tb menigitis
TRANSCRIPT
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Central Nervous System
The central nervous system (CNS) is the largest
part of the nervous system, and includes the
brain and spinal cord. The spinal cavity holds
and protects the spinal cord, while the head
contains and protects the brain. The CNS is
covered by the meninges, a three layered
protective coat. The brain is also protected bythe skull, and the spinal cord is also protected
by the vertebrae.
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Central Nervous System (CNS) is the part of the nervous
system that functions to coordinate the activity of all
parts of the bodies of multicellular organisms. In
vertebrates, the central nervous system is enclosed in the
meninges. The meninges (singular meninx) is the system
of membranes which envelops the central nervous
system. The meninges consist of three layers: the dura
mater, the arachnoid mater, and the pia mater. The
primary function of the meninges and of the
cerebrospinal fluid is to protect the central nervous
system. It contains the majority of the nervous system
and consists of the brain (in vertebrates which have
them), and the spinal cord.
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The meninges (singular meninx) is the system of
membranes which envelops the central nervoussystem. The meninges consist of three layers:
the dura mater, the arachnoid mater, and the pia
mater. The primary function of the meninges
and of the cerebrospinal fluid is to protect thecentral nervous system. The space between
these membranes is bathed with a spinal fluid
much like lymph, which serves as a protectivecushion for the delicate nerve tissue, and allows
some expansion space for the brain when its
blood supply is increased
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3 layers of meninges:
Dura mater - (also rarely called meninx fibrosa, or
pachymeninx) is a thick, durable membrane, closest to theskull. It consists of two layers, the periosteal layer, closest to
the calvaria and the inner meningeal layer. It contains larger
blood vessels which split into the capilliaries in the pia mater.
It is composed of dense fibrous tissue, and its inner surface iscovered by flattened cells like those present on the surfaces
of the pia mater and arachnoid. The dura mater is a sac which
envelops the arachnoid and has been modified to serve
several functions. The dura mater surrounds and supports thelarge venous channels (dural sinuses) carrying blood from the
brain toward the heart.
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The falx cerebri separates the hemispheres of the
cerebrum. The falx cerebelli separates the lobes of
the cerebellum.
The tentorium cerebelli separates the cerebrum from
the cerebellum.
The epidural space is a potential space between the
dura mater and the skull. If there is hemorrhaging in
the brain, blood may collect here. Adults are morelikely than children to bleed here as a result of closed
head injury.
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The subdural space is another potential
space. It is between the dura mater and
the middle layer of the meninges, thearachnoid mater. When bleeding occurs in
the cranium, blood may collect here and
push down on the lower layers of themeninges. If bleeding continues, brain
damage will result from this pressure.
Children are especially likely to havebleeding in the subdural space in cases of
head injury.
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Arachnoid mater - The middle element
of the meninges is the arachnoid
membrane, so named because of its
spider web-like appearance. It provides
a cushioning effect for the centralnervous system. The arachnoid mater
exists as a thin, transparent
membrane. It is composed of fibroustissue and, like the pia mater, is
covered by flat cells also thought to be
impermeable to fluid.
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subarachanoid space lies between the
arachnoid and pia mater. It is filled with
cerebrospinal fluid. All blood vessels
entering the brain, as well as cranialnerves pass through this space. The
term arachnoid refers to the spider
web like appearance of the blood
vessels within the space
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Pia mater - T e pia or pia mater is a very
delicate membrane. It is the meningeal
envelope which firmly adheres to the surface ofthe brain and spinal cord. As such it follows all
the minor contours of the brain (gyri and sulci).
It is a very thin membrane composed of fibroustissue covered on its outer surface by a sheet of
flat cells thought to be impermeable to fluid.
The pia mater is pierced by blood vessels which
travel to the brain and spinal cord, and its
capillaries are responsible for nourishing the
brain.
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Cerebrospinal fluid - is a clear liquidproduced within spaces in the brain
called ventricles. Like saliva it is a
filtrate of blood. It is also found inside
the subarachnoid space of the
meninges which surrounds both thebrain and the spinal cord.
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Choroid Plexus
All of the ventricles contain choroid
plexuses which produce cerebrospinal
fluid by allowing certain componentsof blood to enter the ventricles. The
choroid plexuses are formed by the
fusion of the pia mater, the most
internal layer of the meninges and the
ependyma, the lining of the ventricles.
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The Ventricles
These four spaces are filled
with cerebrospinal fluid and
protect the brain by
cushioning it and supporting
its weight.
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The two lateral ventricles extendacross a large area of the brain. The
anterior horns of these structures are
located in the frontal lobes. They
extend posteriorly into the parietal
lobes and their inferior horns arefound in the temporal lobes.
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The third ventricle lies between the two thalamic
bodies. The massa intermedia passes through it and
the hypothalamus forms its floor and part of its lateral
walls.
The fourth ventricle is located between the
cerebellum and the pons.The four ventricles are connected to one another.
The two foramina of Munro, which are also know as
the interventricular foramina, link the lateral
ventricles to the third ventricle.
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The Aqueduct of Sylvius which is also
called the cerebral aqueduct connectsthe third and fourth ventricles.
The fourth ventricle is connected to
the subarachnoid space via two lateral
foramina of Luschka and by one medialforamen of Magendie.
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ANATOMY OFTHE CNS
BRAIN
The center of the nervous system. The brain is
located in the head, protected by the skull andclose to the primary sensory apparatus of
vision, hearing, balance, taste, and smell.
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The frontal lobe is concerned with higher
intellectual functions, such as abstract thought
and reason, speech (Broca's area in the lefthemisphere only), olfaction, and emotion.
Voluntary movement is controlled in the
precentral gyrus (the primary motor area). The parietal lobe is dedicated to sensory
awareness, particularly in the postcentral gyrus
(the primary sensory area). It is also concerneswith abstract reasoning, language interpretation
and formation of a mental egocentric map of
the surrounding area.
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The brain can be subdivided into several distinct regions:
1. Brainstem consists of medulla oblongata, pons and midbrain.
Medulla oblongata - is the lower portion of the brainstem. It
deals with autonomic functions, such as breathing and blood pressure.
The cardiac center is the part of the medulla oblongata responsible for
controlling the heart rate.
Pons - relays sensory information between the cerebellum andcerebrum; aids in relaying other messages in the brain; controls arousal,
and regulates respiration (see respiratory centres). In some theories, the
pons has a role in dreaming.
Midbrain (mesencephalon) - The mesencephalon is considered
part of the brain stem. Its substantia nigra is closely associated withmotor system pathways of the basal ganglia.
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2. Cerebellum - is a region of the brain that plays
an important role in the integration of sensory
perception, coordination and motor control. In order
to coordinate motor control, there are many neural
pathways linking the cerebellum with the cerebral
motor cortex (which sends information to the muscles
causing them to move) and the spinocerebellar tract(which provides proprioceptive feedback on the
position of the body in space). The cerebellum
integrates these pathways, like a train conductor,using the constant feedback on body position to fine-
tune motor movements.
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Diencephalon - (or interbrain) is the region
of the brain that includes the thalamus,
hypothalamus, epithalamus, prethalamus
or subthalamus and pretectum. The
diencephalon is located at the midline of
the brain, above the mesencephalon of the
brain stem. The diencephalon contains the
zona limitans intrathalamica asmorphological boundary and signalling
center between the prethalamus and the
thalamus.
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Thalamus - plays an important role in
regulating states of sleep and wakefulness.
Thalamic nuclei have strong reciprocal
connections with the cerebral cortex,
forming thalamo-cortico-thalamic circuits
that are believed to be involved with
consciousness. The thalamus plays a major
role in regulating arousal, the level ofawareness, and activity. Damage to the
thalamus can lead to permanent coma.
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Epithalamus is a dorsal posterior
segment of the diencephalon (a
segment in the middle of the brain also
containing the hypothalamus and the
thalamus) which includes thehabenula, the stria medullaris and the
pineal body. Its function is the
connection between the limbic system
to other parts of the brain.
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Hypothalamus - is a small part of the brain
located just below the thalamus on both sides
of the third ventricle. Lesions of thehypothalamus interfere with several vegetative
functions and some so called motivated
behaviors like sexuality, combativeness, andhunger. The hypothalamus also plays a role in
emotion. Specifically, the lateral parts seem to
be involved with pleasure and rage, while themedial part is linked to aversion, displeasure,
and a tendency to uncontrollable and loud
laughing.
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Cerebrum - or top portion of the brain, is
divided by a deep crevice, called thelongitudinal sulcus. The longitudinal sulcus
separates the cerebrum in to the right and left
hemispheres. In the hemispheres you will find
the cerebral cortex, basal ganglia and the limbic
system. The two hemispheres are connected by
a bundle of nerve fibers called the corpus
callosum. The right hemisphere is responsible
for the left side of the body while the opposite
is true of the left hemisphere.
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PHYSIOLOGY OFTHE CNS
Medulla
The medulla is the control center for respiratory,
cardiovascular and digestive functions. Pons
The pons houses the control centers for
respiration and inhibitory functions. Here it
will interact with the cerebellum.
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Cerebellum
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cerebellum is the part of the brain that is
located posterior to the medulla oblongataand pons. It coordinates skeletal muscles to
produce smooth, graceful motions. The
cerebellum receives information from oureyes, ears, muscles, and joints about what
position our body is currently in
(proprioception). It also receives output
from the cerebral cortex about where these
parts should be. The main function of the
cerebellum is coordination.
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The Limbic System is a complex set of
structures found just beneath thecerebrum and on both sides of the
thalamus. It combines higher mental
functions, and primitive emotion, into onesystem. It is often referred to as the
emotional nervous system. It is not only
responsible for our emotional lives, butalso our higher mental functions, such as
learning and formation of memories.
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The Limbic system explains why some
things seem so pleasurable to us, such
as eating and why some medical
conditions are caused by mental stress,such as high blood pressure. There are
two significant structures within the
limbic system and several smaller
structures that are important as well.
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They are:
1. The Hippocampus
2. The Amygdala
3. The Thalamus
4. The Hypothalamus
5. The Fornix and Parahippocampus6. The Cingulate Gyrus
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Structures of the Limbic System
Hippocampus
The Hippocampus is found deep in the temporal
lobe, shaped like a seahorse. It consists of twohorns that curve back from the amygdala. It is
situated in the brain so as to make the
prefrontal area aware of our past experiences
stored in that area. The prefrontal area of thebrain consults this structure to use memories to
modify our behavior. The hippocampus is
responsible for memory.
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Amygdala
The Amygdala is a little almond shaped structure,
deep inside the anteroinferior region of the temporal
lobe, connects with the hippocampus, the septi
nuclei, the prefrontal area and the medial dorsal
nucleus of the thalamus. These connections make it
possible for the amygdala to play its important role onthe mediation and control of such activities and
feelings as love, friendship, affection, and expression
of mood. The amygdala is the center for identificationof danger and is fundamental for self preservation.
The amygdala is the nucleus responsible for fear.
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Thalamus
Lesions or stimulation of the medial, dorsal, and anterior
nuclei of the thalamus are associated with changes inemotional reactivity. However, the importance of these nuclei
on the regulation of emotional behavior is not due to the
thalamus itself, but to the connections of these nuclei with
other limbic system structures. The medial dorsal nucleusmakes connections with cortical zones of the prefrontal area
and with the hypothalamus. The anterior nuclei connect with
the mamillary bodies and through them, via fornix, with the
hippocampus and the cingulated gyrus, thus taking part inwhat is known as the Papez's circuit.
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Hypothalamus
The Hypothalamus is a small part of thebrain located just below the thalamus on
both sides of the third ventricle. Lesions of
the hypothalamus interfere with several
vegetative functions and some so called
motivated behaviors like sexuality,combativeness, and hunger. The
hypothalamus also plays a role in emotion.
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Specifically, the lateral parts seem to be
involved with pleasure and rage, while the
medial part is linked to aversion, displeasure,and a tendency to uncontrollable and loud
laughing. However, in general the hypothalamus
has more to do with the expression ofemotions. When the physical symptoms of
emotion appear, the threat they pose returns,
via the hypothalamus, to the limbic centers andthen the prefrontal nuclei, increasing anxiety.
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The Fornix and Parahippocampal
These small structures are important connecting pathways for
the limbic system.
The Cingulate Gyrus
The Cingulate Gyrus is located in the medial side of the brain
between the cingulated sulcus and the corpus callosum.There is still much to be learned about this gyrus, but it is
already known that its frontal part coordinates smells and
sights, with pleasant memories of previous emotions. The
region participates in the emotional reaction to pain and inthe regulation of aggressive behavior.
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