Stored within its ending are vesicles or membranous pouches filled with a

Stored within its ending are vesicles or membranous

This preview shows page 4 - 6 out of 14 pages.

Stored within its ending are vesicles, or membranous pouches, filled with a chemical substance called a neurotransmitter. The neurotransmitter at the NMJ is acetylcholine. Step 2 . The nerve impulse causes the vesicles to move toward and fuse with the membrane at the end of the neuron. ACh is released from the vesicles into the space between the neuron and the muscle membrane. Step 3 . ACh diffuses across the space and binds to the receptor sites on the muscle membrane. Step 4. The ACh stimulates the receptors and causes an electrical signal to develop along the muscle membrane. The ACh then unbinds the receptor site and is immediately destroyed by an enzyme that is found within the NMJ, near the muscle membrane. The name of the enzyme is acetylcholinesterase or cholinesterase. The free binding sites are then ready for additional ACh when the neuron is stimulated again
Image of page 4

Subscribe to view the full document.

Disorders of Neuromuscular Junction Myasthenia gravis o Disease that affects the NMJ. The symptoms of the disease are caused by damaged receptor sites (NM receptors) on the muscle membrane. o The receptor sites are altered so that they cannot effectively bind ACh. Consequently, muscle contraction is impaired, and the person experiences extreme muscle weakness. (The word myasthenia means muscle weakness.) o The muscle weakness first becomes noticeable as low tolerance to exercise. As the disease progresses, the person experiences difficulty in breathing because the breathing muscles are skeletal muscles. Neuromuscular Blockade Caused by Curare . o Curare is a drug classified as a skeletal muscle blocker. Skeletal muscle blockers are often used during surgery to promote muscle relaxation and paralysis. Curare works by blocking the receptor sites on the muscle membrane. o Because the receptors are occupied by the drug, the ACh cannot bind with the receptor sites, and muscle contraction is prevented. o Because the respiratory muscles are also affected by curare, the patient must be mechanically ventilated until the effects of the drug disappear. Otherwise, the patient stops breathing and dies Effects of Neurotoxins on Muscle Function. o Neurotoxins are chemical substances that in some way disrupt the normal function of the nervous system. Neurotoxins are produced by certain bacteria. For example, Clostridium tetani (a bacterium) secretes a neurotoxin that causes excessive firing of the motor nerves. This, in turn, causes excessive release of ACh, overstimulation of the muscle membrane, and severe muscle spasm and tetanic contractions—hence the name tetanus. Because the muscles of the jaw are the first muscles affected, the disease is often called lockjaw. o A second neurotoxin is secreted by the bacterium Clostridium botulinum. This bacterium appears most often when food has been improperly processed and canned. Infection with this organism causes botulism, a very serious form of food poisoning. The neurotoxin works by preventing the release of ACh from the ends of the neurons within the NMJ. Without ACh, the muscle fibers cannot contract, and the muscles, including the breathing muscles, become paralyzed.
Image of page 5
Image of page 6
  • Fall '19
  • muscle weakness, muscle atrophy, functions of muscles

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern

Ask Expert Tutors You can ask 0 bonus questions You can ask 0 questions (0 expire soon) You can ask 0 questions (will expire )
Answers in as fast as 15 minutes