Lecture 2: Meninges, ventricular system and arterial blood supply Flashcards
Arachnoid mater
delicate transparent membrane (NOT dipping into the
sulci)
• connected to the pia mater by fine strands of connective tissue (arachnoid trabecula)
Subarachnoid space
Between the arachnoid mater and pia mater
• Wide space, filled with CSF - watery “cushion”
• Contains blood vessels (poorly protected) - with force will damage and get bleeding
• Bleeding results in blood in the CSF
(subarachnoid haemorrhage)
What does CSF help with
stops the brain from hitting the skull, cushioning, prevents nerve cell damage
Arachnoid Villi
knoblike projections of the arachnoid mater
particularly located at the top, midline
Arachnoid granulations
aggregations of arachnoid villi
drain CSF that is sitting in the subarachnoid space into venous sinuses
Cistern =
enlarged subarachnoid space
List of the major cisterns
Interpeduncular cistern - anterior
Pontine cistern - in front of pons
Superior cistern
Cerebellomedullary cistern (cisterna magna) - biggest cistern that we have
pia mater
gentle mother
Delicate membrane, follows contours of brain i.e. it goes into the sulci
Surrounds blood vessels (since it follows contours)
Sends prolongations into brain tissue along with blood
vessels (forming perivascular space)
Helps form the roof of the ventricles, closely associated with choroid plexus and ependyma
Spinal meninges
all the same except that there is no dural periosteal layer, there is only the meningeal layer
no two layers of dura in the spinal cord because otherwise would anchor spinal cord too much because the spinal requires a much greater degree of flexion and extension
Epidural space
- Between spinal dural sheath and vertebral bony wall
* Contains fat tissue (acts like cushion and protects the spinal cord) & venous plexus
Where is the epidural space largest?
Largest at L2
Epidural anaesthesia
Inject into epidural space and everything inferior to it goes numb
Subarachnoid space in the spin
- Between the arachnoid and pia mater meninges
* Contains CSF
Lumbar cistern
Inferior to spinal cord (below L2)
Lumbar puncture - sampling of the CSF. Monitor inflammation such as whether there are immune cells.
Spinal pia mater makes up
denticulate ligament and filum terminal
Denticulate ligament
fine membrane
support spinal cord with dural sheath - provides lateral support to spinal cord
filum terminale
strand of Pia mater, vertical support
Meningitis
- characterized by inflammation of the pia-arachnoid
- the most common infection of the CNS
- usually caused by a bacterium or a virus
Common symptoms of meningitis
common symptoms: fever, headache, vomiting and stiff neck
Diagnosis of meningitis
diagnosis: performing a lumbar puncture examining the CSF
Treatment of meningitis
treatment: antibiotics quickly, to prevent infection spreading across pia mater to injure neurons in brain (injures neurons if it is not dealt with quickly)
if infection is not prevented then also hydrocephalus, deafness etc can be caused
Ventricular system
there are 4 ventricles - lateral (2), third, fourth
contain CSF
lateral ventricles have one on either side
cerebral aqueduct and inter ventricular foramen and lateral apertures allow form communication and continuity
Cerebral aqueduct
connects the third and fourth ventricle
inter ventricular foramen
The interventricular foramina connect the lateral ventricles to the third ventricle. This allows cerebrospinal fluid produced in the lateral ventricles to reach the third ventricle and then the rest of the brain’s ventricular system.
lateral aperture
exit hole, two of them, open into cisterna magna
Lateral ventricles
anterior horn goes into the frontal lobe, inferior horn goes into the temporal lobe, posterior horn goes into the occipital lobe
i.e. there is a body and three horns
in the lateral ventricles there is choriod plexus which is generating CSF = body and inferior horn
where is the choroid plexus located in the lateral ventricles?
body and the inferior horn
what is choroid plexus?
a secretory tissue found in each of the brain ventricles, the main function of which is to produce cerebrospinal fluid (CSF)
Third ventricle
Between lateral ventricle and cerebral aqueduct
Choroid plexus in roof
narrow cavity in comparison to lateral ventricles
Where is the choroid plexus located in the third ventricle?
Choroid plexus in roof
Fourth ventricle
Lying between cerebellum - pons & medulla •
Three openings
2 lateral apertures (foramina of Luschka) - allow CSF to flow out
1 median aperture (foramen of Magendie)
roof formed by superior medullar velum and inferior medullary velum (choroid plexus) and floor is formed by the brainstem
Where is the choroid plexus located in the fourth ventricle?
Roof which is formed by the superior medullary velum and the inferior medullary velum DOUBLE CHECK THIS
Cerebrospinal fluid (CSF)
• Clear liquid produced by choroid plexus in each ventricle
• Fills cerebral ventricles and spinal canal, as well as the subarachnoid space
• Brain produces & absorbs about 500 mL/day
• Drained into venous sinus through the arachnoid
granulations
• Functions - buoyancy, protection, chemical stability
• Sampling of CSF - lumbar puncture
How much CSF does the brain produce and absorb a day?
500mL/day (shows how active the system is)
Functions of the CSF
• Functions -
buoyancy - pool of water, to support brain, decreases the weight of the brain by 97%
protection - cushioning
chemical stability - enables the brain to maintain chemical homeostasis
Flow of CSF
Producing and absorbing 500 ml/day so the CSF must flow….the flow is …the CSF is produced in the lateral ventricle and then it goes fro the lateral ventricle via the inter ventricular foramen into the third ventricle and then it goes from the third ventricle via the cerebral aqueduct to the fourth ventricle. Once it gets to the 4th ventricle it needs to exit via the median aperture and it also goes down the spinal canal if the spinal cord and exits out the inferior end, so when it comes out the median aperture it circles around the cerebellum up and up and up to the arachnoid granulations and then goes via the arachnoid granulation into the superior Sagittal sinus into the venous system/venous drainage and then it drains out back to the heart
Blood-brain barrier
formed by the tight junctions between endothelial cells of cerebral capillaries
CSF and BBB not related
BBB is about capillaries
• selective for nutrients (glucose, essential amino acids & electrolytes)…. keeps out certain chemicals and drugs ……
A protective mechanism to maintain a stable environment for the brain
• ineffective against fats, fatty acids, O2, CO2 and fat-soluble molecules —> alcohol, nicotine & anaesthetics can affect the brain
BBB is selective for
• selective for nutrients (glucose, essential amino acids & electrolytes)
• keeps out certain chemicals and drugs ……
A protective mechanism to maintain a stable environment for the brain
BBB is ineffective for
• ineffective against fats, fatty acids, O2, CO2 and fat-soluble molecules —> alcohol, nicotine & anaesthetics can affect the brain
Hydroencephalus
characterised by an excessive amount of CSF in the ventricular system (too much CSF on the brain)
• due to increased production of the fluid, or disturbances (blockages) in its circulation
or in absorption into the venous sinus
• enlarged head in newborn baby (because the skull bones have not yet fused) - so brain just gets bigger, when bones fuse there is a fixed space therefore pressure increases resulting in nerve cells dying and being damaged therefore less capable people as a result of this
• gradual ventricular dilation with compression and thinning of brain tissue in older children and adults
clinically treat with shunts for example
Summary of the CSF flow
CSF from choroid plexus goes through the ventricular system and then out to the superior sagittal sinus
Arterial blood supply of the brain
• Brain constitutes only 2% of body weight, but
receives 15% of blood flow (about 750 mL/min)
• Brain consumes 20% of body’s oxygen and
glucose
10 second interruption to blood flow can cause
unconsciousness
1-2 minute interruption to blood flow can cause
impaired neural function
4 minute interruption to blood flow can cause
irreversible brain damage
Common carotid artery
splits into external and internal carotid artery
Internal carotid artery and vertebral arty are
important for supplying the brain with blood
external carotid artery
supplies face and outside of skull
Cerebral arteries list
internal carotid arteries (more anterior when looking at cerebrum inferiorly) Basilar artery Vertebral arteries (2) - on base of brain, join together, go up then horizontal, come together to form basilar
The basilar artery divides into
two posterior cerebral arteries
the internal carotid artery branches into
anterior and middle cerebral arteries
how many cerebral parties are there in total
3 - anterior, middle, posterior (2)
Circle of willis
Basilar artery connects to internal carotid artery via posterior communicating arteries, helping to form the Circle of Willis
To maintain blood supply to entire brain if 1 main artery in Circle is blocked or narrow - safety mechanism
Classic anatomy seen in ~33% of people - there is variation in the circle of willis
Flow of the circle of willis
Basilar artery connects to the internal carotid artery by the posterior communicating arteries which forms part of the circle of Willis and then there is also anterior communicating arteries that is joining the anterior cerebral arteries to form the circle
Posterior cerebral artery supplies …
supplies the medial aspect of the hemisphere (posterior 1/3), occipital lobes, inferior temporal lobe regions, brainstem, 3rd and lateral ventricles
Middle cerebral artery supplies …
Supplies almost all of the lateral surface of cerebral hemispheres
Anterior cerebral artery supplies …
supplies the medial aspect of cerebral hemispheres (anterior 2/3 only) and basal nuclei
Stroke
- refers to the neurological dysfunction that results from a reduction of blood supply to the brain
- due to blockage of a cerebral artery (or vein) leading to cerebral infarction, or haemorrhage from an artery (or vein) (normally a cerebral artery rather than a vein)
- usually caused by an occlusion of a vessel by blood clot or cholesterol deposit or bleeding from a ruptured vessel
- The neurological signs and syndromes associated with a stroke depend on which blood vessels and their branches are involved.
Occlusion of anterior cerebral artery
- contralateral hemiplegia (one artery) or bilateral paralysis (two arteries) & impaired sensation
• greatest in the lower limb
occlusion of middle cerebral artery
- a severe contralateral hemiplegia (paralysis of one side of the body.) & impaired sensation
• most marked in the upper limb & face - severe aphasia (if the dominant hemisphere is affected)
occlusion of posterior cerebral artery
contralateral homonymous hemianopsia - vision impaired on opposite side to the stroke
Anterior cerebral artery neurons innervating
lower limb
Middle cerebral artery neurons innervating
upper limb and face (lateral side of the gyri)
Primary motor cortex =
precentral gyrus
primary sensory cortex =
post central gyrus
Lateral side of homounculus
face and upper limb
medial side of homunculus
lower limb - in sensory also the genitals
