Download the muscular system

THE MUSCULAR
SYSTEM
CHAPTER 8
Objectives
• To explain the structure of muscle
• To list various outcomes of muscular actions
• Describe how connective tissue is part of a
skeletal muscle
• Name the major parts of a skeletal muscle
fiber, and describe the function of each
Introduction
• Muscles are responsible for all types of body
movement
• Use chemical energy stored in nutrients to
contract
• muscle tone, propel body fluids and food,
generate heartbeat, and distribute heat
• Types:
1. Skeletal
2. Smooth
3. Cardiac
Skeletal Muscle
• Attaches to bones
• Tendon: muscle to bone
• Ligament: bone to bone
• Conscious control
• Come in antagonistic pairs:
• flexor (bends a joint) and extensor
(straightens a joint)
• Contract and shorten
Skeletal Muscle (cont.)
• Composed of:
• Skeletal muscle
tissue
• Nervous tissue
• Blood
• Connective tissue
Connective Tissue Coverings
• Fascia: layers of fibrous
connective tissue that separates
an individual skeletal muscle
from adjacent muscles
• Epimysium: layer of connective
tissue that closely surrounds a
skeletal muscle
• Perimysium: extend inward from
epimysium, separates muscle
tissue into small compartments
• Fascicles: bundles of skeletal
fibers
• Endomysium: thin covering of
each fiber within a fascicle
Skeletal Muscle Fibers
• Single cell that
contracts in response
to stimulation, relaxes
when stimulation
ends.
• myofibrils divided
into sections called
sarcomeres
• Sarcomere
• functional unit of
muscle contraction
• contain
myofilaments
(alternating bands
of thin (actin) and
thick (myosin)
Thin Filaments (Actin)
• Complex of proteins
• Helix of actin molecules and tropomyosin fibers
• Tropomyosin fibers secured with troponin molecules
which block the spot where the myosin fiber will attach
(must be moved for muscle contraction)
Thick Filaments (Myosin)
• Each thick filament consists of many myosin molecules
• consist of head, neck and tail
• head binds to actin molecules
*Organization
of filaments
produces
striations*
Neuromuscular Junction
• Motor Neuron stimulates
muscle contraction
• Neuromuscular junction:
connection between motor
neuron and muscle fiber
• Nerve impulse reaches end of
motor neuron axon, vesicles
release neurotransmitter
(acetylcholine)
• Neurotransmitter received by
receptors on muscle cell,
contraction is then stimulated
Animation
Skeletal Muscle Contraction
• Sliding Filament Theory
• Sarcomeres shorten
because cross-bridges
pull on thin filaments
• Thin filaments slide
toward M line
• Width of the A band
remains the same
• Z lines move closer
together
Steps of Contraction
Step 1: Action Potential
1. Nerve action potential releases acetylcholine into synaptic cleft,
opening Na+ channels
2. Action potential spreads across sarcolemma, releases Ca2+ into
sarcoplasm
Steps of Contraction (cont)
Step 2: Myosin-actin binding
1. a. Upon stimulation, Ca2+ binds to receptor on troponin molecule
b. Troponin-tropomyosin complex changes, exposing active
site of actin
2.
Myosin head attaches to actin using energy from ATP, forming
a cross-bridge
Steps of Contraction (cont.)
Step 3: Power Stroke
1. Side arm pivots towards M line so actin and myosin slide by each
other, shortening the sarcomere
2. ADP and P are released
Steps of Contraction (cont.)
Step 4: ATP Binding, Actin-myosin release
1. Myosin head binds another ATP molecule
2. Cross-bridges detach, releasing actin
Steps of Contraction (cont.)
Step 5: ATP Cleavage
1. ATPase splits ATP and captures released energy, detached
myosin head is reactivated
2. Cycle will repeat if Ca2+ is still available
Hmmmmm…..
If a muscle is contracted, what happens if a new molecule of ATP is
not available?
Why does rigor mortis occur?
Place your fingers along the angle of your jaw just in front of your
ear. Grit your teeth and feel what happens. What muscle is
contracting?
Do Now:
• Complete #’s 1-6 on the upper leg. Fill out the
diagram and the function.
Steps of Contraction (all together now!)
https://www.youtube.com/watch?v=YAJ-9nPSqwA
Rigor Mortis
• Occurs 2-4 hours
after death due to
lack of ATP
• Muscles remain
contracted until the
muscle tissue itself
starts to deteriorate.
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
◼ Twitch summation (treppe)- stimulating the muscle before it
completely relaxes
◼ Incomplete tetanus- minimal amt. of relaxation after each
stimulus
◼ Complete tetanus- no relaxation, continuous calcium ion deposit
Objectives (P. 3 2/17)
• To identify the stages of contraction on a
myogram
• To discuss the role of ATP and cellular
respiration in muscle fatigue
• To compare and contrast hypertrophy and
atrophy
• To create dance/workout routines using
anatomical terms of movement
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
Do Now
• Finish the muscles of the leg (functions and
diagram)
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 tetani
bacteria present in
soil
◼ Bacteria produces a
neurotoxin which
blocks the release of
inhibitory
neurotransmitters.
Muscle Workout/Dance Activity
Your group must come up with instructions for a
workout/dance routine that can be done in the classroom.
You must include at least 3 muscles from each section that
we covered. Write out the instructions for the next group.
They will have to do your “dance” and try to guess which
muscles you focused on!
Happy Heart Day!!!