Chapter 10: Muscle Tissue A&P Biology 141 R.L. Brashear-Kaulfers

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Chapter 10Muscle Tissue AP Biology 141R.L.
Brashear-Kaulfers
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Muscle Tissue

• One of 4 primary tissue types, divided into
• skeletal muscle
• cardiac muscle
• smooth muscle
• Without these muscles, nothing in the body would
  move and no body movement would occur

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Skeletal Muscles- Organs of skeletal muscle
tissue - are attached to the skeletal system and
allow us to move

• Muscular System- Includes only skeletal muscles
  Skeletal Muscle Structures
• Muscle tissue (muscle cells or fibers)
• Connective tissues
• Nerves
• Blood vessels

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6 Functions of Skeletal Muscles

• Produce skeletal movement
• Maintain body position and posture
• Support soft tissues
• Guard body openings (entrance/exit)
• Maintain body temperature
• Store Nutrient reserves

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How is muscle tissue organized at the tissue
level? Organization of Connective Tissues
Figure 101
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Organization of Connective Tissues

• Muscles have 3 layers of connective tissues
• 1. Epimysium-Exterior collagen layer
• Connected to deep fascia
• Separates muscle from surrounding tissue
• 2. perimysium- Surrounds muscle fiber bundles
  (fascicles)
• Contains blood vessel and nerve supply to
  fascicles
• 3. endomysium

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3. Endomysium

• Surrounds individual muscle cells (muscle fibers)
• Contains capillaries and nerve fibers contacting
  muscle cells
• Contains satellite cells (stem cells) that repair
  damage

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Muscle Attachments

• Endomysium, perimysium, and epimysium come
  together
• at ends of muscles
• to form connective tissue attachment to bone
  matrix
• i.e., tendon (bundle) or aponeurosis (sheet)

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NervesSkeletal muscles are voluntary muscles,
controlled by nerves of the central nervous system

• Blood Vessels
• Muscles have extensive vascular systems that
• supply large amounts of oxygen
• supply nutrients
• carry away wastes

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What are the characteristics of skeletal muscle
fibers?

• Skeletal muscle cells are called fibers

Figure 102
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Skeletal Muscle Fibers

• Are very long
• Develop through fusion of mesodermal cells
  (myoblasts- embryonic cells))
• Become very large
• Contain hundreds of nuclei multinucleate
• Unfused cells are satellite cells- assist in
  repair after injury

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Organization of Skeletal Muscle Fibers
Figure 103
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The Sarcolemma

• The cell membrane of a muscle cell
• Surrounds the sarcoplasm (cytoplasm of muscle
  fiber)
• A change in transmembrane potential begins
  contractions
• All regions of the cell must contract
  simultaneously

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Transverse Tubules (T tubules)

• Transmit action potential impulses through cell
• Allow entire muscle fiber to contract
  simultaneously
• Have same properties as sarcolemma
• Filled with extracellular fluid

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Myofibrils- 1-2um in diameter

• Lengthwise subdivisions within muscle fiber
• Made up of bundles of protein filaments
  (myofilaments)
• Myofilaments - are responsible for muscle
  contraction
• 2 Types of Myofilaments
• Thin filaments
• made of the protein actin
• Thick filaments
• made of the protein myosin

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Sarcoplasmic Reticulum (SR)

• A membranous structure surrounding each myofibril
  
• Helps transmit action potential to myofibril
• Similar in structure to smooth endoplasmic
  reticulum
• Forms chambers (terminal cisternae) attached to T
  tubules

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A Triad

• Is formed by 1 T tubule and 2 terminal cisterna
• Cisternae
• Concentrate Ca2 (via ion pumps)
• Release Ca2 into sarcomeres to begin muscle
  contraction

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Structural components of the Sarcomeres
-The contractile units of muscle -Structural
units of myofibrils -Form visible patterns
within myofibrils
Figure 104
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Muscle Striations

• A striped or striated pattern within myofibrils
• alternating dark, thick filaments (A bands) and
  light, thin filaments (I bands)

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M Lines and Z Lines

• M line
• the center of the A band
• at midline of sarcomere
• Z lines
• the centers of the I bands
• at 2 ends of sarcomere
• Zone of Overlap
• The densest, darkest area on a light micrograph
• Where thick and thin filaments overlap

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The H Zone

• The area around the M line
• Has thick filaments but no thin filaments
• Titin
• Are strands of protein
• Reach from tips of thick filaments to the Z line
• Stabilize the filaments

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Sarcomere Structure
Figure 105
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Sarcomere Function

• Transverse tubules encircle the sarcomere near
  zones of overlap
• Ca2 released by SR causes thin and thick
  filaments to interact

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Level 1 Skeletal Muscle
Level 2 Muscle Fascicle
Figure 106 (1 of 5)
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Level 3 Muscle Fiber
Level 4 Myofibril
Figure 106 (3 of 5)
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Level 5 Sarcomere
Figure 106 (5 of 5)
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Muscle Contraction

• Is caused by interactions of thick and thin
  filaments
• Structures of protein molecules detemine
  interactions

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A Thin Filament
Figure 107a
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4 Thin Filament Proteins

• F actin
• is 2 twisted rows of globular G actin
• the active sites on G actin strands bind to
  myosin
• Nebulin
• holds F actin strands together
• Tropomyosin
• is a double strand
• prevents actinmyosin interaction
• Troponin
• - a globular protein
• binds tropomyosin to G actin
• controlled by Ca2

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Troponin and Tropomyosin
Initiating Contraction
Ca2 binds to receptor on troponin
molecule Troponintropomyosin complex
changes Exposes active site of F actin
Figure 107b
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A Thick Filament
Contain twisted myosin subunits Contain titin
strands that recoil after stretching
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The Mysosin Molecule

• Tail
• binds to other myosin molecules
• Head
• made of 2 globular protein subunits
• reaches the nearest thin filament

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Mysosin Action

• During contraction, myosin heads
• interact with actin filaments, forming
  cross-bridges
• pivot, producing motion

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Skeletal Muscle Contraction
Sliding Filaments

• Sliding filament theory
• thin filaments of sarcomere slide toward M line
• between thick filaments
• the width of A zone stays the same
• Z lines move closer together

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What are the components of the neuromuscular
junction, and the events involved in the neural
control of skeletal muscles?
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Skeletal Muscle Contraction
Figure 109 (Navigator)
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The Process of Contraction

• Neural stimulation of sarcolemma
• causes excitationcontraction coupling
• Cisternae of SR release Ca2
• which triggers interaction of thick and thin
  filaments
• consuming ATP and producing tension

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Skeletal Muscle Innervation
Figure 1010a, b (Navigator)
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Skeletal Muscle Innervation
Figure 1010c
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The Neuromuscular Junction

• Is the location of neural stimulation
• Action potential (electrical signal)
• travels along nerve axon
• ends at synaptic terminal
• Synaptic Terminal
• Releases neurotransmitter (acetylcholine or ACh)
• Into the synaptic cleft (gap between synaptic
  terminal and motor end plate)

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The Neurotransmitter

• Acetylcholine or ACh
• travels across the synaptic cleft
• binds to membrane receptors on sarcolemma (motor
  end plate)
• causes sodiumion rush into sarcoplasm
• is quickly broken down by enzyme
  (acetylcholinesterase or AChE)

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Action Potential

• Generated by increase in sodium ions in
  sarcolemma
• Travels along the T tubules
• Leads to excitationcontraction coupling

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ExcitationContraction Coupling

• Action potential reaches a triad
• releasing Ca2
• triggering contraction
• Requires myosin heads to be in cocked position
• loaded by ATP energy

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key steps involved in contraction of a skeletal
muscle fiber Exposing the Active Site
Figure 1011
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The Contraction Cycle
Figure 1012 (1 of 4)
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The Contraction Cycle
Figure 1012 (2 of 4)
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The Contraction Cycle
Figure 1012 (3 of 4)
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The Contraction Cycle
Figure 1012 (Navigator) (4 of 4)
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5 Steps of the Contraction Cycle

• Exposure of active sites
• Formation of cross-bridges
• Pivoting of myosin heads
• Detachment of cross-bridges
• Reactivation of myosin

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Fiber Shortening

• As sarcomeres shorten, muscle pulls together,
  producing tension

Figure 1013
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Contraction Duration

• Depends on
• duration of neural stimulus
• number of free calcium ions in sarcoplasm
• availability of ATP

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Relaxation

• Ca2 concentrations fall
• Ca2 detaches from troponin
• Active sites are recovered by tropomyosin
• Sarcomeres remain contracted

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Rigor Mortis

• A fixed muscular contraction after death
• Caused when
• ion pumps cease to function
• calcium builds up in the sarcoplasm

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A Review of Muscle Contraction
Table 101 (1 of 2)
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A Review of Muscle Contraction
Table 101 (2 of 2)
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KEY CONCEPT

• Skeletal muscle fibers shorten as thin filaments
  slide between thick filaments
• Free Ca2 in the sarcoplasm triggers contraction
• SR releases Ca2 when a motor neuron stimulates
  the muscle fiber
• Contraction is an active process
• Relaxation and return to resting length is passive

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What is the mechanism responsible for tension
production in a muscle fiber, and what factors
determine the peak tension developed during a
contraction?
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Tension Production

• The allornone principal
• as a whole, a muscle fiber is either contracted
  or relaxed
• Tension of a Single Muscle Fiber
• Depends on
• the number of pivoting cross-bridges
• the fibers resting length at the time of
  stimulation
• the frequency of stimulation

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Tension and Sarcomere Length
Figure 1014
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LengthTension Relationship

• Number of pivoting cross-bridges depends on
• amount of overlap between thick and thin fibers
• Optimum overlap produces greatest amount of
  tension
• too much or too little reduces efficiency
• Normal resting sarcomere length
• is 75 to 130 of optimal length

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Frequency of Stimulation

• A single neural stimulation produces
• a single contraction or twitch
• which lasts about 7100 msec
• Sustained muscular contractions
• require many repeated stimuli

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Tension in a Twitch

• Length of twitch depends on type of muscle

Figure 1015a (Navigator)
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Myogram

• A graph of twitch tension development

Figure 1015b (Navigator)
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3 Phases of Twitch

• Latent period before contraction
• the action potential moves through sarcolemma
• causing Ca2 release
• Contraction phase
• calcium ions bind
• tension builds to peak
• Relaxation phase
• Ca2 levels fall
• active sites are covered
• tension falls to resting levels

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Treppe

• A stair-step increase in twitch tension

Figure 1016a
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Treppe

• Repeated stimulations immediately after
  relaxation phase
• stimulus frequency lt 50/second
• Causes a series of contractions with increasing
  tension

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Wave Summation

• Increasing tension or summation of twitches

Figure 1016b
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Wave Summation

• Repeated stimulations before the end of
  relaxation phase
• stimulus frequency gt 50/second
• Causes increasing tension or summation of twitches

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Incomplete Tetanus
Twitches reach maximum tension

• If rapid stimulation continues and muscle is not
  allowed to relax, twitches reach maximum level of
  tension

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Complete Tetanus

• If stimulation frequency is high enough, muscle
  never begins to relax, and is in continuous
  contraction

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What factors affect peak tension production
during the contraction of an entire skeletal
muscle, and what is the significance of the motor
unit in this process?
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Tension Produced by Whole Skeletal Muscles

• Depends on
• internal tension produced by muscle fibers
• external tension exerted by muscle fibers on
  elastic extracellular fibers
• total number of muscle fibers stimulated

InterActive Physiology Contraction of Whole
Muscle
PLAY
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Motor Units in a Skeletal Muscle
Figure 1017
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Motor Units in a Skeletal Muscle

• Contain hundreds of muscle fibers
• That contract at the same time
• Controlled by a single motor neuron

InterActive Physiology Contraction of Motor
Units
PLAY
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Recruitment (Multiple Motor Unit Summation)

• In a whole muscle or group of muscles, smooth
  motion and increasing tension is produced by
  slowly increasing size or number of motor units
  stimulated

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Maximum Tension

• Achieved when all motor units reach tetanus
• Can be sustained only a very short time
• Sustained Tension
• Less than maximum tension
• Allows motor units to rest in rotation

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KEY CONCEPT

• Voluntary muscle contractions involve sustained,
  tetanic contractions of skeletal muscle fibers
• Force is increased by increasing the number of
  stimulated motor units (recruitment)

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Muscle Tone

• The normal tension and firmness of a muscle at
  rest
• Muscle units actively maintain body position,
  without motion
• Increasing muscle tone increases metabolic energy
  used, even at rest

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What are the types of muscle contractions, and
how do they differ?

• 2 Types of Skeletal Muscle Tension
• Isotonic contraction
• Isometric contraction

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Isotonic Contraction
Figure 1018a, b
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Isotonic Contraction

• Skeletal muscle changes length
• resulting in motion
• If muscle tension gt resistance
• muscle shortens (concentric contraction)
• If muscle tension lt resistance
• muscle lengthens (eccentric contraction)

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Isometric Contraction
Figure 1018c, d
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Isometric Contraction

• Skeletal muscle develops tension, but is
  prevented from changing length
• Note Iso same, metric measure

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Resistance and Speed of Contraction
Figure 1019
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Resistance and Speed of Contraction

• Are inversely related
• The heavier the resistance on a muscle
• the longer it takes for shortening to begin
• and the less the muscle will shorten

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Muscle Relaxation

• After contraction, a muscle fiber returns to
  resting length by
• elastic forces
• opposing muscle contractions
• gravity

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Elastic Forces

• The pull of elastic elements (tendons and
  ligaments)
• Expands the sarcomeres to resting length

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Opposing Muscle Contractions

• Reverse the direction of the original motion
• Are the work of opposing skeletal muscle pairs
• Gravity
• Can take the place of opposing muscle contraction
  to return a muscle to its resting state

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What are the mechanisms by which muscle fibers
obtain energy to power contractions?
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ATP and Muscle Contraction

• Sustained muscle contraction uses a lot of ATP
  energy
• Muscles store enough energy to start contraction
• Muscle fibers must manufacture more ATP as needed

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ATP and CP Reserves

• Adenosine triphosphate (ATP)
• the active energy molecule
• Creatine phosphate (CP)
• the storage molecule for excess ATP energy in
  resting muscle

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Recharging ATP

• Energy recharges ADP to ATP
• using the enzyme creatine phosphokinase (CPK)
• When CP is used up, other mechanisms generate ATP

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Energy Storage in Muscle Fiber
Table 102
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ATP Generation

• Cells produce ATP in 2 ways
• aerobic metabolism of fatty acids in the
  mitochondria
• anaerobic glycolysis in the cytoplasm

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Aerobic Metabolism

• Is the primary energy source of resting muscles
• Breaks down fatty acids
• Produces 34 ATP molecules per glucose molecule

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Anaerobic Glycolysis

• Is the primary energy source for peak muscular
  activity
• Produces 2 ATP molecules per molecule of glucose
• Breaks down glucose from glycogen stored in
  skeletal muscles

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Energy Use and Muscle Activity

• At peak exertion
• muscles lack oxygen to support mitochondria
• muscles rely on glycolysis for ATP
• pyruvic acid builds up, is converted to lactic
  acid

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Muscle Metabolism
InterActive Physiology Muscle Metabolism
PLAY
Figure 1020a
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Muscle Metabolism
Figure 1020c
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What factors contribute to muscle fatigue, and
what are the stages and mechanisms involved in
muscle recovery?
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Muscle Fatigue

• When muscles can no longer perform a required
  activity, they are fatigued
• Results of Muscle Fatigue
• Depletion of metabolic reserves
• Damage to sarcolemma and sarcoplasmic reticulum
• Low pH (lactic acid)
• Muscle exhaustion and pain

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The Recovery Period

• The time required after exertion for muscles to
  return to normal
• Oxygen becomes available
• Mitochondrial activity resumes

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The Cori Cycle

• The removal and recycling of lactic acid by the
  liver
• Liver converts lactic acid to pyruvic acid
• Glucose is released to recharge muscle glycogen
  reserves
• Oxygen Debt
• After exercise
• the body needs more oxygen than usual to
  normalize metabolic activities
• resulting in heavy breathing

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KEY CONCEPT

• Skeletal muscles at rest metabolize fatty acids
  and store glycogen
• During light activity, muscles generate ATP
  through anaerobic breakdown of carbohydrates,
  lipids or amino acids
• At peak activity, energy is provided by anaerobic
  reactions that generate lactic acid as a byproduct

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Heat Production and Loss

• Active muscles produce heat
• Up to 70 of muscle energy can be lost as heat,
  raising body temperature
• Hormones and Muscle Metabolism
• Growth hormone
• Testosterone
• Thyroid hormones
• Epinephrine

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How do the types of muscle fibers relate to
muscle performance?
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Muscle Performance

• Power
• the maximum amount of tension produced
• Endurance
• the amount of time an activity can be sustained
• Power and endurance depend on
• the types of muscle fibers
• physical conditioning

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3 Types of Skeletal Muscle Fibers

• 1. Fast fibers- Contract very quickly
• Have large diameter, large glycogen reserves, few
  mitochondria
• Have strong contractions, fatigue quickly
• 2. Slow fibers-Are slow to contract, slow to
  fatigue
• Have small diameter, more mitochondria
• Have high oxygen supply
• Contain myoglobin (red pigment, binds oxygen)
• 3. Intermediate fibers-Are mid-sized
• Have low myoglobin
• Have more capillaries than fast fiber, slower to
  fatigue

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Fast versus Slow Fibers
Figure 1021
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Comparing Skeletal Muscle Fibers
Table 103
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Muscles and Fiber Types

• White muscle
• mostly fast fibers
• pale (e.g., chicken breast)
• Red muscle
• mostly slow fibers
• dark (e.g., chicken legs)
• Most human muscles
• mixed fibers
• pink

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Muscle Hypertrophy

• Muscle growth from heavy training
• increases diameter of muscle fibers
• increases number of myofibrils
• increases mitochondria, glycogen reserves
• Muscle Atrophy
• Lack of muscle activity
• reduces muscle size, tone, and power

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What is the difference between aerobic and
anaerobic endurance, and their effects on
muscular performance? Physical Conditioning
Improves both power and endurance
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Anaerobic Endurance

• Anaerobic activities (e.g., 50-meter dash,
  weightlifting)
• use fast fibers
• fatigue quickly with strenuous activity
• Improved by
• frequent, brief, intensive workouts
• hypertrophy

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Aerobic Endurance

• Aerobic activities (prolonged activity)
• supported by mitochondria
• require oxygen and nutrients
• Improved by
• repetitive training (neural responses)
• cardiovascular training

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KEY CONCEPT

• What you dont use, you loose
• Muscle tone indicates base activity in motor
  units of skeletal muscles
• Muscles become flaccid when inactive for days or
  weeks
• Muscle fibers break down proteins, become smaller
  and weaker
• With prolonged inactivity, fibrous tissue may
  replace muscle fibers

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What are the structural and functional
differences between skeletal muscle fibers and
cardiac muscle cells?
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Structure of Cardiac Tissue

• Cardiac muscle is striated, found only in the
  heart

Figure 1022
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7 Characteristics of Cardiocytes

• Unlike skeletal muscle, cardiac muscle cells
  (cardiocytes)
• are small
• have a single nucleus
• have short, wide T tubules

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7 Characteristics of Cardiocytes

• have no triads
• have SR with no terminal cisternae
• are aerobic (high in myoglobin, mitochondria)
• have intercalated discs

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Intercalated Discs

• Are specialized contact points between
  cardiocytes
• Join cell membranes of adjacent cardiocytes (gap
  junctions, desmosomes)
• Functions of Intercalated Discs
• Maintain structure
• Enhance molecular and electrical connections
• Conduct action potentials

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Coordination of Cardiocytes

• Because intercalated discs link heart cells
  mechanically, chemically, and electrically, the
  heart functions like a single, fused mass of cells

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4 Functions of Cardiac Tissue

• Automaticity
• contraction without neural stimulation
• controlled by pacemaker cells
• Variable contraction tension
• controlled by nervous system
• Extended contraction time
• Prevention of wave summation and tetanic
  contractions by cell membranes

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Role of Smooth Muscle in Body Systems

• Forms around other tissues
• In blood vessels
• regulates blood pressure and flow
• In reproductive and glandular systems
• produces movements
• In digestive and urinary systems
• forms sphincters
• produces contractions
• In integumentary system
• arrector pili muscles cause goose bumps

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What are the structural and functional
differences between skeletal muscle fibers and
smooth muscle cells?
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Structure of Smooth Muscle

• Nonstriated tissue

Figure 1023
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Comparing Smooth and Striated Muscle

• Different internal organization of actin and
  myosin
• Different functional characteristics

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8 Characteristics of Smooth Muscle Cells

• Long, slender, and spindle shaped
• Have a single, central nucleus
• Have no T tubules, myofibrils, or sarcomeres
• Have no tendons or aponeuroses

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8 Characteristics of Smooth Muscle Cells

• Have scattered myosin fibers
• Myosin fibers have more heads per thick filament
• Have thin filaments attached to dense bodies
• Dense bodies transmit contractions from cell to
  cell

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Functional Characteristics of Smooth Muscle

• Excitationcontraction coupling
• Lengthtension relationships
• Control of contractions
• Smooth muscle tone

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ExcitationContraction Coupling

• Free Ca2 in cytoplasm triggers contraction
• Ca2 binds with calmodulin
• in the sarcoplasm
• activates myosin light chain kinase
• Enzyme breaks down ATP, initiates contraction

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LengthTension Relationships

• Thick and thin filaments are scattered
• Resting length not related to tension development
• Functions over a wide range of lengths
  (plasticity)

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Control of Contractions

• Subdivisions
• multiunit smooth muscle cells
• connected to motor neurons
• visceral smooth muscle cells
• not connected to motor neurons
• rhythmic cycles of activity controlled by
  pacesetter cells

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Smooth Muscle Tone

• Maintains normal levels of activity
• Modified by neural, hormonal, or chemical factors

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Characteristics of Skeletal, Cardiac, and Smooth
Muscle
Table 104
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SUMMARY (1 of 3)

• 3 types of muscle tissue
• skeletal
• cardiac
• smooth
• Functions of skeletal muscles
• Structure of skeletal muscle cells
• endomysium
• perimysium
• epimysium
• Functional anatomy of skeletal muscle fiber
• actin and myosin

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SUMMARY (2 of 3)

• Nervous control of skeletal muscle fibers
• neuromuscular junctions
• action potentials
• Tension production in skeletal muscle fibers
• twitch, treppe, tetanus
• Tension production by skeletal muscles
• motor units and contractions
• Skeletal muscle activity and energy
• ATP and CP
• aerobic and anaerobic energy

138
SUMMARY (3 of 3)

• Skeletal muscle fatigue and recovery
• 3 types of skeletal muscle fibers
• fast, slow, and intermediate
• Skeletal muscle performance
• white and red muscles
• physical conditioning
• Structures and functions of
• cardiac muscle tissue
• smooth muscle tissue