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Lecture 11

ANAT 1010 Lecture Notes - Lecture 11: Muscular System, Skeletal Muscle, Human Musculoskeletal SystemPremium

7 pages59 viewsFall 2018

Department
Anatomy
Course Code
ANAT 1010
Professor
A. Jaffar
Lecture
11

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Chapter 11: Muscular System
October 5, 2018
[Musculoskeletal system] = an integrated system composed of bones, joints, and skeletal
muscles.
How Skeletal Muscles Produce Movements:
The muscular system is comprised of the voluntarily controlled body muscles, that produce
movements by exerting force on tendons that will in turn, pull on bones or other structures (i.e.
skin). Most of the muscles will cross at least one joint and are usually attached to articulating
(connecting) bones that form the joint.
Skeletal muscles will shorten and pull on the bones on which they are attached to.
In the limbs, the origin (the attachment of the muscle tendon to the more stationary bone the
bone that doesn’t move when the muscle shortens) of a muscle is usually “proximal,” and the
insertion (attachment of muscle tendon to the more movable bone) is usually “distal.”
The insertion is usually pulled towards the origin.
Analogy: “a spring on a door”
- The part of the spring that is attached to the frame is the ORIGIN.
- The part that is attached to the door is the INSERTION.
The fleshy portion of the muscle between the tendons of the muscle is the “belly” (body
similar to the middle portion of the spring). The actions of a muscle are the main movements
that occur when the muscle contracts (i.e. closing of the door in analogy).
Certain muscles are also capable of “reverse muscle action, or CKC” exercises, where during
specific movements of the body, the actions are reversed and thus the positions of the origin
and insertion of a specific muscle are switched. Thus, muscle attachment is better explained as
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“proximal attachment and distal attachment” for limb muscles, and the “superior/inferior
attachment” for trunk muscles.
Muscles that move a body part will often not cover the moving part. although one of the
functions of the biceps brachii muscle is to move the forearm, the belly (body) of the muscle
lies over the humerus and NOT over the forearm.
Also, the muscles that cross two joints (rectus femoris and sartorius of the thigh) have more
complex actions than the muscles that only cross at one joint.
Lever Systems:
[Lever] = rigid structure that can move around a fixed point.
[Fulcrum] = a fixed point (F).
A lever is acted on at two different points by two different forces: the effort (E), which causes
movement (force exerted by muscular contraction), or load (L) “resistance”, which opposes
movement (the load is typically the weight of the body part that is moved/the resistance that
the moving body part is trying to overcome.
^ Motion will occur when the effort that is applied to the bone at the insertion (distal) exceeds
the load.
i.e. the biceps brachii flexing the forearm at the elbow as an object is lifted.
When the forearm is raised, the elbow is the fulcrum.
Load = weight of forearm + weight of the object in the hand.
Effort = force of contraction of the biceps brachii pulling the forearm up.
The relative distance between the fulcrum and the load and the point at which the effort is
applied determines whether a given lever operates at a mechanical advantage or a mechanical
disadvantage.
[Mechanical Advantage] = if a load is closer to the fulcrum and the effort is farther from the
fulcrum, then only a small effort is required to move a large load over a small distance.
[Mechanical Disadvantage] = if a load is farther from the fulcrum and the effort is applied closer
to the fulcrum, then a large effort is required to move a small load (but at greater speed).
Example: chewing something hard (load) with front teeth vs back teeth.
It is much easier to crush the hard food item with the back teeth (mechanical advantage) as
they are closer to the fulcrum (jaw/temporomandibular joint) than are the front teeth.
Effects of Fascicle Arrangement:
[Fascicle] = the bundles that contain skeletal muscle fibers (cells) within a muscle.
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