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Motor Dysfunction

Outline

A. Motor Neuron Pathways

1. Pyramidal- originates in the motor cortex, crosses over in the
        pyramids of the medulla

    2. Extrapyramidal- originates in the basal ganglia, does not cross over in
        the pyramids

    3. Cerebellar- originates in the cerebellum, does not cross over in the
        pyramids

    4. Lower motor neurons (LMN)- located in the ventral horn of cord,
        synapse with upper motor neurons (UMN), (include motor roots
        of cranial nerves which synapse with UMN in brain or brainstem)

B. Disruption of Motor Neuron Pathways
    1. Pyramidal
        a.impairs voluntary movement

        b. hyperactive reflexes, + Babinski

        c. spasticity

    2. Extrapyramidal
        a. difficulty in initiating movement    

        b. rigidity

        c. chorea (quick, jerky, purposeless movements)

        d. athetosis (continuous, slow, writhing, wormlike movements)

        e. ataxia- (uncoordinated movement of muscles)

        f. dysmetria ( inability to predict and measure the ends of a
            movement)

        g. dysarthrias- failure in progression of word formation,
            resulting in explosive, slurred, unintelligible speech

        h. tremors

        i. nystagmus (rapid, involuntary, horizontal, vertical or
            rotary movement of eyeball

    3. Lower motor neurons
        a. hypoactive or absent reflexes

        b. fasciculations (spontaneous isolated contractions of individual
            motor units)

        c. flaccidity

        d. muscle atrophy

C. Parkinson's Disease
    1. neurons which originate in substantia nigra (part of basal ganglia)
        and release dopamine are severely affected.Hence overall levels
        of dopamine are reduced

    2. in the basal ganglia there are two sets of neurons, dopamine secreting,
        and acetylcholine secreting
        a. dopamine has an inhibitory effect on extrapyramidal system
        b. acetycholine has an excitatory effect
        c. normally, the two sets of neurons are able to balance each other
            but if dopamine levels decreased, then there is a net excitatory
            effect on extrapyramidal system, resulting in the symptoms of
            Parkinson's disease

    3. Etiology    
        a. encephalitis
        b. side effects of medications
        c. trauma, hemorrhage, tumor
        d. idiopathic (most common)

    4. Clinical manifestations
        a. tremor- earliest symptom, usually occurs at rest

        b. alternating flexion and contraction of the muscles (pill rolling)

        c. difficulty in initiating movement, especially walking (shuffling gait)

        d. mouth open, saliva drooling (because person cannot move saliva
            to back of mouth to swallow)

        e. speech is slow, monotonous without modulation

        f. autonomic symptoms of constipation, lacrimation,
            urinary incontinence

D. Multiple Sclerosis
    1. cause is unknown, some theories say it may be due to a slow
        growing virus or deficiency of  immune system

    2. presence of demyelinated glial patches (plaques) -represent
        the end of acute myelin breakdown

    3. histological evidence indicates there is remyelinaztion (healing), hence
        clinical picture of remission and exacerbation but healing never
        returns to normal

    4. Clinical manifestations
        a. areas most commonly affected are optic chiasm, optic nerves, brain
            stem, corticospinal tracts, posterior columns of spinal cord and
            cerebellum

b. most common symptoms are paresthesias, optic neuritis, motor weakness , abnormal gait, bladder and bowel dysfunction, vertigo,  diplopia, tremor, fatigue, susceptibility to upper respiratory  infections

        c. may produce motor signs such as spasticity, hyperreflexia,
            nystagmus,   balance disorders, dysarthrias

d. dx usually starts as a slowly progressive weakness in lower
             extremities

e. there is a benign form of the disease and an acute, fulminating form

E. Myasthenia Gravis
        a. a disorder of the neuromuscular junction, there is a deficiency
            of acetylcholine receptors on muscle surface (there may
            be only  20% normal receptors)

        b. muscle receptors are destroyed by an autoimmune process

        c. about 25% of pts have thymic tumors and 80% have changes in
            in the cellular structure of the thymus

        d. clinical manifestations
            a. weakness of striated muscles especially eyes muscles,
                evidenced by ptosis and diplopia
            b. chewing and swallowing difficulties
            c. weakness of muscles of lower face- person needs
                to support chin when talking

        e. distinguish between myasthenic crisis and cholinergic crisis
            1. myasthenic crisis- due to little medication, sudden respiratory
                difficulty, quadriparesis or quadriplegia

            2..cholinergic crisis- due to anticholinesterase drug toxicity,
                respiratory difficulties, but also increased intestinal motility
                leading to  diarrhea, cramping, also bradycardia, pupillary
                constriction, increased salivation and sweating

F. Epilepsy
    1.recurrence of seizures without evidence of reversible metabolic activity

    2. a seizure is a spontaneous, uncontrolled, paroxysmal, transitory
    discharge from cortical centers in the brain, causing bizarre
    muscle movements, strange sensations and perceptions, loss of
    consciousness, it results from
        a. cerebral anoxia
        b. hypoglycemia
        c. disturbances of calcium balance
        d. electrolyte imbalance
        e. disturbances in hydration
        f. response to drugs and poisons
        g. high fevers
        h. metabolic disturbances
        i. epilepsy

  3. secondary (known cause) vs  primary (i.e. idiopathic)

  4. distinguishing partial from generalized and complex partial

5. Partial seizures
    a. if motor involved, activity is usually clonic (i.e rapid
        alternation between rigidity and relaxation), distinguish
        between
        1. without  jacksonian march- remains focal
2. with jacksonian march -spreads to adjacent areas

    b. if sensory- may be no apparent clinical manifestations,
        depending on location in sensory cortex of epiletogenic focus may
        produce symptoms of numbness, tingling, crawling sensations
        sensation of foul odors or tastes in mouth

    c. if autonomic involved- symptoms may include flushing,
        tachycardia, changes in BP, diaphoresis, pupillary changes

  6. complex partial (also called temporal lobe or psychomotor seizures)
        1. large number of presentations
            a. person is able to interact with environment with
                purposeful, although inappropriate movement, person does
                not fall, may appear "wide eyed"

            b.may be characterized by automatisms, e.g. lip smacking,
                chewing, facial grimaces, swallowing movements, patting,
                picking or rubbing oneself or ones clothes

            c. automatism may be preceded by wide variety of sensory
                experiences, including illusions, formed hallucinations,
                primitive gustatory, visceral and olfactory sensations

7. Generalized
    1. absence seizures (true petit mal) - abrupt cessation of activity
        accompanied by momentary loss of consciousness- blank
        stare

    2. atonic - sudden split second loss of muscle tone leading
        slackening of the jaw, dropping of a limb or falling to ground      

    3. myoclonic- bilateral jerking of muscles

    4. tonic- rigid, violent contraction of muscles fixing the limbs
        in a strained position

    5. clonic- repeated relaxation and contraction, diminishing
        in frequency

    6. tonic clonic (gran mal)- most common
            a. begins with sharp tonic contraction of muscles- fall
                to ground - may be incontinent- cyanosis may occur from
                tonic contraction of airway- clonic convulsive movements-
                unconscious 2-5 minutes- deep sleep

             b. no recollection after attack

8. status epilepticus - seizures that do not stop spontaneously or in which
        person passes from  one seizure to another without recovery between
        attacks = major medical emergency

Discussion  

     Parkinson's disease results from an imbalance ( in the basal ganglia) between the two neurotransmitters dopamine and acetylcholine. With dopamine deficient, there is a net imbalance which leads to over excitation of the extrapyramidal nervous system and produces the characteristic symptoms. These are described simply as extrapyramidal symptoms. Some drugs ( for example, the phenothiazines,)  can cause similar symptoms as side effects and, therefore, are said to have "extrapyramidal side effects"
    In treating Parkinson's disease two pharmacological approaches are taken.  Replace that which is deficient. This is the rational for the use of a drug such as levodopa. or 2.try to restore the balance between dopamine and acetycholine by decreasing the levels of acetylcholine. Administration of an anticholinergic drug, such as Cogentin, is consistent with the second approach
    Myasthenia gravis is an autoimune disease with destruction of the Ach receptors located on the muscle surface in the neuromuscular junction (the post synaptic membrane). As of yet there is no way to replace cellular structures, so the goal of   treatment is to either a. increase the work of the remaining receptors to compensate or b suppress the immune system. The first goal is achieved pharmacologically by administration of anticholinesterase drugs. Normally, in the neuromuscular synapse, the release of acetycholine by the neuron is followed by the release of cholinesterase to subsequently break down the Ach after it has bound to the Ach receptor and thus terminate the event. A drug that inhibits cholinesterase will allow the Ach to remain bound to the receptor for a longer period of time, thus causing it to continue to work for a longer period of time. A side effect of this approach may be over stimulatiion of cholinergic receptors in other parts of the body, leading to a "cholinergic" crisis. The remedy for this is to decrease or stop the anticholinesterase medication. Suppression of the immune system can be achieved through the use of steroids or plasmaphoresis which can remove antibodies from the blood stream. A myasthenic crisis occurs when the immune system is accelerating its destruction of Ach receptors. In the case of a myasthenic crisis, plasmaphoresis can be lifesaving 

Clinically  

    Different drugs are more effective for certain types of epilepsy than are others. For this reason it is important to be able to clinically identify the type of seizure which a client is having so that the most effective treatment can be initiated. Febrile seizures tend to occur in children between 9 months and 6 years of age and when the temperature is usually > than 104. It is the most common seizure disorder of childhood, with the incidence being between 3- 4%. It is tonic clonic and generally less then 15 minutes in duration. It may be the first sign of illness. The differential diagnosis is epilepsy, meningitis or lead poisoning. The treatment is to focus on finding the cause of the fever, to administer antipyretics (not aspirin), sponging and treating the underlying infection. About 20- 30% of children have recurrent febrile seizures.