Lecture 6: Skull

Question 1

Optic Canal

Answer 1

CNII (Optic Nerve)

Question 2

Superior Orbital Fissure

Answer 2

CNIII (Oculomotor)
CNIV (Trochlear)
CNVI (Abducens)
CNV–> V1 branch

Question 3

Foramen Ovale

Answer 3

V3 –> Mandibular branch of the trigeminal nerve

Question 4

Foramen Spinosum

Answer 4

Middle Meningeal Artery

Question 5

Internal Carotid Artery

Answer 5

Enters the cranial vault via the CAROTID FORAMEN, passing through the BONY CANAL and entering into the calvaria via the CAROTID CANAL.

Question 6

CNVII (Facial)

Answer 6

Enters the INTERNAL AUDITORY MEATUS.

Exits via the STYLOMASTOID FORAMEN.

Question 7

CNVIII (Vestibulocochlear)

Answer 7

Enters in the INTERNAL AUDITORY MEATUS.

Exits via the EXTERNAL AUDITORY MEATUS.

Question 8

Jugular Foramen

Answer 8

CNIX (Glossopharyngeal)
CNX (Vagus)
CNXI (Spinal Accessory)
***All 3 exit from here.

Question 9

CNXI (Accessory)

Answer 9

Enters via the FORAMEN MAGNUM.

Joins the cranial branches and exits via the JUGULAR FORAMEN.

Question 10

CNXII (Hypoglossal)

Answer 10

Exits via the HYPOGLOSSAL CANAL.

Question 11

What space harbors the bulk of the CSF?

Answer 11

Subarachnoid

Question 12

What two major pairs of arteries provide blood supply to the brain?

Answer 12

Right and Left Internal Carotid Artery.

Right and Left Vertebral Arteries.

Question 13

Where do the common carotid arteries bifurcate?

Answer 13

In the neck, just below the angle of the jaw.

Question 14

What areas does the ECA supply?

Answer 14

face, scalp, and meninges covering the brain

Question 15

Describe the path of the ICA

Answer 15

They ascend and travel through the carotid canal, enter the cranial vault alongside the cavernous sinus. At this point , they make a hairpin turn backwards and continue on as the middle cerebral artery and anterior cerebral arteries.

Question 16

What is the first branch of the ICA?

Answer 16

The ophthalmic arteries, which branch off near the apex of the hairpin turn.

Question 17

Where do the right and left vertebral arteries originate from?

Answer 17

Subclavian arteries.

Question 18

Describe the path of the vertebral arteries

Answer 18

They enter the vertebral foramen bilaterally at the C6 level and travel upward through these foramen, entering the skull via the foramen magnum.
The two join at the junction of the medulla and pons to form the BASILAR ARTERY.

Question 19

What can occur if there is head trauma in the region of the middle meningeal artery?

Answer 19

Bleeding into the epidural space can occur.
**This is a neurological and neurosurgical emergency with death occurring within a few hours if undiagnosed and untreated.

Question 20

Why is the circle of willis important?

Answer 20

It provides the possibility for collateral flow if one or more of the four major arteries supplying the brain are obstructed or occluded.

Question 21

What composes the Circle of Willis?

Answer 21

It consists of the posterior cerebral arteries connected to the internal carotid arteries via the posterior communicating arteries.
The anterior A1 segment of the anterior cerebral arteries and the anterior communicating artery complete the Circle of Willis.

Question 22

What can result of you occlude any of the major sinuses of the brain?

Answer 22

Seizures, tissue injury, or blockage of the CSF circulation.

Question 23

What allows communication between the 3rd and 4th ventricles?

Answer 23

Cerebral Aqueduct (Aqueduct of Sylvius)

Question 24

What allows communication between the lateral ventricles and the midline third ventricle?

Answer 24

Interventricular Formamen of Monro.

Question 25

Where and how is CSF created?

Answer 25

It is made in the choroid plexus by specialized epithelial cells that line the lateral, third and fourth ventricles.

Question 26

Describe the path of CSF

Answer 26

1. Escapes the lateral ventricles into the third via the foramen of mono.
2. Enters the fourth via the aqueduct of Sylvius.
3. Leaves the fourth via the foramen of MEgendie and Luschka.
4. Once in the subarachnoid space, some of the CSF circulates down around the spinal cord where 10% is reabsorbed at the egress point of the nerve roots.
5. The bulk of the CSF (90%) is reabsorbed into the venous sinuses via the arachnoid granulations.

Question 27

What are the arachnoid granulations?

Answer 27

Outpouchings of the arachnoid that protrude into the large venous sinuses.

Question 28

What is the rate of CSF production?

Answer 28

~20mL/hr

Question 29

Obstructive Hydrocephalus

Answer 29

Buildup of intraventricular CSF caused by obstruction of the outflow pathways between the lateral and third and third and fourth ventricles.

Question 30

True or False: Brain capillaries contain fenestrations?

Answer 30

False; Systemic capillaries do though.

Question 31

What creates the BBB?

Answer 31

Tight junctions between capillary endothelial cells.

Question 32

What is the function of astrocytes?

Answer 32

They provide an additional layer of protection to the brain by preventing the direct access of substances in the blood from reaching neurons.

Question 33

Describe the Choroid Plexus

Answer 33

It is created by an outpouching of capillaries and the pia mater into the ventricular space.

It sandwiches capillary blood vessels between layers of the arachnoid membrane and the pia mater.
**There is an additional layer of cells that line the outpouchings of the choroid plexus.

Question 34

Describe the extra layer of cells found in the choroid plexus.

Answer 34

These cells are contiguous with the cells lining the ventricular walls. They are called ependymal cells in the ventricles but are called choroid epithelium when they line the choroid outpouchings.

Question 35

How can you distinguish between ependymal cells and choroid epithelium?

Answer 35

Ependymal cells have normal fenestrations but choroid epithelial cells are found in very close approximation to one another. This prevents passage of particles through the choroid plexus into the ventricular CSF.

Question 36

What are the circumventricular organs? (Brain structures without BBB)

Answer 36

1. Pineal Gland
2. Area Postrema
3. Sublomical Organ?
4. Posterior Pituitary (Neurohypophysis)
5. Median Eminence
6. Organum Vasculosum of the Lamina Terminals (OVLT)

The function of several of these areas is unknown, but the organum vasculosum and neurohypophysis are well known to monitor and regulate electrolyte balance and several important hormones, respectively.