Book 4 - Self Instructional Manual for Cancer Registrars - SEER ...

SkeletalMusclesSome of the skeletal muscles are shown in Figure 68. An extensive list of skeletal muscles isfound in your medical dictionary under "muscle." Dorland's dictionary also contains five plates whichshow most of the more than 600 muscles of the body. Two prominent groups of muscles which havebeen given characteristic names are the hamstrings (lower extremity) and the biceps (upperextremity).The five functional characteristics of muscle tissue are:• Irritability: ability to respond to a stimulus• Conductivity: ability to transmit impulses• Extensibility: ability to stretch• Elasticity: ability to resume former length when the stretching force is removed• Contractibility: ability to shortenThe three general functions of skeletal muscle are:• Movement: sometimes locomotion and sometimes movement within a given area• Heat production: developed by muscle contraction• Posture: alignment of body parts.Posture is maintained by a continual pull of muscles on bones in a directionopposite to the pull of gravity, i.e., by the continual partial contraction of muscles,known as muscle tone. Therefore, posture is indirectly dependent on many otherfactors, such as a normal nervous system and health in general.The names given to muscles describe one or more of the following features of muscle: action,direction of fibers, location, number of divisions, shape, and points of attachment to bone. Musclesmay be classified into groups according to the action or movement performed.• Flexors decrease the angle in a joint.• Extensors increase the angle in a joint and also return a body part to neutralposition after flexion.• Abductors move a body part away from the midline.• Adductors move a body part towards the midline.• Rotators cause a body part to pivot on its axis.• Levators/elevators raise a body part.385