BRAIN STEM FUNCTIONS
CNS BLOCK
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.
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
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.
Cranial Nerves
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
Facial
controls most facial expressions
secretion of tears & saliva
taste
VII
Cranial Nerves
No.
Cranial Nerve
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
Major Functions
The brainstem controls several important
functions of the body including:
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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
MID BRAIN
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Visual reflex center
Auditory reflex center
eye movement, and
body movement.
Pons
1. It is involved in motor control and sensory
analysis... for example, information from the
ear first enters the brain in the pons.
2. It has parts that are important for the level of
consciousness and for sleep.
3. Some structures within the pons are linked to
the cerebellum, these are involved in
movement and posture.
Pons
4. 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.
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.
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.
Respiratory Center
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
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
VASOMOTOR CENTER
VASOMOTOR CENTER
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.
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.
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.
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).
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
Location of
excitatory
and inhibitory areas
of the brain
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
Brain stem death
Brain death occurs when a person no longer has any activity in their brain stem and
no potential for consciousness
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Brain death can occur when the blood and oxygen supply to the brain is stopped
for example due to cardiac arrest, cerebrovascular accident etc
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When brain stem function is permanently and irreversibly lost, the person will be
confirmed dead
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A ventilator machine may maintain ventilation and oxygenation and keep the
heart beating and oxygen circulating through the blood
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But once the brain stem has permanently irreversibly stopped functioning the
heart will eventually stop beating even if a ventilator has been used
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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.
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
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.
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