Anatomy & Physiology
Chapter 13
The Brain
And Cranial Nerves
F ‘12
The Brain
Four major regions of the brain:
1.Cerebrum
2.Diencephalon
3.Cerebellum – contains 50% of neurons in
brain
4.Brainstem – ends at foramen magnum
Directional Terms of Brain
Quadripedal vs Bipedal :
1. Rostral – toward the nose or anterior
2. Caudal – toward the tail or caudal
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Central sulcus
Frontal lobe
Parietal
lobe
Gyrus
Sulcus
Cerebrum
Occipital
lobe
Lateral sulcus
Temporal lobe
Pons
Brainstem
Cerebellum
Medulla oblongata
Spinal cord
(a) Left lateral view
© The McGraw-Hill Companies, Inc./Photo and Dissection by Christine Eckel
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Anterior
Posterior
Central sulcus
Parietal lobe
Frontal lobe
Diencephalon
Parieto-occipital sulcus
Corpus
callosum
Interthalamic
adhesion
Thalamus
Occipital lobe
Pineal gland
Tectal plate
Hypothalamus
Cerebral aqueduct
Pituitary gland
Fourth ventricle
Temporal lobe
Midbrain
Cerebellum
Brainstem
Pons
Medulla oblongata
Spinal cord
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cerebral hemispheres
Anterior
Eye
Frontal lobe
Olfactory bulb
Olfactory tracts
Optic chiasm
Optic nerve
Pituitary gland
Optic tract
Temporal lobe
Cerebrum
Mammillary
bodies
Midbrain
Pons
Brainstem
Medulla
oblongata
Cranial nerves
Cerebellum
Occipital lobe
Posterior
Development of the Brain
1. Neurulation
a. Formation of the neural tube
b. Neural tube becomes the central nervous
system
c. Failure of neuropores to close results in
neural tube defect, Ex. Spina bifida
2. Brain develops from cranial neural tube
3. Spinal cord develops from caudal neural
tube
Neurulation
Neural Tube
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
INTEGRATE
Neural Tube Defects
(a)
Spina bifida cystica
(top): © OJ Staats/Custom Medical Stock Photo; (bottom): © NMSB/Custom Medical Stock Photo
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Rhombencephalon
Prosencephalon
Mesencephalon
Mesencephalon
Prosencephalon
Rhombencephalon
Spinal cord
Spinal cord
4 weeks
5 Secondary Brain Vesicles
Myelencephalon
Telencephalon
Metencephalon
Mesencephalon
Diencephalon
5
Mesencephalon
Diencephalon
Telencephalon
Metencephalon
Spinal cord
Myelencephalon
Spinal cord
5 weeks
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cerebrum
Outline of diencephalon
Cerebrum
Outline of diencephalon
Mesencephalon
Cerebellum
Mesencephalon
Cerebellum
Pons
Medulla oblongata
Pons
Medulla oblongata
Spinal cord
Spinal cord
(c) 13 weeks
(d) 26 weeks
Cerebrum
Diencephalon
Midbrain
Pons
Medulla
oblongata
Cerebellum
Spinal cord
(e) Birth
Table 13.1
Brainstem
Gray & White Matter
1. Gray matter
a. Composed of neuron cell bodies,
dendrites, and synapses
b. Forms surface cortex over cerebrum
and cerebellum
c. Deeper masses of gray matter = nuclei
2. White matter
a. Lies deep to cortical gray matter
b. Composed of tracts, as in spinal cord
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Gray matter
White matter
Inner white
matter
Cortex
Corpus
callosum
Cerebral
nuclei
Internal
capsule
Lateral ventricle
(a) Coronal section of cerebrum and diencephalon
(a)
Cortex (gray matter)
Inner gray matter
Cerebrum
Cerebellum
(b)
Cerebellum
(c)
Medulla oblongata
Fourth ventricle
Inner gray matter
Brainstem
Outer white matter
Spinal cord
(b) Cerebellum and brainstem
Fourth ventricle
Inner gray matter
Outer white matter
(d)
Central canal
Outer white matter
(c) Medulla oblongata
Inner gray matter
(d) Spinal cord
Protection & Support
1. Bony Cranium – rigid support
2. Cranial Meninges – protective connective
tissue membranes
a. Septa – Extensions of dura that partition
3. Cerebrospinal Fluid – physical protection
and chemical stability
4. Blood-brain Barrier – helps prevent
exposure to some potentially harmful
substances in blood
Cranial Meninges
Three connective tissue membranes
1. Dura mater
2. Arachnoid mater
3. Pia mater
Dura Mater
1. Two layers:
a.Outer periosteal layer forms periosteum
on internal surface of cranial bones
b.Inner meningeal layer
i. Fused to periosteal layer except at
dural sinuses
ii. Folds form partitions = dural septa
iii. Continues as dural sheath around
spinal cord
Cranial Meninges
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Skin of scalp
Periosteum
Arachnoid granulation
Bone of skull
Arachnoid villus
Periosteal layer
Meningeal layer
Dural
venous
sinus
Dura mater
Arachnoid trabeculae
Pia mater
Cerebral cortex
White matter
(superior sagittal sinus)
Falx cerebri
Dura Mater
2. Dural sinuses
a. Spaces between two layers of dura
Collect blood that circulates through brain
a. Triangular cross section, no valves
3. Epidural space
a. Potential space between dura and bone of
skull
b. May become real space of blood or fluid
collects within it.
4. Subdural space
b. Separates dura mater from arachnoid mater
c. Also potential space
Cranial Dural Septa
1. Falx cerebri – largest of the septa
a. Vertical fold that dips into longitudinal fissure
and separates cerebral hemispheres
b. Anterior end attaches to crista galli of ethmoid
bone
c. Posterior end attaches to internal occipital
crest
2. Falx cerebelli
a. Runs along vermis of cerebellum
b. Partially separates right and left cerebellar
hemipsheres
Cranial Dural Septa
3. Tentorium cerebelli
a. Horizontal fold that separates cerebrum and
cerebellum
b. Forms a “tent” over cerebellum
4. Diaphragma sellae
a. Forms roof over sella turcica
b. Separates hypothalamus and pituitary gland
Dural Septa
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cranium
Dura mater
Falx cerebri
Diaphragma
sellae
Tentorium
cerebelli
Falx
cerebelli
Midsagittal section
Posterior view
(left): © The McGraw-Hill Companies, Inc./Photo and Dissection by Christine Eckel
Arachnoid Mater
1. Middle layer of meninges
2. Arachnoid trabeculae
a. Web of collagen & elastic fibers
b. Extend through subarachnoid space to pia
3. Subarachnoid space
a. Separates arachnoid from pia
b. Filled with CSF
c. Contains large cerebral blood vessels, but
poorly protected – “supported” by fibers & CSF
4. Arachnoid villi
a. Cauliflower-like extensions of arachnoid mater
that protrude through dura
b. Absorb CSF into venous blood of sinus
Pia Mater
1. “Gentle mother”
2. Innermost meninx
3. Thin vascular layer of areolar connective
tissue
4. Tightly adhered to surface of brain and
follows contours of brain closely – “shrink
wrap”
5. Rich with blood vessels
Cranial Meninges
Skin of scalp
Periosteum
Bone of skull
Arachnoid
villus
Dural venous sinus
Arachnoid mater
(superior sagittal sinus)
Subarachnoid space
Arachnoid trabeculae
Pia mater
White matter
Falx cerebri
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
The Meninges of the Brain
Ventricles
1. Internal chambers of the brain
2. Derived from neural canal of embryonic
neural tube
3. All are lined with ependymal cells and
contain cerebrospinal fluid
4. Cerebrospinal fluid circulates through
ventricles and communicating
passageways.
5. Four ventricles in brain
Ventricles
1 & 2. Two Lateral ventricles
a. Large arc in each cerebral hemisphere
b. Interventricular foramen – connects
lateral ventricles to 3rd ventricle
c. Septum pellucidum - “transparent wall”
3. Third Ventricle
a. Inferior to c. callosum
b. Cerebral (Mesencephalic) aqueduct–
connects 3rd and 4th ventricle
Ventricles
4. Fourth ventricle
a. Between pons & cerebellum
b. Apertures
i. Connect ventricles to subarachnoid space
(median and paired lateral apertures)
ii. From this subarachnoid space, CSF is
returned to blood in sinus by arachnoid villi
c. Fourth ventricle merges with central
canal of spinal cord
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Posterior
Anterior
Interventricular
foramen
Third
ventricle
Lateral
ventricles
Cerebral
aqueduct
Fourth
ventricle
Lateral aperture
Median aperture
Central canal of spinal cord
(a) Lateral view
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cerebrum
Lateral ventricle
Interventricular
foramen
Third ventricle
Cerebral
aqueduct
Fourth ventricle
Central canal of spinal cord
(b) Anterior view
Cerebrospinal Fluid
1. Clear, colorless fluid that bathes
exposed surfaces of CNS
2. Brain produces 500 ml CSF daily
3. Is constantly reabsorbed, so ventricles
contain only about 150 ml (half cup)
4. CSF circulates, not static
a. Driven by pressure
b. Pulsations due to heartbeat
c. Ciliated ependymal cells
Cerebrospinal Fluid
Three important functions:
1. Buoyancy
a. Brain neither sinks nor floats, is suspended
b. Prevents pressure necrosis due to weight
2. Protection – fluid cushion
3. Chemical stability
a. Transports nutrients and rinses wastes
from CNS
b. Regulates environment to prevent
chemical fluctuations
Cerebrospinal Fluid
1. Produced by choroid plexus
a. Layer of ependymal cells and
capillaries of pia mater
b. Ependymal cells connected by tight
junctions
2. CSF formed by modification of plasma
from capillaries
a. Forms as filtrate containing glucose,
O2, vitamins, and some ions
b. Contains very little protein, Ca2+ or K+
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Ependymal
cells
Capillary
Pia mater
Section of
choroid
plexus
Cavity of ventricle
CSF forms and
enters the ventricle
(b) Choroid plexus
CSF Circulation
1. Arachnoid villus – extensions of
arachnoid mater project through dura
mater into dural sinuses
a. One way flow of excess CSF into blood of
dural sinuses
2. Arachnoid granulation – collection of
arachnoid villi
3. Pressure gradient and long cilia of
ependymal cells help move CSF
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Dura
CSF
mater
flow (periosteal
layer)
Arachnoid
villus
Superior sagittal sinus
(dural venous sinus)
Dura mater
(meningeal layer)
Arachnoid mater
Subarachnoid space
Pia mater
Cerebral cortex
(b) Arachnoid villus
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1 CSF is produced by the choroid plexus in the ventricles.
2 CSF flows from the lateral ventricles, through the
interventricular foramen to the third ventricle, and then
through the cerebral aqueduct into the fourth ventricle.
3 CSF in the fourth ventricle flows into the subarachnoid
space by passing through the paired lateral apertures
or the single median aperture, and into the central canal
of the spinal cord.
4 As the CSF flows through the subarachnoid space, it
removes waste products and additional fluid from the
brain, and provides buoyancy to support the brain.
5 Excess CSF flows into the arachnoid villi, then drains
into the dural venous sinuses. The greater pressure
on the CSF in the subarachnoid space ensures that
CSF moves into the venous sinuses without permitting
venous blood to enter the subarachnoid space.
CSF flow
Arachnoid villi
5
Superior sagittal sinus
(dural venous sinus)
4
Venous fluid
flow
Pia mater
Choroid plexus of
third ventricle
1
Choroid plexus of
lateral ventricle
Interventricular foramen
2
Cerebral aqueduct
Lateral aperture
Choroid plexus
of fourth ventricle
3
Median aperture
Dura mater
Subarachnoid space
Central canal of spinal cord
(a) Midsagittal section
Blood-Brain Barrier System
1. Brain only 2% of body weight, but receives
15% of blood and 20% of O2 and glucose
2. Blood supply critical to brain
10 second interuption - lose consciousness
2 minutes – impaired neural function
4 minutes – irreversible brain damage
3. Blood also source of potentially harmful
substances
Antibodies
Macrophages
Proteins/amino acids
Fluctuating ion concentrations
Formation of Barrier
1. Perivascular feet of astrocytes
2. Extra thick, continuous basement
membrane of endothelial cells
3. Tight junctions between endothelial cells
of capillaries
a. Anything leaving blood must pass through
endothelial cells, not between them
b. Least permeable capillaries of the body
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Astrocyte
Nucleus
Perivascular feet
Erythrocyte
inside
capillary
Capillary
Continuous basement
membrane
Tight junction between
endothelial cells
Nucleus of endothelial cell
(a)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Capillary
Basement membrane
Endothelial cells
Lipid-soluble substances
freely pass through the
blood-brain barrier.
Lipid
Perivascular feet
of astrocyte
Glucose
Astrocytes selectively
allow certain substances
to cross the blood-brain barrier.
(b)
Erythrocyte
Blood-Brain Barrier
1. Selective barrier, not an absolute barrier
a. Highly permeable to glucose, water, and
some electrolytes via facilitated diffusion
through transport proteins in ependymal
cell membranes
b. Nonessential amino acids, Ca2+ and K+ are
actively pumped back into blood
c. Barrier ineffective against lipid-soluble
substances such as alcohol, nicotine,
anesthetics, O2 and CO2
2. Is obstacle to delivery of some drugs
Nasal spray – delivery up olfactory nerve
Blood-Brain Barrier
3. Trauma/inflammation can damage barrier
4. Barrier incomplete in newborns
a. Toxic substances can cause problems
not seen in adults, i.e. honey
5. Barrier missing or reduced in some areas:
a. Choroid plexus – tight junctions between
ependymal cells provide protection
b. Vomiting center of medulla – monitors
blood for poisonous substances
c. Pineal gland – must be able to secrete
hormones into blood
Blood-Brain Barrier
5. Barrier missing (continued)
d. Hypothalamus
i.
Samples chemical composition of blood to
control osmolarity, regulate body
temperature, etc.
ii. Also secretes hormones
6. Important to allow exchange between
blood and brain
a. Missing barrier provides route for HIV
The Cerebrum
1. Gyri – extensive folding increases surface area
a. More cell bodies, more processing capabilities
b. One of greatest differences between humans
and many other mammals
2. Cerebral hemispheres divided by longitudinal
fissure.
a. Difficult to assign precise function to specific
region of cerebrum due to considerable overlap
and indistinct boundaries within cortex.
b. Generally both hemispheres control opposite
side of the body.
c. Cerebral lateralization – some functional
specialization
The Cerebrum
5 lobes of cerebrum: See Table 13.3
1. Frontal – voluntary motor control, decision
making, concentration, verbal communication
2. Parietal – sensory interpretation of textures
and tastes, understanding and forming
speech
3. Occipital – principal visual center
4. Temporal – Interpretation of hearing & smell
5. Insula – not well understood, taste &memory
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
(a) Lobes of the Brain and Their
Functional Areas
Central sulcus
Frontal lobe (retracted)
Parietal lobe
Prim ary m otor cortex
(in precentral gyrus)
Prem otor cortex
Prim ary somatosensory cortex
(in postcentral gyrus)
Som atosensory association area
Frontal eye field
Motor speech area
(Broca area)
Parieto-occipital sulcus
Wernicke area
Insula
Occipital lobe
Prim ary gustatory
cortex
Prim ary visual cortex
Gnostic
area
Lateral
sulcus
Visual association area
Tem poral lobe (retracted)
Prim ary auditory cortex
Auditory association area
Prim ary olfactory cortex
Functional Areas of Cerebrum
• Higher mental functions of cerebrum are
dispersed over large areas.
• Distinct motor and sensory functions
located in specific structural areas:
1.Motor Areas
2.Sensory Areas
3.Association Areas
Motor Areas of Cerebral Cortex
1. Primary motor cortex in frontal lobes
a. Axons project contralaterally, so left primary
cortex controls right side skeletal muscle
b. Distribution mapped as motor homunculus
2. Motor Speech Area (Broca Area)
a. Usually in left frontal lobe
b. Controls muscular movements for speech and
regulates breathing patterns for speech.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Primary motor cortex
(within precentral gyrus)
Trunk
Hip
Knee
Ankle
Toes
Pharynx
Lateral
Medial
(a) Primary motor cortex
(somatic motor area)
Sensory Areas of Cerebral Cortex
1. Primary somatosensory cortex
a. Located in parietal lobes
b. Receives general somatic sensory
information
c. Mapped in sensory homunculus
Primary visual cortex – Occipital lobe
Primary auditory cortex – Temporal lobe
Primary olfactory cortex – Temporal lobe
Primary gustatory cortex - Insula
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Hip
Leg
Neck
Primary somatosensory cortex
(within postcentral gyrus)
Trunk
2.
3.
4.
5.
Foot
Toes
Genitals
Intra-abdominal
Medial
Lateral
(b) Primary somatosensory cortex
Association Areas
1. The primary motor and sensory cortical
regions are connected by association
areas.
2. Function to process and interpret
incoming sensory data or coordinate
motor response.
3. Integrate new sensory input with
memories of past experiences.
Association Areas (See pg. 501)
1. Premotor cortex - coordinates learned
skilled motor activities, like playing piano
2. Functional Brain Regions – act as multiassociation areas between lobes
a. Wernicke Area – recognizing & understanding
spoken & written communication
b. Gnostic Area – integrates all somatosensory,
visual and auditory information being
processed by association areas to provide
understanding of current activity, i.e. The Big
Picture
Central White Matter
1. Lies deep to cerebral cortex
2. Composed of myelinated axons
3. Axons grouped into bundles called
tracts. (No nerves in CNS)
Cerebral White Matter Tracts
1. Projection tracts
a. Link cerebral cortex to brain stem, cerebellum,
and spinal cord
b. Example – corticospinal tract
2. Comissural tracts
a. Cross from one cerebral hemisphere to other
b. Usually through corpus callosum
3. Association tracts
a. Connect different regions of same hemisphere
b. Long tracts (longitudinal fasciculi) connect
different lobes
c. Short tracts (arcuate fibers) connect different
gyri within same lobe
Arcuate fibers
(Short tracts)
Corpus callosum
Longitudinal
Fasciculi (Long
tracts)
Parietal lobe
Occipital lobe
Frontal lobe
Anterior commissure
Temporal lobe
(a) Sagittal view
Arcuate fibers
Longitudinal fasciculi
Commissural tracts
Projection tracts
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cerebral Lateralization
1. Petalias – Shape asymmetries of frontal
and occipital lobes
a. Right-handed people have right frontal
petalias
2. Each hemisphere tends to be specialized
for different tasks = cerebral lateralization
3. Higher order centers in each hemisphere
have different but complementary
functions
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Left eye
Right eye
Left Right
visual visual
field field
Left Right
visual visual
field field
Left hand
Right hand
Right hemisphere
(representational hemisphere)
Left hemisphere
(categorical hemisphere)
Verbal memory
Memory for shapes (limited
language comprehension)
Corpus callosum
Speech (motor
speech area)
Left hand
motor control
Right hand
motor control
Feeling shapes with
left hand
Feeling shapes
with right hand
Musical ability
Recognition of faces
and spatial relationships
Superior language and
mathematic comprehension
(Wernicke area)
Right visual field
Left visual field
Primary visual cortex
(b) Cerebral lateralization
Basal Nuclei
1. Also called Cerebral nuclei
2. Masses of gray matter buried deep within
white matter of cerebrum
3. Generally, help regulate movement and
inhibit unwanted movements
4. Each component has specific functions
5. Caudate nucleus and Lentiform nucleus
collectively referred to as Corpus
striatum
Basal Nuclei
1. Caudate nucleus – produces pattern of
movement in arms & legs associated with
walking
2. Amygdala – expression of emotion and
development of moods
3. Lentiform Nucleus
a. Putamen – subconscious control of movement
b. Globus pallidus – adjust muscle tone
4. Claustrum – subconscious visual
processing
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cortex
Corpus callosum
Lateral ventricle
Septum pellucidum
Thalamus
Internal capsule
Lateral sulcus
Insula
Third ventricle
Optic tract
Hypothalamus
Cerebral nuclei
Caudate nucleus
Putamen
Globus
pallidus
Lentiform
nucleus
Corpus
striatum
Claustrum
Amygdaloid body
Coronal section
Cerebrovascular Accidents
1. Single most common nervous system
disorder & 3rd leading cause of death in U.S.
2. Blood circulation is blocked and brain tissue
dies
3. Most common cause is blockage of cerebral
artery by blood clot
4. Other causes – compression by hemorrhage
or edema, narrowingof vessels by
atherosclerosis
Cerebrovascular Accidents
5. Typically, survivors are paralyzed on
one side of body
6. < 35% of CVA survivors are alive 3
years later
7. Not all strokes are “completed”
a. Transient ischemic attacks (TIA’s)
b. Last 5 – 50 minutes
c. Temporary paralysis, but red flags of
potential impending more serious CVA’s
Cerebrovascular Accidents
7. Initial vascular blockage or ischemia
doesn’t cause most damage
a. Damaged neurons release “buckets” of
glutamate (excitatory neurotransmitter)
b. Acts as excitotoxin – changes ion transport,
allows unregulated Ca+2 influx into neuron
c. Generates free radicals that damage or kill
thousands of surrounding healthy neurons
d. Activates microglia and triggers
inflammation which compounds damage
The Diencephalon
1. Epithalamus
a. Pineal gland – secretes melatonin
b. Habenula – relay signals from limbic system,
visceral & emotional response to odors
2. Thalamus - bulk of diencephalon
a. Two oval masses connected by interthalamic
adhesion
b. Each mass divided into multiple nuclei
c. “Gateway” to cerebrum – final relay point
for ascending sensory information, except
smell
3. Hypothalamus
The Diencephalon
Corpus callosum
Diencephalon
Septum pellucidum
Thalamus
Habenular nucleus
Pineal gland
Interthalamic adhesion
Hypothalamus
Cerebral aqueduct
Optic chiasm
Infundibulum
Cerebellum
Pituitary gland
Fourth ventricle
Midsagittal section
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Medial group
Interthalamic adhesion
Lateral group
(a ) Location of thalamus within brain
Pulvinar nucleus
Lateral geniculate
nucleus
Posterior group
Anterior group
Ventral anterior
nucleus
Ventral lateral
nucleus
Ventral posterior
nucleus
Ventral group
(b) Thalamus, superolateral view
Roles of Hypothalamus
1.
2.
3.
4.
5.
6.
7.
8.
Control of Autonomic effects – (ANS)
Center for emotional response
Hormone secretion
Body temperature regulation
Regulation of appetite
Regulation of water intake and thirst
Regulation of wake-sleep cycles
Memory
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Paraventricular nucleus
Dorsomedial nucleus
Preoptic area
Posterior nucleus
Anterior nucleus
Supraoptic nucleus
Mammillary body
Suprachiasmatic nucleus
Ventromedial nucleus
Arcuate nucleus
Optic chiasm
Infundibulum
Pituitary gland
Sagittal section of Hypothalamus
The Brainstem
1. Midbrain
2. Pons
3. Medulla oblongata
Midbrain
1. Cerebral peduncles – contain axons of
corticospinal tracts
2. Substantia nigra
a. Pigmented with melanin
b. Produce dopamine, neurotransmitter
important in movement, emotional response,
pleasure and pain
c. Degeneration of these cells involved in
Parkinson’s disease
Midbrain
3. Tegmentum
a. Integrates information from cerebrum and
cerebellum for involuntary control of posture
b. Contains red nuclei (iron pigment)
c. Reticular formation projects through tegmentum
4. Tectum
a. “Roof” over cerebral aquaduct
b. Cerebral aquaduct extends through midbrain to
reach 4th ventricle
c. Contains Corpora Quadrigemina (visual &
auditory reflex centers)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Posterior
Superior colliculus
Tectum
Cerebral aqueduct
Tegmentum
Reticular formation
Nucleus for oculomotor nerve
Red nucleus
Substantia nigra
Oculomotor nerve (CN III)
Cerebral peduncle
Anterior
Midbrain
Pons
1. “Bridge” chiefly composed of conduction
tracts (white matter)
2. Connects cerebrum to cerebellum and
medulla
3. Many diverse functions:
a. Contains autonomic centers, including
pontine respiratory center which helps
regulate diaphragm.
b. Sound localization
c. Houses nuclei of Cranial Nerves V - VII
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Pontine respiratory center
Pons
Fourth
ventricle
Superior
olivary
nucleus
Medulla
oblongata
Olive
Inferior
olivary
nucleus
Reticular
formation
(a) Longitudinal section (cut-away)
Medulla oblongata
1. Physically connects spinal cord to brain
2. All communication between brain and spinal
cord involves ascending & descending tracts
passing through medulla
3. Pyramids
a. Ridges of corticospinal tracts (pyramidal)
b. Taper at ends – “baseball bats”
c. Decussation of pyramids – axons cross
over for contralateral control
4. Sensory & motor nuclei associated with
cranial nerves IX – XII.
Medulla oblongata
5. Important autonomic centers (often called
vital centers) located in medulla:
a. Cardiac center – rate & force of heartbeat
b. Vasomotor center
i. Vasoconstriction/vasodilation
ii. Regulates blood pressure
c. Medullary respiratory centers
i. Control rate and depth
ii. Dorsal & Ventral Respiratory Groups work
with pontine respiratory center
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Medulla oblongata
Cardiac and
Vasomotor
Centers
Ventral
respiratory
group
Dorsal
respiratory
group
Respiratory
Center
Pyramid
Anterior
Posterior
Reticular formation
Cerebellum
1. Cerebellar hemispheres
a. Bilaterally symmetrical
b. Bridged by vermis
2. Folia – slender folds
3. Divided into 3 regions:
a. Thin outer cortex of gray matter
b. Arbor vitae – deep layer of white matter
c. Four deep cerebellar nuclei
4. Peduncles - three thick nerve tracts that
connect cerebellum to brainstem
Cerebellum
5. Cerebellum does not initiate skeletal muscle
movement, it coordinates and fine tunes
movement
6. Stores memories of learned movement
patterns, like playing a musical instrument
7. Receives proprioception data for body
awareness and to plan movements
The Complex Cerebellum
• Only 10% of brain mass, but more than
50% more surface area than cerebral
cortex
• Contains more than half of all brain
neurons, approx. 100 billion
Functions of Cerebellum
Much more extensive functions than
originally thought:
1. Coordination and locomotor ability
2. Timekeeping center of brain, rhythm
3. Hearing and language output
4. Planning and scheduling
Many children with ADHD have abnormally
small cerebellums
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Anterior
Cerebellar
hemisphere
Anterior
lobe
Vermis
Posterior
lobe
Primary
fissure
Folia
Posterior
(b) Cerebellum, superior view
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cerebral
aqueduct
Tectal plate
White matter
(arbor vitae)
Midbrain
Fourth ventricle
Pons
Medulla oblongata
Folia
Gray matter
(a) Midsagittal section
Motor Control
1. Intention of voluntary movement - begins in
motor association (premotor) area of frontal lobes
2. Primary motor Cortex send signals to brain stem
and spinal cord through upper motor neurons
a. Result in muscle contractions
3. Basal nuclei – feedback circuit involved in
planning and execution of movement
a. Dyskinesia – movement disorders due to
lesions in basal nuclei, Ex. Parkinson’s Ds.
4. Cerebellum – important in motor coordination
and learning motor skills
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Primary motor cortex
Voluntary movements
The primary motor cortex and the basal nuclei
in the forebrain send impulses through the
nuclei of the pons to the cerebellum.
Cerebral hemisphere
Assessment of voluntary movements
Proprioceptors in skeletal muscles and
joints report degree of movement to
the cerebellum.
Integration and analysis
The cerebellum compares the
planned movements (motor signals)
against the results of the actual
movements (sensory signals).
Corrective feedback
The cerebellum sends impulses
through the thalamus to the
primary motor cortex and to
motor nuclei in the brainstem.
Thalamus
Cerebellar cortex
Corpus callosum
Pontine nucleus
Pons
Direct (pyramidal) pathway
Sagittal section
Functional Brain Systems
1. The Limbic System
a. Process and experience emotions
b. Plays an important role in memory
2. The Reticular Formation
a. Has motor and sensory components
b. Reticular Activating System (RAS)
responsible for mental alertness
The Limbic System
1. Prominent components:
a. Cingulate gyrus
b. Hippocampus
c. Amygdala
d. Olfactory bulbs, olfactory tracts & center
2. Involves gratification and aversion centers
3. Interaction with frontal lobes gives important
connection between thoughts and emotions –
emotions can override reason, or vice versa.
The Limbic System
1. Cingulate gyrus – recieves input from other
parts of limbic system, important in expressing
emotions through gestures and resolving
conflict
2. Hippocampus – Important in long-term memory
3. Amygdala – recognizes fearful or angry facial
expressions, assesses danger, and elicits fear
response. Also stores and codes memories
based on emotional perception.
4. Olfaction – emotions & memories deeply
connected to sense of smell
The Limbic System
The Limbic System
Components of the limbic system
Cingulate gyrus
Corpus callosum
Fornix
Anterior commissure
Mammillary body
Hippocampus
Amygdaloid body
Olfactory tract
Olfactory bulb
Midsagittal section
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
The Reticular Formation
1. Gray matter that runs through brainstem and
projects to cerebrum
2. Consists of 100 small neural networks with
different functions:
a. Assists with somatic motor control
b. Assists medulla and pons with cardiovascular
and respiratory control
c. RAS - Filters out repetitive, weak & familiar
signals but passes along unusual or significant
impulses to prevent sensory overload of brain.
Do you have socks on?
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
RAS output to
cerebral cortex
Visual impulses
Reticular formation
Motor tracts
to spinal cord
Auditory
impulses
General sensory tracts
(touch, pain, temperature)
Sensory input to RAS
Motor output from RAS
RAS output to cerebrum
Consciousness
Levels of consciousness exist on continuum
1. Alert = highest level of consciousness
2. Sleep = temporary absence of consciousness
3. RAS is inhibited by sleep centers in
hypthalamus, alcohol, and some other drugs.
4. Severe injury of RAS can result in irreversible
coma
5. Pathological states of unconsciousness
include syncope, stupor, coma and persistent
vegative state.
Memory
1. Sensory memory
a. Form important associations based on sensory
input, but lasts only few seconds.
2. Short-term memory (STM)
a. Limited capacity and short duration (few hours)
3. Long-term memory (LTM)
a. Encoding - Conversion of STM to LTM utilizes
amygdala and hippocampus.
b. Can exist for limitless periods as long as
occasionally retrieve information.
Loss of Memory
1. Memory processing and storage involves many
regions of brain.
a. Type of memory loss and severity depends
upon area of brain damaged.
b. Damage to thalamus & hippocampus most
serious
2. Amnesia
a. Anterograde amnesia – unable to store new
information
b. Retrograde amnesia – unable to recall things
known previously
That’s All Folks!