Basic Neuroanatomy I: The Brain Flashcards
Segments of the brainstem
- Midbrain
- Medulla
- Pons
The medulla transitions seamlessly from midbrain to . . .
. . . the spinal cord
Gyri
The folds of the brain, which help maximize the surface area to volume ratio of the brain.
Sulci
The spaces between the gyri (or folds) of the brain
Fissures
Large divisions of brain material between hemispheres and lobes.
External view of brain hemisphere
Internal/corpus collosum view of brain hemisphere
Longitudinal fissure
Divides the brain into two hemispheres
Central sulcus
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.
Sylvian fissure
Divides the frontal and temporal lobes on a lateral view of the cerebrum.
Parieto-occipital sulcus
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.
Gray matter
Portion of the nervous system composed of neuron cell bodies
White matter
Part of the nervous system composed of myelinated axons
In the brain, cell bodies are found on. . .
. . . 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.
Gray and white matter of the brain (in axial section)
Gray and white matter of the spinal cord (in axial section)
In contrast to the brain, in the spinal cord, . . .
In contrast to the brain, in the spinal cord, the gray matter is on the inside, and the white matter is on the outside.
The meninges
From external to internal: Dura mater, arachnoid mater, pia mater
Falx cerebri and tentorium cerebelli
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
The pia mater is the only three of the meningeal layers that ____.
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.
The pia and arachnoid are collectively referred to as the ____, and the dura mater is referred to as the ____.
The pia and arachnoid are collectively referred to as the leptomeninges, and the dura mater is referred to as the pachymeninges
Why is the distinction between leptomeninges and pachymeninges important?
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.
Epidural space
The space above the dura, but beneath the bone.
Subdural space
The space beneath the dura, but above the arachnoid mater
Subarachnoid space
The space beneath the arachnoid mater, but above the pia mater.
Cerebral venous sinuses
Path of venous drainage from the brain once it exits the sinuses
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.
The superior sagittal sinus empties into. . .
. . . the bilateral transverse sinuses
The transverse sinuses empty into. . .
. . . the sigmoid sinuses, by passing through the tentorium cerebelli
The sigmoid sinuses empty into. . .
. . . the jugular veins.
Venous drainage of deep brain structures
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).
Venous drainage of lateral brain cortices
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
Impaired venous drainage
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.
Choroid plexus
Structure which lines the ventricles and produces CSF. Makes up an important portion of the blood-brain barrier.
Structure of cerebral ventricles
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
Communication between ventricles and subarachnoid space
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
CSF reabsorption
CSF is reabsorbed via the arachnoid granulations into the venous sinuses
CSF flow schematic
Hydrocephalus
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.
In what case of hydrocephalus will you see symmetrical dilation in all ventricles?
Communicating hydrocephalus (failure of reabsorption)
Importance of distinguishing communicating and noncommunicating hydrocephalus
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.
“Anterior circulation” vs “Posterior circulation” in the brain
Anterior circulation is supplied by the paired internal carotid arteries, while posterior circulation is supplied by the paired vertebral arteries.
Each internal carotid artery ultimately gives rise to. . . .
. . . 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.
Brain blood supply schematic
MR angiogram of arterial supply to cerebrum
Vertebral arteries
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.
Posterior cerebral arteries
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.
Circumferential arteries
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]).
The anterior circulation and posterior circulation are linked by the ___, and the ACAs are linked by the ___.
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.
Anatomic variants of the circle of Willis
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.
What is the biggest difference between how subdural and epidural hematomas look on non-contrast CT or other imaging?
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.
Epidural hematomas tend to happen more in . . .
. . . 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.
What is the most frequently cited cause of an epidural hematoma?
Tear in one of the middle meningeal arteries
Acute hematomas will appear ___ on non-contrast CT scan
Acute hematomas will appear bright (when compared to surrounding brain tissue) on non-contrast CT scan
