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Muscles
Human Biology
Functions of the Muscular System
• movement (~75 pairs [out of 434 muscles]
are responsible for movement)
• posture (as well as absorb shock)
• respiration
• heat
• communication
• constriction
• heart beat
Muscle Types
• Skeletal (or
voluntary)
• Smooth (or
involuntary organ)
• Cardiac (or
involuntary heart)
• Muscles are
considered organs
of the muscular
system
Structure of the Muscle
Muscle Structure
• Muscles are surrounded by a thin
connective tissue called fascia.
Muscle Fibers
•
•
•
•
Single muscle cells
Can contract in response to a stimuli
Thin, cylindrical, often multinucleated
Contain fibers called myofibrils that run
parallel along the length of the cell
Myofibrils
• Made of two types of
protein
– Actin (thin)
– Myosin (thick)
– Arranged in bands
• Together, it is called a
sarcomere
• They cause muscle
fibers to look striated
(striped)
Neuromuscular Junction
• Skeletal muscle contracts as a result of a
stimulus
• Stimuli are electrochemical impulses from
a motor neuron carried by a
neurotransmitter
• Motor neurons form between the spinal
column, brain, and muscles.
Muscle Structure
• Humans have about 600 named muscles
in the body
• All muscles have two main parts
– Origin: where the muscle attaches to a fixed
bone
– Insertion: where the muscle attaches to the
bone across a joint
Muscle Naming (handout)
• Size: vastus (huge); maximus (large); longus (long); minimus
(small); brevis (short).
• Shape: deltoid (triangular); rhomboid (like a rhombus with equal and
parallel sides); latissimus (wide); teres (round); trapezius (like a
trapezoid, a four-sided figure with two sides parallel).
• Direction of fibers: rectus (straight); transverse (across); oblique
(diagonally); orbicularis (circular).
• Location: pectoralis (chest); gluteus (buttock or rump); brachii (arm);
supra- (above); infra- (below); sub- (under or beneath); lateralis
(lateral).
• Number of origins: biceps (two heads); triceps (three heads);
quadriceps (four heads).
• Origin and insertion: sternocleidomastoideus (origin on the sternum
and clavicle, insertion on the mastoid process); brachioradialis
(origin on the brachium or arm, insertion on the radius).
• Action: abductor (to abduct a structure); adductor (to adduct a
structure); flexor (to flex a structure); extensor (to extend a
structure); levator (to lift or elevate a structure); masseter (a
chewer).
Muscular Responses
• Threshold stimulus
– The amount of stimuli needed to cause a
muscle contraction
• All or None Response
– A muscle will contract fully with the threshold
stimulus. Muscle fibers can not contract
partially.
– Fibers can, however, contract independently
of each other causing a muscle to contract
partially.
Skeletal Muscles
• Prime movers
– The primary muscle that contracts to move a
body part
• Synergists
– Smaller local muscles that contract to aid the
prime mover
• Antagonists
– Larger muscles that oppose the prime movers
and can act in the opposite direction
Major Muscles
Refer to p 195-205