Copyright © 2010 Pearson Education, Inc. The Muscular System.

Copyright © 2010 Pearson Education, Inc.

The Muscular System


Muscle Fatigue Lab

• Where was the primary source of energy coming from in order to complete the exercises?

• What caused the “burning sensation”?


Video Questions – Copy Down

1. As it relates to the swimmer, where does most of his energy come from?

2. Carbohydrates are converted to ________.

3. Describe what “hitting the wall” is and why it happens?

4. How does the body get a new fuel source?

5. How does training affect the swimmer’s heart rate? Why is this beneficial?


Muscular System

• State the 3 main types of muscles.

• Specify the functions of skeletal muscle tissue.

• Describe the organization of muscle at the tissue level.


Introduction

• 3 types of muscle tissue:

– Skeletal

– Cardiac

– Smooth


7-1: Skeletal Functions

1. Produce movement of skeleton

2. Maintain posture & body position

3. Support soft tissues

4. Guard entrances & exits

5. Regulate body temp


7-2: Skeletal MusclesA. Muscle cells are called fibers

B. Blood Vessels

C. Nerves

D. 3 Layers of Connective Tissue

1. Epimysium: outermost layer, separates muscle from surrounding tissues

2. Perimysium• Surrounds muscle fiber bundles (fascicles)• Contains blood vessels & nerves

A. Endomysium

A.Surrounds individual muscle fibers

B.Contains stem cells for repair


– Collagen from 3 CT layers form:• tendons

– attach muscle to bone• aponeurosis (sheets)

– connect muscles


Let’s Recap1.What are the 3 layers of CT in a muscle? List

them from superficial to deep.2.What is the difference between a tendon and

an aponeurosis?3.What is one skeletal function other than

movement and support?


7-3: Skeletal Muscle Fibers• Sarcolemma (PM)

• Sarcoplasm (cytoplasm)

• Transverse tubules - transmit nerve impulses thru entire fiber

• Sarcoplasmic reticulum - surrounds each myofibril, Stores Ca2+


7-3: Skeletal Muscle Fibers

• Myofibrils are bundles of protein filaments called myofilaments:– 2 types:

1. Thin filaments made of actin2. Thick filaments made of myosin


7-3: Skeletal Muscle Fibers• Sarcomeres - smallest functional unit

– Z lines: boundaries of sarcomere

– I Band: Actin A Band: Myosin

– Zone of overlap: where thick and thin filaments overlap

– H Band: area around the M line

• has thick filaments but no thin filaments

• Striations – alternating thick & think filaments


Striations



• Thin filaments

– Tropomyosin: covers active sites of actin

• prevents actin–myosin interaction

– Troponin: holds tropomyosin in position

• Thick filaments – head attaches to active site of actin during contraction, forming a cross-bridge



• Sliding filament theory

1. SR releases Ca2+

2. Ca2+ binds to troponin causes shape Δ

3. tropomyosin swings away exposes active site

4. myosin & actin form cross-bridge contraction


Sarcomere Shortening

Figure 7-3


7-4: Neuromuscular Junctions (NMJ)

• NMJ – link btwn motor neuron & muscle fiber (Fig 7-4)

– Action potential (electrical signal) arrives

– Neurotransmitter acetylcholine (Ach) is released

into synaptic cleft

– Ach binds to muscle cell at motor end plate

influx of Na+

– Action potential travels across sarcolemma & down

T tubules


Structure and Function of the Neuromuscular Junction

Figure 7-4 b


7-5: Tension

• The all-or-none principle: a muscle fiber is either

contracted or relaxed

• But muscle Tension varies

– frequency of stimulation ([Ca2+] in sarcoplasm)

– fiber’s resting length (length of zones of overlap)


Effects of Repeated Stimulations

• Complete Tetanus (tetany)

– maximum tension produced when rate of stimulation eliminates relaxation phase

Figure 7-7


7-5: Tension

• Motor unit – all the muscle fibers controlled by a single

motor neuron

– Tension varies based on the # of motor units activated

– smaller motor unit more precise control

• Recruitment – activation of more and more motor units in

a muscle smooth ↑ in tension


Motor Units

Figure 7-8


7-5: Tension

• Muscle tone – tension at rest stabilizes bones & joints

• Isotonic contraction: muscle Δ’s length

• Isometric “ ”: muscle develops tension but does

NOT Δ length


7-6: ATP (cellular E)

• Glucose is stored in muscles as glycogen

• Creatine phosphate (CP)

– stores excess ATP in resting muscle

– can provide E for ~15 sec.


7-6: ATP

A. Aerobic metabolism in mitochondria

• resting fibers use ATP to form glycogen & CP

• Contracting fibers use glycogen 1st, then fat for ATP production

• provides 95% of ATP in resting cell

• yields ~34 ATP

B. Glycolysis (anaerobic) - breakdown of glucose in sarcoplasm

primary E source for peak activity

• results in lactic acid formation if no O2 is present

• yields 2 ATP


7-6: ATP

• Muscle fatigue results from exhaustion of E reserves

OR lactic acid accumulation

• Recovery period Liver converts lactic acid to pyruvic

acid & releases glucose into blood to recharge muscle

glycogen reserves

– Oxygen debt: additional O2 is needed


7-7: Fiber Type & Conditioning

• Hypertrophy: muscle growth

– ↑’s # of myofibrils, mitochondria & glycogen reserves & muscle fiber diameter

• Atrophy: fibers become small & weak due to lack of stimulation

– ↓’s muscle size & tone



• Anaerobic activities: use fast fibers

– improved by frequent, brief, intense workouts

• Aerobic activities (endurance):

– supported by mitochondria

– improved by cardiovascular training



• Fast fibers– strong, quick

contractions – large diameter, few

mitochondria– fatigue quickly– large glycogen

reserves

• Slow fibers– slow to contract– small diameter, more

mitochondria

– high O2 supply

– contain myoglobin (red pigment that stores O2)


7-8: Cardiac & Smooth Muscle

• Cardiac Muscle Cells– 1 nucleus– striated, involuntary– branched

– connected by intercalated discs

• contain gap junctions allow ion movement btwn cells pass action potentials from cell to cell


7-8: Cardiac & Smooth Muscle

– Automaticity: contraction w/o neural stimulation

• controlled by pacemaker cells

– Longer contraction time

– No tetanus (sustained contractions)…why is this important?

– Ca2+ come from SR and ECF

– Aerobic metabolism only


7-8: Cardiac & Smooth Muscle• Smooth Muscle Cells

– 1 nucleus– nonstriated, involuntary– spindle-shaped– found in walls of blood

vessels & organs• regulate movement of

materials• form sphincters (rings)


7-8: Cardiac & Smooth Muscle– Ca2+ mostly from ECF– contract over greater range of lengths enable large

Δ’s in volume– many cells not innervated (involuntary)

• contract automatically (by pacesetter cells)• or in response to surrounding conditions


7-12: Effects of Aging

• Skeletal muscle fibers become:

– smaller in diameter • fewer myofibrils, myoglobin, glycogen, ATP, CP

– less elastic (increasing amounts of fibrous tissue (fibrosis) restricts movement & circulation)

• Decreased tolerance for exercise– Slower delivery of blood to muscles during exercise, faster fatigue

– Impaired ability to eliminate heat overheating

• Decreased ability to recover from injury

• Rate of decline in muscle performance is = in all people

Copyright © 2010 Pearson Education, Inc. The Muscular System.

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