Bio211 Lecture 16

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Mariebs Human Anatomy and Physiology Ninth
Edition Marieb w Hoehn
Chapter 9 Muscles and Muscle Tissue Lecture 16
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Lecture Overview

• Types, characteristics, functions of muscle
• Structure of skeletal muscle
• Mechanism of skeletal muscle fiber contraction
• Energetics of skeletal muscle contraction
• Skeletal muscle performance
• Types of skeletal muscle contractions
• Comparison of skeletal muscle with smooth muscle
  and cardiac muscle

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Muscular System
Review - Three Types of Muscle Tissues

• Skeletal Muscle
• usually attached to bones
• under conscious control (voluntary)
• striated
• multinucleated

• Cardiac Muscle
• wall of heart
• not under conscious control
• striated
• branched

• Smooth Muscle
• walls of most viscera, blood vessels, skin
• not under conscious control
• not striated

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Functions of Muscle

• Provide stability and postural tone
• Fixed in place without movement
• Maintain posture in space
• Purposeful movement
• Perform tasks consciously, purposefully
• Regulate internal organ movement and volume
  (mostly involuntary)
• Guard entrances/exits (digestive/urinary)
• Generation of heat (thermogenesis)

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Characteristics of All Muscle Tissue

• Contractile
• Ability to shorten with force
• CANNOT forcibly lengthen
• Extensible (able to be stretched)
• Elastic (returns to resting length)
• Excitable (can respond electrical impulses)
• Conductive (transmits electrical impulses)

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Structure of a Skeletal Muscle
Figure from Holes Human AP, 12th edition, 2010

• epimysium (around muscle)
• perimysium (around fascicles)
• endomysium (around fibers, or cells)

Alphabetical order largest to smallest fascicle,
fiber, fibril, and filament
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Skeletal Muscle Fiber (Cell)
Fully differentiated, specialized cell its
structures are given special names

• sarcolemma (plasma membrane)
• sarcoplasm (cytoplasm)
• sarcoplasmic reticulum (ER)
• transverse tubule
• triad
• cisternae of sarcoplasmic reticulum (2)
• transverse tubule
• myofibril (1-2 µm diam.)

Figure from Saladin, Anatomy Physiology,
McGraw Hill, 2007
Transverse tubules contain extracellular fluid (?
Na, ? K) Sarcoplasmic reticulum is like the
ER of other cells but it contains ? Ca2
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Structure of the Sarcomere
Figures From Marieb Hoehn, Human Anatomy
Physiology, 9th ed., Pearson, 2013

• I band
• A band
• H zone
• Z line
• M line

( 2µm long)
The sarcomere is the contractile unit of skeletal
(and cardiac) muscle
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Structure of the Sarcomere
A in A band stands for Anisotropic (dArk) I
in I band stands for Isotropic (LIght)
Zones of non-overlap I band (thin filaments),
and H zone (thick filaments) A sarcomere runs
from Z line (disk) to Z line (disk) (From Z to
shining Z!)
Figure from Saladin, Anatomy Physiology,
McGraw Hill, 2007
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Preview of Skeletal Muscle Contraction

• Major steps
• Motor neuron firing
• Depolarization (excitation) of muscle cell
• Release of Ca2 from sarcoplasmic reticulum
• Shortening of sarcomeres
• Shortening of muscle/CTs and tension produced

T Tubule
Sarcoplasmic reticulum
Physiology here we come!!
Figure from Martini, Anatomy Physiology,
Prentice Hall, 2001
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Grasping Physiological Concepts

• The steps in a physiological process give you the
  when, i.e. tell you when things happen and/or
  the order in which they happen.
• For each step in a process, you should MUST ask
  yourself the following questions - and be sure
  you get answers!
• How? (How does it happen?)
• Why? (Why it happens and/or why its important?)
• What? (What happens?)

See Figures 9.7 and 9.8 in your textbook for
excellent overall summaries of the muscle
contraction process
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Contraction of the Sarcomere
When skeletal muscle contracts - H zones and I
bands get smaller - Areas of overlap get
larger - Z lines move closer together - A band
remains constant
BUT lengths of actin and myosin filaments dont
change
How can this be explained?
Figure from Martini, Anatomy Physiology,
Prentice Hall, 2001
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Sliding Filament Theory
Figure from Holes Human AP, 12th edition, 2010
Theory used to explain these observations is
called the sliding filament theory

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Myofilaments

• Thick Filaments
• composed of myosin
• cross-bridges

• Thin Filaments
• composed of actin
• associated with troponin and tropomyosin

Figures From Marieb Hoehn, Human Anatomy
Physiology, 9th ed., Pearson, 2013
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Mechanism of Sarcomere Contraction
Figure from Holes Human AP, 12th edition, 2010
When you think myosin, think mover 1. Bind2.
Move3. Detach4. Reset
Ca2 ? troponin
myosin ? actin
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Mechanism of Sarcomere Contraction
Figure from Holes Human AP, 12th edition, 2010
1. Bind
4. Reset

2. Move
3. Detach
What would happen if ATP was not present?
Cycle repeats about 5 times/secEach power stroke
shortens sarcomere by about 1So, each second
the sarcomere shortens by about 5
See Textbook Figure 9.12 (Focus Cross Bridge
Cycle)
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Neuromuscular Junction

• site where axon and muscle fiber communicate
• motor neuron
• motor end plate
• synaptic cleft
• synaptic vesicles
• neurotransmitters

The neurotransmitter for initiating skeletal
muscle contraction is acetylcholine (ACh)
Ca2
SR
Ca2
Ca2
Ca2
Ca2
Figures from Saladin, Anatomy Physiology,
McGraw Hill, 2007
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Stimulus for Contraction Depolarization

• nerve impulse causes release of acetylcholine
  (ACh) from synaptic vesicles
• ACh binds to acetylcholine receptors on motor
  end plate
• generates a muscle impulse
• muscle impulse eventually reaches sarcoplasmic
  reticulum (via T tubules) and Ca2 is released
• acetylcholine is destroyed by the enzyme
  acetylcholinesterase (AChE)

Figure from Martini, Anatomy Physiology,
Prentice Hall, 2001
Linking of nerve stimulation with muscle
contraction is called excitation-contraction
coupling (See Fig 9.11 in textbook)
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Summary of Skeletal Muscle Contraction
Figure from Martini, Anatomy Physiology,
Prentice Hall, 2001
Contraction
Relaxation
See Textbook Figure 9.12 (Focus Cross Bridge
Cycle)
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Modes of ATP Synthesis During Exercise
Muscle stores enough ATP for about 4-6 seconds
worth of contraction, but is the only energy
source used directly by muscle. So, how is
energy provided for prolonged contraction?
Continual shift from one energy source to another
rather than an abrupt change
Figures From Marieb Hoehn, Human Anatomy
Physiology, 9th ed., Pearson, 2013
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Energy Sources for Contraction
Figures From Marieb Hoehn, Human Anatomy
Physiology, 9th ed., Pearson, 2013
myoglobin stores extra oxygen so it can rapidly
supply muscle when needed
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Oxygen Debt (Excess Post Exercise O2 Consumption
EPOC)
EPOC - amount of extra oxygen needed by liver to
convert lactic acid to glucose, resynthesize
creatine-P, make new glycogen, and replace O2
removed from myoglobin.

• when oxygen is not available
• glycolysis continues
• pyruvic acid converted to lactic acid (WHY?)
• liver converts lactic acid to glucose

Figure from Holes Human AP, 12th edition, 2010
(The Cori Cycle)
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Muscle Fatigue

• Inability to maintain force of contraction
  although muscle is receiving stimulus to contract
• Commonly caused by
• decreased blood flow
• ion imbalances
• accumulation of lactic acid
• relative (not total) decrease in ATP
  availability
• decrease in stored ACh
• Cramp sustained, involuntary contraction

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Length-Tension Relationship
Figures From Marieb Hoehn, Human Anatomy
Physiology, 9th ed., Pearson, 2013
Maximum tension in striated muscle can only be
generated when there is optimal (80-100) overlap
between myosin and actin filaments
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Muscular Responses

• Threshold Stimulus
• minimal strength required to cause contraction
  in an isolated muscle fiber

Figure From Marieb Hoehn, Human Anatomy
Physiology, 9th ed., Pearson, 2013

• Record of a Muscle Contraction myogram
• latent period
• period of contraction
• period of relaxation
• refractory period
• all-or-none response

An individual muscle fiber (cell) is either on
or off and produces maximum tension at that
resting length for a given frequency of
stimulation
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Treppe, Wave Summation, and Tetanus
Wave (Temporal) Summation
Treppe (10-20/sec)
Little/no relaxation period
Complete Tetanus (gt50/sec)
Incomplete Tetanus (20-30/sec)
Tetany is a sustained contraction of skeletal
muscle
Figure from Martini, Anatomy Physiology,
Prentice Hall, 2001
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Treppe, Wave Summation, and Tetanus

• Treppe, Wave Summation, and Tetanus
• all involve increases in tension generated in a
  muscle fiber after more frequent re-stimulation
• The difference among them is WHEN the muscle
  fiber receives the second and subsequent
  stimulations
• Treppe stimulation immediately AFTER a muscle
  cell has relaxed completely.
• Wave Summation Stimulation BEFORE a muscle
  fiber is relaxed completely
• Incomplete (unfused) tetanus partial relaxation
  between stimuli
• Complete (fused) tetanus NO relaxation between
  stimuli

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Motor Unit

• single motor neuron plus all muscle fibers
  controlled by that motor neuron

Figure From Marieb Hoehn, Human Anatomy
Physiology, 9th ed., Pearson, 2013
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Recruitment of Motor Units

• recruitment - increase in the number of motor
  units activated to perform a task

• whole muscle composed of many motor units

• as intensity of stimulation increases,
  recruitment of motor units continues, from
  smallest to largest, until all motor units are
  activated

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Sustained Contractions

• smaller motor units recruited first
• larger motor units recruited later
• produces smooth movements
• muscle tone continuous state of partial
  contraction

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Types of Contractions

• concentric shortening contraction

• isotonic muscle contracts and changes length

• eccentric lengthening contraction

• isometric muscle contracts but does not
  change length

Figure from Holes Human AP, 12th edition, 2010
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Types of Skeletal Muscle Fibers
Slow Oxidative (SO) (REDSOX) Fast Oxidative-Glycolytic (FOG) Fast Glycolytic (FG)
Alternate name Slow-TwitchType I Fast-TwitchType II-A Fast-Twitch Type II-B
Myoglobin (color) (red) (pink-red) (white)
Metabolism Oxidative(aerobic) Oxidative and Glycolytic Glycolytic (anaerobic)
Strength Small diameter, least powerful Intermediate diameter/strength Greatest diameter, most powerful
Fatigue resistance High Moderate Low
Capillary blood supply Dense Intermediate Sparse
All fibers in any given motor unit are of the
same type
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Types of Skeletal Muscle Fibers
All fibers in any given motor unit are of the
same type
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Smooth Muscle Fibers

• Compared to skeletal muscle fibers
• shorter
• single nucleus
• elongated with tapering ends
• myofilaments organized differently
• no sarcomeres, so no striations
• lack transverse tubules
• sarcoplasmic reticula not well developed
• exhibit stress-relaxation response

Figure from Martini, Anatomy Physiology,
Prentice Hall, 2001
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Types of Smooth Muscle

• Single-unit smooth muscle
• visceral smooth muscle
• sheets of muscle fibers that function as a
  group, i.e., a single unit
• fibers held together by gap junctions
• exhibit rhythmicity
• exhibit peristalsis
• walls of most hollow organs, blood vessels,
  respiratory/urinary/ reproductive tracts

• Multiunit Smooth Muscle
• fibers function separately, i.e., as multiple
  independent units
• muscles of eye, piloerector muscles, walls of
  large blood vessels

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Smooth Muscle Contraction

• Resembles skeletal muscle contraction
• interaction between actin and myosin
• both use calcium and ATP
• both depend on impulses

• Different from skeletal muscle contraction
• smooth muscle lacks troponin
• smooth muscle depends on calmodulin
• two neurotransmitters affect smooth muscle
• acetylcholine and norepinephrine
• hormones affect smooth muscle
• have gap junctions
• stretching can trigger smooth muscle contraction
  (but briefly, then relaxation again occurs)
• smooth muscle slower to contract and relax
• smooth muscle more resistant to fatigue
• smooth muscle can undergo hyperplasia, e.g.,
  uterus

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Cardiac Muscle

• only in the heart
• muscle fibers joined together by intercalated
  discs
• fibers branch
• network of fibers contracts as a unit (gap
  junctions)
• self-exciting and rhythmic
• longer refractory period than skeletal muscle
  (slower contract.)
• cannot be tetanized
• fatigue resistant
• has sarcomeres

Figure from Martini, Anatomy Physiology,
Prentice Hall, 2001
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Review

• Three types of muscle tissue
• Skeletal
• Cardiac
• Smooth
• Muscle tissue is
• Contractile
• Extensible
• Elastic
• Conductive
• Excitable

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Review

• Functions of muscle tissue
• Provide stability and postural tone
• Purposeful movement
• Regulate internal organ movement and volume
• Guard entrances/exits
• Generation of heat
• Muscle fiber anatomy
• Actin filaments, tropomyosin, troponin
• Myosin filaments
• Sarcomere
• Bands and zones

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Review

• Muscle contraction
• Sliding filament theory
• Contraction cycle (Bind, Move, Detach, Release)
• Role of ATP, creatine
• Metabolic requirements of skeletal muscle
• Stimulation at neuromuscular junction
• Muscular responses
• Threshold stimulus
• Twitch latent period, refractory period
• All or none response
• Treppe, Wave summation, and tetanus

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Review

• Muscular responses
• Recruitment
• Muscle tone
• Types of muscle contractions
• Isometric
• Isotonic
• Concentric
• Eccentric
• Fast and slow twitch muscle fibers
• Slow Oxidative (Type I) (think REDSOX)
• Fast Oxidative-glycolytic (Type II-A)
• Fast Glycolytic (Type II-B)