Week 5 - CNS, External Features and Ventricles Flashcards
Name the three coverings of the CNS external to internal
- Dura Mater
- Arachnoid Mater
- Pia Mater
Name the spaces between the meningeal layers
- Extradural (Epidural)
- Subdural
- Subarachnoid
- Intracranial
Define ‘Meninges’
Connective tissue membranes that line the neurocranium and vertebral canal to enclose the nervous system.
What are the functions of the meninges?
- Protection of brain and spinal cord - keep brain in place within the skull
- Meninges support and accompany blood vessels to and from CNS tissue
- Channels CSF around the surfaces of the brain and spinal cord - providing buoyancy (reduces pressure on inferior brain tissue against base of skull)
What is a common viral/bacterial pathology seen relating directly to the meninges?
Meningitis (inflammation of the meninges).
If it becomes severe it may become encephalitis (inflammation of the brain).
How does spinal and cranial dura mater differ?
Spinal
- single layered
- consists of meningeal layer only
- does not form folds
- epidural space present
Cranial
- double layered
- consists of inner meningeal layer and outer endosteal layer
- forms folds, e.g. falx cerebri
- Epidural space only present in causes of pathology, i.e. epidural haemorrhage
What regions are covered by spinal dura?
Spinal dura extends from the foramen magnum to the lower border of S2 vertebrae
What is found within the epidural space?
Loose areolar tissue Semi-liquid (epidural) fat Internal vertebral venous plexus Lymphatics Nerve roots
What are the names and functions of the two dural layers?
Outer Endosteal layer
- attached to inner surface of cranial cavity
- conveys blood vessels and fibrous processes that pass into the cranial bones
Inner Meningeal layer
- completely envelops brain and around the spinal cord
- provides sheaths for the cranial nerves as they leave the CNS
Usually both fused together.
Inner layer comes away from outer layer to form dural folds.
Name the different dural folds (x4)
Falx Cerebri
Falx Cerebelli
Tentorium Cerebelli
Diaphragma Sellae
What is the falx cerebri and what is its function?
Largest dural fold
Sickle-shaped fold in the midline
Acts to separate the two cerebral hemispheres into right and left
What is the falx cerebelli and what is its function?
Vertical infolding that lies inferior to the tentorium cerebelli.
Acts to separate the two cerebellar hemispheres.
What is the tentorium cerebelli and what is its function?
Crescent-shaped and forms a roof over the posterior cranial fossa
Acts to separate the cerebrum and cerebellum
Also called tentorial inscisure or incisura tentorii.
What i the Tentorial Notch?
A gap in the tentorium cerebelli for the passage of the midbrain.
What is the diaphragma sellae and what is its function?
Smallest dural folding that covers the pituitary gland and sella turcica to form the roof.
Covers the pituitary gland except for a small opening for the stalk of the pituitary gland to pass through
What is the Trigeminal/Meckel’s cave?
A dural recess in the posteromedial portion of the middle cranial fossa.
Acts as a conduit for the trigeminal nerve (CNV) between the prepontine cistern and the cavernous sinus.
How are the dural sinuses formed?
When the two layers of dural mater split, where the inner layer forms the dural folds, spaces are formed. These spaces are filled with venous blood.
What are the main venous sinuses of the brain? Which are paired/unpaired?
(7 Paired/5 Unpaired)
Unpaired: Superior sagittal sinus Inferior sagittal sinus Straight sinus Occipital sinus Intercavernous sinus
Paired Transverse sinuses Sigmoid sinus Cavernous sinuses Superior (greater) petrosal sinuses Inferior (lesser) petrosal sinuses Sphenoparietal sinuses Basilar sinuses
Describe the arachnoid mater
Thin and delicate Transparent Avascular Impermeable Found under the dura mater Continuous with the brain Invests spinal cord loosely
What is the function of the subarachnoid space?
Space between arachnoid and pia mater.
Forms subarachnoid cisterns which are filled with circulating CSF.
Provides a pathway for circulation and absorption of CSF after release from 4th ventricle.
What are arachnoid villi?
Where the arachnoid herniates (protrudes) through small holes in the dura and into the venous sinuses.
Aggregation, seen in adults, are known as arachnoid granulations or Pacchionian bodies.
Define ‘Pia Mater’
A microscopically thin, highly vascularised membrane that closely invests the spinal cord and continues below the spinal cord as a thin thread-like prolongation - the filum terminale.
Very closely adhered to the cerebrum - making it indistinguishable without a microscope.
Define ‘Extradural space’
A potential space between the cranial bones and the endosteal (outer) layer of the dura.
Normally only appreciable when there is an underlying pathology, i.e. extradural haematoma
How might an extradural haematoma occur?
How would it look on a CT scan?
The middle meningeal artery (MMA) travels through the extradural space and underneath the pterion (weakest point of the skull).
If the skull is damaged there in trauma the vessel can be damaged leading to a collection of blood between the dura and cranium.
Egg shaped on CT scan
Define ‘Subdural space’
What is contained within the subdural space?
A potential space that exists between the dura and arachnoid mater, only existing in a pathological condition.
Contains lymph (in form of thin film of tissue fluid).
Nerves and vessels pierce the dura and arachnoid mater at the same place but never run along between the membranes.
How might a subdural haematoma occur?
How would it look on a CT scan?
Bridging veins which drain blood from the brain to the superior sagittal sinus if damaged may lead to a collection of blood in the subdural space.
Crescent shaped on CT scan
What is the Subarachnoid space? How does it differ?
Interval between arachnoid and pia mater.
Over gyri the arachnoid and pia mater are in close contact, whereas over sulci, triangular spaces develop due to the close adhering of the pia mater to the cerebral cortex.
At some points the arachnoid and pia mater are separated by wide intervals that communicate freely with each other - called subarachnoid cisterns.
What does the subarachnoid space contain?
Contains delicate connective tissue trabeculae and intercommunicating channels containing CSF. Providing a pathway for the circulation and absorption of CSF after release from 4th ventricle.
What is a collection of blood in the subarachnoid space called?
What does it look like in a CT scan?
An extra-axial intracranial haemorrhage
More central (depending on location of bleed) compared to extradural and subdural.
What is a common cause of an intracranial haematoma?
Bursting of an aneurysm
What is the ‘Filum Terminale’?
Contains a few nerve fibres considered to be the rudiments of 2nd, 3rd and 4th coccygeal nerves.
It is around 20cm long and mostly composed of non-nervous fibrous tissue (pia mater).
What is the function of the pia mater?
Forms part of the blood-brain-barrier (BBB).
Contains blood vessels
Invests the surface of the cerebrum to the depths of the deepest fissures and sulci, following the brain curvatures.
What is the lumbar cistern?
What clinical function does this have?
A pool of CSF that forms in the subarachnoid space around the filum terminale.
A lumbar puncture can be done around the level L3/4 to take out the CSF for analysis or where an epidural can be carried out for anaesthetic purposes.
Define Gyri (gyrus)
a convoluted ridge between anatomical grooves
Define Sulci (sulcus)
a shallow furrow on the surface of the brain separating adjacent convolutions
What is the central sulcus?
the sulcus that separates the frontal and parietal lobes
also separates the motor and sensory cortices
What is the lateral sulus/Sylvian fissure?
a deep fissure of the lateral aspect of each cerebral hemisphere that divides the temporal lobe from the parietal and frontal lobes
What are occipital poles?
an anatomical landmark corresponding to the posterior portion of the occipital lobe.
formed by the convergence of superior and inferior occipital gyri (the middle occipital gyrus also contributes when present)
What brain activity occurs at the occipital pole?
What Brodmann area is it related to?
Macular (central vision) as part of the primary visual cortex.
Brodmann area 17
What are the mammillary bodies?
What is the function of them?
two small, rounded bodies that project from the posterior hypothalamus.
receive input from the hippocampus via the fornix, and relay impulses to the anterior nuclei of the thalamus.
thought to play a role in memory