Download the muscular system

THE MUSCULAR SYSTEM
SKELETAL MUSCLE CHARACTERISTICS
•  Most are attached by tendons to bones
•  Cells are multinucleate
•  Striated – have visible banding
•  Voluntary – subject to conscious control
•  Cells are surrounded and bundled by connective tissue =
great force, but tires easily
SMOOTH MUSCLE CHARACTERISTICS
•  Has no striations
•  Spindle-shaped cells
•  Single nucleus
•  Involuntary – no conscious
control
•  Found mainly in the walls of
hollow organs
•  Slow, sustained and tireless
CARDIAC MUSCLE CHARACTERISTICS
•  Has striations
•  Usually has a single nucleus
•  Joined to another muscle cell at
an intercalated disc
•  Involuntary
•  Found only in the heart
•  Steady pace!
MUSCULAR MOVEMENT
¡  skeletal muscles come in
antagonistic pairs
¡  flexor vs. extensor
¡  They contract (shorten) when activated
¡  Tendons
¡  connect bone to muscle
¡  ligaments
¡  connect bone to bone
SKELETAL MUSCLE
¡  Composed of skeletal muscle
tissue, nervous tissue, blood,
and connective tissues.
CONNECTIVE TISSUE COVERINGS
¡  Fascia: layers of fibrous connective tissue that
separate an individual muscle from adjacent
muscles.
¡  Epimysium: tissue closely surrounding muscle
¡  Perimysium: separates muscle tissue into
small compartments.
¡  Fascicles: bundles of skeletal muscle fibers
¡  Endomysium: surrounds each fiber within a
fascicle.
STRUCTURE OF STRIATED SKELETAL MUSCLE
¡  Muscle Fiber
¡  muscle cell
¡  divided into sections = sarcomeres
¡  Sarcomere
¡  functional unit of muscle contraction
¡  alternating bands of
thin (actin) & thick (myosin) protein
filaments
THICK & THIN FILAMENTS
¡  Myosin tails aligned together & heads pointed away from
center of sarcomere
THIN FILAMENTS: ACTIN
¡  Complex of proteins
¡  braid of actin molecules & tropomyosin fibers
¡  tropomyosin fibers secured with troponin molecules which block the spot
where the myosin fiber will attach. (this must be moved in order for the
muscle to contract)
SLIDING FILAMENT THEORY
¡  Sliding filament theory
¡  Thin filaments of sarcomere slide toward M line after the myosin
crossbridges form
¡  The width of the A band remains the same
¡  Z lines move closer together
NEUROMUSCULAR JUNCTION
¡  Place where a motor neuron meets
a muscle cell
¡  Action potential travels down
neuron, stimulates release of
acetylcholine from vesicles,
received by receptors on muscle
cell, action potential is propogated
and stimulates contraction.
STEPS OF CONTRACTION
1.  A. Upon stimulation, Ca2+ binds to receptor on troponin molecule.
B. The troponin–tropomyosin complex changes, exposing the
active site of actin.
2. The myosin head attaches to actin, forming a cross-bridge.
STEPS OF CONTRACTION
3.  The attached myosin head bends/pivots towards the sarcomere, and
ADP and P are released.
4.  The cross- bridges detach when the myosin head binds another ATP
molecule.
5.  The detached myosin head is reactivated as ATPase splits the ATP and
captures the released energy.
MOLECULAR EVENTS OF THE CONTRACTION PROCESS
Figure 7-5
MOLECULAR EVENTS OF THE CONTRACTION PROCESS
Figure 7-5
MOLECULAR EVENTS OF THE CONTRACTION PROCESS
Figure 7-5
MOLECULAR EVENTS OF THE CONTRACTION PROCESS
Figure 7-5
MOLECULAR EVENTS OF THE CONTRACTION PROCESS
Figure 7-5
MOLECULAR EVENTS OF THE CONTRACTION PROCESS
Figure 7-5
MUSCLE GROWTH
TENSION PRODUCTION
¡  The all-or-none principle
¡  As a whole, a muscle fiber either contracts completely or
does not contract at all
NUMBER OF MUSCLE FIBERS ACTIVATED
¡  Muscle tone
¡  The normal tension (partial contraction) and firmness of a
muscle at rest
¡  Muscle units actively maintain body position, without
motion
¡  Increasing muscle tone increases metabolic energy used,
even at rest
MUSCLE CONTRACTION
¡  A muscle fiber will contract
after threshold stimulus has
been reached.
¡  Once stimulated, the entire
fiber completely contracts
which is called the all-or-none
response.
MYOGRAM
¡  Twitch= single muscle contraction
¡  Latent period: time between
stimulation and response
¡  Period of contraction: muscle is
contracted
¡  Relaxation: fiber returns to
former length
ATP AND MUSCLE CONTRACTION
¡  Sustained muscle contraction uses a lot of ATP
energy
¡  Muscles store enough energy to start contraction
¡  Muscle fibers must manufacture more ATP as needed
MUSCLE FATIGUE
¡  Cells undergo both aerobic and anaerobic respiration to supply ample atp (lactic acid
fermentation)
¡  Lactic acid creates an oxygen debt because the liver cells must now use oxygen to break
down the lactic acid (can take several hours)
¡  Lactic acid lowers the ph, which diminishes the muscle fibers response to stimulation
¡  More exercise = more glycolytic enzymes = increased capacity for glycolysis= increased capacity
for aerobic respiration!! … start working out J
HYPERTROPHY VS. ATROPHY
¡  Hypertrophy- muscles respond
to exercise and enlarge
¡  Slow twitch fibers activated by
low intensity exercise such as
swimming or running, develop
more mitochondria and capillaries,
prolonging fatigue
¡  Fast twitch fibers activated by
weight lifting can produce new
myofilaments & enlarge the muscle
(they are still fatigable)
¡  Atrophy- when regular exercise
stops, capillary networks shrink,
mitochondria decrease, actin &
myosin decrease, and muscle
shrinks.
TETANUS
¡  Caused by Clostridium bacteria
present in soil
¡  Bacteria produces a neurotoxin
which blocks the release of
inhibitory neurotransmitters.