinal and
corticobulbar fibers
-- roughly 75-90% of the corticospinal
fibers decussate to the opposite side
near the caudal border of the medulla
form the lateral corticospinal tract
--- fibers control the neck and upper
extremities cross first (more rostral)
--- fibers control the lower extremities cross at lower medulla
-- the rest descend ipsilaterlly form the anteral corticospinal tract
-- corticobulbar fibers leave the pyramid and terminate on cranial
nerve nuclei
Brainstem (I)
Medulla Oblongata
level of pyramidal decussation
posterior columns
and nuclei
spinothalamic tract
spinocerebellar tract
Brainstem (I)
level of pyramidal decussation
posterior (dorsal) columns and nuclei
- touch and proprioception from the body
- afferents from C1 to T6 (upper limb)
ascend in the fasciculus cuneatus
and project to the nucleus cuneatus
- afferents below T6 (lower limb)
ascend in the fasciculus gracilis
and project to the nucleus gracilis
spinothalamic tract (anterolateral fasciculus)
- pain and temperature from the body
spinocerebellar tract
- anterior and posterior
- proprioception from the body
Medulla Oblongata
Brainstem (I)
Medulla Oblongata
level of pyramidal decussation
spinal trigeminal
tract and nucleus
medial longitudinal
fasciculus
Brainstem (I)
Medulla Oblongata
level of pyramidal decussation
spinal trigeminal nucleus and tract
- caudal part (nucleus caudalis) : pain,
temperature from the ipsilateral face
- rostral part (nucleus oralis) : tactile
from the oral mucosa
- intermediate part (nucleus interpolaris) :
dental pain
medial longitudinal fasciculus
- contains ascending/descending fibers derived from various
cranial nerve nuclei and reticular formation
- displaced laterally as pyramidal fibers decussate
Brainstem (I)
Medulla Oblongata
level of sensory decussation
posterior columns
and nuclei
internal arcuate
fibers
sensory decussation
medial lemniscus
Medulla Oblongata
Brainstem (I)
level of sensory decussation
medial lemniscus and lemniscal decussation
- primary afferents from C1 to T6
ascend in the fasciculus cuneatus and
project to the nucleus cuneatus
- primary afferents below T6 ascend in the
fasciculus gracilis and project to
the nucleus gracilis
- axons of 2nd neurons in the posterior
column nuclei course ventromedially
(as the internal arcuate fibers) and
cross to the opposite side (sensory
decussation) above the pyramids
to form the medial lemniscus.
- in the decussation, fibers from nucleus
gracilis lie more ventrally
C1-T6
Below T6
Brainstem (I)
Medulla Oblongata
level of sensory decussation
accessory
(lateral or external)
cuneate nucleus
Brainstem (I)
Medulla Oblongata
level of sensory decussation
accessory (lateral or external)
cuneate nucleus
- is part of the spinocerebellar system
(not post. column system)
-- primary sensory fiber above T1
entering
the spinal cord ascend with
dorsal column fibers in the
fasciculus cuneatus and terminate in the accessory cuneate
nucleus
-- 2nd neurons send axons as the external arcuate fibers
and reach the cerebellum via the restiform body
(inferior cerebellar peduncle)
- mediates proprioception of neck and upper limb
Brainstem (I)
Medulla Oblongata
level of sensory decussation
medial
longgitudinal
fasciculus
arcuate nuclei
Brainstem (I)
Medulla Oblongata
level of sensory decussation
arcuate nucleus
- anterior to the pyramids
- input : controlateral cerebral cortex
- output : cerebellum of both sides
(via the restiform body)
-- ventral external arcuate fibers :
along the outer surface
of the medulla
-- stria medullares :
arcuatocerebellar fibers
along the midline, cross,
and turn laterally
course
Brainstem (I)
Medulla Oblongata
level of inferior olive
inferior olive
complex
Brainstem (I)
Medulla Oblongata
level of inferior olive
inferior olive complex
- three major groups
-- principal olive
-- dorsal accessory olive
-- medial accessory olive
- inputs
-- cerebral cortex (via corticospinal tract)
-- basal ganglia (via central tegmental tract)
-- posterior column nuclei (controlateral side)
-- deep cerebellar nuclei (via superior cerebellar peduncle)
-- spinal cord
- outputs
-- controlateral cerebellum (via olivocerebellar tract within
inferior cerebellar peduncle)
Brainstem (I)
Medulla Oblongata
level of inferior olive
restiform body
(inf. cerebellar
peduncle)
Brainstem (I)
level of inferior olive
Restiform body (inferior cerebellar peduncle)
- ascending fibers :
-- olivocerebellar tracts,
dorsal spinocerebellar tract,
reticulocerebellar tract,
cuneocerebellar tract,
arcuatocerebellar tract,
trigeminocerebellar tract,
vestibulocerebellar tract
- descending fibers :
-- cerebelloolivary tract,
cerebelloreticular tract,
cerebellovestibular tract,
cerebellospinal tracts
Medulla Oblongata
Brainstem (I)
level of inferior olive
Medulla Oblongata
Pons
Brainstem (I)
Ventral surface of Pons
Pontine protuberance
Pontine sulcus : contains basilar artery
Cerebellopotine angle :
- between pons, medulla and cerebellum
- vestibulocochlear (VIII) and facial (VII) nerves
Between pons and medulla : abducenes (VI) nerve
Rostrolatetral pons : two components of trigeminal (V) nerve
(larger sensory and smaller motor)
Pons
Brainstem (I)
Dorsal surface of Pons
Floor of the fourth ventricle
Midline sulcus
Facial colliculi : surface landmark of the genu of the facial
nerve and the underlying nucleus of abdecens nerve
Pons
Brainstem (I)
Internal structures of Pons
Basilar pons (ventral)
- pontine nuclei
- fiber tracts
Tegmentum (dorsal)
- motor nuclei of cranial nerve
- sensory nuclei and tracts
Pons
Brainstem (I)
Internal structures of Pons
Dorsal tegmentum
- medial longitudinal
fasciculus
- tectospinal tract
Basal tegmentum
- sensory lemniscus system :
medial lemniscus
trigeminal tract
spinothalamic tract
- trapezoid body:
transverse fibers from the cochlear nuclei, course through
tegmentum and form the lateral lemniscus (specific sensory)
- central tegmental tract:
fibers from the basal ganglia and midbrain to inferior olive
Brainstem (I)
level of facial colliculus
Pons
Brainstem (I)
Pons
Corticopontocerebellar fibers
- relayed in various pontine nuclei on the
way to cerebellum (pontocerebellar
fibers) via middle cerebellar peduncle
- rapid correction of movement
inferior and middle
cerebellar peduncles
Brainstem (I)
level of trigeminal nerve
Pons
Brainstem (I)
level of pons-midbrain junction
Pons
Midbrain
Brainstem (I)
Dorsal surface of midbrain
Corpora quadrigemina
- superior colliculus : involved in visual reflex and eye
movement
- inferior colliculus : relay nucleus in the auditory
pathway
Trochlear (IV) nerve emerges caudal to inferior colliculi
Midbrain
Brainstem (I)
Ventral surface of midbrain
Cerebral peduncles (crus cerebri):
- corticofugal fibers (efferents come out of cerebral cortex)
to the lower levels
- continue into the internal capsule rostrally
Interpeduncular fossa : oculomotor (III) nerve emerges
Trochlear (IV) nerve appears at the lateral borders of the
cerebral peduncles
Brainstem (I)
Midbrain
level of inferior colliculus
cerebral aqueduct
inferior colliculus
superior cerebellar
peduncle
cerebral peduncle
substantia nigra
trochlear nucleus
Brainstem (I)
level of inferior colliculus
Nucleus of the inferior colliculus
- relay nucleus in the auditory
pathway
- receives afferents from lateral
lemniscus, controlateral inferior
colliculus, ispilateral medial
geniculate body, primary auditory
cortex and cerebellum
- send efferents to medial
geniculate body, controlateral
inferior colliculus and cerebellum
- also plays role in sound localization
Midbrain
Brainstem (I)
level of inferior colliculus
Brachium conjunctivum (superior
cerebellar peduncle) :
- fibers form the deep cerebellar
nuclei decussate in the midbrain
- continue rostrally to the
ventrolateral nucleus of the
thalamus
Cerebral peduncle :
corticopotine, corticobulbar and
corticospinal (middle 3/5) fibers
Midbrain
Brainstem (I)
level of inferior colliculus
Substantia nigra :
- pigmented mass between cerebral
peduncle and tegmentum
-- ventral zona reticulata contains
iron compounds (receiving part)
-- dorsal zona compacta contains
melanin pigment (projecting part)
--- cell loss in Parkinson’s disease
- dendrites of neurons in the
zona compacta arborize
in the zona reticulata
Midbrain
Brainstem (I)
Midbrain
Substantia nigra :
- inputs
-- from striatum (GABAergic) : mostly to zona reticulata
-- from external part of globus pallidus (GABAergic) : mainly to
zona reticulata
-- from subthalamic nucleus (Glutamatergic) : mainly to zona
reticulata
-- from reticular formation : midbrain raphe nuclei (serotonergic)
and pedunculopontine nucleus (cholinergic)
- outputs
-- zona compacta to striatum (caudate and putamen) : nigrostriate
fibers (dopaminergic)
-- zona compacta to cerebral cortex (limbic system) : nigrocortical
tract (dopaminergic)
Brainstem (I)
Midbrain
level of superior colliculus
superior colliculus
red nucleus
Oculomotor
nucleus
Brainstem (I)
Midbrain
level of superior colliculus
Nucleus of superior colliculus
- involved in visual reflex and eye movement
- inputs
-- from cerebral cortex (visual areas ) : corticocollicular fibers
-- from retina
-- from spinal cord : ascend with spinothalamic tract
-- from inferior colliculus : eye and head are turned toward the
source of a sound
- outputs :
-- to spinal cord
-- to cerebellum
-- to reticular formation
-- to thalamus
--- tectothalamic tract to the lateral posterior nucleus, lateral
geniculate nucleus and pulvinar of the thalamus, relay
stations to the cortex
Brainstem (I)
Midbrain
level of superior colliculus
Red nucleus
- rich vascularity gives its pinkish hue
- involved in motor control
- inputs
-- from deep cerebellar nuclei
-- from motor-related cortical areas (corticorubral fibers)
- outputs
-- spinal cord (rubrospinal fibers)
--- project to the same laminae the corticospinal fibers
terminate
--- corticorubral fibers and rubrospinal fibers together
are the “indirect” or “extrapyramidal” motor system
-- cerebellum : via superior cerebellar peduncle
-- reticular formation
-- inferior olive : via central tegmental tract
Brainstem (I)
Midbrain
level of pretectal nucleus
Pretectal nucleus - pupilary light reflex
Medial geniculate nucleus (body) - relay in the auditory pathway
Lateral geniculate nucleus (body) – relay in the visual pathway
Oculomotor nucleus / Edinger-Westphal nucleus
Ventral tegmental area – dopaminergic neurons
Brainstem (I)
level of pretectal nucleus
Pretectal nucleus (mesencephalic-diencephalic junction)
- pupilary light reflex
- input : from retina
- output : to E-W nu.
Midbrain
F
E
D
C
B
A