Chapter 21 Neurotransmitters and Pathways


3. Descending ceruleospinal pathway ■ projects from the locus ceruleus to the spinal cord. ■ inhibits tract neurons that give rise to ascending pain pathways.

B. Parkinson disease ■ results from degeneration of dopaminergic neurons found in the pars compacta of the substan tia nigra, which results in reduction of dopamine in the striatum and in the substantia nigra. ■ results in resting tremor, bradykinesia, postural instability (shuffling gait), and rigidity. C. Huntington disease (Huntington chorea) ■ results from loss of ACh- and GABA-containing neurons in the striatum (caudatoputamen). ■ results in loss of GABA in the striatum and substantia nigra. D. Lambert-Eaton myasthenic syndrome ■ caused by a presynaptic defect of ACh release. ■ results in weakness in the limb muscles but not in the bulbar muscles. Muscle strength im proves with use, unlike in myasthenia gravis, where muscle use results in fatigue. ■ associated with neoplasms (eg, lung, breast, prostate) in 50% of cases. ■ leads to autonomic dysfunction, with dry mouth, constipation, impotence, and urinary incontinence.


Alzheimer disease is the most common type of dementia, affecting approxi mately 6 million individuals in the United States, most of whom are older than 65

years. It is a progressive disease characterized primarily by memory problems and cognitive impair ment. Caused by a combination of factors, including age-related changes in the brain (eg, amyloid plaques, neurofibrillary and tau tangles, and the degeneration of neurons in the basal nucleus of Meynert) and genetic and environmental factors.


Myasthenia gravis is an autoimmune disease that occurs in the presence of antibodies to the nicotinic ACh receptor. It is caused by the action of antibod

ies that reduce the number of receptors in the neuromuscular junction resulting in muscle paresis. Myasthenia gravis is most common in women younger than 40 years and men older than 60 years. It involves the extraocular and eyelid muscles (eg, in diplopia, ptosis) and bulbar muscles (eg, in nasal speech, jaw fatigue) and leads to weaker limbs proximally and stronger limbs distally. It may be di agnosed with intravenous edrophonium and can be effectively treated with thymectomy, followed by corticosteroid therapy.

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