N245: Alterations in Brain Function

Cerebral Hypoxia

What: Low levels of oxygen in the brain (well tolerated)

Causes: Reduced atmospheric pressure, CO poisoning, severe anemia, choking, drowning

Cerebral Ischemia

What: Reduced blood flow to the brain

Causes: Cerebral artery occlusion, cardiac arrest, hypotension

Focus Ischemia

What: Reduced blood flow to a specific part of the brain

Causes: Cerebral artery occlusion

Cerebral infarct

An area of the brain that becomes ischemic and necrotic due to lack of blood supply

Global ischemia

What: Reduced blood flow throughout the brain

Causes: Cardiac arrest, severe hypotension --> shrinking/swelling of neurons

Cerebral Edema

What: Increase in brain fluid --> increased volume of brain tissue

Vasogenic edema

What: A form of cerebral edema

Causes: Hemorrhage, traumatic brain injury, or infections --> leaky capillaries --> increases of extracellular fluid

Cytotoxic edema

What: A form of cerebral edema

Causes: Hypoxic or ischemic injury --> impairment of the Na+ /K+ pumps --> increase of intracellular fluid

S+S: Narrow sulci (depressions in the cerebral cortex), flat gyri (ridges on cerebral cortex)

HACE

What: High altitude cerebral edema

Causes: Climbing to high altitudes quickly

S+S: Extreme fatigue, altered mental status after rapidly ascending to very high altitudes --> death

Consciousness

Being aware of one's self, being aware of and responsive to one's environment

Confusion

Disorientation, impaired ability to think clearly, slightly reduced responses to stimuli

Delirium

Physical restlessness, transient hallucinations, incoherence of thought and speech

Obtundation

Lethargy, very slow responses to stimuli, excessive drowsiness when awake

Stupor

Unresponsiveness, little or no spontaneous activity, patient can be aroused by vigorous and repeated stimuli

Coma

Deep unconsciousness, complete unresponsiveness, patient cannot be aroused by external stimuli

Glasgow Coma Scale

Assesses patients' coma scale based on eye opening, verbal response, motor response (3 = coma, 15 = full consciousness)

Normal pupillary reflexes

Constrict equally when exposed to light

Pupil characteristics during compression of the oculomotor nerve

Fixed (non-reactive) dilated pupil on the same side as damage

Pupil characteristics during lesions of the brainstem

Fixed (non-reactive) pinpoint pupils in both eyes

Pupil characteristics during irreversible cessation of brain function ("braindeath")

Fixed (non-reactive) dilated pupils in both eyes

Decorticate posturing

Involuntary flexion of arms --> indicates damage to the cerebral hemispheres

Decerebrate posturing

Involuntary extension of arms --> indicates damage to the brainstem

Intracranial Pressure (ICP)

The amount of pressure inside the skull

Intracranial volumes that contribute to the ICP

Brain tissue -- 80% of volume

Blood -- 10% of volume

CSF -- 10% of volume

Brain ventricles

A series of cavities in the CNS that contain cerebrospinal fluid

Monro-Kellie hypothesis

Because of limited space in the skull, an increase in any one of components of the skull (brain tissue, blood, CSF) will cause a change in the volume of the others

How do increases in ICP result in brain injury?

1. Physical damage to the neurons --> sensory or motor deficits

2. Compression of blood flow --> ischemia --> hypoxia

3. Herniation/displacements of the brain tissue

Falx cerebri

Septum that separates the two cerebral hemispheres

Tentorium cerebelli

Septum that separates cerebrum from cerebellum

Brain Herniation

Brain shifts from areas of high intracranial pressure to low intracranial pressure

Supratentorial brain herniation

Herniation of cerebral cortex above the tentorium cerebelli

Transtentorial brain herniation

Herniation of the cerebral cortex through the tentorial notch

Tentorial notch

Triangular opening through which the brainstem, blood vessels and oculomotor nerve [CN III] pass

Infratentorial brain herniation

Herniation of the cerebellum below the tentorium cerebelli

Cerebrospinal Fluid (CSF)

Clear fluid that circulates in and around the brain and spinal cord; produced in the ventricles

Pathway for CSF

Choroid plexus in ventricles --> subarachnoid space --> arachnoid villi --> heart --> capillaries --> ventricles

Hydrocephalus

What: Abnormal accumulations of CSF in the ventricles --> enlargement of ventricles

Causes:

1. Overproduction of CSF

2. Impaired reabsorption of CSF

3. Obstruction to the flow of CSF

S+S: Headache, nausea, and vomiting, abnormal eye movements, blindness, weakness, decreased memory

Traumatic Brain Injury

A blow to the head that damages the brain

What is the leading cause of TBIs?

Falls

Focal TBI

Specific, local brain injuries; contusions and hematomas

Global TBI

Widespread, broad brain injuries; concussions

Contusions

What: Bruise on the surface of the brain

Causes: Blunt force to the head --> brain accelerates within the skull --> decelerates abruptly after hitting the inner skull surfaces

S+S: Various neurological defects

Coup injury

Contusions directly under the site of impact with an object

Contrecoup injury

Contusions on the opposite side of the site of impact (whiplash injury)

Intracranial Hematomas

What: Abnormal collection of blood in the cranium

Causes: Injury to blood vessels of the brain

Cranial Meninges

Dura mater, arachnoid mater, pia mater

Pia mater

Thin, delicate inner membrane of the meninges

Arachnoid mater

Weblike middle layer of the three meninges

Dura mater

Thick, outermost layer of the meninges

Epidural hematoma

What: Bleeding that develops between the skull and the dura mater

Causes: Severe head trauma --> arterial rupture

S+S: LOC --> Lucid interval of consciousness --> LOC again

Subdural hematoma

What: Bleeding that develops between the dura mater and the arachnoid mater

Causes: Severe head trauma --> venous rupture

S+S: LOC

Intracerebral hematoma

What: Blood clot that develops in the brain tissue

Causes: Severe head trauma, rupture of a cerebral aneurysm

Concussions

What: Mechanical injury --> transient brain dysfunction

Causes: Sports injuries

S+S: Headaches, amnesia, insomnia, confusion

Stroke

What: Non traumatic disruption of blood flow to the brain --> acute neurological deficits; "brain attack"/CVA

S+S: Sensory, motor, verbal, or cognitive deficits depending upon the area of brain affected

Ischemic stroke

A stroke in which the blood flow disruption is caused by a blood clot/blockage

Hemorrhagic stroke

A stroke in which the blood flow disruption is caused by the rupture of a blood vessel

Transient Ischemic Attack

What: Temporary disruption of blood flow to the brain --> brief episode of neurological dysfunction; "mini stroke"

Dementia

What: Deterioration of cognitive function that interferes with social/occupational ADLs

Causes: Drugs, emotional disorders, metabolic disorders, eye/ear problems, normal pressure hydrocephalus, tumors, infections, anemia

S+S: Reduced ability to perceive sensory input, learn and manipulate new information, recognize familiar objects, recall past experiences, solve problems, think abstractly, or make judgments

Alzheimer's Disease

What: Most common cause of dementia

Causes: Reduced concentrations of acetylcholine, genetics

S+S: Damage to hippocampus --> inability to store memories

Early stage of Alzheimer's Disease

Memory lapses (denied by the patient but reported by caregivers)

Middle stage of Alzheimer's Disease

Confusion, frustration, anger, social withdrawal, altered sleep patterns, personality and behavioral changes including suspiciousness

Late stage of Alzheimer's Disease

Loss of awareness of recent experiences and surroundings, difficulty in communicating, incontinence, death

Neurofibrillary tangle

Hallmark of Alzheimer's --> defective tau proteins accumulate inside the neurons

Senile (amyloid) plaque

Hallmark of Alzheimer's --> Amyloid plaques form around the outside of the neuron