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Muscles
Skeletal muscle
Cross- Section Longitudinal
Smooth Muscle
Cross- Section
longitudinal
Muscle Tissue Components
• tendon - connects skeletal muscle to bone
• epimysium - fibrous connective tissue around belly of skeletal muscle
• fasiculi - bundles of muscle fibers
• perimysium - connective tissue surrounding fasiculi
• endomysium - connective tissue surrounding the individual muscle fibers (muscle cell)
Muscle components
• muscle fiber - single muscle cell (threadlike in shape)
• sarcolemma - membrane surrounding the muscle fiber
• sarcoplasm - specialized cytoplasm of muscle fiber containing multiple nuclei and mitochondria
• myofibrils - "rod-like" structures running through the muscle fibers that contain actin and myosin make muscle appear striated
Muscle types
• Myosins are protein motors. Upon interaction with actin filaments, they utilize energy from ATP hydrolysis to generate mechanical force.
• Muscles are typed based upon the types of myosin protein fibers present
• there are different forms of the muscle myosins – TYPE I (Slow Twitch) – Type IIa/IIx (Fast Twitch)
Muscle types
• Are determined both genetically & functionally based upon how fast they can produce a contractile twitch
• every muscle composed of varying % composition of two types
TYPE I - SLOW TWITCH Tonic muscles (red) - Leg muscles
TYPE II - (IIa & IIx) FAST TWITCH Tetanic muscles (white) - Pectoral muscles
slower contraction times (100-110 msec)
faster contraction times (50 msec)
contain myoglobin (red) no myoglobin (white)
continuous use muscles - prolonged performancefor endurance performance ( marathoners)
one time use muscles - brief performances for power & speed (sprinters)
marathoner: 80% type I & 20% type II sprinter: 20% type I & 80% type II
best in long slow sustained contractions
best in rapid (short) contractions
not easily fatigued easily fatigued
more capillary beds, greater VO2 max less capillary beds
smaller in size larger in size
lower glycogen content higher glycogen content
poor anaerobic glycolysis* predominantly anaerobic glycolysis easily converts glycogen to lactate wo O2
higher fat content lower fat content
poorly formed sarcoplasmic reticulum well formed sacroplasmic reticulum
Distribution of slow/fast twitch fibers
Relative Distributions of Slow Twitch & Fact Twitch Myosin forms (Type I & Type II)
Type I (slow)
Type II (fast) Type IIa Type IIx
Average person
50% 50% 40% 10%
spinal injury 4% 96% 48% 48%
sprinter 20% 80% 45% 35%
couch potato
40% 60% 30% 30%
marathoner 80% 20% 20% 0%
MUSCLES CONTRACT!!!
• Muscles can not push, they may only CONTRACT (pull)
• A muscle contraction is called a muscle TWITCH
The sarcomere
• basic repeat unit of striated muscle, delimited by Z-lines
sarcomere
• SARCOMERE REGIONS• I band - "clear zone" around
Z-line • A band - "dark region" in
center of sarcomere• M line - mid point of the
sarcomere• H zone - "clear zone" in the
center of sarcomere around M line
Sliding Filament Theory
• A band remains constant in its size dimensions
• H Zone becomes denser
• I band varies in length becoming shorter & disappearing
4 parts of a Muscle twitch
• 1) latent period – – 5 msec time between application of Action Potential &
initiation of contraction
• 2) contraction – (slow twitch)– 40 msec muscle shortens & does its work
• 3) relaxation – – 50 msec muscle elongates & returns to original
position
• 4) refractory period – – 2 msec time of recovery between stimulations of
muscle
Muscle contraction cycle• Step 1
– Arrival of the action potential
• Action potential causes AcH to be released.
• ACH binds to receptors on sarcolemma
• Receptors open, causing Na+ to flood in changing membrane potential.
Muscle contraction #2
Muscle contraction #3
• Step 3 – Release of
Calcium
Muscle Contraction #4
• Step 4:– calcium
changes tropomyosin shape
– Exposes myosin binding sites on actin
Muscle contraction #5
• #5– ATP binds to cross
bridge• Myosin head changes
shape releases from actin
– ATP hydrolyzes• Head is in high energy
configuration
– Head binds to actin– ADP+P are released
from myosin• Head moves actin
towards center
Types of contractions
DOMS• Occurs usually at the beginning of a new training
program.– Characterized by stiffness, soreness– More often occur after activities with eccentric contractions.– causing damage to the muscle cell membrane, which sets
off an inflammatory response. – This inflammatory response leads to the formation of
metabolic waste products, – These chemicals stimulate pain nerves and attract
neutrophils (a type of white blood cell) to the site of injury. – There, neutrophils generate free radicals (molecules with
unshared electrons), which also damage the cell membrane.
– Swelling is also common, and can lead to pain.
Effect of exercise on muscle
• Eccentric contractions produce muscle hypertrophy – Eccentric contractions put your muscle fibers under a great
deal of tension causing microtears and severe DOMS. – if you can induce muscle fiber injury, satellite cells are
activated. • Satellite cells are myogenic stem cells which regenerate muscle.• Satellite cells proliferate (undergo mitosis) and give rise to new
immature muscle cells. • These new cells fuse with an existing muscle fiber causing that fiber
to get bigger (i.e., hypertrophy)
Maintaining muscle over time
• Muscle strength in people increases until the early 20’s– It remains fairly stable
until about 50 in untrained people
– Loss of maximal strength is due to atrophy of type II fibers.
– People of any age can show strength gains through regular strength training
Strength training benefits for women
• Enhanced bone modeling to increase bone strength and reduce the risk of osteoporosis
• Stronger connective tissues to increase joint stability and help prevent injury
• Increased functional strength for sports and daily activity • Increased lean body mass and decreased nonfunctional
body fat • Higher metabolic rate because of an increase in muscle and
a decrease in fat • Improved self-esteem and confidence • Some factors may reduce these benefits including
– including the exclusive use of weight training machines, training with loads that are too light, and not progressing in resistance or intensity.