15.1 The Cerebrovascular System and Cerebral Vascular Accidents

Areas of the Brain

The structure of the brain itself can be broken down into three main areas: the cerebrum, the brainstem, and the cerebellum. These areas contain multiple structures that work in concert to control almost every aspect of life. The cranial nerves are a critical component of the central nervous system (CNS), the body’s processing and functional control center; they transfer motor and sensory information between the brain and different areas of the face and trunk. It is imperative for the nurse to understand the structure and function of the brain to allow for early recognition of cues for impaired function.

The Cerebrum

The cerebrum is comprised of the left and right cerebral hemispheres (Figure 15.2). The hemispheres are mirror images of each other, each containing half of the frontal, parietal, temporal, and occipital lobes.

Figure 15.2 The four lobes of the cerebrum are the frontal, parietal, temporal, and occipital. (credit: modification of work from Anatomy and Physiology 2e. attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

The frontal lobe, the largest area of the brain, found at the front of the cerebrum, is responsible for many higher-level functions such as:

• reasoning
• abstract thought
• executive function
• concentration
• information storage for memory
• personality
• inhibition
• judgment

Also under the control of the frontal lobe is some voluntary motor function, particularly that of speech (e.g., Broca’s area). The frontal lobe contains a motor strip that controls the motor coordination of the corresponding parts of the body (Figure 15.3). Finally, the frontal lobe plays a role in the involuntary functions of respiration, gastrointestinal movement, and blood pressure.

Figure 15.3 This image illustrates the motor strip of the frontal lobe and the corresponding areas of the body over which it has control. (credit: modification of work from Anatomy and Physiology 2e. attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

The parietal lobe houses the sensory cortex and is responsible for sensory recognition in the same areas as the motor strip. Sensory awareness consists of touch, pressure, vibration, and a person’s proprioception, or awareness of their own body position and movement in relation to the space around them.

The temporal lobe is primarily for auditory association. It is important for memory and language interpretation. This lobe also houses Wernicke’s area, which encompasses the auditory cortex on the lateral sulcus. Past experiences with music, art, conversation, and taste are stored here. The temporal lobe is responsible for multi-modal sensory integration.

Last, the occipital lobe is where visual perception, interpretation, and memory take place. The occipital lobe also has a role in visual reflexes and smooth eye movement.

The thalamus, hypothalamus, and pituitary area are housed deep within the cerebrum. They are key players in vital functions such as the stress response, thermal regulation, hormone regulation, sleep-wake cycle, emotional response, blood pressure regulation, appetite control, and general control of the autonomic nervous system.

The Brainstem

The brainstem comprises the midbrain, pons, and medulla (Figure 15.4). The midbrain coordinates sensory representations of the visual, auditory, and somatosensory perceptual spaces. The pons is the main connection with the cerebellum. The pons and the medulla regulate several crucial functions, including heart rate and respiratory rate.

Figure 15.4 The brainstem comprises three regions: the midbrain, the pons, and the medulla. (credit: modification of work from Anatomy and Physiology 2e. attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

The Cranial Nerves

The cranial nerves (Figure 15.5) are primarily responsible for the sensory and motor functions of the head and neck. (One of these nerves targets organs in the thoracic and abdominal cavities as part of the parasympathetic nervous system.) There are twelve cranial nerves, which can be classified as sensory nerves, motor nerves, or a combination of both (Table 15.1). The nurse can recognize deficits in specific cranial nerve function when brain vasculature has affected tissue where the nerve originates.

Figure 15.5 The cranial nerves originate from the base of the brain. (credit: modification of work from Anatomy and Physiology 2e. attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

Number	Name	Responsible for . . .
I	Olfactory nerve	Sense of smell
II	Optic nerve	Vision
III	Oculomotor nerve	Eye movements (by controlling four of the extraocular muscles) Lifting the upper eyelid when the eyes point up Pupillary constriction
IV	Trochlear nerve	Eye movement and ability to track
V	Trigeminal nerve	Sensations of the face Controlling the muscles of mastication
VI	Abducens nerve	Eye movement (different extraocular muscle from the trochlear nerve)
VII	Facial nerve	Muscles involved in facial expressions Anterior part of the tongue Production of saliva
VIII	Vestibulocochlear nerve	Senses of hearing and balance
IX	Glossopharyngeal nerve	Controlling muscles in the oral cavity and upper throat Posterior part of the tongue Production of saliva
X	Vagus nerve	Contributing to homeostatic control of the organs of the thoracic and upper-abdominal cavities
XI	Spinal accessory nerve	Controlling the muscles of the neck to allow for shrugging of the shoulders and rotation and tilting of the head
XII	Hypoglossal nerve	Controlling the muscles of the lower throat and tongue

Table 15.1 Cranial Nerves

Protecting the Brain

From superior to inferior, the layers of the dura mater, arachnoid mater, and pia mater comprise the meninges, which are membrane layers of connective tissue. The skull and meninges are designed to protect the vital and dynamic brain. The skull is a rigid, skeletal structure encasing the brain in a finite space (Figure 15.6).

Figure 15.6 The three connective tissue layers of the meninges protect the brain: the dura mater, arachnoid mater, and pia mater. The subdural and subarachnoid spaces are the small areas below the respective layers. This image also includes the skull bone, directly above the dura mater. (credit: modification of work from Anatomy and Physiology 2e. attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

• The dura mater is a thick, fibrous layer that acts as a strong protective sheath over the entire brain. The name comes from the Latin for “tough mother,” to represent its physically protective role.
• The middle layer is the arachnoid mater, which is a membrane of thin, fibrous tissue that forms a loose sac around the brain. The name also comes from Latin; it means “spiderweb-like mother” because the layer looks like a spiderweb. It is filled with circulating cerebrospinal fluid (CSF), which provides a liquid cushion to the brain.
• Finally, directly adjacent to the surface of the brain is the pia mater, which is Latin for “tender mother.” This innermost layer is a thin fibrous membrane that fits into the grooves and indentations of the brain’s surface. It is thought to have a continuous layer of cells providing a fluid-impermeable membrane.

Of note, the meninges surround the entire CNS, which includes the brain and spinal cord.

Signs and Symptoms of CVA

The signs and symptoms of a CVA can vary greatly. This variance exists because an occlusion can occur anywhere within the cerebral vasculature and cause an infarct, or area of necrotic tissue, in any part of the brain that the occluded vessel should supply. The most commonly occluded artery is the middle cerebral artery (MCA), which is responsible for blood supply to parts of the cerebrum, including the temporal, frontal, and parietal lobes. Depending on the involvement of one to up to four of the MCA branches, signs and symptoms of an occlusion could include:

• hemiplegia, or complete paralysis on the side of the body opposite the CVA
• hemiparesis, or weakness on the side of the body opposite the CVA
• sensory changes of the face and arm on the side of the body opposite the CVA
• aphasia, or loss of language skills affecting expression, comprehension, or both, depending on the severity of the CVA
• homonymous hemianopsia, or a deficit causing a loss of vision in the same halves of the visual field in each eye

The anterior cerebral circulation includes the vessels that originate from the carotid arteries, and occlusions result in lateralizing neurological signs and symptoms. Occlusions in the internal carotid artery (ICA) can result in:

• paralysis of and sensory changes in the face, leg, and arm on the side of the body opposite to the CVA
• aphasia
• apraxia, or the inability to perform tasks, movements, or gestures
• homonymous hemianopsia

Anterior cerebral artery (ACA) occlusions can result in:

• paralysis and sensory changes of the foot or leg on the side of the body opposite the CVA
• gait impairments
• cognitive impairment
• urinary incontinence
• flat affect
• increased distractibility
• lack of interest in surroundings

In contrast, the posterior cerebral circulation includes the vessels that originate from the vertebrobasilar arteries and results in diffuse neurological signs and symptoms. Occlusions in the vertebral artery (VA), which supplies the cerebellum and brainstem, can cause dizziness, nystagmus (rapid, uncontrolled eye movements), dysphagia (trouble swallowing), dysarthria (trouble speaking), gait abnormalities, and facial weakness and numbness on the same side of the body as the stroke. Another vessel responsible for posterior supply is the basilar artery (BA). Occlusions there can result in quadriplegia, weakness of the mouth and throat, or even locked-in syndrome, a rare condition in which patients retain consciousness but develop paralysis of the entire body except in the muscles of eye movement. A CVA of the posterior inferior cerebellar artery (PICA) causes nausea, vomiting, dysphagia, dysarthria, nystagmus, ataxia, vertigo, and loss of sensation of pain and temperature on the side of the body opposite the stroke. Finally, occlusions in the posterior cerebral artery (PCA) can result in visual and memory deficits, perseveration (continuous and repetitive speech, behavior, or thoughts), abnormalities in pupils, and sensory loss. Table 15.2 summarizes these deficits for the major stroke locations.

The signs and symptoms of a hemorrhagic versus an ischemic stroke may not differ much. Whether blood flow is impaired by the presence of a clot (ischemic stroke) or a leak or rupture in the vasculature of brain (hemorrhagic stroke), function can still be impaired in the same way. An infarct of either kind in the occipital lobe still manifests with visual impairment. An infarct of either kind in the cerebellum may still cause balance and coordination problems. The main differences that may be appreciated involve extra findings in hemorrhagic stroke. Patients with hemorrhagic strokes will more often complain of neck pain, photosensitivity, or nausea and vomiting; patients often present with subjective complaints of the worst headache of their life. These patients are much more likely to have a decreased level of consciousness than patients with ischemic strokes. A hemorrhagic stroke is usually more devastating than an ischemic stroke (Salvadori et al., 2020).

Emergency CVA Treatment

Recognizing the signs of a CVA and initiating quick treatment are essential for preserving as much brain tissue, and therefore function, as possible. The phrase “time is brain” is often repeated for emphasis on rapid care, highlighting this fact. Upon arrival to the emergency department (for patients in the community) or after a stroke notification has been sent to the appropriate responding team (for hospitalized patients), a head computed tomography (CT) scan is performed to determine whether the symptoms are being caused by an ischemic or hemorrhagic stroke. To certify a hospital as “Acute Stroke Ready,” the Joint Commission expects to see CTs initiated in ≤ 25 minutes of patient arrival and a radiologist reading within 45 minutes (Joint Commission, 2023).

If a hemorrhagic stroke is ruled out by the absence of a bleed, a clot is the assumed cause of the infarction. A tissue plasminogen activator (tPA) can then be administered intravenously to dissolve the clot and restore perfusion. To be effective at reversing brain ischemia, tPA must be administered within 3 to 4.5 hours of stroke onset, or the time when the patient was last seen as normal (“last known well”).

If bleeding is present, signifying a hemorrhagic stroke, immediate care must be taken to determine the source of the bleeding and control the bleed or pressure within the skull (Caplan, 2023). Just as with a clot in an ischemic stroke, the brain cells are not being properly perfused, which damages brain tissue and impairs function. If the time between stroke onset or “last known well” is past the 3–4.5 hour time frame for intervention, measures to restore perfusion may not be effective in saving the brain. The longer the time to treatment, the more brain cells die, causing irreparable neurological damage that may result in paralysis, permanent disability, or even death.

Continued CVA Treatment

Subsequent emergency care focused on minimizing tissue infarction, support, and monitoring for multiple systems is essential. In the inpatient setting, a patient’s blood pressure must be stabilized, nutrition must be optimized, and intracranial pressure changes, vital signs, blood glucose, neurologic status, and cardiac rhythm should be monitored. Causative factors are investigated, measures to prevent secondary stroke are initiated, and the rehabilitation process begins. The rehabilitation process could include an inpatient rehabilitation stay or even a transition to a long-term care facility when disability is severe. Care after a stroke involves not only the physical care and reconditioning of the body but also care to meet the patient’s psychosocial and emotional demands. Continued stroke care requires the collaboration of individuals from many disciplines.