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Transcript
Brain stem
Medulla oblongata
Directional terms – brainstem & spinal cord
rostral
superior
ventral
anterior
dorsal
posterior
caudal
inferior
CNS divisions
Medulla oblongata – boundaries & size
Extends from the lower pontine margin to a
transverse plane, above the first pair of cervical
spinal nerves
Intersects the upper border of the atlas (v.1)
dorsally and the centre of the dens of axis (v.2)
ventrally
~3 cm in length and ~2 cm in diameter at its
widest
Brainstem divisions
Midbrain
Mesencephalon
Pons
Cerebellum
Metencephalon
Medulla
Myelencephalon
Ventral brainstem
cerebral peduncle
middle
cerebellar
peduncle
pyramid
Dorsal medulla
oblongata
Vagal Trigone
Hypoglossal Trigone
Obex
Gracile
Tubercle
Cuneate
Tubercle
Ventral medulla
oblongata
Cranial Nerve IX
Cranial Nerve X
Cranial Nerve XI
Ventral medulla
oblongata
Pyramid
Cranial Nerve XII
Olive
Brainstem – macroscopic overview
Dorsal view
posterolateral sulcus
median sulcus
Ventral view
anterolateral sulcus
CNS derives from the ectoderm
Ectoderm
Neurulation
Differentiation of a subset of neuroectodermal
cells into neural precursor cells
Neural plate
Neural fold
Neural tube
Key consequences of neurulation
formation of neural tube – central nervous system
formation of neural crest - all neurons outside of the
brain and spinal cord + numerous dispersed cell
types
Neural tube folding
Day 21
→
→
day 26
Neural tube closure → end of neurulation
Cranial neuropore closes on day 25
Caudal neuropore closes on day 27
Human Brain Development - Overview
Origin of CNS subdivisions
Primary vesicles
Encephalic subdivisions (~7 weeks, CS21)
Purves, et al, Neuroscience, 3rd ed.
http://www.visembryo.com
Secondary vesicles
Neural tube (& embryo) folding
Neural tube folding (5th -8th wk)
Embryo folding (4th wk)
The neural tube is divided into three layers
Ventricular zone
Mantle zone (layer)
Basal plate
Alar plate
Marginal zone (layer)
mantle layer
divides into
Ventricular
zone
Sulcus Limitans
Ventricular
zone
Groove dividing alar from basal plate along
the walls of the ventricular system
Remains in the adult tissue in the brainstem
(4th ventricle) and diencephalon (3rd
ventricle--hypothalamic sulcus, which
divides the thalamus from the
hypothalamus)
Separates the cranial nerves into motor
(basal) and sensory (alar) nuclei
Nuclear columns in the brain
stem are further differentiated
from those in the spinal cord
alar plate
sulcus
limitans
basal plate
sulcus
limitans
sulcus
limitans
Additional motor &
sensory columns
The primitive central canal widens
into a four-sided pyramid shape
with a rhomboid floor → 4th
ventricle (extends over the future
pons and the medulla
As in the spinal cord, the
embryonic brain stem has a
central gray core with an alar
plate (consisting mostly of
sensory components) and a basal
plate (composed primarily of
motor components)
Alar vs. Basal plate derivatives
dorsal
Alar plate = afferent = sensory
Basal plate = efferent = motor
infeior olivary
nucleus
ventral
somatic
visceral
visceral
somatic
Alar vs. Basal plate derivatives
somatic
dorsal
special - hearing
general - pain
visceral
special - taste
general – int. organs
Alar plate = afferent = sensory
Basal plate = efferent = motor
visceral
infeior olivary
nucleus
ventral
special
general
somatic
special = branchial - pharynx, larynx
general - skeletal
Alar vs. Basal plate derivatives
Estimated time of development of various brain regions
Modified from Bayer SA et al. Neurotoxicology 14:83–144, 1993
Longitudinal zones in the brain stem
cranial
Structures in Medulla oblongata:
Nuclei = gray matter → neuronal bodies
Reticular formation → neuronal bodies
Tracts = white matter → neuronal axons
caudal
tracts from cortex to medulla or spinal cord
tracts from medulla or spinal cord to cortex
Medulla oblongata – upper/open
alar
basal
Medulla oblongata – lower/closed (by the 4th
ventricle)
alar
basal
Level of CN VIII, IXMedulla
Inferior
Cerebellar
Peduncle
Pyramids
Inferior
Olivary
Nucleus
Level of CN X, XIIMedulla
Inferior
Cerebellar
Peduncle
Pyramids
Inferior
Olivary
Nucleus
Inferior olivary nuclei
Convoluted laminae of gray
matter dorsal to the pyramids
Consists of 3 nuclear groups:
principal olive (the largest)
dorsal accessory olive
medial accessory olive
Surrounded by a mass of
fibers - amiculum olivae
Estimated to contain 0.5
million neurons
Inferior olivary complex is a relay station
between the cortex, subcortical structures, the
spinal cord, and the cerebellum
The major output of the inferior olivary complex is to the cerebellum (olivocerebellar tract)
The medulla is connected with the cerebellum
via the inferior cerebellar peduncle (=restiform body)
Saggital view
Dorsal view
Composition of the
inferior cerebellar
peduncle
Olivocerebellar tract (the largest
component of this peduncle):
inferior olive → cerebellum
Dorsal spinocerebellar tract:
nucleus dorsalis (Clarke's nucleus)
→ cerebellum
Reticulocerebellar tract: reticular
formation → cerebellum
Cuneocerebellar tract: accessory
cuneate nucleus → cerebellum
(homologous to the dorsal
spinocerebellar tract)
Arcuatocerebellar tract from the
arcuate nucleus to the cerebellum
Brainstem - ascending pathways
Saggital view
Dorsal view
Gracile/cuneate fascicles
& spinothalamic tract
carry sensory information
from body to cortex
Gracile/cuneate fascicles
→ gracile/cuneate nucleus
→ medial lemniscus –
touch & vibration
Spinothalamic tract →
transit via medulla – pain &
temperature
Purves, et al, Neuroscience, 3rd ed.
Level of Sensory DecussationCaudal Medulla
Nucleus
Cuneatus
(externaltubercle)
Nucleus
Gracilis
(externaltubercle)
Spinal nucleus CN V
(external- trigeminal
eminence)
Inferior
Olivary
Nucleus
Pyramids
Level of Motor Decussation
Caudal Medulla
Fasciculus Gracilis
Fasciculus Cuneatus
Spinal nucleus CN V
Pyramidal
Decussation
The pyramids contain corticospinal &
corticobulbar fibers
Corticospinal
Arm
Trunk
Leg
90% decussate → lateral
corticospinal tract
10% not decussate –
ventral corticospinal tract
Fibers for neck & upper
limb cross first – level of
dens axis – somatotopic
arrangement
Rostral lesion → bilateral
upper limb paralysis without
lower limb paralysis
Caudal lesion → hemiplegia
cruciata
Corticospinal and corticobulbar tracts
Corticobulbar tracts
Motor input to:
Reticular formations – mesencephalic, pontine,
medullary reticular formations
Red Nucleus
Cranial Nerve motor nuclei – V, VII, Ambiguus,
Spinal Accessory & Hypoglosal Nuclei
Note – No direct connections from the primary motor cortex to III,
IV, and VI; these nuclei get input from frontal and parietal cortex
Cranial nerve nuclei in brain stem
Name
Nerve Nuclei
Oculomotor
III
Oculomotor, Edinger–Westphal
Trochlear
IV
Trochlear
Trigeminal
V
Abducens
VI
Main sensory, spinal (descending), mesencephalic, motor
(masticatory)
pons
Abducens
Facial
VII
Facial, superior salivatory, gustatory (solitary)**
Vestibulocochlear
VIII
Cochlear (2 nuclei), vestibular (4 nuclei)
Glossopharyngeus
IX
Ambiguus*, inferior salivatory, solitary**
Vagus
X
Dorsal motor, ambiguus**, solitary*
Accessory
XI
Spinal accessory (C1–5), ambiguus**
Hypoglossal
XII
Hypoglossal
midbrain
medulla
** The solitary nucleus is common for CN VII, IX, and X
* The ambiguus nucleus is common for CN IX, X, and XI
CN IX: Glossopharyngeal
Origin:
Course:
Termination:
Laterality:
Nucleus Ambiguus,
Salivatory nucleus,
glossopharyngeal
ganglion
CNIX, through jugular
foramen
Stylopharyngeus muscle,
Psym to parotid gland,
nucleus solitarius
Ipsilateral
CN IX: Glossopharyngeal
salivatory
solitarius
ambiguus
Motor Portion
Origin:
CN X: Vagal
Course:
Termination:
Laterality:
Nucleus Ambiguus,
dorsal motor nucleus
CNX, exit jugular
foramen
Muscles of larynx,
pharynx, palate; Psym to
esophagus, trachea,
digestive organs, heart,
etc.
Ipsilateral
Sensory Portion
Origin:
Afferent Ganglion of X
Course:
CNX, exit jugular
foramen
Termination:
Nucleus Solitarius
Laterality:
Ipsilateral
CN X: Vagal
Dorsal motor
Ambiguus
Solitarius
CN XI: Accessory
Nucleus solitarius → Ambiguus:
swallowing reflex
eating and drinking
↓
oropharynx stimulation
↓
CN IX
↓
n. solitarius
↓
n. ambiguus
↓
CN X
↓
nasopharynx & larynx are closed
Nucleus solitarius is divided into 2 zones
Rostral part – taste
sensation
Caudomedial part –
cardiorespiratory centers
→ nucleus solitarius is
coextensive with the
physiologically defined
medullary respiratory
center, which includes the
nucleus ambiguus and
surrounding portions of
the reticular formation
CN XII: Hypoglossal
Origin:
Course:
Termination:
Laterality:
Hypoglossal Nucleus
Hypoglossal canal
Muscles of the tongue
Ipsilateral
CN XII: Hypoglossal
Hypoglossal
lesions
CN XII + medial lemniscus
medial lemniscus
CN XII + pyramid
pyramid
Right hypoglossal paralysis
Brainstem - descending pathways
Saggital view
Dorsal view
Upper Medulla oblongata
Motor
somatic
visceral
Sensory
visceral
somatic
Medial longitudinal fasciculus
Middle Medulla oblongata
Motor
somatic
visceral
Sensory
visceral
somatic
Lower Medulla oblongata
Motor
somatic
visceral
Sensory
visceral
somatic
Blood supply of medulla oblongata
Vascular territories:
Paramedian
Olivary
Lateral
Dorsal
Arteries:
Vertebral
Anterior spinal
Posterior spinal
Posterior inferior cerebellar (PICA)