Overview of the Brain, Cranial Nerves, Blood Supply and Meninges

Overview of the Brain, Cranial Nerves, Blood Supply and Meninges

Objectives Name the parts of the brain and describe their main anatomical features Describe the attachments of the cranial nerves to the surface of the brain List the main branches of the vertebral, basilar and internal carotid arteries Name the arteries that form the cerebral arterial circle (of Willis) Indicate the location of the septa formed by the crania dura mater Indicated the location of the dural venous sinuses and understand the direction of blood flow through them Describe the anatomical relations of the cavernous sinus

Parts of the Brain brainstem: medulla oblongata pons midbrain
cerebellum diencephalon: thalamus hypothalamus telencephalon (cerebral hemispheres)

thalamus hypothalamus

Brainstem External Features (Anterior Surface)
medulla: anterior median fissure  continuous inferiorly with anterior median fissure of spinal cord pyramids  2 longitudinal columns (1 on each side of anterior median fissure) olive  oval elevation lateral to upper part of pyramid pre-olivary sulcus  located between pyramid and olive  attachment of rootlets of hypoglossal nerve (CN XII) retro-olivary sulcus  located posterior to olive  attachment of rootlets of glossopharyngeal (CN IX) ( Sensory taste from post 1/3 of tongue & motor to stylopharyngeus that assists with swallowing -+ werer4

Medulla Continued: Vagus (CN X) Motor to pharnx & larynx, & esophagus. Parasympathetics to smooth muscle & glands of trachea, bronchi, digestive tract, coronary arteries, and heart conduction system. Accessory nerve/CN XI) Motor to SCM & trapezius

medulla: nerves that attach along pontomedullary junction (from medial to lateral): abducens (CN VI) (Motor to lateral rectus muscle) facial nerve (CN VII) (Muscles of facial expression) vestibulocochlear nerve (CN VIII) (vestibular sensation & hearing) Pons: it becomes continuous on each side with a large bundle of fibers that terminates in cerebellum  middle cerebellar peduncle boundary between pons and middle cerebellar peduncle  attachment of trigeminal nerve (CN V) (Sensation to the face & motor to the muscles of masitcation.

midbrain: 2 columns of descending fibers (1 on each side)  cerebral crura (cerebral peduncles) oculomotor nerve (CN III) (motor to superior, inferior, and medial recti, inferior obliquue, and levator palpebrae.; parasympathetic to pupillary sphincter muscles.) Interpeduncular fossa  space between 2 cerebral peduncles

Brainstem External Features (Posterior Surface)
4th ventricle  cavity between cerebellum (posteriorly) and pons and upper medulla (anteriorly)  communicates inferiorly with central canal of spinal cord and superiorly with cerebral aqueduct (cavity of midbrain)  it also communicates with subarachnoid space posterior surface of upper medulla and posterior surface of pons form floor of 4th ventricle (rhomboid fossa)

Brainstem External Features (Posterior Surface)
posterior surface of upper medulla and posterior surface of pons form floor of 4th ventricle (rhomboid fossa) pineal body (gland) is located between superior colliculi (belongs to diencephalon) trochlear nerve (CN IV) (motor to superior oblique eye muscle) emerges immediately below inferior colliculi. It is the only cranial nerve attached to posterior surface of brainstem.

Cerebellum Parts: vermis (midline)
2 cerebellar hemispheres (1 on each side of vermis) it is connected to brainstem by 3 pairs of large fiber bundles  superior, middle and inferior cerebellar peduncles consists of: an outer layer of gray matter, which is highly folded  cerebellar cortex myelinated axons running to and from cerebellar cortex form an inner core of white matter immediately deep to cortex  subcortical white matter a series of masses of gray matter embedded in subcortical white matter  cerebellar nuclei

cerebellar hemispheres
vermis

Diencephalon it is located superior to midbrain
it is almost totally hidden by cerebral hemispheres  only a small part can be seen on inferior aspect of brain has 2 main components: thalamus hypothalamus right and left parts of diencephalon are separated by a cavity (3rd ventricle)  communicates with lateral ventricles (cavities of cerebral hemispheres) and with cerebral aqueduct

hypothalamus thalamus

hypothalamus

right thalamus left thalamus

Cerebral Hemispheres components:
superficial layer of gray matter (cerebral cortex)  highly folded to form complex pattern of ridges (gyri) and grooves (sulci) myelinated axons (fibers) running to and from cerebral cortex form extensive mass of white matter immediately deep to cortex  subcortical white matter embedded in white matter are various masses of gray matter  basal nuclei cavity of cerebral hemisphere: lateral ventricle

Cerebral Hemispheres surfaces:
superolateral surface  it is convex and conforms to concavity of internal surface of cranial vault (calvaria) medial surface  flat and vertical  faces opposite cerebral hemisphere inferior surface  faces floor of cranial cavity  rests on anterior and middle cranial fossae and tentorium cerebelli (fold of dura mater that separates occipital lobes of cerebral hemispheres from cerebellum)

subcortical white matter
cerebral cortex basal nuclei lateral ventricle subcortical white matter

Superolateral Surface of the Left Cerebral Hemisphere

Medial Surface of the Left Cerebral Hemisphere

Inferior Surfaces of the Cerebral Hemispheres

Cerebral Hemisphere lobes: frontal, parietal, temporal, occipital and insular 2 main sulci in superolateral surface: central sulcus  separates frontal and parietal lobes lateral sulcus  separates temporal lobe from frontal and parietal lobes

central sulcus lateral sulcus insula

Lateral Ventricles there are 2 of them, 1 in each cerebral hemisphere
parts: anterior (frontal) horn body (within parietal lobe) inferior (temporal) horn posterior (occipital) horn trigone (atrium)  area where body, inferior horn and posterior horn meet each other each lateral ventricle communicates with 3rd ventricle via interventricular foramen (of Monro)

Cranial Meninges

Dura Mater of the Brain meningeal layer forms 4 septa  divide cranial cavity into freely communicating compartments cerebral falx (falx cerebri)  sickle-shaped fold that lies in the midline between two cerebral hemispheres cerebellar tentorium (tentorium cerebelli)  crescent-shaped fold that roofs over posterior cranial fossa (separates cerebellum from occipital lobes of cerebral hemispheres) tentorial notch  space between anterior, free border of tentorium cerebelli and dorsum sellae  filled mostly by midbrain cerebellar falx (falx cerebelli)  small sickle-shaped fold in posterior cranial fossa that projects between two cerebellar hemispheres sellar diaphragm (diaphragma sellae)  small circular fold that roofs over sella turcica (has small opening for pituitary stalk)

Dura Mater of the Brain layers:
endosteal (outer layer)  equivalent to periosteum covering inner surface of skull bones meningeal (inner layer)  dura mater proper, faces the brain the two layers are closely united, except where they separate to form dural venous sinuses

endosteal layer of dura mater
meningeal layer of dura mater

What cranial nerve is missing?
How does all of the blood from the cerebral sinuses get back to the heart?

Dural Venous Sinuses located between inner and outer layers of dura mater receive blood from brain (via superficial and deep cerebral veins) as well as cerebrospinal fluid from subarachnoid space (via arachnoid granulations) blood collected by dural venous sinuses drains ultimately into internal jugular veins

Dural Venous Sinuses superior sagittal sinus: runs along upper border of falx cerebri  begins anteriorly at foramen cecum and terminates posteriorly in confluence of the sinuses (over internal occipital protuberance) inferior sagittal sinus: runs along lower, free border of falx cerebri, joins great cerebral vein (largest of the deep cerebral veins) to form straight sinus straight sinus: runs in midline, along junction of falx cerebri and tentorium cerebelli  terminates posteriorly in confluence of the sinuses

Dural Venous Sinuses transverse sinus: begins in confluence of the sinuses and runs along posterior border of tentorium cerebelli  when it reaches petrous part of temporal bone, it turns down to become continuous with sigmoid sinus sigmoid sinus: direct continuation of transverse sinus  terminates in jugular foramen, where it becomes continuous with internal jugular vein occipital sinus: small sinus that runs along posterior border of falx cerebelli  ends superiorly in confluence of the sinuses and inferiorly communicates with internal vertebral venous plexus (within vertebral canal)

Dural Venous Sinuses cavernous sinus:
located in middle cranial fossa, one on each side of sella turcica drains contents of orbit, parts of cerebral hemisphere, pituitary gland and sphenoparietal sinus internal carotid artery and abducens nerve are located inside cavernous sinus cranial nerves III and IV and V1 and V2 divisions of trigeminal nerve are embedded in lateral wall of sinus it is drained posteriorly by superior and inferior petrosal sinuses

Dural Venous Sinuses superior petrosal sinus: runs along superior border of petrous part of temporal bone  connects cavernous sinus with terminal part of transverse sinus inferior petrosal sinus: runs along inferior border of petrous part of temporal bone (between petrous part and occipital bone)  connects cavernous sinus with internal jugular vein sphenoparietal sinus: small sinus that runs along posterior border of lesser wing of sphenoid  drains into cavernous sinus

So What?

Questions to Consider 1 What symptoms might a patient present with if they develop a pituitary tumor pressing on the optic chiasm? 2 If you have a pimple on the side of the nose, what risk is there to manipulating it? Consider the “danger triangle of the face” and how the systemic drainage of the face meets up with cavernous sinus.

Arterial Supply of the Brain
it is provided by 2 pairs of arteries: vertebral and internal carotid vertebral artery: enters cranial cavity via foramen magnum right and left vertebral arteries join each other at pontomedullary junction to form basilar artery basilar artery runs along midline of anterior surface of pons and ends at upper end of pons by dividing into 2 posterior cerebral arteries vertebral and basilar arteries give branches that supply spinal cord, brainstem, cerebellum and posterior parts of cerebral hemispheres

internal carotid artery: begins at bifurcation of common carotid artery (at level of upper border of thyroid cartilage) parts: cervical (from origin to base of the skull) petrous (within carotid canal in petrous part of temporal bone) cavernous (within cavernous sinus  dural venous sinus located in middle cranial fossa, just lateral to sella turcica) cerebral (from the point it exits cavernous sinus to its termination, where it divides into anterior and middle cerebral arteries)

internal carotid artery (cont.): main branches: ophthalmic artery  enters orbit via optic canal together with optic nerve posterior communicating artery  joins posterior cerebral artery 2 terminal branches: anterior and middle cerebral arteries (right and left anterior cerebral arteries are connected by anterior communicating artery)

Cerebral Arterial Circle (of Willis)
formed by large cerebral arteries and their interconnections on ventral surface of the brain components: anterior communicating a. anterior cerebral a. internal carotid a. posterior communicating a. posterior cerebral a. serves as a potential vascular shunt, assisting in development of collateral circulation if one of the proximal vessels is occluded

cerebral part cavernous part petrous part cervical part

cerebral part of internal carotid artery
cavernous part of internal carotid artery