Chapter 9 The Muscular System

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Chapter 9The Muscular System
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Skeletal Muscle Structure

• Tendon connect
• muscle to bone
• Fascia outermost
• covering covers entire muscle continuous
• w/tendon separates
• muscle from adjacent
• muscles
• Aponeuroses- connect muscle to
• muscle

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Skeletal Muscle Structure

• Coverings
• Epimysium covers entire muscle
• (under fascia)
• Perimysium covers
• muscle bundle (fascicle)
• Endomysium
• covers each fiber (cell)
• Sarcolemma cell
• membrane

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Skeletal Muscle Structure Cont.
Skeletal Muscle Structure

• Sarcoplasmic reticulum (SR) channels for
  transport
• Myofibrils threads that compose muscle fibers
  contain protein filaments
• 1. actin thin
• 2. myosin thick

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Skeletal Muscle Structure
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Muscle Fiber (muscle cell)

• Cisternae of SR
• enlarged portions
• Transverse tubules
• (T-tubules)
• important
• in muscle contraction
• Sarcoplasm cytoplasm

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Breakdown of Skeletal Muscle
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Parts of a Sarcomere (functional unit of a muscle)

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Parts of a Sarcomere

• Z lines end points
• M line middle
• I band on either
• side of Z line actin
• filaments only
• H zone on either
• side of M line
• myosin filaments only
• A band overlapping
• actin myosin filaments

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Parts of a Sarcomere
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Neuromuscular Junction junction b/t motor
neuron muscle

• Motor neuron carries
• impulse from brain or
• spinal cord
• to muscle
• Motor end plate end
• of muscle fiber many
• nuclei mitochon-
• dria located here

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Neuromuscular Junction

• Neurotransmitters
• (ntm) chemicals that
• help carry impulses
• Motor unit 1 motor
• neuron fibers that
• it stimulates
• Synaptic vesicles
• store neurotransmitter
• most common acetylcholine (ACh)

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Electron Micrograph Neuromuscular Junction
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Neuromuscular Junction Animation

• Neuromuscular Junction Animation

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4 Proteins in Muscle Cells
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Troponin Tropomyosin

• 4 proteins are found in muscle cells actin,
  myosin, troponin tropomyosin
• troponin appear
• as globules provide
• a binding site for Ca²
• tropomyosin
• appear as ribbons
• cover the myosin
• cross-bridge
• binding sites in a
• relaxed muscle

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Sliding Filament Theory (How Muscles Contract)

• Muscle fiber stimulated by release of ACh from
  synaptic vesicles of neuron
• ACh causes impulse to travel to muscle cell
  membrane
• Transverse tubules (T-tubules) carry impulse deep
  into muscle fibers
• Sarcoplasmic reticulum releases Ca ions (Ca²)
• Ca² bind to troponin, tropomyosin moves,
  exposing binding sites on actin filaments

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Cross Bridge Animation

• cross bridge animation

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Sliding Filament Theory (How Muscles Contract )

• Linkages form b/t actin myosin
• Actin filaments move inward, shortening the
  sarcomere
• Muscle fiber relaxes when Ca² are transported
  back to S.R.
• The enzyme cholinesterase (or AChesterase)
  decomposes ACh

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Sliding Filament Theory

• Relaxed muscle binding sites on actin are
  covered by tropomyosin

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Sliding Filament Theory

• Ca² binds to troponin
• Tropomyosin
• slides out of the way
• Myosin binds to actin
• pulls inward
• Sarcomeres
• shorten muscle
• contracts

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Sliding Filament Animation

• sliding filament animation

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Sliding Filament Theory
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Energy for Muscle Contraction

• ATP (adenosine triphosphate)
• provides the energy for muscle contraction
• When ATP is converted to ADP (adenosine
  diphosphate) by losing the last phosphate,
  energy is released.

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Energy for Muscle Contraction

• Cells depend on cellular respiration
• of glucose to synthesize ATP
• An additional source is creatine phosphate

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Energy for Muscle Contraction

• Creatine phosphate stores excess energy
• Can be used to convert ADP back into ATP
• Anaerobic respiration (in the absence of O2)
  provides few ATPs, while aerobic resp. (in the
  presence of O2) provides many ATPs

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Creatine Phosphate
High amts. of ATP - ATP is used to Low
amts. of ATP CP is used synthesize CP, which
stores energy to resynthesize ATP. for
later use.
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Importance of Myoglobin

• l.a. carried by blood to
• liver liver can convert
• l.a. to glucose, but
• requires ATP (ATP being
• used for muscle contraction)
• myoglobin stores O2
• in muscle cells gives
• muscle its red color

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Aerobic vs. Anaerobic Respiration
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Aerobic vs. Anaerobic Respiration

• Carried by
  blood to liver liver
  can convert l.a. to glucose, but
  requires ATP (ATP being used for
  muscle contraction)
• Imp. b/c blood supply
• during muscle contr.
• may decrease
• As l.a.
  accumulates, O2 debt occurs

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Oxygen Debt

• Strenuous exercise leads to O2 deficiency
  lactic acid buildup
• ATP provides energy for muscle contraction
• Amt. of O2 needed to convert accumulated l.a. to
  glucose restore ATP levels O2 debt
• L.A. accumulation leads to muscle fatigue b/c pH
  of muscle cell is lowered muscle cannot contract

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Muscle Cramp

• Muscle cramp fatigued muscle has lack of ATP
  needed to move Ca² back into S.R. cross
  bridges not broken
• Rigor mortis takes up to 72 hrs. to occur
  sarcolemma becomes more permeable to Ca² ATP
  levels insufficient

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Myogram

• Pattern or graph of
• a muscle contraction
• A single contraction is
• called a muscle twitch
• 3 parts
• Latent (lag) phase
• brief pd. of delay
• b/t when the stimulus is applied actual
  contraction occurs
• Contraction
• Relaxation return to
• original state

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Patterns of Contraction

• a) Muscle Twitch
• single contraction
• b) Staircase Effect
• many stimuli closely
• spaced w/complete
• relaxation in b/t each
• contraction generate
• incr. force

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Patterns of Contraction

• c) Summation when
• the 2nd stimulus occurs
• during the relaxation
• pd. of 1st contr. the
• 2nd contr. generates
• more force
• d) Tetany when
• twitches fuse into
• 1 sustained contr.

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Muscle Facts

• If a muscle is stimulated twice in quick
  succession, it may not respond the 2nd time
  called refractory period
• Threshold the minimum stimulus needed to cause
  a contraction
• All-or-none increasing the strength of the
  stimulation does NOT incr. the degree of
  contraction (a muscle contracts completely or not
  at all)

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More Facts

• Incr. stimulation from motor neurons causes a
  greater of motor units to contract vice versa
• Called recruitment of motor units
• Incr. the rate of stimulation also incr. the
  degree of contraction
• Muscle tone a sustained contraction caused by
  nerve impulses from s.c. to a small of muscle
  fibers in the back, neck, etc. maintains posture

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Origin Insertion

• Origin end of muscle
• that attaches to stationary
• bone
• Insertion end of muscle
• that attaches to moving
• bone
• During contr., insertion
• is pulled toward origin

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Muscle Functions in Groups

• Prime mover responsible for most of the
  movement (ex.- biceps)
• Synergist aids the prime mover
• Antagonist resists the prime mover
  causes movement in the opposite
  direction (ex. - triceps)

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Structural Differences of 3 Types of Muscle
Skeletal Muscle Smooth Muscle Cardiac Muscle
Cells elongated w/multiple nuclei/cell Cells spindle-shaped w/1 nucleus/cell Cells branching w/1 nucleus/cell
T-tubules present No T-tubules T-tubules lg. releases lg. amts. of Ca can contract longer (Ca channel blockers)
Striated/voluntary Non-striated/invol. Striated/invol.
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Functional Differences of 3 Types of Muscle
Skeletal Muscle Smooth Muscle Cardiac Muscle
Needs nerve impulse for contraction Displays rhythmicity cells stimulates each other (as in peristalsis) Displays rhythmicity self-excitation
Ca² binds to troponin Ca² binds to calmodulin Ca² binds to troponin
Not affected by hormones Hormones may affect contraction Hormones may affect rate of contr.
Contracts relaxes rapidly Slower to contract but can maintain contraction longer Contracts relaxes at a certain rate
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Functional Differences - Continued
Skeletal Muscle Smooth Muscle Cardiac Muscle
Not affected by stretching Stretching of fibers may stimulate contr. (ex.-stomach) Remains in a refractory pd. until contraction ends (tetany wont occur)

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Fast Twitch vs. Slow Twitch Muscle
Fast Twitch Slow Twitch
Contracts quickly, tires easily (sprinter) Contracts slowly, tires slowly (long distance)
Fewer mitochondria More mitochondria
Less myoglobin More myoglobin
White muscle Red muscle
Composes smaller muscles (eyes, hands, etc.) Composes lg. muscles (legs, back, etc.)
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Levers

• Parts of a lever
• wt., force, pivot
• 3 types of levers
• 1st class W-P-F
• (seesaw/scissors)
• 2nd class P-W-F
• (wheelbarrow)
• 3rd class W-F-P
• (forceps)

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Bones Muscles as Levers

• Forearm bends 3rd class lever (biceps attaches
  at a pt. on the radius below the elbow joint)
• Forearm straightens - 1st class lever ((triceps
  attaches at a pt. on the ulna
• above the elbow joint)

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Bones Muscles as Levers
Standing on tip-toe 2nd class
lever (P-W-F)