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.