Functional
Neuroanatomy
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Next week’s reading…
STRUCTURE AND FUNCTIONS OF CELLS OF THE
NERVOUS SYSTEM
*CARLSON, N. R.
XRX.57772 SCOTT
SCOTT-RESV (Available: 2HOUR)
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Overview
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A word about the funny
names, and a few definitions
Anatomy versus Function:
The Triune Brain Hypothesis
The Brainstem
The Limbic System
Cerebral Cortex
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A word about the funny names…
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Early anatomists named most brain
structures (in Latin, for the most part)
according to their similarity to commonplace
objects:
amygdala = almond,
hippocampus = sea horse,
genu = knee,
cortex = bark
pons = bridge
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A few definitions
Locations in the Brain
 Described relative to neuraxis - an
imaginary line drawn through the spinal
cord up to the front of the brain
 The front end is anterior
 The back end is posterior
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The terms rostral (toward the head) and
caudal (toward the tail) are also used when
referring to parts of the brain
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A few definitions
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Dorsal (back) refers to the top of the head
and the back
The ventral (front) surface faces the
ground.
These directions are somewhat more
complicated in humans because our
neuraxis bends, so that the top of the head
is now perpendicular to the back.
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The Neuraxis
Dorsal
Anterior
Posterior
Ventral
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The Neuraxis
Dorsal
Anterior
Ventral
Dorsal
Posterior
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A few definitions
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Lateral means to the side (away from the
neuraxis)
Medial (or mesial) means toward the
middle (towards the neuraxis)
Proximal: Areas of the brain that are near
to one another
Distal: Areas that are far from one another
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A few definitions
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Ipsilateral refers to structures on the same
side of the body
E.g. the olfactory bulbs send ipsilateral
connections to the brain - the right bulb
connects to the right hemisphere, and the
left bulb connects to the left hemisphere
Contralateral refers to structures on
opposite sides of the body
E.g. the left motor strip connects to the
right side of the body
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A few definitions
Slices of the brain
 Transversely, like a loaf of bread - also
called frontal or cross sections
 Parallel to the ground, giving us horizontal
sections
 Perpendicular to the ground and parallel to
the neuraxis - sagittal section - midsagittal
plane divides the brain in half along the
longitudinal fissure
 Because of our upright posture, cross
sections of our spinal cord are actually
parallel to the ground
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Transverse/
Cross section
Horizontal
section
Sagittal
section
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Gross Anatomy of the Brain
M ajor D iv is ion S ubdivis ion
Forebrain
M idbrain
H indbrain
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P rinc ipal S truc tures
C erebral C ortex
T elenc ephalon B as al G anglia
L imbic S ys tem
T halamus
D ienc ephalon
H ypothalamus
T ec tum
M es enc ephalon
T egmentum
C erebellum
M etenc ephalon
P ons
M yelenc ephalon M edulla O blongata
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Gross Anatomy of the Brain
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Functional divisions based on evolutionary criteria
Triune Brain Hypothesis (MacLean)
“In its evolution, the forebrain of advanced
mammals has expanded as a triune structure
that anatomically and chemically reflects
ancestral commonalities with reptiles, early
mammals, and late mammals.” (1985)
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Mammalian brain structure reflects its phylogeny
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Gross Anatomy of the Brain
The three brains…
1. Reptiles (R-complex) = Brainstem
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Basic regulatory and vegetative functions,
“instincts”
2. Early Mammals = Limbic Cortex
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Limbus = border or margin (Latin)
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Explicit memories, emotion
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Care and protection of offspring
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Establishing territory
3. Late Mammals = Neocortex
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Abstract reasoning, long-term planning and
behaviour, higher sensory functioning, etc.
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Is the Triune Brain
Hypothesis Useful?
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Intuitive, “textbook” way of dividing the
structure of the brain based on its evolutionary
usefulness and function
Most textbooks dealing with brain function use
the triune division
Accounts how the mammalian brain evolved
and became specialized, beyond basic survival
functions common to all animals
Accounts for disproportionately large
telencephalon
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Is the Triune Brain
Hypothesis Useful?
2. Emphasizes a distributed “systems” approach
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As opposed to a modular approach
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Processing of information proceeds through
increasing levels of complexity
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Multiple brain areas accomplish complex tasks
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Diversity/redundancy of systems (I.e. memory)
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Explains why partial functioning or recovery is
possible
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Is the Triune Brain
Hypothesis Useful?
3. Competition between different brain areas
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Conflict between different phylogenic areas of
the brain--situations where different functions
come into conflict. (I.e. smoking)
Antagonistic or inhibitory areas exist in the
brain.
Mental disease may reflect an imbalance: overor underactivity of a brain area
Role of drug or treatment is to restore balance
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The Brainstem
• Consists of all structures from the
thalamus to the spinal cord
• Regulatory functions: Eating, drinking,
body temperature, sleep and waking,
basic movement and learning
• Generally speaking, these structures
rule functions that are hard-wired,
automatic, and not very plastic
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The Brainstem
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The Brainstem
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Thalamus: A relay centre for sensory
information (touch, vision, hearing);
located near the middle of the cerebral
hemispheres.
• Fibres project to primary sensory areas in
neocortex
• There are separate nuclei for vision, touch,
hearing
• Not a “passive” structure because the majority
(80%) of its connections are not from sensory
neurons, but from the neocortex (including
motor areas).
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The Brainstem
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Hypothalamus: Controls all aspects of
motivated (pleasure and pain) and
regulatory behaviour
• Autonomic (vegetative) system
• Superior to the pituitary gland, reciprocal
connections with it
• “Master gland”: Closely involved in the
regulation and secretion of hormones
• 0.3% of the brain’s weight
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The Brainstem
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Reticular Formation: Constellation
of 90+ nuclei at the base of the
brainstem
• Bundles of fibres as well as projections
that pass through to the forebrain from
the spinal cord
• A host of regulatory vegetative
functions
• connections with cerebral cortex and
thalamus
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The Brainstem
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Cerebellum: conspicuous bulbous
structure protruding from the
posterior brain; “little brain”
• Distinctive narrow folds (folia), similar
to sulci in neocortex
• Involved in aspects of learning and
coordination of skilled or smooth
movement
• Posture, walking, equilibrium
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The Brainstem
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By and large, there is little that
distinguishes mammals from reptiles in
terms of brainstem structure and function
An evolutionary turning point occurred
with the specialization of limbic cortex in
mammals
Functions of brainstem aren’t replaced;
rather, they are modified or enhanced by
interacting with newer phylogenic
structures.
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The Limbic Cortex
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Three-layer cortical structure
covering the periphery of the
brainstem, on the ventral surface of
the lateral ventricles
Primarily known for its role in
emotion, (emotional) learning and
memory
Also plays a role in spatial learning
and olfaction (memories of odour)
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The Limbic Cortex
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The Limbic Cortex
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Hippocampus: Located next to the lateral
ventricle in the temporal lobe.
Along with the fornix, mammillary bodies, and
cingulate gyrus is involved in learning and
memory.
Amygdala: located anterior to the hippocampus
only part of the limbic system responsible for
emotional responses
Other areas involved with learning and memory
of emotions (recognition of emotional events)
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The Limbic Cortex
Fornix: a bundle of axons that connects
hippocampus with other regions of the
brain, including the mammillary bodies
(containing some of the hypothalamic
nuclei)
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Cerebral Cortex
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Six-layered structure
Includes most of the two symmetrical
cerebral hemispheres.
The cerebral hemispheres contain the
limbic cortex
The majority of the surface of the cerebral
hemispheres is called the neocortex
Part of the cerebral cortex is buried in the
frontal lobes (I.e. insula – taste,
sensation, and memory)
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Cerebral Cortex
 In humans the cerebral cortex is very convoluted
 About two-thirds of the brain surface is found in
the sulci and fissures
 The total surface area of the cortex is
approximately 2360cm3 , 3 mm thick
 Sulci - small grooves
 Fissures - large grooves
 Gyri - bulges between sulci or fissures
 Greatly enlarge the surface area of brain
 Provides additional neurons for higher cognitive
functions
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Cerebral Cortex
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The cortex is made up mostly of glia
(support cells), and the cell bodies,
dendrites, and interconnecting axons of
neurons.
Neuron cell bodies are grayish brown- that
is why the cortex is called gray matter
Beneath the cerebral cortex run millions of
axons ensheathed in myelin--white matter-that connects the neurons of the cerebral
cortex with those located elsewhere
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Cerebral Cortex
Significant individual differences in the sulci
and gyri. However, there are major
landmarks common to everyone:
The longitudinal fissure divides most of
the cortex into left and right sides.
The central sulcus provides an important
dividing line between the anterior and
posterior regions of the cerebral cortex
Anterior: planning and executing
movements
Posterior: sensation, perception and
learning
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Cerebral Cortex
• Although the two cerebral hemispheres
cooperate with each other, they do not
perform identical functions.
 Some functions are lateralized – located
primarily on one side of the brain
 The left hemisphere is involved in
analysis of information – extraction of
elements that make up a whole
 For instance the left hemisphere is good
at recognizing serial events.
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Cerebral Cortex
 The right hemisphere is specialized for
synthesis – putting isolated elements together
to perceive a whole.
 During normal functioning of the brain we are
not aware of lateralization
 Our perceptions and memories are unified by
the corpus callosum – a band of axons that
connects the two cerebral hemispheres
 Connects topographically – i.e. Areas of the
brain that are the same region on both sides
 The corpus callosum is the largest commissure
of the brain – cross-hemispheric connection
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Cerebral Cortex
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Basal ganglia: A collection of subcortical nuclei in the
forebrain.
Lie beneath the anterior portion of the lateral ventricles.
The major parts: caudate nucleus, putamen, and the globus
pallidus.
These structures are involved in the control of movement
(frontal lobe).
Parkinson’s disease results from degeneration of the
connections between the midbrain and the caudate nucleus
and putamen.
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Basal Ganglia
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Cerebral Cortex
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Its divided into 4 areas, or lobes, named for the
bones of the skull that cover them
 Frontal lobes - includes everything in front
of the central fissure
 Parietal lobe - is located on the side of the
cerebral hemisphere, just behind the central
sulcus and caudal to the frontal lobe
 Temporal lobe - lateral and ventral to the
frontal and parietal lobe
 Occipital lobe - back of the brain - caudal
to the parietal and temporal lobes
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Cerebral Cortex
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Three areas of the cerebral cortex receive
contralateral information from the sensory organs.
Primary visual cortex - back of the brain on the
inner surfaces of the cerebral hemispheres - upper
and lower parts of the calcarine fissure
Primary auditory cortex is located on the upper
surface of a deep fissure in the side of the brain lateral fissure
Primary somatosensory cortex - vertical strip of
cortex caudal to the central sulcus - receives
information from the body senses primarily touch,
pressure, pain
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Cerebral Cortex
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Cerebral Cortex
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Primary motor cortex - just anterior to
the central sulcus and the primary
somatosensory cortex
most directly involved in the control of
movement
neurons in different parts of the motor
cortex are connected to different muscles in
the body (homunculus)
connections to muscles are contralateral
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Cerebral Cortex
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The primary parts of the cortex take up a
small proportion of the cortex
The rest of the cortex is made up of
association areas.
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Cerebral Cortex
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Each primary sensory area of the cerebral cortex
sends information to the adjacent regions sensory association cortex
 Usually posterior
 Circuits of the neurons in these areas
analyze the information received from the
primary sensory cortex
 Perception takes place there and memories
are stored there
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Cerebral Cortex
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The regions of the sensory association cortex
located closest to the primary cortices receive
information from only one sensory system
E.g. region closest to primary visual cortex is
involved in visual perception and stores visual
memories
Regions further away from the primary cortices
integrate information multiple sensory systems involved in several kinds of perception and
memories
Combining vision and hearing to recognize a face or
to understand language
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Cerebral Cortex
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The frontal association cortex is involved in
the planning and execution of movements
 The motor association cortex is located
directly rostral to the primary motor cortex
 This region controls the primary motor
cortex - direct control over behaviour
 The rest of the frontal lobe, rostral to the
motor association cortex is known as the
prefrontal cortex - formulation of plans and
strategies
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Summary
1. Divisions of the brain based on structure
and function may be different.
2. Normal brain functioning requires the
interaction of many (inhibitory) systems.
3. Normal brain functioning requires a
balance between all “three” brains.
4. If not, there is disease and dysfunction.
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fornix
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Basal ganglia
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The Limbic Cortex
Hippocampus
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