Musculoskeletal System

skeletal muscle

• innervated by somatic nervous system

• voluntary movement

• fxn unit: sarcomere

• striated look

• multinucleated

smooth muscle

• innervated by autonomic nervous system

• involuntary movement

• fibers are disorganized

cardiac muscle

• combo of skeletal + smooth characteristics

• contains gap jxns and intercalated discs

• uninucleated, striated, autonomic

sarcolemma

cell membrane of skeletal muscle cells

carry its own action potential (AP)

steps to muscle contraction

• neuron fires Ach into neuromuscular jxn

• Ach binds to receptor = sarcolemma depolarizes

• AP carried to T tubules

• Ap transferred to sarcoplasmic reticulum = release Ca2+ myocyte

• Ca2+ binds o Ca2+ binding site of troponin

• conformational change makes tropomyosin move from actin

• myosin binding groove of actin is exposed

• globular myosin heads bind to actin on myosin binding site

• myosin power stroke shortens sarcomere (contraction) → ADP + Pi dissociate

• ATP binds myosin and hydrolyzes → resets tropomyosin position (ends contraction)

compact bones

dense

spongy bones

• cavity/lattice structure

• bone marrow (yellow/fat and red/hematopoiesis)

main composition of bones

hydroxyapatite: Ca10(PO4)6(OH)2

flexion

decrease angle of joint

abduction

move away from body (eg.: extend arm away from body)

rotation

• internal: toward body

• external: away from body

calcitonin

• activates osteoblasts

• decrease serum ca2+

parathyroid hormone

• activates osteoclasts

• increase serum Ca2+