MODULE 15B - [Anatomy 2.0] GENERAL ORGANIZATION OF THE NERVOUS SYSTEM

• Dura Mater

• Arachnoid Mater

• Pia Mater

MENINGES OF THE BRAIN

DURA MATER

• Outermost meningeal layer.

• A tough layer of tissue fused with the endosteum or inner periosteum of the skull.

• When it separates from the periosteum, the intervening

  space becomes the dural venous sinus.

• As the dura extends into the cranial cavity, it

  compartmentalizes the brain and facilitates its stability

  inside the skull.

• Falx Cerebri

• Tentorium Cerebelli

The two folds dural partitions that stabilize the brain

DURAL VENOUS SINUSES

Formed in areas where the periosteal layers separate from the meningeal layer

emissary veins

Dural Venous Sinuses are valveless and connected to the diploic veins of the skull and veins of the scalp by the _____

cerebral veins; subarachnoid space; arachnoid villi; internal jugular vein

VENOUS DRAINAGE OF DURA MATER

• The sinuses receive blood from the _____ and cerebrospinal fluid from the _____ through the _____ to ultimately drain into the _____

Cavernous Sinus

• Receives venous flow from multiple sources

• Extends from superior orbital fissure to the apex of petrous part of temporal bone

middle cranial fossa

The cavernous sinus is found in the ______ on each side of the body of the sphenoid bone

• (1) From the Face via Angular and Ophthalmic Veins

• (2) From the Middle Ear via Petrous Sinus

• (3) From the Teeth, Maxillary Sinus, and Cervical Vertebra via the Pterygoid Plexus, which empties into the Inferior Ophthalmic Vein

• (4) From the Sphenoid Sinus as a direct extension or draining emissary vein

• (5) From Infected Internal Jugular Vein, Lateral Sinus, and Petrosal Sinus

Routes through which cavernous sinus/septic thrombosis may occur

CN VI (abducens nerve)

Usually, the first CN to be affected by septic thrombosis because of its direct course through the sinus.

Ophthalmoplegia

may result from the orbital congestion and infection of the orbital muscles and ocular nerves.

pain receptors; brain parenchyma

The meninges contain _____ which are absent in the _____

Trigeminal Nerve (CN V)

The dura above Tentorium Cerebelli, which comprises the anterior and middle cranial fossa, is innervated by the _____

upper three cervical nerves (C1-C3); Vagus (CN X); Hypoglossal Nerves (CN XII)

The dura below Tentorium Cerebelli, (posterior cranial fossa) are innervated from the _____ and branches of the _____ and _____

trigeminocervical nucleus

• Mechanical irritation, such as tension from a raised or

  lower CSF (cerebrospinal fluid) pressure, dilatation of

  the arterial walls or stretch, or chemical irritations or

  Inflammations are detected by the _____

• The essential nociceptive nucleus of the head, throat, and upper neck

headache

All nociceptive afferents from the trigeminal, facial, glossopharyngeal, Vagus, C1-C3 spinal nerves ramify into the single column of grey matter, and will be interpreted as _____

• External carotid

• Maxillary

• Ascending Pharyngeal

• Occipital

• Vertebral

Enumerate the dural arterial supply

Middle meningeal artery

The most clinically important meningeal artery

maxillary artery; foramen spinosum

The Middle Meningeal Artery arises from the _____ and enters the cranial cavity via the ______

meningeal; endosteal layers

The Middle Meningeal Artery Lies between the _____ and _____

Intracranial Epidural Hematomas

Results from a brief linear contact force to the calvaria

periosteal dura; shearing stress

Intracranial Epidural Hematomas cause separation of the _____ from bone and disruption of interposed vessels due to _____

2%

Intracranial Epidural Hematomas occur in _____ of patients with head injury

5 to 15% of patients with fatal head injury are:

• 58%: acute

• 31%: sub-acute

• 11%: chronic

_____ to _____% of patients with fatal head injury are:

• _____%: acute Intracranial Epidural Hematomas

• _____%: sub-acute Intracranial Epidural Hematomas

• _____%: chronic Intracranial Epidural Hematomas

Temporo-parietal region; middle meningeal artery; 66% of cases

_____and _____: involved in _____% of Intracranial Epidural Hematomas cases

Anterior Ethmoidal Artery

_____: may be involved in frontal injuries

Epidural Hemorrhage

• A layer of dura is separated from the periosteum of the skull

  • The dense medial margin represents the dura

• Shape: biconvex or lenticular

• Does not cross suture lines

• Injury: middle meningeal artery

biconvex-shaped or lenticular

Epidural Hemorrhage appears as ______, and do not cross suture lines.

Subdural Hematomas

• Occur from bleeding into the potential space between the dura mater and arachnoid mater from a traumatic head injury

• Shape: crescent

• Crosses suture lines

• Injury: bridging veins

abusive head trauma

Subdural Hematoma is one of the intracranial injuries associated with _____, especially in pediatric patients

Bridging veins

_____ crosses the subdural space connecting superficial veins in the subarachnoid space with the venous sinuses

• May rupture when directly opposing forces rupture their thin walls, releasing blood under the dura mater forming a subdural hematoma

ARACHNOID MATER

• An avascular impermeable membrane that bridges over the sulci on the surface of the brain

• Its outermost cells are bonded to one another by tight

  junctions that seal the arachnoid space

• Enumerable arachnoid trabeculae cross the space to

  reach the pia mater

SUBARACHNOID SPACE

• Filled with cerebrospinal fluid (CSF)

• where all the cerebral arteries, veins, and cranial nerves lie

• Provides buoyancy to the brain

• Protects nervous tissue from mechanical forces applied to the skull

• Removes waste products associated with neuronal activity

Primary purposes of the CSF

Arachnoid villi

structures that transfer CSF from the subarachnoid space to be cleared to a lacuna connected to the superior sagittal sinus

subarachnoid cisterns

Along the base of the brain and the sides of the brainstem, pools of CSF occupy _____

• Cisterna magna

• Cisterna pontis

• Interpeduncular cistern

• Cisterna ambiens

Enumerate the different subarachnoid Cisterns

Cisterna magna

• Largest among the subarachnoid cisterns

• In the interval between the cerebellum and the medulla oblongata

Cisterna pontis

A Subarachnoid Cistern that is more rostral, ventral to the pons

Interpeduncular cistern

A Subarachnoid Cistern in between the cerebral peduncles

Cisterna ambiens

Subarachnoid Cistern at the side of the midbrain

Subarachnoid Hemorrhages

This may be caused by head trauma, ruptured cerebral aneurysm, or arteriovenous malformations

80% of cases

How many percentage of cases of Subarachnoid Hemorrhages are caused by a ruptured cerebral aneurysm

Cerebral aneurysms

most frequent cause of subarachnoid bleedings

immediate and strong headaches; vomiting and changes in consciousness

Ruptured cerebral aneurysm causes _____ and _____ headaches combined with _____ and _____

PIA MATER

• Tightly associates with the surface of the brain

• Invests the brain closely following its contours and lining the various sulci

• Like the arachnoid mater, it is FIBROCELLULAR

  • Cellular component: External & permeable to CSF

  • Fibrous component: Occupies a narrow subpial space, continuous with perivascular spaces around cerebral blood vessels penetrating brain surface

SPINAL DURA MATER

Continuous with the meningeal layer of the dura mater covering the brain through the foramen magnum

Extradural space

contains loose areolar tissue and vertebral venous plexus

SPINAL ARACHNOID MEMBRANE

• Continuous with the arachnoid of the brain covering the brain via the foramen magnum

• Ends inferiorly on the filum terminale at the lower border of the S2 vertebra

• This space is filled with cerebrospinal fluid (CSF)

SPINAL PIA MATER

• Closely covers the spinal cord

• Extends along each nerve root and becomes continuous with connective tissue surrounding each spinal nerve

Ligamentum denticulatum (denticulate ligament)

This ligament passes laterally to adhere to the arachnoid and dura

Brain

• Epidural: Potential

• Subdural: Potential

• Subarachnoid: Actual

Spinal Cord

• Epidural: Actual

• Subdural: Potential

• Subarachnoid: Actual

COMPARISON BETWEEN SPACES IN THE BRAIN AND SPACES IN THE SPINAL CORD

EPIDURAL ANESTHESIA

Space in the spinal cord is an actual space where anesthetics may be injected

CRANIUM BIFIDUM

Otherwise known as Encephalocele and is a rare birth defect where the skull doesn't close properly during fetal development, leading to brain tissue and meninges protruding through the defect

Ventricles

fluid-filled cavities within the brain derived from central lumen of the embryonic neural tube

Ventricular system composition: Paired lateral ventricles with frontal anterior horn, central part, occipital posterior horn, and temporal inferior horn

1st Ventricular system composition

Ventricular system composition: Third ventricle

2nd Ventricular system composition

Ventricular system composition: Cerebral aqueduct

3rd Ventricular system composition

Ventricular system composition: Fourth ventricle

4th Ventricular system composition

Foramen of Monro

separate interventricular foramen that connects each lateral ventricle to the third ventricle

Cerebral aqueduct

• connection between the third and fourth ventricles

• found in the midbrain

Fourth ventricle

This ventricle contains three (3) openings to drain CSF to the subarachnoid space between arachnoid and pia mater of the brain and spinal cord

• Median aperture or Foramen of Magendie (1)

• Paired lateral apertures or Foramen of Luschka (2)

Enumerate the three openings of the fourth ventricle that drain CSF to the subarachnoid space between arachnoid and pia mater of the brain and spinal cord,

cerebral hemispheres

Lateral ventricles tell the physician that he/she is

examining the _____

Location: Frontal Lobe

Location of the Anterior Horn Ventricle

Location: Parietal Lobe

Location of the Body

Location: Occipital Lobe

Location of the Posterior Horn

Location: Temporal Lobe

Location of the Inferior Horn

Third Ventricle

• Slit-like cleft between two thalami

Fourth ventricle:

• is at the level of the pons and cerebellum

Central canal

is at the level of the medulla and spinal cord

BLOOD-BRAIN BARRIER

Unique properties of blood vessels that vascularize CNS

• Allows blood vessels of the CNS to tightly regulate the movement of ions, molecules, and cells between the blood and the brain

• Precise control of the CNS homeostasis allows for proper neuronal function

• Protects neural tissue from toxins and pathogens

Properties of the Blood-Brain Barier

• (1) Continuous, non-fenestrated capillary wall

• (2) Astrocytic feet (ensheaths capillary)

• (3) Pericytes (embedded in the thick capillary basement

  membrane)

COMPONENTS OF THE BLOOD-BRAIN BARRIER

Inversely Related

Permeability of the Blood-Brain Barrier with size of molecules

Directly Related

Permeability of the Blood-Brain Barrier with Lipid Solubility

Blood-CSF Barrier

• at the choroid plexus epithelial cells joined together by tight junctions

Microvilli

Present on the CSF-facing surface, greatly increase the apical membrane surface area, and aid in fluid secretion

• Diffusion and facilitated diffusion

• Active transport into cerebrospinal fluid (CSF)

• Active transport of metabolites from CSF to blood

The blood-CSF barrier demonstrates these activities in the choroid plexus:

CIRCUMVENTRICULAR ORGANS

• Lack the blood-brain barrier

• Capable of monitoring the plasma blood milieu

• Characteristic features:

  • Strong vascularization

  • Modified ependyma

  • Formation of blood-CSF barrier, instead of blood-brain barrier

Circumventricular Organ: Neurohypophysis

1st Circumventricular Organs

Circumventricular Organ: Median eminence

2nd Circumventricular Organs

Circumventricular Organ: Pineal gland

3rd Circumventricular Organs

Circumventricular Organ: Vascular organ of the lamina terminalis

4th Circumventricular Organs

Circumventricular Organ: Subfornical Organ

5th Circumventricular Organs

Circumventricular Organ: Subcommissural organ

6th Circumventricular Organs

Circumventricular Organ: Area Postrema

7th Circumventricular Organs

Vascular organ of the lamina terminalis & Subfornical organ

This circumventricular organ regulates blood volume, blood pressure, hormone secretion (e.g. angiotensin, somatostatin)

Subcommissural organ

This circumventricular organ is present only in the fetus and newborn

Area Postrema

This circumventricular organ triggers vomiting

• Chemoreceptor activation = protective body mechanism

  • Exemplified by centrally induced vomiting in response to ingestion of spoiled food

  • Removes potentially harmful substances from the body

Dopamine and Serotonin

Area Postrema contains numerous ______ and ______ receptors

Choroid plexuses

• Produces most of the cerebrospinal fluid

• The circulating volume is about 150mL

• Exchanged constantly with the daily CSF production volume of approx. 500mL

• Pulsations of the choroid plexuses and the cilia of the ependymal cells

• Cerebral arteries

• Spinal arteries

• Movements of the vertebral column

• Respiration

• Coughing

• Changes in body position

The flow of CSF is assisted by the following

arachnoid villi

Absorption of the CSF is via _____ which project into the dural venous sinuses

• Occurs when the CSF pressure exceeds venous sinus pressure

HYDROCEPHALUS

Disturbances of formation, flow, or absorption of cerebrospinal fluid leads to an increase in volume occupied by the cerebrospinal fluid in the central nervous system.

Communicating Hydrocephalus

Caused by overproduction of CSF, defective absorption of CSF, and venous drainage insufficiency.

Non-Communicating Hydrocephalus

CSF flow is obstructed within the ventricular system or in its outlets to the subarachnoid space.

15-20%

The Central Nervous System requires _____ to _____% of the resting cardiac output to properly function.

• Internal carotid artery

• Vertebral arteries

Main arteries of supply of the brain that senses the momentary pressure changes

medullary chemosensitive area

Arterial oxygen tension is controlled by a _____ that monitors respiratory gas levels in the internal carotid artery and the cerebrospinal fluid.