Brainstem & Cranial Nerves
Lecture note
Morgan e
Development
Ventricles in brainstem
• Mesencephalon  cerebral aqueduct
• Metencephalon  4th ventricle
• Mylencephalon  4th ventricle
Corpus callosum
Posterior commissure
Fornix
Occipital
Lobe
Thalamus
Anterior
commissure
Quadrigeminal
cistern
Hypothalamus
vermis
Optic nerve
4th ventricle
Mammillary body
pyramid
Anterior view of brainstem
basal ganglia
internal capsule
optic chiasm
optic nerve
optic tract
hypothalamus
mammillary body
cerebral peduncle
interpeduncular fossa
pons
flocculus
inferior olivary
nuclear complex
cerebellar tonsil
cerebellum
pyramidal decussation
pyramid
Lateral view of brainstem
optic tract
cerebral
peduncle
trigeminal nerve
optic nerve
middle cerebellar peduncle
optic chiasm
vestibulocochlear nerve
flocculus
hypothalamus
cuneate tubercle
pons
inferior olivary nuclear complex
anterior median fissure
pyramid
Posterior view of brainstem
Superior colliculus
Cerebral
peduncle
Superior cerebellar
peduncle
Middle cerebellar
peduncle
Inferior colliculus
4th ventricle
Inferior cerebellar
peduncle
Medulla
Components of the brainstem
•
•
•
•
•
Sensory ascending pathways (dorsal)
Motor descending pathways (ventral)
Cerebellar pathways
Cranial nerve sensory and motor tracts
CPGs: rhythmic chewing, respiration,
cardiovascular regulation & gain adjustments
for reflexes
• Modulatory systems: locus coeruleus, raphe
& substantia nigra
Brainstem: 3 major divisions
•Midbrain
•Pons
•Medulla
Ascending sensory pathways
Fine discriminitive touch, conscious proprioception
• Fasciculus gracilis: Terminates in the nucleus gracilis (medulla)
• Fasciculus cuneatus: Terminates (medulla) in the cuneate and
accessory cuneate nuclei
Sensations of pain and temperature
• Lateral Spinothalamic Tract
– origin dorsal horn cells of the gray matter
– Fibers cross contralaterally through the anterior commissure and
ascend to the VPL nucleus
Transmits sensations of touch
• Ventral Spinothalamic Tract
– origin cells of the posterior horn
– Fibers cross to the opposite side in the anterior commissure
Descending motor pathways
Voluntary movement
• Lateral Corticospinal Tract
– Originates in large pyramidal cells (precentral gyrus)
– cross to the opposite side of the cord at the pyramidal decussation &
terminate in the dorsal horn cells
• Ventral Corticospinal Tract
– Originates in the pyramidal cells (motor area of the cortex)
Impulses related to equilibrium and antigravity reflexes
• Vestibulospinal Tract
– Fibers originate in the vestibular nuclei of the medulla and terminate
at level of the sacral spinal nerves
Connects vestibular complex and head and eye movement
coordination center in medulla
• Medial Longitudinal Fasciculus
– Contains both ascending and descending fibers
Motor Hierarchy
•Lateral group (extremities;
fine motor control)
•Corticospinal tract
•Rubrospinal tract
•Medial group (axial
musculature; rhythmic and
postural movements)
•Vestibulospinal tract
•Tectospinal tract
•Reticulospinal tract
•“Final common path”:
motor pool
Reticular Formation
• “Core” of brainstem
(midbrain, pons and medulla)
composed of loosely
organized neurons, outside of
the major nuclear groups of
the brainstem.
• Medial-to-lateral: raphe
nuclei, gigantocellular region,
small cell region
• Participate in widespread
connections
• Rostral continuation of
interneuronal network found
in spinal cord
Cerebellar pathways
Conduct impulses from the leg and trunk muscles for
unconscious proprioception
• Dorsal & Ventral Spinocerebellar Tracts
– Enter cerebellum via inferior cerebellar peduncle
Summary of Spinal Cord Tracts
Brainstem Internal Anatomy
Components of the brainstem
• Sensory ascending pathways (dorsal):
– Relay nuclei, tracts
• Motor descending pathways (ventral)
– Tracts, motor nuclei brainstem
• Cerebellar pathways
– Tracts, cerebellar afferent and efferent nuclei
• Cranial nerve sensory and motor tracts
– Cranial nerve nuclei, nerve entry and exit points
• CPGs: rhythmic chewing, respiration, cardiovascular
regulation & gain adjustments for reflexes
• Modulatory systems: locus coeruleus, raphe &
substantia nigra
– Chemically coded nuclei
Dorsal Column/Medial Lemniscal system
•Secondary neuron is in
brainstem: nucleus gracilis and
cuneatus=dorsal column nuclei
•Output of dorsal column nuclei
crosses midline and forms
recognizable bundle: medial
lemniscus
•Medial lemniscus fibers synapse
in the thalamus in the
ventroposterior nuclei
•Thalamic axons synapse in
primary somatosensory cortex in
several somatotopic maps with
some segregation of
submodalities
http://cas.bellarmine.edu/tietjen/HumanBioogy/central_n
ervous_system.
Tracing through the brainstem:
Dorsal Column/Medial Lemniscal
System
Corticospinal Tract
Caudal Medulla
Caudal Medulla
“Closed” medulla
Caudal Medulla
Caudal Medulla
Caudal Medulla
Caudal Medulla
Caudal Medulla
Caudal Medulla
Medulla
Medulla
Medulla
Medulla
Rostral Medulla
Rostral Medulla
Rostral Medulla
Rostral Medulla
Medulla-Pons Junction
Medulla-Pons Junction
Caudal Pons
Caudal Pons
Caudal Pons
Caudal Pons
Pons
Pons
Rostral Pons
Rostral Pons
Rostral Pons
Rostral Pons
Pons- Mesencephalon Junction
Pons- Mesencephalon Junction
Mesencephalon
Mesencephalon
Mesencephalon
Mesencephalon
Mesencephalon- Diencephalon Junction
Mesencephalon- Diencephalon Junction
The Cranial Nerves
• The head and neck are not innervated
by spinal nerves
• Sensory information is received and
motor information is sent via 12 cranial
nerves
• Considered part of the PNS  they
convey messages to and from the
body's muscles and glands.
Each cranial nerve….
• Can be referred to by a name or
number!
• Has a general function
• Has at least a motor, sensory or
parasympathetic component
• Some have more than one component
• Has associated brainstem nuclei
• Innervates a structure(s)
Cranial nerves can be identified
on the ventral surface of the brain
I
I
II
III
VII
IV
V
VI
VIII
IX
X
XI
XII
Some tricks to learning cranial nerve
numbers, names & components…
I
II
III
IV
V
VI
VII
VIII
IX
X
XI
XII
Olfactory
On
Some
Optic
Occulomotor
Trochlear
Trigeminal
Abducens
Facial
Auditory/Vestibulocochlear
Glossopharyngeal
Vagus
Spinal/Accessory
Hypoglossal
Old
Olympus
Towering
Tops
A
Frenchman
And
German
Viewed
Some
Hops
Say
Marry*
Money
But
My
Brother*
Says
Big*
Business*
Makes
Money
S = Sensory
M = Motor
B = Both/Mixed Sensory & Motor
* = Parasympathetic
Arrangement of
brainstem
cranial nerve
nuclei in
columns
• Midbrain
• Pons
• Medulla
Insert picture with
different levels
differentiated
General Rules of Thumb
•Most motor nuclei are
associated with a single
cranial nerve
•Afferent nuclei often receive
fibers from several cranial
nerves
•All associated with a
single function however,
e.g., nucleus of solitary
tract
Functions of Cranial Nerves
www.neurophys.com/EMG/Cranial_Nerves/
Cranial Nerve I: Olfactory
Component:
Sensory
Function:
Smell
Tract:
Olfactory cells of nasal mucosa 
Olfactory Bulbs  pyriform cortex
Cranial Nerve II: Optic
Component(s):
Sensory
Function:
Vision
Tract:
retinal ganglion
cells  optic
chiasm 
thalamus 
primary visual
cortex in
occipital lobe
Cranial Nerve III: Oculomotor
Component #1:
Motor
Function(s):
Movement of eyeball &
lens accomodation
Structure(s)
Innervated:
4 eyeball muscles & 1
eyelid muscle
Component #2:
Parasympathetic
Nucleus location:
midbrain
Function:
pupil constriction
Structure(s)
Innervated:
ciliary muscle and
pupillary constrictor
muscles
Cranial Nerve III: Oculomotor
Cranial Nerve IV: Trochlear
Component:
Motor
Function:
moves eyeball
Nucleus location:
midbrain
Structure(s)
Innervated:
superior oblique muscles
Cranial Nerve V: Trigeminal
Component #1:
Sensory(impulses of
touch, pain, heat and
cold)
Locations of nuclei:
pons & medulla
Function:
(1) sensations; (2)
general sensory from
tongue; (3)
proprioception
Structure(s)
Innervated:
(1) face, scalp, teeth,
lips, eyeballs, nose &
throat lining; (2) anterior
2/3 of tonque; (3)
muscles of mastication
Cranial Nerve V: Trigeminal
Component #2:
Motor
Function:
chewing
Nucleus location:
trigeminal motor nucleus
in pons
Structure(s)
Innervated:
muscles of mastication
Cranial Nerve V: Trigeminal
Cranial Nerve VI: Abducens
Component:
Motor
Function:
Eyeball movement
Nucleus:
abducens nucleus in
pons
Structure(s)
Innervated:
lateral rectus muscle of
eye
Cranial Nerve VII: Facial
Component #1:
Sensory
Nucleus location:
medulla
Function:
(1) taste & (2)
proprioception
Structure(s)
Innervated:
(1) anterior 2/3 of tongue
& (2) face and scalp
Component #2:
Motor
Nucleus location:
facial motor nucleus in
pons
Function:
facial expressions
Structure(s)
Innervated:
muscles of the face
Cranial Nerve VII: Facial
Component #3:
Parasympathetic
Nucleus location:
Superior salivatory
nucleus in medulla
Function:
salivation and lacrimation
(drooling and tears)
Structure(s)
Innervated:
salivary and lacrimal
glands via
submandibular and
pterygopalatine gamglia
Cranial Nerve VIII: Vestibulocochlear
(aka acoustic or auditory nerve)
Component:
Sensory
Functions:
(1) Balance
(2) Hearing
Nucleus:
In pons and medulla
Structure(s)
Innervated:
• vestibular apparatus of
internal ear
• cochlear of internal ear
 auditory cortex in the
temporal lobes
Cranial Nerve VIII: Vestibulocochlear
(aka acoustic or auditory nerve)
Cranial Nerve IX: Glossopharyngeal
Component #1:
Sensory
Nucleus location:
medulla
Function:
(1) taste; (2)
proprioception for
swallowing & (3) blood
pressure receptors
Structure(s)
Innervated:
(1) posterior two thirds of
tongue; (2) throat
muscles & (3) carotid
sinuses
Cranial Nerve IX: Glossopharyngeal
Component #2:
Motor
Nucleus location:
medulla
Function:
(1) swallowing and gag
reflexes & (2) tear
production
Structure(s)
Innervated:
(1) throat muscles and
(2) lacrimal glands
Cranial Nerve IX: Glossopharyngeal
Component #3:
Parasympathetic
Function:
saliva production
Structure(s)
Innervated:
parotid glands
Cranial Nerve X: Vagus
Component #1:
Sensory
Nucleus location:
medulla
Function:
(1) chemoreceptors; (2)
pain receptors; (3)
sensations; (4) taste
Structure(s)
Innervated:
(1) blood oxygen
concentration, carotid
bodies; (2) respiratory &
digestive tracts; (3)
external ear, larynx &
pharynx (4) tongue
Cranial Nerve X: Vagus
Component #2:
Motor
Nucleus location:
medulla
Function(s):
(1) heart rate & stroke
volume; (2) peristalsis;
(3) air flow; (4) speech &
swallowing
Structure(s)
Innervated:
(1) pacemaker &
ventricular muscles; (2)
smooth muscles of the
digestive tract (3) smooth
muscles in bronchial
tubes (4) muscles of
larynx a & pharynx
Cranial Nerve X: Vagus
Component #3:
Parasympathetic
Structure(s)
Innervated:
smooth muscles and
glands of the same areas
innervated by motor
component, as well as
thoracic and abdominal
areas
Cranial Nerve XI: Spinal Accessory
Component:
Motor
Function:
head rotation (& shoulder
shrugging!)
Nucleus location:
accessory nucleus in
medulla
trapezius &
sternocleidomastoid
muscles
Structure(s)
Innervated:
Cranial Nerve XII: Hypoglossal
Component:
Motor
Function:
Speech and swallowing
Nucleus location:
In medulla
Structure(s)
Innervated:
Throat and tongue
muscles
Cranial Nerve XII: Hypoglossal
Dorsal Column/Medial
Lemniscal system
•Secondary neuron is in
brainstem: nucleus gracilis and
cuneatus=dorsal column nuclei
•Output of dorsal column nuclei
crosses midline and forms
recognizable bundle: medial
lemniscus
•Medial lemniscus fibers synapse
in the thalamus in the
ventroposterior nuclei
•Thalamic axons synapse in
primary somatosensory cortex in
several somatotopic maps with
some segregation of
submodalities
http://cas.bellarmine.edu/tietjen/HumanBioogy/central_n
ervous_system.