CNS Neuroanatomy 5

Longitudinal fissure

Deep midline groove that separates the left and right cerebral hemispheres and orients cortical lobes.

Common carotid artery

Major neck artery that ascends the neck and bifurcates into the internal and external carotid arteries.

External carotid artery

Branch of the common carotid supplying the neck and superficial head structures (facial, lingual, occipital, superficial temporal arteries).

Internal carotid artery

Branch of the common carotid that enters the skull to supply the brain and gives rise to the ophthalmic, anterior cerebral, and middle cerebral arteries.

Carotid sinus

Dilated region at the base of the internal carotid containing baroreceptors and chemoreceptors that monitor blood pressure and blood chemistry.

Vertebral arteries

Pair of arteries that ascend through the transverse foramina of cervical vertebrae, enter the skull, and fuse to form the basilar artery.

Basilar artery

Single midline artery formed by fusion of the vertebral arteries; gives off pontine branches and bifurcates into the posterior cerebral arteries.

Circle of Willis (cerebral arterial circle

Ring-like anastomosis at the base of the brain formed by anterior/posterior communicating arteries connecting ACA, MCA, and PCA territories to provide collateral flow.

Anterior cerebral artery (ACA)

Branch of the internal carotid that supplies medial and superior frontal lobes and medial parietal lobes; supplies motor/sensory cortices for the lower extremity.

Middle cerebral artery (MCA)

Continuation of the internal carotid supplying the lateral convexity of frontal, parietal, and temporal lobes; supplies face/upper limb motor and sensory cortices, Broca/Wernicke regions, and auditory cortex.

Posterior cerebral artery (PCA)

Branch of the basilar artery that supplies inferior/medial temporal lobe (including hippocampus), inferior/medial occipital lobe (primary visual cortex), and portions of the thalamus.

Anterior communicating artery

Small vessel connecting the two anterior cerebral arteries that completes the anterior part of the Circle of Willis and enables cross-flow between hemispheres.

Posterior communicating artery

Connects posterior cerebral artery with internal carotid/middle cerebral circulation, forming the posterior connection in the Circle of Willis for collateral flow.

Ophthalmic artery

First intracranial branch of the internal carotid that supplies the orbit and the eye.

Superior cerebellar artery

SCA; branch of the basilar artery supplying superior cerebellum and parts of midbrain.

Anterior inferior cerebellar artery (AICA

Branch of the basilar artery supplying the anterior-inferior cerebellum and portions of the pons.

Posterior inferior cerebellar artery (PICA

Branch of the vertebral artery supplying inferior cerebellum and lateral medulla; PICA infarct causes lateral medullary (Wallenberg) syndrome.

Cerebral perfusion pressure (CPP)

Net pressure driving cerebral blood flow at the capillary level calculated as CPP = MAP − ICP; determines adequacy of brain perfusion.

Intracranial pressure (ICP)

Pressure within the rigid cranial vault produced by brain tissue, blood, and CSF; increases reduce CPP if MAP is unchanged.

Monro-Kellie doctrine

Principle stating the cranial cavity has fixed volume; increases in blood, CSF, or tissue volume must be compensated by decreases in another component or ICP will rise.

Normal ICP and CPP (typical values

Normal ICP ~5–15 mmHg; target CPP ~60–80 mmHg; CPP falls as ICP rises for a given MAP.

MAP (mean arterial pressure)

Average arterial pressure over one cardiac cycle; primary determinant of CPP when ICP is stable.

Acute effects of cerebral ischemia

Total interruption: seconds → loss of consciousness; ~4 minutes → risk of irreversible neuronal damage due to lack of oxygen/glucose.

Collateral circulation role

Communicating arteries and anastomoses provide alternate routes for blood flow that can preserve tissue when a primary artery is occluded.

MCA stroke typical deficits

Contralateral weakness and sensory loss predominantly of face and arm; aphasia if dominant hemisphere is affected; visual field deficits (contralateral homonymous hemianopia).

ACA stroke typical deficits

Contralateral weakness and sensory loss predominantly of the lower limb and medial frontal lobe signs such as executive dysfunction or abulia.

PCA stroke typical deficits

Contralateral visual field loss (homonymous hemianopia), memory disturbances when hippocampus is involved, thalamic sensory loss if thalamus affected.

Lateral medullary (Wallenberg) syndrome (PICA infarct signs

Contralateral body pain/temp loss, ipsilateral facial pain/temp loss, dysphagia, hoarseness, vertigo, and cerebellar signs.

Cerebellar artery infarct consequences

Ataxia, dysmetria, vertigo, nausea/vomiting, and potentially mass effect with increased ICP and herniation if large.

Large-vessel occlusion consequences

Extensive territory ischemia causing rapid neurologic deficits, high risk of swelling, increased ICP, and secondary herniation if untreated.

Watershed (border-zone) infarcts

Ischemia in regions between major arterial territories (e.g., ACA–MCA) often due to systemic hypotension or reduced CPP; causes proximal limb weakness and higher-order deficits.

Internal capsule ischemia (lacunar infarct consequence

Small penetrating artery occlusion producing pure motor or sensory stroke due to dense corticospinal/corticobulbar fiber concentration.

Internal capsule

Compact bundle of projection fibers between basal nuclei and thalamus containing major corticospinal and corticobulbar tracts; vulnerable to small-vessel disease.

Projection fibers

White-matter tracts connecting the cerebral cortex with subcortical structures, brainstem, and spinal cord; include corticospinal (pyramidal) fibers.

Association fibers

White-matter tracts that interconnect cortical regions within the same hemisphere (e.g., arcuate fasciculus linking language areas).

Commissural fibers

Tracts connecting homologous cortical areas between hemispheres, largest example being the corpus callosum.

Pyramidal (corticospinal) tract

Direct descending pathway from primary motor cortex through internal capsule and medulla (pyramids) to spinal ventral horn LMNs for fine voluntary movements.

Extrapyramidal motor pathways

Indirect descending systems (rubrospinal, reticulospinal, vestibulospinal, tectospinal) that regulate posture, tone, reflexes, and gross movement patterns.

Rubrospinal tract

Originates in the red nucleus and modulates limb tone and motor coordination; part of extrapyramidal system.

Reticulospinal and vestibulospinal tracts

Brainstem pathways that maintain posture, balance, and muscle tone in response to vestibular and reticular formation inputs.

Effect of increased ICP on CPP

As ICP rises toward MAP, CPP decreases and cerebral blood flow falls, risking global ischemia; aggressive ICP control may be necessary in TBI.

TBI management goals related to perfusion

Lower ICP (e.g.,

60 mmHg to preserve cerebral blood flow and oxygen delivery.

Mass effect and herniation sequence

Intracranial mass → increased ICP → brain shift → herniation → brainstem compression → loss of autonomic control → global ischemia and death.

Time sensitivity of stroke treatment

Because neuronal loss begins within minutes, rapid restoration of blood flow (reperfusion therapies) is critical to reduce permanent deficits.

Ophthalmic artery occlusion consequence

Loss of retinal perfusion causing sudden monocular vision loss (clinical correlate of internal carotid proximal occlusion).

Basilar artery occlusion consequences

Severe posterior circulation stroke causing brainstem dysfunction, locked-in syndrome, coma, or death if untreated.

Posterior communicating artery aneurysm clinical relevance

PCom aneurysms can compress oculomotor nerve causing eye movement palsies and are near the Circle of Willis where rupture causes subarachnoid hemorrhage.