AP1 Chapter 10 1

Chapter 10

Muscular System:

Gross Anatomy

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Chapter 10 Outline

I. General PrinciplesA. 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

Fig 10.27Pg 353

Fig 10.15Pg 339

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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

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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

Pg 322Fig 10.2

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A. Muscle Shapes1. 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

Pg 322Fig 10.2

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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

Pg 322Fig 10.2

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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 classes1. Class I

2. Class II

3. Class III

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 LeversDetermined 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