SEM 3 ANATOMY: The Brain and Spinal Cord

What are the three meningeal layers?

Dura mater, arachnoid mater, pia mater.

What is the dura mater?

An outer periosteal layer and an inner meningeal layer. Its a tough and shiny fibrous tissue that lines the cranial cavity.

What is the extradural space?

The pathological space between the dura and cranial cavity where blood can leak from meningeal vessels and push the periosteum away from the cranium.

What is the arachnoid mater?

A thin, avascular membrane that is pushed up against the surface of the dura mater due to pressure from CSF.

What is the pia mater?

A thin, vascularised membrane that follows the sulci and gyri of the brain.

What are the 4 reflections/foldings of the dura mater?

Tentorium cerebelli, falx cerebri, falx cerebelli and diaphragmatic sellae.

What is the tentorium cerebelli and its attachments?

Reflection of dura that seperates the occipital lobe from the cerebellum. Attachments: clinoid process of the sphenoid, petrous part of the temporal bone, internal surface of the occipital bone and part of the parietal bone.

What is the falx cerebelli and its attachments?

Reflection of dura that partially splits the two cerebellar hemispheres. Attachments: internal occipital crest.

What is the falx cerebri and its attachments?

Dural reflection that sits in the longitudinal fissure and seperates the cerebral hemispheres. Attaches to the crista galli of the ethmoid bone, frontal crest and the internal occipital protuberance.

What is the diaphragmatic sellae and its attachments?

A sheet of dura mater that provides an opening for the infundibulum and hypophyseal veins and covers the pituitary gland. Attaches to the clinoid process of the sphenoid.

What main artery supplies the dura mater and what is its course?

The middle meningeal artery. It arises from the maxillary artery in the infratemporal fossa and enters the cranium through the foramen spinosum, where it runs between the periosteal and meningeal layers of the dura mater and forms grooves on the skull.

Why is the frontal branch of the middle meningeal artery at risk following trauma?

Because it cross the thinnest part of the skull, where the frontal, parietal, sphenoid and temporal bones meet.

What is the venous drainage of the dura mater and its course?

Middle meningeal veins that accompany the arteries, exit the skull through the foramen spinosum and drain into the pterygoid plexus.

What is the dura mater innervated by?

Vagus nerve, trigeminal nerve, CN I, II and III.

What significance does the tentorium cerebelli have in terms of headache?

Stimulation of receptors above the TC results in a headache on the same side of the head; stimulation of receptors below the TC results in pain on the back of neck and scalp.

What are the spinal meninges?

Dura mater: forms the dural sac.
Arachnoid mater: lines the dural sac and dural root sheaths.
Pia mater: covers the spinal cord, the roots of the spinal nerve and the spinal blood vessels.

What is the subarachnoid space?

The space between the arachnoid and pia that contains CSF.

What are dural root sheaths?

Lateral extensions of the spinal dura mater which surround the nerve roots.

What is the epidural space?

A space that exists between the dura mater and the periosteum of vertebrae and contains fat and venous plexuses.

What is the lumbar cistern?

An enlargement of the subarachnoid space at L2-S2, caudal to the conus medullaris, to contain the cauda equina and CSF.

What is the denticulate ligament?

A fibrous sheath of pia mater that suspends the spinal cord in the dural sac by extending laterally.

Where does the spinal cord terminate and where do the meninges terminate and how is that clinically relevant?

Spinal cord terminates at L1; spinal meninges terminate at S2. A sample of CSF can be obtained in this space through a lumbar puncture between L3-L4 or L4-L5.

What forms cerebrospinal fluid?

Choroid plexuses in the ventricles formed of ependymal cells.

What is the route of flow of CSF?

Lateral ventricles --> Interventricular foramen --> 3rd ventricle --> cerebral aqueduct --> 4th ventricle --> median and lateral apertures --> subarachnoid space.

How is CSF returned to the venous system?

Through arachnoid villi which project into the dural venous sinuses.

What are the 6 sub-arachnoid cisterns?

Cisterna ambiens; quadrigeminal cistern; cerebromedullary cistern; chiasmatic cistern; pontocerebellar cistern; interpeduncular cistern.

Where is the cisterna ambiens?

The lateral aspect of the midbrain, continuous with the quadrigeminal cistern.

Where is the quadrigeminal cistern and what does it contain?

Posterior part of the corpus callosum and cerebellum; contains parts of the cerebral vein and pineal gland.

Where is the cerebellomedullary cistern and where does it receive CSF from?

Between the cerebellum and medulla and receives CSF from medial and lateral apertures.

Where is the chiasmatic cistern and what does it contain?

Inferior and anterior to the optic chiasm; contains decussation of optic nerve fibres.

Where is the pontocerebellar cistern?

Anterior to pons.

Where is the interpeduncular cistern?

Between vertebral peduncles.

Where are dural venous sinuses located?

At the site of attachment of the dural reflections, between the periosteal and meningeal layers of the dura.

Where do dural venous sinuses drain?

Internal jugular vein.

Why is the cavernous sinus different from the other dural venous sinuses?

It is tranversed by a number of trabeculae that give it a sponge-like appearance so flow through the sinus is slow.

What artery traverses the cavernous sinus?

The internal carotid.

What five cranial nerves are associated with each cavernous sinus and where do they lie?

Four lie in the lateral wall: oculomotor, trochlear, ophthalmic and maxillary.
One runs though the sinus lateral to the internal carotid: abducens

What does the internal carotid arise form and what does it bifurcate into?

Arises from the common carotid and bifurcates into middle and anterior cerebral arteries.

What does the internal carotid enter the skull through?

Carotid canal?

What does the vertebral artery arise from and what does it form?

Arises from the subclavian; unites to form the basilar artery which divides into the posterior cerebral arteries.

Where does the middle cerebral artery run?

Between the frontal and temporal lobe in the lateral fissure.

Where does the anterior cerebral artery run?

In the longitudinal fissure after going behind the optic chiasm.

What forms the straight sinus?

The inferior sagittal sinus and great cerebral vein of Galen.

Where does the superior cerebral vein drain into?

The superior sagittal sinus.

Where do the inferior and superficial middle cerebral veins drain into?

Straight, transverse and superior petrosal sinus.

Where do the superior and inferior cerebellar veins drain into?

Transverse and sigmoid sinus.

What bones make up the neurocranium?

Parietal, ethmoid, frontal, occipital, temporal and sphenoid.

What bones make up the viscerocranium?

Zygomatic, lacrimal, nasal, vomer, inferior nasal concha, mandible, maxilla and palatine.

What are most of the joints of the skull?

Immoveable fibrous joints.

What are the 3 sutures of the skull?

Frontal, sagittal and lamdoidal.

When do the different fontanelles close?

Anterior: after 2-2.5 years
Posterior: at 3 months
Anterolateral (sphenoid): 3 months
Posterolateral: 1 year

What are the different fontanelles called when they close?

Anterior: Bregma
Anterolateral: pterion
Posterolateral: asterion
Posterior: Lambda

What is the metopic suture?

The suture that unites the frontal bones that usually fuses by 7 years of age.

What type of joint is the TMJ?

Synovial, modified hinge joint.

What are the superior and inferior articulating surfaces of the TMJ and what are they covered in?

Superior: mandibular fossa and articular tubercle of temporal bone.
Inferior: mandibular condyle.
Covered in fibrocartilage.

What does the joint capsule of the TMJ form when it thickens laterally?

The lateral temporomandibular ligament, which helps prevent posterior dislocation.

What 2 ligaments are associated with the TMJ?

Stylomandibular and sphenomandibular.

What is translation of the TMJ?

When the head of the mandible has to slide forward from the mandibular fossa onto the articular tubercle when the jaw needs to fully open.

What do the different cranial fossa contain?

Anterior: frontal lobes
Middle: pituitary gland and temporal lobes
Posterior: cerebellum, pons and medulla

What are the boundaries of the temporal fossa?

superior/posterior: inferior temporal lines
anterior: frontal process of zygomatic
lateral: zygomatic arch
medial: parietal and temporal bones
inferior: infratemporal crest of sphenoid
floor: parts of 4 bones that from pterion
roof: temporalis m.

What are the boundaries of the infratemporal fossa?

Superior: greater wing of sphenoid
Anterior: maxillary tuberosity
Medial: lateral pterygoid plate
Lateral: ramus and coronoid process of mandible

What are the boundaries of the pterygopalatine fossa?

Superior: inf surface of body of sphenoid
Anterior: maxillary tuberosity
Medial: vertical plane of palatine
Lateral: pterygomaxillary fissure
Inferior: pterygopalatine canal
Posterior: pterygoid process of sphenoid

What is kyphosis and lordosis?

Kyphosis: exaggerated sagittal curvature of thoracic region.
Lordosis: inward curvature of lumbar and cervical spine

What are features of lumbar vertebrae?

Large, kidney-shaped body; triangular vertebral foramen; flat, short and quadrangular spinous processes; inf. articular facets face medially; sup. articular facets face laterally

What are features of cervical vertebrae?

Small, broad body; large triangular vertebral foramen; sup. articular facet faces posteriorly and superiorly; inf. articular facet faces anteriorly and inferiorly; has a foramen transversarium; small and bifid spinous process.

What are features of thoracic vertebrae?

Heart shaped body; long and downward-pointing spinous process; small, circular vertebral foramen; sup. articular facets face posterolaterally; inf. articular facets face anteromedially; costal facets on body and transverse processes.

Why is the atlas an atypical vertebrae?

Doesn't posses a body/spinous process, just anterior and posterior arches and two lateral masses.

Why is the axis an atypical vertebrae?

Possesses an odontoid process that projects superiorly from body.

Why is C7 an atypical vertebrae?

Possesses a long, non-bifid spinous process. Foramen transversarium is small and transmits only the vertebral vein, not artery.

What is the atlanto-occipital joint (type, articular surfaces, movement)?

Found between the occipital condyles and superior facets of the lateral masses of the atlas; condyloid synovial joint; allows flexion, extension and lateral flexion.

What ligaments support the atlanto-occipital joint?

Anterior atlanto-occipital ligament: connects anterior arch of atlas to anterior margin of foramen magnum.
Posterior atlanto-occipital ligmanent: connects posterior arch of atlas to posterior margin of foramen magnum.

What are the 3 atlanto-axial joints (articulations, types)?

Two lateral joints: plane; between inferior facet of atlas and superior facet of axis.
One medial: pivot; between anterior arch of atlas and odontoid process of axis.

What are the 5 supporting ligaments of the atlanto-axial joints?

Apical: connects dens to anterior margin of FM
Alar: connects dens to medial side of occipital condyles
Transverse part of cruciate: attached to inner aspect of lateral masses to hold dens against anterior arch of atlas.
Vertical cruciate: between post surface of body of axis to ant border of FM
Membrane Tectoria: extension of post longitudinal ligament, attaches to occipital bone and covers dens and other ligaments.

What are the zygophophyseal joints of the vertebral column?

Between adjacent superior and inferior articular facets; synovial plane joints.

What ligaments support the zygophophyseal joints?

Intertransverse: extends between adjacent transverse processes.
Ligamentum flavum: extends between lamina of adjacent vertebrae
Supraspinous: runs between the tips of adjacent spinous processes

What are the two parts of the intervertebral discs?

Annulus fibrosis and nucleus pulposus.

What are features of annulus fibrosis?

Forms periphery of intervertebral disc; made up of concentric layers of fibrocartilage; inserts into the epiphyseal rim of vertebral body; binds to ant. and post. longitudinal ligaments.

What are features of nucleus pulposus?

Composed of semifluid gelatinous substance that is 90% water. It is avascular. It is able to change shape and permit movement between vertebrae and act as a shock absorber.

What two ligaments support the vertebral column?

Anterior longitudinal ligament: from anterior surface of sacrum to occipital bone; limits extension.
Posterior longitudinal ligament; limits flexion.

What are the 31 spinal segments?

Cervical region: 8
Thoracic region: 12
Lumbar region: 5
Sacral region: 5
Coccygeal region: 1

Where do the lumbar, sacral and coccygeal nerve roots arise from?

Conus medullaris.

Where do ventral and dorsal rami exit in the sacral region?

Ventral rami: anterior sacral foramina
Dorsal rami: posterior sacral foramina

What is the blood supply to the spinal cord?

Anterior spinal artery: arises from vertebral; runs in anterior median fissure; supplies anterior aspect.
Two posterior spinal arteries: arise from vertebral or posterior inferior cerebellar arteries.
Radicular arteries: branches of ascending and deep cervical, vertebral, posterior intercostal and lumbar.

What is the blood supply to the vertebrae?

Branches of vertebral, ascending cervical, posterior intercostal, subcostal, lumbar, iliolumbar, lateral and medial sacral arteries.

What is the venous drainage of the spinal cord?

Drains into internal vertebral plexus --> regional vessels.

What is venous drainage of the vertebral column?

Drains into internal venous plexus, which then bleeds into the external venous plexus.

What are the nerve plexuses?

Cervical: C1-C5
Brachial: C5-T1
Lumbar: L1-L4
Sacral: L4-54

What is the course of the sciatic nerve?

Arises from L4-S3; emerges from greater sciatic foramen; enters buttock from under piriformis; lies deep to gluteus maximus; crosses ischial tuberosity; descends on obturator internus, gemelli and quadriceps femoris; lies deep to hamstrings and is crossed by long head of biceps; bifurcates into tibial and common peroneal.