Chapter 14
The Brain and Cranial Nerves
• Largest organ in the body?
• Brain functions in sensations, memory, emotions,
decision making, behavior
19-1
19-2
Principal Parts of the Brain
Embryonic Brain Development
Telencephalon
Prosencephalon
Optic vesicle
Diencephalon
Mesencephalon
Metencephalon
Rhombencephalon
Myelencephalon
Spinal cord
(a) 4 weeks
(b) 5 weeks
Telencephalon
Forebrain
Diencephalon
Mesencephalon Midbrain
Pons
Cerebellum
Metencephalon
Hindbrain
Myelencephalon
(medulla oblongata)
Spinal cord
(c) Fully developed
Figure 14.4
• Cerebrum
• Diencephalon
– thalamus
– hypothalamus
– Epithalamus
– Pineal gland
• Cerebellum
• Brainstem:
– Medulla oblongata
– pons
– midbrain
14-3
19-4
Protective Coverings of the Brain
Meninges of the Brain
• Bone, meninges
& CSF
• Meninges same
as around the
spinal cord
– dura mater
– arachnoid
mater
– pia mater
19-5
Skull
Dura mater:
Periosteal layer
Meningeal layer
Subdural space
Subarachnoid
space
Arachnoid villus
Arachnoid mater
Superior sagittal
sinus
Blood vessel
Falx cerebri
(in longitudinal
fissure only)
Pia mater
Brain:
Gray matter
White matter
Figure 14.5
14-6
1
Cerebrospinal Fluid 80 -150 ml (3 – 5 oz)
Blood Supply to Brain
• 2% of weight - uses 20% of our oxygen
• Internal carotid & vertebral arteries to circle of Willis
Vessels on surface of brain----penetrate tissue
• Blood-brain barrier (BBB)
– protects cells from some toxins and pathogens
– a couple of areas without BBB (glucose, pH,
osmolarity)
• Blood-CSF barrier at ependymal cells of choroid
plexus
• Clear liquid – water, oxygen, glucose, proteins, & ions
• Continuously circulates around brain (ventricles,
central canal, subarachnoid space)
• Functions:
– Buoyancy
– Mechanical protection
– Chemical protection (homeostasis)
• ionic concentrations for AP’s
• removes some metabolic products from nervous
tissue
19-7
19-8
Ventricles
Flow of Cerebrospinal Fluid
Arachnoid villus
8
Superior
sagittal
sinus
Arachnoid mater
1 CSF is secreted by
choroid plexus in
each lateral ventricle.
Subarachnoid
space
Dura mater
1
2 CSF flows through
Interventricular foramina
into third ventricle.
2
Choroid plexus
Third ventricle
3
3 Choroid plexus in third
ventricle adds more CSF.
7
4
Cerebral
aqueduct
4 CSF flows down cerebral
aqueduct to fourth ventricle.
Lateralaper ture
5 Choroid plexus in fourth
ventricle adds more CSF.
– 2 lateral ventricles, one within each cerebral
hemisphere, 3rd ventricle, fourth ventricle
– CSF produced by choroid plexus (ependymal cells
Fourth ventricle
6
5
6 CSF flows out two lateral apertures
and one median aperture.
Median aperture
7 CSF fills subarachnoid space and
bathes external surfaces of brain
and spinal cord.
7
8 At arachnoid villi, CSF is reabsorbed
into venous blood of dural
venous sinuses.
– Circulation
Centralcanal
of spinal cord
Subarachnoid
space of
spinal cord
19-9
Principal Parts of the Brain
• Brain stem
• Medulla oblongata
- Relays motor & sensory brain and spinal cord
- all fibers going to/from
brain/spinal cord
- consciousness/alert
- cardiovascular center
- respiratory center
- bv diameter
- motor control
- sensory info.
• CSF is reabsorbed through arachnoid villi
19-11
19-12
2
Brain Stem: Medulla Oblongata
Medulla and Pons
Nuclei of 5 cranial nerves:
Diencephalon:
Thalamus
1.
2.
Infundibulum
Optic tract
Mammillary body
Cranial nerves:
Midbrain:
3.
Optic nerve (II)
Cerebral peduncle
Oculomotor nerve (III)
4.
5.
Trochlear nerve (IV)
Trigeminal nerve (V)
Vestibulochochlear (VIII):
Glossopharyngeal (IX): (taste, saliva,
swallow)
Vagus (X): pharynx larynx, thoracic
and abdom orgs
Accessory (XI): swallowing
Hypoglossal (XII): tongue &
swallowing
Abducens nerve (VI)
Pons
Facial nerve (VII)
Vestibulocochlear nerve (VIII)
Glossopharyngeal nerve (IX)
Vagus nerve (X)
Accessory nerve (XI)
Medulla oblongata:
Pyramid (Decussation)
Hypoglossal nerve (XII)
Regions of the brainstem
Diencephalon
Anterior median fissure
Midbrain
Pyramidal decussation
Spinal nerves
Spinal cord
Pons
Medulla oblongata
(a) Anterior view
Figure 14.8a
14-13
19-14
Brain Stem: Pons
•
•
•
•
•
•
•
•
One inch long
Tracts (a & d)
Respiratory nuclei
Sensory info to
cerebellum
Trigeminal (V) (head &
face)
Abducens (VI) eye
movement
Facial Nerves (VII) head
and face, chew, taste
Vestibulocochlear (VIII)
equilibrium
Brain Stem: Midbrain
(Mesencephalon)
19-15
•
One inch in length
• Extends from pons to
diencephalon
• Cerebral aqueduct
connects 3rd to 4th
ventricle
• Cerebral peduncles:
- anchor cerebrum to
brainstem
- impusles to/from
cerebellum
- inhibitory signals to
thalamus
- Relays sensory & motor
impulses
• Tectum:
-superior and inferior
colliculi (reflexes)
Oculomotor (III) eye
movement & sight
Trochlear (IV) eye 19-16
movements
Midbrain -- Cross Section
Diencephalon:
Thalamus
Posterior
Infundibulum
Superior colliculus
Optic tract
Mammillary body
leaves
Tectum
Cerebral aqueduct
Cranial nerves:
Medial geniculate nucleus
Midbrain:
Optic nerve (II)
Cerebral peduncle
-Anchor cerebrum to
brainstem
Reticular formation
Oculomotor nerve (III)
Central gray matter
Cerebral peduncle:
Oculomotor nucleus
Medial lemniscus
Tegmentum
Trochlear nerve (IV)
Red nucleus
Trigeminal nerve (V)
(a) Midbrain
Substantia nigra
Abducens nerve (VI)
Pons
Facial nerve (VII)
Cerebral crus
(b) Pons
Vestibulocochlear nerve (VIII)
Oculomotor nerve (III)
Glossopharyngeal nerve (IX)
Anterior
Vagus nerve (X)
Accessory nerve (XI)
Medulla oblongata:
Pyramid
Hypoglossal nerve (XII)
Diencephalon
Anterior median fissure
Midbrain
Pyramidal decussation
Spinal nerves
Spinal cord
Pons
Medulla oblongata
(a) Anterior view
(c) Medulla
(a) Midbrain
Regions of the brainstem
14-17
1. Tegmentum - with cerebellum for fine motor control
2. Substantia nigra
motor center relays inhibitory signals to thalamus & basal
nuclei preventing unwanted body movement
3. Cerebral crus: fibers that connects cerebrum to the pons
carries corticospinal tracts
3
Reticular Formation
Radiations to
cerebral cortex
Thalamus
Functions of Reticular Formation
• reticular formation – loosely
organized web of gray matter that run
vertically through all levels of the
brainstem
• has connections with many areas of
cerebrum and cerebral cortex
Auditory input
Visual input
• Somatic motor control
– adjust muscle tension (maintain tone, balance, and posture)
– relays signals from eyes and ears to the cerebellum
• integrates visual, auditory, and balance and motion stimuli
into motor coordination
• cardiovascular control: cardiac and vasomotor centers of M.O.
• pain modulation
– One route pain signals may take to reach cerebral cortex
• sleep and consciousness
– central role in states of consciousness!!!!!!!!
• Habituation (filter)
Reticular formation
Ascending general
sensory fibers
Descending motor
fibers to spinal cord
14-19
14-20
Cerebellum
Cerebellum
Superior colliculus
Inferior colliculus
relay
Pineal gland
Posterior commissure
Cerebral aqueduct
Mammillary body
Midbrain
White matter
(arbor vitae)
Gray matter
Oculomotor nerve
Fourth ventricle
Pons
Medulla oblongata
• 2 cerebellar hemispheres and vermis (central area)
• Function
– Sensory input from muscles
– Receives fibers from cerebral cortex associated with
vision, hearing, coordination
• i.e., correct voluntary muscle contraction and
posture & balance
– skilled “fine tuned” movements indirectly by sending
information to midbrain
– knowledge/language/emotional component??
(a) Median section
• cerebellar peduncles – three pairs of stalks that connect the
cerebellum to the brainstem
– inferior peduncles – connected to medulla oblongata
– middle peduncles – connected to the pons
– superior peduncles – connected to the midbrain
14-22
19-21
Diencephalon
The Forebrain
1. diencephalon
• encloses the third
ventricle
• 3 major areas
– thalamus
– hypothalamus
– epithalamus
2. Telencephalon
• cerebrum
Telencephalon
Forebrain
Diencephalon
Midbrain
Mesencephalon
Pons
Metencephalon
Cerebellum
Hindbrain
Myelencephalon
(medulla oblongata)
Spinal cord
(c) Fully developed
14-23
19-24
4
Thalamus: Gateway to the Cerebral Cortex
• 1 inch long mass of gray mater
• Relay station for sensory information on way up to
cerebral cortex
• Motor control: relay information from cerebellum to
cerebrum
• Crude perception of some sensations
Thalamus
• relays auditory and visual impulses, taste and
somatic sensations, touch, pain, temperature
• receives sensory impulses from cerebellum re.
motor control
• autonomic activities & consciousness (RAS)
19-25
19-26
Hypothalamus
Functions of Hypothalamus
• Controls & integrates activities of ANS
• Synthesizes hormones that controls the anterior
pituitary
• Regulates rage, aggression, pain, fear, pleasure,
contentment

•
•
•
•
– even arousal & orgasm
Feeding, thirst & satiety centers
Controls body temperature
Sleep and circadian rhythms
Memory
• Many nuclei (masses of grey matter)
• Major regulator of homeostasis!!!!!!!!!!
19-27
19-28
19-29
19-30
Cerebrum
• Composed of 2 cerebral
hemispheres
• Cerebral cortex is gray matter
– 2 - 4 mm thick contains
billions of cells
• Folds (gyri) & grooves (sulci
or fissures)
Cerebral hemispheres
• Longitudinal fissure:
separates L & R Cerebral
Hemispheres
• Corpus callosum band of
white matter connects L & R
cerebral hemis.
• Each hemisphere is
subdivided into 4 lobes
5
Lobes and Fissures
• Longitudinal fissure
(green)
• Frontal lobe
• Central sulcus
(yellow)
• Parietal lobe
• Parieto-occipital
sulcus (red)
• Occipital lobe
• Lateral sulcus (blue)
• Temporal lobe
• Insula
Cerebral Cortex
• 2 principal types of neurons:
1. stellate cells
• receive sensory input &
process information on a
local level
2. pyramidal cells
• tall, conical.
• output neurons of the
cerebrum
• only neurons that leave the
cortex and connect to other
parts of CNS
Cortical surface
I
Small pyramidal
cells
II
III
Stellate cells
IV
• neocortex – six layered tissue that
constitutes about 90% of the
human cerebral cortex
Large pyramidal
cells
V
VI
14-32
White
matter
19-31
Cerebral White Matter
The Basal Nuclei
Cerebrum
Corpus callosum
Lateral ventricle
Thalamus
Internal capsule
Caudate nucleus
Putamen
Insula
Lentiform
nucleus
Third ventricle
Globus pallidus
Hypothalamus
Subthalamic nucleus
Optic tract
Corpus
striatum
Pituitary gland
Figure 14.16
1. Association fibers - between gyri in same hemi.
2. Commissural fibers - from one hemi. to other
3. Projection fibers - form descending & ascending tracts
(info to and from whole body)
• masses of gray matter buried deep in white matter, lateral to the
thalamus
– receive & send info to midbrain & motor areas of cerebral cortex
– involved in motor control
• At least three areas form basal nuclei
– caudate nucleus
– putamen
– globus pallidus
14-34
19-33
Important center of emotion and learning
• most anatomically prominent components
are:
Limbic System
– cingulate gyrus – arches over the top of
the corpus callosum in the frontal and
parietal lobes
– hippocampus – in the medial temporal
lobe - memory
– amygdala – immediately rostral to the
hippocampus - emotion
Limbic System
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Medial
prefrontal
cortex
Corpus
callosum
Cingulate
gyrus
Fornix
Orbitofrontal
cortex
Mammillary
body
Basal nuclei
Hippocampus
• limbic system components are connected
through complex loop of fiber tracts .
• limbic system structures have centers for
both gratification and aversion
– gratification – sensations of pleasure
or reward
– aversion –sensations of fear or sorrow
Thalamic
nuclei
Amygdala
Temporal lobe
• Amygdala, cingulate gyri, & hippocampus
• Emotional brain--intense pleasure & intense pain
• Strong emotions increase efficiency of memory
14-36
19-35
6
Functional organization of the cerebral cortex
Movements
Sensations:
Touch,
Pain,
Temp.
Thought
Forethought
Judgment
Understanding
written & spoken
language
Feelings
Speech
Emotions
Recognition
Memory
19-37
7