1. Dr. Farah Nabil Abbas
MBChB, MSc, PhD

2. Brain Stem midbrain Pons medulla oblongata Consists of three regions:
Similar to spinal cord – deep gray matter surrounded by white tracts but contains embedded nuclei in the white matter.

3. Brain Stem
Controls automatic behaviors necessary for survival (breathing, digestion, heart rate, blood pressure)
Provides the pathway for tracts between higher and lower brain centers
Associated with 10 of the 12 pairs of cranial nerves.

4. Midbrain
Located between diencephalon and pons
Midbrain structures include:
Cerebral peduncles – two structures that contain descending pyramidal motor tracts.
Cerebral aqueduct – hollow tube that connects the third and fourth ventricles
Various nuclei

5. Midbrain Nuclei
Nuclei that control cranial nerves III (oculomotor) and IV (trochlear).
Corpora quadrigemina - 4 domelike protrusions of dorsal midbrain.
2 Superior colliculi - visual reflex centers; coordinate head and eye movement when we follow a moving object (does not have to be a conscious decision).
2 Inferior colliculi - auditory relay centers between hearing receptors to sensory cortex.
Reflexive responses to sound – turn head toward sound.

6. Midbrain Nuclei
Substantia nigra – functionally linked to basal nuclei, contains melanin pigment (precursor of dopamine - NT).
Red nucleus – largest nucleus (rich blood supply) of the reticular formation; relay nuclei for some descending motor pathways.

7. Pons Location: between midbrain and medulla oblongata
Forms part of anterior wall of 4th ventricle
Fibers of the pons:
Connect higher brain centers and spinal cord
Relay impulses between motor cortex and cerebellum
Origin of cranial nerves V (trigeminal), VI (abducens), and VII (facial)
Contains nuclei of the reticular formation.

8. Lateral Gaze Palsy

12. Medulla Oblongata Most inferior part of brain stem.
With pons forms ventral wall of 4th ventricle.
Contains choroid plexus of 4th ventricle.
Pyramids – two longitudinal ridges formed by corticospinal tracts descending from motor cortex.

13. Medulla Oblongata
Before entering spinal cord corticospinal tracts crossover.
The point in which crossover occur is called decussation of the pyramids.
Results in controlling of each cerebral hemisphere in movements of opposite side.

14. Medulla Nuclei
Inferior olivary nuclei - gray matter that relays sensory information regarding stretch of muscle and joints
Cranial nerves IX (glosopharyngeal, X (vagus), XI (accessory; neck muscle), and XII (hypoglossal; tongue).
Vestibular nuclear complex - synapses that mediate and maintain equilibrium
Ascending sensory tract nuclei, including nucleus cuneatus and nucleus gracilis
Serve as relay station for general somatic sensation.

16. Medulla Nuclei
Medulla has an important role in autonomic reflex center that maintain homeostasis:
Cardiovascular control center – adjusts force and rate of heart contraction
Respiratory centers – control rate and depth of breathing
Additional centers – regulate vomiting, hiccupping, swallowing, coughing, and sneezing
There is an overlap between medulla and hypothalamus that uses medullary centers to carry out instructions.

18. Reticular formation
Network of nuclei and nerve fibers in different areas of brainstem with projection to cerebrum.
Functions as reticular activating system (RAS)
Involved in attention and in transition from sleep to wakefulness
RAS sends impulses to cortex to arouse it from sleep.

19. RAS and Motor Function
In addition to its RAS functions, reticular formation:
Helps control unrefined motor movements - maintain tone and posture
Relay signals from eyes and ears to the cerebellum so it can integrate these signals into its motor coordination
Autonomic centers regulate visceral motor functions such as cardiovascular control (centers found in the medulla).