Module 8: Anatomy of the Nervous System

Lesson 3: Circulation of the Central Nervous System

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Dưới đây là danh sách những thuật ngữ Y khoa của module Anatomy of the Nervous System.
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Medical Terminology: Anatomy of the Nervous System

abducens nerve
sixth cranial nerve; responsible for contraction of one of the extraocular muscles
alar plate
developmental region of the spinal cord that gives rise to the posterior horn of the gray matter
amygdala
nucleus deep in the temporal lobe of the cerebrum that is related to memory and emotional behavior
anterior column
white matter between the anterior horns of the spinal cord composed of many different groups of axons of both ascending and descending tracts
anterior horn
gray matter of the spinal cord containing multipolar motor neurons, sometimes referred to as the ventral horn
anterior median fissure
deep midline feature of the anterior spinal cord, marking the separation between the right and left sides of the cord
anterior spinal artery
blood vessel from the merged branches of the vertebral arteries that runs along the anterior surface of the spinal cord
arachnoid granulation
outpocket of the arachnoid membrane into the dural sinuses that allows for reabsorption of CSF into the blood
arachnoid mater
middle layer of the meninges named for the spider-web–like trabeculae that extend between it and the pia mater
arachnoid trabeculae
filaments between the arachnoid and pia mater within the subarachnoid space
ascending tract
central nervous system fibers carrying sensory information from the spinal cord or periphery to the brain
axillary nerve
systemic nerve of the arm that arises from the brachial plexus
basal forebrain
nuclei of the cerebrum related to modulation of sensory stimuli and attention through broad projections to the cerebral cortex, loss of which is related to Alzheimer’s disease
basal nuclei
nuclei of the cerebrum (with a few components in the upper brain stem and diencephalon) that are responsible for assessing cortical movement commands and comparing them with the general state of the individual through broad modulatory activity of dopamine neurons; largely related to motor functions, as evidenced through the symptoms of Parkinson’s and Huntington’s diseases
basal plate
developmental region of the spinal cord that gives rise to the lateral and anterior horns of gray matter
basilar artery
blood vessel from the merged vertebral arteries that runs along the dorsal surface of the brain stem
brachial plexus
nerve plexus associated with the lower cervical spinal nerves and first thoracic spinal nerve
brain stem
region of the adult brain that includes the midbrain, pons, and medulla oblongata and develops from the mesencephalon, metencephalon, and myelencephalon of the embryonic brain
Broca’s area
region of the frontal lobe associated with the motor commands necessary for speech production and located only in the cerebral hemisphere responsible for language production, which is the left side in approximately 95 percent of the population
Brodmann’s areas
mapping of regions of the cerebral cortex based on microscopic anatomy that relates specific areas to functional differences, as described by Brodmann in the early 1900s
carotid canal
opening in the temporal bone through which the internal carotid artery enters the cranium
cauda equina
bundle of spinal nerve roots that descend from the lower spinal cord below the first lumbar vertebra and lie within the vertebral cavity; has the appearance of a horse’s tail
caudate
nucleus deep in the cerebrum that is part of the basal nuclei; along with the putamen, it is part of the striatum
central canal
hollow space within the spinal cord that is the remnant of the center of the neural tube
central sulcus
surface landmark of the cerebral cortex that marks the boundary between the frontal and parietal lobes
cephalic flexure
curve in midbrain of the embryo that positions the forebrain ventrally
cerebellum
region of the adult brain connected primarily to the pons that developed from the metencephalon (along with the pons) and is largely responsible for comparing information from the cerebrum with sensory feedback from the periphery through the spinal cord
cerebral aqueduct
connection of the ventricular system between the third and fourth ventricles located in the midbrain
cerebral cortex
outer gray matter covering the forebrain, marked by wrinkles and folds known as gyri and sulci
cerebral hemisphere
one half of the bilaterally symmetrical cerebrum
cerebrum
region of the adult brain that develops from the telencephalon and is responsible for higher neurological functions such as memory, emotion, and consciousness
cervical plexus
nerve plexus associated with the upper cervical spinal nerves
choroid plexus
specialized structures containing ependymal cells lining blood capillaries that filter blood to produce CSF in the four ventricles of the brain
circle of Willis
unique anatomical arrangement of blood vessels around the base of the brain that maintains perfusion of blood into the brain even if one component of the structure is blocked or narrowed
common carotid artery
blood vessel that branches off the aorta (or the brachiocephalic artery on the right) and supplies blood to the head and neck
corpus callosum
large white matter structure that connects the right and left cerebral hemispheres
cranial nerve
one of twelve nerves connected to the brain that are responsible for sensory or motor functions of the head and neck
cranial nerve ganglion
sensory ganglion of cranial nerves
descending tract
central nervous system fibers carrying motor commands from the brain to the spinal cord or periphery
diencephalon
region of the adult brain that retains its name from embryonic development and includes the thalamus and hypothalamus
direct pathway
connections within the basal nuclei from the striatum to the globus pallidus internal segment and substantia nigra pars reticulata that disinhibit the thalamus to increase cortical control of movement
disinhibition
disynaptic connection in which the first synapse inhibits the second cell, which then stops inhibiting the final target
dorsal (posterior) nerve root
axons entering the posterior horn of the spinal cord
dorsal (posterior) root ganglion
sensory ganglion attached to the posterior nerve root of a spinal nerve
dura mater
tough, fibrous, outer layer of the meninges that is attached to the inner surface of the cranium and vertebral column and surrounds the entire CNS
dural sinus
any of the venous structures surrounding the brain, enclosed within the dura mater, which drain blood from the CNS to the common venous return of the jugular veins
endoneurium
innermost layer of connective tissue that surrounds individual axons within a nerve
enteric nervous system
peripheral structures, namely ganglia and nerves, that are incorporated into the digestive system organs
enteric plexus
neuronal plexus in the wall of the intestines, which is part of the enteric nervous system
epineurium
outermost layer of connective tissue that surrounds an entire nerve
epithalamus
region of the diecephalon containing the pineal gland
esophageal plexus
neuronal plexus in the wall of the esophagus that is part of the enteric nervous system
extraocular muscles
six skeletal muscles that control eye movement within the orbit
facial nerve
seventh cranial nerve; responsible for contraction of the facial muscles and for part of the sense of taste, as well as causing saliva production
fascicle
small bundles of nerve or muscle fibers enclosed by connective tissue
femoral nerve
systemic nerve of the anterior leg that arises from the lumbar plexus
fibular nerve
systemic nerve of the posterior leg that begins as part of the sciatic nerve
foramen magnum
large opening in the occipital bone of the skull through which the spinal cord emerges and the vertebral arteries enter the cranium
forebrain
anterior region of the adult brain that develops from the prosencephalon and includes the cerebrum and diencephalon
fourth ventricle
the portion of the ventricular system that is in the region of the brain stem and opens into the subarachnoid space through the median and lateral apertures
frontal eye field
region of the frontal lobe associated with motor commands to orient the eyes toward an object of visual attention
frontal lobe
region of the cerebral cortex directly beneath the frontal bone of the cranium
gastric plexuses
neuronal networks in the wall of the stomach that are part of the enteric nervous system
globus pallidus
nuclei deep in the cerebrum that are part of the basal nuclei and can be divided into the internal and external segments
glossopharyngeal nerve
ninth cranial nerve; responsible for contraction of muscles in the tongue and throat and for part of the sense of taste, as well as causing saliva production
gyrus
ridge formed by convolutions on the surface of the cerebrum or cerebellum
hindbrain
posterior region of the adult brain that develops from the rhombencephalon and includes the pons, medulla oblongata, and cerebellum
hippocampus
gray matter deep in the temporal lobe that is very important for long-term memory formation
hypoglossal nerve
twelfth cranial nerve; responsible for contraction of muscles of the tongue
hypothalamus
major region of the diencephalon that is responsible for coordinating autonomic and endocrine control of homeostasis
indirect pathway
connections within the basal nuclei from the striatum through the globus pallidus external segment and subthalamic nucleus to the globus pallidus internal segment/substantia nigra pars compacta that result in inhibition of the thalamus to decrease cortical control of movement
inferior colliculus
half of the midbrain tectum that is part of the brain stem auditory pathway
inferior olive
nucleus in the medulla that is involved in processing information related to motor control
intercostal nerve
systemic nerve in the thoracic cavity that is found between two ribs
internal carotid artery
branch from the common carotid artery that enters the cranium and supplies blood to the brain
interventricular foramina
openings between the lateral ventricles and third ventricle allowing for the passage of CSF
jugular veins
blood vessels that return “used” blood from the head and neck
kinesthesia
general sensory perception of movement of the body
lateral apertures
pair of openings from the fourth ventricle to the subarachnoid space on either side and between the medulla and cerebellum
lateral column
white matter of the spinal cord between the posterior horn on one side and the axons from the anterior horn on the same side; composed of many different groups of axons, of both ascending and descending tracts, carrying motor commands to and from the brain
lateral horn
region of the spinal cord gray matter in the thoracic, upper lumbar, and sacral regions that is the central component of the sympathetic division of the autonomic nervous system
lateral sulcus
surface landmark of the cerebral cortex that marks the boundary between the temporal lobe and the frontal and parietal lobes
lateral ventricles
portions of the ventricular system that are in the region of the cerebrum
limbic cortex
collection of structures of the cerebral cortex that are involved in emotion, memory, and behavior and are part of the larger limbic system
limbic system
structures at the edge (limit) of the boundary between the forebrain and hindbrain that are most associated with emotional behavior and memory formation
longitudinal fissure
large separation along the midline between the two cerebral hemispheres
lumbar plexus
nerve plexus associated with the lumbar spinal nerves
lumbar puncture
procedure used to withdraw CSF from the lower lumbar region of the vertebral column that avoids the risk of damaging CNS tissue because the spinal cord ends at the upper lumbar vertebrae
median aperture
singular opening from the fourth ventricle into the subarachnoid space at the midline between the medulla and cerebellum
median nerve
systemic nerve of the arm, located between the ulnar and radial nerves
meninges
protective outer coverings of the CNS composed of connective tissue
mesencephalon
primary vesicle of the embryonic brain that does not significantly change through the rest of embryonic development and becomes the midbrain
metencephalon
secondary vesicle of the embryonic brain that develops into the pons and the cerebellum
midbrain
middle region of the adult brain that develops from the mesencephalon
myelencephalon
secondary vesicle of the embryonic brain that develops into the medulla
nerve plexus
network of nerves without neuronal cell bodies included
neural crest
tissue that detaches from the edges of the neural groove and migrates through the embryo to develop into peripheral structures of both nervous and non-nervous tissues
neural fold
elevated edge of the neural groove
neural groove
region of the neural plate that folds into the dorsal surface of the embryo and closes off to become the neural tube
neural plate
thickened layer of neuroepithelium that runs longitudinally along the dorsal surface of an embryo and gives rise to nervous system tissue
neural tube
precursor to structures of the central nervous system, formed by the invagination and separation of neuroepithelium
neuraxis
central axis to the nervous system, from the posterior to anterior ends of the neural tube; the inferior tip of the spinal cord to the anterior surface of the cerebrum
occipital lobe
region of the cerebral cortex directly beneath the occipital bone of the cranium
occipital sinuses
dural sinuses along the edge of the occipital lobes of the cerebrum
oculomotor nerve
third cranial nerve; responsible for contraction of four of the extraocular muscles, the muscle in the upper eyelid, and pupillary constriction
olfaction
special sense responsible for smell, which has a unique, direct connection to the cerebrum
olfactory nerve
first cranial nerve; responsible for the sense of smell
optic nerve
second cranial nerve; responsible for visual sensation
orthostatic reflex
sympathetic function that maintains blood pressure when standing to offset the increased effect of gravity
paravertebral ganglia
autonomic ganglia superior to the sympathetic chain ganglia
parietal lobe
region of the cerebral cortex directly beneath the parietal bone of the cranium
parieto-occipital sulcus
groove in the cerebral cortex representing the border between the parietal and occipital cortices
perineurium
layer of connective tissue surrounding fascicles within a nerve
phrenic nerve
systemic nerve from the cervical plexus that innervates the diaphragm
pia mater
thin, innermost membrane of the meninges that directly covers the surface of the CNS
plexus
network of nerves or nervous tissue
postcentral gyrus
primary motor cortex located in the frontal lobe of the cerebral cortex
posterior columns
white matter of the spinal cord that lies between the posterior horns of the gray matter, sometimes referred to as the dorsal column; composed of axons of ascending tracts that carry sensory information up to the brain
posterior horn
gray matter region of the spinal cord in which sensory input arrives, sometimes referred to as the dorsal horn
posterior median sulcus
midline feature of the posterior spinal cord, marking the separation between right and left sides of the cord
posterolateral sulcus
feature of the posterior spinal cord marking the entry of posterior nerve roots and the separation between the posterior and lateral columns of the white matter
precentral gyrus
ridge just posterior to the central sulcus, in the parietal lobe, where somatosensory processing initially takes place in the cerebrum
prefrontal lobe
specific region of the frontal lobe anterior to the more specific motor function areas, which can be related to the early planning of movements and intentions to the point of being personality-type functions
premotor area
region of the frontal lobe responsible for planning movements that will be executed through the primary motor cortex
prevertebral ganglia
autonomic ganglia that are anterior to the vertebral column and functionally related to the sympathetic chain ganglia
primary vesicle
initial enlargements of the anterior neural tube during embryonic development that develop into the forebrain, midbrain, and hindbrain
proprioception
general sensory perceptions providing information about location and movement of body parts; the “sense of the self”
prosencephalon
primary vesicle of the embryonic brain that develops into the forebrain, which includes the cerebrum and diencephalon
putamen
nucleus deep in the cerebrum that is part of the basal nuclei; along with the caudate, it is part of the striatum
radial nerve
systemic nerve of the arm, the distal component of which is located near the radial bone
reticular formation
diffuse region of gray matter throughout the brain stem that regulates sleep, wakefulness, and states of consciousness
rhombencephalon
primary vesicle of the embryonic brain that develops into the hindbrain, which includes the pons, cerebellum, and medulla
sacral plexus
nerve plexus associated with the lower lumbar and sacral spinal nerves
saphenous nerve
systemic nerve of the lower anterior leg that is a branch from the femoral nerve
sciatic nerve
systemic nerve from the sacral plexus that is a combination of the tibial and fibular nerves and extends across the hip joint and gluteal region into the upper posterior leg
sciatica
painful condition resulting from inflammation or compression of the sciatic nerve or any of the spinal nerves that contribute to it
secondary vesicle
five vesicles that develop from primary vesicles, continuing the process of differentiation of the embryonic brain
sigmoid sinuses
dural sinuses that drain directly into the jugular veins
somatosensation
general senses related to the body, usually thought of as the senses of touch, which would include pain, temperature, and proprioception
spinal accessory nerve
eleventh cranial nerve; responsible for contraction of neck muscles
spinal nerve
one of 31 nerves connected to the spinal cord
straight sinus
dural sinus that drains blood from the deep center of the brain to collect with the other sinuses
striatum
the caudate and putamen collectively, as part of the basal nuclei, which receive input from the cerebral cortex
subarachnoid space
space between the arachnoid mater and pia mater that contains CSF and the fibrous connections of the arachnoid trabeculae
subcortical nucleus
all the nuclei beneath the cerebral cortex, including the basal nuclei and the basal forebrain
substantia nigra pars compacta
nuclei within the basal nuclei that release dopamine to modulate the function of the striatum; part of the motor pathway
substantia nigra pars reticulata
nuclei within the basal nuclei that serve as an output center of the nuclei; part of the motor pathway
subthalamus
nucleus within the basal nuclei that is part of the indirect pathway
sulcus
groove formed by convolutions in the surface of the cerebral cortex
superior colliculus
half of the midbrain tectum that is responsible for aligning visual, auditory, and somatosensory spatial perceptions
superior sagittal sinus
dural sinus that runs along the top of the longitudinal fissure and drains blood from the majority of the outer cerebrum
sympathetic chain ganglia
autonomic ganglia in a chain along the anterolateral aspect of the vertebral column that are responsible for contributing to homeostatic mechanisms of the autonomic nervous system
systemic nerve
nerve in the periphery distal to a nerve plexus or spinal nerve
tectum
region of the midbrain, thought of as the roof of the cerebral aqueduct, which is subdivided into the inferior and superior colliculi
tegmentum
region of the midbrain, thought of as the floor of the cerebral aqueduct, which continues into the pons and medulla as the floor of the fourth ventricle
telencephalon
secondary vesicle of the embryonic brain that develops into the cerebrum
temporal lobe
region of the cerebral cortex directly beneath the temporal bone of the cranium
terminal ganglion
autonomic ganglia that are near or within the walls of organs that are responsible for contributing to homeostatic mechanisms of the autonomic nervous system
thalamus
major region of the diencephalon that is responsible for relaying information between the cerebrum and the hindbrain, spinal cord, and periphery
third ventricle
portion of the ventricular system that is in the region of the diencephalon
tibial nerve
systemic nerve of the posterior leg that begins as part of the sciatic nerve
transverse sinuses
dural sinuses that drain along either side of the occipital–cerebellar space
trigeminal ganglion
sensory ganglion that contributes sensory fibers to the trigeminal nerve
trigeminal nerve
fifth cranial nerve; responsible for cutaneous sensation of the face and contraction of the muscles of mastication
trochlear nerve
fourth cranial nerve; responsible for contraction of one of the extraocular muscles
ulnar nerve
systemic nerve of the arm located close to the ulna, a bone of the forearm
vagus nerve
tenth cranial nerve; responsible for the autonomic control of organs in the thoracic and upper abdominal cavities
ventral (anterior) nerve root
axons emerging from the anterior or lateral horns of the spinal cord
ventricles
remnants of the hollow center of the neural tube that are spaces for cerebrospinal fluid to circulate through the brain
vertebral arteries
arteries that ascend along either side of the vertebral column through the transverse foramina of the cervical vertebrae and enter the cranium through the foramen magnum
vestibulocochlear nerve
eighth cranial nerve; responsible for the sensations of hearing and balance
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Dưới đây là các bài văn nằm ở bên trái. Ở bên phải là các bài luyện tập (practice) để đánh giá khả năng đọc hiểu của bạn. Sẽ khó khăn trong thời gian đầu nếu vốn từ vựng của bạn còn hạn chế, đặc biệt là từ vựng Y khoa. Hãy kiên nhẫn và đọc nhiều nhất có kể, lượng kiến thức tích tụ dần sẽ giúp bạn đọc thoải mái hơn.
The CNS is crucial to the operation of the body, and any compromise in the brain and spinal cord can lead to severe difficulties. The CNS has a privileged blood supply, as suggested by the blood-brain barrier. The function of the tissue in the CNS is crucial to the survival of the organism, so the contents of the blood cannot simply pass into the central nervous tissue. To protect this region from the toxins and pathogens that may be traveling through the blood stream, there is strict control over what can move out of the general systems and into the brain and spinal cord. Because of this privilege, the CNS needs specialized structures for the maintenance of circulation. This begins with a unique arrangement of blood vessels carrying fresh blood into the CNS. Beyond the supply of blood, the CNS filters that blood into cerebrospinal fluid (CSF), which is then circulated through the cavities of the brain and spinal cord called ventricles.
A lack of oxygen to the CNS can be devastating, and the cardiovascular system has specific regulatory reflexes to ensure that the blood supply is not interrupted. There are multiple routes for blood to get into the CNS, with specializations to protect that blood supply and to maximize the ability of the brain to get an uninterrupted perfusion.

A. Arterial Supply

The major artery carrying recently oxygenated blood away from the heart is the aorta. The very first branches off the aorta supply the heart with nutrients and oxygen. The next branches give rise to the common carotid arteries, which further branch into the internal carotid arteries. The external carotid arteries supply blood to the tissues on the surface of the cranium. The bases of the common carotids contain stretch receptors that immediately respond to the drop in blood pressure upon standing. The orthostatic reflex is a reaction to this change in body position, so that blood pressure is maintained against the increasing effect of gravity (orthostatic means “standing up”). Heart rate increases—a reflex of the sympathetic division of the autonomic nervous system—and this raises blood pressure.

The internal carotid artery enters the cranium through the carotid canal in the temporal bone. A second set of vessels that supply the CNS are the vertebral arteries, which are protected as they pass through the neck region by the transverse foramina of the cervical vertebrae. The vertebral arteries enter the cranium through the foramen magnum of the occipital bone. Branches off the left and right vertebral arteries merge into the anterior spinal artery supplying the anterior aspect of the spinal cord, found along the anterior median fissure. The two vertebral arteries then merge into the basilar artery, which gives rise to branches to the brain stem and cerebellum. The left and right internal carotid arteries and branches of the basilar artery all become the circle of Willis, a confluence of arteries that can maintain perfusion of the brain even if narrowing or a blockage limits flow through one part (Figure 1).

B. Venous Return

After passing through the CNS, blood returns to the circulation through a series of dural sinuses and veins (Figure 2). The superior sagittal sinus runs in the groove of the longitudinal fissure, where it absorbs CSF from the meninges. The superior sagittal sinus drains to the confluence of sinuses, along with the occipital sinuses and straight sinus, to then drain into the transverse sinuses. The transverse sinuses connect to the sigmoid sinuses, which then connect to the jugular veins. From there, the blood continues toward the heart to be pumped to the lungs for reoxygenation.
The outer surface of the CNS is covered by a series of membranes composed of connective tissue called the meninges, which protect the brain. The dura mater is a thick fibrous layer and a strong protective sheath over the entire brain and spinal cord. It is anchored to the inner surface of the cranium and vertebral cavity. The arachnoid mater is a membrane of thin fibrous tissue that forms a loose sac around the CNS. Beneath the arachnoid is a thin, filamentous mesh called the arachnoid trabeculae, which looks like a spider web, giving this layer its name. Directly adjacent to the surface of the CNS is the pia mater, a thin fibrous membrane that follows the convolutions of gyri and sulci in the cerebral cortex and fits into other grooves and indentations (Figure 3).

A. Dura Mater

Like a thick cap covering the brain, the dura mater is a tough outer covering. The name comes from the Latin for “tough mother” to represent its physically protective role. It encloses the entire CNS and the major blood vessels that enter the cranium and vertebral cavity. It is directly attached to the inner surface of the bones of the cranium and to the very end of the vertebral cavity.

There are infoldings of the dura that fit into large crevasses of the brain. Two infoldings go through the midline separations of the cerebrum and cerebellum; one forms a shelf-like tent between the occipital lobes of the cerebrum and the cerebellum, and the other surrounds the pituitary gland. The dura also surrounds and supports the venous sinuses.

B. Arachnoid Mater

The middle layer of the meninges is the arachnoid, named for the spider-web–like trabeculae between it and the pia mater. The arachnoid defines a sac-like enclosure around the CNS. The trabeculae are found in the subarachnoid space, which is filled with circulating CSF. The arachnoid emerges into the dural sinuses as the arachnoid granulations, where the CSF is filtered back into the blood for drainage from the nervous system.

The subarachnoid space is filled with circulating CSF, which also provides a liquid cushion to the brain and spinal cord. Similar to clinical blood work, a sample of CSF can be withdrawn to find chemical evidence of neuropathology or metabolic traces of the biochemical functions of nervous tissue.

C. Pia Mater

The outer surface of the CNS is covered in the thin fibrous membrane of the pia mater. It is thought to have a continuous layer of cells providing a fluid-impermeable membrane. The name pia mater comes from the Latin for “tender mother,” suggesting the thin membrane is a gentle covering for the brain. The pia extends into every convolution of the CNS, lining the inside of the sulci in the cerebral and cerebellar cortices. At the end of the spinal cord, a thin filament extends from the inferior end of CNS at the upper lumbar region of the vertebral column to the sacral end of the vertebral column. Because the spinal cord does not extend through the lower lumbar region of the vertebral column, a needle can be inserted through the dura and arachnoid layers to withdraw CSF. This procedure is called a lumbar puncture and avoids the risk of damaging the central tissue of the spinal cord. Blood vessels that are nourishing the central nervous tissue are between the pia mater and the nervous tissue.
Cerebrospinal fluid (CSF) circulates throughout and around the CNS. In other tissues, water and small molecules are filtered through capillaries as the major contributor to the interstitial fluid. In the brain, CSF is produced in special structures to perfuse through the nervous tissue of the CNS and is continuous with the interstitial fluid. Specifically, CSF circulates to remove metabolic wastes from the interstitial fluids of nervous tissues and return them to the blood stream. The ventricles are the open spaces within the brain where CSF circulates. In some of these spaces, CSF is produced by filtering of the blood that is performed by a specialized membrane known as a choroid plexus. The CSF circulates through all of the ventricles to eventually emerge into the subarachnoid space where it will be reabsorbed into the blood.

A. The Ventricles

There are four ventricles within the brain, all of which developed from the original hollow space within the neural tube, the central canal. The first two are named the lateral ventricles and are deep within the cerebrum. These ventricles are connected to the third ventricle by two openings called the interventricular foramina. The third ventricle is the space between the left and right sides of the diencephalon, which opens into the cerebral aqueduct that passes through the midbrain. The aqueduct opens into the fourth ventricle, which is the space between the cerebellum and the pons and upper medulla (Figure 4).

As the telencephalon enlarges and grows into the cranial cavity, it is limited by the space within the skull. The telencephalon is the most anterior region of what was the neural tube, but cannot grow past the limit of the frontal bone of the skull. Because the cerebrum fits into this space, it takes on a C-shaped formation, through the frontal, parietal, occipital, and finally temporal regions. The space within the telencephalon is stretched into this same C-shape. The two ventricles are in the left and right sides, and were at one time referred to as the first and second ventricles. The interventricular foramina connect the frontal region of the lateral ventricles with the third ventricle.

The third ventricle is the space bounded by the medial walls of the hypothalamus and thalamus. The two thalami touch in the center in most brains as the massa intermedia, which is surrounded by the third ventricle. The cerebral aqueduct opens just inferior to the epithalamus and passes through the midbrain. The tectum and tegmentum of the midbrain are the roof and floor of the cerebral aqueduct, respectively. The aqueduct opens up into the fourth ventricle. The floor of the fourth ventricle is the dorsal surface of the pons and upper medulla (that gray matter making a continuation of the tegmentum of the midbrain). The fourth ventricle then narrows into the central canal of the spinal cord.

The ventricular system opens up to the subarachnoid space from the fourth ventricle. The single median aperture and the pair of lateral apertures connect to the subarachnoid space so that CSF can flow through the ventricles and around the outside of the CNS. Cerebrospinal fluid is produced within the ventricles by a type of specialized membrane called a choroid plexus. Ependymal cells (one of the types of glial cells described in the introduction to the nervous system) surround blood capillaries and filter the blood to make CSF. The fluid is a clear solution with a limited amount of the constituents of blood. It is essentially water, small molecules, and electrolytes. Oxygen and carbon dioxide are dissolved into the CSF, as they are in blood, and can diffuse between the fluid and the nervous tissue.

B. Cerebrospinal Fluid Circulation

The choroid plexuses are found in all four ventricles. Observed in dissection, they appear as soft, fuzzy structures that may still be pink, depending on how well the circulatory system is cleared in preparation of the tissue. The CSF is produced from components extracted from the blood, so its flow out of the ventricles is tied to the pulse of cardiovascular circulation.

From the lateral ventricles, the CSF flows into the third ventricle, where more CSF is produced, and then through the cerebral aqueduct into the fourth ventricle where even more CSF is produced. A very small amount of CSF is filtered at any one of the plexuses, for a total of about 500 milliliters daily, but it is continuously made and pulses through the ventricular system, keeping the fluid moving. From the fourth ventricle, CSF can continue down the central canal of the spinal cord, but this is essentially a cul-de-sac, so more of the fluid leaves the ventricular system and moves into the subarachnoid space through the median and lateral apertures.

Within the subarachnoid space, the CSF flows around all of the CNS, providing two important functions. As with elsewhere in its circulation, the CSF picks up metabolic wastes from the nervous tissue and moves it out of the CNS. It also acts as a liquid cushion for the brain and spinal cord. By surrounding the entire system in the subarachnoid space, it provides a thin buffer around the organs within the strong, protective dura mater. The arachnoid granulations are outpocketings of the arachnoid membrane into the dural sinuses so that CSF can be reabsorbed into the blood, along with the metabolic wastes. From the dural sinuses, blood drains out of the head and neck through the jugular veins, along with the rest of the circulation for blood, to be reoxygenated by the lungs and wastes to be filtered out by the kidneys (Table 1).

OpenStax. (2022). Anatomy and Physiology 2e. Rice University. Retrieved June 15, 2023. ISBN-13: 978-1-711494-06-7 (Hardcover) ISBN-13: 978-1-711494-05-0 (Paperback) ISBN-13: 978-1-951693-42-8 (Digital). License: Attribution 4.0 International (CC BY 4.0). Access for free at openstax.org.

The blood supply to the brain enters through the internal carotid arteries and the vertebral arteries, eventually giving rise to the circle of Willis.

Blood drains from the brain through a series of sinuses that connect to the jugular veins.

The layers of the meninges in the longitudinal fissure of the superior sagittal sinus are shown, with the dura mater adjacent to the inner surface of the cranium, the pia mater adjacent to the surface of the brain, and the arachnoid and subarachnoid space between them. An arachnoid villus is shown emerging into the dural sinus to allow CSF to filter back into the blood for drainage.

The choroid plexus in the four ventricles produce CSF, which is circulated through the ventricular system and then enters the subarachnoid space through the median and lateral apertures. The CSF is then reabsorbed into the blood at the arachnoid granulations, where the arachnoid membrane emerges into the dural sinuses.

Location in CNSBlood vessel structure
Lateral ventriclesCerebrumChoroid plexus
Third ventricleDiencephalonChoroid plexus
Cerebral aqueductMidbrainNone
Fourth ventricleBetween pons/upper medulla and cerebellumChoroid plexus
Central canalSpinal cordNone
Subarachnoid spaceExternal to entire CNSArachnoid granulations
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Script:
  1. The CNS has a privileged blood supply established by the blood-brain barrier.
  2. Establishing this barrier are anatomical structures that help to protect and isolate the CNS.
  3. The arterial blood to the brain comes from the internal carotid and vertebral arteries, which both contribute to the unique circle of Willis that provides constant perfusion of the brain even if one of the blood vessels is blocked or narrowed.
  4. That blood is eventually filtered to make a separate medium, the CSF, that circulates within the spaces of the brain and then into the surrounding space defined by the meninges, the protective covering of the brain and spinal cord.
  5. The blood that nourishes the brain and spinal cord is behind the glial-cell–enforced blood-brain barrier, which limits the exchange of material from blood vessels with the interstitial fluid of the nervous tissue.
  6. Thus, metabolic wastes are collected in cerebrospinal fluid that circulates through the CNS.
  7. This fluid is produced by filtering blood at the choroid plexuses in the four ventricles of the brain.
  8. It then circulates through the ventricles and into the subarachnoid space, between the pia mater and the arachnoid mater.
  9. From the arachnoid granulations, CSF is reabsorbed into the blood, removing the waste from the privileged central nervous tissue.
  10. The blood, now with the reabsorbed CSF, drains out of the cranium through the dural sinuses.
  11. The dura mater is the tough outer covering of the CNS, which is anchored to the inner surface of the cranial and vertebral cavities.
  12. It surrounds the venous space known as the dural sinuses, which connect to the jugular veins, where blood drains from the head and neck.
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