To understand what happens when a myotonic goat is frightened and faints, it's helpful to first take a look at what happens under normal conditions. If a person were to chase after a goat unaffected by myotonia congenita, the animal's eyes and ears would relay the perceived threat to the brain, which would then send an electrical signal to the skeletal muscles (such as those in the leg and neck involving voluntary movement), causing a momentary tensing. This is often referred to as the fight or flight response.
Just think how it feels to be startled, or have a friend remind you. You'll find your voluntary muscles contract and tighten for a second. This is your brain telling your muscles that the time has come to possibly confront or run away from an immediate threat.
Normally, this tensing is followed by an immediate relaxing of the affected muscles, allowing a typical goat to actually turn and run away from a perceived threat. With myotonia congenita, however, the muscles tense and stay tensed before slowly relaxing. Think about that moment of muscle tension following a sudden fright -- now imagine it lasting 10 to 20 seconds.
Due to abnormalities at the cellular level, the voluntary muscles of myotonic animals receive the electric signal from the brain to tense and keep tensing instead of releasing -- sort of like a skipping record.
This happens because myotonia congenita affects a particular gene called CLCN1 (Choloride Channel 1). This gene is involved in the production and regulation of proteins, which are vital to the flexing and relaxing of skeletal muscles. Positively charged sodium ions relay the brain's message for the muscle cells to contract. Negatively charged chloride ions, which CLCN1 affects, tell the muscle cells to relax. Mytonia congenita results in an abnormal channel of chloride ions, which throws this relationship out of balance. The muscle cells wind up with more than enough sodium but not enough chloride, which causes abnormal repetitive electrical signals from the brain (such as those associated with being startled) to result in stiffness.
While the fainting goats often receive the most press, myotonia congenita can be found in various other animals as well, all the way up from mice to human beings.
The condition is hereditary, and can be either a dominant trait (the gene only has to be inherited from one parent) or recessive trait (the gene is carried by both parents). Where fainting goats differ from other myotonic animals, however, is that they're actually bred to encourage myotonia congenita in their offspring.
Some humans with the disorder take medication or undergo physical therapy in order to manage their condition, and a number of miniature schnauzer breeders use genetic screening to avoid producing myotonic puppies, but the fainting goat is bred, raised and encouraged to seize up and tumble.
In the next section, we'll look at why a goat breeder would consider myotonia congenita a desired trait.