Topic 8-9 Part 3 Muscular System

Discovering that Dr. O. Clarkson is actually half Brazilian, a student thought it would be a funny joke to shoot him with a blowdart containing curare, which is used by Brazilian and Peruvian Amazonains. Curare is derived from the Amazonian plant Chondrodendron tomentosum among other plants, and has a long history of use by indigenous people for hunting and warfare. Curare works by binding to nicotinic acetylcholine receptors on the motor endplate, preventing acetylcholine from binding to these receptors. What would be curare's effect on Dr. O?

• Curare would have no effect on Dr. O.
• Curare would prevent muscle contraction, paralysing Dr. O.

• Curare would cause Dr. O to experience spastic paralysis.

• Curare would cause Dr. O to become stronger and more agile.

Dr. O eventually succumbs to the toxic effect of curare and dies. 12 hours later, two of Dr. O's anatomy and physiology students find his corpse, which is now stiff as a rock. Recalling their lecture on the muscular system, the students exclaim, "Dr. O is experiencing rigor mortis, also known as postmortem rigidity!" The students then discuss the mechanism of rigor mortis which involves:

• Depletion of ATP and the release of cross-bridges of myosin heads and actin filaments

• Decreased pH levels due to lactic acid accumulation

• Loss of calcium ions and reduced troponin-tropomyosin complex activation

• Depletion of ATP and the inability to release of cross-bridges of myosin heads and actin filaments

How long would it take for proteins to degrade in rigor mortis, allowing for relaxation of the affected muscles?

• 1-2 months

• 24-48 hours
• 1-2 hours
• 1-2 weeks

A large quantity of ACh in the neuromuscular junction would result in

• excessive muscle contractions or spasms
• decreased muscle tone
• muscle weakness
• impaired muscle coordination

John Doe, a 45-year-old farmer, presented to the emergency department with a chief complaint of muscle spasticity, nausea, vomiting, and difficulty breathing. He reported that the symptoms had started approximately 6 hours after he was spraying his crops with pesticides. He described the pesticides he had used as acetylcholinesterase inhibitors and admitted to accidental exposure due to inadequate personal protective equipment. What is happening at the neuromuscular junction? Select all that apply

• Decreased acetylcholine synthesis
• Decreased acetylcholine breakdown
• Decreased acetylcholine release
• Acetylcholine accumulation and overstimulation of muscles

Emma, a 6-month-old female, was brought to the emergency department by her parents with a chief complaint of weakness, poor feeding, and difficulty breathing. Her parents reported that these symptoms had progressively worsened over the past few days. Emma was a previously healthy infant who had been exclusively breastfed, but they had recently introduced small amounts of honey into her diet. As it turns out, the honey was contaminated with Clostridium botulinum. What is the underlying mechanism of botulinum toxicity?

• Inhibition of acetylcholine release at the neuromuscular junction
• Activation of acetylcholine release at the neuromuscular junction
• Blockade of acetylcholine receptors at the neuromuscular junction
• Inhibition of dopamine release at the neuromuscular junction

Sarah, a 35-year-old woman, presented with a history of progressive muscle weakness, which had developed over several months. She described experiencing difficulty in keeping her eyes open and swallowing, and her symptoms typically worsened as the day progressed. Physical examination revealed: Bilateral ptosis (drooping eyelids). Muscle weakness in the limbs, notably the proximal muscles. Facial muscle weakness leading to a "mask-like" expression. Reduced ability to swallow. What is this patient's diagnosis?

• Parkinson's disease
• Multiple Sclerosis
• Amyotrophic lateral sclerosis (ALS)
• Myasthenia Gravis

Myasthenia gravis is an autoimmune disorder that involves:

• Antibodies destroying Acetylcholinesterase

• Antibodies blocking and/or destroying ACh receptors

• Antibodies destroying Ca2+ channels

• Antibodies against ACh

Motor units attach to muscle fibers at the ___

• muscle tendon junction
• neuromuscular junction
• muscle fiber junction
• skeletal junction

Muscles that require precise movement have ___ motor units and muscles that require powerful movements have ___ motor units

• fewer, more
• fewer, fewer

• more, fewer

• more, more