Brainstem Anatomy Lab

Front 1

Brain stem contains

Back 1

- 10 cranial nerves
- cranial nuclei
- medial lemniscus (gracile and cuneate tracts)
- spinal lemniscus (spinothalamic tract)
- corticospinal tract

Front 2

Midbrain Cranial Nuclei

Back 2

CNIII

Front 3

Pons Nuclei

Back 3

CN IV, V, VI, VII, VIII

Front 4

Medulla Nuclei

Back 4

CN, IX, X, XI, XII

Front 5

Damage to III

Back 5

III – oculomotor: supplies all extrinsic eye muscles: medial, superior, and inferior rectus,
inferior oblique and levator palpebrae muscles. Damage results in diplopia (double vision),
ptosis (drooping eyelid), and outward deviation of the eye.

Front 6

Damage to IV

Back 6

IV – trochlear: supplies the superior oblique muscle. Damage results in upward deviation
of the eye and thus diplopia.

Front 7

Damage to V

Back 7

V – trigeminal: supplies general sensory to the face (touch, proprioception, pain, heat),
the muscles of mastication as well as tensor tympani, tensor palati and digastric. Damage
results in decreased sensitivity of face (possible numbness), brief attacks of pain, weakness
and wasting of jaw muscles and asymmetric chewing.

Front 8

Damage to VI

Back 8

VI – abducens: supplies the lateral rectus muscle. Damage results in inward deviation of the eye and thus diplopia.

Front 9

Damage to VII

Back 9

facial: supplies the muscle of facial expression, stapedius muscle, taste to the
anterior 2/3rds of the tongue and lacrimal and salivary glands. Damage results in paralysis of
the facial expression muscles and loss of taste of ant 2/3rds of tongue

Front 10

Damage to VIII

Back 10

vestibulocochlear: supplies the vestibular apparatus and the cochlear. Damage results in deafness (sometimes tinnitus) and disequilibrium

Front 11

Damage to IX

Back 11

IX – glossopharyngeal: supplies sensation to the palate and taste to the posterior 1/3rd of the tongue and stylopharyngeal muscle. Damage results in pain spasms in posterior pharynx and loss of taste in posterior 1/3rd of tongue.

Front 12

Damage to X

Back 12

X – vagus: supplies autonomics and transmits sensory information to/from the viscera and
heart, muscle of pharynx and larynx. It also supplies the muscles of the pharynx and larynx.
Therefore damage results in hoarseness, poor swallowing and loss of gag reflex.

Front 13

Damage to XI

Back 13

XI – accessory: supplies trapezius and sternocleidomastoid muscles. Damage results in
wasting in the neck with weak neck rotation - cant shrug.

Front 14

Damage to XII

Back 14

XII – hypoglossal: supplies the intrinsic muscles of the tongue, hyoglossus, styloglossus and genioglossus muscles. Damage results in wasting of tongue and tongue deviation to side of lesion on protrusion.

Front 15

Neural tube forms _____ vesicles to begin with called ______________. They then form the ____________ secondary.

Back 15

3.
(1). Prosencephalon: telecephalon (cerebral hemispheres) and diencephalon (thalamus/hypothamalus);
(2) Mesencephalon - forms the midbrain
(3) Rhombencephalon - forms the brainstem -metencephalon (pons and cerebellum) and the
myelencephalon (medulla oblongata)

Front 16

brainstem surface anatomy

Back 16

Front 17

Pyramids

Back 17

• pyramids (pyr): A pair of columnar elevations on the ventral surface of the medulla, either
side of the midline. They comprise the descending motor fibres (corticospinal tracts).
These fibres originate in the cerebral cortices, most of the fibres cross the midline in the
lower medulla (pyramidal decussation; Px), to form the lateral corticospinal tract. Above,
the pyramids are continuous with cerebral peduncle.

Front 18

Olives

Back 18

• olives: A pair of elevations lateral to pyramids in the upper medulla, formed by the ‘olivary
nuclei’ located just below the surface. The olivary nuclei supply information regarding motor
control to the cerebellum – a region concerned with coordination of movement.

Front 19

rhomboid fossa

Back 19

• rhomboid fossa: The quadrilateral shaped floor of the 4th ventricle, on the dorsal surface of
brainstem. Sections of the brainstem which cut through the lower end of the rhomboid fossa
are commonly referred to as sections of the 'open medulla'; below the level of rhomboid fossa
they are referred to as 'closed medulla'.

Front 20

superior cerebellar peduncle

Back 20

The cerebellum is attached to the brainstem by 3 pairs
of large fibre bundles called cerebellar peduncles. The cut surfaces of these peduncles are
visible. The superior cerebellar peduncle mostly comprises fibres that pass from the
cerebellum into the midbrain beneath the colliculi and continue to the red nucleus and
thalamus. This motor outflow from the cerebellum is concerned with motor coordination

Front 21

gracile (Gr) and cuneate (Cu) tubercles

Back 21

2 pairs of eminences on dorsal surface of
medulla, immediately below the lower margin of the 4th ventricle. The most medial pair is
the gracile tubercles; the more lateral pair is the cuneate. Beneath these tubercles lie nuclei of
the same name. These nuclei comprise cells which receive synapses from fibres of the dorsal
column tract (gracile and cuneate tracts) just before they cross the midline. Axons originate
from the gracile and cuneate nuclei cross the midline and ascend to the thalamus as the
medial lemniscus. Remember that the cuneate and gracile tracts are carrying sensory
information from the spinal cord up to the thalamus and cerebral cortex. What sensory
information do they carry and from which side of the body?

Front 22

inferior cerebellar peduncle

Back 22

• inferior cerebellar peduncle (icp): An indistinct bulge on the lateral aspect of the medulla,
comprising fibres which carry information about position and balance to the cerebellum. That
is, spinocerebellar fibres and vestibular fibres.

Front 23

pons and middle cerebellar peduncle

Back 23

• pons and middle cerebellar peduncle (mcp): A prominent, horizontally elongated feature
on the ventral surface of the brainstem, comprising nuclei (cells) that receive synapses from
descending motor fibres (corticopontine fibres) and give rise to ‘pontocerebellar fibres’ that
cross the midline (hence the lack of a midline groove at this level) and enter the cerebellum.
This is the major connection between cerebral cortex and cerebellum.

Front 24

inferior colliculi

Back 24

• inferior colliculi (IC): Pair of structures on dorsal brainstem at level of cerebral peduncles,
They are relay nuclei in the hearing pathway.

Front 25

superior colliculus

Back 25

• superior colliculus (SC): Pair of structures on dorsal aspect of brainstem (rostral to former)
What is their role in vision?

Front 26

Location of sensory and motor in brainstem

Back 26

- sensory nuceli; dorsolateral aspect
- motor nuclei; medial aspect
- central canal; dorsal and lateral to form the 4th ventricle

Front 27

Migration of alar and basal plates in brainstem

Back 27

- closed medulla; migrate in a relatively simple fashion forming the dorsal and ventral horns respectively
- open medulla and rostral; as above

Front 28

Closed Medulla Crossection; MOTOR DECUSSATION

Back 28

Front 29

Closed Medulla Crossection: SENSORY DECUSSATION

Back 29

Fibres ascending in the
dorsal columns synapse on cells in nuclei of the corresponding names (CuN and GrN) and, before
continuing their progress rostrally, pass ventrally and medially to cross the midline anterior to the
central grey. The crossing fibres are referred to as the internal arcuate fibres (IntAr; sensory
decussation). Having crossed the midline these fibres assemble together adjacent to the midline and
form the medial lemniscus (ML).
• The ScT and StT are still lying lateral in this region of the brainstem, although the ScT has shifted to
the edge and more dorsal.
• At this level, as indeed in most of the others that follow, there are broad, more central regions
designated as the brainstem reticular formation (BRF).

Front 30

Open Medulla Crossection

Back 30

Front 31

Open medulla Nuclei

Back 31

Front 32

Pons Nuclei

Back 32

Front 33

Pons Crossection

Back 33

lying more lateral to the medial lemniscus, a distinct set of auditory nuclei (Audn;
eg, trapezoid body, superior olivary, nucleus, nucleus of the lateral lemniscus) and the auditory
decussation form across the midline (Audx). A distinct MLT is apparent also at this level

Front 34

Pontocerebellar Axons

Back 34

Pontocerebellar axons (PcT) originate from the cells of the pontine nuclei; their axons cross the
midline and enter the cerebellum via middle cerebellar peduncle (mcp). The bulk of the inputs to the
pontine nuclei are from the corticopontine tract.

Front 35

Caudal Midbrain

Back 35

Just dorsal to the cp, lies the massive
substantia nigra. This nucleus is made up of 2 major subnuclei called substantia nigra pars reticulata
(SNr) and substantia nigra pars compacta (SNc). SNc house the melanin rich dopaminergic cells so
crucial in proper motor control. Just medial to the substantia nigra lies another group of dopaminergic
cells of the ventral tegmental area (VTA).

- superior cerebellar peduncle (scp). cross to the
contralateral side at the level of the inferior colliculi (IC)

The grey matter of the midbrain appearing
dorsal to the cerebral aqueduct and periaqueductal grey is generally referred to as the tectum.
- • Surrounding the mesencephalic aqueduct (MAq) lies the periaqueductal grey matter (PAG).

Front 36

Brain stem Blood Supply

Back 36

- paired vertebral aa.

Front 37

Vertebral aa.

Back 37

These are branches of
the subclavian artery and ascend to the base of the skull by passing through the foramina
transversaria of the cervical vertebrae. The vertebral arteries enter the cranial cavity through
the foramen magnum and are found on the lateral aspect of the medulla. They pass ventrally
and rostrally to unite at the caudal border of the pons, forming the basilar artery

most people are left vertebral aa. dominant

Front 38

posterior inferior cerebellar artery

Back 38

• The posterior inferior cerebellar artery (PICA) is a branch of the vertebral artery, given
off a centimeter or so below the pons. It supplies the lateral medulla (dorsolateral to the olive,
including the inferior cerebellar peduncle), as well as the ventral surface of the cerebellum.
Medially the brainstem is supplied directly by small branches of the vertebral artery; the
territory goes at least as deep as the medial lemniscus.

Front 39

anterior inferior cerebellar artery

Back 39

The anterior inferior cerebellar artery (AICA) is a branch of the basilar artery and
occupies the groove between the pons and the medulla; the superior cerebellar artery is
also a branch of the basilar and is found towards the rostral end of the pons. The pons is
supplied by the basilar artery and the anterior inferior and superior cerebellar arteries.

Front 40

Basilar aa.

Back 40

The basilar artery ends by dividing to form the 2 posterior cerebral arteries. The posterior
cerebral arteries supply the cerebral peduncles and midbrain before passing laterally to the
cerebral hemispheres

Front 41

Brainstem BS

Back 41

stroke -85% blockage and 15% rupture

Front 42

1) Paramedian/basal arteries in the midbrain.

Back 42

damage to the midline
corticospinal and corticobulbar tracts, damage to the reticular formation and loss of the
oculomotor nuclei. This can result in the "locked in with ocular palsy" syndrome. The
patients typically have sudden onset of vomiting and may have transient loss of
consciousness. There is acute onset quadriplegia (corticospinal tracts), bilateral facial
paralysis (corticobulbar tracts), loss of speech (corticobulbar tracts for cranial nerve nuclei
controlling larynx, pharynx, tongue and lips) and loss of voluntary eye movements (loss of
oculomotor nuclei).

Front 43

2) Paramedian/basal arteries in the pons.

Back 43

Occlusion of pontine paramedian/basal arteries also results in damage to the midline
corticospinal and corticobulbar tracts and damage to the reticular formation. The oculomotor
nuclei are spared. This can result in "locked in syndrome without ocular palsy" so the patient
still has voluntary eye movements. Facial muscles are paralysed due to damage to
corticobulbar fibres.

Front 44

3) Superior cerebellar artery

Back 44

Main symptoms are ipsilateral cerebellar ataxias (loss of middle and/or superior cerebellar
peduncles), nausea and vomiting, slurred speech, loss of pain and temperature over the
opposite side of the body. Partial deafness, an ipsilateral Horner syndrome.

Front 45

4) Anterior inferior cerebellar artery

Back 45

The second most common brainstem stroke involves the anterior inferior cerebellar artery. It
supplies the more anterior portions of the inferior surface of the cerebellum (e.g., the
flocculus). It also supplies parts of the caudal pons. The labyrinthine or internal auditory
artery usually takes its origin from AICA and supplies the inner ear.
These patients present with sudden onset vertigo, vomiting and falling to one side. They have
usually marked horizontal nystagmus but the characteristic features are absent sensation on
one side of the face, ipsilateral facial paralysis and ipsilateral hearing loss. They also lean to
the affected side when you make them sit. The ipsilateral loss of sensation in the face may
easily lead one to make a misdiagnosis of Wallenberg syndrome, ie, the lateral medullary
syndrome, but facial paralysis and hearing loss are not features of Wallenberg syndrome. The
combination of ipsilateral hearing loss, facial paralysis and loss of facial sensation is a very
typical feature of anterior inferior cerebellar artery occlusion syndrome.
CN VII is at the pontomedullary junction and the anterior inferior cerebellar artery affects the
anterior and inferior part of pons, so it often involves the exiting fibers of the 7th nerve
(facial paralysis) and the neighbouring auditory nerve nucleus (ipsilateral hearing loss) and
the chief sensory nucleus of V (absent sensation on the face including touch, pain and
temperature). Damage to the inner ear may be the cause of the nystagmus and vertigo.

Front 46

5) Posterior inferior cerebellar artery

Back 46

(i) the spinal tract and nucleus of cranial nerve V (loss of pain and temperature sensation on
the ipsilateral side of the face),
(ii) nucleus ambiguus - (ipsilateral paralysis of soft palate, pharynx and larynx leading to
dysphagia and dysarthria),
(iii) vestibular nuclei (leading to vertigo and nystagmus - saccadic dysmetria (overshoot) or
saccadic pulsion (pulling of the eye during vertical saccades toward the side of lesion).
(iv) contralateral sensory deficit, the spinal lemniscus (contains the crossed spinothalamic
tract) is located laterally in the medulla and is damaged by this stroke resulting in loss of pain
and temperature sensation on the body below the head. Remember this odd combination of
loss of pain and temperature sensation on the ipsilateral side of the head and contralateral
side of the body.
(v) Ipsilateral ataxia since PICA supplies part of the cerebellum.
(vi) Ipsilateral Horner’s syndrome characterised by ptosis, miosis and facial anhidrosis. This
is due to due to damage to the descending sympathetic fibres located close to the spinal
lemniscus

Front 47

6) Vertebral artery

Back 47

The vertebral arteries supply the lateral section of the medulla and a complete block of this
artery can also result in "Wallenberg Syndrome".
The region supplied by the vertebral artery contains the spinal trigeminal nucleus, the inferior
olivary nucleus, nucleus ambiguous, sympathetics, and the spinothalamic tract. As a result a
blockage of this artery would result in loss of pain and temperature sensation in the ipsilateral
face, ipsilateral facial pain (SpV), contralateral pain and temperature loss of the body
(spinathalamic tract), ipsilateral ataxia and gait ataxia (IO), hoarseness and dysphagia (NA)
and Horner's syndrome.

Front 48

7) Anterior spinal artery

Back 48

The anterior spinal artery supplies the territory which contains the pyramidal tract, the medial
lemniscus and the hypoglossal nucleus.
As a result, an occlusion of this artery would result in contralateral weakness of both the
upper and lower extremities (pyramidal tract before it crosses), contralateral sensory loss, e.g.
vibration, propriception (not pain and temperature), and ipsilateral tongue weakness
(hypoglossal nucleus).

Front 49

Crossections Through Medulla

Back 49

A. MEDIAL STRUCTURES:
1. hypoglossal nucleus
2. ML
3. Pyramid
B. LATERAL STRUCTURES:
1. NA (CN IX, X, XI)
2. Vestibular nuclei (CNVIII)
3. Inferior cerebellar peduncle (dorsal spinocerebellar, cuneocerebellar and olivocerebellar tracts)
4. L StT (Spinal Lemniscus)
5. Spinal Trigeminal nucleus and tract of CNV

Front 50

Crossection through Pons

Back 50

- dorsal tegmentum and ventral base
MEDIAL:
1. MLF
2. CNVI nucleus (underlies facial colliculus)
3. Genu of CNVII (underlies VII)
4. CNVI fibres
5. ML
6. CsT
LATERAL
1. VII nucleus
2. VII fibres
3. Spinal trigeminal nucleus and tract
4. L StT
5. Vestibular nuclei
6. Cochlear nuclei

Front 51

Crossection through Midbrain

Back 51

- has a drosal tectum, intermediate tegmentum and a base
- aqueduct between the tectum and tegmentum
DORSAL STRUCTURES:
- superior colliculi
TEGMENTUM:
1. CNIII nucleus
2. MLF
3. Red nucleus
4. Substantia nigra
5. Dentatothalamic tract (crossed)
6. ML
7. Lateral StT
CRUS CEREBRI; CsT in middle 3/5
- also ahs the corticobulbar tract

Front 52

Corticobulbar Fibres

Back 52

project bilaterally to all motor cranial nerve nuceli except facial nucelus.
- the upper face orbicularis oculi and above recieves bilateral corticobulbar input
- lower face only recieves contralateral corticobulbar input

Front 53

Brainstem Reticular Formation
2 main functions

Back 53

1. Arousal-mood setter (eg hangover to allow repair)
2. Autonomic Policeman: monitors and inturn influences crucial reflexes

Front 54

BRF Pathways

Back 54

1. reticulo-spinal tract; somatic (eg pain) and visceral (eg GIT)
2. Raphe nuclei

Front 55

Raphe Nuclei

Back 55

• LOCALE: raphe nuclei
• CONNECTIONS: all over
• FUNCTIONS:
- behaviour
- mood (depression)
- aggression (hypothalamus, amygdala, hippocampus)
- pain (inhibits cells in dorsal horns)
- blood flow control (causes vasconstriction at high levels and so may be the initiating fator of migraine AURA- due to hypoxia) the resulting vasodilation aggitates V1 causing headache

Front 56

BRF ACh Groups

Back 56

• LOCALE: BRF Ach groups
• CONNECTIONS: all over
• FUNCTIONS:
- arousal
- memory (attention)
- ANS control
- pain
- dreamer

Front 57

BRF DA

Back 57

• LOCALE: substantia nigra, ventral tegmental area
• CONNECTIONS: forebrain
• FUNCTIONS:
- behaviour regulation
- focus (movements and suppresses unwanted moves, eg unable to suppress tremor in PK)
- pleasure/motivation

Overactivity @ cortex causes +ve Sx of schizo while uderactivity causes -ve Sx of pshyco

Front 58

BRF NA

Back 58

• LOCALE: locus coeruleus
• CONNECTIONS: all over
• FUNCTIONS:
- ANS control
- pleasure/motivation (cocaine and amphetamines stop reuptake of NA & DA)
- blood flow control
- neural plasticity
- global attention (INC. sens. info inputs, preps for emergency)