Muscular System

Muscle fiber

muscle cell

sarcolemma

cell membrane of muscle fiber

Sarcoplasm

cytoplasm of muscle fiber

Epimysium 

(outer) surrounds the entire muscle & is continuous with the Tendon

Perimysium

(“middle”/surround) separates individual fascicles & is where blood vessels + nerves travel through

Endomysium

(inner) surrounds individual muscle fibers

Myofibril 

made up of individual sarcomeres place end to end, next to each other, within muscle fibers. 100s of myofibril per fiber!

Myofilaments

protein components that allow for muscle contraction 

Skeletal muscles are

unique, huge & multinucleated

Tendons

made of dense connective tissue (CT) & transmit force to limbs/muscles, which conserves energy b/c they do not contract. Decreases need for bulky muscle, allowing for more freedom of movement.

Muscle Homology Evidence

Muscles don’t leave fossil records, but their positions can be inferred from bony sites. Origin & Insertion

1.) Embryonic origin: if similar, then typically similar innervation + function

2.) Nervous Innervation; nerve tells muscle to contract, this rarely changes over time

Hypomere/Lateral Mesoderm 

Becomes smooth muscle layers of GI tract, basically all gut musculature. 

-includes visceral musculature

-source of cardiac muscle & smooth muscle 

-some shedding of Mesenchymal cells for appendicular muscle/ cartilage/ bone/ tendon/ ligament/ vasculature 

Hypobranchial musculature

throat region, from somite’s- nervous supply from cervical and ventral tips migrate down

Epaxial +Hypaxial Muscles

swimming muscles in fish that contract side to side. Lateral undulations help fish push against water to propel froward