Basic Neuroanatomy I: The Brain

Question 1

Segments of the brainstem

Answer 1

• Midbrain
• Medulla
• Pons

Question 2

The medulla transitions seamlessly from midbrain to . . .

Answer 2

. . . the spinal cord

Question 3

Gyri

Answer 3

The folds of the brain, which help maximize the surface area to volume ratio of the brain.

Question 4

Sulci

Answer 4

The spaces between the gyri (or folds) of the brain

Question 5

Fissures

Answer 5

Large divisions of brain material between hemispheres and lobes.

Question 6

External view of brain hemisphere

Answer 6

Question 7

Internal/corpus collosum view of brain hemisphere

Answer 7

Question 8

Longitudinal fissure

Answer 8

Divides the brain into two hemispheres

Question 9

Central sulcus

Answer 9

Divides the superior aspect of the brain into the frontal and parietal lobes.

The somatosensory and motor cortices of the parietal and frontal lobes, respectively, border this sulcus.

Question 10

Sylvian fissure

Answer 10

Divides the frontal and temporal lobes on a lateral view of the cerebrum.

Question 11

Parieto-occipital sulcus

Answer 11

The parietal lobe and occipital lobe have no clear boundary on the lateral surface of the brain, but are separated by the parieto-occipital sulcus on the medial surface of the brain.

Question 12

Gray matter

Answer 12

Portion of the nervous system composed of neuron cell bodies

Question 13

White matter

Answer 13

Part of the nervous system composed of myelinated axons

Question 14

In the brain, cell bodies are found on. . .

Answer 14

. . . the cortex, on the outer surface of the brain. Their axons and all of the connections take place beneath the surface, in the sub-cortical white matter.

However, there are also islands of subcoritcal gray matter, which make up the basal ganglia and thalamus.

Question 15

Gray and white matter of the brain (in axial section)

Answer 15

Question 16

Gray and white matter of the spinal cord (in axial section)

Answer 16

Question 17

In contrast to the brain, in the spinal cord, . . .

Answer 17

In contrast to the brain, in the spinal cord, the gray matter is on the inside, and the white matter is on the outside.

Question 18

The meninges

Answer 18

From external to internal: Dura mater, arachnoid mater, pia mater

Question 19

Falx cerebri and tentorium cerebelli

Answer 19

Falx cerebri: Folds of the dura mater that extend between the hemispheres

Tentorium cerebelli: Folds of the dura mater that extend between the cerebral hemispheres and cerebellum

Question 20

The pia mater is the only three of the meningeal layers that ____.

Answer 20

The pia mater is the only three of the meningeal layers that invaginates into the sulci of the brain, and therefore makes contact with its entire surface area.

Question 21

The pia and arachnoid are collectively referred to as the ____, and the dura mater is referred to as the ____.

Answer 21

The pia and arachnoid are collectively referred to as the leptomeninges, and the dura mater is referred to as the pachymeninges

Question 22

Why is the distinction between leptomeninges and pachymeninges important?

Answer 22

In general, infectious meningitis predominantly affects the leptomeninges and inflammatory meningitis predominantly affects the pachymeninges, although there are exceptions

(e.g., neurosarcoidosis can affect the leptomeninges, and tuberculosis and fungal infections can affect the pachymeninges). Metastatic cancer may affect either.

Question 23

Epidural space

Answer 23

The space above the dura, but beneath the bone.

Question 24

Subdural space

Answer 24

The space beneath the dura, but above the arachnoid mater

Question 25

Subarachnoid space

Answer 25

The space beneath the arachnoid mater, but above the pia mater.

Question 26

Cerebral venous sinuses

Answer 26

Question 27

Path of venous drainage from the brain once it exits the sinuses

Answer 27

The venous drainage from the brain ultimately ends up in the **internal jugular veins** that travel through the **subclavian veins** to the **superior vena cava.**

Question 28

The superior sagittal sinus empties into. . .

Answer 28

. . . the bilateral **transverse sinuses**

Question 29

The transverse sinuses empty into. . .

Answer 29

. . . the **sigmoid sinuses**, by passing through the tentorium cerebelli

Question 30

The sigmoid sinuses empty into. . .

Answer 30

. . . the jugular veins.

Question 31

Venous drainage of deep brain structures

Answer 31

Drained by the **internal cerebral veins** and the **basal veins of Rosenthal,** which then empty into the central **Great vein of Galen** and **Straight Sinus**. The Straight Sinus then joins the Superior Sagital Sinus at the **Confluence**, and **both empty into the Transverse Sinuses (aka the torcula).**

Question 32

Venous drainage of lateral brain cortices

Answer 32

The lateral hemispheres are drained by superficial cortical veins. The largest of these are the veins of **Trolard** and **Labbé.** Mnemonic: **Trolard** is on **top** and **Labbé** is **lower** and more **lateral.** **#9 and 11** in the attached image

Question 33

Impaired venous drainage

Answer 33

When venous drainage is impaired (e.g., due to venous sinus thrombosis), **intracranial pressure rises**, which can cause **headache, visual disturbances,** and ultimately **coma.** If pressure in the venous system rises to a sufficient level, **intracerebral or subarachnoid hemorrhage** can occur, causing **focal deficits.**

Question 34

Choroid plexus

Answer 34

Structure which lines the ventricles and produces CSF. Makes up an important portion of the blood-brain barrier.

Question 35

Structure of cerebral ventricles

Answer 35

The **two lateral ventricles** drain into the **third ventricle** via the **foramina of Monro (bilateral).** The CSF then flows from the **third ventricle to the fourth ventricle** (between the brainstem and cerebellum) by way of the **cerebral aqueduct** in the midbrain. The fourth ventricle is **continuous with the central canal of the spinal cord**

Question 36

Communication between ventricles and subarachnoid space

Answer 36

From the fourth ventricle, CSF can exit the ventricular system into the subarachnoid space via the **foramen of Magendie (midline)** and the **foramina of Luschka (lateral)** to bathe the outer surface of the brain and spinal cord

Question 37

CSF reabsorption

Answer 37

CSF is reabsorbed via the **arachnoid granulations** into the **venous sinuses**

Question 38

CSF flow schematic

Answer 38

Question 39

Hydrocephalus

Answer 39

Caused by disruption of CSF flow by **obstruction anywhere along the CSF pathway.** May be classified as **communicating** or **noncommunicating**. Communication refers to the **ability of the ventricles to communicate** with one another. Generally speaking, **noncommunicating** indicates an **obtruction within CSF flow** system, while **communicating** indicates **failure of reabsorption.**

Question 40

In what case of hydrocephalus will you see symmetrical dilation in all ventricles?

Answer 40

Communicating hydrocephalus (failure of reabsorption)

Question 41

Importance of distinguishing communicating and noncommunicating hydrocephalus

Answer 41

Important because it guides whether or not **lumbar puncture** is an effective therapy. In **communicating hydrocephalus**, **lumbar puncture may relieve pressure** from the ventricular system and reduce symptomatology. In **noncommunicating hydrocephalus**, elevated intracranial pressure proximal to the obstruction can lead to **herniation** if fluid is removed from below by lumbar puncture.

Question 42

"Anterior circulation" vs "Posterior circulation" in the brain

Answer 42

**Anterior** circulation is supplied by the paired **internal carotid arteries**, while **posterior** circulation is supplied by the paired **vertebral arteries.**

Question 43

Each internal carotid artery ultimately gives rise to. . . .

Answer 43

. . . a paired **middle cerebral artery (MCA)**,an **anterior cerebral artery (ACA)**, an **ophthalmic artery,** and an **anterior choroidal artery.** These arteries together **supply the majority of the cerebral hemispheres** including the **frontal** lobes, **parietal** lobes, and **superior and lateral temporal** lobes. The ophthalmic artery **supplies the retina**, and the anterior choroidal artery **supplies the posterior thalamus and internal capsule**.

Question 44

Brain blood supply schematic

Answer 44

Question 45

MR angiogram of arterial supply to cerebrum

Answer 45

Question 46

Vertebral arteries

Answer 46

The vertebral arteries **arise from the subclavian arteries**, **then join** to form the **basilar artery** at around the level of the pontomedullary junction, and end by giving off the **posterior cerebral arteries (PCAs)** at the level of the upper midbrain.

Question 47

Posterior cerebral arteries

Answer 47

Supplied by the basilar arteries, and thus ultimately by the vertebral arteries. Supply the regions of the cerebral hemispheres not supplied by the MCAs and ACAs: the **occipital lobes** and **inferior and medial temporal lobes.**

Question 48

Circumferential arteries

Answer 48

Before giving rise to the PCAs, the **vertebrobasilar system** gives off **three paired circumferential arteries** that supply the **lateral brainstem and cerebellum** (superior cerebellar arteries [SCAs], anterior inferior cerebellar arteries [AICAs], and posterior inferior cerebellar arteries [PICAs]).

Question 49

The anterior circulation and posterior circulation are linked by the \_\_\_, and the ACAs are linked by the \_\_\_.

Answer 49

The anterior circulation and posterior circulation are linked by the **posterior communicating arteries**, and the ACAs are linked by the **anterior communicating artery.** **These connections form the circle of Willis** on the inferior surface of the brain, which provides routes for collateral flow.

Question 50

Anatomic variants of the circle of Willis

Answer 50

**Not all patients have a complete circle of Willis!** And some will have a complete circle, but different vascular structure stemming off. Be aware that **there may be anatomical variants** and you won't always see the full ring.

Question 51

What is the biggest difference between how subdural and epidural hematomas look on non-contrast CT or other imaging?

Answer 51

Both appear as bright masses which are 'squishing' the brain and make the ventricles appear misshapen. However, **subdural hematomas are not bound by sutures,** whereas **epidural hematomas are bound by sutures and will not cross suture lines.**

Question 52

Epidural hematomas tend to happen more in . . .

Answer 52

. . . **young patients**, and are more associated with bone breakages in the skull that tear superficial arteries. On the other hand, subdurals are associated with vein tearing, which is a more degenerative/chronic process and happens more commonly in older patients.

Question 53

What is the most frequently cited cause of an epidural hematoma?

Answer 53

Tear in one of the **middle meningeal arteries**

Question 54

*Acute* hematomas will appear ___ on non-contrast CT scan

Answer 54

*Acute* hematomas will appear **bright (when compared to surrounding brain tissue)** on non-contrast CT scan