1. BRAIN STEM FUNCTIONS
CNS BLOCK

2. Objectives Describe the components of Brain stem.
Enumerate different functions of brainstem.
Know the reticular formation and its activating & inhibiting system
Role of brainstem in brain death.

3. Brain Stem
Critical connecting link between spinal cord and higher brain regions
Oldest region of the brain
Continuous with spinal cord
All incoming and outgoing fibers traversing between periphery and higher brain centers must pass Brain Stem
Consists of
Medulla
Pons
Midbrain

6. BRAINSTEM
Most of the cranial nerves come from the brainstem. The brainstem is the pathway for all fiber tracts passing up and down from peripheral nerves and spinal cord to the highest parts of the brain.

7. Cranial Nerves

8. Cranial Nerves No. Cranial Nerve Major Functions I Olfactory smell II
Optic
vision 
III
Oculomotor
eyelid and eyeball movement IV
Trochlear
innervates superior oblique turns eye downward and laterally  V
Trigeminal
chewing  face & mouth touch & pain VI
Abducens
turns eye laterally 
VII
Facial
controls most facial expressions  secretion of tears & saliva taste 

9. Cranial Nerves No. Cranial Nerve Major Functions VIII
Vestibulocochlear (auditory) 
hearing  equilibrium sensation  IX
Glossopharyngeal
taste  senses carotid blood pressure  X
Vagus
senses aortic blood pressure  slows heart rate  stimulates digestive organs taste  XI
Spinal Accessory
controls trapezius & sternocleidomastoid controls swallowing movements
XII
Hypoglossal
controls tongue movements 

10. The brainstem controls several important functions of the body including:
Alertness
Arousal
Breathing
Blood Pressure
Digestion
Heart Rate
Other Autonomic Functions
Relays Information Between the Peripheral Nerves and Spinal Cord to the Upper Parts of the Brain

11. MID BRAIN Visual reflex center Auditory reflex center
eye movement, and
body movement.

12. Pons
It is involved in motor control and sensory analysis... for example, information from the ear first enters the brain in the pons.
It has parts that are important for the level of consciousness and for sleep.
Some structures within the pons are linked to the cerebellum, these are involved in movement and posture. 

13. Pons
The pons is a bridge-like structure which links different parts of the brain and serves as a relay station from the medulla to the higher cortical structures of the brain. It contains the respiratory center.

14. Medulla Oblongata
The medulla oblongata functions primarily as a relay station for the crossing of motor tracts between the spinal cord and the brain. It also contains the respiratory, vasomotor and cardiac centers, as well as many mechanisms for controlling reflex activities such as coughing, gagging, swallowing and vomiting.

15. Respiratory Centers
Dorsal respiratory group (DRG)
Contains inspiratory center
Functions in every respiratory cycle
Ventral respiratory group (VRG)
Contains expiratory center
Used only during forced breathing
Pneumotaxic center in pons, play a role in switching between inspiration and expiration
Apneustic center in pons, promotes inspiration by stimulating the inspiratory neurons in the medulla.

16. Respiratory Center

17. Chemoreceptor Reflexes
Respond to chemical changes in blood, CSF
Centers:
Carotid bodies and aortic bodies (peripheral)
Sensitive to pH, PCO2, PO2 in arterial blood
Medulla (central chemoreceptor)
Sensitive to pH and PCO2 in CSF
Stimulation
Stimulation: increase in depth and rate of respiration

18. Chemoreceptor Reflexes
Much more sensitive to changes in PCO2 than PO2
Due to small increase in PCO2 stimulates receptors (regulates under normal conditions)
PO2 generally does not decline enough to stimulate receptor
Cannot hold your breath

19. VASOMOTOR CENTER

20. VASOMOTOR CENTER

22. THE DEGLUTITION CENTER
The deglutition (swallowing) center are areas in the medulla and pons that respond to the incoming impulses by sending motor signals back to the pharynx and the upper esophagus (swallowing reflex). These motor impulses travel via the cranial nerves (V, IX, X, XII) and a few superior cervical nerves.

23. The Reticular Formation
it can influence the heart rate, respiration, posture and equilibrium.
The so-called reticular activating system plays a critical role in sustaining consciousness. It regulates sleep and wakefulness.
The mechanism that triggers REM sleep is located in the pontine reticular formation.

24. Activating Systems of the Brain
Cerebrum requires a constant input to remain active.
Signals from the brainstem activate wide areas of the cortex (background activation) or specific areas to perform discrete tasks.

25. Excitatory Signals from the Brainstem
Bulboreticular facilitory area
sends excitatory signals to the antigravity muscles
sends excitatory signals to the thalamus and from here they are distributed to widespread areas of the cortex
Bulboreticular area is excited by signals from the periphery, especially pain signals and also signals from the cortex (positive feedback).

26. Inhibitory Signals from the Brainstem
reticular inhibitory area
sends inhibitory signals to the bulboreticular area
when the inhibitory area is excited, it will decrease the activity of the excitatory area and decrease the activity of the cortex

27. Location of excitatory
and inhibitory areas
of the brain

28. Brain stem and essential functions for life
The brain stem regulates most of the automatic functions of the body that are essential for life. Examples are:
breathing
heartbeat
blood pressure
The brain stem relays information to and from the brain to the rest of the body.
It plays a very important role in the brain’s core functions, such as consciousness, awareness and movement.
Once brain death has occurred, there is no possibility for consciousness

29. Brain stem death
Brain death occurs when a person no longer has any activity in their brain stem and no potential for consciousness
Brain death can occur when the blood and oxygen supply to the brain is stopped for example due to cardiac arrest, cerebrovascular accident etc
When brain stem function is permanently and irreversibly lost, the person will be confirmed dead
A ventilator machine may maintain ventilation and oxygenation and keep the heart beating and oxygen circulating through the blood
But once the brain stem has permanently irreversibly stopped functioning the heart will eventually stop beating even if a ventilator has been used
Brain death is considered as a clinical syndrome charcterized by the absence of reflexes that have pathways through the brain stem in a deeply comatose, ventilator-dependent, patient.

30. Brain stem death
The diagnosis of brain death may be considered (but needs to be confirmed) when:
A person fails to respond to any outside stimulation.
The person is unconscious.
The person's heartbeat and breathing can only be maintained using a ventilator.
There is clear evidence that serious damage to the brain has occurred, and it cannot be cured.
Reversible causes and factors such as drug overdose, severe hypothermia, severe hyperglycaemia etc have been excluded

31. Brain stem death
Rarely, there are some conditions that can make it appear as though someone is brain dead, such as: drug overdose, severe hypothermia, severe hyperglycaemia. These may be reversible.
So various tests can be carried out to find out whether brain death has actually occurred for example: pupils reaction to light, cold calorics test, corneal reflex, gag response etc.

33. Summary Functions Most of cranial nerves arise from brain stem
Neuronal clusters within brain stem control heart and blood vessel function, respiration, and many digestive functions
Plays role in regulating muscle reflexes involved in equilibrium and posture
Reticular formation within brain stem receives and integrates all incoming sensory synaptic input
Reticular activating & inhibiting system activate or inhibit the activity of higher centers
Centers that govern sleep are in brain stem (evidence suggests center promoting slow-wave sleep lies in hypothalamus)
Brain stem death due to vital centers in mid brain