Cranial Cavity

Cranial Cavity: Circulation and Cranial Nerves

Meninges – coverings that protect the parts of the nervous system that lie within the cranial cavity and spinal canal

Dura Mater – "tough mother"; outermost covering

bilaminar; the venous channels that carry blood from the brain to the heart (dural sinuses) are located between the bilayers

Falx cerebri – an invagination of the inner layer of the dura that separates the cerebral hemispheres medially

Tentorium cerebelli – tent-like dura that covers the cerebellum; runs infreriolaterally from the midline bilaterally

Arachnoid–middle menix; has CSF; "cobweb-like" filaments attach it to pia mater; forms cisterns where brain invaginates

Pia Mater – "soft mother"; innermost menix; smooth, translucent membrane that adheres to the outer surface of the CNS

Vessels – the circulation of the brain is unique in that the venous drainage has little to do with the arterial supply

(1) Sinuses – bridging veins collect blood from brain venules and cross subarachnoid space to enter the dural sinuses

Superior sagittal sinus – runs along the superior aspect of the falx cerebri to the confluence

Inferior sagittal sinus – runs along the inferior aspect of the falx cerebri to the straight sinus

Transverse sinus – runs laterally along the tentorium cerebelli from confluence to sigmoid

Straight sinus –from the joining of the inferior sagittal and the great vein of Galen to the confluence, runs in the midline, under the attachment of the falx cerebri to the tentorium cerebelli

Confluence – the joining of the superior sagittal, straight, and transverse sinuses

Internal Jugular Vein – the sigmoid sinus drains into the internal jugular vein

Cavernous sinus – located on either side of the sella turcica, contains the 180^o turn of the Internal Carotid

Superior petrosal – drains the cavernous sinus, ends at the sigmoid

Inferior petrosal – drains directly into the internal jugular vein

Sigmoid – all sinuses except inferior petrosal drain into this sinus which drains into the internal jugular vein

Cavernous sinus – formed by 3 vessels (superior and inferior ophthalmic veins and sphenoparietal sinus)

contains internal carotid artery and CN VI; on lat. wall of cavernous sinus within dura are (superior to inferior): CN III, IV, V₁ and V₂

Jugular foramen – in posterior cranial fossa, where internal jugular vein, sigmoid sinus, and inferior petrosal sinus meet and cross

CN IX, CN X, and CN XI exit; ascending pharyngeal and occipital arteries enter

(2) Circle of Willis – vertebral arteries and internal carotid arteries give rise to an anastomosis that supplies the brain

Internal Carotid Arteries – enter at the carotid canal in the temporal bone, makes a 180^oturn in the cavernous sinus, upon leaving the cavernous sinus gives off the ophthalmic artery (to the orbit) and then contributes to the circle

Vertebral Arteries – enter through foramen magnum, join in midline to form the basilar artery and contribute to the circle

the vertebral arteries supply ~25% of the brain’s blood, the internal carotids supply ~75% of the brain’s blood

nine arteries of the circle of Willis (not counting the Basilar artery) – listed anterior to posterior:

anterior communicating artery
right and left anterior cerebral – the anterior cerebral arteries supply most of the medial and superior surfaces and the frontal lobe
right and left internal carotid – the internal carotids give off the middle cerebral artery after contributing to the circle
right and left posterior communicating
right and left posterior cerebral

aneurysms occur at branch points, often where posterior communicating artery comes off internal carotid artery; also at basilar artery

Cerebral Spinal Fluid – protein-free plasma ultrafiltrate with altered ion concentration (perhaps evolved to prevent seizures)

Choroid plexus – produce ~400mL of CSF daily; ependymal cells (specialized glial cells) in cerebral ventricles actively transport HCO₃^-into ventricles, and H₂O and Na⁺ follow to produce CSF

CSF made in lateral ventricles travels through 3^rd ventricle and empties into 4^th ventricle via cerebral aqueduct; 2 lateral apertures and 1 median aperture allow CSF to enter subarachnoid space, where it circulates around the CNS

Arachnoid villi – protrusions of arachnoid into the dural venous sinuses; act as one-way valves

resorption is pressure-dependent; CSFÞ venous sinuses if venous pressure < subarachnoid pressure

the capacity of the subarachnoid space and ventricles is ~200mL, so CSF must return to the bloodstream in 12 hrs

the endothelium of the arachnoid villi is fenestrated; arachnoid cells are the only separation between CSF and blood

Ventricles – cavities in the brain where the CSF is made and circulates prior to entering the subarachnoid space

Lateral ventricles – ventricles #1 and 2, one located in each cerebral hemisphere

3^rd ventricle – located in the midline, between cerebral hemispheres in the upper brainstem

4^th ventricle – connected to the 3^rd via the cerebral aqueduct, located in the pons, anterior to the cerebellum

Cranial Nerves and Fossae

Cribiform plate of ethmoid – Olfactory nerve (CN I)

Optic canal of sphenoid bone – Optic nerve (CN II)

Superior orbital fissure of sphenoid – Oculomotor nerve (CN III), Trochlear nerve (CN IV), ophthalmic branch of Trigeminal (CN V₁), Abducens (CN VI)

Foramen rotundum of sphenoid – Maxillary branch of the Trigeminal nerve (CN V₂)

Foramen ovale of sphenoid – Mandibular branch of the Trigeminal nerve (CN V₃)

Internal acoustic meatus of temporal bone – Facial nerve (CN VII), and Vestibulocochlear (CN VIII)

Jugular foramen located between temporal and occipital bones – Glossopharyngeal nerve (CN IX), Vagus nerve (CN X), and Accessory nerve (CN XI)

Hypoglossal canal of occipital bone – Hypoglossal nerve (CN XII)

CN VII: Facial - mixed motor and sensory

Has two distinct roots: (1) Facial nerve proper (motor, larger root trunk) (2) Nervus intermedius (sensory root)

Emerge from the brain stem at the caudal border of pons, lateral to the superior end of the olive.

Both roots enter the internal acoustic meatus form the geniculate ganglion then exit skull at stylomastoid foramen.

Branches of the facial nerve

Greater petrosal nerve: branches off at the geniculate ganglion to exit via the hiatus of the facial canal

contains taste and parasympathetic fibers,
merges with the deep petrosal nerve (sympathetic fibers) in the pterygoid canal to form the Vidian nerve
then enters the pterygopalintine ganglion, which sends the sympathetic and postynaptic parasympathetic fibers to the lacrimal gland and the mucosa of the palate, nasopharnyx, and nasal cavity via connections to V₂ and then branches of its Zygomatic branch.

Chorda tympani nerve branches in the facial canal and exits the skull via the petrotympanic fissure

Joins the lingual nerve (branch of V₃) which runs to anterior 2/3 of tongue and provides taste sensation (CN V).
Parasympathetics in the lingual nerve synapse in the submandibular ganglion then supply the submandibular and sublingual glands

Stapedius nerve arises in the facial canal and is motor to the muscle on the stapes.

Suprahiod motor branches exits stylomastoid foramen then supplies the stylohiod m, posterior belly of the digastric and the 5 Facial branches which arise within the parotid gland – temporal, zygomatic, buccal, mandibular, cervical

Nuclei of the facial Nerve:

Facial Motor nucleus gives rise to the motor fibers and is located in the ventro lateral part of tegmental pons

Nucleus Solitarius (rostral portion) receives the afferent taste roots

Geniculate ganglion contains the cell bodies of the for 1^o sensory neurons; the pain, touch and thermal sensations from around the ear end in the descending trigeminal nucleus.

Lesions of the facial nerve: cause facial paralysis, loss of taste (anterior 2/3 of tongue) and decreased salivation.

paralysis of the lower face only signifies an upper motor neuron lesion only due to bilateral CNS innervation of each side of facial motor nucleus cell innervation the upper face.

Could be caused by ischemia to the internal capsule or cortex.

Paralysis of the upper face indicates that the motor neurons from the facial nucleus are being affected.

Bell’s palsy, facial nerve is affected as it passes through the facial canal. Being encased by bone, any swelling due to inflammation or infection result in constriction of the nerve Þ paralysis.

Symptoms depend on location. Proximal to geniculate ganglion affects all CN VII function, distal only motor.

Severe cases destroy the nerve, mild case allow the nerve to regenerate.

CN V: Trigeminal – mixed motor sensory : largest cranial nerve

one small motor nerve for the muscles of mastication and three principal general sensory nerves from the head.

CN V₁ (Opthmalic Nerve): purely sensory from superficial and deep parts of superior region of the face.

passes anteriorly in the lateral wall of the cavernous sinuses, inferior to the trochlear nerve.
All 3 of its branches pass enter the orbit through the superior orbital fissure.

Frontal nerve: largest branch travels anteriorly to the supra orbital area giving off the supra orbital branch that provides sensation from the upper eyelid and scalp; and the supratrochlear nerve that also provides sensory from the upper eyelid and forehead.

Naso cilliary nerve: enters orbit through the central tendinous ring on its way to innervating the medial wall.

Lacrimal nerve: smallest of the main branches; enters via the superior orbital fissure on its way to lacrimal gland and nearby structures.

CN V₂ (Maxillary Nerve): purely sensory; arises from the Trigeminal ganglion running anteriorly in the inferior cavernous sinus, inferior to the Opthmalic nerve.

leaves the middle cranial fossa through the foramen rotundum entering the pterygopalatine fossa exiting via the pterygomaxillary fissure.

Enters the orbit via the inferior orbital fissure after which it is called the infraorbital nerve which exits via the infra orbital canal and foramen.

Meningeal branches: arise in the middle cranial fossa to supply the dura.

Ganglionic branches: enter the pterygopalantine ganglion as its sensory root

Posterior superior alveolar nerves: supply the maxillary sinus and roots of maxillary premolars via the posterior superior alveolar foramen.

Middle superior alveolar nerve: arises from infraorbotal portion to supply the mucosa of the maxillary sinus and front maxillary molars

Anterior superior alveolar nerve: passes through the infra orbital foramen to supply maxillary sinus, nasal septum and roots of maxillary incisors and canines.

CN V₃ (Mandibullar Nerve): mixed sensory and motor; arises after the Trigeminal ganglion to enter the foramen ovale with the motor root of the Trigeminal nerve.

Meningeal and middle meningeal reenter the cranium through the foramen spinosum to supply the dura

Anterior division: Motor and buccal nerves Posterior division (sensory) auriculo temporal, lingual, inferior alveolar supplying the teeth gingiva, sensory to anterior 2/3 of tongue (Lingual), and para mandinbular gland.