Chapter 10 The Muscular System J.F. Thompson, Ph.D. & J.R. Schiller, Ph.D. & G. Pitts, Ph.D.

The Muscular System Interactions of Skeletal Muscles in the Body muscles usually work in groups, i.e., perform “group actions” muscles are usually arranged in antagonistic pairs –ex: flexor-extensor –ex: abductor-adductor –etc.

How Skeletal Muscles Produce Movements muscles exert a force on tendons which pull on bones muscles usually span a joint muscle contraction changes the angle or position of one bone relative to another bone brachialis flexes forearm

Terms Relative to Skeletal Muscle Movements origin: the attachment of the muscle to the bone which remains stationary insertion: the attachment of the muscle to the bone which moves belly: the fleshy part of the muscle between the attachments at origin and insertion origin insertion belly

Functional Roles of Skeletal Muscles Prime Mover (= Agonist): the principle muscle which causes a movement –ex: biceps brachii  flexion of forearm Antagonist: the principle muscle that causes the opposite movement –ex: triceps brachii  extension of forearm

Functional Roles of Skeletal Muscles Synergists: muscles that assist the prime mover in its movement –ex: extensor carpi (wrist) muscles are synergists for the flexor digitorum muscles when you clench your fist or hold a beverage while walking Fixators: synergists that stabilize the origin of a prime mover –ex: several back muscles stabilize the scapula when the deltoid abducts the arm

Functional Roles of Skeletal Muscles Group Actions: most movements need several muscles working together –while the prime movers (agonist and synergists) are contracting to provide the desired movement –other muscles (antagonists) are relaxing & being stretched out passively –agonist and antagonist change roles depending on the action –e.g., abduction versus adduction Synergists and Fixators become Agonists and Antagonists in different movements

Naming Skeletal Muscles Location of the muscle Shape of the muscle Relative Size of the muscle Direction/Orientation of the muscle fibers/cells Number of Origins Location of the Attachments Action of the muscle Know the muscle names as described in your Lab Guide 6.

Arrangement of Fascicles range of motion: depends on length of muscle fibers (fascicles); long fibers = large range of motion –parallel and fusiform muscles power: depends on total number of muscle fibers; many fibers = great power –convergent, pennate, bipennate, multipennate

Arrangement of Fascicles circular (sphincters), ex: orbicularis oris parallel (strap-like), ex: sartorius fusiform (spindle shaped), ex: biceps femoris convergent, ex: pectoralis major long parallel fibers offer greater range of movement

Arrangement of Fascicles pennate ("feather shaped") unipennate ex: flexor pollicis longus bipennate, ex: rectus femoris multipennate, ex: deltoid short oblique fibers offer greater power

Leverage Systems lever: a rigid rod that moves on some fixed point, e.g., a bone fulcrum: a fixed point for lever motion, e.g., a joint resistance: the force opposing movement effort: the force exerted to achieve action

Leverage Lever Systems and Leverage –lever a rigid rod that moves on some fixed point = the fulcrum bones = levers, joints = fulcrums –a lever is acted upon at 2 different points by: 1)resistance or load –the force that opposes movement –the load or object (bone or tissue) to be moved 2)effort –the force exerted to achieve a movement –the effort is provided by muscle(s) –motion is produced when the effort exceeds the resistance (isotonic contraction)

Mechanical Advantage Lever allows an effort to move a larger load or move a load faster –mechanical advantage the load is near the fulcrum; the effort is farther away only a small effort is required to move an object mechanical advantage allows a heavy object to be moved with a small effort – e.g., car jack

Power and Range of Motion leverage: the mechanical advantage gained by using a lever power: muscle tension (effort) farther from joint (fulcrum) produces stronger contraction (opposes greater resistance) range of motion (ROM): muscle tension (effort) closer to joint (fulcrum) produces greater range of motion.

Mechanical Disadvantage –the load is far from the fulcrum; the effort is near the fulcrum –a large effort is required to move the object –this allows object to be moved rapidly -- a “speedy lever” e.g., throwing a shovel full of dirt or throwing a baseball

Additional Information You do not need to memorize the details of the different leverage system types for Exam 3. See slides of the three types of lever systems after the “end” slide in this presentation. Slides with some examples of the naming of muscles can be found in the PowerPoint presentation for Lab 6 and after the “end” slide in this presentation.

Skeletal Muscles Know the muscles, their origins and insertions as described in your Lab Guide 6.

End Chapter 10 There are some additional slides you can review on uour own after this slide.

Antagonists of the Forearm

Antagonists of the Thigh

Antagonists of the Foot

Arrangement of Fascicles Parallel (strap- like), ex: sartorius Fusiform (spindle shaped), ex: biceps femoris

Arrangement of Fascicles Pennate ("feather shaped"), ex: extensor digitorum longus Bipennate, ex: rectus femoris Multipennate, ex: deltoid

Arrangement of Fascicles Convergent, ex: pectoralis major Circular (sphincters), ex: orbicularis oris

Muscles Named by Location Epicranius (around cranium) Tibialis anterior (front of tibia) tibialis anterior

Muscles Named by Location frontalis (frontal bone) tibialis anterior (front of tibia) [Note: naming by number of origins: the quadriceps (“four heads”) has four origins] tibialis anterior

Muscles Named by Shape Shape: –deltoid (triangle) –trapezius (trapezoid) –serratus (saw-toothed) –rhomboideus (rhomboid) –orbicularis and sphincters (circular) rhomboideus major

Muscles Named by Size maximus (largest) minimis (smallest) longus (longest) brevis (short) major (large) minor (small) Psoas major Psoas minor

Muscles Named by Direction of Fibers Rectus (straight)-parallel to long axis Transverse Oblique Rectus abdominis External oblique

Muscles Named by Direction of Fibers rectus (straight) - parallel to the muscle’s long axis –ex: rectus abdominis transversus (transverse) – at right angles to the muscle’s long axis oblique rectus abdominis

Muscles Named by Direction of Fibers ex: external oblique external oblique abdominis

biceps (2) triceps (3) quadriceps (4) Muscles Named for Number of Origins Biceps brachii

Muscles Named for Origin and Insertion Sternocleidomastoid originates from sternum and clavicle and inserts on mastoid process of temporal bone origins insertion

Muscles Named for Action Flexor carpi radialis (extensor carpi radialis) – flexes wrist Abductor pollicis brevis (adductor pollicis) –flexes thumb Abductor magnus – abducts thigh Extensor digitorum – extends fingers Adductor magnus

Leverage Systems and Leverage Lever: i.e. bones, a rigid rod that moves on some fixed point Fulcrum: i.e. joint, a fixed point Resistance: the force opposing movement Effort: the force exerted to achieve action

Muscle Mechanics – 1 st Class Lever three classes of levers –first-class lever [E-F-R = effort-fulcrum-resistance] the fulcrum is placed between the effort and the resistance (load) e.g., seesaw, scissors skull (head)/atlas and cervical vertebrae –the muscles of the back (splenius, trapezius, etc.) provide the effort –the mass of the skull provides the resistance (load)

second-class lever [F-R-E = fulcrum-resistance-effort] the fulcrum is at the end of the lever, the effort is at the opposite end, and the resistance (load) is in between, e.g., a wheelbarrow 2 nd class levers provide greater power to move a large resistance (load) raising the body on the toes –the mass of body is the resistance –the ball of the foot is the fulcrum –the contraction of the calf muscles to lift the heel upward is the effort 2 nd Class Lever three classes of levers (cont.)

–third-class lever [F-E-R = fulcrum-effort-resistance] the fulcrum is at one end, the resistance is at opposite end, and the effort is in between, e.g., tweezers the most common type of lever in the body 3 rd class levers provide for rapid motion e.g., flexing the forearm or adducting the thigh such movements can still be powerful 3 rd Class Lever

End of Extra Review Slides for Chapter 10