Brain Injury Lawyers: Neuroanatomy
Neuroanatomy is an almost impossible topic to discuss in its entirety.
To serve the topic justice, it would take volumes of writings. Moreover,
once the volumes were written, they would virtually be out of date given
our ever expanding knowledge of the topic matter. Given this, only a basic,
cursory attempt is herein made to cover this bewildering subject.
The philosophers of Hippocrates’ era long wrote in acknowledgment
that the organ that is our brain is the source of who we are. Our pleasure,
communication, sarcasm, grief, hurt, and pain all emanate from our brain.
It is our source of meta cognition, a recognizing of who we are as human
beings. Through the brain we are able to taste, sense, smell, hear and think.
Arguably, the human brain is the most complex structure in the universe.
So complex is it, that there are probably more things about it of which
we are unaware, than those about which we know with certainty.
The relationship between the brain and behavior is an even more difficult
topic to grasp. We understand enough to know that the reason for a given
event is not limited to activity within a particular cortical region.
Although we can speak generally about certain areas of the brain having
control over certain functions, to paint in such terms is to paint with
an extremely broad brush. Any given behavior is the product of a myriad
of complex neurophysiological and biomechanical interactions involving
the whole brain. Yet an injury focal to one area of the brain can completely
disrupt one type of activity, even though different areas of the brain
demonstratively control the particular activity in question.
In order to fully understand neuroanatomy, and
traumatic brain injury, we must first examine the skull, or casing holding the brain. As we know,
the skull is a closed bony container encasing the brain. When we refer
to the skull as “closed”, we do so with the understanding
that as newly born, our skulls are not “closed”. The fontanel
refers to the two soft spots on a baby’s skull at birth. Fontanelles
enable the soft bony plates of the skull to flex during birth in order
the head passes through the birth canal. Fontanelles are usually completely
hardened by a child’s second birthday, and will eventually form
the sutures of the neuro cranium.
Once the fontanelles harden, the skull protects the brain from the general
traumas of routine life. A common mistaken conception, however, is that
the inside of the skull is smooth. Far from it, the inside of the skull
is comprised of numerous bony protuberances. These sharp-edged ridges
are located in close proximity to nerve tissue and blood vessels, especially
near the frontal lobes. When the brain collides with these protuberances
during trauma, a primary brain injury can easily occur.
Secondary damage to the brain can thereafter occur due to the progress
of physiological processes of a destructive nature. Intracranial pressure,
brain swelling/edema, hypoxia/ischemia, fever and infection are all secondary
complications that may be set in process at the time of the primary injury
leading to secondary damage of the brain.
The brain, often mistakenly referred to as having the texture of Jell-O,
weighs approximately 3 pounds. In fact, the strata of the brain are of
different density levels. Due to the difference in density, and the fact
that specialized nerve cells called neurons transect different layers
of the brain, when trauma occurs, diffuse axonal injury may occur. A neuron
consists of the cell body and extending “transmittal pathway”
called axons and dendrites. When the axons and dendrites transect multiple
layers of the brain, and where the layers of the brain are of different
density, and the brain is subjected to a sudden acceleration/deceleration
movement, a shearing of the axons and dendrites occurs when the layers
of the brain move at different speeds. This process is referred to as
“diffuse axonal injury”, or DAI. Angular acceleration, or
rotational forces are generally thought to be much more influential in
Other types of events likewise cause traumatic brain injury. For example,
penetrating head injuries occur when an object literally penetrates the
skull into the brain itself. This can occur as a result of the head and
skull coming into contact with an object, or where an object comes into
contact with the head and skull. Penetrating head injuries are associated
with a high rate of epilepsy. Anoxic brain injury results from a deprivation
of oxygen to the brain. Medical negligence is likewise a cause of brain
injury – from the failure to diagnose or treat stroke to the failure
to properly deliver a child. Sadly, brain injury can and does result from
a wide array of events.
Approximately 80% of the brain is comprised in three general areas-the
cerebral cortex (cerebrum), the cerebellum, and lastly the brain stem.
In evolutionary terms, the oldest part of the brain consists of the brain
stem. The brain stem is the stock of the brain. The brain stem is made
up of the mid-brain, the medulla, and the pons. The brainstem performs
vital functions, basic in nature, allowing breathing, circulation, movement
and other basic function. It is responsible for respiratory centers controlling
breathing and arousal. Where a lesion occurs on the brainstem, death often
results. Since the brainstem interacts between the brain above it and
the spinal cord below it, catastrophic injury to the brainstem can result
in “locked-in” syndrome, wherein an individual is completely
alert, but without the ability to move.
The cerebellum (which in Latin stands for “little brain”),
is a region of the brain that plays an important role in the integration
of sensory perception and motor output. The cerebellum is located in the
inferior posterior portion of the head (the hindbrain), directly dorsal
to the pons, and inferior to the occipital lobe. The cerebellum contains
nearly 50% of all neurons in the brain, but only takes up 10% of the total
brain volume. The cerebellum is divided into two large hemispheres, much
like the cerebrum, and contains 10 smaller lobules. Based on evolutionary
age, the cerebellum can be divided into three parts:
Vestibulocerebellum – regulates balance and eye movements. It receives the vestibular
input from both the semicircular canals and from the vestibular nuclei,
and sends fibers back to the medial and lateral vestibular nuclei. It
also receives visual input. Lesions of this area cause disturbance of
balance and gate.
Spinocerebellum – regulates body and limb movements. It receives input from the
dorsal columns of the spinal canal the trigeminal nerve, as well as from
visual and auditory systems. It sends fibers to deep cerebellar nuclei
which in turn project to both the cerebral cortex and the brainstem, thus
providing modulation of the sending motor systems.
Cerebrocerebellum – is involved in planning movement and evaluating sensory information
for action. It receives input exclusively from the cerebral cortex via
the pontine nuclei, and sends fibers mainly to the ventral lateral thalamus.
It is involved in planning movement that is about to occur and has purely
cognitive functions as well.
CEREBRAL CORTEX (CEREBRUM):
The largest part of the brain is the cerebral cortex (cerebrum). It is
divided into two hemispheres connected at the midline by a bridge known
as the corpus callosum and other nerve fibers.
The cerebral cortex comprises what most people think of as the “brain”.
It lies on top of the brainstem and is the largest and most well-developed
of the five major divisions of the brain. It is the newest structure in
an evolutionary sense, with mammals having the largest and most well-developed
among all species.
The cerebrum surrounds the older parts of the brain. Cognitive and volitive
systems project fibers from cortical areas of the cerebrum to the thalamus
and two other regions of the brainstem. The neural networks of the cerebrum
facilitate complex learned behaviors, such as language, and contain white
matter and gray matter.
Among other things, the two hemispheres of the cerebrum control such functions
as memory, intelligence, olfaction, movement, and language and communication.
“Cerebral lateralization”, refers to the fact that the right
hemisphere of the brain controls movement and receives nerve data from
the left side of the body, while the left hemisphere of the brain controls
movement and receives nerve data from the right side of the body.
The two cerebral hemispheres are further subdivided into four separate
sections called lobes. These include the frontal lobes, the parietal lobes,
the temporal lobes, and the occipital lobes.
SCEREBRAL CORTEX: LOBES:
Frontal lobes – the frontal lobes are located at the front of each cerebral hemisphere,
in front of (anterior to) the parietal lobes. The frontal lobes are the
largest portion of the brain. The frontal lobes play a part in impulse
control, language production, memory, judgment, motor function, spontaneity,
socialization, and sexual behavior. The frontal lobes assist in planning,
coordinating, controlling, and executing behavior. The so-called executive
functions of the frontal lobes involve the ability to recognize future
consequences resulting from current actions, to choose between good and
bad actions, to override and suppress unacceptable social responses, and
determine similarities and differences between things or events. The frontal
lobes are also responsible for retaining long-term memories. These include
memories with associated emotions, derived from input from the brain’s
apostrophe limbic system. Neuropsychological testing which measures frontal
lobe function through tests including Finger tapping, Wisconsin Card Sorting
Tasks, and other measures of verbal and figural fluency. Frontal lobe
syndrome and executive dysfunction occur when the frontal lobes are subject
Temporal lobes – lie at the sides of the brain, beneath the lateral or Sylvian
fissure. The temporal lobes are involved in auditory processing and are
home to the primary auditory cortex. Temporal lobes are involved in semantics
both in speech and vision. The temporal lobe contains the hippocampus
and is therefore involved in memory formation as well.
Occipital lobes – are the visual processing center of the brain. The primary visual
cortex is Brodmann area 17. It is located on the medial side of the occipital
lobe within the Cal calcarine sulcus. The occipital lobes are the smallest
of the four true lobes in the human brain. Located in the rearmost portion
of the skull, the occipital lobes are part of the forebrain structure.
The lobes rest on the tentorium cerebelli, a process of dura matter that
separates the cerebrum from the cerebellum. If one occipital lobe is damaged,
the result can be vision loss from similarly positioned field cuts in
each eye. Occipital lesions can cause visual hallucinations. Lesions in
the parietal-temporal- occipital areas can result in color agnosia, movement
agnasia, and agraphia. The function of the exit the occipital lobe is
to control vision and color recognition.
Parietal lobes – the parietal lobe is positioned above (superior to) the occipital
lobe and behind (posterior to) the frontal lobe. The parietal lobe integrates
sensory information from different processes, particularly determining
spatial sense and navigation. The parietal lobe plays important roles
in integrating sensory information from various parts of the body, knowledge
of numbers and their relations, and the manipulation of objects. Portions
of the parietal lobe are involved with visuospatial processing. Much less
is known about the parietal lobes than about the other three lobes mentioned above.
Cerebrospinal Fluid and the Ventricles:
The brain floats in a bath of cerebrospinal fluid (CSF). Inside the brain
are two large areas of pooled CSF. These areas are called ventricles.
Ventricles are connected by channels to form a continuous system. In healthy
human beings, the body continually produces and absorbs CSF. Hydrocephalus
occurs where there is a blockage in the system and CSF accumulates, causing
increased pressure thereby causing the ventricles to expand. CSF is sterile.
Meningitis can occur where bacteria invades the CSF. Fractures to the
skull can cause CSF leaks.
The surface of the brain is covered by a tough, protective membrane called
dura matter. The dura protects the brain, somewhat, from the bony skull.
Dura fills the area between the hemispheres and around the spinal cord.
Bleeds that occur below the dura are called subdural hematomas, and blood
clots or bleeds that form above the dura are called epidural hematomas.
Circulation And Blood Flow:
Oxygen is delivered to the brain via blood vessels and arterial delivery.
There are four major arteries delivering oxygen to the brain. The carotid
arteries (both right and left) are major deliverers to the front of the
brain and are part of the “anterior circulation”. The smaller
vertebral arteries travel up the back of the neck to supply the back of
the brain and form part of the “posterior circulation”. The
Circle of Willis sits at the base of the brain and feeds blood vessels
to the brain itself. These are the right and left anterior cerebral, middle
cerebral, and posterior cerebral arteries, which supply the front, middle
and back of the cerebral hemispheres with blood.