rdiacCaCardiac muscles are involuntary and found only in the heart. They arecontrolled by the brain, which controls involuntary action throughoutyour body.Think about how horrible it would be to have to consciously tell yourheart to beat, with the consequence of forgetting being death. Whatabout when you went to sleep!?!But luckily enough, the braindoes all that for us.Your heart cells come in longstrips, each containing asingle nucleus. Its mainfunction is to propel bloodinto circulation.
SmoothYour smooth muscles, like your cardiovascular muscles, are involuntary. Theymake up your internal organs, such as your stomach, throat, small intestine,and all the others, except your heart.Unlike cardiovascular muscles, smooth muscles are generally spherical, as mostother human cells are, and each contains one nucleus.
SkeletalThe skeletal muscles are the only voluntary muscles of your body, and make upwhat we call the muscular system. They are all the muscles that move your bonesand show external movement.Unlike either of the other two classes, skeletal muscles contain multiple nuclei,because of its large size. They are in strips up to a couple of feet long.You have over 600 skeletal muscles.
Your muscles work with your bonesTry this. Put your elbow on the table and lift a book. Move it in alldirections.Your elbow is life a fulcrum and your arm a lever. You can move thebook because of muscle contractions.
Skeletal muscles cant expand, or make themselves longer, but they can contract, ormake themselves shorter, so they generally work in pairs. One contracts, and indoing so stretches the other, and reverses its effects on the joint.For example, when you contract your major arm muscle, which is called the bicep, inreturn the lower arm muscle, called the tricep, extends. So as you contract onemuscle the other one extends
Skeletal muscles can be brokendown into groups based on theirmovement.·Flexors·Extensors·Adductors·Abductors
FlexorsFlexors bend at the joint.The bicep, is a flexor of the elbow joint, bringingthe fist towards the shoulder. Extendors Opposites of flexors, extensors unbend at the joint, increasing the interior angle. The tricep, is an extensor ofthe elbow joint, taking the fist farther away from the shoulder.
Abductors Abductors take the bones away from the body, likelifting the arm to the side.Spreading out your fingers uses abductors, becauseyou are taking away yourfingers from an imaginary linerunning down yourarm.AdductorsAdductors, the opposites of abductors, move toward thebody. Add- means to increase or include. By lowing an armraised to the side, or moving your fingers together whilekeeping them straight, your muscles are adducting.
Tendons and LigamentsMuscles alone cant do the job. At every joint, tendons and ligaments also helpout. Muscles wouldnt be very useful alone because they dont directly connect tothe bone.Muscles are connected to tendons, which are connected to the bones. When themuscles contract, they pull on the tendons, which in turn pull on the muscles, andthat causes movement.Ligaments are what holdthe bones together. Theyconnect at the ends ofmuscles and keep themfrom slipping and sliding, and force them to bend.
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