Muscular System

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Chapter 9

• Muscular System

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Function of Skeletal Muscles

• The functions include movement, heat production,
  and posture.
• Movement - contraction of muscles.
• Heat production - maintains homeostasis of
  temperature.
• Posture - maintenance of partial muscle
  contraction.
• Allows sitting, standing

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Muscle and Muscle Fiber Structure

• A muscle is composed of many muscle fibers
  (muscle fiber muscle cell). The individual
  muscles are separated from each other and held in
  place by a covering called the FASCIA. This
  fascia also forms TENDONS and APONEUROSES
  connecting muscles to bones and muscles to
  muscles.

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Microscopic Structure of Skeletal Muscles

• Composed of bundles of fibers, not cells.
• Fibers
• Sarcolemma - plasma membrane of the muscle.
• Sarcoplasma - cytoplasm of a fiber.
• Sarcoplasmic reticulum like the endoplasmic
  reticulum, tunnels throughout fiber.
• Contains many mitochondria and several nuclei -
  more ATP production.

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Microscopic Structure of Skeletal Muscles
Continued

• Fibers
• Myofibrils - bundles of very fine fibers that
  extend through the sarcoplasm.
• Each myofibril is made of many protein filaments
  called myofilaments.

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2 Types of Myofilaments

• Myosin -Thick filaments
• Actin - Thin filaments

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Movement

• Actin and Myosin filaments are arranged in an
  overlapping pattern of light (I bands) and dark
  (A bands). In the middle of each I band is a
  line called a Z line. The section of a
  myofibril from one Z-line to the next Z-line is
  called a SARCOMERE. The arrangement of these
  sarcomeres next to each other produces the
  STRIATIONS of the skeletal muscle fibers.

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Movement Continued

• Myosin and actin interact
• Myofibrils pull toward sarcomere
• Sarcomeres shorten, myofibrils shorten, muscle
  shortens contraction.
• All-or-None Law
• contract with all force possible under conditions
  or do not contract at all.

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Energy Sources

• ATP - Adenosine Triphosphate
• Breakdown bonds between the phosphate groups
  provides energy for contraction.
• Creatine Phosphate provides energy for the
  regeneration of ATP.
• For more intense contractions, generation of ATP
  comes from food intake - Cellular respiration.
• ATP is made in the mitochondria.

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Energy Sources Continued

• Only 25 of energy produced during cellular
  respiration is used in metabolic processes the
  rest is in the form of HEAT. This is what
  produces our body heat and maintains body
  temperature. More muscle activity more heat.

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Connective Tissue Components

• Epimysium - sheath that envelopes each muscle
• Perimysium - extension of sheath between fiber
  bundles - like a partition.
• Endomysium - extension of sheath between
  individual fibers.

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Connective Tissue Components Continued

• Tendon - extention of three above structures from
  the muscle to its other end which is continuous
  with the periosteum (fiberous tissue that covers
  bone)
• Shin splints - tendon not torn because of
  strength, but can be pulled away from bone.
• Tendon sheath - tube shaped structure, encloses
  certain tendons - ex. wrist, ankle
• Lined with synovial fluid
• Allows easy movement

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Connective Tissue Components Continued

• Deep fascia - extension from epi, peri, and
  endomysium of muscles and their attachment to
  bone.

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Muscle Names

• Reason for muscle names
• Action - Flexor, extensor
• Direction of fibers
• Location - Femoris
• Number of divisions
• Shape
• Points of attachment

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Examples Deltoid - shaped like a
triangleOrbicularis - orbit, circular
muscleMajor/Minor - large/small or sometimes
upper and lowerVastus - largeDorsi or Dorsal -
backsideInfra / Supra - lower and upperLongis /
Brevis - long/ short (brief) Medialis /
Lateralus - medial (toward the inside), lateral
(toward the outside) Some muscles are named for
the region or the bone they are attached to, for
example biceps femoris - two headed muscle
attached to the femurextensor carpi radialis
longus - long muscle that runs the length of the
radius (bone) to the carpals (wrist bones) that
extends the fingers
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Muscle Groupings

• Muscles are grouped according to location.
• Muscles are grouped according to function.

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5
1
2

                        
6
7
3
Trapezius
4
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Anterior Muscles
1
2
3

4
5
14
6
                        
15
7
16
9
10
19
18
11
20
21
12
13
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Posterior Muscles
1
2
3

6
                        
12
13
7
9
15 Rectus femoris
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14
10
11
16
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Principles of Skeletal Muscle Function

Contract only if stimulated (nerves)
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Principles of Skeletal Muscle Function Continued

• Types of Contractions
• Tonic - continual, partial contraction - tautness
  (occurs only when awake).
• Isotonic - contraction remains the same, but
  length of muscle changes shortens (walking,
  running, lifting an object).
• Isometric - muscle length remains the same,
  muscle tension increases (push against wall).
• Convulsions - abnormal, uncoordinated
  contractions.

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Principles of Skeletal Muscle Function
Continued

• Produce movement by pulling on bones
• Bones serve as levers, and joints serve as
  fulcrums of the levers.
• Muscles move parts other than where they lie.

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Principles of Skeletal Muscle Function
Continued

• Act in groups
• Prime movers - contraction produces movement
  (primarily responsible for producing an action).
• Antagonists - relaxation of muscle while prime
  movers are contracting.
• antagonist of a flexor is an extensor
  
  
• Synergists - contract at same time as prime,
  assist in movement.

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Skeletal Muscle Contraction

• Neurotransmitter must stimulate muscle -
  acetylcholine for muscle contraction.
• ATP must be present at the same time
• Decrease acetylcholine muscle relaxation

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Energy Sources for Contraction
           Creatine phosphate 1. contains high
energy phosphate bonds 2. stores excess energy
released from mitochondria 3. decrease ATP----
energy from creatine turns to ADPADP is coverted
to ATP 4. creatine is depleted rapidly in active
muscles 5. can ingest extra creatine to increase
body supply.

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Muscle Fatigue

• Inability of muscle to contract
• Due to accumulation of lactic acid
• Could coincide with cramping due to a lack of ATP

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Rigor Mortis

• Partial muscle contraction after death
• Can continue for 72 hours

                        
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Posture

•   Maintenance
• Muscles exert continual pull on bone in
  opposite direction (extensors).
• 2. Tonicity (elastic tension of living muscles)
  allows pull against gravity
• a. Absent during sleep
• b. Will not counteract gravity
• c. Cannot sleep standing up

                        
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Posture Continued
Importance of good posture 1. Decreases work
on muscles 2. Bad posture puts strain on
ligaments 3. Bad posture interferes with
respiration, digestion, etc