THE MUSCULAR SYSTEM
OBJECTIVES
 To understand the structure of muscle.
 To explain the components and significance of the sarcomere.
 To identify the parts of the neuromuscular junction
 To explain how muscle contracts.
MUSCULAR MOVEMENT
 skeletal muscles come in
antagonistic pairs
 flexor vs. extensor
 They contract (shorten) when activated
 Tendons (t=two!)
 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
WHAT AM I?
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
1
Put it all together…
2
3
ATP
7
4
6
ATP
5
DO NOW
 Read the article and answer the questions.
OBJECTIVES
 To understand how muscles “grow” and explain the
benefits of resistance workouts.
 To identify the parts of a myogram and explain the
different graphs used to depict muscle contraction.
 To build on prior knowledge from Biology to explain
muscular fatigue.
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
 Recruitment (multiple motor unit summation)
 In a whole muscle or group of muscles, increasing tension is
produced by slowly increasing the size or number of
motor units stimulated
MOTOR UNITS
Figure 7-8
NUMBER OF MUSCLE FIBERS ACTIVATED
 Muscle tone
 The normal tension 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.
 *the extent of shortening
depends on resistance.
MYOGRAM
 Twitch= single muscle
contraction
 Latent period: time between
stimulation and response
 Period of contraction: muscle is
contracted
 Relaxation: fiber returns to
former length
TYPES OF GRAPHS
 Twitch- full contraction
 Summation- force of
each twitch combines
 Incomplete tetanus-
minimal amt. of
relaxation after each
stimulus
 Complete tetanus- no
relaxation, continuous
calcium ion deposit
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 
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.
ISOMETRIC VS. ISOTONIC
 Isometric- no change in
muscle length
 Isotonic- muscle length
changes
MUSCLES OF THE FACE