Chapter 10 Muscular System:

Gross Anatomy

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Chapter 10 Outline

I.  General Principles A.  Muscle Shapes B.  Nomenclature C.  Movements accomplished by muscles D.  Muscle Anatomy

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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

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Fig 10.27 Pg 353

Fig 10.15 Pg 339

I. G

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Pg 321 Figure 10.1

Muscle Terminology •  Origin:

–  (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

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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).

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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 6

A. Muscle Shapes

•  Shape & size of a muscle influence the degree to wh/ it can contract & amount of force generated.

•  3 major classes based on fasciculi orientation: 1.  Pennate 2.  Straight 3.  Orbicular

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Pg 322 Fig 10.2

A. Muscle Shapes 1.  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

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Pg 322 Fig 10.2

A. Muscle Shapes 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 3.  Orbicular

–  Fasiculi are arranged in a circle around an opening & act as sphincters to close and opening

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Pg 322 Fig 10.2

Muscles are named according to: A.  Location:

–  Examples: Pectoralis (chest) ; Gluteus (Buttock); Brachial (arm) B.  Size

–  Gluteus maximus (Large); Gluteus minimus (Small); Longus (long); Brevis (short)

C.  Shape –  Deltoid (triangular); Quadratus (rectangular); teres (round)

D.  Orientation of fasciculi –  Rectus (Straight); Oblique (slanting or inclined; diagonal)

E.  Origin & insertion –  Brachioradialis (origin in arm [brachii] and insertion at radius)

F.  Number of heads –  Biceps have 2 heads (Triceps 3 heads)

G.  Functions –  Adductor moves toward midline –  Abductor moves away from midline –  Masseter Chews

B. Nomenclature

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Examples of shapes pg 323 Fig 10.3

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C. Movements accomplished by muscles •  Contracting muscles

generate force that acts on bones (Levers) across joints (Fulcrums) to create movement.

•  3 classes 1.  Class I 2.  Class II 3.  Class III

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Resistance

Load (L)

Lever Systems & Leverage •  Lever

–  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

Resistance

Load (L)

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

3rd Class Lever •  E is between the F

and the L •  Forceps

2nd Class Lever •  L is between the F

and the E •  Wheelbarrow