Download Muscle Physiology Notes

Functions of skeletal muscles
 Movement
 Maintain posture and body position
 Support soft tissues, ex abdominal wall
supports ventral body organs
 Guards entrances and exits- openings of
digestive tract are encircled w/ muscle
 Maintain body temperature
Anatomy of Skeletal Muscle
 Epimysium- dense layer of collagen that
surrounds the entire muscle
 Perimysium- divide muscle into smaller
compartments called fascicles, which
contain blood vessels and nerves
 Endomysium- surrounds individual muscle
fibers
 These 3 fibers join together at the end of
muscles to form tendons
Microanatomy of muscle tissue
 Skeletal muscle cells are also called fibers
 Myoblasts fuse together to make muscle
fibers
The Sarcolemma
 Sarcolemma- cell membrane of muscle fiber
 Sarcoplasm- cytoplasm of muscle fiber
 Transverse Tubules “T tubules”-
passageways through the muscle
 Electrical impulses, also called action
potentials, travel through T tubules to begin
muscle contraction
Myofibrils
 Unit of muscle fibers
 Contains myofilaments, thin “actin, and
thick “myosin”
 Myofilaments are organized into repeating
units called sarcomeres
Sliding Filament Theory
Zones of overlap get larger (overlap of actin
and myosin)
 Z lines get closer
Neuromuscular Junction
 A neuron controls each muscle fiber using
acetylcholine, which makes the muscle
fibers more permeable to sodium causing an
action potential to begin
 The action potential triggers muscle fibers
to allow Ca to pass into cells (quick .03s)
 Ca binding to the active site of the thin
filaments starts the contraction cycle
Contraction cycle
 Cross bridges from between thick and thin
filaments
 Myosin heads of thick filaments pivot,
shortening muscle fiber
Relaxation
 Acetylcholinesterase breaks down
acetylcholine to stop action potential
 Ca is pumped out of muscle fibers into the
extracellular fluid
 Ca is transported back into the sarcoplasmic
reticulum
 Active site is covered up again
Types of contractions
Isotonic- tension increases, and muscle
shortens, walking and running
Isometric- tension produces, but
muscle size stays the same, pushing on
a door
Aerobic Metabolism
Energy produced in muscle tissue in the
presence of oxygen
Muscle cells only keep small reserves of
ATP
Cellular respiration allows muscle cells
to produce more ATP using glycogen and
glucose reserves
Anaerobic Metabolism
Demands on muscle exceed bodies
ability to supply oxygen
Lactic acid is produced and builds up in
the muscle tissue
Muscle Fatigue- muscles can’t contract
despite neural stimulation
– Short peak levels (spinting)
– Prolonged excertion, Ca can’t be
regulated (marathon)
Recovery Period
 Conditions in muscle fibers return to normal
 Oxygen converts lactic acid into pyruvate
which can then become ATP or glycogen
 Oxygen debt occures after exercise until your
cells use new incoming oxygen to generate
ATP
 85% of heat needed to thermoregulate comes
from skeletal muscles
Muscle Performance
 Fast twitch fibers “white muscle”- anaerobic,
high intensity and short duration, low
myoglobin, fewer mitochondria
 Slow twitch fibers “red muscle”- opposite of
above
 Intermediate fibers- characteristics between
fast and slow
 % of fast to slow muscle fibers is genetically
determined
Cardiac Muscle Tissue
Found only in the heart
Contracts with out neural stimulation
Longer contractions
Intercalated discs ensure cells contract
in unison
Smooth Muscle Tissue
Oval shaped cells with a central
nucleus
Found in almost every organ
Doesn’t have myofibrils or
sarcomeres, so no striations
Involuntary control