neuroanatomy introduction

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Neuroanatomy Introduction Dr Ikram I. QAYSIA

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Neuroanatomy Introduction

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Neuroanatomy

Introduction

Dr Ikram I. QAYSIA

Introduction

• Objectives of the course:

• 1- Understand the basic organization of the main structures that form the NS

• 2- 3.D appreciation of the position of the various brain nuclei

• 3- Localisation and diagnosis of neurological problems.

Outline

• Skull, meninges and their blood supply • Cerebral hemispheres • Structure and functional localization of the cerebral cortex • Basal ganglia • Brain stem • Cerebellum • Diencephalon • Reticular formation & limbic system • Ventricular system and CSF • Blood supply of nervous system • Spinal cord structure and functional tracts • Peripheral nervous system • Autonomic nervous system

The Skull

• Bones of the skull:

• The frontal bone

• The parietal bone

• The temporal bone

• The sphenoid bone

• The occipital bone

Bones of the skull

Bones of the face

• The nasal bone

• The maxillae

• The mandible

• The zygomatic bone

The cranial fossae

• The anterior cranial fossa

• Middle cranial fossa

• Posterior cranial fossa

Cranial fossae

Foramina & other apertures in the cranial fossae & their contents

• 1 Foramen Caecum 2 Optic Canal 3 Superior orbital fissure 4 Foramen rotundum 5 Foramen ovale 6 Foramen Spinosum 7 Foramen Lacerum 8 Carotid Canal 9 Foramen magnum 10 Hypoglossal Canal 11 Jugular Foramen 12 Internal acoustic meatus

Ant cranial fossa

• Foramen Caecum

• * for transmission of small vein from nasal mucosa to superior sagital sinus (nasal emissary vein)

• Foramina in the cribriform plates: axons of olfactory cells in olfactory epithelium that form olfactory N

• Anterior and posterior ethmoidal formania: vesseles & nerves with the same names

Middle cranial fossa

• Optic Canal • * Optic nerve • * Ophthalmic artery • Superior orbital fissure • * Nerves • o CN V1 (ophthalmic N)

o trochlear nerve, IV o occulomotor nerve, III o abducent nerve, VI o sympathetic fibers

ophthalmic veins

Middle cranial fossa

• Foramen rotundum: maxillary nerve (CN V2)

• Foramen ovale

• *mandibular nerve, CN V3 * lesser petrosal nerve * accessory meningeal artery

Middle cranial fossa

• Foramen Spinosum • * middle meningeal artery and vein • * meningeal branch of mandibular nerve (V3) • Foramen Lacerum • * filled by cartilage • * Internal carotid artery & its accompanying

sympathetic & venous plexuss • Hiatus of greater petrosal N: Gr Pet N and petrosal br

of middle meningeal art • Carotid Canal • * internal carotid artery

Post cranial fossa

• Foramen magnum * Medulla oblongata

* ascending parts of spinal accessory nerves * ant & post spinal arteries

• Jugular formen: CN IX, X, XI, sup bulb of internal jugular vein, inf petrosal & sigmoid sinuses, meningeal br of ascending pharyngeal & occipital art

• Hypoglossal canal: CN XII (hypoglossal N) • Condylar canal: emissary vein that passes from

sigmoid sinus to vertebral veins in neck • Mastoid foramen: mastoid emissary vein from sigmoid

sinus and menigeal br of occipital art

Cranial meninges and CSF

• Understanding of the meninges & their relationship to the CSF is an essential basis for understanding intracranial diseases & head injuries

• The 3 membranes along with the CSF provide support and protection for the brain

• The brain is enveloped by 3 membranes:

1. Dura mater (hard, tough…mater= mother)

2. Arachnoid mater (spider resemblance)

3. Pia mater (tender)

The Cranial Meninges

Functions of the 3 layers 1. protect the brain 2. provide supporting

framework for a. & v. 3. enclose fluid-filled cavity (CSF) 3 layers: Dura mater Arachnoid mater Pia mater

Meninges

Meninges

The Dura mater

• Is the outermost & toughest layer • Composed of collagenous cennective tissue • Adheres so closely to the internal periosteum except

where there are dural venous sinuses • Described as 2 layered membrane because it adheres

to the int periosteum • Continous with the spinal dura at foramen magnum • It provides tubular sheaths for the CN as they pass

through the foramina in the floors of the cranial fossae • Outside the skull, the dural sheaths fuse w the

epineurium of the CN

Dura Mater

most external part

double layered membrane

2 layers:

ext. periosteal layer

(periosteum of calvarian bones)

Int. meningeal layer

- tough, thick fibrous membrane

continues at F. magnum to SC

* Brain Venous Sinuses are located between periosteal & meningeal layers of dura

Processes of dura mater

1. Falx cerebri

2. Tentorium cerebelli

3. Falx cerebelli

4. Diaphragma sellae

Dural Reflections

Foldings of internal meningeal layer between brain compartments (septa) to restrict the rotatory displacement of the brain (fxn.)

4 main reflections:

falx cerebri

falx cerebelli

tentorium cerebelli

sellar diaphragm

Falx cerebri

• A median process • Sickle- shaped • Lies in the longitudinal fissure btn the 2 hemispheres • Attached to the crista galli in front and in the back it

fuses with the tentorium cerebelli • The upper convex border of the falx encloses the

superior sagittal sinus, and is attached to the inner aspect of the skull (frontal, parietal & occipital bones)

• The lower concave border containes the inf sagittal sinus. As it lies above the corpus callosum and it follows its curvature

Dural Reflections

Foldings of internal meningeal layer between brain compartments (septa) to restrict the rotatory displacement of the brain (fxn.)

4 main reflections:

falx cerebri

falx cerebelli

tentorium cerebelli

sellar diaphragm

Tentorium cerebelli

• It forms a tent over the cerebellum • It supports the occipital lobes of the cerebral hemispheres • Its external border encloses the transverse sinus posteriorly

and its attached to the inner aspect of the skull (occipital and parietal bones)

• The anterior part of this margin encloses the superior petrosal sinus & its attached to the petrous temporal bone anteriorly to the clinoid process.

• Because of this arrangement, any increase in the intracranial pressure may go downward and displacement of the brain stem and herniation of the forebrain structures could take place

• Space occupying lesions, may cause herniation of the brain.

Dural Reflections

Foldings of internal meningeal layer between brain compartments (septa) to restrict the rotatory displacement of the brain (fxn.)

4 main reflections:

falx cerebri

falx cerebelli

tentorium cerebelli

sellar diaphragm

Falx cerebelli

• Is sickle- shaped and lies below the tentorium

• Its upper border is attached to the lower aspect of the tentorium

• Its posterior border is attached to the occipital bone

• Its anterior border projects between the two cerebellar hemispheres

Diaphragma sellae

• This fold of dura forms a dural roof for the sella turcica

• It covers the hypophysis and presents an opening for the infundibulum

• The optic chiasma lies over the diaphragma

Cranial fossae

Dural Reflections

Foldings of internal meningeal layer between brain compartments (septa) to restrict the rotatory displacement of the brain (fxn.)

4 main reflections:

falx cerebri

falx cerebelli

tentorium cerebelli

sellar diaphragm

• In almost all areas of the cranial cavity, the fibrous dura fuses with the endostium, as such no epidural space.

• So the epidural space for example with an epidural hemorrhage occupies the space between the bone and endostium

Innervation of the dura

• By trigeminal and cervical nerves, • Autonomic fibers go to the vessels in the dura • Dura of the ant cranial fossa: innervated by the

ophthalmic division of the 5th CN, through the ant and post ethmoidal br

• Dura of the middle cranial fossa: by menigeal br of the maxillary & mandibular nerves

• Post fossa: meningeal branches of the vagus and hypoglossal neves (both of these nerves contain spinal root fibers C1 & C2)

Innervation of the dura

• Tentorium and falx cerebri:

• By tentorial branch of the ophthalmic br.

• Falx cerebri and related venous sinuses are also innervated by the ophthalmic branch of the 5th cranial nerve.

Dural Venous Sinuses

Blood filled spaces within dura matter that lined with endothelium and drain all bld. from brain and meninges.

Location: Between the periosteal and meningeal layers of dura,

where dural infoldings attach.

Main :

Sup. Sgittal sinus

Inf. Sagittal sinus

Straight sinus

Transverse sinus (2)

Sigmoid sinus (2) IJV

Cavernous sinus (2):

venous plexus lat. to sella turcica

Receives sup. & inf. Ophthalmic v.

From the orbit

Venous sinuses

Venous sinuses

• The walls of the dural venous sinuses are composed of dura mater lined with endothelium.

• They differ from other blood vessels in that they lack the tunica media, a characteristic of arteries and veins.

• Large veins from the surface of the brain and from diploic veins empty into the sinuses, and all ultimately drain into the internal jugular vein.

Venous sinuses of the dura mater

Superior saggital sinus:

• Single sinus lies in the falx cerebri

• It begins in the front of the crista galli, here rarely it may receive a vein from the nose

• Travels to the back, near the internal occipital protuberance and divides into R and L transverse sinuses or joins the straight sinus

• Tributaries: receives superior cerebral veins

Venous sinuses

Venous sinuses of the dura

Inferior saggital sinus:

• Single one

• Located in the concave border of the falx cerebri

• Drains into the straight sinus

Venous sinuses

Venous sinuses of the dura

Straight sinus:

• Single one

• Lies at the junction of the falx cerebri with the tentorium cerebelli

• Receives the great cerebral and some cerebellar veins

Venous sinuses

Venous sinuses of the dura

Transverse sinuses: • 2 (R & L) • Each begins in the confluence at the internal occipital

protuberance • Each transverse sinus runs laterally and forward in the

convex border of the tentorium cerebelli. Upon reaching the petrous fossa, they become the sigmoid sinuses

• It is connected to the suboccipital venous plexus • Surface markings: each transverse sinus extends from

the ext occipital protuberance to the base of the mastoid process

Venous sinuses

Venous sinuses of the dura

Confluence of sinuses:

• Is where the superior sagittal & staright sinuses end at the right and left. Transverse sinuses begin (near the internal occipital protuberance)

Cavernous sinus

• This sinus extends from the superior orbital fissure to the petrous temporal bone behind

• It consists of one or more venous channels in a dural compartment bounded by the sphenoid bone and the tentorium

• This dural compartment contains also the internal carotid artery, a symathetic plexus, CN III, IV, VI and the ophthalmic & maxillary divisions of the CN V.

• The sinus receives: superior ophthalmic vein, superficial middle cerebral vein and the sphenoidal sinus

• It communicates with the internal juguar vein and transverse sinuses

Cavernous sinus

In the walls: 1 oculomotor 2 trochlear 4 V1 5 V2

Within: 3 abducent 6 autonomic plexus 7 internal carotid artery 8 pituitary gland 9 body of sphenoid bone

Venous sinuses of the dura

Sigmoid sinus:

• S shaped and is located in the posterior cranial fossa

• Continuation of the transverse sinus

• Curves downward and medially to mastoid part of the temporal bone.

• In the jugular foramen, it becomes continous with the internal jugualr vein

Venous sinuses

Meninges

Arachnoid Mater

Thin, intermediate layer that attaches to pia mater through web-like arachnoid trabeculae

Avascular layer

Held against dura by pressure of CSF

Subarachnoid space:

between arachnoid & pia

contains: arachnoid trabeculae & Cerebrospinal fluid (CSF)

Pia Mater

Very thin & delicate membrane that is highly vascularized

Adheres to brain surface & follows its contours

Meningeal Spaces

Epidural Space:

between dura & bone

not present normally

happens pathologically

(as hemorrhage)

Subdural Space:

between ?

not present normally

Subarachnoid Space:

a real space

contains CSF

Arterial Supply to Meninges (Dura & Calvaria)

Middle Meningeal a. & Accessory Meningeal a.:

Main meningeal artery, arises from the maxillary artery (br of ext CA)

2 Anterior meningeal a.:

From ethmoidal a. br of the ophthalmic a

4 Post. Meningeal a.:

2 from ascending pharyngeal a: br of the ext CA

& other 2 smaller branches

Blood supply of the dura

Middle Meningeal Artery is a branch of the maxillary artery

• and the principal & the largest artery of the supratentorial dura

• It enters the skull through the foramen spinosum. The pterion is known as the weakest part of the skull. Clinically, the pterion is relevant because the anterior division of the middle meningeal artery runs beneath it, on the inner side of the skull, which is quite thin at this point.

• A blow to the pterion (e.g. in boxing) may rupture the

artery causing an epidural hematoma.

Blood supply of the dura

• The anterior meningeal artery (2) is a branch of the anterior ethmoidal artery. Supplies floor of anterior cranial fossa.

• The Posterior Meningeal arteries (4): 2 from the ascending pharyngeal, 1 from the occipital and 1 from the vertebral art Supply the posterior cranial fossa below tentorium cerebelli.

Clinical correlations

• Meningeal hemorrhage: Epidural, subdural and subarachnoid hemorrahge

• Venous sinus thromboses: cavernous sinus thrombosis

• Meningitis