Muscle
• Smooth - uninucleate, fusiform cells
without striations. Visceral function. ANS
innervation.
• Cardiac - Uninucleate (mostly) cells which
are striated, branch and communicate via
intercalated discs. Intrinsic beat. ANS
• Striated - multinucleated cells which are
striated. Voluntary control. Somatic
functions. Sarcomere is contractile unit.
Classification Based on Function
Somatic:
• orient and move animal within environment
• located in body wall, appendages and tail
• originate in myotomes
• include (1) muscles of body wall, (2)
hypobranchial and tongue muscles, (3) extrinsic
eye muscles and (4) appendicular muscles
Visceral:
• maintain homeostasis
• innervated by autonomic n.s.
• include (1) branchiomeric, (2) cardiac, (3)
intrinsic eye and erector muscles, and (4)
smooth muscles of tubes, vessels, and
hollow organs
Skeletal vs non-skeletal:
• skeletal attach and move skeletal elements
• non-skeletal include all other muscles
(involuntary)
Skeletal Muscles
Muscular and tendinous elements
• Tendons attach muscle to bone - extensions
of the epimysium (fascia).
• Red fibers - high myoglobin content and a
rich blood supply. Contract slowly, resist
fatigue, allow extended function.
• White fibers - lack myoglobin, contract
rapidly, fatigue quickly.
Origin, Insertion, Action
• Origin - site of attachment that remains
fixed and does not move.
• Insertion - attachment site that is displaced
when muscle contracts.
• Action - describes the function movement
of the muscle.
Names and Homologies
• Names - denote fiber direction (oblique,
rectus), location or position (supraspinatus),
number of subdivisions (quadriceps), shape
(deltoid), origin and/or insertion
(sternocleidomastoid), action (levator
scapulae), size (pectoralis major) or other
criteria...
• Homologies - even though muscles in two
species have the same name they may not
be homologous. Muscles may alter shape,
size and attachment site(s) during evolution.
Homologous muscles have the same
embryonic origin rather than the adult
characteristics.