suzanne s. stensaas © linda pauwels wilson. brainst… · nerves: anatomy and clinical comments...

Brainstem dental 2011.doc

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Dental Neuroanatomy January 20 and 27, 10-12, 2011

Suzanne S. Stensaas, Ph.D.

Dear Students: Please print these notes and bring them with you. My style is to use a Tablet PC and I draw on either a Word or pdf copy with colors. Be prepared to draw. Have at least 5 colors. Please try to look at the notes AHEAD OF TIME for each lecture in this course. This way you can see the direction and organization of the lecture and be more familiar with the terms. There will be a quiz (that does not count) at the beginning to cover topics in the two gross anatomy lectures by Dr. Morton in Phase 1. They are G 17B and GL 18 Waxman, S Clinical Neuroanatomy, 26th ed.2010. THE OLD EDITION IS FINE TOO. Review Ch 5 on the spinal cord organization, but not the tracts in the middle or lesions at the end of the chapter. Also review the basic concept of a reflex. Review or skim Ch 12 on the vascular supply of the brain. Just look at pictures and legends for the clinical part at the end. NEW material: Chapter 7 Waxman, Brainstem, but not the cerebellum part. NEW material: Chapter 8 Waxman, Cranial nerves, all of it including autonomic. BEWARE THE CRANIAL NERVES ARE KILLERS! There are about 50 copies of the following bright yellow paperback book, which can be checked out from the Eccles Health Sciences Library and kept for the duration of the course. They are on reserve as: Cranial nerves: anatomy and clinical comments Linda Wilson-Pauwels, 1988 Toronto; Philadelphia: B.C. Decker; Saint Louis, Mo.

ORIENTATION TO BRAIN STEM AND CRANIAL NERVE MOTOR NUCLEI Objectives for first two lectures: (some of these objectives will be covered next week) 1. Name all the cranial nerves and know their components and functions 2. Identify and locate the cranial nerves associated with the medulla, the pons and the

midbrain. 3. Explain how cranial nerves differ from spinal nerves 4. List the cranial nerves that contain parasympathetic fibers and their function? 5. Recognize the major internal and external landmarks on the dorsal and ventral surface

of the brain stem, so that you can determine if a gross or stained cross section is medulla, pons or midbrain.

6. Identify on cross sections the brain stem nuclei containing motor neurons, except for the salivatory nuclei.

7. Explain why cranial nerves are so important in localizing lesions. 8. Name reflexes that test these nerves. Describe the afferent and efferent limbs of these

reflexes. Lecture Contents I. Medulla Oblongata - associated with CN’s 9,10,11,12 II. Pons. - Associated with CN's 5, 6, 7, 8 III. Mesencephalon (= Midbrain) associated with CN’s 3 and 4


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Suzanne S. Stensaas © Linda Pauwels Wilson ©

David Morton original drawings©


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I. Medulla Oblongata - associated with CNs 9,10,11,12 A. External Anatomy. 1. Three prominent features on the ventral surface -- pyramids, olives, pyramidal

decussation. 2. Associated cranial nerves (only motor components will be considered): CN’s 9,

10, 11, 12. a. Hypoglossal nerve -- XII. (1) Homologue of a ventral root; is somatic motor. (2) Innervates the somatic (striated) muscle of the tongue. b. Vagus nerve -- X. Two motor components. (1) Visceral motor component -- preganglionic parasympathetic axons. (2) Branchiomeric component -- innervates constrictor muscles of the pharynx

and the intrinsic muscles of the larynx. These muscles are striated and under voluntary control.

NOTE: Although branchiomeric muscles are striated, they do not develop from somites. Hence, they are not considered to be somatic muscles. Instead, they develop from the mesenchyme of the pharyngeal (branchial, gill) arches. Therefore, their motor neurons are in different nuclei.

c. Glossopharyngeal nerve -- IX. Two motor components. (1) Visceral motor component -- preganglionic parasympathetic axons to the

otic ganglion. (2) Branchiomeric component -- innervates the stylopharyngeus muscle. d. Spinal accessory nerve -- XI. . It is considered to be branchiomeric in this

course, where we try to simplify. The spinal portion innervates the sternocleidomastoid muscle and part of the trapezius

[The accessory nerve is divided into cranial and spinal portions. The cranial part, which innervates the intrinsic laryngeal muscles, quickly joins the vagus nerve and is considered part of the vagus nerve clinically and in this course.]


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B. Internal Anatomy.

1. The fate of the alar and basal laminae. The basic plan: why brain stem sensory nuclei are lateral to motor nuclei. 2. The IV ventricle floor.

SomaticSensory

VisceralSensoryVisceralMotorSomaticMotor

SpecialVisceral Motor(Branchiomeric)

Sulcus LimitansAlar

Basal

Alar

Basal

SulcusLimitans

Spinal Cord Medulla


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TYPICAL SECTION THROUGH ONE HALF OF THE MEDULLA C. Cranial nerve motor nuclei. 1. Hypoglossal nucleus. Somatic motor. (a) Origin of N. XII. (b) Is comparable to the ventral horn. 2. Dorsal nucleus of vagus. Visceral motor. (a) Origin of the preganglionic parasympathetic axons of X.

(b) Is comparable to the lateral horn. 3. Inferior salivatory nucleus. Visceral motor. (a) Origin of the preganglionic parasympathetic axons of IX to the

otic ganglion. (b) This tiny nucleus is rostral to the dorsal motor nucleus of X.

Inferior SalivatoryNucleus

Sulcus Limitans

IV Ventricle

HypoglossalNucleus

Dorsal MotorNucleus

IX n.X n.

TegmentumRF Nucleus

Ambiguus

Pyramid

Alar

BasalInferior CerebellarPeduncle

Olive

Inferior olivary nucleus


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(c) Is comparable to the lateral horn. (d) You cannot see it. 4. Nucleus ambiguus. Branchiomeric. Called branchial motor in Y and Y and

special visceral motor in other books. (a) Origin of the branchial motor axons of both IX and X. (b) Axons of neurons in the rostral part of the nucleus join the IX nerve and those of

neurons in the middle part, join X. NOTE: Each of these nuclei can be divided into small clusters of neurons that innervate specific muscles. This is referred to as a somatotopic organization.

D. Reticular formation. 1. This forms the "central core” of the brain stem. 2. Its nuclear groups are not very obvious and the intermingling of nerve cell bodies and axons give the formation its name.

3. A "primitive" homeostatically important part of the CNS; in the medulla it contains cardiovascular and respiratory centers.

E. Functional significance of the Medulla: Vital Motor Regulatory Centers. 1. Reflex control of the cardiovascular system. 2. Reflex control of respiration. 3. Reflex control of swallowing and vomiting. 4. Important in phonation = control of tongue, pharynx, larynx F. Vascular supply -- The vertebral artery and its branches. 1. PICA = Posterior Inferior Cerebellar Artery 2. Anterior Spinal Artery

Young, Young and Tolbert, Ch. 3, 2008 ©


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II. Pons. - Associated with CN's 5, 6, 7, 8 A. External Anatomy.

1. Characteristic landmark features: basilar pons=pons proper, middle cerebellar

peduncle, basilar artery and IV ventricle. Recall ventricle IV associated with pons and medulla.

2. Associated cranial nerves a. Nerves at the level of caudal pons:

(1) Vestibulocochlear nerve -- VIII. Ignore for now. (2) Facial nerve -- VII. Two motor components

(a) Visceral motor component -- preganglionic parasympathetic axons to the pterygopalatine and submandibular ganglia.

(b) Branchiomeric component -- innervates the facial muscles, the muscles of facial expression.

(3) Abducens nerve -- VI. (a) Comparable to a ventral root so is somatic motor. (b) Innervates the lateral rectus muscle of the eye.

(4) Trigeminal nerve (V) The motor component is branchiomeric and it

innervates the muscles of mastication.

Caudal Pons Level

Sulcus Limitans

Superior SalivatoryNucleus

MiddleCerebellarPeduncle

FacialNucleus

R. F.

Caudal Pons

PontineTegmentum

PonsProper

AbducensNucleus

Facial Colliculus

VII

VIBasilarArtery

IV Ventricle


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B. Internal anatomy of pontine cranial nerve motor nuclei located within the tegmentum of pons.

1. Caudal Pons a. Facial nucleus. (1) Is a branchiomeric nucleus. (2) Axons innervate the muscles of facial expression. b. Abducens nucleus. Somatic motor nucleus. (1) Origin of N. VI. (2) Is a homologue of the ventral horn. c. Superior salivatory nucleus. (1) Visceral motor. (2) Its axons form the preganglionic parasympathetic component of VII.

2. Mid-pons Motor nucleus of the trigeminal

a Axons innervate the muscles of mastication. b Is a branchiomeric nucleus.

NOTE: This nucleus is located in the dorsolateral tegmentum at the level of mid-pons, thus we have to draw it on a section a bit more rostral.

C. Functional Significance of the Pons

1. Reflex control of the micturition and respiratory systems. 2. Important in eye movements and coordinated movement of the eyes and head. 3. Corneal reflex

D. Vascular Supply – the Basilar Artery and it median and circumferential branches.


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Mid-pons Level

MID-PONS

Corneal Reflex- a consensual reflex

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Ventricle IV

MotorNucleus V

TegmentumR. F.

Pons Proper

Axons of theSensory Part of V

Axon of tMotor Par


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III. Mesencephalon (= Midbrain) associated with CN’s 3 and 4

Brain Stem at the Level of the Inferior Colliculus Neuroanatomy Interactive Syllabus. John Sundsten and Kate Mulligan,

U. of Washington. 1998 ©

A. External Anatomy. 1. Quadrigeminal plate = Tectum. This is the dorsal aspect of the midbrain and it

forms a roof over the aqueduct. It occurs as two sets of mounds. a. Superior colliculus associated with CN III

b. Inferior colliculus. associated with CN IV 2. Cerebral peduncles (crus cerebri) -- form the ventral aspect of the midbrain. 3. Associated cranial nerves: 3, 4 a. Trochlear nerve -- IV. Somatic motor. (1) The homologue of a ventral root (even though it has an aberrant course).

(2) Innervates the superior oblique muscle of the eye. (Intorter, depressor, abductor when tested with the eye adducted.)

(3) A small nucleus of motor neurons at level of inferior colliculus. (4) Its axons cross the midline dorsal to aqueduct. The only cranial nerve

whose axons cross before emerging from the brain stem. (5) Emerges caudal to the inferior colliculus on opposite side. (6) Lesions of the nucleus produce deficit on the opposite (7) Lesion of the nerve produce deficit on the same side.

b. Oculomotor nerve -- III. Two motor components: (1) Somatic motor component -- innervates all of the extraocular muscles

not supplied by IV or VI and levator palpebrae superioris. (2) Visceral motor component -- preganglionic parasympathetic axons to the ciliary ganglion.

(a) Postganglionic axons to ciliary muscle and body. (b) Postganglionic axons to pupillary constrictors in iris. Constriction is

Tectum


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called miosis. What is dilatation of the pupil called? B. Internal Anatomy. 1. Tectum -- is dorsal to the aqueduct and includes the central gray and colliculi 2. Central gray matter -- surrounds the aqueduct (= periaqueductal gray) 3. Red nucleus. 4. Substantia nigra. 5. Cerebral peduncles -- the ventral surface.

SuperiorColliculus

Central Gray

SubstantiaNigra

RedNucleusOculomotor

Nucleus

Edinger-WestphalNucleus

Aqueduct

III

TEGMENTUM

R. F.

TECTUM

CEREBRAL PEDUNCLE

R. F.

Midbrain at Level of Superior Colliculus

6. Tegmentum a. Is located between the aqueduct and tectum dorsally and the cerebral peduncles substantia nigra ventrally. b. Contains cranial nerve motor nuclei: trochlear (IV), oculomotor (III) and Edinger Westphal (III) c. Other contents are the reticular formation and the red nucleus.

C. Functional Significance of the Midbrain.

1. The tectum is important in visual and auditory reflexes that orient the eyes, ears, head, and body toward visual and acoustic stimuli.

2. Coordinated eye movements. 3. Reflexes that control the diameter of the pupil and focusing the lens.

4. Consciousness and arousal: The mesencephalic ascending reticular activating system.

D. Vascular Supply – Branches of the basilar and posterior cerebral arteries


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This is a Self-evaluation Test to do AFTER you have reviewed your classroom discussion notes, and gone through the material in HyperBrain Ch. 4, and read your textbook. If you can do this you are set for Monday.

1. What level of the brain stem is the a. Corneal reflex testing? b. Gag reflex testing? c. Pupillary light reflex testing? 2. Now ask yourself what cranial nerves is each of the above reflexes testing? a. b. c. 3. Next state the location (nucleus) of the neurons for the afferent and efferent limbs of each of these reflexes.

a. Afferent a. Efferent b. Afferent b. Efferent c. Afferent c. Efferent

4. You have a patient who cannot look to the right with the right eye or smile or wrinkle

the right side of their face. Characterize the lesion as to level, side, structure(s) involved.


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Mid-sagittal radiograph with nuclei superimposed. 5. Which side of the photo is rostral or anterior?

a. Can you locate the following MOTOR nuclei we have just studied? We only discussed motor nuclei. (Special visceral refers to striated muscle derived from the branchial arches.) Ignore the sensory nuclei for now.

Ambiguus Facial Hypoglossal Trochlear Dorsal Vagal Abducens Oculomotor Motor nucleus of V Edinger-Westphal

b. Associate each nucleus with a particular level of the brain stem?

c. Describe the motor function of each nucleus?

d. Describe the sign or symptom of dysfunction of each of these nuclei?


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6. Can you locate and name the motor nuclei associated with CNs 3,4,5,6,7,9,10,11, and

12? The preceding picture may help you. 7. Brain stem reflex testing involves motor neurons for the efferent limb of the reflex.

For the following reflexes name the nucleus where the efferent neuron is located. a. Corneal reflex b. Gag reflex c. Pupillary light reflex


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8. Next state the location of the neurons for the afferent limbs of the following reflexes. (You might have to remember your gross anatomy.)

a. Corneal reflex b. Gag reflex

9. Now ask yourself what two cranial nerve(s) is each of the above reflexes testing?

a. Corneal b. Gag c. Pupillary

10. You have a patient who cannot look to the right with the right eye or smile or

wrinkle the right side of their face. Characterize the lesion as to level, side, structure(s) involved

11. A cerebrovascular occlusion affects the area the arrow is pointing to. First realize this

is a myelin stained section and tracts are black and nuclei gray.

a. What level is this? b. Identify the nucleus.

c. What reflex involves cells in this nucleus? Is it the afferent or efferent limb of the reflex? d. If you could only test one reflex, which one would be most diagnostic for localizing the level of the lesion? e. You are on the stroke team and you tell the neuroradiologist to look carefully for a lesion in the distribution of the ______________________________artery.


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12. What reflex would be abnormal in a patient with a lesion that included the circled

area? 13. This is a gross pathology cross section 10 days after a stroke. The patient was in a

coma the entire time.

a. What level is this? b. Since he is in a coma, what reflex are you going to test? c. Why was he in a coma? d. What vessel do you think was occluded?

suzanne s. stensaas © linda pauwels wilson. brainst… · nerves: anatomy and clinical comments...

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