Chapter 10a.docx

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21 Apr 2012
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Chapter 10a
A Primer of Neurobiological Concepts
- Clients need assistance with serious problems that are best understood from a neurological
standpoint
o Problems typically arise due to a head injury, learning disability, memory impairment,
language disorder or attentional difficulties
- In the United States:
o Estimated 5 to 8 million children struggle with learning disability
o 13 to 16 million adults live with memory loss or other symptoms related to dementia
o 2 million people experience a head injury each year
The Human Brain: An Overview
- By convention the nervous system is divided into the central nervous system consisting of the
brain and spinal cord and the peripheral nervous system that includes the cranial nerves and the
network of the nerves emanating from the spinal cord
- The brain is intimately involved in thinking, feeling and behaving
- Brain is the most protected brain in the human body
o The first line of defence against physical trauma is the skull consisted of several
intermeshed, rigid, bones that almost completely encase the brain
o Beneath the skull, the brain is also surrounded by MENINGES , a thin layering of three
tough membranes that encases the brain and spinal cord, providing additional
protection
o The middle spongy level of the meninges is filled with another form of protection,
cerebrospinal fluid, which buffers the brain against sudden acceleration and
deceleration, such as from a blow to the head
- Buoyancy reduces the effective weight of the organ to a few ounces, vastly reducing pressure
upon the base of the brain
o WITHOUT THIS THE BRAIN CAN BRUISE EASILY WITH THE RAPID MOVEMENT OF THE
BRAIN!!!
- When unbuoyed the brain weights LESS than THREE POUNDS
o It is composed principally of 5 elements:
Gray matter
White matter
Glial cells
Cerebrospinal fluid (CSF)
Blood vessels of the vascular system that provide the brain with oxygen adn
nutrients
Gray matter and White matter
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- The gray matter consists of densely packed cell bodies of neurons, which are also called nerve
cells
o When activated a neuron or nerve cell conducts an electrochemical impulse outward
from the cell body down an elongated structure called the axon allow neurons to
communicate with each other
o Axons are wrapped in a white, fatty substance called myelin sheath that provides
insulation and enhances neural transmission
- The myelin sheath gives white matter its distinctive appearance
o Axons can be up to several inches in length and provide up to 90 percent of the total
volume of some nerve cells
- A few neurological ailments called demyelinating diseases, attack the white matter and impair
the ability of nerve cells to communicate with one another
- MULTIPLE SCLEROSIS is probably the most common disorder of demyelinization
o Symptoms are highly varied depending upon the sites of attack upon the myelin sheath,
but might include blurred vision, muscle weakness, partial numbness and loss of
coordination
- CONTROVERSY: for decades it has been believed that the neurons that compose the gray
matter and white matter do not reproduce BUT recent research suggests that adult human may
have a limited capacity to reproduce neurons especially in areas of the brain important for
learning and memory
- Neurons communicate by sending all or no electrochemical impulses to one another
o Each neuron might send transmissions to thousands perhaps tens of thousands of other
neurons at near and distant sites called synapses
o Chemical communication across the synapses can occur up to a thousand times a
second
Glial Cells
- Glial cells constitute another important element of the brain
- Their functions include structural support for the neurons, transport of nutrient to the neurons,
cleaning up brain debris and insulating axons in the central and peripheral nervous systems
- Neurons are involved in modulating the excitability of individual neurons
- They do not directly conduct nerve impulses they indirectly affect this crucial form of brain
activity
Cerebrospinal Fluid and the Ventricular System
- Cerebrospinal fluid (CSF) is a clear liquid that is continuously produces and replenished within
the ventricles
- The ventricles are hollow, interconnected chambers found in the middle of the brain
- There are four ventricles:
o Two side by side ventricles called the LATERAL ventricles
o Two midline ventricles known as THIRD and FORTH ventricles
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- The CSF is produced by the choroid plexus, bilateral structures, found within these lateral
ventricles
- About ¾ of a liters of CSF is produced each day
- The fluid flows slowly from the lateral ventricles down through the third and fourth ventricles by
means of channels and aqueducts until it reaches the meninges on the outer surface of the brain
and spinal cord
- In children the increase in pressure can lead to enlargement of the ventricles and compression
of the brain against the skull
o In time, the skull can even enlarge
CONDITION IS KNOWN AS HYDROCEPHALUS or literally “water on the brain”
The consequence of this can be mental retardation and early mortality
- The location and size of the ventricles are important clues to the health of the brain
o Ex: a tumour might displace the lateral ventricles so that they are no longer symmetrical
The Vascular System of the Brain
- The Brain is a highly active organ, needing substantial supplies of oxygen and glucose to function
effectively
o These energy sources are supplies by the flow of the blood through the cardiovascular
system
- Two parts of the arteries carry blood to the brain
o These are the left and right internal carotid arteries found in the front of the neck, and
the left and right vertebral found in the back of the neck
The vertebral arteries come together just below the brain to form a single
artery, the basilar artery
- These three arteries the left and right internal carotids and the basilar artery all feed into a
circular arterial structure at the base of the brain known as the circle of the Willis
o This circular network ensures that the brain receives a continual supply of blood, even if
one of the input arteries is compromised
- From this circular arterial system at the base of the brain, three arteries branch upward on each
side to the roughly symmetrical cerebral hemispheres of the brain:
o The anterior cerebral arteries supply blood to the left and right frontal lobes and some
midline structures
o The middle cerebral arteries provide blood to the vast majority of the lateral surface of
each hemisphere, including the frontal, parietal and temporal lobes and to some
internal structures
o The posterior cerebral arteries supply blood to the left and right occipital lobes and to
additional subcorital structures
- Advancing age, it can cause for one or more arteries in the brain to become completely
obstructed by a condition known as ATHEROSCLEROSIS which is the gradual build up of fatty
plaque- the brain tissue supplied the vessel dies because it is deprived of oxygen
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