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Brain Stem
• Located b/w the cerebrum
and the spinal cord
– Provides a pathway for
tracts running b/w 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!
• Located b/w the diencephalon and
the pons.
– 2 bulging cerebral peduncles on
the ventral side contain:
• Descending fibers that go to
the cerebellum via the pons
• Descending pyramidal tracts
– Running through 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
Cerebral
aqueduct
Midbrain contains the
headquarters of the reticular
activating system and the
nuclei for Cranial nerves 3&4
(oculomotor and trochlear).
Midbrain
• On each side, the midbrain
contains a red nucleus and a
substantia nigra SN.
– 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 SN,
which contain dopamine
releasing neurons that
terminate in the basal nuclei.
Pons
•
•
•
Literally means “bridge”
Wedged b/w 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
Medulla
Oblongata
• Most inferior region of
the brain stem.
• Ventrally, 2 ridges (the
medullary pyramids) are
visible.
– These are formed by
the large motor
corticospinal tracts.
– Right above the
medulla-spinal cord
junction, most of
these fibers crossover (decussate).
Brainstem:
- Medulla Oblongata = Most
nerve impulses coming to
brain from spinal cord cross
over (decussation) in medulla
Medulla
Oblongata
Continuous with spinal cord at
foramen magnum. Contains 3
nuclei (“vital” centers)
functions:
- respiratory center
- cardiac center
- vasomotor center
Brainstem:
- Medulla Oblongata
- reflexes coughing,
vomiting, swallowing, sneezing
-contains two prominent
enlargements on the anterior
surfacepyramids
Medulla Oblongata
•
•
Contains sensory & motor
nuclei of 5 cranial nerves:
– Auditory/Vestibular (8),
Glossopharyngeal (9),
Vagus (10), Accessory
(11), and Hypoglossal
(12)
Contains relay nuclei that
pass somatosensory info to
the thalamus and relay
nuclei that conveys info
from the spinal cord,
cerebral cortex, and the
brainstem to the cerebellar
cortex.
How many brain
structure can you
ID?
Other structures:
 limbic system = olfactory cortex,
diencephalon & cerebrum
functions: emotions & memory
Limbic System
Reticular formation =
Function: maintains a state
of attention & wakefulness
(consciousness) by arousal
of the cerebral cortex
(sleep disorders: Narcolepsy
& cataplexy)
Protection
• What is the major protection for
the brain?
• There are also 3 connective
tissue membranes called the
meninges:
• Cover and protect the CNS
• Protect blood vessels
• Contain cerebrospinal fluid
• The 3 meninges from superficial
to deep:
• Dura mater
• Arachnoid mater
• Pia mater
meninges = connective tissue
membrane surrounding
both the brain & spinal cord
- 3 meninges (function
nourishes and protects)
Skin
Galea Aponeurotica
Connective Tissue
Bone
Dura Mater
Arachnoid mater
- 3 meninges
dura mater = tough outer,
fibrous conn. tissue
-Just inside cranium and is tightly attached
to the periosteum of the skull.
-Surrounded by epidural space in the vertebral
column
arachnoid mater = thin,
web-like layer
pia mater = innermost layer
tightly bound to brain
surface
subarachnoid space = space
between arachnoid and pia
mater contains Cerebral Spinal
Fluid (CSF).
Meninges
Ventricles
• Ventricles are within the cerebral
hemispheres and brain stem and
consist of a series of
interconnected cavities
• Continuous with the central canal of
the spinal cord
• Contain cerebrospinal fluid
Ventricles of the brain
• Largest-Lateral ventricles (1st
and 2nd ventricles)
– Occupies part of the
hemispheres and portions of
the frontal, temporal and
occipital lobes
Ventricles of the brain
• Third ventricle-a narrow space
in the midline of the brain
beneath the corpus callosum
– Communicates with the lateral
ventricles through openings in
its anterior
endinterventricular foramina
Ventricles of the brain
• Fourth ventricle-in the brain stem just
anterior to the cerebellum
– Connected to the third ventricle via
the cerebral aqueduct
– Continuous with the central canal of
the spinal cord and has openings in its
roof that lead into the subarachnoid
space of the meninges.
Ventricles & CSF
- ventricles = fluid-filled
(Cerebral Spinal Fluid, CSF)
cavities within brain
- CSF clear fluid produced by
the choroid plexus
serves as protection and
provides nourishment
Ventricles
Cerebrospinal Fluid
• Fills the space b/w the
arachnoid and pia mater, as
well as the internal cavities of
the brain (ventricles) and
spinal cord.
• Functions:
– Shock absorption
– Support
– Nourishment
• A choroid plexus consists of a combination of specialized
ependymal cells and permeable capillaries for the production
of CSF.
– 2 extensive folds originate in the roof of the 3rd
ventricle (located b/w the lateral walls of the
diencephalon) and extend through the interventricular
foramina and cover the floors of the lateral ventricles.
A region of choroid plexus is also found in the 4th
ventricle b/w the cerebellum and pons.
• Ependymal cells selectively secrete capillary filtrate
into the ventricles. They also remove waste
products from the CSF and adjust its composition
over time. CSF differs markedly from blood in its
[soluble protein] and cellular content.
• About 500mL of CSF is produced per day. The
total volume of CSF at any given moment is 150mL
• CSF circulates from the choroid plexus through the
ventricles and the central canal of the spinal cord.
As it circulates, there is unrestricted diffusion b/w
it and the interstitial fluid of the CNS.
CSF reaches the subarachnoid
space through foramina in the
wall and roof of the 4th
ventricle. CSF then flows
through the subarachnoid space
surrounding the brain, spinal
cord, and cauda equina
Along the axis of the superior
sagittal sinus, fingerlike
extensions of the arachnoid
membrane, called arachnoid villi,
penetrate the dura. In adults,
clusters of villi form arachnoid
granulations.
Flow of CSF
CSF is absorbed
into the general
circulation at
the arachnoid
granulations