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Muscular System
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Anatomy & Physiology (Open + Free)
Unit 1:: Introduction to Anatomy and Physiology
Introduction
Module 2 /
Introduction of Sy stem s
Muscular System
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Describe the m uscular sy stem :
list the m ajor organs and
structures, describe the m ajor
functions, and use anatom ical
planes and directional term s to
identify organs and their
relationships to each other.
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Muscular System
Muscular System - Function
The muscular (musculoskeletal) system generates force for movement of bones around articulations, facial
expression, breathing, posture, and assists with temperature regulation. The muscular system only contains
skeletal muscle, although the body also has smooth and cardiac muscle tissue, which are important in other
body systems. There are over 650 skeletal muscles in the human body!
The skeletal muscle converts signals from the nervous system into movement via muscle contractions.
Muscles, like the biceps and triceps, are the organs of the skeletal muscular system. The main functions of
skeletal muscles include:
responding to neural information (conscious control)
applying forces to the bones to cause movement
producing heat to warm the body
changing the size of the thoracic cavity for breathing
applying forces for conscious control of openings to the outside of the body (sphincters)
The muscular system contains muscle tissues and interconnects with both the nervous system and skeletal
system. Nerves control the muscles and allow us to consciously direct movements. Some muscles, such as the
muscles that control the pupil of your eye, cannot be controlled consciously but react to nerve stimuli. The
skeletal system provides a stiff support for muscles to pull on. Muscles generate force to lift as well as to
balance us. The energy produced by contracting muscles (such as when shivering) in the muscle system helps
keep us warm. There are many muscle fiber types throughout the body that vary based on function. Parallel
muscles form along the long bones, pennate and convergent muscle fibers attach to tendons and circular
muscles assist with closing our eyes or puckering our lips.
Muscular System - Organs
The major structures within the muscular system are:
skeletal muscles
tendons
Skeletal muscles are voluntary muscles that attach to, and contract to move the bones. Skeletal muscles
often work in pairs. When one muscle is contracting, the other is relaxing. For example, to bend your arm at
the elbow, your biceps muscle contracts, and your triceps muscle relaxes. To straighten your arm, the biceps
relaxes, and the triceps contracts. The diaphragm is skeletal muscle that contracts and relaxes for inhalation
and exhalation. Hiccups are a spasm in your diaphragm muscle.
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Muscular System
Skeletal muscles are made of long cylinder shaped cells called muscle fibers, which have many nuclei within
each cell. Therefore we say that skeletal muscle is multi-nucleate. The functional unit within a skeletal muscle
fiber, called a sarcomere (note that “sarc” means flesh), contains filaments of the proteins actin and myosin.
Myosin is a thicker protein (appears darker) than actin and the two proteins create a pattern so the muscle
appears striped or striated. Notice the appearance of skeletal muscle in this transmission electron microscope
view.
Sarcom ere - By Louisa Howard Hum an skeletal m uscle tissue 1 ). Public Dom ain.
A muscle contraction occurs when the myosin filaments pull on the actin to shorten the sarcomere. This
results in shortening of the muscle fiber and ultimately the entire muscle shortens or contracts to pull on the
bone.
An electrical signal from the nervous system is necessary to cause a skeletal muscle contraction. The area
where the nerve meets the muscle to stimulate it is termed neuromuscular junction. When a nerve
signal reaches the neuromuscular junction, the muscle fiber is stimulated and the muscle contracts.
In the image below the #1 is termed the axon or the part of a neuron that carries the instructions from the
brain and spinal cord. #2 is the end of the axon called the axon terminal or synaptic vesicle. #3 is the muscle
and #4 is a group or bundle of muscle fibers.
Neurom uscular Junction - By
Sy napse_diag3 .png: User: DakeMusculus_diagram .sv g: *Skeletal_m uscle.jpg:
User:Deglr6 3 2 8deriv ativ e work: Marek M (talk)deriv ativ e work: Marek M Neurom uscular.sv g)CC-BY-SA-3 .0
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Muscular System
Tendons are grouped in both the skeletal system and the muscular system since they connect the two
systems (connect muscle to bone). Tendons play a role in transmitting force from the muscles to the bones to
permit movement.
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Other Muscle Types
Although only skeletal muscle is part of the muscular system, there are three types of muscle tissue. Smooth
muscle and cardiac muscle are similar to skeletal muscle, but perform specialized functions in the body. Most
of these functions are involuntary and do not include the skeletal system.
Smooth muscles control involuntary functions of the body, such as arterial contractions to move blood and
peristaltic contractions in the digestive system to move food. Smooth muscles lack striations thus, are termed
smooth due to their appearance. They are composed of muscle fibers with a single nucleus in each cell and are
uninucleate. Smooth muscles do not have any attachment to the skeletal system. Smooth muscle has the
ability to produce its own contractions involuntarily. However, as with skeletal muscle, electrical signals from
the nervous system can modulate the activities of smooth muscle. The organization of smooth muscle on a
cellular level is irregular and unorganized. Therefore, smooth muscle does not contain sarcomeres.
Cardiac muscle contains similarities to both skeletal and smooth muscle. Like skeletal muscle, cardiac
muscle is composed of organized muscle fibers and sarcomeres, and is striated. However, cardiac muscle does
not attach to the skeletal system and is under involuntary control, and is uninucleate. Cardiac muscle is not
long and cylinder shaped like skeletal muscle but is more branched.
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Muscular System
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Muscular System - Anatomy and Direction
Like bones, skeletal muscles are found throughout the body. Skeletal muscles are found under the skin of the
integumentary system and attached to and surrounding the bones of the skeletal system.
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