Chapter 9 Anatomy and Physiology I.docx - Chapter 9 Anatomy...

Chapter 9 Anatomy and Physiology I
 Characteristics of Muscles
o Functions:
 Movement
 Posture
 Joint stability
 Less likelihood of injury
 Heat production
 Example is shivering
o All tissues exhibit:
 Excitability (irritability)
 Respond to stimulus
 Contractility
 Extensibility
 Flexing or stretching
 Elasticity
 Skeletal Muscle
o Voluntary and striated
 Straited by myosin and actin arrangement
o Usually attached to bone
o Muscle generates tension in muscle fibers and that is follow by
external tension in order to move a load.
o Muscle fiber

 Muscle cell with multiple nuclei
o Know connective tissue wrappings!
 Muscle fiber is wrapped by endomysium
 Perimysium wraps the fascicle
 Epimysium is continuous with the tendon and wraps many
fascicles
 Muscle fiber
o Myofilaments make up a muscle fiber and are made of
myofilaments
o In order of largest to smallest:
 Whole muscle
 Muscle fascicle
 Muscle fiber (cell)
 Myofibrils
 Myofilaments
o Plasma membrane is called sarcolemma
o Cytoplasm is called sarcoplasm and contains glycogen and
myoglobin for ATP production
o Sarcoplasmic reticulum joins with T tubules to form a terminal
cistern.
 Cistern holds calcium like a cistern/ well
 Sarcoplasmic reticulum is like endoplasmic reticulum
 Triad is 2 cisterns and 1 tubule
 Myofilaments (Actin and Myosin)
o Two kinds:
 Thick myofilaments
2

 Multiples myosin stuck together
 Binds to actin
 Thin myofilaments
 2 strands of actin wound together
 Binds to myosin
 Tropomyosin cover bonding sites during relaxation
 Troponin binds to calcium and ATP to remove
tropomyosin
 Contraction
o Myosin and actin bind together and engage
o Sarcomere is shortened
o An analogy would be a crew of rowers and the oars are myosin
while the water is actin
 Contraction and relaxation
o Key players:
 Brain and skeletal muscles communicate through motor
neurons to contract
 Spinal cord  axon  axon terminus  muscle fibers
 Axon terminus and muscle fibers form the
neuromuscular junction, but it is not perfectly sealed
o Steps:
 1 st step delivers excitation
 Nerve impulse to motor neuron,
 Calcium goes into end of motor neuron
3

 Calcium entry causes ACh (acetylcholine) to be
released by exocytosis of the motor neuron into
synovial junction
 ACh binds to receptor on the sarcolemma (muscle