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Hole’s Human Anatomy and Physiology
Shier, Butler & Lewis
Twelfth Edition
Chapter 9 Outline
9.1: Introduction
A. Three (3) Types of Muscle Tissues
1. Skeletal Muscle
a. Usually attached to bones
b. Under conscious control
c. Somatic
d. Striated
2. Smooth Muscle
a. Walls of most viscera, blood vessels and skin
b. Not under conscious control
c. Autonomic
d. Not striated
3. Cardiac Muscle
a. Wall of heart
b. Not under conscious control
c. Autonomic
d. Striated
Functions of the Muscles:
1. Move Skeleton
- control openings
ex: mouth, anus
2. Stabilize Joints
- maintain posture
3. Produce Heat
- exercise
4. Produce Facial Expressions
- sad, happy, fearful
5. Protection
- close eye, mouth
9.2: Structure of Skeletal Muscle
A. Skeletal Muscle
1. Organ of the muscular system
a. Skeletal muscle tissue
b. Nervous tissue
c. Blood
d. Connective tissues
2. Fascia – dense connective tissue that separates muscles and holds
muscles in position
3. Tendons – connects muscles to bone, dense regular connective tissue
4. Aponeuroses – broad, fibrous sheets that connect muscle to bone
Connective Tissue Coverings
A. Muscle coverings:
1. Epimysium – closely surrounds skeletal muscle
2. Perimysium – separates muscle tissue into smaller sections
Fascicles: bundles of skeletal muscle fibers
3. Endomysium – surrounds a muscle fiber
Fascicles – bundles of skeletal muscle fibers
Thick and thin myofilaments
1. Actin and myosin proteins
2. Titin is an elastic myofilament
Skeletal Muscle Fibers
A. Sarcolemma – muscle cell membrane
B. Sacroplasm – cytoplasm
Contains myofibrils
Thick and thin myofilaments
1. Actin and myosin proteins
2. Titin is an elastic myofilament
C. Sarcoplasmic reticulum (SR) – membranous channels that surrounds each
myofibril; store Ca++
D. Transverse (‘T’) tubule – a set of membranous channels that extend into the
sarcoplasm as invaginations continuous with the sarcolemma and contains
extracellulat fluid
E. Triad
1. Cisternae of SR
2. T tubule
F. Sarcomere: the structural and function unit of a myofibril
9.3: Skeletal Muscle Contraction
A. Movement within the myofilaments
B. I band (thin) – light bands composed of thin actin filaments
C. A band (thick and thin) – dark bands, composed of myosin filaments
overlapping thin actin filaments
D. H zone (thick) – central region of A band, only thick filaments
E. Z line (or disc) – appear in center of I bands
F. M line – protein that holds thick filament in place
* A sarcomere extends from one Z line to the next
Myofilaments
A. Thick myofilaments
1. Composed of myosin protein
2. Form the cross-bridges
B. Thin myofilaments
1. Composed of actin protein
2. Associated with troponin and tropomyosin proteins
Neuromuscular Junction
A. Also known as NMJ or myoneural junction
B. Site where an axon and muscle fiber meet
C. Parts to know:
1. Motor neuron
2. Motor end plate
3. Synapse
4. Synaptic cleft
5. Synaptic vesicles
6. Neurotransmitters
Motor Unit
A. Single motor neuron
B. All muscle fibers controlled by motor neuron
C. As few as four fibers
D. As many as 1000’s of muscle fibers
Stimulus for Contraction
A. Acetylcholine (ACh)
B. Nerve impulse causes release of ACh from synaptic vesicles through
exocytosis
C. ACh binds to ACh receptors on motor end plate
D. Generates a muscle impulse
E. Muscle impulse eventually reaches the SR and the cisternae
Excitation-Contraction Coupling
A. Muscle impulses cause SR to release calcium ions into cytosol
B. Calcium binds to troponin to change its shape
C. The position of tropomyosin is altered
D. Binding sites on actin are now exposed
E. Actin and myosin molecules bind via myosin cross-bridges
The Sliding Filament Model of Muscle Contraction
A. When sarcromeres shorten, thick and thin filaments slide past one another
B. H zones and I bands narrow
C. Z lines move closer together
Cross Bridge Cycling
A. Myosin cross-bridge attaches to actin binding site
B. Myosin cross-bridge pulls thin filament - POWERSTROKE
C. ADP and phosphate released from myosin
D. New ATP binds to myosin
E. Linkage between actin and myosin cross-bridge break
F. ATP splits
G. Myosin cross-bridge goes back to original position – RECOCKING
Relaxation
A. Acetylcholinesterase – rapidly decomposes Ach remaining in the synapse
B. Muscle impulse stops
C. Stimulus to sarcolemma and muscle fiber membrane ceases
D. Calcium moves back into sarcoplasmic reticulum (SR)
E. Myosin and actin binding prevented
F. Muscle fiber relaxes
RIGOR MORTIS – a few hours after death, the skeletal muscles contract, fixing the
joints. Results from an increase in membrane permeability which promotes cross bridge
attachment, and a decrease in the availability of ATP
Oxygen Debt
A. Oxygen debt – amount of oxygen needed by liver cells to use the accumulated
lactic acid to produce glucose
1. Oxygen not available
2. Glycolysis continues
3. Pyruvic acid converted to lactic acid
4. Liver converts lactic acid to glucose
Muscle Fatigue
A. Inability to contract muscle
B. Commonly caused from:
1. Decreased blood flow
2. Ion imbalances across the sarcolemma
3. Accumulation of lactic acid
C. Cramp – sustained, involuntary muscle contraction
PEOPLE WHO EXERCISE REGULARLY PRODUCE LESS LACTIC ACID
WHY?
1. Training increases new capillaries in muscle
2. Training adds mitochondria in muscle
Lactic acid threshold – when lactic acid begins to accumulate in the bloodstream.
Exercise at or below this, lactate is removed by the body without
building up
Heat Production
A. By-product of cellular respiration
B. Muscle cells are major source of body heat
C. Blood transports heat throughout body core
9.4: Muscular Responses
A. Muscle contraction can be observed by removing a single skeletal muscle fiber
and connecting it to a device that senses and records changes in the overall length
of the muscle fiber.
Threshold Stimulus
A. Minimal strength required to cause contraction
Recording of a Muscle Contraction
A. Recording a Muscle Contraction
1. Twitch
a. Latent period
b. Period of contraction
c. Period of relaxation
2. Refractory period
3. All-or-none response
* A twitch does not produce anything useful, all normal activities involve
sustained muscular contractions
Length-Tension Relationship
Summation
A. Process by which individual twitches combine
B. Produces sustained contractions
C. Can lead to tetanic contractions
Sustained Contractions
A. Smaller motor units (smaller diameter axons) - recruited first
B. Larger motor units (larger diameter axons) - recruited later
C. Produce smooth movements
D. Muscle tone – continuous state of partial contraction
Types of Contractions
A. Isotonic – muscle contracts and changes length
B. Eccentric – lengthening contraction
C. Concentric – shortening contraction
D. Isometric – muscle contracts but does not change length
Fast Twitch and Slow Twitch Muscle Fibers
A. Slow-twitch fibers (Type I)
1. Always oxidative
2. Resistant to fatigue
3. Red fibers
4. Most myoglobin
5. Good blood supply
B. Fast-twitch glycolytic fibers (Type IIa)
1. White fibers (less myoglobin)
2. Poorer blood supply
3. Susceptible to fatigue
C. Fast-twitch fatigue-resistant fibers (Type IIb)
1. Intermediate fibers
2. Oxidative
3. Intermediate amount of myoglobin
4. Pink to red in color
5. Resistant to fatigue
Myoglobin – pigment that gives muscle cells the reddish brown color
- Loosely binds to oxygen, temporarily stores it
Hemoglobin = blood
- Myoglobin = muscle
Myoglobin is NOT found in smooth muscles
Terminology
Origin – the end of a muscle that attaches to a relatively immovable part
Insertion – the end of a muscle attached to a movable part
Origin
Tibialis Anterior
Insertion
Lateral Condyle and
Cuneiform and 1st metatarsal
lateral surface of tibia
Agonist (prime mover) – the muscle primarily responsible for producing a
movement
Synergist – muscles that contract and assist the prime mover
Antagonist – muscles that oppose a prime mover
Naming Muscles
Pectoralis Major – large muscle in chest region
Deltoid – shaped like a delta or triangle
Extensor Digitorum – extends digits
Biceps Brachii – 2 headed muscle in the arm
Sternocleidomastoid – attached to sternum, clavicle, and mastoid process
External oblique – located near the outside with fibers that run obliquely or in a slanting
direction
Steps of a Muscle Contraction
1.
Neuromuscular control
- Action potential passes down nerve
- Nerve releases Acetylcholine (ACh)
2.
ACh binds to the sarcolemma
3. Muscle Fiber Action Potential
- ACh binds with receptors and opens Na+ channels
- Na+ channels open and Na+ moves in to muscle fiber
- decrease in resting potential
- Na+ rushes in and the sarcolemma depolarizes
- Depolarization spreads over the muscle fiber
- K+ channels open and the region repolarizes
4.
Ca++ is releases from the sarcoplasmic reticulum
- Ca++ is stored in the sarcoplasmic reticulum
- Depolarization releases the Ca++
- The Ca++ attaches to troponin and clears the actin binding sites
5.
Sliding Filament theory of Contraction
- Myosin head attaches to actin (high energy ADP + P configuration)
- Power stroke: myosin head pivots, pulling the actin filament to the
center
- The cross bridge detaches when a new ATP binds to the myosin
- Cocking of the myosin head occurs when ATP  ADP + P. Another
cross bridge can form
-
The distance between the Z lines shortens
The H zone disappears
The dark A band increases because the actin and myosin overlap more
The light I band shortens