Transcript CranialN11

Motor Functions of the Cranial
Nerves I
(Somatic Motor Functions)
Just as the trigeminal system parallels spinal sensory
(ascending) pathways, [cranial nerves nuclei are analogous
to ventral horn nuclei].
E.g., especially evident in the lowest n. XI – spinal accessory.
Review 3 Functional Categories (we will go over 2 today).
-located medially relative to sensory nuclei, in columns.
-review the cranial nerves associated with these [Fig. 6-1,
3].
We will also review the cerebral control of the functions of
these motor nuclei:
1. The long-associated corticocerebellar system
2. The other cerebral areas responsible for controlling eye
muscles.
Fig. 6-1
Columnar Organization of Cranial Nerve Nuclei:
Fig. 6-3A
Columnar organization (cont’d)
[Fig. 6-3]
Fig. 11-1
I.
II.
III.
IV.
V.
The 3 classes of cranial nerve motor nuclei and
their columnar organization.
Cortical control of cranial motor functions.
A. Corticobulbar tracts (head, neck muscles).
B. Cortical areas involved in eye movement
control.
General somatic motor column (eye, tongue
muscles) of somatic origin.
Special visceral motor column (face, throat, neck
muscles) derived from branchial arches.
Regional anatomy of the brainstem nuclei
reviewed today.
3 Classes of Cranial Nerve Motor Nuclei and
their Columnar Organization
• Review Figs 6-1, 3, 11-1.
A. General somatic motor (eye, tongue): III, IV, VI, XII –
developmentally derived from occipital somites.
B. Special visceral motor (face, throat, neck): V, VII, IX, X,
XI – also striated muscle under voluntary control, but
developmentally derived from branchial arches.
C. General visceral motor: autonomous control of cranial
glands and body organs: III (pupil), VII, IX, X – under
hypothalamic control – will cover in next lecture, which
will be a good seguay into the hypothalamus and the ANS.
II. Cortical Control of Cranial Motor
Function
A. Corticobulbar tract
Review Note: Regarding unilateral and bilateral
projections from cortex to sc (or bs nuc  sc) that we
viewed when examining the descending motor systems of
the limbs and axes.
Note that the trend for lateral descending tracts serving the
limbs to have unilateral (crossed) projections, and medial
tracts to serving the axis to have bilateral.
Functional or clinical significance? Muscles working in
concert – unilateral lesion  no unilateral deficit.
This is frequently the scenario with descending tracts for the
head as well: bilateral projections
Fig. 11-2.
Corticobulbar tract
(XII)
Fig. 11-4.
Corticobulbar tract
(V, VII, IX, X, XI)
B. Cortical areas involved in eye movement control.
Rapid and slow eye movements:
Rapid: saccades: quick movements of eyes in
tandem to bring the fovea to an image.
Slow: smooth pursuit: eyes in tandem to track a
moving object
Slow: convergence: disconjugate eye movement
for viewing an object at a close distance.
These movements are not controlled by 1° motor
cortex (Note no eyes in homonculus, Fig. 10-7),
but rather, by a number of important areas
throughout the cortex:
Look!! No eyes!
Fig. 10-7
Look! No eyes!
Cortical areas for Rapid Eye Movement Control
Fig. 12-5.
For REMs (saccades):
frontal eye field,
post parietal cortex
(area 7).
Cortical Areas for Slow Eye Movement Control
Fig. 12-6.
For slow movements:
middle temporal and
mid-superior temporal
(involvement of cortical
visual axons and
cerebellum).
III. General Somatic Motor Column Nuclei
[eyes, tongue (from somatic)]
III. Oculomotor n.  4/6 extraocular muscles
and one elevator of eyelid (Fig. 12-3):
IV. Trochlear n.  superior oblique muscle (Fig. 123).
In Fig. 12-4 (not shown here), note that in the
dorsal brainstem, all axons decussate.
VI. Abducens n.  lateral rectus muscle.
XII. Hypoglossal n.  all intrinsic tongue muscles
and travel in corticobulbar tract (Fig. 11-2).
Note the bilateral projections
For tongue disruption on exam, lesion would
have to be relatively peripheral.
IV. Special Visceral Motor Column Nuclei –
Branchial Arch-derived.
V. Trigeminal motor  muscles of mastication bilateral
projection (chewing is bilaterally coordinated).
VII. Facial motor  muscles of facial expression laterally of
projection – more complex.
Upper face: bilateral projections from both hemispheres.
Lower face: projection only from contralateral motor cortex
(IX, X, XI).
Fig. 6-8
Nucleus ambiguous (IX, X, XI)  striatal muscles of palate,
pharynx, and larynx.
Most neurons project through X.
IX  1 pharyngeal muscle
XI  cranial root comes from n. ambiguous and joins vagus
n. (X) to innervate some muscles.
Nucleus ambiguous and
spinal accessory nucleus.
Spinal accessory nucleus
 2 upper shoulder muscles
(sternocleidomastoid,
trapesiuz) – part of transition
between cranial and spinal
nuclei [really part of ventral
horn of upper cervical sc].
Note: unilateral projection (part of limbs) and
separate sc root.
Note: branchial arch-derived.
V. Regional Anatomy of the Brainstem
Nuclei
• Spinal accessory nucleus at pyramidal
decussation (spinal-medullary junction).
Fig. 11-4
• Medial medullary section
Compare this figure to Fig. 11-1 columns
(hypoglossal, motor vagus, n. ambiguous).
And sensory: vestibular, solitary n., trigeminal.
Fig. 11-12
Rostral medulla (Fig. 11-12): n. ambiguous, sensory
nuclei, exit of IX (glossopharyngeal)
Pons: Abducens, facial n., trigeminal motor
Fig. 11-11
Pons: Abducens, facial n., trigeminal motor
Fig. 11-11
• Midbrain: (level of inferior colliculus): trochlear
n. Fig. 11-9.
Midbrain (at level of superior colliculus):
oculomotor n. Fig. 11-8.
Sensory: mesencephalic trigeminal n.: corticospinal, corticobulbar,
corticopontine tracts.
Motor Functions of the Cranial
Nerves II
Visceral Motor Functions
I. Functional Anatomy – the General
Visceral Motor Cell Column:
This column contains neurons that regulate
the function of smooth muscle and
endocrine glands.
II. Regional Anatomy - Review
Fig. 6-4
I. Functional Anatomy
• Once again – look at columnar
organization: general visceral motor = the
most lateral of the 3 motor columns (Fig. 64):
X – dorsal motor nerve of vagus.
VII, IX superior and inferior salivatory in
pons.
III Edinger-Westphal – midbrain (level of
superior colliculus).
These neurons are part of the parasympathetic
nervous system (ANS).
• Recall that skeletal muscle has 1 important
innervation by a single motor neuron.
• Smooth muscle and glands: innervation by
2 separate neurons (ganglia involved =
preganglionic and postganglionic).
• Preganglionic neurons: located in the
brainstem or spinal cord nuclei.
• Postganglionic neurons: located in
peripheral autonomic ganglion.
Extraocular Eye Muscles
A. Edinger-Westfall Nucleus: located in
pretectal region and midbrain (near III cn
 ciliary ganglion)  ciliary muscle,
constrictor muscle of iris.
Functions of 2 important visual reflexes:
1. Pupillary light reflex  pupil constriction.
2. Accommodation reflex  curvature of lens in
response to near vision (“plump up”).
Fig. 11-8
Pupillary reflex:
Visual input from retina 
pretectal nuclei 
preganglionic
neurons of EWN via
bilateral
projections  ciliary
ganglion  constriction of
muscle of iris.
What is the importance or
consequence of bilateral
projection?
B. Preganglionic Neurons of Pons and Medulla.
General scheme:
Nuclei  cn  ganglia  target
Terminal ganglion associated with vagus nerve:
located in visceral of thoracic and abdominal
cavities (proximal to splenic flexure).
Function: regulate heart rate, gastric motility,
bronchial muscle control, bronchial secretions.
Distal to flexure: innervated by preganglionic n of
sacral spinal cord.
II. Regional Anatomy
• General Visceral Motor column