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Human Biology, Bios 103 Dr. Harry Schutte. CHAPTER 6 The Muscular System. The Muscular System. Figure 6.2 Slide 6.1. Principle function Contraction: shorten distance between bones Skeletal muscle moves bone Muscle groups

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Human Biology, Bios 103

Dr. Harry Schutte

CHAPTER 6The Muscular System


The Muscular System

Figure 6.2

Slide 6.1

muscle function produce movement or generate tension
Principle function

Contraction: shorten distance between bones

Skeletal muscle moves bone

Muscle groups

Synergistic: groups work together (hamstring group contracts together to extend lower leg)

Antagonistic: groups oppose each other (biceps and triceps, ex.)

Muscle Function:Produce Movement or Generate Tension

Slide 6.2

muscle structure
Fascicles: bundles, CT(connective tissue) covering on each one

Muscle fibers: muscle cells

Muscle Structure

Figure 6.3

Slide 6.3

skeletal muscle contractile unit
Sarcomere: individual contractile units of the muscle (from one Z Line to the next Z Line) May be 100,000 sarcomeres in one myofibril arranged end-to-end.

Myofibrils: bundles of contractile tube-like structures that make up the muscle cell

Actin and myosin: the proteins of muscle contraction in the myofibrils

Z Lines: attachment points for sarcomeres

Skeletal Muscle Contractile Unit

Slide 6.4A

nerve activation of individual muscle cells
Acetylcholine released from motor neuron at neuromuscular junction. This same neurotransmitter used at ALL nerve- skeletal muscle junctions in the body. KNOW THIS.

Electrical impulse transmitted along T tubules

Calcium released from sarcoplasmic reticulum

Nerve Activation of Individual Muscle Cells

Slide 6.5A

calcium initiates the sliding filament mechanism
Thick filaments: myosin – studded with cross bridge “heads”

Thin filaments: strands of actin molecules – slide between the myosin filaments

Contraction = formation of cross bridges between thin and thick filaments (“sliding filament” mechanism)

Calcium Initiates the Sliding Filament Mechanism

Slide 6.6A

mechanism of muscle contraction
Calcium released from sarcoplasmic reticulum

Calcium binds to troponin

Troponin-tropomysin complex shifts position

Myosin binding site exposed

Myosin heads form cross-bridges with actin

Actin filaments pulled toward center of sarcomere

Without calcium – no muscle contraction; too much calcium – muscles in spasm (can’t relax)

Mechanism of Muscle Contraction

Slide 6.7A

muscle relaxation
Nerve activation ends, contraction ends

Calcium pumped back into sarcoplasmic reticulum

Calcium removed from troponin

Myosin-binding site covered

No calcium = no cross-bridges

Too much calcium (or not removed) = spasm

Muscle Relaxation

Slide 6.8

energy required for muscle activity
Principle source of energy: ATP

ATP needed to 1) “cock” the myosin heads in the “ready to fire” position 2) allows the cross-bridge to disengage

After death, the lack of ATP keeps cross-bridges engaged: this is the cause of rigor mortis (KNOW THIS)

ATP replenished by variety of means

Creatine phosphate (assists in the bonding of P to ADP)

Creatine supplements are not needed or used by the body, all you are doing is making “expensive urine” – the body makes plenty of creatine, it is not stored when a supplement is taken [the textbook is WRONG on this point – page 133]

Stored glycogen used for initial 3-5 minutes of exercise

Aerobic catabolism of glucose, fatty acids, and other high-energy molecules for long term energy and exercise

Energy Required for Muscle Activity

Slide 6.9

activity of muscles can vary
Isotonic contractions: muscle shortens, movement occurs

Isometric contractions: muscle doesn’t shorten, no movement

Degree of nerve activation influences force

Motor unit: a nerve and all of the muscle cells it innervates

Muscle tension: the mechanical force generated by muscles when they contract

All-or-none principle: muscle cells never contract on their own and a contraction is never partial – the myofibril bundles ALL contract and ALL perform a complete contraction

Twitch: complete cycle of contraction and relaxation

Muscle tone: some motor units are contracting and some relaxing at any one time in a whole muscle – creates an intermediate level of “background” force in the muscle

Recruitment: increasing tone (or force of contraction) by activating more motor units

Activity of Muscles Can Vary

Slide 6.10

muscle contraction myogram
Latent period: from stimulation to contraction starts

Contraction: time during which muscle shortens

Relaxation: muscle returns to its original length

Muscle Contraction: Myogram

Summation: increasing muscle force by increasing rate of motor unit stimulation

Tetanus: stimulation rate so frequent that muscle cannot relax and stays in continuous maximum contraction (spasm)

Figure 6.10

Slide 6.11

muscle activity
Slow twitch vs. fast twitch fibers

Slow twitch: endurance, long duration contraction, contain myoglobin (thigh muscles of a marathon runner, ex.)

Jogging, swimming, biking

Fast twitch: strength, white muscle, short duration contraction (forearms of baseball slugger, ex.)

Sprinting, weight lifting, tennis

Muscle Activity

Slide 6.12

exercise training
Strength training

Resistance training

Short, intense

Builds more fast-twitch myofibrils

Aerobic training

Builds endurance

Increases blood supply to muscle cells

Target heart rate (65-85% of [220 – your age]) at least 20 minutes, three times a week

Exercise Training

Slide 6.13

features of cardiac and smooth muscles
Activation of cardiac and smooth muscles


Specialized adaptations in each

Speed and sustainability of contractions

Arrangement of myosin and actin filaments

Regular arrangement in cardiac

Attachments at various angles in smooth muscle, not regular

Features of Cardiac and Smooth Muscles

Slide 6.14

diseases and disorders of the muscular system
Muscular dystrophy: genetic disorders that lack a particular muscle protein (dystrophin), loss of muscle fibers, muscle wasting and weakness

Tetanus: “lock jaw”, a common problem before vaccinations, now is very rare, caused by bacteria toxin that over stimulates motor unit nerves

Muscle cramps: “charley horse” uncontrolled muscle contractions due to ATP, potassium, muscle fatigue, dehydration or build-up of lactic acid

Pulled muscles: a “strain”, muscle fibers are torn with bleeding, swelling, pain

Plantar Fasciitis: inflammation of the broad ligament in sole of foot, very painful, treated with steroid injections

Diseases and Disorders of the Muscular System

Slide 6.15