Transcript Section 33.2 Muscular System

33.2 Muscular System
Student Learning Objective: SWBAT describe the
three types of muscle in humans and explain how
muscles contract.
Essential Question: What is the significance of muscle
contraction?
Brain POP: Where
is the smallest and
largest muscle
located.
stapedius, 5.08
millimeters located
in the middle ear
33.2 Muscular System
Vocabulary Terms:
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muscular system
muscle fiber
skeletal muscle
tendon
smooth muscle
cardiac muscle
myofibril
sarcomere
actin
myosin
synaptic cleft
acetylcholine
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motor unit
motor neuron
neuromuscular junction
acetylcholine
action potential
all-or-none law
axon
axon terminals
cross bridges
fast-twitch
slow-twitch
sarcolemma
33.2 Muscular System
Humans have three types of muscle.
• The muscular system moves substances throughout the
body.
– Motion
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bones of the skeletal system
food through digestive system
blood through circulatory system
fluids through excretory system
– Maintenance of posture
– Heat production
33.2 Muscular System
• There are three types of muscle tissue.
– skeletal muscle
– smooth muscle
– cardiac muscle
SKELETAL MUSCLE
SMOOTH MUSCLE
CARDIAC MUSCLE
33.2 Muscular System
• Smooth muscle is involuntary.
– muscle of the viscera (internal organs) eg. Lining/walls of
blood vessels, intestine, other 'hollow' structures/organs
in the body)
– move food through digestive organs SMOOTH MUSCLE
– empty liquid from the bladder
– control width of blood vessels
Smooth muscle
around this artery allows the
artery to regulate blood flow
by shrinking and expanding.
33.2 Muscular System
• Cardiac muscle is found only in the heart.
– pumps blood throughout body
– controlled by pacemaker
– contains more mitochondria than skeletal muscle cells
CARDIAC MUSCLE
33.2 Muscular System
• Skeletal muscle attaches to the skeleton by tendons.
– Tendons connect muscle to bone.
– Skeletal muscles are mostly voluntary
– Striated muscle (repeating sarcomeres)
– Contraction of a muscle fiber is an all-or-nothing event
SKELETAL MUSCLE
33.2 Muscular System
Structure:
Composed of
myofibrils
Epimysium-connective tissue ensheaths entire muscle
Perimysium- sheath of connective tissue that groups muscle fibers into
bundles or fascicles
Endomysium- connective tissue that ensheaths each individual muscle fiber
33.2 Muscular System
Muscles contract when the nervous systems causes
muscle filaments to move.
• Muscle fibers are CELLS of the muscular system.
• Myofibrils are long strands of protein in the muscle fiber
• Each myofibril is divided into sarcomeres.
muscle fiber
myofibril
sarcomere
muscle
• Sarcomeres contain filaments that cause contraction.
33.2 Muscular System
• Each myofibril is divided into sarcomeres.
• Sarcomeres contain filaments that cause contraction.
– Actin filaments are pulled during contraction.
– Myosin filaments pull actin during contraction.
Cell membrane
organelle
where Ca+
is stored
33.2 Muscular System
How does contraction in skeletal muscles occur?
Neuron Structure
33.2 Muscular System
How does contraction in skeletal muscles occur?
• Motor neuron stimulates muscle at the neuromuscular junction.
• Motor unit-single motor neuron and all the muscles that it stimulates
(the functional unit)
• One motor neuron may stimulate up to 2000 skeletal muscle fibers
neuromuscular
junction
neuron
MUSCLE
33.2 Muscular System
How does contraction in skeletal muscles occur?
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Begins at the neuromuscular junction=axon terminal and muscle fiber meet
Synaptic cleft=gap between axon terminal and muscle fiber
33.2 Muscular System
Resting Potential- when a neuron is at rest
• Contains potential energy needed to transmit an impulse
• Occurs because there are unequal concentrations of ions inside and
outside the neuron.
−More channels for K+ than for Na+ , so positive charges leave the cell
much faster than they enter : unequal diffusion of ions along a gradient
−Sodium-potassium pump, uses energy to actively transport Na+ ions
out of the cell and bring K+ ions into the cell.
The neuron has a net
negative charge compared with its
surroundings because there are
fewer positive ions inside the neuron.
33.2 Muscular System
Action Potential
Because more sodium enters than potassium exits,
the net effect inside is a positive charge (Depolarization)
33.2 Muscular System
Action Potential
33.2 Muscular System
The Neuromuscular Junction
When impulse reaches the
axon terminal a
neurotransmitter is
released=acetylcholine makes
sarcolemma temporarily
permeable (chemical signal)
33.2 Muscular System
The Neuromuscular Junction
NA+ channels open and
a net positive
charge is created because Na+
Rushes in at a faster rate then
K+ exits
33.2 Muscular System
– Impulse travels along the
Sarcoplasmic Reticulum (SR),
the calcium gates in the
membrane of the SR open. As a
result, CALCIUM diffuses out of
the SR and among the
myofilaments
– Calcium exposes binding sites.
– Myosin binds to actin and pulls
it.
– As the sarcomere
shortens, the muscle
contracts.
Calcium ions move into the sarcomere from storage sites
by facilitated diffusion (spontaneous passage of
molecules/ions across a biological membrane passing
through a specific channel) due to its concentration
gradients
Ca+
Cross-bridges:
head of myosin
attach to actin
actin
myosin
Z line
33.2 Muscular System
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