Download •Muscle Tissue

AN INTRODUCTION TO MUSCLE TISSUE
• Muscle Tissue- 3 Types
• Skeletal muscle (focus on these)
• Cardiac muscle
• Smooth muscle
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FUNCTIONS OF SKELETAL MUSCLES
• Produce movement of the skeleton
• Maintain posture and body position
• Support soft tissues
• Guard entrances and exits
• Maintain body temperature
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SKELETAL MUSCLE STRUCTURES
• Muscle tissue (muscle cells or fibers)
• Connective tissues
• Blood vessels and nerves
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Organization of Connective Tissues
ORGANIZATION OF CONNECTIVE
• Muscles have three layers of
connective tissues
• Epimysium:
• Separates muscle from surrounding tissues
• Perimysium:
• Surrounds muscle fiber bundles (fascicles)
• Endomysium:
• Surrounds individual muscle cells (muscle fibers)
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THE ORGANIZATION OF A SKELETAL
MUSCLE
Figure 7-1
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ORGANIZATION OF CONNECTIVE
TISSUES
• Endomysium, perimysium, and epimysium come
together to form a tendon: attaches muscle to
bone
• Ligament: attaches bone to bone
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BLOOD VESSELS AND NERVES
• Nerves
• Skeletal muscles are voluntary muscles,
controlled by nerves of the central nervous
system (brain and spinal cord)
• Blood Vessels
• Muscles have extensive vascular systems
that:
• Supply large amounts of oxygen and nutrients
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SKELETAL MUSCLE FIBERS
• The sarcolemma
• The cell membrane of a muscle fiber (cell)
• Surrounds the sarcoplasm (cytoplasm of muscle fiber)
• A change in transmembrane potential begins
contractions
• Transverse tubules (T tubules)
• Transmit action potential through cell
• Allow entire muscle fiber to contract simultaneously
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SKELETAL MUSCLE FIBERS
• Myofibrils
• Subdivisions within muscle fiber
• Made of myofilaments
• responsible for muscle contraction
• Types:
• Thin filaments:
• actin (protein)
• Thick filaments:
• myosin (protein)
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SKELETAL MUSCLE FIBERS
• The sarcoplasmic reticulum (SR)
• A membranous structure surrounding each
myofibril
• Helps transmit action potential to myofibril
• Forms chambers called terminal cisternae,
attached to T tubules
• Triad:
• Is formed by one T tubule and two terminal cisternae
• concentrate Ca2+ and release into sarcomeres to
begin muscle contraction
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ORGANIZATION OF A SKELETAL
MUSCLE FIBER
Figure 7-2a
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SKELETAL MUSCLE FIBERS
• Sarcomeres
• Smallest contractile units of muscle
• There are multiple within a myofibril
• Forms visible patterns –muscle striations
• Caused by alternating dark, thick filaments (A
bands) and light, thin filaments (I bands)
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SKELETAL MUSCLE FIBERS
• Sarcomeres
• Zone of overlap:
• densest, darkest areas
• thick and thin filaments overlap
• The H Band:
• area around the M line
• Has thick but no thin filaments
• changes length during contraction
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ORGANIZATION OF A SKELETAL
MUSCLE FIBER
Figure 7-2 b-c
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SKELETAL MUSCLE FIBERS
• Sarcomere Function
• T tubules encircle the
sarcomere near zones of overlap
• T-tubules transmit action potential to
terminal cisternae of SR
• Terminal cisternae release Ca2+ , which
causes thin and thick filaments to interact
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Thin and Thick Filament Structure
Thin filaments:
• F-actin
• two twisted rows
• Tropomyosin;
• prevents actin–myosin interaction
• Troponin:
• controlled by Ca2+
Thick filaments:
• Contain twisted myosin subunits
• Tail and Globular Head
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THE PROCESS
• Ca2+ binds to receptor on troponin molecule
• Troponin–tropomyosin complex changes
• Exposes active site of F-actin
• Myosin head of thick filament attaches and pulls
thin filament.
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SARCOMERE SHORTENING
Figure 7-3
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SARCOMERE SHORTENING
Figure 7-3
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THE NEUROMUSCULAR JUNCTION
• Action potential (electrical signal)
• Travels along nerve axon
• Ends at synaptic terminal:
releases neurotransmitter acetylcholine (ACh) into
the synaptic cleft (gap between synaptic terminal
and motor end plate)
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STRUCTURE AND FUNCTION OF THE
NEUROMUSCULAR JUNCTION
Video
Figure 7-4 a
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THE NEUROMUSCULAR JUNCTION
• The release of ACh from the synaptic terminal results
in changes in the sarcolemma that trigger
contractions of muscle fiber.
Figure 7-4 b
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THE CONTRACTION CYCLE
• Five 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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MOLECULAR EVENTS OF THE
CONTRACTION PROCESS
Figure 7-5
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MOLECULAR EVENTS OF THE
CONTRACTION PROCESS
Figure 7-5
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MOLECULAR EVENTS OF THE
CONTRACTION PROCESS
Figure 7-5
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MOLECULAR EVENTS OF THE
CONTRACTION PROCESS
Figure 7-5
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MOLECULAR EVENTS OF THE
CONTRACTION PROCESS
Figure 7-5
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MOLECULAR EVENTS OF THE
CONTRACTION PROCESS
Figure 7-5
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TENSION PRODUCTION
• The all-or-none principle
• As a whole, a muscle fiber is either
contracted or relaxed, but…
• Tension (active force) of a single
muscle fiber can vary depending on:
• number of pivoting cross-bridges
• fiber’s resting length at the time of stimulation
• frequency of stimulation
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FREQUENCY OF MUSCLE FIBER
STIMULATION
• A single neural stimulation produces a
single contraction or twitch.
• about 7–100 msec
• Sustained muscular contractions require
repeated stimuli
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FREQUENCY OF MUSCLE FIBER
STIMULATION
• Three 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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NUMBER OF MUSCLE FIBERS
ACTIVATED
• Motor Unit: all muscle fibers controlled by a single
motor neuron.
Multiple muscle fibers are controlled by a single motor neuron
• Eye = 2-3 muscle fibers
• Leg = 2,000 muscle fibers
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NUMBER OF MUSCLE FIBERS
ACTIVATED
• Recruitment
• smooth motion and increasing tension are produced
by slowly increasing the size or number of motor
units stimulated
• Maximum tension = when all motor units reach tension
• sustained only a very short time
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NUMBER OF MUSCLE FIBERS
ACTIVATED
• Muscle tone
• The normal tension and firmness of a muscle at rest
• Muscle units actively maintain body position, without motion
• Atrophy: muscle becomes smaller and weaker when not
regularly stimulated
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NUMBER OF MUSCLE FIBERS
ACTIVATED
• Isotonic and Isometric Contractions
• Isotonic contraction:
• Skeletal muscle changes length:
• resulting in motion
• Isometric contraction:
• Skeletal muscle develops
tension but does not
change length
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NUMBER OF MUSCLE FIBERS
ACTIVATED
• Muscle Elongation After Contraction
• Elastic forces:
• The pull of tendons and ligaments expands the sarcomeres
back to resting length
• Opposing muscle contractions and gravity: reverse the
direction of the original motion
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TYPES OF SKELETAL MUSCLE FIBERS
• Fast fibers
• Contract very quickly
• Have large diameter, few mitochondria
Therefore: Have strong contractions, fatigue quickly
• Slow fibers
• slow to contract, slow to fatigue
• small diameter, more mitochondria
• Have high oxygen supply
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TYPES OF SKELETAL MUSCLE FIBERS
• The Distribution of Muscle Fibers and Muscle
Performance
• 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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PHYSICAL CONDITIONING
• 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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Copyright © 2010 Pearson Education, Inc.