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 Moreover, once the volumes were written, they would virtually be out of date given our ever expanding knowledge of the topic matter.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
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 resulting DAI.
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
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
- 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.
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 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.
- 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 to trauma.
- 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
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.