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
- Arachnoidmiddle 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
(2) Circle of Willis vertebral arteries and internal carotid arteries give rise to an anastomosis that supplies the brain
- (1) Sinuses bridging veins collect blood from brain venules and cross subarachnoid space to enter the dural sinuses
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 180o 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
enter at the carotid canal in the temporal bone, makes a 180o turn 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
- Internal Carotid Arteries
nine arteries of the circle of Willis (not counting the Basilar artery) listed anterior to posterior:
- the vertebral arteries supply ~25% of the brains blood, the internal carotids supply ~75% of the brains blood
aneurysms occur at branch points, often where posterior communicating artery comes off internal carotid artery; also at basilar artery
- 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
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 3rd ventricle and empties into 4th 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
- 3rd ventricle located in the midline, between cerebral hemispheres in the upper brainstem
- 4th ventricle connected to the 3rd 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
Chorda tympani nerve branches in the facial canal and exits the skull via the petrotympanic fissure
- 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.
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:
- 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
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.
Bells 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.
- 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 1o sensory neurons; the pain, touch and thermal sensations from around the ear end in the descending trigeminal nucleus.
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.