Transcript Chapter 10 - Muscle System

Chapter 10
The Muscular System
J.F. Thompson, Ph.D. & J.R. Schiller, Ph.D. & G. Pitts, Ph.D.
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
– ex: flexor-extensor
– ex: abductor-adductor
– etc.
How Skeletal Muscles
Produce Movements
• muscles exert a force on
tendons which pull on
bones
• muscles usually span a
joint
• muscle contraction
changes the angle or
position of one bone
relative to another bone
brachialis
flexes forearm
Terms Relative to Skeletal
Muscle Movements
origin
• origin: the attachment of the
muscle to the bone which
remains stationary
• insertion: the attachment of
the muscle to the bone which
moves
• belly: the fleshy part of the
muscle between the
attachments at origin and
insertion
belly
insertion
Functional Roles
of Skeletal Muscles
• Prime Mover (=
Agonist): the
principle muscle
which causes a
movement
– ex: biceps brachii 
flexion of forearm
• Antagonist: the
principle muscle that
causes the opposite
movement
– ex: triceps brachii 
extension of forearm
Functional Roles
of Skeletal Muscles
• Synergists: muscles that assist the prime
mover in its movement
– ex: extensor carpi (wrist) muscles are synergists
for the flexor digitorum muscles when you
clench your fist or hold a beverage while walking
• Fixators: synergists that stabilize the origin
of a prime mover
– ex: several back muscles stabilize the scapula
when the deltoid abducts 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
•
•
•
•
•
•
•
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
• Know the muscle names as described in your
Lab Guide 6.
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
Arrangement of Fascicles
• circular (sphincters), ex:
orbicularis oris
• parallel (strap-like), ex:
sartorius
• fusiform (spindle shaped),
ex: biceps femoris
• convergent, ex: pectoralis
major
• long parallel fibers offer
greater range of movement
Arrangement of Fascicles
• pennate ("feather
shaped")
• unipennate ex:
flexor pollicis longus
• bipennate, ex:
rectus femoris
• multipennate, ex:
deltoid
• short oblique fibers
offer greater power
Leverage Systems
• lever: a rigid rod that moves on some fixed
point, e.g., a bone
• fulcrum: a fixed point for lever motion, e.g., a
joint
• resistance: the force opposing movement
• effort: the force exerted to achieve action
Leverage
•
Lever Systems and Leverage
– lever
•
•
a rigid rod that moves on some fixed point = the
fulcrum
bones = levers, joints = fulcrums
– a lever is acted upon at 2 different points by:
1) resistance or load
– the force that opposes movement
– the load or object (bone or tissue) to be moved
2) effort
– 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)
Mechanical Advantage
• Lever allows an effort to move a larger load or move a
load faster
– mechanical advantage
• the load is near the fulcrum; the effort is farther away
• only a small effort is required to move an object
• mechanical advantage allows a heavy object to be moved with a
small effort – e.g., car jack
Power and Range of Motion
• leverage: the mechanical advantage gained
by using 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 Disadvantage
– the load is far from the fulcrum; the effort is near the
fulcrum
– a large effort is required to move the object
– this allows object to be moved rapidly -- a “speedy lever”
• e.g., throwing a shovel full of dirt or throwing a baseball
Additional Information
• You do not need to memorize the details
of the different leverage system types for
Exam 3. See slides of the three types of
lever systems after the “end” slide in this
presentation.
• Slides with some examples of the naming
of muscles can be found in the PowerPoint
presentation for Lab 6 and after the “end”
slide in this presentation.
Skeletal Muscles
Know the muscles, their
origins and insertions as
described in your Lab Guide 6.
End Chapter 10
There are some additional
slides you can review on
uour own after this slide.
Antagonists of the Forearm
Antagonists of the Thigh
Antagonists of the Foot
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
Muscles Named by
Location
• Epicranius (around
cranium)
• Tibialis anterior
(front of tibia)
tibialis
anterior
Muscles Named by Location
• frontalis (frontal
bone)
• tibialis anterior
(front of tibia)
• [Note: naming by number of
origins: the quadriceps
(“four heads”) has four
origins]
tibialis
anterior
Muscles Named by Shape
• Shape:
–
–
–
–
–
deltoid (triangle)
trapezius (trapezoid)
serratus (saw-toothed)
rhomboideus (rhomboid)
orbicularis and
sphincters (circular)
rhomboideus
major
Muscles Named by Size
•
•
•
•
•
•
maximus (largest)
minimis (smallest)
longus (longest)
brevis (short)
major (large)
minor (small)
Psoas
minor
Psoas
major
• Rectus (straight)-parallel to Rectus
long axis
abdominis
• Transverse
• Oblique
External
oblique
Muscles Named by
Direction of Fibers
Muscles Named by
Direction of Fibers
• rectus (straight) parallel to the muscle’s
long axis
– ex: rectus abdominis
• transversus
(transverse) – at right
angles to the muscle’s
long axis
• oblique
rectus
abdominis
Muscles Named by
Direction of Fibers
• ex: external oblique
external
oblique
abdominis
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
Leverage 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
Muscle Mechanics – 1st Class Lever
• three classes of levers
– first-class lever [E-F-R = effort-fulcrum-resistance]
• the fulcrum is placed between the effort and the resistance (load)
• e.g., seesaw, scissors
• skull (head)/atlas and cervical vertebrae
– the muscles of the back (splenius, trapezius, etc.) provide the effort
– the mass of the skull provides the resistance (load)
2nd Class Lever
• second-class lever [F-R-E = fulcrum-resistance-effort]
• the fulcrum is at the end of the lever, the effort is at the
opposite end, and the resistance (load) is in between, e.g., a
wheelbarrow
• 2nd class levers provide greater power to move a large
resistance (load)
• raising the body on the toes
– the mass of body is the resistance
– the ball of the foot is the fulcrum
– the contraction of the calf muscles to lift the heel upward is the effort
three classes of levers (cont.)
3rd Class Lever
• three classes of levers (cont.)
– third-class lever [F-E-R = fulcrum-effort-resistance]
• the fulcrum is at one end, the resistance is at opposite end, and the
effort is in between, e.g., tweezers
• the most common type of lever in the body
• 3rd class levers provide for rapid motion
• e.g., flexing the forearm or adducting the thigh
• such movements can still be powerful
End of Extra Review
Slides for Chapter 10