Cranium/Meninges/Ventricles/CSF Flashcards
Note the location of the optic canal through which cranial nerve II (the optic nerve) passes.The optic nerve carries visual information from the retina of the eye back to the brain allowing for vision.
Note also the superior orbital fissure through which the following cranial nerves pass: Cranial nerve III (the occulomotor nerve), IV (the trochlear nerve), VI (the abducens nerve), and V1 (the first branch of the 5th cranial nerve also known as the ophthalmic division of the trigeminal nerve). The first three of these nerves control the orbital muscles that move the eye. The occulomotor nerve also carries a fascicle or bundle of nerves that constricts the pupil.
The ophthalmic branch of the trigeminal nerve, V1, transmits sensory information from the ipsilateral forehead and scalp to the brainstem.
This slide presents the intracranial view of the skull and the bony openings through which the cranial nerves exit the skull.
What passes through the cribriform plate?
which tiny delicate fibers from the overlying olfactory bulb pass to reach the nasal epithelium. Trauma often shears these fibers to produce anosmia
Note the optic canal for the optic nerve. The superior orbital fissure carries cranial nerves III, IV, VI and V1.
What passes throguh the foramen rotundum?
The foramen rotundum provides the passage for the maxillary branch of the trigeminal nerve or V2.
What passes through the foramen ovale? Foramen spinosum?
The foramen ovale provides passage for the third branch, that is the mandibular branch, of the trigeminal nerve, also called V3.
The foramen spinosum permits entry of the middle meningeal artery into the skull.
Describe the basic path of the facial nerve (CN VII)
Cranial nerve VII enters the internal auditory canal or meatus, (also called acoustic meatus) and exits the skull via the stylomastoid foramen.
NOTE: Cranial nerve VIII (vestibulocochlear) enters the same canal via the internal auditory meatus and exits the cranial vault via the external auditory meatus
What passes through the jugular foramen?
permits exit of cranial nerves IX (glossopharyngeal), X (vagus), and XI (spinal accessory).
The spinal branches of cranial nerve XI pass rostrally through the foramen magnum, join the cranial branches and exit via the jugular foramen.
Cranial nerve XII (the hypoglossal nerve) exits the calvarium via the _______
hypoglossal canal.
This slide presents a ventral view of the skull and identify important foramen through which some of the cranial nerves emerge from the skull.
Again:
V3, the mandibular branch of the trigeminal nerve, passes through the foramen ovale.
The middle meningeal artery enters the skull via the foramen spinosum.
Describe the route of internal carotid a. in the skull
The internal carotid artery gains entry to the cranial vault through the carotid foramen, passing through a bony canal and entering the calvarium via the carotid canal. The slide shows the juxtaposition of the foramen lacerum with the carotid canal but the former is blocked by connective tissue and the internal carotid artery does not pass through the foramen lacerum.
This slide presents a view of the floor of the calvarium after the dorsal skull and brain have been removed. The anterior, middle, and posterior fossas are seen.
Note how the lesser wing of the sphenoid bone and the petrous ridge of the temporal bone create bony prominences against which the brain can rub and be injured if accelerated or de-accelerated quickly through head trauma.
The large hole in the center is the foramen magnum through which the spinal cord connects to the brainstem
This slide presents a diagram of the connective tissue coverings of the brain. The purpose of these coverings is to protect the brain from injury by providing mechanical support and to bath it in a fluid solution to buffer it against chemical and mechanical forces
Describe the meningal layers
The meninges are comprised of three layers. From the brain outward they consist of a thin layer of cells tightly approximated to the brain surface called the pia mater, a somewhat thicker layer called the arachnoid mater, and the thickest layer, a double membrane called the dura mater.
What is dura mater composed of?
The dura mater is comprised of a layer closest to the brain called the meningeal layer and an outer layer just beneath the periosteum called the periosteal layer.
The two layers of dura mater separate in the midline and at the lateral aspects of the brain to create what?
large venous sinuses called the superior sagittal sinus and the lateral sinuses, respectively.
Coming together in the midline and the lateral aspects of the brain, the meningeal layers create a thick membrane that separates the left and right cerebral hemispheres called what?
the falx cerebri.
The dura mater layers also form the tentorium cerebelli, often simply called the tentorium. What does it do?
supports the cerebral hemispheres and separates them from the underlying cerebellar hemispheres in the posterior fossa. The tentorium separates the supratentorial compartment from the infratentorial compartment
There are three important spaces associated with the meninges. Two of these are so called “potential” spaces since under normal circumstances these spaces do not exist. They are the epidural space and subdural space.
Head trauma and other conditions may cause bleeding into the epidural space (usually arterial) called epidural hemorrhage or into the subdural space (usually venous) called subdural hemorrhage.
What is the only true space?
The third space, the subarachnoid space, is a true space that is lined by the arachnoid above and the pia mater below.
What does the subarachnoid space contain?
most of the cerebrospinal fluid that baths the brain.
The passages in the subarachnoid space resemble that of a spider web and hence the term arachnoid. The large blood vessels, arteries and veins positioned at the base of the brain and surrounding the brain, also lie in the subarachnoid space. Rupture of any of these vessels leads to subarachnoid hemorrhage with accumulation of blood in the subarachnoid space.
How do the meningeal layers continued caudually?
The three meningeal layers described for the brain are continuous with similar membranes surrounding the spinal cord. Two of these membranes, the dura mater and the arachnoid continue out into the peripheral nerve forming the epineurium and perineurium, respectively
Is the dura mater surround the spinal cord exactly the same as in the brain?
A trivial point – the dural membrane surrounding the spinal cord is comprised of only a single layer in contrast to the double layer covering the brain.
Again, what forms the epineurium of peripheral nerves?
dura
The brain is served by two major pairs of arteries, namely:
the right and left internal carotid and the right and left vertebral arteries
The right and left common carotid arteries bifurcate in the neck just below the angle of the jaw into external and internal carotid arteries (respectively labelled ECA and ICA). What do the ECA supply?
The external carotid arteries supply the face, scalp, and the meninges overlying the brain.
Describe the route of the ICAs
The internal carotid arteries ascend and travel through the carotid canal, enter the cranial vault along side the cavernous sinus. At this point they make a hairpin like turn backwards and continue on as the middle cerebral artery or MCA and the anterior cerebral artery or ACA. The ophthalmic artery branches off near the apex of the hairpin turn and thus represents the first branch of the internal carotid artery.
What do the right and left vertebral aa. originate from?
The right and left vertebral arteries originate from the respective subclavian arteries.
How do the vertebral aa. ascend?
They enter the vertebral foramen bilaterally at the C6 level and travel upward through these foramen, entering the calvaria through the foramen magnum. The two vertebral arteries or VA join at the junction of the medulla and pons to form the basilar artery or BA.
This slide depicts the path of the middle meningeal artery after it has branched off the external carotid artery.
Note its close approximation to the inner aspect of the skull. In the lower figure the outline of the middle meningeal artery is seen in outline created by grooves in the inner table of the skull bone where the middle meningeal artery travels.
Head trauma with skull fracture across regions of the middle meningeal artery can rupture this vessel causing bleeding into the epidural space. This is a neurological and neurosurgical emergency with death occurring within a few hours if undiagnosed and untreated.
What is the Circle of Willis composed of?
The circle is comprised of the posterior cerebral arteries connected to the internal carotid arteries via the posterior communicating arteries. The anterior segment of the anterior cerebral artery, called A1, and the anterior communicating artery complete the Circle of Willis.
Other important arteries in this figure include the basilar artery, superior cerebellar artery, middle cerebral artery, lateral striate arteries, the vertebral arteries, the superior, anterior inferior and posterior inferior cerebellar arteries.
These are lateral and sagittal views of the brain and its arterial supply.
This slide depicts the important draining veins of the brain. Occlusion of any of the major venous sinuses may cause seizures, tissue injury, and blockage of CSF circulation.
This is a lateral view of a transparent brain showing the left lateral ventricle and the midline components of the third and fourth ventricles (outlined in brown).
Note the physical relationships between the components of the lateral ventricle with the frontal, parietal, occipital, and temporal lobes of the brain.
The lateral ventricles communicate with the midline third ventricle through what?
the interventricular foramen of Monro
The third and fourth ventricles communicate via what?
the cerebral aqueduct of Sylvius also known as the Sylvian aqueduct.
The table compares the composition of CSF and blood plasma. Note that the CSF protein is roughly one hundredth the concentration of protein in the blood.
The blood glucose is roughly two-thirds that of the blood and it takes about two hours for the CSF to equilibrate with the peripheral blood glucose, an important point in a brittle diabetic whose blood sugars may fluctuate markedly during the course of the day.
This slide depicts the formation of the arachnoid villi by outpouchings of the arachnoid membrane.
Note the egress of CSF from the subarachnoid space via the arachnoid villi, also know as the pacchionian granulations, into the venous sinus.
This slide shows a typical capillary in a systemic organ such as the liver (on the left) and the capillary structure found within the brain (on the right).
Note the gap between cells called fenestrations in the systemic capillary and the lack of such fenestrations in the brain capillary.
Note that the so called “blood brain barrier” is created by brain capillary endothelial cells that closely approximate one another thereby eliminating the usual fenestration seen in systemic organs.
This is an artist’s rendition of a brain capillary and the cells that form the blood brain barrier.
Note that astrocytes line the capillaries with their “end feet” and help to prevent substances in the blood from crossing into the CSF space. Despite this additional layer of protection, the blood brain barrier is mediated primarily by tight junctions between capillary endothelial cells.
What is the choroid plexus made from?
it is created by an outpouching of capillaries and the pia mater into the ventricular space. The choroid plexus sandwiches capillary blood vessels between layers of the arachnoid membrane and pia mater.
Note that there is an additional layer of cells that line the outpouchings of the choroid plexus. The latter layer of cells is contiguous with the cells lining of the ventricular walls and consists of two types of cells, one called ventricular ependymal cells when they line the ventricular wall and the other called choroid epithelial cells when they line the choroid outpouchings.
An important distinguishing feature of these two cell types is what?
Ventricular ependymal cells possess the normal fenestration (that is a space) between adjacent cells (shown by the green arrows) while the choroid epithelial cells are tightly approximated to one another (shown by the red arrows). The tight connections between choroid epithelial cells are shown as tiny black rectangles connecting these cells. They form “tight junctions” whose purpose is to limit potentially toxic substances circulating in the capillaries from entering the CSF space. Large and small molecules must pass through and cannot pass around the choroid epithelial cells to enter the ventricular CSF.
It is important to recognize the BBB and Blood CSF barriers are distinct anatomic barriers. This slide demonstrates the blood CSF barriers that function to prevent direct access of substances in the blood from moving into the CSF.
On the left are shown the tight junctions of the choroid epithelial cells defined on the previous slide. On the right, similar tight junctions between arachnoid villus cells prevent backflux of substances from the venous sinuses into the CSF.
Several brain areas function to monitor and regulate fluctuations in blood chemistry and therefore require rapid and direct access to blood born chemicals. Describe these areas
These areas lack a blood brain barrier and are labeled and highlighted in red in this slide. They typically line the ventricular system and are thus called circumventricular organs.
The function of several of these regions is unknown but, for example, the areas of the organum vasculosum and neurohypophysis are well understood to monitor and regulate electrolyte balance and several important hormones, respectively.
Describe the glympathic system
The pathway features a para-arterial inflow path for CSF to enter the brain and a clearance mechanism for the removal of interstitial fluid and extracellular solutes from the CNS.
Exchange of solutes between the CSF and the interstitial fluid is driven by arterial pulsation and regulated during sleep by the expansion and contraction of brain’s extracellular space. Soluble proteins, waste products, and excess extracellular fluid are cleared via convective bulk flow of the interstitial fluid, facilitated by astrocytic aquaporin 4 water channels.
Here is another diagram of the glymphatic system.
Glymphatic flow was initially believed to answer a long standing question of how the CNS could function in the presumed absence of lymphatic drainage for extracellular proteins, excess fluid, and metabolic waste products. Recent research, however, has discovered that the dural sinuses and meningeal arteries are in fact lined with conventional lymphatic vessels and that this long-elusive vasculature forms the connecting pathway for the entrance and exit of lymphatic fluid and immune cells from the meningeal compartment to the glymphatic system.
This is much more active during sleep. So sleep might be a mechanism for the brain to remove waste products
- Cerebral aqueduct
peduncles and colliculi are laterally displaced
Should be a 6 yo girl
- In Meningitis, the DURA has the nerve endings and causes the pain/HA
Tx meningitis empirically with penicllin before CT/spinal tap. Dont delay
3.
- increased CSF pressure (pulsations decrease due to collapse due to pressure)
decreased CSF pressure sign = venous pulsations increase
4.
- Know b/c the fourth ventricle is normal sized; enlarged in communicating hydrocephalus
4.
2.
