The Skeletal and Muscle Systems
Putting your body in motion.

Locomotion
 Movement is essential to all animals for
finding and capturing food.
 On land, if an animals wants to move, it needs
to be able to support its body and move
against gravity.
 Also, animals must be able to maintain their
balance. Humans, which are bipedal animals,
keep part of one foot on the ground at all
times in order to stay balanced.
 Movement results from muscles working
against some type of skeleton. Microfilaments
are the contractile elements of muscle cells.
The Function of the Skeleton
 The skeleton has three
functions: support, protection,
and movement.
 Humans have an endoskeleton
consisting of a combination of
cartilage and bone.
 This skeleton is made up of
206 bones connected by
ligaments at joints to allow for
movement.
http://www.ruinaudio.com/files/images/black_skeleton_sitting.pr
Bones
 Almost all of the bones in the human body have the
same components:

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http://alinelheiser.com/images/530_BoneDiagram_ACSI.jpg
To see how these
bone parts are
arranged in a
bone go to:
kidshealth

Periosteum – a thin but dense membrane containing
nerves and blood vessels to nourish the bone. The
inner part of the periosteum creates new bone and
adapts existing bone to new conditions.
Compact bone – this layer of bone tissue is smooth
and very hard and it is located beneath the
periosteum.
Cancellous bone – resembles a sponge. It is softer
than compact bone but still strong and it protects the
bone marrow.
Bone marrow – the innermost part of the bone. It has
a jelly-like texture and there are two types: yellow
and red bone marrow. Red marrow creates the
components of blood (red and white blood cells as
well as platelets). Yellow marrow stores fat.
Skeleton
The vertebral frame is broken down into two parts: the axial skeleton and the
appendicular skeleton.
AXIAL SKELETON:
The components of the axial skeleton
are:
- the skull which serves to protect
the brain from injury and also fixes the
eyes and ears to allow for better sight
and sound reception.
- the vertebral column, or
backbone, supports the head and arms,
and it allows you to stand upright and
maintain your balance. Also, it protects
the spinal cord and is an attachment
point for the ribs as well as other muscles
and organs.
- the rib cage which protects the
APPENDICULAR SKELETON:
The components of the appendicular skeleton
are:
- the limb bones
- the pectoral girdle provides an
attachment point between the arms and the
axial skeleton as well as for muscles that allow
for movement of the shoulder and elbow
joints.
- the pelvic girdle protects the bladder,
reproductive organs and the developing fetus
in a woman. Also it supports the weight of the
vertebral column and the upper body.
*each appendage has several types of joints to
allow for a variety of movements.
Parts of the Skeleton
http://embryology.med.unsw.edu.au/notes/images/skmus/axial_skeleton1.jpg
http://embryology.med.unsw.edu.au/notes/images/skmus/appendicular_skeleton1.jpg
Muscle Contractions Result in Movement
 The only action muscles can perform is
contraction, they extend passively.
 Muscles are arranged on the skeleton in
antagonistic pairs where each works against the
other.
http://www.rogers.k12.ar.us/users/ehutches/antagonisticmuscles.jpg
Skeletal Muscle
 This type of muscle is attached to the
bones and is responsible for the
movement of the skeleton.
 Each muscle consists of a bundle of
long fibers and each fiber is a single
cell with many nuclei. This means
that the fiber was created through
the fusion of many embryonic cells.
 Each fiber can further be broken
down into a bundle of myofibrils and
each myofibril is composed of 2 kinds
of myofilament (thick and thin).
http://www.medical-look.com/systems_images/Skeletal_Muscle_Fibers.gif
Skeletal Muscle (continued)

Skeletal muscle is also called striated muscle.

The basic functional unit of a muscle is the
sarcomere, which is composed of thick and thin
myofilaments bordered by Z lines.

When the muscle is at rest, there is a region only
occupied by thin filaments and this region is
called the I band.

The A band is the length of the thick filaments.

The H zone is in the center of the sarcomere and
because the thin filaments don’t extend the
whole length of the sarcomere, the H zone
contains only thick filaments. (diagram on pg.
1015)
http://content.answers.com/main/content/img/oxford/Oxford_Body/019852403x.skeletal-muscle.2.jpg
Sarcomere
http://www.ucl.ac.uk/%7Esjjgsca/MuscleSarcomere.gif
Sarcomere
http://www.peprotech.de/uploadedimages/Sarcomere2.jpg
Muscle Contraction-How does it work?
 When muscles contract, the length of the
sarcomere is shortened.
 However, the length of each A band does not
change. Instead, the H zone disappears and the I
bands shorten, brining the thin filaments of the
sarcomere further into the center.
 IMPORTANT NOTE: neither the thick nor thin
filaments change in length during muscle
contraction.
 Muscle contraction can be explained by the sliding-
filament model.
Sliding-Filament Model
 This model maintains that neither type of filament is shortened
during contraction. Instead, the degree of overlap between the
two types of filaments increases, which means that the region
only occupied by thin filaments and the region only occupied by
thick filaments must decrease in length.
 Muscle contraction through the sliding of filaments is made
possible by the interaction of the actin and myosin that make
up the myofilaments.
Myosin Structure
 Myosin has a head region and a tail region
 The tails of myosin molecules cohere and in this
way form thick filament. The head is what powers
muscle contractions.
http://www.ucl.ac.uk/%7Esjjgsca/muscleSlidingFilamen
The Process of Muscle Contraction
 The process starts when ATP binds to the myosin
head and is hydrolyzed into ADP and inorganic
phosphate. This releases energy.
 Some of the energy that is released is transferred to
the myosin which changes shape to a high-energy
configuration. The energized myosin then binds to a
specific site on actin, forming a cross-bridge.
 The energy the myosin obtained from the
hydrolyzation of ATP is released and the myosin
goes back to its low-energy configuration.
More Muscle Contraction…
http://www.agen.ufl.edu/~chyn/age2062/lect/lect_19/178.gif

The action of reverting back to its lowenergy configuration causes the myosin
to bend back on itself and, in the process
of bending, the myosin pushes the thin
filaments toward the center of the
sarcomere.

The cross bridge between myosin and
acting breaks when a new ATP molecule
binds to the myosin and the process
starts over.

Each muscle cell only stores enough ATP
for a few contractions. Most of the
energy needed for repetitive muscle
contractions is stored in creatine
phosphate. This molecule can provide a
phosphate group and change ADP to ATP.
The Sliding Filament Model
http://trc.ucdavis.edu/biosci10v/bis10v/week10/slidingfilament.gif
Regulation of Muscle Contraction

A skeletal muscle will only contract if it
receives a stimulus from a motor neuron.

At rest, myosin binding sites on actin
molecules are blocked by tropomyosin.

Also, there is tropomyosin on the thin
filaments and its position is controlled by
regulatory proteins called the troponin
complex.

If the muscle cell is to contract, the myosin
binding sites must be uncovered first.

Calcium ions can uncover the binding sites
by binding to the troponin. This causes the
tropomyosin-troponin complex to expose
the binding sites by changing its shape.

THEREFORE: muscles can only contract
when Calcium ions are present.
http://www2.warwick.ac.uk/fac/sci/chemistry/research/mass-spectrometry/projects/troponinc
Tropomyosin-Troponin Complex
http://www.hmc.org.qa/heartviews/VOL8NO1/images/Image_Heart_7No4/8
http://www.bio.miami.edu/~cmallery/150/neuro/49x29.jpg
Sarcoplasmic Reticulum
http://media-2.web.britannica.com/eb-media/41/2841-004-8EA13F0E.gif

The sarcoplasmic reticulum, a specialized
endoplasmic reticulum, controls the
calcium ion concentration in the
cytoplasm.

The reticulum stores calcium ions by
actively transporting them across its
membrane and into its internal space

The calcium is stored in the sarcoplasmic
reticulum until an action potential, the
stimulus that causes muscle
contractions, reaches the muscle cell.

The action potential spreads to the
interior of the cell along transverse
tubules, which are infoldings of the
plasma membrane
More Sarcoplasmic Reticulum
 The transverse tubules have contact with the
sarcoplasmic reticulum at certain spots.
 As the action potential reaches these areas, it
changes the permeability of the sarcoplasmic
reticulum, causing it to release calcium ions.
 The ions then bind to troponin and the muscle can
contract.
 Contraction stops when the sarcoplasmic reticulum
pumps the ions out of the cytoplasm.
Muscle Fiber
http://academic.kellogg.cc.mi.us/herbrandsonc/bio201_McKinley/f10-3_formation_struct
Diverse Body Movements Require
Variation in Muscle Activity

Different actions require a differing degree of muscle contraction.

The nervous system has two main ways of creating graded muscle
contractions.

One is through releasing the appropriate number of action
potentials:
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1 action potential will cause a 100 msec. contraction
If another action potential arrives before the first twitch is over,
there will be a greater response
A continuous, overlapping series of action potentials will produce
the greatest response, with the tension in the muscle dependent on
how quickly the action potentials are released.
Tetanus happens when the stimulation from many action potentials
is fast enough to blur individual twitches into one smooth, sustained
contraction.
Motor Units
 Another way to control the degree of
muscle contraction is to organize
muscle cells into motor units.
 Each motor unit is made up of one
motor neuron and all of the fibers it
controls. When it fires an action
potential, all of the fibers it controls
react to it together. Therefore, the
tension depends on how many muscle
fibers are being controlled by the unit.
 Tension can be increased by activating
more motor units that are located in the
muscle. This process is called
recruitment.
http://www.bio.miami.edu/~cmallery/150/neuro/c49x38motor-un
Fast and Slow Muscle Fibers
http://mfuz.com/contentimages/musclefibertype.JPG

Action potentials cause contractions, but the
length of the contraction is controlled by the
calcium ions and how long they are present in the
cytoplasm.

This divides muscle fibers into fast and slow fibers.

Fast muscle fibers are used for quick, powerful
contractions.

Slow muscles fibers are often found in posture
muscles because they are used for long
contractions. The slow fibers have less
sarcoplasmic reticulum than the fast muscle fibers
so the calcium ions can stay in the cytoplasm
longer. Also, they have many mitochondria to
provide a steady energy supply, a rich blood
supply, and myoglobin.
Other Types of Muscle

Cardiac muscle

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Found only in the heart.
This muscle is striated, just like skeletal
muscle.
The main difference between cardiac and
skeletal muscle is that there are gap
junctions between cardiac muscle cells so
that when an action potential reaches one
cell, it spreads to all the other cells, and
the whole heart contracts.
Also, cardiac muscle cells can generate
action potentials on their own, something
skeletal muscle cells cannot accomplish
unless they receive a stimulus.
In cardiac muscle, action potentials last
longer and they help control the duration
of muscle contraction.
http://cellbio.utmb.edu/microanatomy/muscle/muscle12.j
Other Types of Muscle (continued)
 Smooth muscle
 Not striated because it does not have as
much myosin. Also, the arrangement of
thick and thin filaments is different.
 Contractions do not create as much
tension, but they contract over a greater
range of time.
 There is no transverse tubule system and
no sarcoplasmic reticulum. Instead,
calcium ions enter via the plasma
membrane during action potentials.
 Therefore, contractions are slow but they
can be controlled better.
 This type of muscle is found in digestive
organs and blood vessels.
http://cytochemistry.net/Cell-biology/Medical/08_023.jpg