Bear and bigcats anatomy

[parvez]

A good article about fast twitching, slow twitching muscle fibres, as this topic is on cats, i will post about cats and bear related. 

http://neurosoma.com/primate-muscles-eit...ow-twitch/

Other members of the animal kingdom can have muscles that are all or almost all slow or fast-twitch fiber. For example, a chicken’s breast is all fast-twitch, which is why it is white in color, and a cat’s soleus muscle is mostly long-enduring slow-twitch fibers, allowing the cat to creep in stealth mode without fatiguing. When it comes time to pounce, cats use their gastrocnemius, which is almost all anaerobic fast-twitch fibers producing massive amounts of pyruvic acid, along with a few aerobic fast-twitch fibers to process the pyruvic acid. Cats can creep, pounce, and leap 10 times their height because both their nervous system and their skeletal muscle are different from ours. We primates tend to wear out rapidly when we slink around in stealth mode because all our muscles are about 50% fast-twitch, which exhaust rapidly.

Confusion also exists as to whether or not the different types of skeletal muscle fiber use different blood and nerve supply; but because fast-twitch is dependent upon slow-twitch for its metabolism, the 2 types of fiber must co-exist side by side. And because they are intermingled and interface one with another, they live within the same fascicles (bundles of muscle fiber), which means they share the same corridors between their fascicles; therefore they must share and utilize the same nerve and blood supply. However the slow-twitch fiber uses the blood supply differently because its metabolism is aerobic; more capillaries cluster around the slow-twitch fiber, making more blood available to the slow-twitch fiber in order to deliver more oxygen to its aerobic powerhouse mitochondria.

Small slow-twitch fibers are ½ to ⅓ the size of fast-twitch fibers and have weaker contractions, but they have longer endurance. They carry energy with adenosine: ADP coming to the mitochondria to be oxidized to ATP, and ATP traveling back into the interior of the cell with its energy. Slow-twitch also contain large amounts of myoglobin, an iron-containing protein similar to hemoglobin in red blood cells. Myoglobin combines with oxygen and stores it until needed, then engages in its principal function of speedily transporting oxygen to the aerobic mitochondria energy factories. It is iron-carrying myoglobin that gives slow-twitch muscle fibers their red color.

While slow-twitch fibers make fewer contractions per second, they are able to adapt rapidly to changes in their environment, and therefore don’t react to nerve potentials not sustained for a certain period of time. As an example, in an electrical power system, a 20-amp slow-blow fuse can temporarily take “transients” or sudden pulses of voltage over 20 amps without blowing. That sudden spike would blow an ordinary 20-amp fuse, but a slow-blow fuse will adjust to that sudden transient spike – even one of 50 amps – providing the spike doesn’t last very long. In order for a 50-amp transient to heat the element enough to blow a 20-amp slow-blow fuse, it must sustain for a period of time.

Large Fast-twitch fibers twitch 3 times faster, and are 2 to 3 times larger than slow-twitch fibers; this extra size gives them greater strength of contractions, but because they use no oxygen and twitch faster, they exhaust rapidly. Fast-twitch fibers carry energy with creatine phosphate. There is no myoglobin in fast-twitch fibers, but they do store glycogen (starch) throughout their interior for energy. Remember that the body’s sugar – glucose – is stored as glycogen in both the liver and muscles until it is needed.

Although fast-twitch fibers twitch faster and exhaust faster than slow-twitch fibers, they adapt more slowly than slow-twitch fibers; it takes a high number of nerve pulses per second to trigger them. Although they squeeze more contractions into less time, they are slower to adapt to changes in their environment and will fire with short spikes of stimulation. This is important because it is what allows NeuroSoma to stimulate the flower spray nerve endings coming from the fast-twitch intrafusal chain fibers within the muscle spindle, while slipping under (not firing) the annulospiral nerve endings coming from the slow-twitch intrafusal bag fibers. This difference in adaptation rate is our ‘in’, and is why we can avoid activating the stretch reflex mechanism by stroking across the grain of muscle fibers. Reply