Contents of the Neurocranium,
Part II
The Brain, its Blood Supply
and the Cranial Nerves
Embryology
• Central nervous system begins as
neural tube
• Anterior portion of neural tube
differentiates into three primary
divisions:
– Hindbrain
– Midbrain
– Forebrain
Embryology
• Lateral walls of the forebrain
expand and protrude from both
sides of the neural tube
• Median portion of forebrain is
the diencephalon
• Lateral projections form the
telencephalon
Embryology
Two primary axes of
growth in the
developing brain
1. Longitudinal
flexion of anterior
neural tube
2. Inferior spiral
rotation of the
telencephalon
Ventricles
• Lumen of neural tube
becomes the CNS ventricular
system
• Shape of ventricular system
reflects developmental
deformation of neural tube
Ventricles
• Lateral ventricles
–
–
–
–
Anterior horn
Body
Posterior horn
Inferior horn
• Third ventricle
– Interventricular foramen (of
Monro)
– Cerebral aqueduct
• Fourth ventricle
Hindbrain
Cerebellum
• Motor coordination
• Cognitive functions
– temporal coordination
– planning
Hindbrain
Medulla Oblongata
• Anatomical and
physiological junction of
brain and spinal cord
• Initiates respiration
• Regulates heart rate
• Origin of cranial nerves
IX, X, XI, and XII
Hindbrain
Pons
• Bridge between
cerebellum and the rest
of the brain
• Origin of cranial nerves
V, VI, VII, and VIII
Midbrain
• Least differentiated
primary brain
division
• Contains cerebral
aqueduct
• Origin of cranial
nerves III and IV
(from dorsal surface)
Midbrain
Corpora Quadrigemina
Superior Colliculi
• Visual tracking
• Coordination of head turning
& eye movements
• Inferior Colliculi
• Sound location
• Focusing attention to
auditory stimuli
Midbrain
Substantia Nigra
• Darkly pigmented (neuromelanin) nucleus
• Produces dopamine
• Parkinson’s disease—
destruction of the cells of the
substantia nigra
Midbrain
Substantia Nigra
• In 1982, 6 drug addicts in Santa Clara, CA
manifested with Parkinson’s disease (oldest
patient was 41 yrs. old)
• Each had injected synthetic heroin—MPPP (1methyl-4-phenyl-4-propionpiperidine), an analog
of meperidine (Demerol)
• The poorly synthesized designer drug contained a
contaminant—MPTP (1-methyl-4-phenyl-1,2,5,6tetrahydropyridine), which kills the cells of the
substantia nigra
Midbrain
Cerebral Peduncles
• Major fiber bundles connecting
forebrain to hindbrain
• Contain descending axons of
upper motor neurons from
cortex
Diencephalon
Thalamus
• Potato-shaped structure
• Sensory relay for all
afferents except olfaction
Diencephalon
Thalamus
• Thalami form walls
of 3rd ventricle
Diencephalon
Hypothalamus
• 4 g neural structure
• Connected to pituitary gland
• Regulates:
– Body
temperature
– Hunger
– Thirst
– Sexual
activity
– Goal-seeking
behavior
– Endocrine
functions
– Affective
behavior
– Visceral motor
system
Telencephalon
• Caudate nucleus
• Globus pallidus
• Putamen
Basal Ganglia
• Modulate and integrate components
of motor activity (and cognitive
functions)
• System depends
on dopamine—
affected by
Parkinson’s
disease
Telencephalon
Amygdala
• Lies at tail of caudate
nucleus but is not
functionally part of the
basal ganglia
• Involved in the control
of rage, aggression and
sexuality
Telencephalon
Hippocampus
• Composed of three-layered
cortex (archicortex)
• Fornix—major output pathway
• Involved in the formation of
new episodic memories
Telencephalon
Cerebrum
• Composed of six-layered neocortex and deep white matter
• Center of sensory input, motor output, and higher
cognitive functions
Cerebrum
Primary Fissures
• Longitudinal cerebral
fissure
Cerebrum
Primary Fissures
• Lateral fissure
• Central sulcus
Cerebrum
Lobes
•
•
•
•
Frontal
Parietal
Occipital
Temporal
Cerebrum
Lobes
• Insula
Cerebrum
White Matter
• Corpus
callosum—
primary
connection
between left and
right cerebral
hemispheres
Cerebrum
White Matter
• Internal capsule—primary
pathway of fibers
ascending to cortex from
thalamus and descending
from cortex to cerebral
peduncles
Motor Cortex
• Primary motor
cortex lies along the
precentral gyrus in
the frontal lobe
• Motor output
projects to
contralateral side
Motor Output Pathways
• Voluntary
movement—conducted
to lower motor neurons
via the pyramidal
pathway
Motor Output Pathways
• Balance,
posture, limb
coordination
information
conducted by
numerous
extrapyramidal
pathways
Somatosensory Cortex
• Primary
somatosensory
cortex lies along the
postcentral gyrus in
the parietal lobe
• Representation of
body is from
contralateral side
Somatosensory Cortex
Somatosensory cortex (like motor cortex) is mapped
somatotopically and proportionate to sensitivity,
not size
Other Sensory Cortices
• Visual cortex—
occipital lobe
• Auditory cortex—
superior portion of
temporal lobe
• Rhinal (olfactory)
cortex—anterior
medial temporal lobe
• Gustatory (taste)
cortex—inferior
aspect of postcentral
gyrus
Language Areas
• Occur only in the left
hemisphere of most people
(96 % of right-handed
individuals, 72% of lefthanded individuals)
• Broca’s area—motor speech
center, in frontal lobe
• Wernicke’s area—language
interpretation center, in
temporal & parietal lobes
Cranial Nerves
I.
II.
III.
IV.
V.
VI.
VII.
VIII.
IX.
X.
XI.
XII.
Olfactory
Optic
Occulomotor
Trochlear
Trigeminal
Abucens
Facial
Vestibulocochlear
Glossopharyngeal
Vagus
Spinal Accessory
Hypoglossal
Cranial Nerves
Exit from Neurocranium
I Cribriform
plate
Cranial Nerves
Exit from Neurocranium
II Optic canal
Cranial Nerves
Exit from Neurocranium
III, IV, VI Superior orbital fissure
Cranial Nerves
Exit from Neurocranium
V1 Superior orbital fissue
V2 Foramen rotundum
V3 Foramen ovale
Cranial Nerves
Exit from Neurocranium
VII, VIII Internal auditory meatus
Cranial Nerves
Exit from Neurocranium
IX, X, XI Jugular foramen
Cranial Nerves
Exit from Neurocranium
XII Hypoglossal Canal
Cranial Nerves
Exit from Neurocranium
Blood Supply
• Vertebral arteries
– Provide ~30% of blood
supply to brain
• Internal carotid arteries
– Provide ~70% of blood
supply to brain
Circle of Willis
Vertebral aa.  basilar a. 
posterior cerebral aa.
Internal carotid a.
 middle cerebral aa.
 anterior cerebral aa.
Posterior communicating
arteries connect posterior
cerebral aa. and internal
carotid aa.
Anterior communicating
ARTERY (sing.) connect
anterior cerebral arteries
Blood Supply
Blood Supply
Venous Drainage
• Blood from the
cortex drains to
surface veins that
drain into the dural
venous sinuses
Venous Drainage
• Blood from the deep
brain (thalamus,
basal ganglia) drains
into great cerebral
vein (of Galen)
before entering the
straight sinus
• Blood from the
lower brainstem
drains through the
foramen magnum
into the vertebral
venous plexus
Cerebrovascular Accident (CVA)
• Ruptured aneurysm—failure of a localized
defect in the elasticity of a vessel
• Arterial thrombus—blockage of an artery
• Embolism—clot from elsewhere in the body
that lodges in a cerebral artery
• Hypertensive apoplexy—sudden effusion of
blood into cerebral tissue due to rise in
blood pressure