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Lecture 11

ANAT 101 Lecture Notes - Lecture 11: Masseter Muscle, Agonist, Temporal MusclePremium

5 pages71 viewsFall 2016

Department
Anatomy
Course Code
ANAT 101
Professor
Michael Bruneau
Lecture
11

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ANAT CH 11
Muscle Attachment
- Skeletal muscles make movement by exerting force on the tendons which then are attached to and
pull on bones to make movement
- When a muscle contracts, one articulate bone is drawn to the other
o One bone is stationary due to other muscles stabilizing the bone by contracting or pulling
the other way or because it has a less movable structure while the other bone moves
- Reverse muscle action (RMA): actions are reversed in the body; origin and insertion switch
Origin and Insertion
- Origin: the attachment of a muscles tendon to the stationary bone
o proximal
- Insertion: the attachment of the muscles other tendon to the movable bone
o Distal
o Pulled toward the origin
- Belly: fleshy portion of muscle between the tendons
o Ex: triceps
Lever System
- Bones are levers and joints are fulcrums
- Lever: rigid structure that can move around a fixed point (fulcrum)
o Lever is acted on by the effort (causes movement) and the load/ resistance (opposes
movement)
- Effort: force exerted by contraction
- Load: weight of body part being moved or the resistance the body part is trying to overcome
- Motion = E > Load
- Ex: bicep curl
o Elbow Is the fulcrum
o Weight of forearm + dumbbell is the load
o Force of contraction of the bicep brachii pulling the forearm up is the effort
Mechanical Advantage and Disadvantage
- Determined by the distance between the fulcrum and load and the point at which the effort is
applied
- Mechanical advantage: load is closer to fulcrum
o Small effort is required to move a large load over a small distance
- Mechanical disadvantage: load further from fulcrum and effort applied closer to fulcrum
o Large effort needed to move a small load at greater speed
Types of Levers
1) First Class
a. Fulcrum between the effort and load
b. Can make mechanical advantage or disadvantage depending on whether E or L is closer
to F
c. seesaw
2) Second class
a. Load is between the fulcrum and effort
b. Mechanical advantage
i. Load closer to fulcrum
ii. Favors force
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c. Makes most force
d. Ex: calf raise
3) Third class
a. Effort between fulcrum and load
b. Mechanical disadvantage
i. Favors speed and range of motion
c. Ex: bicep curls
Fascicle Arrangement
- Muscle fibers are parallel and arranged in bundles called fascicles
- Fascicles are in different patterns w/ respect to the tendon:
o Parallel
Greater range of motion and less power
Parallel to longitudinal axis of muscle
Terminate at either end in flat tendons
Ex: sternohyloid muscle of the neck
o Fusiform (narrow ends and wide middle)
Nearly parallel
Terminate in flat tendons
Ex: digastric muscle
o Circular
Concentric circular arrangement
Form sphincter muscles
o Triangular
Spread over broad area at thick central tendon
Ex: pec major
o Pennate (feather)
Short fascicles
More power and smaller range
Unipennate:
Fascicles arranged on one side of the tendon
Bipennate:
Fascicles arranged on both sides of centrally positioned tendons
Multipennate:
Fascicles attach obliquely from many directions to several tendons
- Fascicle arrangement affects the muscles power and range of motion
o Longer fiber = greater range of motion
o More fibers per unit of cross sectional area = more power
Coordination among Muscles
- Several skeletal muscles act as a group to make movement
- Most muscles are arranged in opposing pairs at the joints
- Agonist/ prime mover: contracts to cause an action/ generates movement
- Antagonist: yields to the effect of the agonist
- Synergists: contract and stabilize intermediate joints
o Prevents unwanted movement at intermediate joints or aids movement of the prime
mover
- Fixators: stabilize the origin of the prime mover so it can act more efficiently by steadying the
proximal end while movement occurs
- Compartment: group of skeletal muscles, blood vessels and nerves
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