Acute Neurologic Disorder

• Brain


  The communication and control center of the body. It receives processes and evaluates many kinds of input, decides on the response or action to be taken and then initiates the response.
• Meninges


  Three continuous connective tissue membranes covering the brain and spinal cord. They invaginate at four points, forming a supportive partition between portions of the brain.
• Meninges and contents of spaces between layers

  • Dura mater (outer layer, tough, fibrous, doubled layered membrane that separates at specific points to form dural sinuses)
  • Subdural space (potential space lying beneath the dura)
  • Arachnoid matter (middle layer, loose, web-like covering)
  • Subarachnoid space (contains CSF and cerebral arteries and veins, lies beneath the arachnoid)
  • Arachnoid villi (projections of arachnoid into the dural sinuses at several places around the brain, through which CSF can be absorbed into the venous blood)
• Cerebrospinal fluid (CSF)


  Provides a cushion for the brain and spinal cord. Formed constantly in the choroid plexuses in the ventricles, flows into the subarachnoid space, circulates around the brain and spinal cord and eventually passes through the arachnoid villi, returning into the venous blood.
• Cerebral hemispheres


  Make up the largest and most obvious portions of the brain. The outer surface is covered by elevations (gyri) separated by grooves (sulci).
• Diencephalon


  The central portion of the brain.
• Brainstem


  The inferior portion of the brain, the connecting link to the spinal cord. Composed of the pons (bundles of afferent and efferent fibers), medulla oblongata (vital control centers for respiratory and cardiovascular function, coordinating centers for cough, swallowing, vomiting), and cerebellum (coordinates movement, maintains posture and equilibrium).
• Major functional areas of the brain

  • Frontal lobe (intellectual function, personality, skilled movements, voluntary movements, speech expression)
  • Parietal lobe (sensation, e.g. touch and pain)
  • Occipital lobe (vision)
  • Temporal lobe (hearing, smell, comprehension of speech, memory)
  • Cerebellum (body balance and position, coordinated movements)
  • Medulla oblongata (control and coordination of respiration and cardiovascular activity, swallow reflex, vomiting reflex, cough reflex, cranial nerve nuclei)
  • Hypothalamus (autonomic nervous system, endocrine system, body temperature, fluid balance, thirst, hunger)
  • Thalamus (sensory sorting and relay center)
  • Basal nuclei (coordination and control of body movement)
  • Reticular activating system (arousal or awareness)
  • Limbic system (emotional responses)
• Cranial nerves


  • I. Olfactory (special sensory - smell)
  • II. Optic (special sensory - vision)
  • III. Oculomotor (motor - eye movements, upper eyelid, iris, ciliary muscle)
  • IV. Trochlear (motor - eye movements - superior oblique eye muscle)
  • V. Trigeminal (sensory - face, oral cavity, teeth; motor - muscles of mastication)
  • VI. Abducens (motor - eye movements - lateral rectus eye muscle)
  • VII. Facial (sensory - taste, facial expression; motor - facial muscles, lacrimal gland, nasal mucosa, salivary glands)
  • VIII. Vestibulocochlear (special sensory - hearing and balance)
  • IX. Glossopharyngeal (sensory - taste, pharynx, carotid sinus; motor - pharyngeal muscles, parotid salivary gland)
  • X. Vagus (sensory - pharynx, larynx, thoracic and abdominal viscera; motor - pharynx, soft palate, heart, lungs, digestive system)
  • XI. Spinal accessory (motor - palate, pharynx, larynx, head movements)
  • XII. Hypoglossal (motor - muscles of tongue)
• Neurons


  Highly specialized, nonmitotic cells that conduct impulses throughout the nervous system. Supported and protected by glial (neuroglia) cells.
• Glial cells


  Several types including astroglia (astrocytes) that provide a link between neurons and capillaries, oligodendroglia that provide myelin for axons in the CNS, microglia with phagocytic activity, and ependymal cells that line the ventricles and neural tube cavity.
• Neuron regeneration


  Neurons cannot undergo cell division. If the cell body is damaged, the neuron dies. In the peripheral nervous system, axons may be able to regenerate if the cell body is viable.
• Conduction of impulses


  Stimulus increases permeability of neuronal membrane, allowing sodium ions to flow inside and depolarize it, generating an action potential. The change in electrical charge propagates along the membrane. Recovery or repolarization occurs as potassium ions move outward and the sodium-potassium pump restores normal ion distribution.
• Autonomic nervous system


  Incorporates the sympathetic and parasympathetic nervous systems, which generally have antagonistic effects, aiding in maintaining homeostasis. Provides motor and sensory innervation to smooth muscle, cardiac muscle, and glands.
• Effects of stimulation of the autonomic nervous system

  • Sympathetic (increases activity, fight-or-flight response): Increased heart rate and contractility, vasoconstriction, bronchodilation, pupil dilation, increased sweat secretion, decreased digestive secretions and peristalsis, constriction of urinary sphincters, ejaculation
  • Parasympathetic (dominates digestive system, aids recovery from sympathetic activity): Decreased heart rate and contractility, vasodilation, bronchoconstriction, pupil constriction, decreased sweat secretion, increased digestive secretions and peristalsis, relaxation of urinary sphincters, erection
• Sympathetic nervous system


  The thoracolumbar nervous system that increases the general level of activity in the body, augmented by increased secretions of the adrenal medulla.
• Parasympathetic nervous system


  The craniosacral nervous system that dominates the digestive system and aids in the recovery of sympathetic activity. Ganglia are scattered and located close to the target organ, and the neurotransmitter at both preganglionic and postganglionic synapses is acetylcholine.
• Cholinergic receptors


  Nicotinic receptors (always stimulated by acetylcholine, located in all postganglionic cholinergic neurons in the PNS and SNS) and muscarinic receptors (located in all effector cells, may be stimulated or inhibited by acetylcholine depending on the organ).
• Neurologic dysfunction


  The effects of damage to different areas of the brain and spinal cord have many similarities, as specific areas have established functions. Damage can result in local (focal) effects related to the specific area affected, or more widespread effects depending on the location (supratentorial vs. infratentorial lesions).
• Level of consciousness


  Determined by the cerebral cortex and the reticular activating system in the brainstem. Information must be processed in the association areas of the cortex before an individual can be fully aware of their environment.
• Lesion


  Damage or abnormality in the brain or spinal cord
• Lesion effects


  • Paresis or paralysis of the right arm from damage to the left frontal lobe
  • Loss of vision from damage to the occipital lobe
• Expanding lesion


  Additional impairment as adjacent areas become involved
• Supratentorial lesion


  Lesion in the cerebral hemispheres above the tentorium cerebelli
• Supratentorial lesions


  • Specific dysfunction in a discrete area
  • Lesion must be very large before affecting consciousness
• Infratentorial lesion


  Lesion in the brainstem, or below the tentorium
• Infratentorial lesions


  • Affect many motor and sensory fibers, resulting in widespread impairment
  • May impair respiratory, circulatory function and level of consciousness with a relatively small lesion
• Level of consciousness


  The degree of awareness and responsiveness to the environment
• Determinants of level of consciousness

  • Cerebral cortex
  • Reticular activating system (RAS) in the brainstem
• Information must be processed in the association areas of the cortex before one is conscious of the information
• Extensive supratentorial lesions must be present to cause loss of consciousness, while relatively small infratentorial lesions can affect the RAS and impair consciousness
• Levels of reduced consciousness

  • Lethargy
  • Confusion
  • Disorientation
  • Memory loss
  • Unresponsiveness to verbal stimuli
  • Difficulty of arousal
• Glasgow Coma Scale


  Measure of the most serious level of loss of consciousness or coma, where the person does not respond to painful or verbal stimuli and the body is flaccid
• Vegetative state


  Loss of awareness and mental capabilities, with preserved brainstem function supporting basic bodily functions
• Locked-in syndrome


  Condition where an individual is aware and capable of thinking but is paralyzed and cannot communicate, except perhaps by eye movements
• Brain death


  Cessation of brain function, including the cortex and brainstem, confirmed by specific criteria
• Upper motor neuron damage

  Interference with voluntary movements, causing weakness or paralysis on the opposite side of the body
• The contralateral effect is due to the crossover of the corticospinal tracts in the medulla
• Effects of upper motor neuron damage

  • Increased muscle tone and reflexes (spastic paralysis)
  • Contractures in affected limbs
• Lower motor neuron damage

  Weakness or paralysis on the same side of the body, at and below the level of damage, with flaccid muscles and absent reflexes