Download Slide 1

Cranial Nerves and Brainstem
12 Tribes, 12 Disciples, 12 Eggs/Dozen
12 Cranial Nerves
Harvey Karten
• Make up your
own mnemonic
Some Basic Organizational Principles
• Alar and Basal Plate
• Cranial Nerves:
– Sensory
– Motor
– Sensory and Motor (Mixed)
• Motor neurons lie INSIDE the brain (with a
notable exception – postganglionic
autonomics)
• Sensory neurons lie OUTSIDE the brain
(with a notable exception – Mesencephalic
nuc. Trigem)
•
FIGURE 13 The early spinal cord and hindbrain are divided into dorsal (alar) and ventral (basal) plates by the limiting sulcus. This
morphology reflects early ventral differentiation of the mantle layer (2), which is accompanied by an early ventral thinning of the
neuroepithelial or ventricular layer of the neural tube (it remains as the ependymal lining of the adult ventricular system). The mantle layer
develops into adult gray matter. This schematic drawing, which was traced from a transverse section of the spinal cord, also shows dorsal
(sensory) and ventral (motor) roots of the spinal cord; dorsal root ganglia, which contain the somata of sensory neurons derived from the
neural crest; and mixed (sensory and motor) spinal nerves distal to the ganglia. The peripheral area (3) is called the marginal zone and
develops into the spinal cord white matter or funiculi, which contain ascending and descending fiber tracts.
Sulcus Limitans,
Alar and Basal Plate
Sulcus Limitans forms a boundary zone
Alar Plate: Sensory Inputs
Basal Plate: Motor Neurons
•
FIGURE 13 The early spinal cord and hindbrain are divided into dorsal (alar) and ventral (basal) plates by the limiting sulcus. This
morphology reflects early ventral differentiation of the mantle layer (2), which is accompanied by an early ventral thinning of the
neuroepithelial or ventricular layer of the neural tube (it remains as the ependymal lining of the adult ventricular system). The mantle layer
develops into adult gray matter. This schematic drawing, which was traced from a transverse section of the spinal cord, also shows dorsal
(sensory) and ventral (motor) roots of the spinal cord; dorsal root ganglia, which contain the somata of sensory neurons derived from the
neural crest; and mixed (sensory and motor) spinal nerves distal to the ganglia. The peripheral area (3) is called the marginal zone and
develops into the spinal cord white matter or funiculi, which contain ascending and descending fiber tracts.
Alar Plate
e.g.,
Visceral Sensory (Vagal)
Cochlear Nuclei
Vestibular nuclei
Trigeminal sensory nuclei
HOW FAR FORWARD?
Superior and Inferior Colliculi, Thalamus,
Telencephalon, Olfactory Bulb???
Basal Plate
e.g.,
Visceral Motor (Vagal)
Hypoglossal
Facial
Trigeminal sensory nuclei
?Oculomotor?
Rhombomeres and Segmentation
FIGURE 9 Distribution of neuronal
types in the chick embryo
hindbrain in relation to
rhombomeres. (A). Shown on
the right side are
branchiomotor neurons,
forming in r2+r3 (Vth cranial
nerve, trigeminal), r4+r5 (VIIth
nerve, facial), and r6+r7 (IXth
nerve, glossopharyngeal), and
contralaterally migrating
efferent neurons of the VIIIth
nerve (vestibuloacoustic),
which are in the floor plate (fp)
of r4 at the stage shown.
Shown on the left side are
somatic motor neurons, forming
in r1 (IVth nerve, trochlear),
r5+r6 (VIth nerve, abducens),
and r8 (XIIth nerve,
hypoglossal). Cranial nerve
entry/exit points and sensory
ganglia associated with r2
(trigeminal), r4 (geniculate,
vestibuloacoustic), r6
(superior), and r7 (jugular) are
shown, as is the otic vesicle
(ov). Colored bars represent
the AP extent of Hox gene
expression domains; note that
one of these, Hoxb1, is
expressed at a high level only
in r4. Modified from Lumsden
and Keynes, (1989). (B). In
addition to branchiomotor
neurons, each rhombomere
also contains six classes of
interneuron, as defined by
position and axon trajectory. r4
(as shown here) also contains
contralaterally migrating
vestibuloacoustic neurons
(cva). (C). Later in
development, branchiomotor
neurons complete their laterally
directed migration (arrows) and
condense as defined nuclei
close to their exit points.
Similarly, cva neurons have
complete their migration across
the midline (arrow) and form a
grouping in r4 and r5.
Cranial Nerves
• Not all cranial nerves are NERVES
– Two are brain tracts I & II (Olfactory and
Optic)
• Sensory
• Motor
• Mixed (Sensory and Motor)
• Alar and Basal Plate
• Cranial Nerves:
– Sensory
– Motor
– Sensory and Motor (Mixed)
Major Sensory Inputs
•
•
•
•
•
•
Olfaction (I)
Vision (II)
Trigeminal sensation (V)
Hearing, Vestibular (VIII) + centrifugals
Gustatory (VII, IX-X)
Internal visceral sensation (IX-X)
Major Motor Outputs
• Vision – oculomotor and accessory oculomotor
(III, IV, VI, Edinger-Westphal for pupillary control
and accommodation)
• Trigeminal motor – feeding, expression, hearing
control (V motor)
• Facial motor (VII)
• Hearing, Vestibular – Centrifugal (VIII)
• Heart, lungs, GI tract, pancreas, (IX-X)
• Spinal Accessory – trapezius, sternocleidomastoid (XI)
• Tongue (XII)
• Make up your
own mnemonic
Specialized Polymodal Chemical
Systems
– Catecholamines
• Locus Ceruleus
• Substantia Nigra compacta
• Nuc. Tractus Solitarius
– Serotonin
• Raphe nuclei
– Acetylcholine
• Locus Ceruleus
• Nucleus Basalis of Meynert
Cerebellum
Superior cerebellar
peduncle
Mesencephalic tract & nuc V
Middle cerebellar
peduncle
Sens nuc V
4th ventricle
Motor nuc V
MLF
Superior
olivary
nucl.
Fascicles
of cn. V
CN V
Trapezoid body
Trigeminothalamic tract
Corticospinal &
corticobulbar fibers
Pons: see basis pontis; mid pons: see fascicles of cn V
Spinal lemniscus
Medial lemniscus
Pontine nuclei
Basis pontis
Choroid plexus
Hypoglossal nucl.
Inf. cerebell peduncle
Dorsal motor nucl. of vagus
Solitary tract
Solitary nucl.
Ventricle IV
Spinal
trigem.
nucl. +
tract
Nucl.
ambiguus
cn. X
Hypoglossal
fascicles
Spinal
lemniscus
Medial
longitudinal
fasciculus
Inf. olivary
nucl,
cn. XII
Pyramidal tracts
Open medulla: pyramids, IV ventricle, nucleus of the inferior olive
Medial lemniscus
Reticular Formation
• Medial Reticular Formation
– Descending pathways
• Lateral Reticular Formation
– Local networks
• ASCENDING RETICULAR ACTIVATING
SYSTEM (ARAS)
– sleep, wakefulness, attention
Choroid plexus
Hypoglossal nucl.
Inf. cerebell peduncle
Dorsal motor nucl. of vagus
Solitary tract
Solitary nucl.
Ventricle IV
Spinal
trigem.
nucl. +
tract
Nucl.
ambiguus
cn. X
Hypoglossal
fascicles
Spinal
lemniscus
Medial
longitudinal
fasciculus
Inf. olivary
nucl,
cn. XII
Pyramidal tracts
Open medulla: pyramids, IV ventricle, nucleus of the inferior olive
Medial lemniscus
Cerebellum
Superior cerebellar
peduncle
Mesencephalic tract & nuc V
Middle cerebellar
peduncle
Sens nuc V
4th ventricle
Motor nuc V
MLF
Superior
olivary
nucl.
Fascicles
of cn. V
CN V
Trapezoid body
Trigeminothalamic tract
Corticospinal &
corticobulbar fibers
Pons: see basis pontis; mid pons: see fascicles of cn V
Spinal lemniscus
Medial lemniscus
Pontine nuclei
Basis pontis
• Descending inputs – majority of axons in
cerebral peduncle of cortical origin end in
RF:
– Motor cortex largely to Medial RF
– Sensory cortex largely to Lateral RF
• Ascending spinal inputs: many to Lateral
RF
• Cerebellar Outputs from deep Cbllar
Nuclei
Reticular Formation
• ASCENDING RETICULAR ACTIVATING
SYSTEM (ARAS)
– sleep, wakefulness, attention
Cranial Nerves
• Alar and Basal Plate
Cranial Nerves
Cranial Nerves
Corticospinal tract
•Also called pyramidal tract
•Arises primarily from primary motor cortex,
premotor and supplementary motor cortex
•Somatosensory cortex also contributes
•70-90% of fibers cross in the lower medulla
(decussation of pyramids)
•Crossed = lateral corticospinal tract
•Uncrossed = anterior/ventral corticospinal tract
•Synapses with:
•Alpha and gamma motor neurons
• Propriospinal neurons
• Interneurons
Corticospinal tract
Cerebral Cortex: precentral gyrus
Corona Radiata
lnternal Capsule (posterior limb)
Crus Cerebri (middle portion)
Longitudinal pontine fibers
Pyramid - pyramidal decussation
Corticospinal Tract - Lateral and Anterior
Termination: Spinal Gray (Rexed IV-IX)
Midbrain
pons
medulla
decussation
spinal cord
Dorsal column/medial lemniscus
1. Dorsal Root Ganglion
dorsal root - dorsal column
2. Dorsal Column Nuclei (N.
gracilis or N.cuneatus)
internal arcuate fiber - lemniscal
decussation- medial lemniscus
3. Thalamus (VPL)
internal capsule -corona radiata
4. Primary sensory cortex (S I)
Nucl. Grac & Cuneat.-Arcuate fibers-Medial
lemniscus-Thalamus
Anterolateral system
(spinothalamic)
•Pain and temperature on
contralateral side of body
•Crosses in spinal cord
•Thalamus via spinal
lemniscus
(spinoreticular,
spinomesencephalic
tracts)
Fasciculus gracilus
Fasciculus cuneatus
Median dorsal sulcus
Gracile nucleus
Cuneate nucleus
Central canal
Dorsal motor
nucl. of vagus
Spinal
trigeminal
nucleus
and
tract
Hypoglossal
nucl.
Internal
Arcuate
Fibers
Dorsal
spinocerebellar
tract (small font)
Reticular
formation
Ventral
spinocerebellar
tract (small font)
Medial
lemniscus
Pyramidal
decussation
Spinal
lemniscus
Nucleus of the
Inferior Olive
Pyramid
Caudal medulla: pyramids, no IV ventricle
Vertebral
artery
Ventral median fissure
Spinocerebellar tract
Modality: Unconscious Proprioception
Receptor: Muscle spindle, Golgi tendon organ
1. Dorsal Root Ganglion
dorsal root
2. a. Clarke’s column (C8-L2)
Posterior/dorsal Spinocerebellar Tract ipsilaterally
project to cerebellum via inferior cerebellar peduncle
b. Secondary neuron: dorsal horn
crossing- form anterior Spinocerebellar Tract on contralateral
side-cross again before entering via superior cerebellar
peduncle
3. Cerebellar Cortex on ipsilateral side