Brainstem

David A. Morton, Ph.D.Jan 10th, 2013

Midbrain and Pons

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

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

Cranial nerve overview

Brainstem

• Midbrain

• Pons

• Medulla

Brain Overview

Medulla

Pons

Midbrain

Diencephalon

• Thalamus

• Hypothalamus

• Pineal gland

Brain Overview

PHTh

Th

• Corpus callosum

• Lateral ventricle

• 3rd ventricle

• Cerebral aqueduct

• 4th ventricle

Brain Overview

4

Corpus callosum

3

LV

aq

Spinal Cord and Spinal Nerve Review

Alar

Basal

Sulcus limitans

Spinal cord

Som S

VS

VM

SM

Spinal nerve anatomy

• Dorsal root

• Somatic sensory neurons

• Visceral sensory neurons

• Ventral root

• Visceral motor neurons

• Somatic motor neurons

Internal anatomy of brainstem

Alar

Basal

Sulcus limitans

Spinal cord

Som S

VS

VM

SM

Alar

Basal

Sulcus limitans

Medulla

Som S

VSVM

SMBM

The fate of the alar and basal laminae

• Why are brain stem sensory nuclei lateral

to motor nuclei in brainstem?

External anatomy:

• Quadrigeminal plate

• Superior colliculus

• Inferior colliculus

• Cerebral peduncles

• CN IV

Midbrain (mesencephalon)

SC

CPIC

IV

Dorsal view of brainstem

External anatomy:

• Quadrigeminal plate

• Superior colliculus

• Inferior colliculus

• Cerebral peduncles

• CN III (arrows)

Midbrain (mesencephalon)

Rostral midbrain

Caudal midbrain

SC

IC

CP

CP

Dorsal view of midbrain

CP

Ventral

Ventral

Cranial nerve nuclei

• Rostral midbrain

• Oculomotor nucleus

• Edinger-Westphal nucleus

• Caudal midbrain

• Trochlear nucleus

Oculomotor nucleus

Edinger-Westphal nucleus

Trochlear nucleus

Midbrain

MotorSensory

Internal anatomy

• Tectum

• Tegmentum

• Central gray matter

• Red nucleus

• Substantia nigra

• Cerebral peduncles

Midbrain (Rostral)

Subs

tantia n

igra

Cere

bral

pedu

ncle

Aq

Tectum

Tegmentum

Rn

Rostral midbrain

Internal anatomy

• Oculomotor nucleus

• Edinger-Westphal nucleus

Midbrain (Rostral)

Subs

tantia n

igra

Cere

bral

pedu

ncle

Aq

Rostral midbrain

Internal anatomy

• Trochlear nucleus

Midbrain (Caudal)

Caudal midbrain

Horizontal section

Red nucleus

Substantia nigra

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

Midbrain

Pupi

llary

and

Acc

omm

odati

on R

eflex

es

CN II

Bilateral contraction of sphincter pupillae and

ciliary muscles

CN III

External anatomy:

• Basilar pons (pons proper)

• Middle cerebellar peduncle (MC)

• Basilar artery

• 4th ventricle

• CNN V, VI, VII, VIII

Pons

MC

V

VI VIIVIII

Pons

4th vent.

Horizontal section

MC

4th

4th

Cranial nerve nuclei

• Rostral Pons

• Trigeminal nucleus

• Caudal Pons

• Abducens nucleus

• Facial nucleus

• Sup salivatory nucleus

Trigeminal nucleus

Facial nucleus

Abducens nucleus

Pons

MotorSensory

Sup salivatory nucleus

4th Ventricle

Motor nucleus of V

TegmentumR.F.

Pons Proper

Axons of the sensory part of V

Axons of the motorpart of V

Pons (Rostral/Mid)

Internal anatomy

• Trigeminal motor nucleus

• Functional significance

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

Spinal trigem. Nucleus & Tract

• Consensual reflex

• Sensory: CN V-1 to spinal trigeminal nucleus

• Motor: Facial nucleus out to the temporal branch of CN VII

Corneal ReflexSemilunar ganglion

of CN V

CN V-1

L R

Spinal trigeminal nucleus

Touch the cornea

Blink(Orbicularis occuli muscle)

Facial motor nucleus

Temporal branch of CN VII

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?

b. Gag reflex testing?

c. pupillary light reflex testing?

I

II

III

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