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Muscular System 1
Muscular System 1

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Muscular System 1...
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Muscular System 1:
The ability to move is an essential activity of the human body, which is made possible by the unique function of the contractility in muscles.  Between 40%-45% of our body weight is composed of muscle mass.

Muscles are highly specialized tissues that enable the body and it's parts to move.  There are over 650 different muscles in the human body.  Muscles are responsible for all of our body movement.  They allow us to move from place to place as well as performing involuntary functions such as the heart beating and breathing.  Muscles give our bodies form and shape and they are responsible for producing most of our body heat.  

All muscle cells shorten or contract  by converting chemical energy obtained from food into mechanical energy that is translated into movement.  


skeletal- striated and voluntary
smooth or visceral - non striated or involuntary
cardiac- striated with intercalated disks

They can also be described as striated, spindle shaped and nonstriated because of the way the cells may look under a microscope.  Each fine thread is called a muscle fiber.

Smooth muscles are unmarked by any distinctive striations.  Unattached to bones, they act slowly, so not tire easily and can remain contracted for a long time.  They are also called involuntary muscles because they are not under conscious control.  Their actions are controlled by the autonomic nervous system.  Smooth muscles are found in the walls of the internal organs including the stomach, intestines and blood vessels.  They help to push food through the alimentary canal , contract uterus and constrict or dilate the blood vessels.

Cardiac muscles are found only in the heart.  Cardiac muscles are striated and branched and they are involuntary.  They contract rapidly and are very strong.  Cardiac muscles require a continuous supply of O2 to be functional.  These muscles also have unique dark bands that are called intercalated disks.  

 A skeletal muscle is composed primarily of striated muscle cells and connective tissue.  Most skeletal muscles attach to 2 bones that have a movable joint between them.  Muscles extend from one bone across a joint to another bone.  One of the two bones is usually more stationary than the other.
The muscle's attachment  to this more stationary bone is called its origin.  The muscle's attachment to the more movable bone is called the muscle's insertion.  The rest of the muscle is called the body of the muscle.
The fleshy body parts are made of skeletal muscles.

Small fluid filled sacs called bursae lie between some tendons and bones, they are made up of connective tissue and are lined with synovial membranes which secrete the slippery lubricating fluid known as synovial fluid.  

Muscle tissues consist of specialized contractile cells or muscle fibers that are grouped together in a highly organized way.  Each muscle fiber is filled with two different kinds of very fine and threadlike structures called thick and thin myofilaments.

Thick myofilaments are formed from a protein called myosin and the thin myofilaments are formed mostly of a protein called actin.

The functional unit of the skeletal muscle is the sarcomere it is considered the contractile unit.  
When looking under a microscope there are numerous arrangements of both thick and thin myofilaments which lie parallel to each other and overlap with  a separating dark band called a Z band.  A sarcomere is the length of the myofibrils between the Z bands.

Contraction of a muscle causes the two types of myofilaments to slide toward each other and shorten the sarcomere thus the muscle itself.  When the muscle relaxes the sarcomere can return to its resting length and the filaments return to their resting positions.

Calcium is a vitally needed mineral for our muscles to function.  Calcium is released into the cytoplasm when the muscle is stimulated to contract.  In addition to calcium the shortening of a muscle cell requires energy.  This is supplied by the breakdown of ATP molecules or the energy storage molecules of the cell.    


All muscles regardless of their type have 3 characteristics in common.  
contractility:  this quality is possessed by no other body tissue.  When a muscle shortens or contracts, it reduces the distance between the parts of it's contents or the space it surrounds.  The contraction of skeletal muscles which connect a pair of bones brings the attachment points together.  This causes the bones to move or they can reduce the area in the heart chambers upon contraction or cause the diameter of the vessels to decrease upon contraction.
extensibility:  which means the ability to be stretched.  When we    bend our forearm, the muscles on the back of it are stretched or extended
elasticity:  means the ability of a muscle to return to it's original length  when relaxing.  
irritability:  means that a muscle will respond to a stimulus.


The 3 primary functions of the muscular system are:
posture or muscle tone
heat production
For any of these muscles to produce movement  in any part of the body it must be able to exert a force upon a movable object.  Muscles must be attached to bones for leverage in order to have something to pull against.  
Muscles are attached to the bones by nonelastic cords called tendons.  Bones are connected by joints.  So when the skeletal muscles contracts the bone to which it is attached will move.
Muscles are attached at both ends to bones, cartilage, ligaments, tendons, skin and sometimes to each other.
Muscles move bones by pulling on them.  As a rule only the insertion bone moves.  The origin bone stays put, holding firm while the insertion bone moves toward it.


The muscles of the body are arranged in pairs.  One produces movement in a single direction called the prime mover.  The other does so in the opposite direction is called the antagonist.  This arrangement of muscles with opposite actions is known as an antagonist pair.   
The synergist muscle is the muscle that helps the prime mover.  A flexor muscle such as the biceps allows for bending.  An extensor muscle allows for straightening or extension and an example of this would be the triceps.
Levator and depressor muscles raise and lower body parts.  Dilator muscles assist with the decreasing or increasing of openings.

When muscles do their work to move body parts they also produce heat.  Between 98.6-99.8 is the normal temperature to maintain body heat.  

ATP or adenosine triphosphate must be present for muscles to contract.  To produce ATP however, the cell requires O2 and glucose, which is supplied by our circulating blood.

When a muscle is stimulated ATP is released producing heat that our bodies need and the energy for the muscles to contract.  

Types of contractions of the muscles
twitch- is a single stimulus
tetany-  sustained contracture or lockjaw i.e. from Clostridium tetani
treppe-  successive threshold of stimuli from the same intensity i.e. warm up of athletes

Muscle Tone

Muscle tone refers to the continued state of partial contraction present in the muscles.  
Muscle tone maintains posture and makes sure that the body is ready for action.  Skeletal muscles are stimulated to contract by special nerve cells called motor neurons.  Acetylchoine is the neurotransmitter that diffuses across the synaptic cleft to stimulate the muscle fiber.

Rigor Mortis literally means the stiffness of death.  Within a short time after death, the ATP breaks down so there is no longer any ATP available to bridge the actin and the myosin.  Therefore, the myofilaments are blocked in a contracted or rigid position.
The rigor mortis can last for up to 2 days then the protein, which makes up the myofilaments breaks down and the rigor mortis subsides or disappears.

when the tension exceeds the weight load and the muscle shortens and produces movement or when the muscle produces movement between two body parts
when tension increases but does not exceed the weight load, there is no shortening or movement or to say that there is an increased muscle tension without a production of movement.

muscle fatigue happens when there is an increase in the lactic acid in the muscles
(lactic acid is a waste product of cell metabolism)

During vigorous activity the blood cannot transport enough O2 for glucose to be utilized.  Without O2 muscles start to contract anerobically.  After exercise, you must stop to rest and take in the O2 to change the lactic acid back to glucose.


Retraining of an injured or unused muscle is a type of rehabilitation or therapeutic science.  

occurs to muscles, which are used infrequently.  They shrink in size and they lose the muscle strength.  An example of this is a stroke or a CVA where the muscles are understimulated and gradually waste away.  Another example of this may be immobilization of a limb in a cast or abrace or from prolonged bed rest.
Muscle atrophy can be minimized by direct electrical stimulation, massage and electrical stimulation.

is muscle pain and is characterized by many M-S disorders such as a strain or sprain.  

this is when there is an inflammation of the tendon as in a charley horse.  Charley horse versus cramps is the difference between a larger degree of inflammation and the potential for some muscle fiber damage with a charley horse to the imbalance of oxygen and the intricate balance of glucose, ATP, calcium and lactic acid associated with muscle cramping.

result from a weakening of the leg muscles that support the arch.  Muscle strength can be increased by exercise, massage, and electrical stimulation.

or a rupture may occur in a weak place in the muscular abdominal wall.  It is caused by bulging of the intestine through an opening in the abdominal cavity normally containing it.  An inguinal hernia is in the groin area.

is a condition in which the muscle enlarges and grows stronger.  It results from overworking and overexercising.  This leads to an increase in the diameter or the size of the muscle as opposed to an increase in the number of the muscle cells.  This increase in girth then changes the force of the muscle's contraction.

may be due to an inflammation of the trapezius muscle.  The rigidity is the result of an unusual overuse of a muscle or when looking at a sustained muscle contraction or spasm there may be an underlying injury of muscle fiber disorder.

is an infectious disease that is usually fatal.  It is characterized by continuous spasms of the voluntary muscles.  It is caused by Clostridium tetani, which can enter the body through an open wound, puncture wound or burn.

is not any one single disorder but a group of genetic diseases that is characterized by atrophy of skeletal muscle tissues.  The cause remains unknown.  Some forms are fatal.  MD most often appears in childhood and the most common form of the disease is called Duchenne's MD where muscle atrophy is replaced by fat and fibrous tissue.  Death is usually due to respiratory or cardiac muscle weakness.

is a progressive muscular weakness and paralysis especially in the face or throat.  It then progresses to a wider muscular involvement.  The cause is unknown but is considered to  be an immune disorder.


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