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CONTENTS
7
THE VISUAL SYSTEM 135
Introduction 136
Structure of the eye 136
Visual pathways 139
Visual field defects 141
Pupillary light reflexes 141
Focusing of light on the retina 142
Control of eye movements 144
Structure and function of the retina 146
Processing of visual information 151
Summary 155
Self- assessment case study 155
8
HEARING AND BALANCE: THE AUDITORY AND
VESTIBULAR SYSTEMS 157
Introduction 158
Auditory system 158
Vestibular system 169
Comments on the case history 175
Self-assessment case study 176
11
STROKE AND HEAD INJURY 223
Introduction 224
Physiological control of cerebral blood flow 225
Blood supply to the brain 226
Stroke 229
Head injury 243
Focal pathology in relation to vascular injury 245
Treatment of head injury 251
Comments on the case history 253
Self- assessment case study 254
12
INFECTION IN THE CENTRAL NERVOUS SYSTEM 255
Introduction 256
Types of infection of the central nervous system 256
The meninges 257
Cerebrospinal fluid production and circulation 259
Meningitis 263
Encephalitis 268
Cerebral abscesses 269
Brain infections in the immunocompromised
patient 270
Self- assessment case study 271
9
MOTOR SYSTEMS I: DESCENDING PATHWAYS AND
CEREBELLUM 177
Introduction 178
Skeletal muscle contraction 179
Reflexes 182
Descending pathways 186
Clinical importance of reflexes 191
The cerebellum 194
Self- assessment case study 200
10
MOTOR SYSTEMS II: THE BASAL GANGLIA 201
Introduction 202
Basal ganglia: structure and organization 202
Parkinson’s disease 204
Huntington’s disease 218
Self- assessment case study 221
13
EPILEPSY 273
Introduction 274
General description of epilepsy 274
Epidemiology and causes of epilepsy 275
Diagnostic investigations of epilepsy 276
Examples of types of seizure 282
Pharmacological treatment of epilepsy 287
Other treatments for epilepsy 291
Treatment of status epilepticus 292
Social consequences of epilepsy 292
Self- assessment case study 293
14
DEMENTIA 295
Introduction 296
Causes and diagnosis of dementia 296
Neurobiology of learning and memory 299
Alzheimer’s disease 302
Treatment of Alzheimer’s disease 308
Other types of dementia 312
General considerations in the management of
Alzheimer’s disease and other types of dementia 314
Self- assessment case study 315
CONTENTS
15
SCHIZOPHRENIA AND NEURODEVELOPMENTAL
DISORDERS 317
Introduction 318
Schizophrenia: the clinical diagnosis 318
Aetiology of schizophrenia 321
Neurobiology of schizophrenia 322
Treatment of schizophrenia 327
Comments on the management of schizophrenia and
the long- term prognosis 330
Other psychoses and neurodevelopmental
disorders 331
Self- assessment case study 332
16
DEPRESSION AND ANXIETY 333
Introduction 334
Classification of mood disorders 334
Clinical features of mood disorders 334
Epidemiology of depressive and bipolar disorders and
their natural evolution 335
Genetics of mood disorders 339
Neurobiology of depression 339
Treatment of depression 341
Bipolar disorder and its treatment 345
General comments on mood disorders 346
Need for new therapeutic targets 347
Comments on case history 348
Anxiety disorders 348
Treatment of anxiety disorders 349
Insomnia 351
Self- assessment case study 354
17
ADDICTION 355
Introduction 356
Addiction and drug misuse: general comments 356
Neurobiology of addiction 357
Addiction and rehabilitation: general comments 371
Self-assessment case study 372
Index 373
ORGANIZATION OF
THE NERVOUS SYSTEM
Chapter summary
1. The nervous system comprises two parts: the central nervous system
(CNS), consisting of the brain and spinal cord, and the peripheral
nervous system (PNS), which is divided into somatic, autonomic and
enteric divisions.
2. The brain consists of three structural parts: two cerebral hemispheres
and the cerebellum. They are composed of a thin external layer
of cortex, consisting of grey matter densely packed with neurons.
Below this is white matter, consisting of pathways that connect the
different grey matter areas. The white matter aspect is conferred by
the presence of myelinated fibres. Embedded in the white matter
are nuclei, which are grey matter clusters of neurons that perform a
similar function.
3. The brain has three main divisions: (1) the forebrain, comprising the
cerebral cortex, which performs cognitive, perceptual and motor
functions, and the diencephalon that controls information flow
to the cortex (through the thalamus) and regulates homeostasis
(through the hypothalamus); (2) the midbrain, which is important in
consciousness and sleep functions and (3) the hindbrain, comprising
the cerebellum, pons and medulla, which is concerned with motor
coordination (cerebellum), cranial nerve functions and maintenance
of life support systems.
1
4. The spinal cord has a central grey matter core divided into a dorsal
sensory half and a ventral motor half. Surrounding the grey matter is
white matter, which comprises axons travelling to or from the brain
to convey sensory information or motor commands to neurons in the
grey matter.
1
5. The somatic nervous system consists of 31 pairs of spinal nerves
and 12 pairs of cranial nerves that give rise to specific peripheral
innervation of the skin and skeletal muscles. The vast majority of
nerves are mixed, in that they contain both sensory and motor axons,
while a few are purely sensory or motor.
6. The autonomic nervous system (ANS) is distinguished from the
somatic system by its disynaptic motor output, which consists of
preganglionic and postganglionic motoneurons. The ANS has a major
role in the control of visceral organs. It comprises three subdivisions:
the sympathetic nervous system, which is an alarm system, and the
parasympathetic nervous system, which is a rest and recuperation
system. Their primary function is the maintenance of homeostasis. The
third subdivision is the enteric system, which regulates gut function
and operates semiindependently of the other divisions.
ORGANIZATION OF THE NERVOUS SYSTEM
Introduction
The nervous system consists of the brain, spinal cord
and peripheral nerves and is a highly specialized and
complex structure. It is an information- processing
system that regulates all the physiological functions
of the organism. In addition, the nervous system performs unique functions that operate independently of
other systems in the body. These underlie consciousness, memory, rationality, language and the ability to
project our mental images forwards or backwards in
time. Representations of the external world are transmitted, transformed and manipulated by the nervous system to affect behaviour. It has four important
functions:
1. sensory function (gathering of information from the
external environment)
2. integration (integration of information from all
sources for assessment)
3. effector function (production of a motor response)
4. internal regulation (homeostasis for optimum
performance).
The net result is the creation of a sensory percept of
the external world, a behavioural response and, importantly, the creation of knowledge that is used to guide
future behaviour in response to changes in the surrounding environment and experience.
In order to appreciate how the nervous system produces behaviour, it is necessary to understand how it
is organized functionally and anatomically. The experience of examining a brain is very similar to the experience of buying a car. Before buying a car, you inspect
it, and then take it for a test drive to make sure that it
operates normally and runs smoothly without faults.
Then you open up the bonnet to look at the engine.
Unless you happen to be a trained mechanic or have
an interest in car engines, you might be able to name a
few parts, for example, the radiator, the battery and
the fan belt, but not the rest of the mass of wires, spark
plugs and assorted boxes. Moreover, the name does not
always indicate what the function is or how all the different parts combine to burn petrol to make the car run.
It is the same with the nervous system; you may be
able to name some of the parts, such as the cortex, cerebellum and brainstem, and have some idea of what a
few of the different parts do but have little idea of how
they accomplish a task, such as reading this sentence.
Moreover, when the car breaks down, we call the automobile rescue services. When the nervous system breaks
down or misfires, we call neurologists, neurosurgeons or
psychiatrists.
Although the anatomy of the nervous system appears
complex and daunting, its organization is governed by
a set of relatively simple developmental, organizational
and functional rules that bring order to it, as summarized in Table 1.1.
The aim of this chapter is to provide a functional overview of the neuroanatomy of the brain, spinal cord and
nerves. To do this, it is necessary to consider the basic
parts of the nervous system to identify what they do and
how they are related. Finally, we can see how the different parts interact, using the principles outlined in Table
1.1, to produce behaviour.
The nervous system comprises two parts: the peripheral nervous system (PNS) and the central nervous system (CNS). These two systems are anatomically separate
but functionally interconnected and integrated (Fig. 1.1).
SYSTEMS OF THE BODY
2
1
The PNS consists of nerve fibres that transmit specific
sensory and motor information to the CNS, which comprises the spinal cord, brainstem and brain. The CNS is
housed within the bony structures of the vertebral canal
and skull for protection. Additional mechanical buffering protection of the CNS is afforded by the surrounding
meninges and the fluid in the ventricular system.
Overview of brain anatomy
Based on neural development, the nervous system is
initially comprised of three anatomical regions: the
forebrain, midbrain and hindbrain. As the brain further
develops, the CNS becomes six anatomically distinct
regions: the cerebral cortex and diencephalon (thalamus
Table 1.1 Principles underlying the functioning of the nervous
system
Behaviour is produced by processing information in a sequence of
‘in → integrate → out’
Separate sensory and motor divisions exist throughout the nervous
system
The nervous system has multiple levels of function
The nervous system is organized both in parallel and in series
Most neural pathways relaying information decussate from one side
of the central nervous system to the other
The nervous system regulates activity through excitation and
inhibition
There is both symmetry and asymmetry in brain anatomy and
function
Some of the functions of the brain are located in specific regions of
the brain, while others are distributed
and hypothalamus), which together form the forebrain;
the midbrain, pons, medulla and cerebellum, which
together comprise the hindbrain; and the spinal cord
(Fig. 1.2). The best way to understand the anatomy is to
look at the external and internal topography to identify
anatomical structures and their relationships, and then to
define the functions of the identified structures.
Meninges
If the skull cap is removed, the first thing seen is the
membranes that cover the brain, called meninges. These
membranes surround and protect the CNS. There are
three layers: the dura mater, arachnoid and pia mater.
The dura mater forms folds that separate different
brain regions from each other and demarcate anatomical boundaries within the skull cavity. These layers are
described in more detail in Chapter 12.
Cortical lobes
When the meninges are removed, one can observe the
gross anatomy of the CNS. Anatomically, the cortex is
described according to lobes that are named in relation
to skull bones. Four lobes are visible on its lateral surface: the occipital, temporal, parietal and frontal lobes.
However, there is one lobe that is not visible: the limbic lobe. It comprises the medial portions of the frontal,
parietal and temporal lobes, forming a rim around the
corpus callosum (a fibre tract that connects the two cortical hemispheres). Another cortical area, the insula, lies
buried in the medial wall of the lateral fissure, overlain
by parts of the frontal, parietal and temporal lobes; it is
functionally associated with the limbic lobe. The lobes
are divided into regions that are associated with specific
functions (see Table 1.2).
ORGANIZATION OF THE NERVOUS SYSTEM
Nervous system
Central
nervous system
Brain Brainstem Spinal cord
Fig. 1.1 Overview of the anatomical organization of the nervous system.
nervous system
Parasympathetic
nervous system
Somatic
Peripheral
nervous system
Autonomic
nervous system
Sympathetic
nervous system
Enteric
nervous system
THE NERVOUS SYSTEM
3
1
Peripheral ending
(muscle)
Cerebellum
Table 1.2 Functions of brain lobes
Cortex
Basal ganglia
Thalamus
Midbrain
Pons
Autonomic nervous
system ganglia
ORGANIZATION OF THE NERVOUS SYSTEM
Spinal ganglia
Peripheral nerve
Medulla
Spinal cord
Important functional
Lobe
Frontal Primary motor cortex Control of movement
Parietal Primary somatosensory
Temporal Primary auditory cortex Hearing
Occipital Primary visual cortex Vision
Limbic Medial temporal lobe
areas Function
Broca’s area Expressive speech
Motor association cortex Intelligence, movement
planning, intuition,
rationalisation, object
tracking
Sensation
cortex
Association cortex Spatial awareness
Taste cortex Taste sensation
Wernicke’s area Language comprehension
Visual association cortex Visual spatial awareness,
colour processing
Emotions, memory
(uncus)
Medial prefrontal cortex Motivation, personality,
emotional behaviour,
risk- reward, working
memory
Cingulate cortex Cognition, emotional affect
Orbitofrontal Olfaction, emotional
behaviour
Fig. 1.2 Schematic representation of the major parts of the nervous
system. Light shading: structures of the supratentorial level. Dark
shading: structures of the posterior fossa level. No shading: structures
of the spinal level.
Surface features: sulci and gyri
The cortical surface is highly convoluted and is subdivided into fissures (deep grooves), gyri (elevated
folds; singular = gyrus) and sulci (shallow grooves
between folds; singular = sulcus). Gyri massively
increase the surface area of the cortex. The longitudinal fissure separates the two cortical hemispheres, the
lateral fissure (of Sylvius) separates the temporal lobe
from the parietal and frontal lobes and the transverse
fissure separates the forebrain from the hindbrain. The
central sulcus and the parieto- occipital sulcus define
the boundaries of the frontal and parietal, and parietal
and occipital lobes, respectively. On the lateral surface of the hemispheres, the boundaries between the
parietal, occipital and temporal lobes are established
by continuing the line of the parieto- occipital sulcus
downwards, to the inferior surface of the hemisphere,
and the line of the lateral fissure backwards to meet
this line (Fig. 1.3B).
The pattern of sulci and gyri is extremely variable,
and defining even the major sulci and gyri is not always
easy. In general, the surface of each lobe can be divided
into three gyri by two sulci; this is easily seen in the
frontal and temporal lobes, where the gyri are called
superior, middle and inferior gyri. The sulci provide
landmarks for identifying lobes and functional areas
of the brain. The main lobes, gyri and sulci, are shown
in Fig. 1.3. The central sulcus marks the position of two
important functional areas: the primary somatosensory
cortex and primary motor cortex. The latter lies anterior
to this sulcus, in the precentral gyrus; the former lies posterior to the sulcus, in the postcentral gyrus.
On the medial surface (see Figs 1.3C and 1.5), the
cingulate sulcus follows approximately the curvature
of the corpus callosum, extending through both the
frontal and parietal lobes. Below this sulcus is the cingulate gyrus (functionally associated with the limbic
lobe). This sulcus terminates by passing upwards to
form a sulcus that continues onto the lateral surface of
the hemisphere as the postcentral sulcus (Fig. 1.3B). The
central sulcus is usually the sulcus immediately anterior to this sulcus (on the lateral surface). The gyrus in
between these two sulci is the postcentral gyrus, which
4 SYSTEMS OF THE BODY
Longitudinal
sulcus
Postcentral sulcus
Inferior view
Lateral view
A B
fissure
Olfactory
sulcus
Olfactory
gyrus
Postcentral gyrus
Precentral
gyrus
1
ORGANIZATION OF THE NERVOUS SYSTEM
Precentral sulcus
Parieto-occipital
sulcus
Angular gyrus
Parahippocampal
gyrus
contains the primary somatosensory cortex. Anterior
to the point where the cingulate sulcus crosses (to the
lateral surface of the brain) is the paracentral lobule,
which contains the lower limb primary motor and
somatosensory cortical function regions. The parietooccipital and calcarine sulci are very prominent on the
posteromedial part of the brain, to the extent that some
consider them fissures rather than sulci. The lingual
gyrus and cuneus region are located either side of the
calcarine sulcus in the posterior part of the brain, and
are associated with vision.
On the inferior surface (Fig. 1.3A) of the temporal
lobe, the three gyri separated by two sulci are also obvious. The most medial gyrus is the parahippocampal
gyrus, which expands at its anterior end to form the bulbous, hook- like uncus. These are evolutionarily old parts
of the cerebral cortex and are concerned, in part, with
the olfactory (smell) system and memory. It is separated
from the middle gyrus, called the occipitotemporal (fusiform) gyrus, by the collateral sulcus, which becomes the
rhinal sulcus at its anterior end, to separate it from the
uncus. The most lateral sulcus is the inferior temporal
gyrus (which is visible from the lateral and inferior surfaces). It is separated from the occipitotemporal gyrus by
the occipitotemporal sulcus.
The orbitofrontal cortex (the part that sits above the
orbit in the skull) is part of the inferior surface of the
frontal lobe. Three gyri are also visible here: the gyrus
rectus is the most medial and is the inferior continuation
of the superior frontal gyrus. Adjacent to it are located
two olfactory gyri, which are the inferior continuations
of the middle and inferior frontal gyri from the lateral
surface of the frontal lobe. The olfactory tract and bulb
run over the surface of the olfactory sulcus between the
Uncus
Medial view
C
Cingulate sulcus
Key to lobes
Frontal
Temporal
Occipital
Limbic
Parietal
Fig. 1.3 Main gyri, sulci, fissures and lobes of the brain.
Parieto-occipital
sulcus
Calcarine
sulcus
Collateral
gyrus rectus and olfactory sulcus. These cortical areas
form part of the limbic system, which is involved in emotional processing and perception.
Cerebellum
Also visible on the inferior surface of the brain is the
cerebellum. The cerebellum is the broccoli- like structure separated from the overlying occipital cortex by the
transverse fissure. The function of the cerebellum is coordination of movements, including muscle tone, movement range, smoothness and equilibrium, as detailed in
Chapter 9.
The cerebellum consists of a deeply convoluted cortex composed of numerous small gyri called folia and
a core of white matter, within which are embedded the
deep nuclei of the cerebellum (Fig. 1.4). The cerebellum
has three lobes, the anterior, posterior and flocculonodular lobes (Fig. 1.4A, B), which are further subdivided into
lobules. In the horizontal plane, there are three regions:
the midline vermis separates the two lateral hemispheres.
In the sagittal plane, the cerebellum forms the roof of the
fourth ventricle (Fig. 1.4C), and it can be subdivided into
three functional areas, the vestibulocerebellum, spinocerebellum and cerebrocerebellum (Fig. 1.4D), based on the
source of afferent input. Each subdivision is associated
with a pair of deep cerebellar nuclei. Input and output to
the cerebellum are via three pairs of peduncles: the inferior, middle and superior cerebellar peduncles that attach
to the different regions of the brainstem. The inferior cerebellar peduncle arises from the medulla and provides
the predominant input to the anterior lobe from different
body regions. The middle cerebellar peduncle is the largest and projects to the posterior lobe from the pontine
Lateral fissure
Cingulate gyrus
Corpus callosum
Basal ganglia
Thalamus
5THE NERVOUS SYSTEM
1
Paramedian
A
Posterior lobe
Vestibulocerebellum
Interposed nuclei
ORGANIZATION OF THE NERVOUS SYSTEM
Anterior
lobe
Posterior
lobe
B
Nodulus
C
Midbrain
Pons
Fourth ventricle
Inferior olivary
nucleus
Medulla
D
Fastigial nucleus
Globose
Emboliform
Cerebrocerebellum
Spinocerebellum
Fig. 1.4 Anatomy of the cerebellum: (A) superior view, (B) inferior
view, (C) sagittal view and (D) horizontal view. (D) Shows the
functional subdivisions and their associated deep cerebellar nuclei.
Vermis
zone
Primary
fissure
Tonsil
Flocculonodular
lobe
Folium
Anterior lobe
Cerebellar
cortex
Tonsil
Dentate nucleus
Cerebellar
cortex
White
matter
Flocculus
Nodule
nuclei of the pons, carrying information from the motor
cortex commissural fibres from one side of the cerebellum
to the other. The superior cerebellar peduncle connects the
posterior lobe to the midbrain and is predominantly an
output pathway from the deep cerebellar nuclei, in particular, the dentate nucleus.
Also present on the inferior surface are the cerebellar
tonsils, which lie lateral to the vermis of the cerebellum
(Fig. 1.4B). They are easily identifiable, as their sulci are
oriented at right angles to the general direction of the
other cerebellar sulci. They are anatomically important
because they may herniate through the foramen magnum (in severe cases of raised intracranial pressure, see
Chapter 11), resulting in compression on the respiratory
centres of the medulla and possible death due to respiratory depression.
Brainstem
The brainstem is located within the posterior fossa of
the skull and consists of three parts: the midbrain, pons
and medulla. These relay information to and from the
periphery to higher centres such as the cortex and cerebellum. The brainstem also receives direct input from
the cranial nerves. The functions of these nerves and
the internal anatomy of the brainstem are described in
Chapter 6.
Medulla
On the ventral surface of the medulla are the pyramids
(see Fig. 6.1) that contain descending motor fibres from
the cerebral cortex that form the corticospinal (or pyramidal) tract (CST) of the spinal cord. The pyramidal
decussation is where most of the CST fibres cross to the
other side to become the lateral CST. The decussation
marks the location of the spinomedullary junction, which
is where the spinal cord ends and the brainstem begins.
Lateral to the rostral part of the pyramids are two oval
swellings that identify the inferior olivary nuclei (ION),
which are functionally associated with the cerebellum.
They provide a surface landmark for the emergence
of cranial nerves IX–XII; nerve XII emerges between
the ION and the pyramids (at the preolivary sulcus),
whereas nerves IX–XI emerge laterally to the ION (from
the postolivary sulcus).
On the dorsal surface of the brainstem, the medulla consists of two parts, the open and closed medulla, due to the
emergence of the central canal from the spinal cord opening into the fourth ventricle. The point at which this occurs
is called the obex. The closed part of the medulla shows a
pair of gracile and cuneate tubercles that mark the positions of the gracile and cuneate nuclei (see Fig. 6.1), which
transmit sensory information to higher brain centres.
Pons
The ventral pons has a transversely ridged appearance,
with a shallow groove running along the midline, called
the basilar sulcus, which contains the basilar artery. The
ridged appearance is due to fibres entering the cerebellum from the nerve cells in the pons, which, in turn, are
the recipients of a major input from the cerebral cortex
(see Fig. 6.1). The trigeminal nerve is the only nerve to
emerge from this ridged region, while cranial nerves VII
and VIII exit at the cerebellopontomedullary angle. The
position of cranial nerves VI–VIII identifies the pontomedullary junction on the ventral surface.
6 SYSTEMS OF THE BODY
1
The pons is sharply demarcated both rostrally and
caudally from the other parts of the brainstem. The open
medulla and pons together form the floor of the fourth
ventricle, which is diamond- shaped. The closure of the
rostral part of the fourth ventricle to form the cerebral
aqueduct and the cerebral peduncles demarcates the
transition from the pons to the midbrain.
Midbrain
The midbrain (see Fig. 6.1) is short, and very little of it can
be seen in the undissected brain. Ventrally, the cerebral
peduncles are located lateral to two small, circumscribed
mounds, which are the mammillary bodies (part of the
hypothalamus). The peduncles are large bundles of fibres
descending from the motor cortex to the brainstem and
spinal cord and mainly comprise the pyramidal and corticopontine fibre systems. The dorsal surface of the midbrain is called the tectum and has two paired swellings,
the inferior and superior colliculi, which are involved in
auditory and visual reflexes. These are buried beneath the
overlying cerebral hemispheres. Two cranial nerves exit
the midbrain, cranial nerve III at the midbrain–pons junction and cranial nerve IV on the dorsal surface.
Spinal cord
The spinal cord connects the brain to the PNS. It is the
part of the CNS located outside the skull, below the foramen magnum but within the vertebral column. The spinal level of the nervous system extends from the skull
to the sacrum. The spinal cord receives input from the
periphery, relays it to the brain and sends response signals back to the periphery. The spinal cord is not segmented; rather, the distribution of the peripheral nerve
spinal roots gives it a functional segregation. The details
of spinal cord function are described in Chapter 4. The
spinal cord consists of grey matter and white matter,
like the brain (except that in the spinal cord, the white
matter is on the outside). The grey matter contains cells
and is surrounded by white matter that mainly contains
bundles of axons ascending and descending in the spinal
cord.
Box
Brain topography
1.1
Anatomical descriptions of images and tissue sections are
based on four anatomical planes: sagittal, horizontal, transverse and median (Fig. 1.6). The horizontal (axial) plane is a
plane across the brain that would be horizontal if the patient
were standing up. The median plane is one that slices the
brain vertically along the midline into two symmetrical halves;
sagittal sections are vertical planes through the brain parallel
to the median plane. The coronal (frontal) plane is one slicing
the brain vertically across (e.g. from ear to ear).
In addition, structures towards the front of the brain are
termed anterior (or rostral), and those towards the back are
posterior (or caudal). Those towards the top of the brain are
termed superior, and those towards the bottom are termed
inferior. Structures located laterally are further away from the
midline, and those located medially are nearer the midline.
during rapid head movements and to provide buoyancy
to CNS structures, so that they are, in effect, weightless.
The ventricular system consists of two lateral ventricles, and the midline third and fourth ventricles, connected by the cerebral aqueduct (Fig. 1.5). The lateral
ventricles are the largest cavities and are located deep
within the brain. They are symmetrical structures. Each
communicates with the third ventricle through the interventricular foramen (of Monro), and the latter is connected to the fourth ventricle via the cerebral aqueduct.
CSF drains from the fourth ventricle through a median
and two lateral apertures in its floor (giving it a diamondshaped appearance) into the subarachnoid space. These
apertures are the only means by which the CSF can enter
the subarachnoid space. The cerebellum forms the roof of
the fourth ventricle, called the superior medullary velum.
All the ventricles contain variable amounts of choroid
plexus, which is the main source for the production of
CSF (see Chapter 12). If the flow of CSF becomes blocked
(especially in the cerebral aqueduct), there is a rise in
intracranial pressure. If this happens in infants, they may
develop hydrocephalus and severe brain damage.
Sagittal sections
ORGANIZATION OF THE NERVOUS SYSTEM
Internal anatomy of the brain
The easiest way to see the various anatomical structures
deep inside the brain is to cut it open. However, what is
seen depends on the plane of section; the same structures
look different in different planes (see Box 1.1). Many of
these structures form the walls of the ventricular system.
Ventricular system
The ventricles are irregularly shaped cavities within the
brain that contain cerebrospinal fluid (CSF). The main
functions of the CSF are to provide buffering support
If the brain is sectioned at the midline, cutting along the
longitudinal fissure, the cerebrum is divided into its two
hemispheres, as shown in Fig. 1.7. In this plane, below
the corpus callosum are the deep (diencephalic) structures of the brain: the thalamus, the hypothalamus and
the ventricular system. Moving laterally in this plane,
adjacent sections also reveal the appearance of the basal
ganglia nuclei that are located on top of the thalamus
and form part of the lateral walls of the ventricular
system. The basal ganglia are better viewed in frontal and horizontal sections (see Figs 1.8 and 1.11).
As shown in the upper part of Fig. 1.7, a thin membranous sheet—the septum pellucidum (which is torn in
7THE NERVOUS SYSTEM
1
CD
Superior
1
AB
1
3
Fig. 1.5 Anatomy of the ventricular system
from the (A) superior and (B) posterolateral
aspects. 1, lateral ventricle; 2, posterior horn;
3, inferior horn; 4, interventricular foramen (of
Monro); 5, third ventricle; 6, cerebral aqueduct;
7, fourth ventricle; 8, lateral aperture (of
Luschka) and 9, median aperture (of Magendie).
ORGANIZATION OF THE NERVOUS SYSTEM
Anterior Posterior
1
5
6
7
8
9
A
4
3
8
4
5
6
8
3
2
7
9
2
Inferior
Fig. 1.6 Anatomical planes of sections. Shading: black, ventricles; grey, grey matter; yellow, white matter.
Axial plane (C–D) Sagittal planeCoronal plane (A–B)
this specimen)—obscures them. Most of these structures are
visible in the MRI image shown in the lower part of Fig. 1.7.
Coronal sections
Frontal (coronal) sections are the easiest to visualize
because their orientation is such that viewing them is just
like looking at another person face- on. When sectioning
B
from front to back (Figs 1.8–1.11), the very first section in
a coronal series would consist of just the tips of the frontal lobes, which are located right behind the forehead.
The section shown in Fig. 1.8 is a little further caudal and
is the first to show the internal structures. In these sections, the white matter (axons) appears white and the
grey matter (cell bodies) appears grey. The first thing
to notice is the corpus callosum. This major pathway
8 SYSTEMS OF THE BODY