Muscular System: Gross Anatomy Chapter 10 Muscular System: Gross Anatomy AP1 Chapter 10

Chapter 10 Outline General Principles Muscle Shapes Nomenclature Movements accomplished by muscles Muscle Anatomy AP1 Chapter 10

I. General Principles Most skeletal muscles extend from one bone to another & cross at least 1 joint. Some aren’t facial muscles attach to bone on one end & the skin on the other (moves the face) Muscle contraction causes most body movements by pulling 1 bone toward the other across a movable joint. ACTION: movement accomplished by a muscle when it contracts Fig 10.27 Pg 353 Fig 10.15 Pg 339 AP1 Chapter 10

I. General Principles Muscle Terminology Origin: Insertion: Belly: (fixed end, or head) usually both the most stationary & most proximal end of the muscle. (some have multiple) Insertion: (Mobile end) usually the most distal end attached to the bone undergoing the most movement. Belly: Region between the origin & insertion Tendon: Responsible for attaching muscle to bone Long cable-like structures; broad sheet-like structures called aponeuroses; or short, almost non-existent structures I. General Principles Pg 321 Figure 10.1 AP1 Chapter 10

I. General Principles Muscles (much like the movement discussed in Chapter 8) oppose each other. Agonist: Muscle accomplishing 1 movement (biceps brachii) Antagonist: Muscle opposing the movement of the agonist (Triceps brachii). AP1 Chapter 10

I. General Principles Muscles also tend to functions in groups to accomplish specific movements: Synergists: members of a group of muscles working together to prod a mvmt. Prime Mover: the muscle responsible for the major role accomplishing the desired movement Fixators: muscles that holds one bone in place relative to the body while (normally) a more distal bone is moved Example: Synergists: biceps brachii & brachialis fxn in elbow flexion Prime mover: Brachialis Fixators: muscles in the scapula to keep shoulder stationary while humerus is moving AP1 Chapter 10

A. Muscle Shapes Pg 322 Fig 10.2 Shape & size of a muscle influence the degree to wh/ it can contract & amount of force generated. 3 major classes based on fasciculi orientation: Pennate Straight Orbicular AP1 Chapter 10

A. Muscle Shapes Pennate Bipennate: Semipennate: Multipennate Pg 322 Fig 10.2 Pennate Bipennate: Fasciculi arranged like the barbs of a feather on 2 sides of a common tendon Semipennate: All fasciculi are on 1 side of the tendon (unipennate) Multipennate Fasciculi arranged at many places around the central tendon Ex/muscles extending from the knee AP1 Chapter 10

A. Muscle Shapes Straight Orbicular Pg 322 Fig 10.2 Straight Fasciculi are arranged parallel to the long axis of the muscle. Result: Muscles shorten to a greater degree because of the direct line to the tendon, but contract with less force b/c fewer total fascicles are attached to the tendon. Hyoid muscles Orbicular Fasiculi are arranged in a circle around an opening & act as sphincters to close and opening AP1 Chapter 10

Muscles are named according to: B. Nomenclature Muscles are named according to: Location: Examples: Pectoralis (chest) ; Gluteus (Buttock); Brachial (arm) Size Gluteus maximus (Large); Gluteus minimus (Small); Longus (long); Brevis (short) Shape Deltoid (triangular); Quadratus (rectangular); teres (round) Orientation of fasciculi Rectus (Straight); Oblique (slanting or inclined; diagonal) Origin & insertion Brachioradialis (origin in arm [brachii] and insertion at radius) Number of heads Biceps have 2 heads (Triceps 3 heads) Functions Adductor  moves toward midline Abductor  moves away from midline Masseter  Chews AP1 Chapter 10

Examples of shapes pg 323 Fig 10.3 AP1 Chapter 10

C. Movements accomplished by muscles Contracting muscles generate force that acts on bones (Levers) across joints (Fulcrums) to create movement. 3 classes Class I Class II Class III Load (L) Resistance AP1 Chapter 10

Lever Systems & Leverage Ridged structure that can move around a fixed point Fulcrum The Fixed Point (Elbow) Effort (Pull) Causes the movement Contraction of the Bicep Resistance (Weight) Opposes the movement Load (L) Resistance

3 types of Levers Determined by positions of the Fulcrum, the effort, & the Load 1st Class Lever F is between the L and the E Seesaw 2nd Class Lever L is between the F and the E Wheelbarrow 3rd Class Lever E is between the F and the L Forceps