The Skeletal, Muscular and
Levers System
Muscular Physics
Movement
• The physical constraints to movement
– gravity and frictional drag
– occur in every environment, differing only in
degree
• Involves skeletal and muscular systems
– Muscle have microtubules and microfilaments
• Needs energy
Types of Skeletal Systems
Changes in movement occur because muscles pull
against a support structure, called the skeletal
system
-Zoologists recognize three types:
-Hydrostatic skeletons
-Exoskeletons
-Endoskeletons
3
Hydrostatic Skeletons
Are found primarily in soft-bodied invertebrates,
both terrestrial and aquatic
Locomotion in earthworms
-Involves a fluid-filled central cavity and
surrounding circular & longitudinal muscles
-A wave of circular followed by longitudinal
muscle contractions move fluid down body
-Produces forward movement
4
Hydrostatic Skeletons
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Longitudinal muscles
Anterior
Circular muscles
Longitudinal muscles contracted
Circular muscles
contracted
Longitudinal muscles
contract, and segments
catch up
Circular muscles
contract, and anterior
end moves forward
Circular muscles
contract, and anterior
end moves forward
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Hydrostatic Skeletons
Locomotion in aquatic invertebrates
-Occurs by fluid ejections or jetting
-Jellyfish produce regular pulsations in bell
-Squeezing some of water contained
beneath it
-Squids fill mantle cavity with sea water
-Muscular contractions expel water
forcefully through the siphon, and the
animal shoots backward
6
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Bell
Jellyfish
propelled
upward
Contractile fibers
Bell
pulsates
Water
expelled
from bell
Water
enters
bell
a.
Water expelled
from siphon
b.
Squid
propelled
backward
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Exoskeletons
The exoskeleton surrounds the body as a rigid
hard case
-Composed of chitin in arthropods
An exoskeleton provides protection for internal
organs and a site for muscle attachment
-However, it must be periodically shed, in order
for the animal to grow
-It also limits body size
8
Endoskeletons
Endoskeletons are rigid internal skeletons that
form the body’s framework and offer surfaces
for muscle attachment
-Echinoderms have calcite skeletons, that are
made of calcium carbonate
-Bone, on the other hand, is made of
calcium phosphate
9
Endoskeletons
Vertebrate endoskeletons have bone and/or
cartilage
-Bone is much stronger than cartilage, and much
less flexible
Unlike chitin, bone and cartilage are living tissues
-They can change and remodel in response to
injury or physical stress
10
Joints
Joints are the locations where one bone meets
another
-1. Immovable joints = Join bones
-2. Slightly movable joints = Involve fibrous
connective tissue or cartilage
-3. Freely movable joints = Also called
synovial joints
-Contain a lubricating fluid
11
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Immovable Joint
Bone
Suture
Fibrous
connective
tissue
a.
Freely Movable Joint
Slightly Movable Joints
Fibrous Joints
Fibrous capsule
Synovial fluid
Fibrous
joints
Cartilaginous Joints
Synovial membrane
Articular cartilage
c.
Body of
vertebra
Intervertebral
disk
Articular
cartilage
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b.
Joints
Movable joints can be divided into four types
-Ball-and-socket joints = Permit movement in
all directions
-Hinge joints = Allow movement in only one
plane
-Gliding joints = Permit sliding of one surface
over another
-Pivot joints = Allow rotation
13
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Ball-and-Socket
a.
Gliding Joint
Hinge Joint
b.
c.
Combination Joint
d.
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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.
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
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
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
Muscles Named by Location
• Epicranius (around
cranium)
• Tibialis anterior
(front of tibia)
tibialis
anterior
Naming Skeletal Muscles
Trapezius
• Shape:
– deltoid (triangle)
– trapezius (trapezoid, 2
parallel sides)
Deltoid
– serratus (saw-toothed)
– rhomboideus (rhomboid,
4 parallel sides)
– orbicularis and
sphincters (circular)
Rhomboideus
major
Serratus anterior
Muscles Named by Size
•
•
•
•
•
•
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
Movements
• 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 that opposes movement
– the load or object (bone or tissue) to be moved
• 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)
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
•
•
•
•
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
Web sites
• Interactive muscular system:
http://www.getbodysmart.com/ap/muscularsystem/menu/men
u.html
5-8th grade muscle activity:
http://www.whitakercenter.org/Education/Curriculum%20Guides/Grades%2068/6-8%20Simple%20Machines/Building%20Levers%20Post.pdf
http://teachhealthk-12.uthscsa.edu/curriculum/levers/levers.asp