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1. Brain Stem and Reticular
Formation
TirgarS.
Tehran University Of Medical Sciences

2. Brain stem
Foramen Magnum
Midbrain
Pons
Medulla oblongata
Cerebrum
Diencephalon
Brainstem
Cerebellum

4. Passageway for fiber tracts running between cerebrum and spinal cord
Rigidly programmed automatic behavior necessary for survival:
Respiration, cardiovascular systemand movement control
Heavily involved with innervation of face and head (3 to 12 cranial nerves
attach to it)
Midbrain
Pons
Medulla oblongata

5. Medulla oblongata
Anterior median fissure
Pyramid(corticospinaltract=motor tracts which cross over
in the decussation)
Inferior Olive (Coordination of Body Movements/Cooperate
with cerebellum)
Up: Pons
Down: Spinal cord

6. Contains important control centers
•Heart rate control (sympathetic &
parasympathetic)
•Vasomotor (Blood pressure regulation)
•Respiratory rhythm (chemoreceptor)
•Swallowing
•Vomiting
•Coughing
•Sneezing

7. Injuries or disease affecting:
Middle portion
(dorsal column/medial lemniscus)
Lateral portion
(spinotalamic)
Anterior portion
(pyramidal)
Loss of the senses of touch and
position.
Loss of pain and temperature
sensations of the opposite side of the
body, or loss of coordination.
Loss of motor function of the opposite
side of the body.

8. CN IX –Glossopharyngeal nerve

9. CN X –Vagus nerve

10. CN XI –Accessory nerve

11. CN XII –Hypoglossal nerve

12. Wallenberg syndromeis a rare condition in which an infarction
occurs in the lateral medulla.

13. Pons
Up: midbrain
Down: Medulla oblongata
2.5cm
The bulging center part of the brain stem
The pons is also called thepons Varolii("bridge of Varolius"), after the
Italian anatomist and surgeonCostanzo Varolio(1543–75).
It can be divided into two parts:
Thebasilar part of the pons(ventral pons)
Thepontinetegmentum(dorsal pons)
basilar part of the ponspontinetegmentum

14. Regulation of respiration
Controls involuntary actions
bladder control
Sensory roles in hearing, equilibrium, and taste,
and in facial sensations such as touch and pain
Motor roles in eye movement, facial
expressions, chewing, swallowing, and the
secretion of saliva and tears.
Sleep regulation(The pons is implicated
insleep paralysis, and may also play a role in
generating dreams)
Gray matter White matter
Tractsbetween cerebrum,
cerebellum and medulla.

15. Sleep paralysisis a state,during waking uporfalling asleep, in which a person isawarebut
unable to move or speak.
During an episode, one mayhallucinate(hear, feel, or see things that are not there), which
often results infear.

16. pneumotaxiccenter
This center regulates the change from inhalation to exhalation.

17. Transverse pontine(pontocerebellar) fibers:
Originate from pontinenuclei, cross the midline & pass through the contralateral middle
cerebellar peduncle to enter the opposite cerebellar hemisphere.

18. CN V –Trigeminal nerve

19. CN VI –Abducens nerve

20. CN VII –Facial nerve

21. CN VIII –Vestibulocochlear nerve

22. Locked-in syndrome(LIS), also known aspseudocoma, is a condition in which a
patient is awarebut cannot move or communicate verbally due to complete paralysisof
nearly all voluntary muscles in the body except for vertical eye movements and
blinking. The individual is conscious and sufficiently intact cognitively to be able to
communicate with eye movements.

23. locked-in syndrome is caused by damage to specific portions of the lower brain
andbrainstem, with no damage to the upper brain.
Possible causes of locked-in syndrome include:
•Poisoningcases –More frequently from akraitbite and otherneurotoxicvenoms,
•Brainstem stroke
•Damage to nerve cells, particularly destruction of themyelin sheath(central
pontinemyelinolysis) secondary to excessively rapid correction ofhyponatremia

24. The midbrain plays a major role in:
•Vision
•Hearing
•Motor control
•Sleep and wake cycles
•Arousal (alertness)
•Temperature regulation
Midbrain
Up: Diencephalon
Down: Pons

25. Corpora quadrigemina(Tectum): superior & inferior colliculus
Relay information for vision and hearing
Visual reflexes
Auditory reflexes
Cerebral peduncles

26. Inferior Colliculus:
•Startle reflex
•Neck reflex
•Stapialreflex
Superior Colliculus:
•Eye movements to a sudden noise or light flash
andvoluntary vertical saccades.
•Neck reflex

27. Batsare not, in fact, blind, but they depend much more on echolocation than vision for
navigation and prey capture.
Echoes coming from different directions activate neurons at different locations in the
collicularlayers.
Thus, there is a strong case that the superior colliculusperforms the same sorts of
functions for the auditory-guided behaviorsof bats that it performs for the visual-guided
behaviors of other species.

28. Cerebral aquaduct–3
rd
-4
th
ventricles
Substantianigrais closely associated with motor system pathways
of the basal ganglia (Dopamine).only part of the brain that carries
melanin pigment.
Red nucleus motor coordination

29. Degeneration of substantianigracauses Parkinson’s disease

30. CN III –Oculomotor nerve

31. CN IV –Trochlear nerve

32. With all the labels….

33. Cerebellar peduncles

34. Reticular formation
Is one of the phylogeneticallyoldest portions of the brain.

35. Runs through central core of medulla, pons and midbrain
The reticular formation consists of more than 100 small neural
networks
The reticular formation includes ascending pathways to thecortexin
theascending reticular activating system(ARAS) and descending
pathways to thespinal cordvia thereticulospinaltracts
Function:
Sleep arousal cycle, perception of pain, control of movement, regulation of
visceral activity

36. The reticular formation is divided into three columns:
•Mood
Raphe nuclei
(median)
•Motor coordination
Gigantocellular
reticular nuclei
(larger size of the
cells, medial zone)
•Exhalation
Parvocellular
reticular nuclei
(smaller size of
the cells, lateral
zone).

38. Raphe nuclei
Major serotonin nuclei
Ascending pathways involved in many neurobehavioral
phenomena:
Mood (Depression)
Anxiety
Sleep pattern
Feeding/satiety
Descending pathways modulate spinal cord function:
Suppressing the pain awareness

39. LocusCeruleus
Major norepinephrine nucleus
Projects to Spinal cord, Brain stem,
Cortex
Function:
Arousal
Modulation of stress responses

40. Functions of the reticular formation in general
•Ascending activating system increases
general level of sensory stimulation
thus lead to increased level of
neuronal activities and increased
arousal level. The noradrenergic
neurons and histaminesecreting
neurons also stimulate arousal level.
Injury to the reticular formation can
result in irreversible coma.
•Sleep inducing neurons, like
serotonergicneurons of the raphe
nuclei could inhibit thalamus and
cerebral function thus decrease
arousal level.
Sleep and arousal:
Varying level of consciousness is paralleled by changes in neuronal activities (EEG).

41. Somatic motor control:
Gaze center, Maintaining tone, balance, and posture-especially during body
movements
Visceral activities:
Cardiac and vasomotor centers and breathing.
Pain:
A descending inhibitory pathway could inhibit transmission of pain.
Habituation:
Brain learns to ignore repetitive,
meaningless stimuli while
remaining sensitive to others. A
good example of this is when a
person can sleep through loud
traffic in a large city, but is
awakened promptly due to the
sound of an alarm or crying baby.

42. The original functional differentiation was a division ofcaudal and rostral
Hypersomnia Insomnia
Lesioningof the rostral
reticular formation
This study has led to the idea that the caudal
portion inhibits the rostral portion of the
reticular formation.
Lesioningof the caudal
reticular formation

43. There are several potential factors that may adversely influence the development of the
ascending reticular activating system:
•Preterm birth: Regardless of birth weight or weeks of gestation, premature birth
induces persistent deleterious effects on pre-attentional (arousal and sleep-wake
abnormalities), attentional (reaction time and sensory gating), and cortical mechanisms
throughout development.
•Smoking during pregnancy:Prenatalexposure to cigarette smoke is known to
produce lasting arousal, attentional and cognitive deficits in humans.