Muscle Physiology

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Chapter 6
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• Use the terminology associated with the
  musculature system
• Learn about the following
• Different types of muscle cells
• Muscle tissue development
• Gross and fine muscle structure
• Gross muscle function
• Muscle cell physiology
• Muscle types and actions
• Muscle development and growth
• Understand the aging and pathology of the
  musculature

Chapter 6 The Muscular System
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Overview
Muscle cells change their shape by shortening
along one or more planes this is also called
contraction. Over half the bodys mass is
composed of muscle tissue, and over 90 of this
muscle tissue is involved in skeletal movement.
Chapter 6 The Muscular System
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Functions of the Muscular System

• Moves the skeletal system
• Passes food through the digestive system
• Helps in dilation and constriction of blood
  vessels
• Helps in movement of air in and out of lungs
• Helps with movement of urine out of the bladder.
• Pumping blood throughout the body

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Muscle Tissue

• Muscle is composed of contractile cells.
• Contractile cells can change their shape.
• Over half of the bodys mass is composed of
  muscle tissue.
• 90 of this muscle tissue is involved in skeletal
  movement.
• The rest would be used in cardiac tissue (the
  heart) and smooth muscle tissue (the digestive
  organs and circulatory system)

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Muscle Tissue

• Contractile cells have high energy needs.
• So they need a lot of blood supply.
• Blood supplies muscles (contractile cells) with
• Glucose
• Oxygen
• Electrolytes-ions essential for muscle
  contractions
• Blood removes large amounts of metabolic wastes.
• Muscles along with nervous tissue consume almost
  70 of the food energy taken into the body every
  day.
• Like the skeletal system muscle consumes a lot of
  calcium
• Body Mass Index (BMI) is an indirct measure of
  body density.

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Muscle

• Three types of muscle are found in the human
  body
• Smooth muscle
• Cardiac muscle
• Skeletal muscle

Chapter 6 The Muscular System
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Skeletal Muscle

• Long cylindrical cells
• Many nuclei per cell because several myoblasts
  are fused together
• Striated
• Voluntary
• Rapid contractions

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Cardiac Muscle

• Branching cells
• One or two nuclei per cell
• Striated
• Involuntary
• Medium speed contractions

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Smooth Muscle

• One nucleus per cell
• Nonstriated
• Involuntary
• Slow, wave-like
• Contractions
• Location lining of blood
• vessels, digestive organs,
• urinary system

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Skeletal Muscle Structure

• 1st level- Most basic -the muscle fiber or cell
• Each muscle fiber is covered with a connective
  layer called the endomysium.
• 2nd level- Bundles of muscle cells are called
  fascicles (fasciculi)
• Perimysium-a thin connective tissue covering that
  surrounds each fascicle.
• 3rd and highest organ level of skeletal muscle
  structure Epimysium-a fibrous connective tissue
  that covers the gross muscle and also the tendons
  that attach muscle to bone and skin.

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Development of Muscle tissue

• Myogenesis- process of muscle tissue developing
  from mesoderm cells.
• Myoblasts- stem cells that form muscle tissue.
• Growth factors-are chemicals that act as signals
  to initiate cell division and differentiation of
  muscle tissue.
• Over a dozen genes involved in muscle cell
  development.

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Muscle Cell Structure

• Skeletal muscle cells are long, cylindrical cells
  covered with an excitable membrane and filled
  with a specialized cytoskeleton.
• Sarcolemma-membrane of muscle cells
• Sarcoplasm- cytoplasm of muscle cells
• Cytoskeleton is located in the sarcoplasm --
• Cytoskeleton is composed of bands of proteins
  called myofilaments.
• Three types of myofilaments
• Thick- composed of myosin
• Thin- composed of actin (majority), wrapped
  around a length of tropomyosin, and speckled on
  the coils of the actin are small proteins called
  troponin.
• Vertical- composed of the protein titin, it is
  considered an elastic myofilament.

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Structure of the muscle fiber (muscle cell)

• Myofibrils-long cords of myofilaments (bands of
  proteins making up the cytoskeleton) that form
  parallel bundles that comprise most of a muscle
  cells interior.
• Sarcomere-the contractile unit of a muscle cell.
  (These chains of sarcomeres form myofibrils).
• Muscle cell (fiber)-is made up of many bundled
  myofibrils that run parallel to one another for
  the length of the cell.
• Thick and thin myofilaments arrange to form an
  overlapping pattern within a sarcomere.
• The thin myofilaments (actin) are attached to a
  protein structure called the Z-line.
• The thick myofilaments (myosin) seem to be
  floating between the rungs of the thin
  myofilaments, but they are held in place by
  invisible titin filament that attaches them to
  Z-line.

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Microanatomy of Skeletal Muscle
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Muscle Cell Structure

• Z-line
• Function
• To keep the thick and thin filaments aligned.
• To help control the stretch and recoil limits in
  a muscle.
• Serves a role in muscle contractions.
• It anchors the sarcomeres to the sarcolemma.
• Any movement of the Z-line changes the length of
  the muscle.
• Sarcoplasmic reticulum
• Function
• A system of inner membrane tubes that store and
  transport
• large amounts of calcium needed for muscle
  contraction.

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H Band
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Sarcomere Relaxed
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Sarcomere Partially Contracted
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Sarcomere Completely Contracted
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Muscle cell contraction

• Simultaneous shortening of all the sarcomeres
  within a cell.
• Three stages
• Neural stimulation
• Muscle cell contraction
• Muscle cell relaxation

• Neural stimulation
• Takes place at neuromuscular junction
• Contraction is initiated when end of nerve cell
  releases neurotransmitter
• Neurotransmitter is acetylcholine which binds to
  receptors in sarcolemma
• This causes changes in sarcolemma and allows
  transport of ions across
• the membrane
• Sodium ions flow into the muscle cell and
  potassium flows out of the cell
• Causes sarcoplsmic reticulum to release calcium
• The flow of calcium initiates the muscle
  contraction phase.

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Muscle cell contraction

• Muscle cell contraction
• Calcium binds to troponin on actin myofilamentts
• This causes binding site to open up so that
  myosin can bind to actin
• Also activates the attachment of ATP to myosin
• ATP provides energy for myosin head to swivel and
  hook on to the binding
• site on actin
• The swivel movement brings the two Z lines closer
  together
• This shortens the sarcomere
• The complete contraction of a muscle cell
  requires several cycle of neural
• stimulation and contraction phases.

• Muscle cell relaxation
• This begins when there is no more neural
  stimulations
• The sodium and potassium levels are back like
  they were originally
• The sarcoplasmic reticulum has recovered most of
  the calcium
• This causes a release of the myosin heads from
  actin
• There is no mechanism within the muscle cell for
  lengthening the sarcomere
• The muscle cell remains contracted
• The muscle is fully recovered when a body
  movement causes the sarcomere
• to stretch.

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• Rigor mortis
• Causes when calcium leaks out of the SR into the
  sarcomere.
• This is common after death
• Eventually, muscle cell structures begin to decay
• Causing muscles to become soft and loose

• Other factors that ensure adequate muscle
  contractions
• Having creatine phosphate present
• It is a molecule that stores energy in muscle
  cells
• It collects energy from ATP and can store energy
  for long periods of time.
• It then transfers energy back to ATP when muscle
  contractions require energy
• Having Glycogen present it is a stored form of
  glucose, important source of
• energy reserve for muscle action
• Having Myoglobin present
• It is a red colored chemical that stores oxygen
  for certain muscle cells.
• Having oxygen in muscle cells permits them to
  provide large amounts of ATP
• during continuous or heavy work

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Neuromuscular Junction
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Neuromuscular Junction

• Axon of motor junction 3. Muscle fiber
• 2. Neuromuscular junction 4. Myofibril

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Neuromuscular Junction

• Presynaptic terminal 3. Synaptic vesicles
• 2. Postsynaptic terminal 4. Synaptic cleft
• (sarcolemma) 5. Mitochondria

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Acetylcholine Opens Na Channel
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Muscle Contraction Summary

• Nerve impulse reaches myoneural junction
• Acetylcholine is released from motor neuron
• Ach binds with receptors in the muscle membrane
  to allow sodium to enter
• Sodium influx will generate an action potential
  in the sarcolemma

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ATP
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Creatine

• Molecule capable of storing ATP energy

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Creatine Phosphate

• Molecule with stored ATP energy

Creatine phosphate ADP
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Human Skeletal Muscles