chapter 3 reading - in exam Flashcards
CNS
consists of the brain and
spinal cord
is encased in bone
The brain is the most pro-
tected organ in the body covered by the tough, bony skull, and the spinal cord is con-
tained within the vertebral column.
The brain is made up of neurons,
glia, and other supporting cells and floats in a pool of cerebrospinal fluid (CSF). The
brain requires a large supply of blood and is chemically guarded by the blood–brain
barrier.
The brain continuously receives approximately 20 percent of the blood flow from the
heart.
Other parts of the body, such as the skeletal muscles or digestive system, receive vary-
ing quantities of blood, depending on their needs, relative to those of other regions. But the
brain always receives its share. The brain can store only a small amount of its fuel (primarily
glucose), so a consistent blood supply is essential.
A one-second interruption of the blood
flow to the brain uses up much of the dissolved oxygen; a six-second interruption produces
unconsciousness. After only a few minutes without blood flow, permanent brain damage
results.
The peripheral nervous system
consists of cranial nerves, spinal nerves and peripheral ganglia
The peripheral nervous system is covered with two layers of meninges. The middle layer
(arachnoid membrane), with its associated pool of CSF, covers only the brain and spinal cord.
Outside the central nervous system, the outer and inner layers (dura mater and pia mater) fuse
and form a sheath that covers the spinal and cranial nerves and the peripheral ganglia.
directions in the nervous system
Directions in the nervous
system are normally described relative to the neuraxis, an imaginary
line drawn through the length of the central nervous system, from the
front of the brain to the lower end of the spinal cord.
animals with a straight neuraxis include - humans and alligators
anterior With respect to the central
nervous system, located near or toward
the head.
posterior With respect to the central ner-
vous system, located near or toward the tail.
rostral “Toward the beak”; with respect
to the central nervous system, in a
direction along the neuraxis toward the
front of the face.
caudal - towards the tail - refers to the brain as well as rostral
The top of
the head and the back are part of the dorsal surface, while the ventral
(front) surface faces the ground. (Dorsum means “back,” and ventrum
means “belly.”)
lateral - towards the side
medial - towards the middle
ipsilateral
refers to structures on the same side of the body. If we say that the
olfactory bulb projects axons to the ipsilateral hemisphere, we mean
that axons originating in the left olfactory bulb of the brain termi-
nate in the left hemisphere and axons originating in the right olfac-
tory bulb terminate in the right hemisphere.
contraleteral
refers to
structures on opposite sides of the body. If we say that a particular
region of the left cerebral cortex controls movements of the contralat-
eral hand, we mean that the region controls movements of the right
hand.
we can slice the nervous system in 3 ways
- Coronally, like slicing a loaf of bread, giving us cross sections (also
known as frontal sections when referring to the brain). A coronal
cut to the middle of the brain would divide the brain into front and
back halves. Note that because of our upright posture, cross sec-
tions of the spinal cord are parallel to the ground. - Parallel to the ground, giving us horizontal sections. A parallel cut
to the middle of the brain would result in cutting off the upper half
of the brain. - Perpendicular to the ground and parallel to the neuraxis, giving us sagittal sections.
The midsagittal plane divides the brain into two symmetrical right and left halves.
definitions
cerebral cortex The outermost layer of
gray matter of the cerebral hemispheres.
cross section With respect to the central
nervous system, a slice taken at right
angles to the neuraxis.
frontal section A slice through the brain
parallel to the forehead.
horizontal section A slice through the
brain parallel to the ground.
sagittal section (sadj i tul) A slice
through the brain parallel to the neuraxis
and perpendicular to the ground.
midsagittal plane The plane through the
neuraxis perpendicular tothe ground; di-
vides thebrain intotwosymmetrical halves.
meninges
The entire nervous system—brain, spinal cord, cranial and spinal nerves, and peripheral
ganglia—is covered by tough connective tissue. The protective sheaths around the brain
and spinal cord are referred to as the meninges
meninges (men in jees) The three layers
of tissue that encase the central nervous
system:
the dura mater = durable, thick, tough and flexible but unstretchable
arachnoid membrane = the middle layer, soft and spongy located between the outer dura mater and inner Pia mater
pia mater = clings to the surface of the brain and spinal cord, thin and delicate and contains smaller surface blood vessels of brain and spinal cord
subarachnoid space The fluid-filled
space that cushions the brain; located
between the arachnoid membrane and the
pia mater.
ventricular system
consists of a series of hollow, interconnected chambers
called ventricles (“little bellies”), which are filled with CSF.
The largest cham-
bers are the lateral ventricles, which are connected to the third ventricle.
The third ventricle is
located at the midline of the brain; its walls divide the surrounding part of the brain into sym-
metrical halves.
A bridge of neural tissue called the massa intermedia crosses through the mid-
dle of the third ventricle and serves as a convenient reference point.
The cerebral aqueduct, a
long tube, connects the third ventricle to the fourth ventricle.
The lateral ventricles constitute
the first and second ventricles, but they are never referred to as such.
The ventriclesare more than just open spaces in the brain.They serve the very important
function of producing and containing CSF.
CSF = cerebrospinal fluid
CSF is made by special tissue with a rich blood supply called the choroid plexus, which extends into all four of the ventricles. Once cerebro-
spinal fluid is produced by the choroid plexus of the lateral ventricles, it flows into the third
ventricle. More CSF is produced in this ventricle, which then flows through the cerebral
aqueduct to the fourth ventricle, where still more CSF is produced. TheCSFleaves the fourth
ventricle through small openings that connect with the subarachnoid space surrounding
the brain. The CSF then flows through the subarachnoid space around the CNS, where it is
reabsorbed into the blood supply through the arachnoid granulations which are small projections.
the brain
The brain is very soft and jellylike. The considerable weight of a human brain (approxi-
mately 1400 g), along with its delicate construction, necessitates that it be protected from
shock. Fortunately, the intact brain within a living human is very well protected. It floats
in a bath of CSF contained within the subarachnoid space. Because the brain is completely
immersed in liquid, its net weight is reduced to approximately 80 g. As a result, pressure on
the base of the brain is considerably reduced. The CSF surrounding the brain and spinal cord
also helps reduce the shock to the CNS that would be caused by sudden head movement.
