1. Brainstem Assoc. Prof. Stefan Sivkov, Ph.D.
Dept. of Anatomy, Histology and Embryology

2. Development

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

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

5. Anterior view of brainstem
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

6. Lateral view of brainstem
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

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

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 btwn the cerebrum and the SC
Provides a pathway for tracts running btwn 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 btwn diencephalon and pons.
2 bulging cerebral peduncles on the ventral side. These contain:
Descending fibers that go to the cerebellum via the pons
Descending pyramidal tracts
Running thru 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 that control reflex movements of the eyes, head and neck in response to visual stimuli
2 inferior colliculi that control reflex movements of the head, neck, and trunk in response to auditory stimuli
Midbrain

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 contains numerous blood vessels and receives info from the cerebrum and cerebellum and issues subconscious motor commands concerned w/ 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 would cause what?

14. Pons Literally means “bridge” Wedged btwn 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
Emesis, deglutition, coughing, hiccupping, and sneezing

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