Spinal Cord, Brain, Meninges

Pterion

- Junction of frontal, sphenoid, parietal, and temporal bones - Bone very thin here - Middle meningeal artery (branch of external carotid a.) is right below and can rupture with fractures to the pterion, causing an epidural hematoma, which can be fatal if untreated.

Cauda equina

- Length of dorsal and ventral roots increases as you move caudally due to increasing distance between spinal cord and target - Elongated dorsal and ventral roots form cauda equina (horses tail) - Lies within the lumbar cistern. Subarachnoid block can be performed in lumbar cistern to anesthetize roots in cauda equina

Dural venous sinuses (general)

- Lie between the periosteal and meningeal layers of the dura - Receive blood from the brain (e.g. cerebral veins) - Drain blood into the IJVs

Cranial Dura Mater

- Middle Meningeal artery provides blood supply to the dura mater - Rupture of these vessels can cause blood to accumulate superifical to the dura, forming an epidural hematoma. - In contrast to the spinal dura mater (which was just one layer), the cranial dura mater is composed of two layers: 1. External periosteal layer (lines surface of neurocranium) 2. Internal meningeal layer

Posterior cranial fossa

- Occipital bone - Brainstem and cerebellum are contained within - Foramina: Internal Acoustic Meatus → CN 7, 8 Jugular Foramen → CN 9, 10, 11, IJV Hypoglossal Canal → CN 12 Foramen Magum: CN 11 enters skull; Medulla, meninges, vertebral arteries

Transverse sinuses

- Pass laterally from the confluence of sinuses - Within the posterior border of the tentorium cerebelli

Cavernous Sinus Syndrome

- Refers to damage to the structures passing through the cavernous sinus - Causes include tumor, infection (spread via ophthalmic veins), arterial rupture (internal carotid artery)

Neurocranium

- Skull includes neurocranium (cranial vault) and the viscerocranium (facial skeleton). - Calvaria: forms roof of neurocranium - Basicranium: forms floor of neurocranium Composed of four unpaired bones: frontal, sphenoid, occipital, ethmoid And two paired bones: parietal, temporal

Middle Cranial Fossa

- Temporal and sphenoid bones - Temporal lobes and pituitary gland are contained within - Foramina: Optic canal → optic nerve and ophthalmic artery (branch of internal carotid). Superior orbital fissure→ CN 3, 4, 6, V₁, ophthalmic veins Foramen rotundum: V₂ Foramen ovale: V₃ Foramen spinosum: middle meningeal artery & vein Foramen lucerum: Internal carotid passes horizontally across this region after passing through the carotid canal in the temporal bone

Spinal Dura Mater

- Tough, superficial CT layer - Continuous with cranial DM at the foramen magnum - Forms dural sac around the spinal cord (terminates at S2 vertebral level)

What are the three divisions of the brain?

Cerebrum, Brainstem, Cerebellum

Spinal cord enlargements occur in which regions?

Cervical (C4-T1) and lumbar (L1-L3). Give rise to plexuses in these regions.

Cranial pia mater

Delicate later applied directly to the surface of the brain

Straight sinu

- Formed by the union of great cerebral vein (of Galen) and the inferior sagittal sinus - Lies at the junction of falx cerebri and tentorium cerebelli

Confluence of sinuses

- Formed by the union of superior sagittal, straight, and occipital sinuses

Spinal nerve

- A dorsal and ventral root come together briefly to form a spinal nerve - A pair of spinal nerves is associated with each spinal segment - Spinal nerves traverse the intervertebral foramina - Spinal nerves carry mixed sensory and motor information

Circle of Willis

- Anterior and posterior circulations communicate (anastamose) - Vessels forming the circle include: internal carotid, anterior cerebral, anterior communicating, posterior communicating, posterior cerebral. - Some individuals do not have a complete circle.

Cerebrum

- Cerebral hemispheres are separated by longitudinal fissure (and falx cerebri) - Surface consists of gyri (folds) and sulci (grooves) - Each hemisphere is divided into lobes: frontal lobe, parietal lobe, occipital lobe, temporal lobe

Conus medullaris

- Composed of sacral spinal cord segments (and coccygeal if present) - Terminates at L1 or L2 level in most adults - Lumbar puncture: Performed to extract CSF from subarachnoid space. Insert a needle into L3-L4 or L4-L5 interlaminar space to avoid conus medullaris. Recall iliac crests are at L4, use this landmark to find appropriate space.

Brainstem

- Consists of midbrain (not visible), pons, medulla oblongata - Gives rise to most of the cranial nerves

Sigmoid sinuses

- Continuation of transverse sinuses once they exit the tentorium cerebelli - Form deep grooves in the occipital and temporal bones - Continuous with IJVs at the jugular foramen

Headaches and migraines

- Cranial dura mater are primarily sensory innervated by branches of CN V and X. Important for the development of migraines.

Spinal Arachnoid Mater

- Deep to DM - More delicate CT

Cranial Subarachnoid space

- Deep to arachnoid mater and superficial to pia mater - Contains CSF - Contains Arachnoid trabeculae, or extensions of the arachnoid mater that attach it to the pia mater

Spinal Subarachnoid space

- Deep to arachnoid mater and superficial to pia mater - Extensions of arachnoid mater extend into the space (arachnoid trabecula). They serve to connect the arachnoid and pia maters. - CSF is located in this space and functions to protect the CNS - Lumbar cistern: enlargement of the subarachnoid space in the lower lumbar region of the vertebral column. Extends to the caudal limit of the dural sac at S2.

Spinal Pia mater

- Deep to the subarachnoid space - Thin CT later that is closely adhered to the spinal cord - Denticulate ligaments: lateral extensions of pia mater that pass through the arachnoid layer and attach to the internal surface of the dura mater. - Function to anchor the spinal cord.

Epidural Space

- Deep to the vertebral canal, superficial to DM - Contains fat, CT, veins - Inferior to L2: also contains dorsal and ventral roots - Epidural: needle inserted into epidural space to inject anesthetic.

Dorsal and Ventral Roots of SC

- Each spinal cord segment gives rise to dorsal and ventral rootlets, which converge to form a pair of dorsal (sensory) and ventral (motor) roots and are house within the vertebral canal. - DRG: contain sensory cell bodies and are located in the intervertebral foramina.

Dorsal and ventral ramus

- Each spinal nerve exits the vertebral column and gives rise to a dorsal and ventral ramus (they contain BOTH motor and sensory fibers)

Filum terminale

- Extends from tip of conus medullaris to sacral hiatus, and serves to anchor the spinal cord inferiorly.

Cranial Arachnoid Mater

- Extensions of the arachnoid mater, called arachnoid granulations, are involved in the transfer of CSF to the venous system

Anterior Cranial Fossa

- Formed by frontal, sphenoid, and ethmoid bones - Frontal lobes and olfactory bulbs & tracts are contained within - Foramina and structures transmitted: foramina of the cribiform plate → CN I

Dural reflections (general characteristics and list the four).

- Formed by the fusion of adjacent layers of meningeal dura - Dive between parts of the brain 1. Falx cerebri: lies between the cerebral hemispheres in sagital plane. Anterior attachments include the frontal crest and crista galli. Posterior attachment to the occipital bone. 2. Tentorium cerebelli: lies between the occipital lobes of the brain and the cerebellum in the transverse plane. Anterior attachment include the posterior clinoid processes and petrous ridge. Posterior attachment include the occipital and parietal bones. 3. Falx cerebelli: lies between the cerebellar hemispheres in a sagital plane. 4. Diaphragm sellae: attached to the clinoid processes. Forms roof over pituitary gland, but allows passage of infundibulum (pituitary stalk) and veins.

Cavernous sinuses

- Venous plexuses located on either side of the hypophysial fossa - Venous supply includes the orbit (via ophthalmic veins) and brain (via middle cerebral vein) - Venous return: Posteriorly: superior petrosal sinus (which joins the transverse sinus) Inferiorly: Into the pterygoid plexus - Structures passing through the cavernous sinuses: Internal carotid artery (only structure in body where an artery passes through a vein), and the Abducent Nerve (CN 6). - Structures within the walls of the cavernous sinuses: CN 3, 4, V₁, V₂

List the spinal meninges layers and associated spaces from superficial to deep.

1. Epidural space 2. Dura mater 3. Arachnoid mater 4. Subarachnoid space 5. Pia mater 6. Spinal cord!

Anterior Circulation of the Brain

1. Internal Carotid enters the carotid canal in the temporal bone. 2. It then courses medially and horizontally (superior to cartilage covering foramen lacerum). 3. Then turns superiorly to pass through the cavernous sinus. 4. Then emerges from the cavernous sinus, where it gives rise to the ophthalmic artery, anterior cerebral artery (with anterior communicating artery), and middle cerebral artery.

Posterior Circulation of the Brain

1. Vertebral arteries → branches are from the subclavian arteries, and travel superiorly within the transverse foramina of C6-C1. They then enter the cranium via foramen magnum. 2. These give rise to the basilar artery 3. Then give rise (laterally) to paired posterior cerebral arteries. 4. These give rise (anteriorly) to posterior communicating arteries.

List the number of spinal cord segments in each region.

8 Cervical 12 Thoracic 5 Lumbar 5 sacral 1 coccygeal (can be absent)

Dura-arachnoid junction

A space may develop here as a result of trauma (e.g. rupture of a cerebral vein as it enters the dural venous sinus), forming a dural border (subdural) hematoma

Sutures of the neurocranium

Saggital suture: Between two parietal bones Coronal suture: Between the frontal and parietal bones Lambdoid suture: Between the occipital, temporal, and parietal bones

Inferior Sagittal sinus

Within the inferior border of falx cerebri

Superior sagittal sinus

Within the superior border of falx cerebri