Brainstem Midbrain and Pons David A Morton Ph

Brainstem Midbrain and Pons David A. Morton, Ph. D. Jan 10 th, 2013

Objectives • • • 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 • 3 rd ventricle • Cerebral aqueduct • 4 th ventricle Corpus LV callosu m 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 VM SM Basal Medulla BM VS lim Sulc ita us ns

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 m le nc pe du al br Ce re bs tan tia nig ra Rn Su T u ent m eg Rostral midbrain

Midbrain (Rostral) Internal anatomy • Oculomotor nucleus • Edinger-Westphal nucleus le nc pe du al br re Ce Su bs tan tia nig ra Aq Rostral midbrain

Midbrain (Caudal) Internal anatomy • Trochlear nucleus Red nucleus b Su i nt sta a igr n a 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 III

Pons External anatomy: • Basilar pons (pons proper) • Middle cerebellar peduncle (MC) • Basilar artery 4 th • 4 th ventricle • CNN V, VII, VIII V MC 4 th vent. M C VI Pons Horizontal section VIII 4 th

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 4 th 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.