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
Where is the hypothalamus found?
What is the function of the hypothalamus?
a basal part of the diencephalon that lies beneath the thalamus on each side.
forms the floor of the 3rd ventricle and includes vital autonomic regulatory centres.
What is the function of the frontal lobe?
- controls voluntary movement
- attention
short term memory tasks - motivation
- planning
What is the blood supply to the frontal lobe?
Anterior Cerebral a. - to the medial surface
Medial Cerebral a. - the the lateral surface
What is the function of the parietal lobe?
- perception and processing of sensory information
- integrates proprioceptive and mechnoceptive stimuli
- language processing
What is the blood supply of the parietal lobe?
branches of the Anterior and Posterior Cerebral arteries - medial surface
branches of the Middle Cerebral a. - lateral surface
What is the function of the occipital lobe?
it is the centre for visual processing
What is the blood supply of the occipital lobe?
branches of the Posterior Cerebral a.
What is the function of the temporal lobe?
- decoding sensory inputs into derived meanings for retention of visual memory and language comprehension
- middle temporal gyrus associated with perception of movement within visual field
- inferior temporal gyrus contains Fusiform Face Area (FFA) which is necessary for face recognition
What is the blood supply of the temporal lobe?
branches of the Middle Cerebral a. - lateral surface
branches of Posterior Cerebral a. - inferior surface
What is the function of the insular lobe?
processing and integration of:
- taste sensation
- visceral sensation
- pain sensation
- vestibular functions
What is the function of the limbic lobe?
- modulation of emotions
- modulation of visceral and autonomic functions
- modulation of hormone function
- learning
- memory
What is the function of the cerebellum?
- motor learning
- coordination
- precision of motor function
What does cerebellum degeneration cause?
cerebellar disorders of walking, body tremors nad limb jerkiness
What is the blood supply to the cerebellum?
Superior Cerebellar a.
Anterior Inferior Cerebellar a.
Posterior Inferior Cerebellar a.
What is the function of the brainstem?
Vital functions
- sleep-wake cycle
- consciousness
- respiratory rate
- heart rate
What is the blood supply of the brainstem?
Anterior and Posterior Inferior Cerebellar arteries
Anterior Spinal a.
Pontine branches of Basilar a.
Perforating arteries
How many lobes make up the cerebellum? What are they?
3 main lobes
- Anterior
- Posterior
- Flocculonodular
How many lobules make up the cerebellum?
9 central lobules
5 hemispheric lobules
What are the 9 central lobules? What is the mnemonic to remember them?
Central lobules part of the vermis
Loving Caring Children Donate Food To Poor Unfed Needy
L - Lingula C - Central C - Culmen D - Declive F - Folium T - Tuber P - Pyramid U - Uvula N - Nodule
What are the 5 central lobules? Where are they located?
Horizonal lobules part of the lobes
- Quadrangular - anterior to primary fissure
- Simple - between primary and postlunate fissures
- Superior Semilunar - from postlunate fissure to horizontal fissure
- Inferior Semilunar Lobule - from horizontal fissure onto inferior surface of cerebellum
- Biventer Lobule - bordered by retrotonsillar fissure (anteriorly) and postlunate fissure on inferior surface (posteriorly)
What are the cerebellar tonsils?
characteristic feature of the inferior surface of the posterior lobe.
triangular structures that border the distal inferior vermis
What is the pathway created by the superior cerebellar peduncle?
- connects cerebellum and midbrain
- nerve fibres from cerebellar nuclei to thalamus
- fastigial fibres send information of vestibular nuclei
- impulses enger cerebellum from ventral spinocerebellar tract (proprioception), trigeminal nucleus and locus coeruleus
What is the pathway created by the middle cerebellar peduncle?
- connects cerebellum and pons
- pathway for afferent pontocerebellar fibres to enter the neocerebellum
What is the pathway created by the inferior cerebellar peduncle?
- connects cerebellum to medulla oblongata
- carries dorsal spinocerebellar, olivocerebllar and cuneocerebellar fibres
- restiform body carries only afferent fibres
- jextarestiform body carries both afferent (vestibulocerebellar) and effert (cerebellovestibular) fibres.
Where is the flocculonodular lobe located?
a flattened lobe that lies between the posteriolateral fissure (inferiorly) and the inferior medullary velum and cerebellar peduncles (superiorly)
- What is a lesion in the posterior lobe of the cerebellum called?
- What are the causes?
- Neocerebellar lobe
2. Vascular, e.g. stroke; tumours; neurodegenerative
What are the symptoms?
What is the mnemonic to remember it?
DANISH
D - Dysmetria (lack of coordinated movement) Dysdiadochokinesia (inability to perform rapid alternating movements)
A - Ataxia (full loss of control of body movements)
N - Nystagmus (rapid involuntary movements of the eyes)
I - Intention Tremor (tremor occuring when trying to carry out a precise movement or action)
S - Slurred Speech
H - Hypotonia (also called Floppy Baby Syndrome) (state of low muscle tone)
- What is a lesion in the anterior lobe of the cerebellum called?
- What are the causes?
- What are the symptoms?
- Gait/Limbic Ataxia
- alcohol; malnutrition (often see improved symptoms if stop drinking)
- drunken gait, can’t walk straight; head tremor
- What does a midline lesion of the cerebellum cause?
- What are the causes?
- What are the symptoms?
- Truncal Ataxia
- Medulloblastoma in 4th ventricle - young children. Affects the vestibular nerve.
- fall towards most affected side; may involve eye movements
What are subarachnoid cisterns?
areas where CSF accumulates due to space between the arachnoid and pia maters.
expanded areas filled with CSF are known as cisterns.
they have multiple openings.
- Where is the cerebellomedullary cistern/cisterna magna located?
- What is its role in CSF flow?
- What does it contain?
- largest cistern located between the medulla anteriorly and cerebellum posteriorly
- the cistern receives CSF from the 4th ventricle via the median and lateral apertures
- Contains:
- vertebral aa.
- glossopharyngeal n. (CNIX)
- vagus n. (CNX)
- accessory n. (CNXI)
- choroid plexus - produces CSF
- Where is the pontine cistern located?
2. What does it contain?
- anterior to the pons
- Contains:
- basilar a.
- abducens n. (CNVI)
- anterior inferior cerebellar a.
- superior cerebellar aa.
- Where is the chiasmatic/suprasellar cistern located?
2. What does it contain?
- located above the sella turcica and below the hypothalamus. anterior to interpeduncular cistern, surrounds pituitary infundibulum and optic chiasm
- Contains:
- optic chiasm
- pituitary stalk
- Where is the interpeduncular cistern located?
2. What does it contain?
- relatively wide and cone-shaped cistern occupying the interpeduncular fossa. found between the cerebral peduncles
- Contains:
- bifurcation of basilar a.
- posterior cerebral aa.
- superior cerebellar aa.
- oculomotor n. (CNIII)
- mammillary bodies
- Where is the ambient cistern located?
2. What does it contain?
- between the splenium of corpus callosum and upper surface of cerebellum (dorsal to midbrain). cistern extends posterolaterally to midbrain
- Contains:
- trochlear n (CNIV)
- posterior cerebral aa. (3rd portion)
- superior cerebellar aa. (3rd portion)
- Where is the crural cistern located?
2. What does it contain?
- surrounding the ventrolateral aspect of the midbrain between the parahippocampal gyrus/uncus of temporal lobe and the cerebral peduncle
- Contains:
- cisternal segment of anterior choroidal a.
- Where is the carotid cistern located?
2. What does it contain?
- anterior to the crural cistern between internal carotid a. and ipsilateral optic nerve (CNII)
- Contains:
- posterior communicating a. (1st part)
- internal carotid a.
- Where is the insular/Sylvian cistern located?
2. What does it contain?
- located between temporal lobes and frontal lobes. deep part of Sylvian fissure
- Contains:
- middle cerebral a.
- Where is the cerebellopontine cistern located?
2. What does it contain?
- lateral to pons at the cerebellopontine angle
- Contains:
- facial n. (CNVII)
- vestibulocochlear n. (CNVIII)
- trigeminal n. (CNV)
- posterior inferior cerebellar aa.
- Where is the cistern of the lamina terminalis located?
2. What does it contain?
- found in the shape of a high-top tent, superior to suprasellar cistern, anterior to anterior wall of 3rd ventricle
- Contains:
- anterior cerebral aa.
- anterior communicating a.
- arteries to the hypothalamus
Where is the cistern of the velum interpositum found?
between layers of tela choroidea in the roof of the 3rd ventricle
- Where is the quadrigeminal cistern found?
2. What does it contain?
- between colliculi, splenium of the corpus callosum and superior surface of the cerebellum
- Contains:
- posterior cerebral aa.
- posterior choroidal aa.
- superior cerebellar aa.
- trochlear n. (CNIV)
- venous confluence at junction of vein of Galen, inferior sagittal sinus and straight sinus
Where is the superior cerebellar cistern found?
posterior to the quadrigeminal cistern, between the superior surface of cerebellum and tentorium
Summarise the production, circulation and drainage of CSF
- CSF actively secreted by choroid plexus of lateral ventricles
- CSF flows through interventricular foramina/Foramen of Monro passing into the 3rd ventricle
- CSF produced by choroid plexus in the roof of 3rd ventricle
- CSF flows down the cerebral aqueduct to the 4th ventricle
- CSf produced in the roof of the 4th ventricle
- CSF flows from 4th ventricle either into cerebellomedullary cistern or straight into the central spinal canal
- From the cerebellomedullary cistern, the CSF flows out of the two lateral apertures or one median aperture
- CSF fills and circulates around the subarachnoid space, bathing the external surfaces of the brain
- At arachnoid villi, CSF is reabsorbed into the venous blood of the dural venous sinuses
What is another name for the lateral and median apertures?
Lateral - Foraman of Luschka
Median - Foramen of Magendie
What is the production rate of CSF?
CSF is constantly produced at a secretion rate of 0.35-0.4ml/min
What are the two anterior protrusions of the 3rd ventricle?
Supro-optic recess - located above the optic chiasm
Infundibular recess - located above the optic stalk
Where is the 3rd ventricle located?
between the right and left thalamus
Where is the 4th ventricle located?
posterior of the junction between the pons and medulla oblongata
What is the function of the arachnoid villi?
they provide a valvular mechanism for flow of CSF into the bloodstream without permitting backflow of blood into the CSF
What are the two types of hydrocephalus?
- Non-communicating - obstruction of flow, i.e. congenital abnormalities ; tumours or traumatic lesions that obstruct the interventricular pathway
- Communicating - obstruction in the cisterns or dural sinuses leading to CSF accumulation
What is Encephalomegaly?
An enlarged head that occurs in babies with hydrocephalus before fusion of the fontanelles
What happens if hydrocephalus isn’t treated?
enlarged ventricles
compression of brain tissue - pathological presentation depends on what nuclei/nerves are compressed by excess CSF
eventually lead to herniation and coning
What are the common symptoms of hydrocephalus?
headaches vomiting nausea blurred vision difficulty walking
How is hydrocephalus diagnosed?
CT/MRI
ultrasound (pre-birth)
lumbar puncture
How is hydrocephalus treated? How does it work?
Shunt surgery - tube implanted in the brain to allow excess CSF to flow through the shunt to another part of the body where it can be absorbed into the blood.
ETV (endoscopic third ventriculostomy) - surgeon makes a hole in the floor of 3rd ventricle to allow CSF to escape to the brain surface into the interpeduncular cistern where it can be absorbed
What is the 3 types of shunts used in treating hydrocephalus?
- ventriculo-peritoneal or lumbo-peritoneal shunt (drains into abdomen)
- ventriculo-leural shunt (drains into lung)
- ventriculo-atrial shunt (drains into heart)
What is the ventricular system embryologically derived from?
the lumen of the neural tube
What cells produce cerebrospinal fluid
Ependymal cells of the choroid plexus
What is the arterial blood supply to the choroid plexus?
Lateral and 3rd ventricle
- internal carotid a.
- choroidal branches of the posterior cerebral a.
4th ventricle
- inferior cerebellar aa.
