Transcript The Muscular System - Health Science CCCHS

Chapter 6
The Muscular System
The Muscular System
Interactions of Skeletal Muscles in the Body
• Muscles usually work in groups, i.e. perform
“group actions”
• Muscles are usually arranged in antagonistic pairs
– flexor-extensor
– abductor-adductor, etc.
600+ Skeletal Muscles
5 Golden Rules of Muscle Activity
• With a few exceptions, all muscles cross at least
one joint
• The bulk of the muscle lies proximal to the join
crossed
• All muscles have at least two attachments; the
origin and the insertion
• Muscles can only pull; they never push
• During contraction, the muscle insertion moves
toward the orgin
•
How Skeletal Muscles Produce
Movement
Muscles exert force on
tendons that pull on bones
• Muscles usually span a
joint
• Muscle contraction changes
the angle or position of one
bone relative to another
• Skeletal muscle must be
stimulated by a nerve
impulse to contract
Brachialis
flexes forearm
How Skeletal Muscles Produce
Movement
• Origin: the attachment of
the muscle to the bone
that remains stationary
origin
• Insertion: the attachment
of the muscle to the bone
that moves
belly
• Belly: the fleshy part of
the muscle between the
tendons of origin and/or
insertion
insertion
Interactions of Skeletal Muscles in
the Body
• Prime Mover
(agonist): the
principle muscle that
causes a movement
– ex: biceps brachii,
flexion of forearm
• Antagonist: the
principle muscle that
causes the opposite
movement
– ex: triceps brachii,
extension of forearm
Antagonists of the Forearm
Antagonists of the Thigh
Antagonists of the Foot
Interactions of Skeletal Muscles in
the Body
• Synergists: muscles that assist the prime mover
– ex: extensor carpi (wrist) muscles are synergists for
the flexor digitorum muscles when you clench your
fist
• Fixators: synergists that stabilize the origin of a
prime over
– ex: several back muscles that stabilize scapula when
the deltoid flexes the arm
Functional Roles of Skeletal Muscles
• Group Actions: most movements need several
muscles working together
While the prime movers (agonist and synergists) are
contracting to provide the desired movement
• other muscles (antagonists) are relaxing & being stretched out
passively
• agonist and antagonist change roles depending on the action
• e.g., abduction versus adduction
• Synergists and Fixators become Agonists and
Antagonists in different movements
Naming Skeletal Muscles
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Location of the muscle
Shape of the muscle
Relative Size of the muscle
Direction/Orientation of the muscle fibers/cells
Number of Origins
Location of the Attachments
Action of the muscle
Muscles Named by Location
• Epicranius (around
cranium)
• Tibialis anterior
(front of tibia)
tibialis
anterior
Naming Skeletal Muscles
• Shape:
– deltoid (triangle)
– trapezius (trapezoid)
– serratus (saw-toothed)
– rhomboideus (rhomboid)
– orbicularis and sphincters
(circular)
Rhomboideus
major
Muscles Named by Size
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maximus (largest)
minimis (smallest)
longus (longest)
brevis (short)
major (large)
minor (small)
Psoas
minor
Psoas
major
Muscles Named by Direction of Fibers
• Rectus
(straight)parallel to long
axis
Rectus
abdominis
• Transverse
• Oblique
External
oblique
Muscles Named for Number of
Origins
• biceps (2)
• triceps (3)
• quadriceps (4)
Biceps
brachii
Muscles Named for Origin and
Insertion
Sternocleidomastoid
originates from sternum
and clavicle and inserts
on mastoid process of
temporal bone
insertion
origins
Muscles Named for Action
• Flexor carpi radialis (extensor
carpi radialis) –flexes wrist
• Abductor pollicis brevis
(adductor pollicis) –flexes
thumb
• Abductor magnus – abducts
thigh
• Extensor digitorum – extends
fingers
Adductor
magnus
Arrangement of Fascicles
• Parallel (straplike), ex: sartorius
• Fusiform (spindle
shaped), ex: biceps
femoris
Arrangement of Fascicles
• Pennate ("feather
shaped"), ex:
extensor digitorum
longus
• Bipennate, ex:
rectus femoris
• Multipennate, ex:
deltoid
Arrangement of Fascicles
• Convergent, ex:
pectoralis major
• Circular
(sphincters), ex:
orbicularis oris
Arrangement of Fascicles
• Range of motion:
depends on length of
muscle fibers (fascicles);
long fibers = large range
of motion
– parallel and fusiform
muscles
• Power: depends on total
number of muscle fibers;
many fibers = great
power
– convergent, pennate,
bipennate, multipennate
Lever Systems and Leverage
• Lever: i.e. bones, a
rigid rod that moves
on some fixed point
• Fulcrum: i.e. joint, a
fixed point
• Resistance: the force
opposing movement
• Effort: the force
exerted to achieve
action
Levers
• A lever is acted upon at 2 different points by:
1) resistance or load
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the force that opposes movement
the load or object (bone or tissue) to be moved
2) effort
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the force exerted to achieve a movement
the effort is provided by muscle(s)
• Motion is produced when the effort exceeds the
resistance (isotonic contraction)
Lever Systems and Leverage
• Leverage: the mechanical advantage gained by a
lever
• Power: muscle tension (effort) farther from joint
(fulcrum) produces stronger contraction (opposes
greater resistance)
• Range of motion (ROM): muscle tension
(effort) closer to joint (fulcrum) produces greater
range of motion.
Mechanical Advantage
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Load is near fulcrum, effort is far away
Only a small effort is required to move an object
Allows a heavy object to be moved with a small effort
Example: car jack
Mechanical Disadvantage
• Load is far from the fulcrum, effort is near the
fulcrum
– a large effort is required to move the object
– allows object to be moved rapidly, a “speed lever”
– throwing a baseball
Lever Systems and Leverage
• First-class lever: (EFR) Effort-Fulcrum-Resistance
Leverage Systems and Leverage
• Second class lever: (FRE) Fulcrum-Resistance-Effort
Leverage Systems and Leverage
• Third-class lever: (FER) Fulcrum-Effort-Resistance
Skeletal Muscles
You will need to know all of these!