Lecture 2: Meninges & Orbit Flashcards
What are meninges?
Meninges, singular meninx, three membranous envelopes—pia mater, arachnoid, and dura mater—that surround the brain and spinal cord.
Cerebrospinal fluid fills the ventricles of the brain and the space between the pia mater and the arachnoid. The primary function of the meninges and of the cerebrospinal fluid is to protect the central nervous system.
What are the layers of the meninges?
1) Dura Mater
2) Arachnoid Mater
3) Pia Mater
Name the 2 layers of the Cranial Dura Mater
2 Layers
1) periosteal layer (outer)
- attaches to the bony structures
2) meningeal layer (inner)
What is a major difference between Cranial dura mater and the dura mater in the Spinal Cord?
Only 1 layer of dura mater (meningial layer) exists in the spinal cord, whilst 2 exist in the cranium
The periosteal layer (outer layer) goes out and seals the skull.
What are the Dural partitions formed by the Dura Mater?
Dural partitions formed by the dura mater project inward and incompletely subdivide the cranial cavity.
Dural partitions are named falx cerebri (1), falx cerebeli (2), tentorium cerebeli (3) and diaphragma sellae (4).
- Falx cerebri: downward projection, passes between two cerebral hemispheres.
- Tentorium cerebelli: horizontal projection, separates cerebellum in posterior cranial fossa from posterior parts of cerebral hemispheres; in midline there is an oval opening called tentorial notch, where midbrain passes.
- Falx cerebelli: small midline projection in posterior cranial fossa, runs between two cerebellar hemispheres.
- Diaphragma sellae: small horizontal shelf at the sphenoid bone, opening in centre which infundibulum (connects pituitary gland) and accompanying blood vessels pass.
1) Dura partitions - partial partitions (e.g. falx cerebri, falx cerebelli, tentorium cerebelli)
2) Infundibulum
3) Diaphragma sellae
The infundibulum and the diaphragma sellae sits on top of the pituitary gland.
Name the different Dura partitions
Falx Cerebri (separate cerebrum)
Falx Cerebelli (separate cerebelium)
Tentorium Cerebelli (cerebrum and cerebellum)
Where are the meningial arteries? What is it’s significance?
Between the periosteal layer (outer) and the bony parts of the skull, there are meningial arteries . (Some textbooks say they run between the dura mater)
If they burst, can cause intracranial haemorrhage.
The blood supply of the Dura Mater mainly comes from _______. This artery goes into the skull via the ____________.
The middle meningial artery (majority)
It runs through the foramen spinosum to supply the dura mater (the outermost meninges) and the calvaria.
Where can you find the middle meningeal artery?
Behind the pterion
What arteries supply the anterior part of the meninges?
Anterior part of the middle meningial artery + Anterior meningial artery from the ethmoidal arteries.
What nerve innervates the dura mater?
Trigminal Nerve (V1, 2, 3)
X
C1 C2 C3
Describe the Intracranial Sinus Structures
The intracranial venous structures are running in between the partitions.
Superior sagittal sinus is a venous structure running at the top of the falx cerebrei.
Inferior saggital sinus runs along the lower boarder of the falx cerebrei.
It drains into the Straight Sinus
Straight Sinus meets the Superior sagittal sinus at the confluence of sinuses
Left and Right Transverse Sinus
Cavernous Sinus
These sinuses form the jugular vein.
The only way bacteria/virus can get into the brain is via The Opthalmic vein (which drains to Cvernous sinus)
What is the name of the sinus at the top and middle of the brain/
Superior sagittal sinus
What is the only way virus/bacteria can get into the brain?
VEINS
Opthalmic vein- draining into the cavernous sinus
Emissary vein
What structures are associated with cavernous sinus? (differentiate between what runs in and around the wall of cavernous sinus)
Around the wall:
1) III
2) IV
3) V (1 and 2)
Inside
4) VI
5) Intnernal carotid artery
If someone comes in looking like this, what should you be careful of? (Perioribital cellulitis)
Cavernous Sinus Thrombosis and then Meningitis
What are some symptoms that may be indicative of Cavernous Sinus Thrombosis/Meningitis?
1) Periorobital cellulitis
2) Racoon eyes (accumulation of blood at the base of the skull fracture)
Describe Raccoon Eyes
Accumulation of blood due to a skull fracture.
Periosteum seals the blood in.
If you have a fracture through the periosteal layer, blood can accumulate in the potential space by the eyelid between the muscle and the skin.
The skin and subcutaneous tissue of the
eyelids are not particularly substantial.
The thin subcutaneous tissue is a
potential space, which accumulates
fluid (blood) after injury to the eyes
(image).
The cranial meninges are
continuous with, and similar to
the spinal meninges through the
_____________
The cranial meninges are
continuous with, and similar to
the spinal meninges through the
foramen magnum,
The two layers of dura
separate from each other at
numerous locations to form
two unique types of
structures:
The two layers of dura
separate from each other at
numerous locations to form
two unique types of
structures: intracranial venous
structuresanddural partitions, which proj ectinward and incompletely
separate parts of the brain, and
What is the clinical signifcance of Emissary Veins?
If you have a skull fracture and the skull is exposed to dirty water, you need to start on antibiotics. This is because of the Emissary Vein- which allows bacteria to travel into the meninges.
Emissary Vein runs between the skull and the sinuses
Describe the Venous Drainage of the brain
Cerebral veins drain into the sinuses (runs in the arachnoid layer)
Diploic veins and Emissary veins also exist (Communicate between inside and outside of the skull)
Emissary Vein runs between the skull and the sinuses
This begins internally as networks of
small venous channels to larger veins
{cerebellar veins (1)} and the larger
veins drain into dural venous sinuses
(2) and eventually to the internal
jugular veins.
Other veins that also empty into the
dural venous sinuses are diploic veins
(3) (these run between the internal and
external tables of compact bone) and
emissary veins (4) (these run between
the outside of the cranial cavity and the
dural venous sinuses).
Cerebral (on the left) veins perforate the meningial layer.
What is the Arachnoid Mater
1) Avascular membrane
2) Have Trabeculae
3) Subarachnoid space
4) Does not enter grooves or fissures (except for the Longitudinal fissure)
5) Arachnoid granulations (green puffy things that go into the Saggittal sinus)
(green)
The arachnoid mater is a thin, avascular membrane that
lines the inner surface of the dura mater. It does not enter
the grooves or fissures of the brain, except for the
longitudinal fissure between the two cerebral hemispheres.
Describe the Pia Mater
1) Invests the surface of brain
(red)
Label
1) Pia mater
2) Arachnoid mater
3) Dura mater
4) Cerebral artery
5) Arachnoid granulations
6) Superior sagittal sinus
7) Cerebral veins
8) Subarachnoid space
Label
1) Oculomotor nerve (III)
2) Internal carotid artery
3) Trochloear Nerve (IV)
4) Abducent nerve (VI)
5) Opthalmic division of trigeminal nerve (V1)
6) Maxillary division of trigeminal nerve (V2)
Label
The dural partitions formed by the dura mater project inward and incompletely subdivide the
cranial cavity. The dural partitions are named; falx cerebri
(1), falx cerebeli (2), tentorium
cerebeli (3) and diaphragma sellae (4).
Name the 3 types of Intracranial haemorrhage
1) extradural haemorrhage
2) subdural haemorrhage
3) subarachnoid haemorrhage
Describe the extradural haemorrhage
An extradural haemorrhage
(epidural haemorrhage) is arterial
origin, classically from a torn branch of
the middle meningeal artery in the
temporoparietal region.
It is almost
always associated with a skull fracture.
The blood collects between the
calvarium and Periosteal layer of the dura mater.
Describe the subdural haemorrhage
2) A subdural haemorrhage forms
between periosteal and the menangial layer of the dura mater.
It requires
relatively little force to expand this
space.
Damage to cerebral veins that
cross this space from the brain to the
superior sagittal sinus can cause this
bleed, particularly in individuals with
cerebral atrophy or on anticoagulants.
Chronic subdural haemorrhage is most
common but an acute bleed may follow
high velocity trauma.
Describe the Subarachnoid Haemorrhage
3) A subarachnoid haemorrhage is a bleed into the
* *subarachnoid space.**
It is usually arterial bleeding from a
ruptured cerebral artery aneurysm of the circle of Willis.
Subarachnoid haemorrhage may also be associated with
an intracerebral bleed. It causes sudden s_evere headache,
vomiting and frequently loss of consciousness_
Label
1) Sigmoid sinus
2) Inferior Saggital Sinus
3) Superior Saggital Sinus
4) Straight Sinus
5) Confluence of sinuses
6) Right transverse sinus
7) Great cerebral vein
8) Superior petrosal sinus
9) Cavernous sinus
Label
A) Middle meningeal artery (anterior)
B) Pterion
C) Middle meningeal artery (posterior)
Label
1) Palatine bone
2) Ethmoid bone
3) Lacrimal bone
4) Maxilla
5) Zygomatic Bone
6) Frontal bone
7) Greater wing of sphenoid
Label
1) Skin
2) Subcutaneous tissue
3) Orbicularis oculi muscle
4) Orbital septum (extension of periosteal layer)
5) Conjunctiva
6) Tarsus
The periosteum extends and becomes the …(4)
Orbital septum (joined - periorbita and periosteum)
Periorbita
Common Tendinous ring
Periosteum
Describe the Orbicularis Oculi
2 Parts
1) Orbital part
2) Palpebral part
The orbicalris oculi allow us to forcibly close our eyes
The voluntary muscle of the eyelids
(palpebral part (1) of the orbicularis
oculi) is innervated by the facial nerve
(frontotemporal branch).
Any damage to
the nerve results in the inability to close
or blink the ipsilateral upper eyelid and
the lower eyelid droops away. This is
associated with corneal ulcers and
spillage of tears.
Name the structures around the orbital septum
1) Orbicularis oculi
2) Orbital septum
3) Tarsus
4) Levator palpabrae superioris
5) Superior tarsal muscle
What is the tarsus?
Protects our eyeball
It also has glands in it (Tarsal gland) it has a canal that secretes oily stuff that decreases ther rate of evaporation to keep the eye moist (avoid dry eye).
What is the levator palpebrae superioris muscle innervated by?
Innervated by cranial nerve number 3 (occulomotor)
What is the superior tarsal muscle innervated by?
Sympathetic nerve fibres
What muscles must be damaged for you to get this symptom?
Ptosis (drooping of the eye)
Two muscles associated with the tarsus raise
the eyelid; namely the levator palpebral
superioris muscle (LPS) (2) and the superior
tarsal muscle (ST) (3).
LPS is innervated by the occulomotor nerve.
ST is innervated by postganglionic
sympathetic fibres from the superior cervical
ganglion.
Loss of function of either of these muscles
results in falling of the upper eyelid; namely
complete (LPS) or partial ptosis (ST).
What is the common tendinous ring?
The common tendinous ring (A) is a _thickening of the
periosteum (periorbita)_in the posterior part of the orbit
around the optic canal and the central part of the superior
orbital fissure.
The ring is also the point of origin of the extraocular
muscles (superior, inferior, lateral and medial rectus).
What structures make up the lacrimal apparatus
Lacrimal gland
Lacrimal canaliculi
Lacrimal sac
Nasolacrimal duct
Describe how tears are formed and then comes out of your nose.
1) Lacrimal gland produces tears
2) The tear accumulates at the medial ledge. Here there is a Puncta. These take tears out of your eyes and drain them into Lacrimal canaliculi
3) Tears go into the Lacrimal sac
4) Then into the nasolacrimal duct and then to your nose.
Describe the divisions of the Ophthalmic nerve (CN V1)
V1 supplies the frontal part of your eyeball, forehead and uppereylid
Branches:
- Lacrimal n.: lacrimal gland, conjunctiva, lateral part of upper eyelid.
- _Frontal n.(_supratrochlear, supra-orbital branch): conjunctiva, upper eyelid skin, lower medial forehead skin, middle scalp
-
Nasociliary n.: communicates with ciliary ganglion.
- Parasympathetic ganglion. The postganglionic axons run in the short ciliary nerves and innervate two eye muscles:
- the sphincter pupillae constricts the pupil, a movement known as Miosis. The opposite, Mydriasis, is the dilation of the pupil.
- the ciliaris contracts, releasing tension on the Zonular Fibers, making the lens more convex, also known as accommodation.
- Parasympathetic ganglion. The postganglionic axons run in the short ciliary nerves and innervate two eye muscles:
- After arising from the trigeminal ganglion, the ophthalmic nerve travels laterally to the cavernous sinus and gives rise to the r_ecurrent tentorial branch_ (which supplies the tentorium cerebelli).
- The nerve then then exits the cranium via the superior orbital fissure, where it divides into its three main branches:
- Frontal nerve
- Lacrimal nerve
- Nasociliary nerve
- These three branches provide sensory innervation to the skin and mucous membranes of the structures derived from the frontonasal prominence
What are venous sinuses?
The dural venous sinuses are endothelial-lined spaces between the o_uter periosteal dura mater laye_r and the _inner meningeal dura mater laye_r (intracranial venous structures).
What are the different periosteal layers?
- Periorbita: periosteum that is within orbit, posterior part forms common tendinous ring.
-
Dura mater: periosteum of dura mater within skull/cranial cavity.
- When the periosteal layer of the dura mater comes into the orbit, the foramen it came through is sealed. This is to prevent infection of the eye/orbit from moving into the cranium.
- So the periosteum is always thickened at every foramen, sealing the cranium from the outside.
- Periosteum: outside the orbit, a t_hin layer covering the skull_ (continuation of dura)
- Orbital septum: where periorbita and periosteum meet each other and extend downward to eyeball. Keeps our eye safe, first line of defense
