Download Lecture 7 - Websupport1

Anatomy & Physiology
Lecture 7: Chapter 10
Muscle Tissue
Pages: 283-325
Lecturer: Dr. Barjis
Room: P313 /P307
Phone: (718)2605285
E-Mail: ibarjis@citytech.cuny.edu
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Frederic H. Martini
Fundamentals of
Learning Objectives
• Describe the organization of muscle and the
unique characteristics of skeletal muscle cells.
• Identify the structural components of the
sarcomere.
• Summarize the events at the neuromuscular
junction.
• Explain the key concepts involved in skeletal
muscle contraction and tension production.
Learning Objectives
• Describe how muscle fibers obtain energy for
contraction.
• Distinguish between aerobic and anaerobic
contraction, muscle fiber types, and muscle
performance.
• Identify the differences between skeletal, cardiac
and smooth muscle.
Skeletal muscle tissue and the Muscular System
Three types of muscle
• Skeletal – attached to bone
• Cardiac – found in the heart
• Smooth – lines hollow organs
Skeletal muscle functions
• Produce skeletal movement
• Maintain posture and body position
• Support soft tissues
• Guard entrances and exits
• Maintain body temperature
Anatomy of Skeletal Muscle
Organization of connective tissues
• Epimysium surrounds muscle
• Perimysium sheathes bundles of muscle fibers
• Epimysium and perimysium contain blood
vessels and nerves
• Endomysium covers individual muscle fibers
• Tendons or aponeuroses attach muscle to bone or
muscle
Animation: See tutorial
The Organization of Skeletal Muscles
Skeletal muscle fibers
• Sarcolemma (cell membrane)
• Sarcoplasm (muscle cell cytoplasm)
• Sarcoplasmic reticulum (modified ER)
• T-tubules and myofibrils aid in contraction
• Sarcomeres – regular arrangement of myofibrils
The Structure of a Skeletal Muscle Fiber
Sarcomere Structure, Part I
Myofibrils
• Thick and thin filaments
• Organized regularly
Sarcomere Structure, Part II
Levels of Functional Organization in Skeletal
Muscle Fiber
Thin filaments
• F-actin
• Nebulin
• Tropomyosin
• Covers active sites on G-actin
• Troponin
• Binds to G-actin and holds tropomyosin in
place
Thick filaments
• Bundles of myosin fibers around titan core
• Myosin molecules have elongate tail, globular
head
• Heads form cross-bridges during contraction
• Interactions between G-actin and myosin
prevented by tropomyosin during rest
Thick and Thin Filaments
Sliding filament theory
• Explains the relationship between thick and thin
filaments as contraction proceeds
• Cyclic process beginning with calcium release
from SR
• Calcium binds to troponin
• Trponin moves, moving tropomyosin and
exposing actin active site
• Myosin head forms cross bridge and bends
toward H zone
• ATP allows release of cross bridge
Changes in the appearance of a Sarcomere during
the Contraction of a Skeletal Muscle Fiber
The Contraction of Skeletal Muscle
Tension
• Created when muscles contract
• Series of steps that begin with excitation at the
neuromuscular junction
• Calcium release
• Thick/thin filament interaction
• Muscle fiber contraction
• Tension
An Overview of the Process of Skeletal Muscle
Control of skeletal muscle activity occurs at the
neuromuscular junction
• Action potential arrives at synaptic terminal
• ACh released into synaptic cleft
• ACh binds to receptors on post-synaptic neuron
• Action potential in sarcolemma
Skeletal Muscle Innervation
Skeletal Muscle Innervation
Animation: See tutorial
Excitation/contraction coupling
• Action potential along T-tubule causes release
of calcium from cisternae of SR
• Initiates contraction cycle
• Attachment
• Pivot
• Detachment
• Return
The Contraction Cycle
The Contraction Cycle
The Contraction Cycle
The Contraction Cycle
Relaxation
• Acetylcholinesterase breaks down ACh
• Limits the duration of contraction
Animation: See tutorial
Tension Production
Tension production by muscle fibers
• All or none principle
• Amount of tension depends on number of cross
bridges formed
• Skeletal muscle contracts most forcefully over a
narrow ranges of resting lengths
The Effect of Sarcomere Length on Tension
• Twitch
• Cycle of contraction, relaxation produced by a
single stimulus
• Treppe
• Repeated stimulation after relaxation phase has
been completed
Summation
• Repeated stimulation before relaxation phase has
been completed
• Wave summation = one twitch is added to another
• Incomplete tetanus = muscle never relaxes
completely
• Complete tetanus = relaxation phase is eleminated
The Twitch and the Development of Tension
Effects of Repeated Stimulations
Tension production by skeletal muscles
• Internal tension generated inside contracting
muscle fibers
• External tension generated in extracellular fibers
Internal and External Tension
• Motor units
• All the muscle fibers innervated by one neuron
• Precise control of movement determined by
number and size of motor unit
• Muscle tone
• Stabilizes bones and joints
The Arrangement of Motor Units in a Skeletal
Muscle
Tension production by skeletal muscles
• Internal tension generated inside contracting
muscle fibers
• External tension generated in extracellular fibers
Internal and External Tension
• Motor units
• All the muscle fibers innervated by one neuron
• Precise control of movement determined by
number and size of motor unit
• Muscle tone
• Stabilizes bones and joints
The Arrangement of Motor Units in a Skeletal
Muscle
Contractions
• Isometric
• Tension rises, length of muscle remains constant
• Isotonic
• Tension rises, length of muscle changes
• Resistance and speed of contraction inversely
related
• Return to resting lengths due to elastic
components, contraction of opposing muscle
groups, gravity
Animation: See tutorial
Isotonic and Isometric Contractions
Figure 10.18
Resistance and Speed of Contraction
Animation: See tutorial
Energy Use and Muscle Contraction
Muscle Contraction requires large amounts
of energy
• Creatine phosphate releases stored energy to
convert ADP to ATP
• Aerobic metabolism provides most ATP needed
for contraction
• At peak activity, anaerobic glycolysis needed to
generate ATP
Muscle Metabolism
Muscle Metabolism
Energy use and level of muscular activity
• Energy production and use patterns mirror
muscle activity
• Fatigued muscle no longer contracts
• Build up of lactic acid
• Exhaustion of energy resources
Recovery period
• Begins immediately after activity ends
• Oxygen debt (excess post-exercise oxygen
consumption)
• Amount of oxygen required during resting
period to restore muscle to normal conditions
Muscle Performance
Types of skeletal muscle fibers
• Fast fibers
• Slow fibers
• Intermediate fibers
Fast versus Slow Fibers
Fast fibers
• Large in diameter
• Contain densely packed myofibrils
• Large glycogen reserves
• Relatively few mitochondria
• Produce rapid, powerful contractions of short
duration
Slow fibers
• Half the diameter of fast fibers
• Take three times as long to contract after
stimulation
• Abundant mitochondria
• Extensive capillary supply
• High concentrations of myoglobin
• Can contract for long periods of time
Intermediate fibers
• Similar to fast fibers
• Greater resistance to fatigue
Muscle performance and the distribution of
muscle fibers
• Pale muscles dominated by fast fibers are called
white muscles
• Dark muscles dominated by slow fibers and
myoglobin are called red muscles
• Training can lead to hypertrophy of stimulated
muscle
Physical conditioning
• Anaerobic endurance
• Time over which muscular contractions are
sustained by glycolysis and ATP/CP reserves
• Aerobic endurance
• Time over which muscle can continue to
contract while supported by mitochondrial
activities
Animation: See tutorial
Cardiac Muscle Tissue
Structural characteristics of cardiac muscle
• Located only in heart
• Cardiac muscle cells are small
• One centrally located nucleus
• Short broad T-tubules
• Dependent on aerobic metabolism
• Intercalated discs where membranes contact one
another
Cardiac Muscle Tissue
Functional characteristics of cardiac muscle
tissue
• Automaticity
• Contractions last longer than skeletal muscle
• Do not exhibit wave summation
• No tetanic contractions possible
Smooth Muscle Tissue
Structural characteristics of smooth muscle
• Nonstriated
• Lack sarcomeres
• Thin filaments anchored to dense bodies
• Involuntary
Smooth Muscle Tissue
Functional characteristics of smooth muscle
• Contract when calcium ions interact with
calmodulin
• Activates myosin light chain kinase
• Functions over a wide range of lengths
• Plasticity
• Multi-unit smooth muscle cells are innervated by
more than one motor neuron
• Visceral smooth muscle cells are not always
innervated by motor neurons
• Neurons that innervate smooth muscle are not
under voluntary control
You should now be familiar with:
• The organization of muscle and the unique
characteristics of skeletal muscle cells.
• The structural components of the sarcomere.
• The events at the neuromuscular junction.
• The key concepts involved in skeletal muscle
contraction and tension production.
• How muscle fibers obtain energy for contraction.
• Aerobic and anaerobic contraction, muscle fiber
types, and muscle performance.
• The differences between skeletal, cardiac and
smooth muscle