Flashcards in Lesson 2: Coverings of the Brain and Spinal Cord Deck (52):
What are the meninges made of?
What are fibroblasts?
Meninges are made of sheets of "connective tissue" i.e. fibrous sheets (made by fibroblasts)
Fibroblasts are cells in the body (not the nervous system) that make collagen, fibers that are the source of scar tissue, tendons, ligaments, and wrappings and coverings in the body
What are the 3 meningeal layers and what are their basic functions?
Dura mater: to anchor the brain tissue to the skull; provides meningeal protection to the CNS Arachnoid mater: provide a seal under which the blood vessels and cerebrospinal fluid are contained
Pia mater: provide a (leaky) single cell layer [cheese cloth] that covers the brain itself
What does the skull do?
Protects the brain from trauma; hard like a box, filled with fluid and tissue
Skull Anatomy: What is in the anterior cranial fossa?
The anterior cranial fossa sits over the top of the nasal cavity and orbits and is occupied by the frontal lobe
Skull Anatomy: What is in the middle cranial fossa?
On either side of the area containing the pituitary gland and sigmoid sinus is the middle cranial fossa.
Skull Anatomy: What is in the posterior cranial fossa?
Behind the middle cranial fossa = posterior cranial fossa. Contains the (single) foramen magnum (big hole) through which the spinal cord exits the skull. On either side of the foramen magnum, on the floor of the posterior cranial fossa, lies the cerebellum
Why is the tentorium cerebelli important?
This is an important structure because it is very rigid layer of dura mater that can exert pressure on a swelling brain. Sitting on the tentorium cerebelli, is the occipital lobe
What structures leave through the foramen magnum?
Spinal cord leaves the skull through the foramen magnum. 12 cranial nerves exit or enter the skull through a number of small openings in the base of the skull or throughout the eye socket
What are the major arteries for blood supply to the brain?
Left and right, internal carotid arteries and left and right vertebral arteries
What are the major sinuses that drain blood from the brain?
There is 1 pair of venous sinuses, the left and right sigmoid sinuses, draining the venous blood from the brain and exiting the skull as the left and right internal jugular veins
What are the two layers of dura mater?
Periosteal: lines the skull throughout the entire inner surface of the skull.
Meningeal layer: it invaginates into the longitudinal fissure between the two cerebral hemispheres and a second dura infolding (invagination) caudal to the occipital lobe between the occipital lobe of the cerebrum and the cerebellum
What occurs are the periosteal and meningeal layers come in contact?
Is there space between the layers?
Where the periosteal and visceral layers come in contact, they act as one layer
There is a potential space between the periosteal and meningeal layers
What is this structure in the dura: vertical and between two cerebral hemispheres, attached to skull and the inferior border arches over the corpus callosum (a huge bundle of fibres that connects the left and right cerebrum).
What is this structure in the dura: between two cerebellar hemispheres (very shallow and tiny- also vertical like the falx cerebri)
What is this structure in the dura: invaginates between and separates the temporal lobe and cerebellum - houses it; (attaches to anterior and posterior clinoid processes and rim of petrous portion of the temporal bone)
What surfaces does the arachnoid cover?
What is beneath the mater?
Is it permeable?
Covers the entire brain, following major fissures only (same as the dura mater).
Beneath this impermeable layer (seal) one finds the cerebrospinal fluid (CSF) and blood vessels.
What is the result of the subarachnoid space being sealed?
What happens to CSF?
The constant renewal of CSF maintains a pressure that drives a constant flow from the ventricles, through the space beneath the arachnoid mater (sub arachnoid space) to empty into the superior sagittal sinus
Pia mater: how many layers is it? Is it permeable?
The pia mater is the single cell layer that lies directly on brain tissue and follows every sulcus. It is permeable and allows for the passage of small vessels into the brain tissue.
In peripheral nerve coverings, what are neurons covered with?
Each neuron is covered by endoneurium.
What are nerve fascicles in the PNS? What covers it?
Bundles of these mixed motor and sensory fibres are called "nerve fascicles" and are covered by perineurium.
What makes up a nerve in the PNS, what covers it?
Bundles of nerve fascicles are grouped into a nerve (or peripheral nerve), covered by epineurium.
What is the space between the skull and periosteal layer of the dura mater?
Epidural space (above dura)
What is the space between the visceral layer of dura mater and arachnoid mater?
Subdural space (under dura)
What is the space between arachnoid mater and pia matter?
What does it contain?
Subarachnoid space (under arachnoid)
Contains all the smaller blood vessels that supply the brain, particularly the high pressure arteries and cerebrospinal fluid.
What is the function of the ventricular system?
The ventricular system is the source of CSF to nourish and cushion the brain.
What is CSF produced by***? How is it produced?
CSF is produced by specialized ependymal cells that line the hollow brain tube (ventricular system). Tufts of these specialized ependymal cells, tangled with blood capillaries to form the choroid plexus***, are found in the lateral, 3rd and 4th ventricles. They secrete a protein and add fluid respectively
Where does CSF empty?
The superior sagittal sinus.
What is the route of CSF?
1. Lateral ventricles (paired), through the interventricular foramen (of Munro), to the
2. 3rd ventricle (unpaired), then
3. Flows down cerebral aqueduct (unpaired) into the
4. 4th ventricle with a small amount going into the central canal of cord
5. The majority exits at 4th ventricle into the cisterns (pools) that surround the brain stem in the subarachnoid space
6. Circulates over the entire brain in the subarachnoid space
7. At the superior aspect of the brain, it filters into the superior sagittal sinus through small, leaky fingers of arachnoid mater (arachnoid villi) which poke into the venous sinuses.
What are the 4 ways that a lesion can occur in the ventricular system?
•excess fluid production (tumour of producing cells) - rare
•tumours actually blocking the space- rare
•blockage of the cerebral aqueduct - may be congenital (not very rare)
•diminished absorption (blocking of arachnoid villi after infection, clotted blood etc- fairly common after effect of brain injury or infection).
What is the disorder that occurs when blockage inside the ventricular system enlarges the ventricles upstream from the blockage? Fluid is incompressible, therefore it compresses the brain tissue, destroying it and creating enlarged ventricles.
How can hydrocephalus occur?
Occur as a result of bleeding (from trauma) within the subarachnoid space, or infection, that causes clotting and blockage of the CSF drainage through the arachnoid villi into the superior sagittal sinus
What is damage from an external force from damage due to blockage or rupture of a blood vessel (vascular insult), like a stroke, which can produce physical damage (e.g. crushing, cutting) to an area as well as cellular death from damage to arteries that supplies the area?
Space Occupying Lesions: What is an aneurysm?
A large defect in the blood vessel that bulges like a weak inner tube, puts pressure on both brain tissue and adjacent blood vessels. It can happen rapidly or slowly.
Space Occupying Lesions: What is arterio-venous malformation?
Damaged blood vessels that shunt directly from arteries to veins without a pressure reducing capillary bed between
What do the consequences of space occupying lesions depend on? (3 reasons)
1. The rate at which the pressure is applied
2. Size of lesion
3. Whether the pressure is exerted on vulnerable structures
What are some symptoms from swelling that are obvious from immediate prognosis of trauma?
- Push the brain sideways against the falx cerebri
- Push downward through the tentorial notch, causing herniation of the uncus of the temporal lobe (uncal herniation) with pressure on the midbrain and stretching of the oculomotor nerve (seen as pupil dilation).
- Push the tonsil of the cerebellum through the foramen magnum, causing pressure on the medulla where the cardiac and respiratory centres and the reticular formation that sustains consciousness are found.
What are the 6 factors that affect long-term prognosis of trauma?
•location, size, and specific area damaged
•speed of onset of damage
•size and type of vessels involved and therefore the pressure
•time before intervention can begin
collaterals that may form or are already present
•health and age of individual
What is the role of the ependymal cells?
Prevent diffusion of substances from CSF into the brain
What is the make-up of the lateral ventricles?
C-shaped structures, consist of central part (body), and three extensions – anterior, posterior (occipital), and inferior (temporal) horns.
Where is the third ventricle located?
Between the two thalami and is rostrally connected to the lateral ventricles through the interventricular foramen of Munro
What does the third ventricle become in the midbrain?
In midbrain, the cavity of third ventricle narrows to become the cerebral aqueduct – connects third and fourth ventricles
Why is the cerebral aqueduct an important reference point?
For transition between dorsal and ventral midbrain areas.
Area dorsal to aqueduct (tectum) include corpora quadrigemina in addition to tectal nuclei; region ventral to aqueduct is tegmentum, which contains important structures – red nucleus, reticular formation nuclei
In the fourth ventricle, what are the 3 openings?
- two lateral apertures (foramina of Luschka)
- one medial aperture (foramen of Magendie) – CSF gets access to subarachnoid space surrounding CNS
What is the importance of the free border of the tetorium cerebelli in dura mater?
Anteriorly, the free borders of tentorium constitute the opening – tentorial notch. Brainstem descends through free borders of notch toward foramen magnum
Does the arachnoid membrane adhere to the cortical surface?
No, it bridges cortical surface and pia mater
What and where do the arachnoid granulations go?
Arachnoid granulations, through which CSF drains into vascular system, are predominantly located around superior sagittal sinus
Spinal dura mater: what is its composition? What is it attached to?
-Single-layer meningeal membrane; lacks cranial periosteal layer. Is rostrally attached to foramen magnum – opening in occipital bone through which spinal cord passes
Spinal arachnoid mater: Where does it start/stop?
What is it filled with and invest?
-Begins at foramen magnum and extends to cauda equina. Is filled with CSF; also invests tubular projections of the spinal nerve roots from cord to their foramina of exit.
Spinal pia mater: how is it realted to the spinal cord? What pierces the pia?
-Innermost layer, surrounds and adheres to spinal cord. Fibers of dorsal and ventral spinal roots pierce the pia.
How is the choroid plexus formed? Where is it located?
Formed by extensive network of infolded vascular capillaries, which are covered by vascular pia mater and connective tissue
-Located primarily in center of lateral and fourth ventricles.
How is CSF absorbed? Where are the structures involved?
CSF is absorbed through arachnoid granulations, which are one-way openings. Structures are dorsal along both sides of superior sagittal sinus.