Download Chapter 3 - Victoria College

Chapter 11
The Muscular System
1
How Muscles Produce Movement
• Produce movement by exerting force on tendons which in turn
pull on bones
– Generally cross one joint & are attached to bones of joint
– One bone remains stationary & other moves
– Attachment sites
• Origin = attachmt of muscle tendon to stationary bone
• Insertion = attachmt of tendon to movable bone
• Insertion moves toward origin
– Belly of muscle = fleshy portion between tendons
– Actions = movements occurring when muscle is contracted
2
Fascicle Arrangement
• Effects of fascicle arrangement
– Fibers within fascicles are parallel to each other
– Fascicles within muscles arranged in 1 of 5 patterns
• Parallel
– fascicles parallel to long axis of muscle
– terminate in tendons @ either end of muscle
– ex: stylohyoid
• Fusiform
– fascicles nearly parallel to long axis
– taper toward tendons
– ex: digastric muscle
• Circular
– fascicles arranged in concentric circles
– ex: orbicularis oris
3
Fascicle Arrangement
• Effects of fascicle arrgmt (ct’d)
• triangular
– spread over broad area & converge @ thick,
central tendon
– ex: pectoralis major
• pennate
– short fascicles; tendon extends entire length of
muscle
– 3 subcategories
» unipennate = fascicles on one side of tendon (extensor
digitorum longus)
» bipennate = fascicles on both sides of centrally
positioned tendon (rectus femoris)
» multipennate = fascicles attached obliquely from a # of
directions to several tendons (deltoid)
4
Fascicle Arrangements
• A contracting muscle shortens to about 70% of its length
• Fascicular arrangement represents a compromise between
force of contraction (power) and range of motion
– muscles w/ longer fibers have greater range of motion
– short fiber can contract as forcefully as a long one
5
How Muscles Produce Movement
• Coordination within muscle groups
– movement = result of antagonistic muscle pairs @ joints
– prime mover (agonist) = muscle that contracts to cause
action
– antagonist stretches & yields to prime mover
– within a pair of muscles, roles of antagonist/prime mover
switch with movement produced
• ex: biceps/triceps brachii in flexion/extension of elbow
6
Naming Skeletal Muscles
• Names of most skeletal muscles are based on several types
of characteristics
• Characteristics may be reflected in name of muscle
– direction of fibers
– size of muscle
• major = large  pectoralis major
• minimus = smallest  gluteus minimus
– shape of muscle
• delt = triangular  deltoid
• rhomb = diamond  rhomboid
– action of muscle
• Adduction of thigh  adductor longus
– number/site of origins
• biceps brachii/femoris: 2 sites of origin
• triceps brachii: 3 sites of origin
• quadriceps femoris: 4 sites of origin
7