ch 27 blood supply to the brain

Internal Carotids (2)

Route

rise from the common carotid artery and enter the brain at the level of the optic chiasm.

Supply

• These are the major arteries that supply the brain

Vertebral Arteries (2)

route

run along the lateral aspect of the medulla.

• They connect to form the basilar artery at the base of the pons-medulla junction.

• They give rise to the anterior spinal artery

supply

These arteries supply the lateral medulla areas.

Anterior Spinal Artery (1)

Route

begin as 2 small branches that become 1 main artery.

• The 2 anterior spinal branches rise off of the vertebral arteries and become 1 main artery that travels along the anterior surface of the medulla and spinal cord.

supply

The spinal artery supplies the anterior portion of the medulla and spinal cord.

Posterior Inferior Cerebellar Arteries (2)

Route

The posterior inferior cerebellar arteries rise from the vertebral arteries at the medulla level

Supply

• They supply part of the dorsolateral medulla (including the cerebellar peduncles), the inferior surface of the cerebellum, and the deep cerebellar nuclei

Anterior Inferior Cerebellar Arteries (2)

Route

rise from the vertebral arteries at the pons-medulla junction.

supply

They supply the inferior surface of the cerebellum and the deep cerebellar nuclei.

Superior Cerebellar Arteries (2)

route

rise from the basilar artery at the pons-midbrain junction.

supply

the superior aspect of the cerebellum and parts of the deep cerebellar nuclei

Basilar Artery (1)

does not supply the cerebellum. But it does give rise to the superior cerebellar arteries.

route

• Travels along the anterior aspect of the pons.

• Gives rise to the superior cerebellar arteries.

supply

• Supplies the anterior and lateral aspects of the pons.

Posterior Cerebral Arteries (2)

route

rise from the basilar artery.

supply

the medial and inferior surfaces of the temporal and occipital lobes, the thalamus, and the hypothalamus

Middle Cerebral Arteries (2)

route

rise from the internal carotids and travel through the lateral fissure to the brain’s surface

supply

These arteries supply the lateral surfaces of the frontal, temporal, and parietal lobes.

• They also supply the inferior surface of part of the frontal and temporal lobes.

Anterior Cerebral Arteries (2)

route

rise from the internal carotids.

supply

• These arteries supply the superior, lateral, and medial aspects of the frontal and parietal lobes.

• They also supply part of the basal ganglia and the corpus callosum.1

Posterior Communicating Arteries (2)

Route

• The posterior communicating arteries connect the internal carotids and the posterior cerebral arteries.

Supply

• They supply the diencephalon, internal capsule, and optic chiasm

Anterior Communicating Artery (1)

• The anterior communicating artery connects the 2 anterior cerebral arteries.

Pontine Encircling Arteries (Multiple)

Route

• These arteries rise from the basilar artery and wrap around the pons.

Supply

• They supply the lateral and posterior portions of the pons

The circle of Willis is a circuit of interconnecting arteries that

function to prevent lack of blood flow to the brain due to occlusion

Components of the circle of Willis include the following

° Posterior cerebral arteries

° Posterior communicating arteries

° Internal carotid arteries

° Anterior cerebral arteries

° Anterior communicating artery

Middle Cerebral Arterial Occlusion

s are the most common site of occlusion resulting in cerebrovascular accident (CVA)

supply the lateral surfaces of the frontal, temporal, and parietal lobes, and the inferior surface of portions of the frontal and temporal lobes.

Middle Cerebral Arterial Occlusion in the Left Hemisphere

result in the following:

° Contralateral hemiplegia (on the right side of the body): the primary motor area is lesioned.

° Contralateral hemiparesthesia (on the right side of the body): the primary somatosensory area is lesioned.

° Aphasia: Broca or Wernicke area may be lesioned. Other language areas may also be damaged, resulting in different types of aphasia.

° Cognitive involvement: impairment in cognitive function results from a frontal lobe lesion.

° Affective involvement: often when the left hemisphere is lesioned, the patient may display emotional lability and depression. This is sometimes referred to as a catastrophic response.

Middle Cerebral Arterial Occlusion in the Right Hemisphere

result in the following:

° Contralateral hemiplegia (on the left side of the body): the primary motor area is lesioned.

° Contralateral hemiparesthesia (on the left side of the body): the primary somatosensory area is lesioned.

° Perceptual deficits: left neglect syndromes are common with damage to the right hemisphere, particularly to the posterior multimodal association area.

° Apraxia: the anterior multimodal association area, premotor area, and/or primary motor cortex may be lesioned.

° Cognitive involvement: impairment in cognitive function results from a frontal lobe lesion.

° Affective involvement: often when the right hemisphere is lesioned, the patient may display euphoria or report a sense of well-being. If a neglect syndrome is present, the patient is often unaware of his or her deficits.

Posterior Cerebral Arterial Occlusion

supply the medial and inferior surfaces of the temporal and occipital lobes.

• These arteries also help to supply the thalamus and the hypothalamus; however, a lesion to a posterior cerebral artery will likely not affect the thalamic and hypothalamic functions.

• A lesion to one of the posterior cerebral arteries may result in the following:

° Memory loss due to temporal lobe involvement

° Visual perceptual deficits result from damage of the occipital lobe and the posterior multimodal association area.

° Visual field cuts result from occlusion to the optic chiasm. The optic chiasm is supplied by the posterior communicating arteries, which connect to the posterior cerebral arteries

Anterior Cerebral Arterial Occlusion

supply the superior, lateral, and medial aspects of the frontal and parietal lobes.

• These arteries also help to supply portions of the basal ganglia and corpus callosum.

• A lesion to one of the anterior cerebral arteries may result in the following:

° Contralateral hemiplegia: often of the lower extremities; the primary motor area is lesioned.

° Contralateral hemiparesthesia: often of the lower extremities; the primary somatosensory area is lesioned.

° Cognitive involvement: due to frontal lobe involvement

° Apraxia: the anterior multimodal association area, premotor area, and/or primary motor area may be lesioned.

° Affective involvement: if the left hemisphere is lesioned, emotional lability and depression may occur. If the right hemisphere is lesioned, euphoria or emotional dissociation may occur.

The 3 major symptoms of cerebellar disorders include the following:

1. Incoordination 2. Ataxia 3. Intention tremors

The posterior inferior cerebellar arteries supply the

cerebellar peduncles

Cerebellar arterial occlusion often involves the brainstem structures that are supplied by

the cerebellar arteries.

Posterior Inferior Cerebellar Arterial Occlusion Ipsilateral hypertonicity and hyperactive reflexes

: because the posterior and anterior spinocerebellar tracts travel through the superior cerebellar peduncle, damage to the superior cerebellar peduncles may result in ipsilateral hypertonicity and hyperactive reflexes.

Posterior Inferior Cerebellar Arterial Occlusion Vertigo, nausea, nystagmus, diplopia

because the posterior inferior cerebellar arteries also supply blood to the medulla, an occlusion to this artery may also result in vertigo, nausea, nystagmus, and diplopia as a result of vestibular nerve nuclei loss.

Posterior Inferior Cerebellar Arterial Occlusion

Ipsilateral loss of pain and temperature on the face (due to loss of the spinothalamic tract).

° Contralateral loss of pain and temperature on the trunk and extremities (due to loss of the spinothalamic tract).

° Dysphagia and dysarthria due to involvement of the nucleus ambiguous. ° Ipsilateral Horner syndrome (miosis, ptosis) due to vestibular nuclei involvement.

Anterior Inferior Cerebellar and Superior Cerebellar Arterial Occlusion

• Occlusion to either of these 2 arteries may result in the following

° Ipsilateral ataxia °

Ipsilateral hypotonicity and hyporeflexia

° Dysmetria

° Adiadochokinesia (and dysdiadochokinesia)

° Movement decomposition

° Asthenia

° Rebound phenomenon

° Staccato voice

° Ataxic gait

° Intention tremors

° Incoordination

° Nystagmus

Anterior Inferior Cerebellar and Superior Cerebellar Arterial Occlusion Occlusion to these arteries may also result in the following, due to the arteries’ connection to the blood supply of the medulla:

° Vestibular signs (nystagmus, vertigo, nausea)

° Ipsilateral loss of pain and temperature on the face (due to loss of the spinothalamic tract)

° Contralateral loss of pain and temperature on the trunk and extremities (due to loss of the spinothalamic tract)

° Dysphagia

° Dysarthria

° Bell palsy

Anterior Spinal Artery Occlusions

supply the anterior spinal cord and medulla

° Bilateral motor function loss at and below the lesion level if bilateral corticospinal tract involvement occurs.

° Bilateral loss of pain and temperature at and below the lesion level if bilateral spinothalamic tract involvement occurs.

Vertebral Arterial Occlusion

supply the lateral aspect of the low medulla, including the accessory nuclei.

• Dysphagia may occur if the accessory nerve nuclei are lost.

Basilar Arterial Occlusion

supplies the pons, including the corticospinal tracts and the abducens, trigeminal, and facial nerve nuclei

Contralateral hemiplegia can occur if the opposite corticospinal tract is lost.

° Contralateral sensory loss of the body can occur if the opposite dorsal column tract is lost.

° Ipsilateral sensory loss of the face can occur if the same side trigeminal nerve nuclei are lost.

° Medial or internal strabismus can occur if the abducens nerve nuclei are lost.

° Ipsilateral loss of the masseter reflex and the corneal reflex can also occur if the same side trigeminal nerve nuclei are lost.

° Bell palsy and hyperacusis can occur if the facial nerve nuclei are lost.

° Deviation of the tongue to the affected side results if the hypoglossal nerve nuclei are involved.

° Nystagmus and balance disturbances can result if the vestibular nuclei are involved.

Cerebrovascular Accident

, is an umbrella term applied to conditions in which blood flow to cerebral vessels becomes disrupted, either from clotting or rupture.

• There are 2 primary types of CVA: ischemic and hemorrhagic.

• Ischemic strokes are the most common type of CVA and result from thrombosis (static clot) or emboli (traveling clot).

• Hemorrhagic strokes involve bleeding into brain tissue and can result from hypertension, aneurysms, or head injury. Hemorrhagic strokes are the most fatal type.

• Risk factors include the following: • Age • Cigarette smoking • Sex (men have a 19% greater risk of stroke than women) • Diabetes mellitus • Race (Blacks have a 60% greater risk than the general population) • Prior stroke • Hypertension • Obesity • High cholesterol levels • Heart disease

Thrombotic Strokes

Thrombi are clots formed by plaque development in a vessel wall.

• These are the most common type of ischemic strokes and occur in atherosclerotic blood vessels. • Common sites of plaque formation include larger vessels of the brain, including the origin of the internal carotid arteries, the vertebral arteries, and the junction of the basilar and vertebral arteries.

• __________ usually occur gradually over several days.

• They are frequently seen in older persons with arteriosclerotic heart disease.

• This type of stroke is not associated with exertion or activity and can occur when the person is at rest.

Lacunar Infarcts

are small clots located in the deep regions of the brainstem and subcortical structures.

• They are often found in single deeply penetrating arteries that supply the internal capsule, basal ganglia, and brainstem.

• They commonly result from occlusion of the smaller branches of the large cerebral arteries, most notably the middle and posterior cerebral arteries. Sometimes________ can also occur in the anterior cerebral, vertebral, and basilar arteries.

• Because they are small,________ usually do not cause severe impairment

Embolic Strokes

are clots that dislodge from their site of origin and travel to a cerebral blood vessel, where they become trapped and interrupt blood flow.

• __________ often affect the smaller cerebral vessels. The most frequent site is the middle cerebral artery.

• This type of stroke commonly has a sudden onset and is associated with the presence of cardiac disease (eg, rheumatic heart disease, ventricular aneurysm, and bacterial endocarditis). Cardiac___________ can also occur after a recent myocardial infarction

Hemorrhagic Strokes

are frequently fatal.

• However, if patients can survive the initial ________ damage, prognosis is generally good.

• __________ involve bleeding into brain tissue after the rupture of a blood vessel wall.

• This type of stroke results in edema and compression of brain tissue that, if not medically treated immediately, can be fatal.

• ____________ commonly occur suddenly and are associated with exertion and activity.

• Aneurysmal subarachnoid hemorrhage

◦ An aneurysm is a bulge occurring in a blood vessel wall as a result of clot formation.

◦ Most aneurysms are small saccular structures called berry aneurysms.

◦ Berry aneurysms commonly occur in the circle of Willis or the junction of 2 vessels.

◦ Aneurysms tend to enlarge with time and weaken vessel walls until rupture occurs

Transient Ischemic Attack

are sometimes referred to as mini strokes.

• They are characterized by focal ischemic cerebral incidents that last less than 24 hours; most ______ usually last less than 1 to 2 hours.

• The causes of _____ include atherosclerotic disease and emboli.

• _____may provide a warning of an impending larger stroke.

• Signs include the following

◦ Numbness and mild weakness on one side of the body

◦ Transient visual disturbances (eg, blurred vision, fading vision)

◦ Dizziness

◦ Falls

◦ Confusion and possible blackout