Download The Muscular System

6.2 Types of Muscle Tissue
 All muscle tissue develops from mesoderm in
process called myogenesis
 Begins when stem cells in mesoderm form into
myoblasts
 Myoblasts (stem cells) help develop the 3 muscle
types
Cardiac Muscle
 Heart
 Involuntary, striated
 Provides strong contractions
 Cells have 2 nuclei
 Communicate at special junctions called
intercalated disks
 Intrinsic beat – a natural contraction cycle
Smooth Muscle
 Found in many organ systems
 Nonstriated
 Produce weak involuntary contractions
 Peristalsis – weak, pulsating contractions that
move food and wastes through the digestive
system
Skeletal Muscle
 Focus of this chapter…..
 Provides movement of the bones and joints
 Voluntary, striated
 Powerful contractile capabilities
 Muscle fiber – several myoblasts fused
together, a muscle tissue cell
 Motor nerve cells – contract skeletal muscle
fibers
Muscle Cell Structure
 Skeletal muscles are long, cylindrical cells covered
by excitable membrane filled with specialized
cytoskeleton
 Respond to signals from others cells + environment
 Sarcolemma = membrane (covering) of muscle cells
 Cytoskeleton – composed of band of proteins called
myofilaments
 Thick – composed of protein called myosin
 Thin – 3 proteins – actin, tropomyosis, and troponin
 Titin - elastic
Muscle Cell Structure, cont.
 Sarcomere – contractile unit of muscle cell
 Many thousands run length of muscle cell
 Chains of sarcomeres form myofibrils
 Each muscle fiber is made of many bundled myofibrils
 Thick and thin myofilaments arrange to form overlapping
pattern
 Overlapping is what carries out the muscle cell’s contraction,
and what gives it a striated pattern
 Z line – marks the boundaries between each
sarcomere
 Movement of Z line changes length of muscle
 Sarcoplasmic reticulum – surrounds each sarcomere
 System of tubes that stores and transports calcium
needed for muscle contraction
Muscle Cell Structure
Muscle Cell Function
 Contraction is achieved by simultaneous
shortenings of all sarcomeres in a cell
 Process of contraction
 *Each on individual slide……
 Neural stimulation (1st)
 Muscle cell contraction (2nd)
 Muscle cell relaxation (3rd)
Neural Stimulation (1st)
 Takes place at neuromuscular junction
 Where nerve cells communicate with muscles
 Contraction initiated when end of nerve cell
releases neurotransmitter
 Chemicals used for cell-to-cell communication
 Acetylcholine – neurotransmitter that communicates
with muscle cells
 Binds to acetylcholine receptors, located on sarcolemma
 Sodium-potassium pump – controls the ionic
distribution of Na and K inside and outside of cell
 In resting cell, Na+ is higher outside cell, K+ higher
inside
 Pumps maintains this unequal ion concentrations
 When stimulated, it loses its ability to maintain the
imbalance
 Imbalance opens ions channel’s causing free flow of ions,
initiating the muscle contraction phase……….
Muscle Cell Contraction (2nd)
 Begins when calcium released by
sarcoplasmic reticulum binds to troponin on
thin myofibrils
 Results in temporary rigid tension that keeps
filaments in place
 ATP provides energy
 Swivel motion brings the two Z-lines together,
shortening sarcomere
 Takes another neural stimulation to continue
another cycle
 1 muscle contraction requires several cycles of neural
stimulation
Muscle Cell Relaxation (3rd)
 When no more neural stimulations are exciting
the sarcolemma
 Calcium leakage out of the sarcoplasmic
reticulum into the sarcomere is common after
death
 Rigor mortis – muscle stiffness
 Eventually, this stops
 Creatine phosphate – stores energy in cells
 Collects ATP from cells, can store for long periods of
time
 Glycogen – stored form of glucose
 Myoglobin – stores oxygen for muscle cells