The document discusses the anatomy and organization of the brainstem. It is divided into 3 sections - the midbrain, pons, and medulla. Each section contains nuclei that are involved in sensory and motor functions as well as autonomic processes like respiration. The brainstem also acts as a relay center, transmitting information between the brain and spinal cord via ascending and descending tracts. It produces vital automatic behaviors and modulates states of consciousness through structures like the reticular formation.

1. Brainstem 2
Dr Shittu LAJ

2. Development

3. Ventricles in brainstem
• Mesencephalon  cerebral aqueduct
• Metencephalon  4th
ventricle
• Mylencephalon  4th
ventricle

4. vermis
Occipital
LobeThalamus
Corpus callosum
Hypothalamus
Fornix
Anterior
commissure
Optic nerve
4th
ventricle
Posterior commissure
pyramid
Mammillary body
Quadrigeminal
cistern

5. internal capsule
basal ganglia
optic nerve
optic tract
hypothalamus
mammillary body
cerebral peduncle
interpeduncular fossa
flocculus
inferior olivary
nuclear complex
cerebellum
cerebellar tonsil
pyramid
pyramidal decussation
pons
optic chiasm
Anterior view of brainstem

6. optic tract
optic nerve
hypothalamus
optic chiasm
middle cerebellar peduncle
trigeminal nerve
vestibulocochlear nerve
flocculus
cuneate tubercle
inferior olivary nuclear complex
anterior median fissure pyramid
pons
cerebral
peduncle
Lateral view of brainstem

7. Middle cerebellar
peduncle
Superior colliculus
Inferior colliculusCerebral
peduncle
Superior cerebellar
peduncle
Inferior cerebellar
peduncle
Medulla
4th
ventricle
Posterior view of brainstem

8. 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

9. Brain Stem
• Located between the
cerebrum and the SC
– Provides a pathway for
tracts running between
higher and lower neural
centers.
• Consists of the midbrain,
pons, and medulla
oblongata.
– Each region is about an
inch in length.
• Microscopically, it consists
of deep gray matter
surrounded by white matter
fiber tracts.
• Produce automatic
behaviors necessary for
survival.

10. Brainstem: 3 major divisions
•Midbrain
•Pons
•Medulla

11. Midbrain
• Located between diencephalon
and pons.
– 2 bulging cerebral peduncles on
the ventral side. These contain:
• Descending fibers to the
cerebellum via the pons
• Descending pyramidal tracts
– Running through the midbrain is
the hollow cerebral aqueduct,
which connects the 3rd
and 4th
ventricles of the brain.
– The roof of the aqueduct (the
tectum) contains the corpora
quadrigemina
• 2 superior colliculi - control
reflex movements of the
eyes, head and neck in
response to visual stimuli
• 2 inferior colliculi - control
reflex movements of the
head, neck, and trunk in
response to auditory stimuli

12. •Cranial nerves 3&4
(oculomotor and trochlear)
exit from the midbrain
•Midbrain also contains the
headquarters of the
reticular activating system

13. Midbrain
• On each side, the midbrain
contains a red nucleus and a
substantia nigra
– Red nucleus
- numerous blood vessels;
- receives info from the
cerebrum and cerebellum;
- issues subconscious control
of muscle tone & posture
– Lateral to the red nucleus is
the melanin-containing
substantia nigra ,which
secretes dopamine to inhibit
the excitatory neurons of the
basal nuclei.
• Damage to the substantia
nigra causes Parkinson
disease?

14. Pons
• Literally means “bridge”
• Wedged between the midbrain &
medulla.
• Contains:
– Sensory and motor nuclei for 4
cranial nerves
• Trigeminal (5), Abducens (6),
Facial (7), and Auditory/Vestibular
(8)
– Respiratory nuclei:
• Apneustic & pneumotaxic centers
work w/ the medulla to maintain
respiratory rhythm
– Nuclei & tracts that process and
relay info to/from the cerebellum
– Ascending, descending, and
transverse tracts that interconnect
other portions of the CNS

15. Medulla Oblongata
• Most inferior region of
the brain stem.
• Becomes the spinal
cord at the level of the
foramen magnum.
• Ventrally, 2 ridges (the
medullary pyramids)
are visible.
– These are formed by
the large motor
corticospinal tracts.
– Right above the
medulla-SC junction,
most of these fibers
cross-over (decussate).

16. Medulla Oblongata
• Nuclei in the medulla are
associated w/ autonomic
control, cranial nerves, and
motor/sensory relay.
• Autonomic nuclei:
– Cardiovascular centers
• Alter the rate and
force of cardiac
contractions
• Alter the tone of
vascular smooth
muscle
– Respiratory rhythmicity
centers
• Receive input from
the pons
– Additional Centers

17. Medulla Oblongata
• Sensory & motor nuclei of 5
cranial nerves:
– Auditory/Vestibular (8),
Glossopharyngeal (9), Vagus (10),
Accessory (11), and Hypoglossal
(12)
• Relay nuclei
– Nucleus gracilis and nucleus
cuneatus pass somatic sensory
information to the thalamus
– Olivary nuclei relay info from the
spinal cord, cerebral cortex, and
the brainstem to the cerebellar
cortex.

18. 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

21. 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

22. 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

24. Reticular Formation
• Extensive network of neurons
that runs thru the medulla and
projects to thalamic nuclei that
influence large areas of the
cerebral cortex.
– Midbrain portion of RAS most
likely is its center
• Functions as a net or filter for
sensory input.
– Filter out repetitive stimuli.
Such as?
– Allows passage of infrequent or
important stimuli to reach the
cerebral cortex.
– Unless inhibited by other brain
regions, it activates the cerebral
cortex – keeping it alert and
awake.
How might the “sleep centers”
of your brain work? Why does
alcohol make you tired?

25. 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

26. 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

27. Tracing through the brainstem:
Dorsal Column/Medial Lemniscal
System

28. Corticospinal Tract

29. Cerebral cortex
(MI and SI)
Thalamus
Cerebellar
nucleus
Pontine
nuclei
Red
nucleus
Cerebellar
cortex
From
spinal cord
Rubrospinal
tract
Involvement of the
cerebellum and
pontine nuclei

30. Overview of motor pathways

56. Arterial supply to the brain

57. Blood supply to the brain