Chapter 10
Muscular System:
Gross Anatomy
AP1 Chapter 10
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Chapter 10 Outline
I. General Principles
A.
B.
C.
D.
Muscle Shapes
Nomenclature
Movements accomplished by muscles
Muscle Anatomy
AP1 Chapter 10
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I. General Principles
• Most skeletal muscles
extend from one bone to
another & cross at least 1
joint.
Fig 10.27
Pg 353
– 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 10.15
Pg 339
AP1 Chapter 10
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I. General Principles
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:
Pg 321 Figure 10.1
– 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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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).
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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
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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:
1. Pennate
2. Straight
3. Orbicular
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A. Muscle Shapes
Pg 322
Fig 10.2
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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A. Muscle Shapes
2.
Straight
–
Fasciculi are arranged
parallel to the long axis of
the muscle.
Result:
–
•
•
3.
Pg 322
Fig 10.2
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
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B. Nomenclature
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
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AP1 Chapter 10
Examples of shapes pg 323 Fig 10.3
AP1 Chapter 10
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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
Load (L)
Resistance
1. Class I
2. Class II
3. Class III
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Lever Systems & Leverage
• Lever
– Ridged structure that can
move around a fixed point
• Fulcrum
Load (L)
– The Fixed Point (Elbow)
• Effort (Pull)
– Causes the movement
– Contraction of the Bicep
• Resistance (Weight)
– Opposes the movement
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