The Muscular System and Integumentary System

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The Muscular System and Integumentary System

• Ms. Hoffman
• September 13, 2004

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How do Muscles and Bones Interact?

• Skeletal muscles generate force and produce
  movement by contracting, or pulling on body parts
• Skeletal muscles are joined together by tough
  connective tissues called tendons
• Tendons are attached so that they pull on bones
  and make them work like levers
• Most skeletal muscles work in opposing pairs
• When one muscle contracts, the other relaxes
• Ex. When the biceps muscle contracts, the triceps
  is relaxed and you can curl your arm
• Ex. When the biceps muscle relaxes, the triceps
  muscle contracts and you can extend your arm

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What is Muscle Tone?

• Skeletal muscles remain in a state of partial
  contraction
• At all times, a few muscle cells are being
  stimulated while others are not
• Limited stimulation causes a tightening of some
  muscles called resting muscle tone
• Resting muscle tone is responsible for keeping
  the back and legs straight and the head upright,
  even when you are relaxed
• Regular exercise increases muscle tone

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Muscles

• Provide the forces that put the body into motion
• More than 40 of the mass of the average human
  body is muscle
• Fxns regulate blood pressure, move food through
  the digestive system, power every movement in the
  body

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Types of Muscle Tissue

• Muscle tissue is found everywhere in the
  bodyfrom beneath the skin to deep within the
  body
• There are three different types of muscle tissue
  skeletal, smooth, and cardiac
• Each type of muscle tissue has a different
  structure and plays a different role in the body

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Skeletal Muscles

• Usually are attached to bones
• Responsible for voluntary movements like dancing,
  running, jumping
• Have alternating light and dark bands or stripes
  called striations when viewed under the
  microscope
• Most skeletal muscles are controlled by the
  central nervous system
• Skeletal muscle cells are large cells, have many
  nuclei, and vary in length from 1 mm 30 cm
• May be referred to as muscle fibers because these
  muscle cells are so long and slender
• Complete skeletal muscles consists of muscle
  fibers, connective tissues, blood vessels, and
  nerves

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Skeletal Muscle
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Smooth Muscles

• Usually are not under voluntary control
• Spindle-shaped, one nucleus, no striations
• Found in hollow structures like the stomach,
  blood vessels, and small and large intestines
• Fxns move food through your digestive tract,
  control the way blood flows through your
  circulatory system, decrease the size of the
  pupils of your eyes in bright light
• May function without nervous stimulation
• Connected to one another by gap junctions that
  allow electrical impulses to travel directly from
  one muscle cell to a neighboring muscle cell

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Smooth Muscle
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Cardiac Muscle

• Only found in the heart
• Striated like skeletal muscle
• Usually only have one nucleus like smooth muscle
• Usually not under the direct control of the
  central nervous system
• Cardiac cells are connected to their neighboring
  cells by gap junctions

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Cardiac Muscle
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Muscle Contraction

• Muscle fibers in skeletal muscles are made of
  smaller structures called myofibrils
• Each myofibril is made of even smaller structures
  called filaments
• Thick and thin filaments alternate to create the
  striated appearance of muscle cells
• Thick filaments are made of a protein called
  myosin
• Thin filaments are made of a protein called actin

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Muscle Contraction

• Myosin and actin filaments are arranged along a
  muscle fiber in units called sarcomeres
• Sarcomeres are separated from each other by
  regions called Z discs
• During relaxation of a muscle there are no thin
  actin filaments in the center of a sarcomere

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Muscle Contraction

• Myosin and actin filaments are what cause muscles
  to contract
• A muscle contracts when the thin actin filaments
  in a muscle fiber slide over the thick myosin
  filaments
• For contraction to occur, the thick myosin
  filaments must form a cross-bridge with the thin
  actin filament
• The cross-bridge changes shape and pulls on the
  actin filament which slides toward the center of
  the sarcomere
• The distance between the Z discs decreases
• The cross-bridge detaches from the actin filament
  and the cycle is repeated when the myosin binds
  to another site on the actin filament

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What Supplies the Energy for Muscle Contraction?

• The energy of muscle contraction is supplied by
  ATP
• One molecule of ATP supplies the energy for one
  interaction between a myosin cross-bridge and an
  actin filament
• Lots of ATP is needed!
• ATP can be produced by cells via cellular
  respiration

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Controlling Muscle Contractions

• Motor neurons connect the central nervous system
  (brain and spinal cord) to skeletal muscle cells
• Impulses from motor neurons control the
  contraction of skeletal muscle fibers
• Neuromuscular junction- the point of contact
  between a motor neuron and a skeletal muscle cell

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Controlling Muscle Contractions

• At the neuromuscular junction there are pockets
  (vesicles) in the terminals of the motor neuron
  that release a neurotransmitter called
  acetylcholine
• Neurotransmitters are chemicals used by neurons
  to transmit an impulse across a synapse (space
  where a message can be relayed) to another cell
• Acetylcholine molecules cross the synapse and
  cause an impulse in the cell membranes of the
  muscle fiber
• This impulse causes calcium ions to be releases
  within the fiber
• The calcium ions affect proteins that regulate
  how the actin and myosin filaments interact
• The contraction of a muscle fiber is an all- or
  -none process

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