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