Muscular System
-The skeleton and muscles function together as the
musculoskeletal system.
-This system plays an important homeostatic role:
allowing the individual to move to more favorable
external conditions.
Muscular System
The muscular system is the biological system of
humans that allows to move.
Muscle (from Latin musculus “little mouse”).
• More than 50% of body weight is muscle!!!
• Muscles convert chemical energy into mechanical
energy.
• Muscles NEVER push, they ONLY pull.
Muscular System
Deltoid
Pectoralis major
Biceps brachi
Gluteus maximus
Rectus femoris
Gastrocnemius
Muscular System
Classification of muscles:
I- Voluntary muscles
II- Involuntary muscles
Muscular System
Classification of muscles:
I- Voluntary muscles
- Voluntary muscles are controlled by thinking
about what you want them to do.
- People can run and talk because of voluntary
muscles.
- e.g., skeletal muscles
Muscular System
Classification of muscles:
II- Involuntary muscles
- Involuntary muscles are controlled by the brain
without thinking about them.
- e.g., Heart and blood vessels.
•Some muscles are both voluntary and involuntary, the
muscles that control breathing are an example.
Muscular System
Functions of the muscles
1. Movement
2. Warmth
3. Posture
Muscular System
Functions of the muscles
1. Movement: almost all movements by the
human body result from muscle
contraction.
Muscular System
Functions of the muscles
2. Warmth: any activity by muscles
generates heat as a byproduct, which is
vital in maintaining normal body
temperature
Muscular System
Functions of the muscles
3. Posture: muscle lend support to the
body and help it maintain posture against
the force of gravity.
Muscular System
Muscle Properties
1. Ability to contract
2. Ability to be stretched
3. Ability to respond to a stimulus
Muscular System
•Muscle is attached to the bone by tendons
(tough connective tissue) and other tissues.
•Tendons attach muscle to bone; the origin is the
more stationary bone, the insertion is the more
movable bone.
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Muscular System
Functional Organization of Skeletal Muscle
1)Single Muscle Fibers
i.
A muscle fiber is a single, multinucleated
muscle cell.
ii. A muscle is made up of hundreds or even
thousands of muscle fibers, depending on
the muscle size.
Muscular System
1)Single Muscle Fibers, cont’d
iii. The health of muscle depends on a sufficient
nerve and blood supply, each skeletal
muscle has a nerve ending that controls its
activity (innervation), and an individual
system to supply and drain blood
(vascularization).
Muscular System
Functional Organization of Skeletal Muscle
2) Bundles of Muscles
i.
Muscle fibers consist of bundles of
threadlike structures called myofibrils.
ii.
Each myofibrils is made up of two types of
protein filaments, (Thick called myosin, Thin
called actin).
Muscular System
2) Bundles of Muscles, cont’d
iii. Thin actin filaments are anchored at their
midpoints to a structure called the z-line.
iv. The region from one z-line to the next is
called a sarcomere, which is the functional
unit of muscle contractions.
Muscular System
•All muscle cells produce
adenosine triphosphate (ATP)
molecules which are used to
power the movement of the
myosin.
Myosin
Actin
Sarcomere
Muscular System
-whereas most cells have a single
nucleus, muscle fibers have as
many as 100 or more nuclei
(multinucleated)
- The other difference is that they
can extend the entire length of a
muscle.
Muscular System
- Each of more than 650 muscles is served
by nerves which link the muscle to the brain
and spinal cord (Neuromuscular system).
Muscular System
- When they receive a signal from the brain,
muscle fibers can contract.
- The strength of a muscle contraction depends
on how many fibers contract at the same time.
Muscular System
Muscular System
- In order for a muscle to contract or shorten,
muscle fibers must be stimulated by nerve
impulses sent through motor neurons or nerves
(Neuromuscular junctions).
-These impulses originate in the brain, then
rundown the spine, then they branch out to all
parts of the body.
Muscular System
•In order to create movement, muscles must act
in pairs.
• Muscles are arranged on the skeleton on such
a way that the flexing or contracting of one
muscle is usually balanced by the lengthening
or relaxation of another muscle or group of
muscles. In other words, when one muscle or
set of muscle contracts, the other relaxes.
Muscular System
Muscular System
- When a nerve impulse reaches the end of the
motor neuron at the neuromuscular junction,
acetylcholine (a chemical neurotransmitter) is
released, then it travels across a small gap
between the motor neuron and the muscle fiber
and attaches to receptors on the membrane of
muscle fiber.
Muscular System
Muscular System
Muscle Types
1. Skeletal
2. Smooth
3. Cardiac
Muscular System
Muscular System
1. Skeletal muscles or Striated muscles
• The tissue is made of long fibers, with multiple
nuclei.
• They are attached to bones by tendons.
• Many of these are voluntary, but some are
involuntary.
• The most abundant tissue in the human body.
Muscular System
1. Skeletal muscles: cont’d
• They are controlled by the somatic nervous
system.
• An average adult male is made up of 40-50% of
skeletal muscle
• an average adult female is made up of 30-40%.
Muscular System
2. Smooth muscles or Visceral muscles
• Are involuntary muscles, and found within the
walls of organs and structure such as
esophagus, stomach, intestines etc…
• Smooth muscle is NOT under conscious
control.
• They are also found in blood vessels.
Muscular System
2. Smooth muscles: cont’d
• Smooth muscle occurs at various scales in
almost every organ.
• In the skin (in which it controls erection of body
hair) to the blood vessels and digestive tract (in
which it controls the caliber of the lumen).
• Smooth muscle cells are elongated, have only
one nucleus.
Muscular System
3. Cardiac muscles
• These muscles are attached to other muscles
instead of bones and tendons.
• These muscles are involuntary.
• They are striated with multiple nuclei.
• Is a specialized kind of muscle found only
within the HEART.
Muscular System
3. Cardiac muscles: cont’d
• Cardiac muscle are typically branched like a
tree branch and connect to other cardiac
muscle fiber through intercalated discs.
• Although that they are considered involuntary
muscles, they do respond to psychological
states such as stress and excitement.
Muscular System
•All three muscles use the movement of actin
against myosin to create contraction.
•In skeletal muscle, contraction is stimulated by
electrical impulses transmitted by the nerves.
Muscular System
•Cardiac and smooth muscle contractions are
stimulated by internal pacemakers cells who
regularly contract, and propagate contractions to
other muscle cells they are in contact with.
•All skeletal muscle and many smooth muscle
contractions are facilitated by the
neurotransmitter acetycholine.
Muscular System
• Cardiac and skeletal muscles are “striated”
and they contain sarcomeres and are packed
into highly-regular arrangements of bundles;
smooth muscle has neither.
Cardiac
Smooth
Skeletal
Muscular System
•While skeletal muscles are arranged in regular,
parallel bundles, cardiac muscle connects at
branching, irregular angels.
Cardiac
Smooth
Skeletal
Muscular System
• Striated muscles contracts and relaxes in
short, intense bursts, whereas smooth muscle
sustains longer or even near-permanent
contractions.
Cardiac
Smooth
Skeletal
Muscular System
Muscle tone
• Even when the body is at rest, certain muscle
fibers in all muscles are contracting. This
activity is directed by the brain and cannot be
controlled consciously.
• This state of continuous partial muscle
contraction is known as muscle tone.
Muscular System
Muscle tone
•These contractions are not enough to produce
movement, but do tense and firm the muscles.
In doing so, they keep the muscles firm, healthy
and ready for action.
• Muscle tone is important because it helps
individuals maintain an upright posture.
Muscular System
Muscle facts:
- Smallest muscle in the body: (Stapedius) the
muscle that activates the stirrup, the small bone
that sends vibrations from the eardrum to the
inner ear.
- Largest muscle in the body: (Latissimus dorsi)
the large, flat muscle that covers the middle and
lower back.
Muscular System
Muscle facts:
-Longest muscle in the body: (Sartorius) the
straplike muscle that runs diagonally from the
waist down across the front of the thigh to the
knee.
- Strongest muscle in the body: (Glutus
maximus) the muscle pair of the hip that form
most of the flesh of the buttocks.
Muscular System
Muscle facts:
-Fastest-reacting muscle in the body:
(Orbicularis oculi) the muscle that encircles the
eye and closes the eyelid. It contracts in less
than 0.01 second.
- Contrary to popular belief, the number of
muscle fibers cannot be increased through
exercise; instead, the muscle cells simply get
bigger (hypertrophy) or split (hyperplasia).