Pengantar sistem saraf brain stem

M. Djauhari Widjajakusumah
Fakultas Kedokteran Universitas Indonesia

The brain stem consists of the medulla, pons, and
midbrain
Sherwood
Human
Physiology
From Cells to
System 9e,
2016
Brain Stem
Topography

Sherwood
Human
Physiology From
Cells to System
9e, 2016
Brain Stem
Topography

Sherwood
Human
Physiology
From Cells to
System 9e,
2016
Brain Stem
Topography

Brain Stem Links
The brain stem is a vital link between the spinal cord and higher
brain regions
 All incoming and outgoing fibers traversing between the periphery
and the higher brain centers must pass through the brain stem
 incoming fibers relaying sensory information to the brain
 outgoing fibers carrying command signals from the brain for
efferent output
 Most of these fibers synapse within the brain stem for important
processing
 The brain stem is a critical connecting link between the rest of
the brain and the spinal cord.
Sherwood Human
Physiology From Cells to
System 9e, 2016

Brain Stem Functions
1. Most of the 12 pairs of cranial nerves arise from the brain stem. With one
major exception, these nerves supply structures in the head and neck with
both sensory and motor fibers
 The major exception is cranial nerve X, the vagus nerve. Instead of
innervating regions in the head, most branches of the vagus nerve supply
organs in the thoracic (chest) and abdominal (belly) cavities. The vagus is
the major nerve of the parasympathetic nervous system
2. Collected within the brain stem are neuronal clusters or centers that control
heart and blood vessel function, respiration, and many digestive activities.
 A functional collection of neuronal cell bodies within the CNS is alternately
known as a center, such as the respiratory control center in the brain stem,
or as a nucleus (plural nuclei), such as the basal nuclei.
3. The brain stem helps regulate muscle reflexes involved in equilibrium and
posture.
Sherwood
Human
Physiology
From Cells to
System 9e,
2016

Brain Stem Functions
4. A widespread network of interconnected neurons called the reticular
formation runs throughout the entire brain stem and into the thalamus.
 This network receives and integrates all incoming sensory synaptic input.
 Ascending fibers originating in the reticular formation carry signals upward
to arouse and activate the cerebral cortex.
 These fibers compose the reticular activating system (RAS), which controls
the overall degree of cortical alertness and is important in the ability to
direct attention.
 In turn, fibers descending from the cortex, especially its motor areas, can
activate the RAS.
5. The centers that govern sleep are housed within the brain stem and the
hypothalamus
Sherwood Human Physiology From
Cells to System 9e, 2016

Figure 45–1 The origins of cranial nerves in the brain stem (ventral and lateral views). The
olfactory (I) nerve is not shown because it terminates in the olfactory bulb in the forebrain. All
of the cranial nerves except one emerge from the ventral surface of the brain; the trochlear (IV)
nerve originates from the dorsal surface of the midbrain.
Kandel Principle of Neural Science 5e, 2013

Figure 45–5 Adult cranial nerve nuclei are organized in six functional columns on
the rostrocaudal axis of the brain stem. A. This dorsal view of the human brain stem
shows the location of the cranial nerve sensory nuclei (right) and motor nuclei (left).
B. A schematic view of the functional organization of the motor and sensory
Kandel
Principle of
Neural
Science 5e,
2013

The brain stem as its own master provides many special
control functions

Medulla Oblongata
Control of Respiration, Heart Rate, & Blood Pressure
 The medullary areas for the autonomic reflex control of the circulation,
heart, and lungs are called the vital centers because damage to them is
usually fatal.
 The afferent fibers to these centers originate in a number of instances in
specialized visceral receptors.
 The specialized receptors include not only those of the carotid and aortic
sinuses and bodies but also receptor cells that are located in the medulla
itself.
 The motor responses are graded and delicately adjusted and include
somatic as well as visceral components.
Ganong’s Review of Medical Physiology 22e, 2005

FIGURE 32-2 Basic pathways
involved in the medullary
control of blood pressure.
The rostral ventrolateral medulla
(RVLM) is one of the major sources
of excitatory input to sympathetic
nerves controlling the vasculature.
These neurons receive inhibitory
input from the baroreceptors via
an inhibitory neuron in the caudal
ventrolateral medulla (CVLM). The
nucleus of the tractus solitarius
(NTS) is the site of termination of
baroreceptor afferent fi bers.
The putative neurotransmitters in
the pathways are indicated in
parentheses. Ach, acetylcholine;
GABA, γ-aminobutyric acid; Glu,
glutamate; IML, intermediolateral
gray column; IVLM, intermediate
ventrolateral medulla; NE,
norepinephrine; NTS, nucleus of
the tractus solitarius; IX and X,
glossopharyngeal and vagus
nerves.
Ganong’s Review of Medical Physiology
24e, 2012

REGULATION OF RESPIRATORY ACTIVITY
 A rise in the P co 2 or H + concentration of arterial blood or a drop in its
Po2 increases the level of respiratory neuron activity in the medulla, and
changes in the opposite direction have a slight inhibitory effect.
 The effects of variations in blood chemistry on ventilation are mediated via
respiratory chemoreceptors —the carotid and aortic bodies and
collections of cells in the medulla and elsewhere that are sensitive to
changes in the chemistry of the blood.
 They initiate impulses that stimulate the respiratory center.
 Superimposed on this basic chemical control of respiration, other
afferents provide nonchemical controls that affect breathing in particular
situations
24e, 2012

FIGURE 36-2 Respiratory neurons in the brain stem.
Dorsal view of brain stem; cerebellum removed. The effects of various lesions and
brain stem transections are shown; the spirometer tracings at the right indicate the
depth and rate of
breathing. If a lesion is introduced at D, breathing ceases. The effects of higher
transections, with and without vagus nerves transection, are shown (see text for
details). CP, middle cerebellar peduncle; DRG, dorsal group of respiratory neurons;
IC, inferior colliculus; NPBL, nucleus parabrachialis (pneumotaxic center); VRG,
ventral group of respiratory neurons; 4th vent, fourth ventricle. The roman numerals
identify cranial nerves. (Modified from Mitchell RA, Berger A: State of the art: Review
of neural regulation of respiration. Am Rev Respir Dis 1975;111:206.)
Ganong’s Review
of Medical
Physiology 24e,
2012

24e, 2012

Other Medullary Autonomic Reflexes
 Swallowing, coughing, sneezing, gagging, and vomiting are also reflex
responses integrated in the medulla oblongata.
 Swallowing is controlled by a central program generator in the medulla. It
is initiated by the voluntary act of propelling what is in the mouth toward
the back of the pharynx and involves carefully timed responses of the
respiratory as well as the gastrointestinal system.
 Coughing is initiated by irritation of the lining of the trachea and
extrapulmonary bronchi. The glottis closes, and strong contraction of the
respiratory muscles builds up intrapulmonary pressure, whereupon the
glottis suddenly opens, causing an explosive discharge of air.
 Sneezing is a somewhat similar response to irritation of the nasal
epithelium. It is initiated by stimulation of pain fibers in the trigeminal
nerves.
Medulla Oblongata

Vomiting
 Vomiting is another example of the way visceral reflexes integrated in the
medulla include coordinated and carefully timed somatic as well as visceral
components.
 Vomiting starts with salivation and the sensation of nausea. Reverse
peristalsis empties material from the upper part of the small intestine into
the stomach. The glottis closes, preventing aspiration of vomitus into the
trachea. The breath is held in mid inspiration. The muscles of the
abdominal wall contract, and because the chest is held in a fixed position,
the contraction increases intra-abdominal pressure. The lower esophageal
sphincter and the esophagus relax, and the gastric contents are ejected.
 The "vomiting center" in the reticular formation of the medulla really
consists of various scattered groups of neurons in this region that control
the different components of the vomiting act.
Medulla Oblongata

Ganong’s Review
of Medical
Physiology 22e,
2005

The brain stem helps regulate muscle reflexes involved in
equilibrium and posture

Role of the Brain Stem in Controlling Motor Function
 The brain stem consists of the medulla, pons, and mesencephalon.
 In one sense, it is an extension of the spinal cord upward into the cranial
cavity because it contains motor and sensory nuclei that perform motor
and sensory functions for the face and head regions in the same way that
the spinal cord performs these functions from the neck down.
 In another sense, the brain stem is its own master because it provides
many special control functions, such as the following:
 Control of respiration
 Control of the cardiovascular system
 Partial control of gastrointestinal function
 Control of many stereotyped movements of the body
 Control of equilibrium
 Control of eye movements Guyton & Hall Textbook of Medical
Physioligy 12e, 2011

Support of the Body Against Gravity-Roles of the
Reticular and Vestibular Nuclei

Role of the Brain Stem in Controlling Body Movement and
Equilibrium
 The brain stem serves as a way station for "command signals" from
higher neural centers.
 The brain stem has the role in controlling whole-body movement and
equilibrium.
 Especially important for these purposes are the brain stem's reticular
nuclei and vestibular nuclei.
Guyton & Hall Textbook of Medical

 The reticular nuclei are divided into two major groups:
(1) pontine reticular nuclei, located slightly posteriorly and laterally in the
pons and extending into the mesencephalon,
(2) medullary reticular nuclei, which extend through the entire medulla,
lying ventrally and medially near the midline.
 These two sets of nuclei function mainly antagonistically to each other
 the pontine exciting the antigravity muscles and
 the medullary relaxing these same muscles
Excitatory-Inhibitory Antagonism Between Pontine and
Medullary Reticular Nuclei
Guyton & Hall Textbook of Medical

Figure 55–7
Locations of the
reticular and vestibular
nuclei in the brain
stem.
Guyton & Hall
Textbook of Medical

Pontine Reticular System
 The pontine reticular nuclei transmit excitatory signals downward into the cord
through the pontine reticulospinal tract in the anterior column of the cord,
(figure 55-8).
 The fibers of this pathway terminate on the medial anterior motor neurons
that excite the axial muscles of the body, which support the body against
gravity-that is, the muscles of the vertebral column and the extensor muscles
of the limbs.
 The pontine reticular nuclei have a high degree of natural excitability.
 In addition, they receive strong excitatory signals from the vestibular nuclei, as
well as from deep nuclei of the cerebellum.
 When the pontine reticular excitatory system is unopposed by the medullary
reticular system, it causes powerful excitation of antigravity muscles
throughout the body, so much so that four-legged animals can be placed in a
standing position, supporting the body against gravity without any signals from
higher levels of the brain.
Guyton & Hall Textbook of Medical Physioligy 12e, 2011

Figure 55-8
Vestibulospinal and reticulospinal tracts descending in the spinal cord to excite
(solid lines) or inhibit (dashed lines) the anterior motor neurons that control the
body's axial musculature
Guyton & Hall
Textbook of
Medical Physioligy
12e, 2011

Medullary Reticular System
 The medullary reticular nuclei transmit inhibitory signals to the same
antigravity anterior motor neurons by way of a different tract, the
medullary reticulospinal tract, located in the lateral column of the cord,
(Figure 55-8).
 The medullary reticular nuclei receive strong input collaterals from
(1) the corticospinal tract
(2) the rubrospinal tract
(3) other motor pathways
 These normally activate the medullary reticular inhibitory system to
counterbalance the excitatory signals from the pontine reticular system, so
under normal conditions the body muscles are not abnormally tense.

Medullary Reticular System
 Some signals from higher areas of the brain can "dis-inhibit" the medullary
system when the brain wishes to excite the pontine system to cause
standing.
 At other times, excitation of the medullary reticular system can inhibit
antigravity muscles in certain portions of the body to allow those portions
to perform special motor activities.
 The excitatory and inhibitory reticular nuclei constitute a controllable
system that is manipulated by motor signals from the cerebral cortex and
elsewhere to provide necessary background muscle contractions for
standing against gravity and to inhibit appropriate groups of muscles as
needed so that other functions can be performed

Role of the Vestibular Nuclei to Excite the Antigravity
Muscles
 All the vestibular nuclei, (figure 55-7), function in association with the
pontine reticular nuclei to control the antigravity muscles.
 The vestibular nuclei transmit strong excitatory signals to the antigravity
muscles by way of the lateral and medial vestibulospinal tracts in the
anterior columns of the spinal cord, (figure 55-8).
 Without this support of the vestibular nuclei, the pontine reticular system
would lose much of its excitation of the axial antigravity muscles.
 The specific role of the vestibular nuclei, however, is to selectively control
the excitatory signals to the different antigravity muscles to maintain
equilibrium in response to signals from the vestibular apparatus.

Figure 5-19 The reticular
activating system.
The reticular formation, a
widespread network of
neurons within the brain
stem (in red), receives and
integrates all synaptic
input. The reticular
activating system, which
promotes cortical
alertness and helps direct
attention toward specific
events, consists of
ascending fibers (in blue)
that originate in the
reticular formation and
carry signals upward to
arouse and activate the
cerebral cortex.
Sherwood Human
System 9e, 2016

Reticular Formation
 The reticular formation, occupies the central portion of the medulla and
midbrain, surrounding the fourth ventricle and cerebral aqueduct.
 The reticular formation contains the cell bodies and fibers of many of the
serotonergic, noradrenergic, and cholinergic systems.
 The reticular formation also contains many of the areas concerned with
regulation of heart rate, blood pressure, and respiration.
 The reticular formation plays an important role in determining the level of
arousal, thus it is called the ascending reticular activating system (RAS) .

Reticular Activating System (RAS)
 The RAS is a complex polysynaptic pathway arising from the brain stem
reticular formation and hypothalamus with projections to the intralaminar
and reticular nuclei of the thalamus which, in turn, project diffusely and
nonspecifically to wide regions of the cortex including the frontal,
parietal, temporal, and occipital cortices
 Collaterals funnel into it not only from the long ascending sensory tracts
but also from the trigeminal, auditory, visual, and olfactory systems.
 The complexity of the neuron net and the degree of convergence in it
abolish modality specificity, and most reticular neurons are activated with
equal facility by different sensory stimuli.
 The system is therefore nonspecific, whereas the classic sensory pathways
are specific in that the fibers in them are activated by only one type of
sensory stimulation.

FIGURE 14-3
Cross-section
through the
midline of the
human brain
showing the
ascending reticular
activating
system in the
brainstem with
projections to the
intralaminar
nuclei of the
thalamus and the
output from the
intralaminar
nuclei to many
parts of the
cerebral cortex.
Activation of these
areas can be
shown by positive
emission
tomography scans
when subjects

Consciousness
 The term consciousness refers to subjective awareness of the external
world and self, including awareness of the private inner world of one’s
mind—that is, awareness of thoughts, perceptions, dreams, and so on.
 Even though the final level of awareness resides in the cerebral cortex and
a crude sense of awareness is detected by the thalamus, conscious
experience depends on the integrated functioning of many parts of the
nervous system.
Sherwood Human
System 9e, 2016

Consciousness, The Cellular and Molecular Basis
 The cellular and molecular basis underlying consciousness is one of the
greatest unanswered questions in neuroscience.
 One proposal that is gaining increasing support is the global workspace
theory, which suggests that conscious experience depends on the brain
functioning as a “brainweb” in which some of the separate bits of
subconscious information that are being processed locally at the same
time are momentarily broadcast throughout the brain (that is, to a global
workspace).
 This highly coordinated, widespread information exchange among much of
the cortex gives rise to subjective experience of the information.
 We become conscious of what we are experiencing only when
information received through specialized channels (such as sensory
information) is distributed to much of the cortex, creating a unity of
mind.
Sherwood Human
System 9e, 2016

The centers that govern sleep are housed within the
brain stem and the hypothalamus

Wakefulness and Sleep
 Normal states of consciousness are wakefulness and sleep.
 The sleep–wake cycle is a normal cyclic variation in awareness of
surroundings.
 In the waking state people are alert and aware of their surroundings and
consciously engage in coherent thoughts and actions.
 Wakefulness depends on attention-getting sensory input that “energizes”
the RAS and subsequently the activity level of the CNS as a whole.
 Wakefulness is not a constant level of arousal but varies from maximum
alertness to drowsiness, depending on the extent of interaction between
peripheral stimuli and the brain.
 Different arousal and activity states are characterized by different brain
wave activity as recorded on an electroencephalogram.
Sherwood Human
System 9e, 2016

The sleep–wake cycle
 The sleep–wake cycle is controlled by interactions among three neural
systems
 The sleep–wake cycle, and the various stages of sleep, is controlled by and
result from the cyclic interplay of three neural systems:
(1) an arousal system involving the RAS in the brain stem, which is
commanded by a specialized group of neurons in the hypothalamus;
(2) a slow-wave sleep center in the hypothalamus that contains sleep-on
neurons, which bring on slow-wave sleep; and
(3) a paradoxical sleep center in the brain stem that houses REM sleep-
on neurons, which switches to paradoxical sleep.
Sherwood Human
System 9e, 2016

Brainstem-Hypothalamus Relationship in Sleep-Wake Cycle
1. A group of neurons in the hypothalamus is at the top of the chain of
command for regulating the arousal system.
 These neurons secrete the excitatory neurotransmitter hypocretin,
also known as orexin known as an appetite-enhancing signal, but it is
now known to play an important role in arousal too.
 These hypocretin-secreting neurons fire autonomously and
continuously and keep one awake and alert by stimulating the RAS.
 They must be inhibited to induce sleep, as perhaps by IPSPs generated
by input from the sleep-on neurons.
Sherwood Human
System 9e, 2016

2. The sleep-on neurons in the slow-wave sleep center (in hypothalamus)
appear to be responsible for bringing on sleep, likely by inhibiting the
arousal-promoting neurons by releasing the inhibitory neurotransmitter
GABA.
 This mechanism would explain why we enter slow-wave sleep first
when we fall asleep.
 The sleep-on neurons are inactive when a person is awake and are
maximally active only during slow-wave sleep.
 Scientists do not know much about the factors that activate the sleep-
on neurons to induce sleep.
Sherwood Human
System 9e, 2016

3. The REM sleep-on neurons in the paradoxical sleep center (in the
brainstem) become very active during REM sleep.
 It appears that they can turn off the sleep-on neurons and switch the
sleep pattern from slow-wave sleep to REM sleep.
 The underlying molecular mechanisms responsible for the cyclical
interplay between the two types of sleep remain poorly understood.
Sherwood Human
System 9e, 2016

The Arousal System
 The normal cycle can easily be interrupted, with the arousal system more
readily overriding the sleep systems than vice versa – that is, it is easier to stay
awake when you are sleepy than to fall asleep when you are wide awake.
 The arousal system can be activated by afferent sensory input
 a person has difficulty falling asleep when it is noisy
 The arousal system can be activated by input descending to the brain stem
from higher brain regions.
 Intense concentration or strong emotional states, such as anxiety or
excitement, can keep a person from falling asleep, just as motor activity,
such as getting up and walking around, can arouse a drowsy person.
 One can override the urge to sleep for just so long before the pressure to sleep
becomes irresistible.
Sherwood Human
System 9e, 2016

Pengantar sistem saraf brain stem

Pengantar sistem saraf brain stem

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