Muscular System
KEY TERMS
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Abduction
Adduction
Cardiac muscle
Circumduction
Contract
Contractibility
Contracture
Elasticity
Excitability
Extensibility
Extension
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Fascia
Flexion
Insertion
Involuntary
Muscle tone
Muscular system
Origin
Rotation
Skeletal muscle
Tendons
Visceral (smooth) muscle
Voluntary
Key Points
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Over 600 muscles make up the muscular system
45% of total body weight as an adult
Contraction depends on myofilaments (actin and myosin)
Sliding filament theory
Basic Anatomy of Skeletal Muscle
• Each muscle is an organ
• 100s to 1000s of muscle fibers per muscle
• Endomysium – fine sheath of connective tissue around
each muscle fiber
• Perimysium – collagenic sheath around several muscle
fibers bundled together (fascicles)
Characteristics of Muscles
 Excitability: the ability to respond to a
stimulus such as a nerve impulse
 Contractibility: muscle fibers that are
stimulated contract which causes
movement
 Extensibility: the ability to be stretched
 Elasticity: allows muscle to return to its
original shape after being contracted or
stretched
Three Main Kinds of Muscle
1. Cardiac muscle – forms the
walls of the heart and contracts
to circulate blood
• Involuntary muscle
2. Visceral (smooth) muscle –
found in internal organs of the
body and contracts to cause
movement in these organs
• Involuntary muscle
3. Skeletal muscle – attached to
bones and causes body
movement
• Voluntary muscle
Functions of the Muscular System
 Movement – voluntary and involuntary
 Produce heat and energy for the body
 Help maintain posture by holding the body
erect
 Protect internal organs
 Stabilization of joints
Muscle Attachments
 Tendons- Strong, tough
connective-tissue cords.
• EX. Achilles tendon
 Fascia- Tough, sheet-like
membrane that covers and
protects the tissue.
 Origin- the end of the muscle
attached to the non-moving
bone.
 Insertion- the end of the muscle
attached to the moving bone.
Muscle Movements
• Adduction: moving the body part toward
the midline
• Abduction: moving the body part away
from the midline
• Flexion: decreasing the angle between two
bones, or bending
• Extension: increasing the angle between
two bones, or straightening
• Rotation: turning a body part around its
own axis
• Circumduction: moving in a circle at a joint
Anterior Upper Body
Posterior Upper Body
Anterior Lower
Body
Posterior Lower
Body
Muscular Information
• Muscle tone – the state of partial contraction
• Muscles are partially contracted even
when not in use
• Atrophy – when muscles shrink in size and
lose strength
• Due to injury or severe illness
• Contracture – a severe tightening of a flexor
muscle resulting in bending of a joint
Diseases and Abnormal
Conditions
• Fibromyalgia – chronic, widespread pain
• Symptoms: muscle stiffness, numbness
or tingling in the arms or legs, fatigue,
sleep disturbances, headaches, and
depression
• Cause is unknown, but stress, weather,
and poor physical fitness affect the
condition
• Treatment: directed towards pain relief
Diseases and Abnormal
Conditions
• Myasthenia Gravis
• Chronic condition where nerve
impulses are not properly transmitted to
the muscles
• Leads to progressive weakness and
eventually paralysis
• Cause is unknown
• Thought to me an autoimmune disease
with antibodies attacking the body’s
own tissues
• No cure
Diseases and Abnormal
Conditions
• Tendonitis (tendin/o + -itis)
• Inflammation of the tendon caused
by excessive or repetitive use of a
joint.
• Myalgia (my/o + -algia)
• Muscle tenderness or pain
• Myorrhexis (my/o + -rrhexis)
• Rupture of the muscle
Diseases and Abnormal
Conditions
• Muscular Dystrophy
• Group of inherited disorders that lead to
chronic, progressive muscular atrophy
(shrinking, losing strength).
• Usually appears in childhood, most
types lead to total disability and early
death.
• No cure, but physical therapy is used to
slows the progression.
Diseases and Abnormal
Conditions
• Sprain
• Injury to a joint (ex. - ankle, knee, wrist).
Frequently involves a stretched or torn ligament.
• Ligaments attach bone to bone.
• Strain
• Injury to the body of a muscle or the attachment
of a tendon. Usually associated with overuse
injuries.
• Tendons attach muscle to bone.
• Shin Splint
• Pain caused by muscle tearing away from the
tibia. Usually caused by repeated stress to the
lower leg.
Diseases and Abnormal
Conditions
• Paralysis
• Loss of sensation and voluntary muscle
movement due to disease or injury.
• Damage can be temporary or
permanent.
• Paraplegia
• Paralysis of both legs and the lower
part of the body.
• Spinal cord injury is below cervical
vertebrae
Diseases and Abnormal
Conditions
• Quadriplegia (quadr/i + -plegia)
• Paralysis of all four extremities.
• Spinal cord injury involves the cervical
vertebrae.
• Above C5, respiration is affected.
• Hemiplegia (hemi + -plegia)
• Total paralysis on one side of the body.
Usually associated with stroke or brain
injury.
• Damage to one side of brain causes
paralysis on the opposite side of the body.