Brainstem
Midbrain and Pons
David A. Morton, Ph.D.
Jan 10th, 2013
Objectives
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Explain how spinal nerves differ from cranial nerves
Name all the cranial nerves and know their components and functions
Identify and locate the CN’s associated with the medulla, pons and midbrain
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.
Identify on a typical cross section all the brain stem nuclei containing motor
neurons that end on striated muscle.
List the cranial nerves that contain parasympathetic fibers, the location of their
nuclei, and their function
Explain why cranial nerves are so important in localizing lesions.
Name reflexes that test these nerves and brain stem levels.
Relate branches of the vertebrobasilar blood supply to the medulla and pons
explaining the deficits that would occur with vascular occlusion.
Directional terms with Brain
Cranial nerve overview
CN I – Olfactory nerve
Cranial nerve overview
CN II – Optic nerve
Cranial nerve overview
CN III – Oculomotor nerve
Cranial nerve overview
CN IV – Trochlear nerve
Cranial nerve overview
CN V – Trigeminal nerve
Cranial nerve overview
CN VI – Abducens nerve
Cranial nerve overview
CN VII – Facial nerve
Cranial nerve overview
CN VIII – Vestibulocochlear nerve
Cranial nerve overview
CN IX – Glossopharyngeal nerve
Cranial nerve overview
CN X – Vagus nerve
Cranial nerve overview
CN XI – Spinal accessory nerve
Cranial nerve overview
CN XII – Hypoglossal nerve
Brain Overview
Brainstem
• Midbrain
• Pons
• Medulla
Midbrain
Pons
Medulla
Brain Overview
Diencephalon
• Thalamus
• Hypothalamus
• Pineal gland
Th
HTh
P
Brain Overview
• Corpus callosum
• Lateral ventricle
• 3rd ventricle
• Cerebral aqueduct
• 4th ventricle
LV
3
aq
4
Spinal Cord and Spinal Nerve Review
Spinal nerve anatomy
• Dorsal root
• Somatic sensory neurons
• Visceral sensory neurons
• Ventral root
• Visceral motor neurons
• Somatic motor neurons
Som S
Alar
VS
Sulcus
limitans
VM
SM
Basal
Spinal cord
Internal anatomy of brainstem
Som S
Alar
The fate of the alar and basal laminae
VS
Sulcus
limitans
VM
• Why are brain stem sensory nuclei lateral
to motor nuclei in brainstem?
SM
Basal
Spinal cord
Som S
Alar
VS
VM
SM
BM
Basal
Medulla
Midbrain (mesencephalon)
External anatomy:
• Quadrigeminal plate
• Superior colliculus
SC
CP
IC
IV
• Inferior colliculus
• Cerebral peduncles
• CN IV
Dorsal view of brainstem
Midbrain (mesencephalon)
External anatomy:
SC
• Quadrigeminal plate
• Superior colliculus
• Inferior colliculus
CP
• Cerebral peduncles
• CN III (arrows)
Ventral
Rostral midbrain
IC
CP
CP
Dorsal view of midbrain
Ventral
Caudal midbrain
Midbrain
Oculomotor nucleus
Cranial nerve nuclei
Edinger-Westphal nucleus
• Rostral midbrain
• Oculomotor nucleus
• Edinger-Westphal nucleus
• Caudal midbrain
• Trochlear nucleus
Motor
Sensory
Trochlear nucleus
Midbrain (Rostral)
Internal anatomy
• Tectum
• Tegmentum
• Central gray matter
• Red nucleus
• Substantia nigra
• Cerebral peduncles
Tectum
Aq
Rn
Rostral midbrain
Midbrain (Rostral)
Internal anatomy
• Oculomotor nucleus
• Edinger-Westphal nucleus
Aq
Rostral midbrain
Midbrain (Caudal)
Internal anatomy
• Trochlear nucleus
Red
nucleus
Caudal midbrain
Horizontal section
Midbrain
Functional significance of midbrain:
• Visual and auditory reflexes
• Coordinates eye movements
• Pupillary reflex
• Consciousness and arousal (RAS)
Midbrain
Arterial supply. Branches off the:
• Posterior cerebral artery
• Basilar artery
Pupillary and Accommodation Reflexes
Bilateral contraction of
sphincter pupillae and
ciliary muscles
CN II
CN III
Pons
External anatomy:
• Basilar pons (pons proper)
• Middle cerebellar peduncle (MC)
• Basilar artery
4th
• 4th ventricle
• CNN V, VI, VII, VIII
V
4th vent.
Pons
Horizontal section
VI
VII
VIII
4th
Pons
Cranial nerve nuclei
• Rostral Pons
• Trigeminal nucleus
• Caudal Pons
• Abducens nucleus
• Facial nucleus
Trigeminal nucleus
Abducens nucleus
• Sup salivatory nucleus
Facial nucleus
Sup salivatory nucleus
Motor
Sensory
Pons (Rostral/Mid)
Internal anatomy
• Trigeminal motor nucleus
• Functional significance
4th Ventricle
Axons of the sensory
part of V
Motor nucleus of V
Tegmentum
R.F.
Pons Proper
Axons of the motor
part of V
Pons (caudal)
Facial nucleus
• Branchial motor nucleus
• Innervate muscles of face
Pons (caudal)
Superior salivatory nucleus
• Visceral motor (Para)
• Origin of preganglionic
parasympathetic neurons
Pons (caudal)
Abducens nucleus
• Origin of Abducens n. (CN VI)
• Homolog to ventral horn
Pons (caudal)
Internal anatomy
• Facial nucleus
• Superior salivatory nucleus
• Abducens nucleus
Corneal reflex
• Consensual reflex
• Sensory: CN V-1 to spinal trigeminal nucleus
• Motor: Facial nucleus out to the temporal branch of CN VII
Spinal trigem.
Nucleus & Tract
Corneal Reflex
Touch the
cornea
Semilunar ganglion
of CN V
Spinal trigeminal
nucleus
CN V-1
L
R
Facial motor
nucleus
Temporal branch of
CN VII
Blink
(Orbicularis
occuli muscle)
Pons
Arterial supply. Branches off the:
• Basilar artery
• Median and Circumferential
branches
Match the following reflexes with their associated brainstem level:
a. corneal reflex testing?
b. Gag reflex testing?
c. pupillary light reflex testing?
I
II
III
Match the following reflexes with their associated brainstem level:
a. corneal reflex testing?
I
b. Gag reflex testing?
III
c. pupillary light reflex testing?
II
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.
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.
What reflex would be abnormal in a patient with a lesion that included the circled area?
What reflex would be abnormal in a patient with a lesion that included the circled area?
Abducens nucleus
Facial nucleus