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Term Paper on Cranial Cavity

Term Paper Contents:

  1. Term Paper on the Bony Features of Cranial Cavity
  2. Term Paper on the Contents of Cranial Cavity
  3. Term Paper on the Duramater or Patchy Meninx
  4. Term Paper on the Hypophysis Cerebri (Pituitary Gland)
  5. Term Paper on the Internal Carotid Artery

Term Paper # 1. Bony Features of Cranial Cavity:

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This is a bony highest placed cavity of the body con­taining vital organs like brain enclosed in tough membranous coverings – called meninges. The cranium protects these vital structures and is formed by bones.

Bony Features:

Out of 22 bones of skull 8 bones take part in formation of cranial cavity.

A. Frontal – 1

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B. Parietal – 2

C. Occipital – 1

D. Temporal – 1

E. Sphenoid – 1

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F. Ethmoid – 1.

For descriptive purpose we divide cranial cavity into:

I. Skull Cap or Calvaria:

This forms roof of cranial cavity.

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II. Internal Surface of Base of Skull:

This forms lateral wall and floor of cavity.

Term Paper # 2. Contents of Cranial Cavity:

Cranial cavity contains:

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1. Brain with meninges.

2. Venous dural sinuses.

3. Arteries:

(a) Internal carotid arteries

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(b) Vertebral arteries

(c) Middle meningeal arteries

(d) Accessory meningeal arteries.

4. Roots of 12 cranial nerves and their meningeal branches.

5. Four petrosal nerves:

(a) Deep petrosal nerve

(b) Greater petrosal nerve

(c) Lesser petrosal nerve

(d) External petrosal nerve.

Cranial Fossae:

The interior of the base of skull is divided into three fossae:

1. Anterior cranial fossa

2. Middle cranial fossa

3. Posterior cranial fossa.

They are arranged above downwards.

I. Anterior Cranial Fossa:

It is the highest among the cranial fossae.

Boundaries:

Anterior and sides – Frontal bone.

Posterior – Lesser wing and body of sphenoid bone.

Lesser wing projects postero medially to form the anterior clinoid process.

Floor:

1. Orbital plate of frontal bone.

2. Cribriform plate of ethmoid bone.

3. Lesser wing of sphenoid and anterior portion of body of sphenoid bone.

Anteriorly in the midline – median frontal crest is situated.

Characteristic features of the fossa are:

1. Foramen caecum is present between median frontal crest and crista galli of the ethmoid bone.

In foetus an emissary vein passes through this foramen, which connects olfactory venous plexus with superior sagittal sinus. After birth it obliterates and disappears.

2. Crista galli is an upward projection of perpandicular plate of ethmoid bone. It gives attachment to falx cerebri (Dural fold).

3. Anterior and posterior ethmoidal foramina are found along the sides of ethmoid bone. Anterior ethmoidal foramen transmits the anterior ethmoidal nerve and vessels from the orbit to the nose.

Posterior ethmoidal foramen transmits only posterior ethmoidal artery.

4. Cribriform plate is situated on either side of crista galli. Through this 15 to 20 olfactory nerves passes from the nose to the anterior cranial fossa to join the olfactory bulb.

5. Jugum sphenoidale is situated anterior to the sulcus chiasmaticus sulcus lodges – optic chiasma.

6. Orbital plate of frontal bone has impressions caused by gyri and sulci of frontal lobe of cerebrum.

7. Posterior border of lesser wing of sphenoid is related to spheno-parietal sinus.

8. The anterior clinoid process gives attachment for free border of the tentorium cerebelli.

II. Middle Cranial Fossa:

It is situated inferior to anterior cranial fossa but superior to posterior cranial fossa.

Boundaries:

Anterior – Posterior border of lesser wing of sphenoid.

Posterior – Superior border of sphenoid bone.

Dorsum sellae of sphenoid bone.

Lateral – Squamous part of temporal bone.

Greater wing of sphenoid bone.

Antero inferior angle of the parietal bone.

Floor:

Body of sphenoid.

Greater wing of sphenoid bone.

Petrous part of temporal bone.

Characteristic features are:

i. In the middle of this fossa, sella tursica is situated. It is a depression on the body of sphenoid and lodges pituitary gland.

ii. Behind sella tursica – dorsum sellae is situated. Lateral sides of dorsum sellae projects upwards and forms posterior clinoid processes, it gives attachment to attached border of tentorium cerebelli.

iii. Petrosal process is a spicular process projects laterally below the posterior clinoid process, it connects the apex of petrous temporal bone by the petro-clinoid ligament of Gruber.

iv. On either of sella tursica – carotid grooves are situated – lodges internal carotid artery with sympathetic plexus of nerves around it.

Lateral Aspect of the Fossa:

It is formed by superior surface of greater wing of sphenoid bone, squamous and anterior surface of petrous part of temporal bone.

Greater Wing of Sphenoid Bone:

Takes part in the formation of following foramina:

(a) Superior orbital fissure

(b) Foramen rotundum

(c) Foramen ovale

(d) Foramen spinosum.

Superior surface of squamous part of temporal bone is grooved by middle meningeal vessels.

Anterior surface of petrous part of temporal bone shows following features:

1. Trigeminal impression is situated at the apex – lodges cavum trigeminale containing trigeminal ganglion.

2. Arcuate eminence is caused by anterior semi­circular canal of internal ear.

3. Tegmen tympani is a thin plate of bone which forms the roof of auditory tube, middle ear and mastoid antrum. Two foramina lie on it, which transmit greater and lesser superficial petrosal nerve.

Structures passing through the foramina of middle cranial fossa:

1. Optic Foramen:

(a) Optic nerve with meninges.

(b) Ophthalmic artery with its sympathetic plexus of nerves around it.

2. Superior Orbital Fissure:

Superior orbital fissure is an oblique cleft, forms the apex of orbit.

Boundaries:

Superiorly – Lesser wing of sphenoid.

Inferiorly – Greater wing of sphenoid.

Medially – Body of sphenoid.

A common tendinous ring divides the fissure into three compartments.

(a) Structures passing lateral to the common tendinous ring:

1. Lacrimal nerve.

2. Frontal nerve.

3. Trochlear nerve.

4. Superior ophthalmic vein.

5. Recurrent branch of lacrimal artery is the lateral most structure.

6. Lacrimal branch of middle meningeal artery.

(b) Structures passing within the common tendinous ring:

1. Superior and inferior division of oculomotor nerve (III).

2. Naso ciliary nerve (V1).

3. Abducent nerve (VI).

(c) Structures passing medial to the common tendinous ring:

Inferior ophthalmic vein.

3. Foramen Rotundum:

Transmits maxillary division of trigeminal nerve (V2).

4. Foramen Ovale:

(a) Motor and sensory roots of mandibular nerve (V3).

(b) Accessory middle meningeal artery.

(c) Emissary vein – connects pterygoid venous plexus with cavernous sinus.

(d) Lesser superficial petrosal nerve.

5. Foramen Spinosum:

(a) Middle meningeal artery.

(b) Nervi spinosus (meningeal nerve) (V3).

6. Emissary Sphenoidal Foramen of Vesalius:

Not always present. When present, it transmits emissary vein connecting pterygoid venous plexus with cavernous sinus.

7. Foramen Lacerum:

(a) Meningeal branch of ascending pharyngeal artery.

(b) Emissary vein – connecting cavernous sinus with pharyngeal plexus of veins.

8. Carotid Canal:

(a) Internal carotid artery with sympathetic plexus of nerves around it.

(b) Emissary vein – from pharyngeal plexus to cavernous sinus.

III. Posterior Cranial Fossa:

It is the deepest cranial fossa.

Boundaries:

Anterior:

1. Dorsum sellae.

2. Body of sphenoid.

3. Basilar part of occipital bone.

4. Posterior surface of petrous part of temporal bone.

Posterior:

Squamous part of occipital bone.

Laterally:

1. Mastoid part of temporal bone.

2. Condylar part of occipital bone.

Characteristic features of the fossa are:

A. Internal occipital protuberance is situated in the centre of inner aspect of squamous part of occipital bone.

Confluence of venous sinuses is situated on it and following dural folds are meeting:

1. Falx cerebri

2. Tentorium cerebelli

3. Falx cerebelli.

B. Lateral to foramen magnum, following features is seen:

i. Hypoglossal canal transmits hypoglossal nerve (XII), meningeal branch of ascending pharyngeal artery and emissary vein.

ii. Jugular tubercle is situated above the hypoglossal canal and projects into jugular foramen. It is grooved by rootlets of IXth, Xth and XIth neves.

iii. Jugular foramen transmits terminal part of sigmoid sinus and commencement of internal jugular vein, IXth, Xth and XIth cranial nerves, emissary vein, inferior petrosal sinus and meningeal branch of ascending – pharyn­geal artery.

iv. Posterior Condylar Canal- This is not always present. When present, it transmits an emissary vein connecting occipital venous plexus with sigmoid sinus.

C. Posterior surface of petrous part of temporal bone shows following features:

1. Upper border is grooved by superior petrosal sinus.

2. Posterior and inferior aspect is grooved by sigmoid sinus.

3. Antero inferior aspect is grooved by inferior petrosal sinus.

4. Internal acoustic meatus transmits facial nerve (VII), vestibulo-cochlear nerve (VIII) and labyrinthine artery.

5. Subarcuate fossa is a shallow depression situated postero-lateral to internal acoustic meatus.

6. Aqueduct of vestibule is a slit like opening behind the internal acoustic meatus. It lodges the sacus endolymphaticus and ductus endolymphaticus.

D. Foramen magnum is the largest foramen of the cranium and oval shaped.

It communicates with posterior cranial fossa and vertebral canal.

Structures passing through this are:

1. Medulla oblongata (lower end)

2. Three meninges

3. Apical ligament

4. Membrana tectoria

5. Upper part of the cruciate ligament

6. Right and left vertebral arteries

7. Spinal root of accessory nerves

8. Sympathetic plexus of nerves around vertebral arteries

9. Anterior spinal artery

10. Posterior spinal arteries

11. Veins accompanying the arteries

12. Tonsil of the cerebellum.

Meninges:

Membranes covering the brain and spinal cord are Duramater or patchy meninx.

Arachnoid mater and Pia mater or Leptomeninges.

Term Paper # 3. Duramater or Patchy Meninx:

Double layered tough covering of brain:

(i) Endosteal layer – outer

(ii) Meningeal layer – inner one.

Both layers are closely held together except at Dural Venous sinuses.

(i) Endosteal Layer:

Endosteal layer is connected to skull by sutural ligaments and anchored to borders of foramina at base of skull.

Outer layer is crossed by meningeal vessels.

2. Meningeal Layer:

Reduplicated at certain places to form folds.

(a) Vertical Folds:

(i) Falx cerebri

(ii) Falx cerebelli.

(b) Horizontal Folds:

(i) Tentorium cerebelli

(ii) Diaphragm sellae.

These folds divide the cranial cavity into compartments to lodge various parts of brain.

Falx Cerebri:

Sickle shaped fold.

Present in midline between median fissures of brain.

Separates two cerebral hemisphere.

Attachment:

Anteriorly Crista galli and Median frontal crest.

Posteriorly and inferiorly – joins tentorium cerebelli.

Structure enclosed:

1. Superior sagittal sinus – upper border.

2. In lower border – inferior sagittal sinus and straight sinus.

Tentorium Cerebelli:

Present in posterior cranial fossa and forms roof.

Separates cerebrum from cerebellum.

Has attached and free border.

Attached Border:

Posterior to internal occipital protuberance is attached and also to lips of transverse sulcus.

Anteriorly and laterally attached to upper border of petrous temporal and posterior clinoid process.

Free Border:

Is concave and forms – Tentorial notch which lodges – mid-brain.

Attached to anterior clinoid process between free and attached border is a triangular space called oculomotor triangle.

Below free border (trochlear) – IVth cranial nerve passes.

Relations:

Superiorly – Cerebrum and Falx cerebri.

Inferiorly – Cerebellum and Falx cerebelli.

Anteriorly – Mid- brain.

Venous Sinuses:

Related are:

i. Straight sinus

ii. Confluence of sinuses

iii. Transverse sinuses (right and left)

iv. Superior petrosal sinuses (right and left)

v. Cavum trigeminale – lodges trigeminal ganglion.

Diaphragma Sellae:

It is a small circular, horizontal fold of dura mater forming the roof of hypophyseal fossa.

Anteriorly it is attached to tuberculum sallae.

Posteriorly it is attached to dorsum sallea.

On each side it is continuous with dura mater of middle cranial fossa.

It has a central aperture through which stalk of hypophysis cerebri passes.

Blood Supply of Duramater:

Venous Drainage of Duramater:

Drains venous blood into sinuses.

Arachnoid Mater:

Lies deep to duramater.

Subarachnoid space is filled with C.S.F. (cerebro spinal fluid).

Dilated subarchnoid spaces are called cisterns, e.g.:

a. Cisterna pontis – space anterior to pons and medulla.

b. Inter peduncular cistern – space anterior to mid-brain peduncles.

c. Cerebello – Medullary cistern – space posterior to cerebellum and medulla.

Subarachnoid space lodges blood vessels to supply brain.

Piamater:

Is a thin vascular membrane which closely invests the brain, dipping into various sulci and other irregularities of its surface.

Term Paper # 4. Hypophysis Cerebri (Pituitary Gland):

Is a small endocrine gland and known as Master of Endocrine orchestra.

Lies in Hypophyseal fossa situated in middle cranial fossa, in relation to base of brain – suspending from the floor the third ventricle.

Shape – is oval

Size – Antero-posteriorly 8 mm

Transversely – 12 mm

Weight – about 500 to 600 mm

Development:

(a) Anterior Lobe:

From buccal epithelium an upward growth arises becomes Rathkes pouch and forms of anterior lobe.

(b) Posterior Lobe:

Diencephalic diverticulum – descends downward and forms posterior lobe.

Relations:

1. Superiorly:

i. Diaphragm sellae

ii. Optic chiasma

iii. Tuber cinerium

iv. Infundibular recess of IIIrd ventricle.

2. Inferiorly:

i. Irregular venous plexus

ii. Dura lining the floor of fossa

iii. Pituitary fossa

iv. Sphenoidal air sinus.

3. On Each Side Laterally:

i. Cavernous sinus with its contents.

4. Anteriorly:

Anterior – Inter cavernous sinus.

5. Posteriorly:

Posterior – Inter cavernous sinus.

Arterial Supply:

Superior and inferior hypophyseal artery branch of internal carotid artery.

Parts of Hypophysis Cerebri or Subdivisions:

It has two parts:

I. Adenohypophysis

II. Neurohypophysis.

They differ embryologically, morphologically and functionally.

I. Adenohypophysis:

It develops as an upward growth from ectodermal roof of stomodeum (Buccal epithelium) called Rathke’s pouch.

Forms:

a. Anterior lobe – pars anterior

b. Intermediate lobe – pars inter-media

c. Tuberal extension called pars tuberalis – it extends upwards around the sides of infundibulum.

A cleft is present between anterior and inter­mediate lobe.

It has cells arranged in cords around sinusoids.

Cells are:

a. Acidophilic or alfa cells (chromophils and chromophobe)

b. Basophilic (Chromophils):

i. Beta cells

ii. Delta cells.

i. Beta Cells:

Secrete – T.S.H. (Thyroid Stimulating Hormone) and A.C.T.H. (Adreno Cortico Trophic Hormone).

ii. Delta Cells:

Secrete – F.S.H. (Follicle Stimulating Hormone), Luteinizing Hormone and I.C.S.H. (Interstitial Cell Stimulating Hormone).

Alfa cells secrete – growth hormone and lactogenic hormone (prolactin).

Chromophobes are precursor cells (stem cells).

Intermediate lobe – has plenty of chromophobes and chromophil cells – which secrete M.S.H. (Melanocyte Stimulating Hormone).

Arterial supply of anterior and intermediate lobe is through – superior hypophyseal artery – which forms superior and inferior capillary tuft from which long and short portal vessels arise – carry hormone releasing factor from hypothalamus.

Venous Drainage into neighbouring dura sinuses – Cavernous and inter cavernous sinuses.

Short veins carry hormones secreted by glan­dular cells.

II. Neurohypophysis:

Develops as downward growth from floor of diencephalon and is connected to hypothalamus by neural pathways (axons).

It has:

i. Neuroglial cells or tissue

ii. Neurons – called pituicytes

iii. Axon – forms hypothalmo-hypophyseal tract.

Parts:

It forms – posterior lobe, infundibular stem and median eminence of tubercinerium.

Functions:

1. It provides neural pathway which controls secretary activity of anterior lobe.

2. Vasopressin (A.D.H.) – Antidiuretic hormone acts on kidney and tubules.

3. Oxytocin – Acts on smooth muscles of uterus and breast – causes contraction – both hormones are secreted by neurons of hypothalamus and reaches to posterior lobe.

Term Paper # 5. Internal Carotid Artery:

It begins in the neck as one of the terminal branches of the common carotid artery, at the level of upper border of thyroid cartilage.

Parts:

There are four parts:

1. Cervical Part:

(a) Lies within carotid sheath in the neck.

(b) Gives no branch.

2. Petrous Part:

Lies within petrous part of the temporal bone, i.e., in the carotid canal.

Branches:

(a) Carotico tympanic branch to middle ear cavity.

(b) Artery of pterygoid canal.

3. Cavernous Part of Internal Carotid Artery:

Lies within the cavernous sinus.

It gives:

(a) Cavernous branch to trigeminal ganglion.

(b) Superior hypophyseal branch to hypo­physis cerebri.

(c) Inferior hypophyseal branch to hypo­physis cerebri.

4. Cerebral Part of Internal Carotid Artery:

Lies at the base of brain.

Branches are:

(a) Ophthalmic artery to orbit

(b) Anterior cerebral artery

(c) Middle cerebral artery

(d) Posterior communicating branch

(e) Anterior choroidal artery

Curvatures of petrous, cavernous and cerebral part of internal carotid artery together form an ‘S’ shaped figure (carotid siphon of angiograms).

Trigeminal Ganglion:

It is a sensory ganglion of Vth cranial nerve made up of pseudounipolar nerve cells with a ‘T’ shaped arrangement of their processes.

One process arises from cell body → it divides into a central and a peripheral process.

Shape is cresantric or semilunar and three divisions arise from its convexity.

Concavity:

Receives sensory root of the nerve.

Situation and Meningeal Relations:

Lies on trigeminal impression on the anterior surface of petrous temporal bone near its apex.

Occupies a special space of dura mater called trigeminal cave (Meckel’s cave) it is lined by pia and arachnoid mater so it is surrounded by C.S.F. (cerebro spinal fluid).

Relations:

Medially – Internal carotid artery.

Posterior – part of cavernous sinus.

Laterally – Middle meningeal artery.

Superiorly – Para hippocampal gyrus.

Inferiorly – Motor root of Vth Nerve.

Greater petrosal nerve

Apex of petrous temporal bone and foramen lacerum.

Root and Branches:

Central processes form large sensory root attached to pons.

Peripheral process forms three divisions – V1, V2 and V3 (ophthalmic, maxillary and mandibular).

Motor root is also attached to pons and joins V3 (mandibular) nerve.

Blood supply by branches of internal carotid artery, middle meningeal artery, accessory meningeal artery and meningeal branch of ascending pharyngeal artery.

Applied:

Trigeminal neuralgia – intractable pain.

Treatment:

Injection of alcohol into ganglion or cutting sensory root.