CONCEPTS OF NEUROLOGIC DYSFUNCTION

Alterations in cognitive systems - Consciousness has two distinct componets: arousal and awareness. Arousal is the state of awakeness that an individual exhibits. Awareness encompasses all cognitive functions that embody awarness of self, environment, and affective states.

Alterations in arousal - possible causes with acute onset may be in one of three groups: (1) structural, (2) metabolic, and (3) psychogenic. Coma is produced by either bilateral hemisphere damage or suppression by means of hypoxia, hypoglycemia, drugs, or toxins; or a brain stem lesion or metabolic derangement that damages or suppresses the RAS.

Level of consciousness is the most critical clinical index of nervous system function or dysfunction. It indicates either improvement or deterioration of the individual's condition.

Pattern of breathing encompasses several characteristics and are helpful in evaluating level of brain dysfunction and level of coma.

Pupillary changes - anatomically, brain stem areas that control arousal are adjacent to areas that control pupils. Pupillary changes thus are a valuable guide to evaluating the presence and level of brain stem dysfunction.

Occulomotor responses - resting, spontaneous, and reflective eye movement and oculovestibular undergo change at various levels of brain dysfunction.

Motor responses contribute both to evaluating the level of brain dysfunction and to determining the side of the brain that is maximally damaged. Purposeful movement requires an intact corticospinal system. Nonpurposeful movement is evidence of severy dysfunction of the corticospinal system.

Outcome domains fall into two divisions - mortality and extent of disability (morbidity). Brain death occurs when irreversible brain damage is so extensive that the brain has no potential for recovery and no longer can maintain the body's internal homeostasis. Brain death is considered to have occurred in the absence of cerebral hemisphere function or function of the brain stem's vital centers. A EEG may be used to confirm brain death.

Cerebral death (irreversible coma) is death of the cerebral hemispheres exclusive of the brain stem and cerebellum. The survivor of cerebral death may remain in a coma or emerge into a vegetative state.

Decorticate posturing - hands are pulled into the "core" of the body.
Decerebrate posturing - hands are away from the body.

Akinetic mutism (AM) is a neurobehavioral state characterized by a severe disturbance in behavioral drive. Locked-in syndrome, both the content of thought and level of arousal are intact, but the efferent pathways are disrupted.

SEIZURES

Seizure is a sudden, explosive, disorderly discharge of cerebral neurons and is characterized by a sudden, transient alteration in brain function, usually involving motor, sensory, autonomic, or psychic clinical manifestations and an alteration in level of arousal.

Types of seizures:
  • Generalized - do not have a focal onset, originate from a subcortical or deeper brain focus. Consciousness always is impaired or lost.
  • Partial (focal) - have a focal onset, originate from cortical brain tissue, thereby having a superficial focus. Consciousness may be maintained as long as the seizure activity is limited to one hemisphere.
  • Status epilepticus is the experience of a second seizure, and often subsequent seizures before the person has fully regained consciousness.

Types of seizure syndromes:
  • Epilepsy is applied to conditions in which no underlying correctable cause for the seizures is found so that the seizure activity recurs without treatment because of a primary underlying brain abnormality. Idiopathic refers to syndromes that arise spontaneously without a known cause, presumably having a genetic basis. Symptomatic denotes epilepsies with an identified cause.

ALTERATIONS IN AWARENESS

Sensory inattentiveness is a form or feglect and may be visual, auditory, or tactile.
Selective attention deficit, manifests as a neglect syndrome, rarely, if ever, occurs clinically because typically other deficits are also present.
Declarative memory involves the learning and remembrance of episodic memories and semantic memories.
Nondeclarative memory is the memory of how to carry out an action, behavior, or skill. It is not a languare memory but a motor memory.
Dysmnesia is a disorder of the domain-independent declarative memory network defined as the loss of past memories coupled with an inability to form new memories despite intact attentional networks.


DATA PROCESSING DEFICITS

Agnosia is a defect of pattern recognition - a failure to recognize the form and nature of objects.
Dysphasia is impairment of comprehension or production of language.
Aphasia is loss of the comprehension or production of language.
Expressive dysphasias are characterized primarily by expressive deficits, but a verbal comprehension deficit may be present.

ACUTE CONFUSIONAL STATES

Acute confusional states is an acquired mental disorder characterized by deficits in attention and coherence of thoughts and actions often associated with an altered level of arousal, global cognitive dysfunction, perceptual disturances, etc.

Dementia is a syndrome that may be caused by a number of different illnesses. It is the progressive failure of many cerebral functions that is not caused by an impaired level of consciousness. Dementias can be classified according to etiologic factors.

Alzheimer disease is a common neurologic disorder. It has been demonstrated to be one of the most common couses of severe cognitive dysfunction in older persons.

ALTERATIONS IN CEREBRAL HEMODYNAMICS

Intracranial pressure normally is 5 to 15 mmHg; may result from an increase in intracranial content, edema, excess cerebrospinal fluid, or hemorrhage.
Herniation syndromes - three types: uncal, central and cingulate gyrus.
Cerebral edema is an increase in the fluid content of brain tissue, a net accumulation of water within the brain.
Hydrocephalus refers to a variety of conditions characterized by an excess of fluid within the cranial vault, subarachnoid space, or both.

ALTERATIONS IN EMOTIONS AND MOODS arise from dysfunction in the limbic system; in the hypothalamus, or in the cerebral cortex, especially the temporal and frontal lobes. Changes in emotions, mood, and behavior can result from abscesses, tumors, hemorrhages, metabolic disorders, degenerative disease, and intoxication states.

ALTERATIONS IN MOTOR FUNCTION - movements are complex patterns of activity controlled by the CNS. Dysfunction here can cause motor dysfunction.

ALTERATIONS IN MUSCLE TONE:

Hypotonia - decreased muscle tone.
Hypertonia - increased muscle tone.
Spasticity results from hyperexcitability of the stretch reflexes.
Gegenhalten manifests as resistance to passive movement that varies in direct proportion to the force applied and is associated with frontal lobe injury.
Rigidity is produced by tonic reflex activity mediated by gamma motor neurons may be continuous or intermittent.

ALTERATIONS IN MOVEMENT

Paresis is impairment of motor function, that is, partial paralysis with incomplete loss of muscle power.
Paralysis is loss of motor function, that is, inability of a muscle group to overcome gravity.
Hemiparesis or hemiplegia is paresis or paralysis, respectively, of the upper and lower extremities on one side.
Diplegia is the paralysis of both upper and lower extremities as a result of cerebral hemisphere injuries.
Paraparesis or paraplegia refers to weakness or paralysis, respectively, of the lower extremities.
Quadriparesis or quadriplegia refers to paresis or paralysis of all four extremities.
Pyramidal motor syndrome is a series of motor dysfunction that results from in terruption of the pyramidal system.
Hyperkinesia - excessive movement.
Paroxysmal dyskinesias are abnormal, involuntary movements that occur as spasm.
Tardive dyskinesia is the involuntary movement of the face, trunk, and extremities.
Huntington disease is a relatively rare, hereditary-degenerative disorder diffusely involving the basal ganglia and cerebral cortex.
Hypokinesia - decreased movement.
Akinesia is an absence, poverty, or lack of control of associated and voluntary muscle movements.
Bradykinesia is slowness of voluntary movements.
Parkinson disease is a commonly occurring degenerative disorder of the basal ganglia involving the dopaminergic nigrostriatal pathway.

ALTERATIONS IN COMPLEX MOTOR PERFORMANCE

Disorders of posture: dystonic posture, deceerebrate posture, basal ganglion posture and senile posture.

Dystonia is the maintenance of an abnormal posture through muscular contractions.
Decorticate posture - towards the core.
Decerebrate posture - away from the core.
Basal ganglion posture refers to a stooped, hyperflexed posture with a narrow-based, short-stepped gait.
Senile posture - increasingly flexed posture similar to that caused by basal ganglion dysfunction.

Disorders of gait are upper motor neuron dysfunction gait, cerebellar gait, basal ganglion gait and senile gait.
Spastic gait associated with unilateral injury; shuffling with leg extended and held stiff, causing a scraping over the floor surface.
Scissor gait is associated with bilateral injury and spasticity. Legs are abducted, causing them to touch each other.
Cerebellar gain manifests as a wide-based gait with the feet apart and often turned outward or inward for greater stability.
Basal ganglion gait & senile gait are both broad-based gait.

Disorders of expression involve motor aspects of communication and include hypermimesis, hypomimesis and dyspraxias and apraxias.

Dyspraxia is the partial inability and apraxia is the complete inability to perform purposeful or skilled motor acts in the absence of paralysis, sensory loss, abnormal posture and tone, abnormal involuntary movement, incoordination, or inattentiveness.

Extrapyramidial motor syndromes:

Basal ganglia motor syndromes are movement disorders that involve either a paucity or an excess of movements.
Cerebellar motor syndromes involve the cerebellum and may result in loss of muscle tone acutely, difficulty with coordination of voluntary movements, minor degrees of muscle weakness, tendency toward fatigue, and impairment of associated movements and disorders of equilibrium, posture, and gait.

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