Download Figure 4.8 The human brain stem This composite structure extends

MEDULLA OBLONGATA.
PONS. MIDBRAIN: TECTUM,
CEREBRAL PEDUNCLES,
AQUEDUCT OF BRAIN.
Cerebrum
Diencephalon
Truncus
encephali
Cerebellum
5
Development
Development
Development
Development
Development
11
BRAIN STEM
Figure 7.15a
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
BRAIN STEM
 Attaches to the spinal cord
 Parts of the brain stem
 Midbrain
 Pons
 Medulla oblongata
Brain Stem
• Located btwn the cerebrum and the SC
– Provides a pathway for tracts running btwn higher
and lower neural centers.
• Consists of the midbrain, pons, and medulla
oblongata.
– Each region is about an inch in length.
• Microscopically, it consists of deep gray matter
surrounded by white matter fiber tracts.
• Produce automatic behaviors necessary for
survival.
The human brain stem
This composite structure extends from the top of the spinal cord into the center of
the forebrain. The pons, pineal gland, and colliculi are ordinarily surrounded by
the cerebral cortex.
Brainstem: 3 major divisions
•Midbrain
•Pons
•Medulla
Brainstem
– Cranial nerve deficits
in association with
motor and sensory
deficit
– Diplopi,
– vertigo,
– dysartria,
– dysphagia,
– disequilibrium
VENTRICLES IN BRAINSTEM
• Mesencephalon  cerebral aqueduct
• Metencephalon  4th ventricle
• Mylencephalon  4th ventricle
TRUNCUS ENCEPHALI
MYELENCEPHALON
PONS
MESENCEPHALON
Corpus callosum
Posterior commissure
Fornix
Occipital
Lobe
Thalamus
Anterior
commissure
Quadrigeminal
cistern
Hypothalamus
vermis
Optic nerve
4th ventricle
Mammillary body
pyramid
Anterior view of brainstem
basal ganglia
internal capsule
optic chiasm
optic nerve
optic tract
hypothalamus
mammillary body
cerebral peduncle
interpeduncular fossa
pons
flocculus
inferior olivary
nuclear complex
cerebellar tonsil
cerebellum
pyramidal decussation
pyramid
Lateral view of brainstem
optic tract
cerebral
peduncle
trigeminal nerve
optic nerve
middle cerebellar peduncle
optic chiasm
vestibulocochlear nerve
flocculus
hypothalamus
cuneate tubercle
pons
inferior olivary nuclear complex
anterior median fissure
pyramid
Posterior view of brainstem
Superior colliculus
Cerebral
peduncle
Superior cerebellar
peduncle
Middle cerebellar
peduncle
Inferior colliculus
4th ventricle
Inferior cerebellar
peduncle
Medulla
The Brainstem: Midbrain
Small section superior to the
pons.
Part of the auditory pathways
and visual reflexes
Also involved in regulating
muscle tone/activity and
coordination
Midbrain
 Mostly composed of tracts
of nerve fibers
Reflex centers for vision and
hearing
Cerebral aquaduct – 3rd-4th
ventricles
Midbrain
•
•
•
Contains ascending and descending
tracts to the cerebrum and
thalamus.
Reflex center for eye muscles.
Also involved with processing
visual and auditory information
(connects head movements with
visual and auditory stimuli).
• Located btwn diencephalon and
pons.
– 2 bulging cerebral peduncles on
the ventral side. These contain:
• Descending fibers that go to
the cerebellum via the pons
• Descending pyramidal tracts
– Running thru the midbrain is
the hollow cerebral aqueduct
which connects the 3rd and 4th
ventricles of the brain.
– The roof of the aqueduct (the
tectum) contains the corpora
quadrigemina
• 2 superior colliculi that control
reflex movements of the eyes,
head and neck in response to
visual stimuli
• 2 inferior colliculi that
control reflex movements
of the head, neck, and trunk
in response to auditory
stimuli
Midbrain
•Cranial nerves 3&4 (oculomotor and
trochlear) exit from the midbrain
•Midbrain also contains the
headquarters of the reticular
activating system
Midbrain
• On each side, the midbrain contains a red nucleus and a
substantia nigra
– Red nucleus contains numerous blood vessels and receives
info from the cerebrum and cerebellum and issues
subconscious motor commands concerned w/ muscle tone &
posture
– Lateral to the red nucleus is the melanin-containing
substantia nigra which secretes dopamine to inhibit the
excitatory neurons of the basal nuclei.
• Damage to the substantia nigra would cause what?
Midbrain
THE BRAINSTEM: PONS
Superior to Medulla
oblongata.
Contains more ascending
and descending
pathways.
Relays information from
cerebrum to cerebellum.
Also includes sleep and
respiratory centers.
Pons
 The bulging center part of the brain
stem
 Mostly composed of fiber tracts
 Includes nuclei involved in the control
of breathing
PONS
• Connects the two
halves of the
cerebellum.
• Regulates
breathing.
Pons
• Literally means “bridge”
• Wedged btwn the midbrain &
medulla.
• Contains:
– Sensory and motor nuclei for 4
cranial nerves
• Trigeminal (5), Abducens (6), Facial
(7), and Auditory/Vestibular (8)
– Respiratory nuclei:
• Apneustic & pneumotaxic centers
work w/ the medulla to maintain
respiratory rhythm
– Nuclei & tracts that process and
relay info to/from the cerebellum
– Ascending, descending, and
transverse tracts that interconnect
other portions of the CNS
The Brainstem: Medulla oblongata
Most inferior portion, functions as
a conduction pathway (descending
motor neuron pathways
decussate here)
Reflex centers for:
regulating heart rate
blood vessel
diameter
coughing, sneezing
breathing
swallowing
MEDULLA OBLONGATA




The lowest part of the brain stem
Merges into the spinal cord
Includes important fiber tracts
Contains important control centers
 Heart rate control
 Blood pressure regulation
 Breathing
 Swallowing
 Vomiting
44
MEDULLA OBLONGATA
• Composed of nerve tracts
to and from the brain
(these tracts cross over
left to right and right to
left)
• May be regarded as an
extension of the spinal
cord
• Almost all of the cranial
nerves arise from this
region
Medulla Oblongata
Contains control centers for
many subconscious activities
• Respiratory rate
• Heart rate
• Arteriole constriction
• Swallowing
• Hiccupping
• Coughing
• Sneezing
Medulla Oblongata
Medulla Oblongata
• Most inferior region of the brain stem.
• Becomes the spinal cord at the level of
the foramen magnum.
• Ventrally, 2 ridges (the medullary
pyramids) are visible.
– These are formed by the large motor
corticospinal tracts.
– Right above the medulla-SC junction, most
of these fibers cross-over (decussate).
48
Medulla Oblongata
• Nuclei in the medulla are associated w/
autonomic control, cranial nerves, and
motor/sensory relay.
• Autonomic nuclei:
– Cardiovascular centers
• Alter the rate and force of cardiac contractions
• Alter the tone of vascular smooth muscle
– Respiratory rhythmicity centers
• Receive input from the pons
– Additional Centers
• Emesis, deglutition, coughing,
hiccupping, and sneezing
Medulla Oblongata
•
Sensory & motor nuclei of 5
cranial nerves:
–
•
Auditory/Vestibular (8),
Glossopharyngeal (9), Vagus (10),
Accessory (11), and Hypoglossal
(12)
Relay nuclei
–
–
Nucleus gracilis and nucleus
cuneatus pass somatic sensory
information to the thalamus
Olivary nuclei relay info from the
spinal cord, cerebral cortex, and
the brainstem to the cerebellar
cortex.
Components of the brainstem
• Sensory ascending pathways (dorsal):
– Relay nuclei, tracts
• Motor descending pathways (ventral)
– Tracts, motor nuclei brainstem
• Cerebellar pathways
– Tracts, cerebellar afferent and efferent nuclei
• Cranial nerve sensory and motor tracts
– Cranial nerve nuclei, nerve entry and exit points
• CPGs: rhythmic chewing, respiration, cardiovascular
regulation & gain adjustments for reflexes
• Modulatory systems: locus coeruleus, raphe &
substantia nigra
– Chemically coded nuclei
Ascending sensory pathways
Fine discriminative touch, conscious proprioception
• Fasciculus gracilis: Terminates in the nucleus gracilis (medulla)
• Fasciculus cuneatus: Terminates (medulla) in the cuneate and
accessory cuneate nuclei
Sensations of pain and temperature
• Lateral Spinothalamic Tract
– origin dorsal horn cells of the gray matter
– Fibers cross contralaterally through the anterior commissure
and ascend to the VPL nucleus
Transmits sensations of touch
• Ventral Spinothalamic Tract
– origin cells of the posterior horn
– Fibers cross to the opposite side in the anterior commissure
Descending motor pathways
Voluntary movement
• Lateral Corticospinal Tract
– Originates in large pyramidal cells (precentral gyrus)
– cross to the opposite side of the cord at the pyramidal
decussation & terminate in the dorsal horn cells
• Ventral Corticospinal Tract
– Originates in the pyramidal cells (motor area of the cortex)
Impulses related to equilibrium and antigravity reflexes
• Vestibulospinal Tract
– Fibers originate in the vestibular nuclei of the medulla and
terminate at level of the sacral spinal nerves
Connects vestibular complex and head and eye movement
coordination center in medulla
• Medial Longitudinal Fasciculus
– Contains both ascending and descending fibers
Motor Hierarchy
•Lateral group (extremities; fine
motor control)
•Corticospinal tract
•Rubrospinal tract
•Medial group (axial musculature;
rhythmic and postural
movements)
•Vestibulospinal tract
•Tectospinal tract
•Reticulospinal tract
•“Final common path”: motor pool
Reticular Formation
• Extensive network of neurons
that runs thru the medulla and
projects to thalamic nuclei that
influence large areas of the
cerebral cortex.
– Midbrain portion of RAS most
likely is its center
• Functions as a net or filter for
sensory input.
– Filter out repetitive stimuli.
Such as?
– Allows passage of infrequent or
important stimuli to reach the
cerebral cortex.
– Unless inhibited by other brain
regions, it activates the cerebral
cortex – keeping it alert and
awake.
How might the “sleep
centers” of your brain
work? Why does alcohol
make you tired?
Reticular Formation
• “Core” of brainstem
(midbrain, pons and medulla)
composed of loosely
organized neurons, outside of
the major nuclear groups of
the brainstem.
• Medial-to-lateral: raphe
nuclei, gigantocellular region,
small cell region
• Participate in widespread
connections
• Rostral continuation of
interneuronal network found
in spinal cord
Dorsal Column/Medial Lemniscal system
•Secondary neuron is in
brainstem: nucleus gracilis and
cuneatus=dorsal column nuclei
•Output of dorsal column nuclei
crosses midline and forms
recognizable bundle: medial
lemniscus
•Medial lemniscus fibers
synapse in the thalamus in the
ventroposterior nuclei
•Thalamic axons synapse in
primary somatosensory cortex
in several somatotopic maps
with some segregation of
submodalities
Tracing through the brainstem: Dorsal
Column/Medial Lemniscal System
Corticospinal Tract
Ядра
черепних
нервів
Ядра
черепних
нервів
вегетативное ядро III
моторное ядро III
моторное ядро IV
среднемозговое
чувствит. ядро V
мостовое чувствит. ядро V
моторное ядро VI
пучок ядра одиночного пути
слюноотделительные
ядра VII и IX
ядра нижней оливы
дорзальное ядро X
(вегетативное)
моторное ядро XII
двойное ядро (IX и X)
спинальное чувствит. ядро V
III
IV
Ganglion
n. trigeminalis
V
VI
VII
VIII
ganglii
r. spinalis XI
IX
r. cranialis XI
ганглии
X
Нижня
поверхня
мозку
Восходящие и
нисходящие пути
ствола головного
мозга и мозжечка
Роль нейронов дыхательного центра
ствола головного мозга в управлении
дыханием.
101