Acute Neurological Disorders: Pathophysiology and Effects on the Nervous System, Study notes of Pathophysiology

Download Acute Neurological Disorders: Pathophysiology and Effects on the Nervous System and more Study notes Pathophysiology in PDF only on Docsity! 1 Acute Neurological Disorders Bio 375 Pathophysiology Acute Neurological Disorders Ventricular system with choroid plexuses that form cerebrospinal fluid Meninges consist of three continuous connective tissue membranes covering the brain and spinal cord Functional Areas of the Brain 2 Blood Supply to the Brain Cranial Nerves Spinal Cord and Spinal Nerves 5 Cerebral cortex and RAS in the brainstem determine the level of consciousness Usually extensive supratentorial lesions must be present in the cerebral hemispheres to cause loss of consciousness, whereas relatively small lesions in the brainstem can affect the RAS Systemic disorders, such as acidosis or hypoglycemia can depress the CNS and reduce the level of consciousness Various levels of reduced consciousness Lethargy Confusion Disorientation Memory loss Unresponsiveness to verbal stimuli Difficulty of arousal Coma Motor Dysfunction Damage to upper motor neurons in cerebral cortex (frontal lobe) or to the corticospinal tracts in the brain interferes with voluntary movements Causes weakness or paralysis on the contralateral side of the body Muscle tone and reflexes may be increased (hyperreflexia) leading to contractures in the affected limbs (spastic paralysis) 6 Damage to lower motor neurons in the anterior horns of the spinal cord causes weakness or paralysis on the same side of the body, at and below the level of damage In the area of damage the muscles are usually flaccid (lack tone) and reflexes are absent (flaccid paralysis) Sensory Deficits (Paresthesias) Sensory loss may involve: Touch, pain, temperature, position and special senses of vision, hearing, taste and smell The specific site of lesion in the somatosensory cortex (parietal lobe) determines the deficit for skin senses Visual Loss 7 Language Disorders Aphasia refers to an inability to comprehend or to express language There are many types of aphasia Expressive Receptive Global Dysphasia refers to partial impairment Other language disorders: Dysarthria in which words cannot be articulated clearly, is a motor dysfunction that usually results from cranial nerve damage or muscle impairment Agraphia is impaired writing ability Alexia is impaired reading ability Agnosia is loss of recognition or association, e.g. visual agnosia indicates an inability to recognize objects visually Seizures Seizures or convulsions are caused by spontaneous excessive discharge of neurons in the brain Seizures may be precipitated by inflammation, hypoxia or bleeding in the brain Seizure may be focal, being related to a particular site of irritation but may become generalized Seizure disorders are chronic and considered later 10 TIA’s may occur singly or in a series TIA’s can serve a useful purpose if used as a warning signal leading to diagnosis and treatment before a stroke occurs Not all strokes are preceded by a TIA The manifestations of a TIA are directly related to the location of the ischemia Examples include Muscle weakness in an arm or leg Visual disturbances Numbness or parathesias in the face Transient aphasia or confusion The attack may last a few minutes or longer but rarely more than 1-2 hours Cerebrovascular Accidents (CVA) A CVA, stroke or brain attack is an infarction of brain tissue from lack of blood Tissue necrosis may result from total occlusion of a vessel by atheroma or embolus or it may be a result of a ruptured vessel Five minutes or less of ischemia causes irreversible cell damage raw pa) | [i = | Types of Strokes 11 12 Blood Supply to the Brain Colorized NMR showing disruption in blood flow to the left side (viewers right) of the brain. 15 Hematomas A hematoma is a collection of blood in the tissue that develops from ruptured blood vessels Hematomas and hemorrhages are classified by their location in relation to the meninges: Epidural (extradural) hematoma Subdural hematoma Subarachnoid hemorrhage Intracerebral hematoma A. Subdural hematoma B. Compression of brain tissue 16 Spinal Cord Injuries Usually results from fracture or dislocation of the vertebrae Causes compression, stretching or tearing of the spinal cord Supporting ligaments and intervertebral discs may be damaged also Most injuries occur in two areas of the vertebral column: C1 to C7 and T12 to L2 Dermatome Map Testing dermatomes can be useful in assessing the extent of damage and recovery. A dermatome map is used to assess which spinal segments are functioning. Common Types of Spinal Cord Injuries Cervical spine injuries involving hyperextension or hyperflexion of the neck with possible fracture Leads to disc and ligament damage Loss of alignment of the vertebrae Causes compression and stretching of cord Dislocation of any vertebra may crush or compress spinal cord and interfere with blood supply 17 Compression fractures cause injury to the cord when great force is applied to the top of the head or to the feet and transmitted up or down the spine Shattered bone is compressed and exerts pressure horizontally against the cord Sharp edges of the bone fragments may lacerate nerve fibers and blood vessels Spinal cord damage may also occur from penetration injuries such as stab wounds or bullet wounds Classification of Vertebral Fractures Simple (single line break) Compression (crushed or shattered bone with multiple fragments) Wedge (displaced angular section of bone) Dislocation (vertebra forced out of its normal position) Avoiding Secondary Damage Because spinal cord injuries are often unstable, immediate and appropriate immobilization is essential to prevent secondary damage. 20 Signs and Symptoms-Two Stages in post-traumatic period Recovery and recognition of the extent of functional loss Recovery and recognition of the extent of functional loss: This stage is indicated by the gradual return of reflex activity below the level of injury Hyperreflexia generally develops due to lack of the normal inhibitory impulses that come from the brain Spastic paralysis, sensory deficits and reflex control of bladder and bowel activity are present below the level of damage Cervical injuries affect sensory and motor functions in arms, trunk and legs Respiratory function: intercostal and phrenic nerves Sympathetic nervous system function Blood pressure and body temperature may be unstable due to lack of central control of vasomotor tonus and diaphoresis (sweating) 21 Autonomic Dysreflexia Damage to the cervical spine can result in serious and potentially life threatening sympathetic responses A sensory response like a distended bladder or decubitus ulcer can send impulses up the cord resulting in a massive response of the sympathetic nervous system which cannot be regulated by the brain (hypothalamus and cardiovascular reflex centers in the brainstem The stimulus can activate the chain ganglia leading to excessive vasoconstriction and a sudden increase in blood pressure, headache and visual disturbances Baroreceptors sense the increase in BP and stimulate bradycardia via vagus Without immediate resolution a stroke or heart failure may follow Removing the cause of the stimulus and administering blood pressure lowering drugs 22 Terminology with Spinal Cord Injuries Paralysis of all four extremities is termed quadriplegia Paralysis of the lower part of the truck and legs is termed paraplegia NOTE that lumbar cord injury interferes with function of the lower extremities as well as sacral parasympathetic fibers Complications with Spinal Cord Injuries Muscle spasms Decubitus ulcers Respiratory and urinary infections Sexual dysfunction Reproductive dysfunction