The scientists who discovered the lethal activity of the botulinum toxin nearly 200 years ago probably didn't know that the intentional injection of a very dilute form of botulinum toxin would become the most common non surgical cosmetic procedure performed by many physicians.
A few decades later, a Belgian researcher named Emile Pierre van Ermengem identified the specific bacterium responsible for producing the botulinum toxin, which could cause symptoms such as paralysis and respiratory failure.
By the 1920s, medical scientists at the University of California had obtained the toxin in pure form, which allowed them to determine that it acted by preventing nerves from communicating with muscles, specifically by interfering with the release of acetylcholine from the axon terminals of motor nerves.
A lucky break occurred that eventually would open the medical community's eyes to the greater potential of the diluted toxin.
When Jean Carruthers used it to treat her patients' eye conditions, she noticed that some of their wrinkling had stopped.
One night at a family dinner, Dr. Carruthers shared information with her husband, a dermatologist, who decided to investigate whether he could reduce the deep wrinkling of some of his patients by injecting the dilute toxin into their skin.
Although they were initially considered crazy, the Carrutherses eventually were able to convince the scientific community that botulinum toxin is effective in treatingwrinkles, but they never patented it for that use, so they missed out on much of the $1.3 billion in annual sales the drug now earns for.
The FDA approved the use of botulinum toxin for the treatment of frown lines in 2002.
The company is trying to get approval for more uses of botulinum toxin.
The market forotulinumtoxinA is expected to reach $3 billion in the next few years.
Progress would have been slower even without the observations of an eye doctor.
"Chance favors the prepared mind" is what the French microbiologist Louis Pasteur said in 1854.
The page provides the energy for muscle contraction.
muscle contraction can't be directly participated in by cratine phosphate.
When all of the creatine phosphate is gone, the mitochondria may not be able to produce enough energy for muscle contraction.
If not, the second way for muscles to supply ATP is through fermentation.
When strenuous exercise begins, it is likely that a short time will be needed for the production of ATP and lactate.
There is a question as to whether or not lactate causes fatigue on exercising.
We all have had the experience of needing to continue breathing after exercising.
This continued intake of oxygen, which is required to complete the metabolism of lactate and restore cells to their original energy state, offsets what is known as oxygen debt.
20% of the lactate is broken down to carbon dioxide and water in the bile duct.
The reconversion of 80% of the lactate to glucose is done by the use of the ATP gained by this respiration.
In people who regularly exercise, the number of mitochondria increases, and the muscles rely on them rather than on ferment.
There is less oxygen debt and less lactate being produced.
Motor nerve fibers cause muscles to contract.
The sarcolemma of a muscle fiber is close to the axon terminal of the nerve fibers.
A small gap separates the axon terminal from the sarcolemma.
This is the entire region.
The axon terminal is separated from the sarcolemma by a cleft.
impulses begin to lead to muscle contraction when the neurotransmitter is received by the sarcolemma.
The synaptic vesicles in the axon terminal are filled with the neurotransmitter acetylcholine.
When nerve impulses travel down a motor neuron to an axon terminal, they are released into the synaptic cleft.
Alemma quickly diffuses across the cleft.
The sarcolemma creates impulses that travel over the sarcolemma to the sarcoplasmic reticulum.
The release of calcium from the sarcoplasmic reticulum causes the sarcomeres to slide.
The results of sarcomere contraction are myofibril contraction, muscle fiber and muscle contraction.
Due to reasons we will discuss next, muscle contraction ceases when the AChE breaks down.
Figure 39.15 shows the placement of two other proteins associated with a thin filament, which is composed of a double row of twisted actin molecule.
The sarcoplasmic reticulum has released Ca2+ and troponin.
The myosin binding sites are exposed after the binding occurs.
Upon release, calcium exposes myosin binding sites.
Many heads are active at the same time, despite only one myosin head being featured.
There are bundles of myosin molecules.
Myosin heads work as myosinidases, splitting the ATP into two parts.
The heads can bind to actin with this reaction.
The actin heads attach to the myosin heads and form cross-bridges.
Cross-bridges change their positions because of the release of ADP and P.
The power stroke pulls the thin filaments towards the middle of the sarcomere.
Cross-bridges are broken when myosin heads detach from actin.
Each time the cycle is repeated, the actin filaments move closer to the center of the sarcomere.