Skeletal Muscle Shapes

Fusiform muscles –thick in middle and tapered at ends Parallel muscles have parallel muscle fibers Convergent muscle –broad at origin and tapering to a narrower insertion Muscle Descriptions

Muscle Descriptions Cont…. Pennate muscles –fascicles insert obliquely on a tendon –unipennate, bipennate or multipennate Circular muscles –ring around body opening (ex: iris, mouth)

Interactions of Skeletal Muscles Muscles can only pull, they can’t push Actions must be “undone” by a different muscle Muscles that produce opposite movements usually lie on opposite sides of a given joint

Muscles Work together to move a joint Agonist: “prime mover”, major responsibility for producing a specific movement Antagonist: oppose or reverse a particular movement –Usually contract a little to prevent overshooting the mark or slow the agonist’s action near the end –Are being “stretched” or can remain relaxed when agonist works Antagonists for one movement can be agonists for another Antagonist Agonist

Synergists help prime movers –Add a little extra force to the same movement –Or reduce undesirable extra movements (e.g. making a fist without flexing at wrist) Fixators: hold a bone firmly so agonist has a stable base on which to move a body part (e.g. fixing scapula when arm moves)

Muscles work in concert… the elbow Flexion Prime Movers: responsible for flexing arm) –Biceps Brachii (lifts radius in forearm) –Brachialis (lifts ulna in forearm) Synergists: helps stabilizes elbow joint –Brachioradialis Antagonists: (resists movement of prime movers) –Triceps Brachii Fixators: (hold shoulder in place) –Deltoid –Trapezius

Type of Contractions Isometric Contraction –Muscles are contracting but there is no movement –Muscles trying to allow for body movement but can’t – spinning wheels Isotonic Contractions –Movement occurs when muscles contract Bending knee, smiling, rotating arms Pushing on a wall Lifting weights