Transcript The Muscular System - Cal State LA

The Muscular System
Functions
Gross Structure of Skeletal Muscle
Muscles Working Together
Shapes of Muscles
Naming Muscles
Muscles act through Levers
Functions of Muscle
Movement
Stability
Energy source
Heat source
Food source
Structure of Muscles at the Gross Level




Muscles must be attached at two
sites (tendinous origin and
insertion)
The origin is defined as the
attachment which is less mobile on
contraction
The insertion is defined as the
attachment that is more mobile on
contraction
The origin is also called the head
of the muscle; the thicker, fleshy
part is the belly
Muscles do not work individually to control
movement



Synergists: work together to cause a movement
example: biceps brachii and the brachialis flex forearm
Antagonists: muscles working in opposition to movement
caused by synergists
example: the triceps is an antagonist to the biceps brachii
Prime Mover: the main synergist resposible for an action
example: brachialis
Muscles do not work individually to control
movement

Fixator: stabilizes a joint
which is crossed by a prime
mover
example: muscles controlling
wrist extension stabilize the
wrist so that flexors of the
fingers can act
Shapes of Muscles
Pennate
(feather-like)
Parallel
Convergent
Shapes of Muscles
Geometric
Shapes
Multiple
Heads
Naming of Muscles
Muscles are named for:
- their location (pectoralis; brachialis)
- their size (major, minor, maximus, minimus, longus,
brevis, etc.)
- their shape (deltoid, teres, quadratus)
- orientation (oblique, rectus)
- origin & insertion (sternocleidomastoid, brachioradialis)
- number of heads (biceps, triceps, quadriceps)
- function (abductor, adductor, flexor, extensor, etc)
Muscles act through Levers





Muscles act by causing a pulling force across a lever
A lever is a rigid shaft which moves across a pivot point
(fulcrum) against resistance (weight)
In the body, the shaft is bone and the fulcrum is a joint
There are three classes of levers, which differ by the
relative location of the pulling force, fulcrum, and weight
along the shaft
Each class has different capabilities: how much weight is
moved, and how far
Types of Levers: Class I



In a Class I lever, the fulcrum is located between the
pulling force (tendon attachment) and the weight being
lifted.
Example: seesaw
easily move a small amount of weight a small distance
fulcrum
weight
force
Types of Levers: Class I

Example in the body:
atlanto-occipital joint
Types of Levers: Class II



In a Class II lever, the weight is located between the
fulcrum and the force.
Example: wheelbarrow
Able to lift a large amount of weight a short distance
Weight
Force
Fulcrum
Types of Levers: Class II

Example in the body:
lifting the body by
plantarflexion
Types of Levers: Class III




In a Class III lever, the force is
located between the fulcrum and
the weight
Most common type of lever in the
body
Example: lifting dirt in a shovel
Less weight can be lifted, but
lifted a greater distance
Types of Levers: Class III

Example in the body: flexion of the forearm
Next Lecture...
Histology of Skeletal Muscle