Muscle Tissue
sarcoplasmic reticulum
- A fluid‐filled system of membranous sacs - encircles each myofibril - similar to smooth endoplasmic reticulum in nonmuscular cells - stores calcium ions (Ca2+)
terminal cisterns
- Dilated end sacs of the sarcoplasmic reticulum - butt against the T tubule from both side
Troponin
- Holds tropomyosin in place - regulatory protein - Regulatory protein that is a component of thin filament; when calcium ions (Ca2+) bind , Ca2+ changes shape; this conformational change moves tropomyosin away from myosin‐binding sites on actin molecules, and muscle contraction subsequently begins as myosin binds to actin.
aerobic cellular respiration
- Used when sufficient amounts of oxygen are used during rest or light exercise. - ATP used for muscular activity is produced from a series of oxygen‐requiring reactions - pyruvic acid enters the mitochondria, where it is completely oxidized in reactions that generate ATP, carbon dioxide, water, and heat - One molecule of glucose yields about 36 molecules of ATP
Fascia
- a dense sheet or broad band of irregular connective tissue that lines the body wall and limbs and supports and surrounds muscles and other organs of the body - holds muscles with similar functions together
Anaerobic cellular respiration
- a series of ATP‐producing reactions that do not require oxygen - used during Large amounts of exercise when not enough oxygen is available - produces a net gain of 2 molecules of ATP. - When muscle activity continues and the supply of creatine phosphate within the muscle fibers is depleted, glucose is catabolized to generate ATP - Glucose easily passes from the blood into contracting muscle fibers via facilitated diffusion, and it is also produced by the breakdown of glycogen within muscle fibers. Then, a series of reactions known as glycolysis quickly breaks down each glucose molecule into two molecules of pyruvic acid. Glycolysis occurs in the cytosol. - convert most of the pyruvic acid to lactic acid in the cytosol. - About 80% of the lactic acid produced in this way diffuses out of the skeletal muscle fibers into the blood. - Liver cells can convert some of the lactic acid back to glucose; conversion reduces acidity of the blood. Anaerobic cellular respiration can provide enough energy for about 30 to 40 seconds of maximal muscle activity.
cardiac muscle tissue
- forms most of the heart wall - is striated - is involuntary
Fast Oxidative - Glycolytic FIbers
- intermediate in diameter between the other two types of fibers - can generate considerable ATP by aerobic cellular respiration, which gives them a moderately high resistance to fatigue - generate ATP by anaerobic glycolysis - "fast" because the ATPase in their myosin heads hydrolyzes ATP three to five times faster than the myosin ATPase in SO fibers, which makes their speed of contraction faster - reach peak tension more quickly than those of SO fibers but are briefer in duration—less than 100 msec - fibers contribute to activities such as walking and sprinting
Fast Glycolytic Fibers
- largest in diameter and contain the most myofibrils - can generate the most powerful contractions - have low myoglobin content - relatively few blood capillaries - few mitochondria - appear white in color - contain large amounts of glycogen and generate ATP mainly by glycolysis - contract strongly and quickly - adapted for intense anaerobic movements of short duration - for Weightlifting or throwing a ball
Smooth muscle tissue
- located in the walls of hollow internal structures, such as blood vessels, airways, and most organs in the abdominopelvic cavity - found in the skin, attached to hair follicles - lacks the striations - usually involuntary - regulated by neurons that are part of the autonomic (involuntary) division of the nervous system
Skeletal muscle tissue
- move bones of the skeleton - is striated: Alternating light and dark protein bands (striations) are seen when the tissue is examined with a microscope - works mainly in a voluntary manner - activity can be consciously controlled by neurons - controlled subconsciously to some extent; i.e.- Diaphragm and posture muscles
2 Sources of oxygen
- oxygen that diffuses into muscle fibers from the blood and - oxygen released by myoglobin within muscle fibers
Endomysium
- penetrates the interior of each fascicle and separates individual muscle fibers from one another - mostly reticular fibers
tropomyosin
- regulatory protein - are also part of the thin filament - Blocks myosin from binding with actin - held in place by troponin molecules - Regulatory protein that is a component of thin filament; - when skeletal muscle fiber is relaxed, covers myosin‐binding sites on actin molecules, thereby preventing myosin from binding to actin.
Slow Oxidative Fibers
- smallest in diameter and thus are the least powerful type of muscle fibers - appear dark red because they contain large amounts of myoglobin and many blood capillaries - generate ATP mainly by aerobic cellular respiration - said to be "slow" because the ATPase in the myosin heads hydrolyzes ATP relatively slowly and the contraction cycle proceeds at a slower pace than in "fast" fibers - slow speed of contraction - very resistant to fatigue and are capable of prolonged, sustained contractions for many hours - fatigue‐resistant fibers are adapted for maintaining posture and for aerobic, endurance‐type activities such as running a marathon.
myofibrils
- the contractile organelles of skeletal muscle - extend the entire length of a muscle fiber - prominent striations make the entire skeletal muscle fiber appear striped (striated)
sarcoplasm
- the cytoplasm of a muscle fiber - Within the sarcolemma - includes a substantial amount of glycogen, which is a large molecule composed of many glucose molecules. Glycogen can be used for synthesis of ATP
Eccentric isotonic contraction
- the length of a muscle increases during a contraction. - lower the book to place it back on the table - the tension exerted by the myosin cross‐bridges resists movement of a load (the book, in this case) and slows the lengthening process. - walking downhill
Myosin
- the main component of thick filaments and functions as a motor protein in all three types of muscle tissue - shaped like two golf clubs twisted together - tail (twisted golf club handles) points toward the M line in the center of the sarcomere
myoglobin
- the sarcoplasm contains a red‐colored protein - protein, found only in muscle, binds oxygen molecules that diffuse into muscle fibers from interstitial fluid - releases oxygen when it is needed by the mitochondria for ATP production - lie in rows throughout the muscle fiber, strategically close to the contractile muscle proteins that use ATP during contraction so that ATP can be produced quickly as needed
Isotonic Contraction
- the tension (force of contraction) developed in the muscle remains almost constant while the muscle changes its length. - used for body movements and for moving objects
Concentric isotonic contraction
- the tension generated is great enough to overcome the resistance of the object to be moved, the muscle shortens and pulls on another structure, such as a tendon, to produce movement and to reduce the angle at a joint - Picking a book up off a table involves
Isometric Contraction
- the tension generated is not enough to exceed the resistance of the object to be moved, and the muscle does not change its length - example would be holding a book steady using an outstretched arm - important for maintaining posture and for supporting objects in a fixed position
Actin
1
I Band
1
Sacromere
1
Z Disc
1
Functions of Muscular Tissue
1) Producing body movements 2) Stabilizing body positions 3) Storing and moving substances within the body 4) Generating heat
3 types of Skeletal muscle fibers
1) Slow oxidative fibers 2) fast oxidative-glycolytic fibers 3) fast glycolytic fibers
Properties of Muscular Tissue
1)Electrical excitability 2)contractility 3) extensibility 4) Elasticity
Contraction Cycle
1. ATP hydrolysis. 2. Attachment of myosin to actin to form cross‐bridges. 3. Power stroke. 4. Detachment of myosin from actin
nerve impulse (nerve action potential)
1. Release of acetylcholine. 2. Activation of ACh receptors. 3. Production of muscle action potential. 4. Termination of ACh activity.
Epimysium
10
I Band
10
Sacromere
10
Z Disc
10
Fasicle
11
Perimysium
12
Muscle FIber (cell)
13
Myofibril
14
Endomysium
15
Perimysium
16
Somatic Motor Neuron
17
Blood Capillary
18
Endomysium
19
H Zone
2
M Line
2
Thin Filament (Actin)
2
Troponin
2
Z Disc
2
Nucleus
20
Muscle Fiber
21
Striations
22
Sarcoplasm
23
Sarcolemma
24
Myofibril
25
Filament
26
H Zone
3
I Band
3
Thick Filament (Myosin)
3
Tropomyosin
3
A Band
4
Bone
4
Fascicle
4
I Band
4
M Line
4
Myosin-binding site (covered by Tropomyosin)
4
Z Disc
4
A Band
5
Periosteum
5
Z Disc
5
Sarcomere
6
Tendon
6
Thick Filament (Myosin)
6
Thin Filament, Actin
6
Epimysium
7
H Zone
7
Thick Filament, Myosin
7
Thin Filament (actin)
7
Belly of skeletal muscle
8
I Band
8
Z Disc
8
A Band
9
I Band
9
M Line
9
Perimysium
9
Acetylcholine
A neurotransmitter liberated by many peripheral nervous system neurons and some central nervous system neurons. It is excitatory at neuromuscular junctions but inhibitory at some other synapses (for example, it slows heart rate).
triad
A transverse tubule and the two terminal cisterns on either side
2
ACh binds to ACh receptor
2
ACh diffuses across synaptic cleft, binds to its receptors in the motor end plate, and triggers a muscle action potential (AP).
4
ACh is broken down
1
ACh is released from synaptic vessel
3
Acetylcholinesterase in synaptic cleft destroys ACh so another muscle action potential does not arise unless more ACh is released from motor neuron.
synaptic cleft
At most synapses a small gap
1
Axon collateral of somatic motor neuron
3
Axon terminal
autorhythmicity
Built-in heart rhythm
Fascicle
Bundle of muscle fibers wrapped in perimysium.
5
CA2+ binds to troponin on the thin filament, exposing the binding sites for myosin.
7
CA2+ release channels in the SR close and CA2+ active transport pumps use ATP to restore low level CA2+ in sarcoplasm.
2
Ca2+
5
Ca2+ Release channels Closed
13
Ca2+ binds to troponin, which changes the shape of the troponin-tropomyosin complex and uncovers the myosin-binding sites on actin.
6
Ca2+ release channels open
sarcoplasmic reticulum
Ca2+‐storing tubular system similar to smooth endoplasmic reticulum
Filaments (myofilaments)
Contractile proteins within myofibrils that are of two types: thick filaments composed of myosin and thin filaments composed of actin, tropomyosin, and troponin; sliding of thin filaments past thick filaments produces muscle shortening.
5
Contraction cycle continues if ATP is available and Ca2+ level on sarcoplasm is high.
6
Contraction: power strokes use ATP; myosin heads bind to actin, swivel, and release; thin filaments are pulled toward center of sarcomere.
A Band
Dark, middle part of sarcomere that extends entire length of thick filaments and includes those parts of thin filaments that overlap thick filaments.
I Band
Lighter, less dense area of sarcomere that contains remainder of thin filaments but no thick filaments. A Z disc passes through center of each
Muscle fiber (cell)
Long cylindrical cell covered by endomysium and sarcolemma; contains sarcoplasm, myofibrils, many peripherally located nuclei, mitochondria, transverse tubules, sarcoplasmic reticulum, and terminal cisterns. The fiber has a striated appearance.
synaptic vesicle
Membrane‐enclosed sac in a synaptic end bulb that stores neurotransmitters.
8
Motor end plate
4
Muscle AP traveling along transverse tubule opens CA2+ release channels in the sarcoplasmic reticulum (SR) membrane, which allows calcium ions to flood into the sarcoplasm.
4
Muscle action potential
3
Muscle action potential is produced
9
Muscle relaxes
6
Myofibril
11
Myosin
1
Myosin Heads Hydrolyze ATP and become reoriented and energized
3
Myosin cross-bridges rotate toward center of sarcomere (Power Stroke)
4
Myosin heads bind ATP, the cross-bridges detach from actin
2
Myosin heads bind to actin, forming cross-bridges
10
Myosin-binding site on actin
H Zone
Narrow region in center of each A band that contains thick filaments but no thin filaments.
Z Disc
Narrow, plate‐shaped regions of dense material that separate one sarcomere from the next.
4
Nerve impulse
1
Nerve impulse arrives at axon terminal of motor neuron and triggers release of acetylcholine (ACh).
neurotransmitter
One of a variety of molecules within axon terminals that are released into the synaptic cleft in response to a nerve impulse, and that change the membrane potential of the postsynaptic neuron.
Skeletal muscle
Organ made up of fascicles that contain muscle fibers (cells), blood vessels, and nerves; wrapped in epimysium.
M Line
Region in center of H zone that contains proteins that hold thick filaments together at center of sarcomere.
Motor End Plate
Region of the sarcolemma of a muscle fiber (cell) that includes acetylcholine (ACh) receptors, which bind ACh released by synaptic end bulbs of somatic motor neurons.
1
Sarcolemma
7
Synaptic cleft (space)
6
Synaptic end bulb
3
Terminal Cistem of SR
axon terminal
Terminal branch of an axon where synaptic vesicles undergo exocytosis to release neurotransmitter molecules. Also called telodendria (tel′‐o‐DEN‐drea).
Muscle Fatigue
The inability of a muscle to maintain force of contraction after prolonged activity
muscular hypertrophy
The muscle growth that occurs after birth occurs by enlargement of existing muscle fibers
somatic motor neurons
The neurons that stimulate skeletal muscle to contract
epimysium
The outermost layer of dense, irregular connective tissue, encircling the entire muscle
Motor Unit Recruitment
The process in which the number of active motor units increases
Myogram
The record of a muscle contraction
7
Thin Filament (actin)
Myofibril
Threadlike contractile elements within sarcoplasm of muscle fiber that extend entire length of fiber; composed of filaments.
2
Transverse Tubules (T-Tubes)
9
Tropomyosin
8
Troponin
12
Troponin holds tropomyosin in position to block myosin-binding site on actin.
8
Troponin-tropomyosin complex slides back into position where it blocks the myosin binding sites on actin.
1
Voltage-Gated Ca2+ Channel
twitch contraction
a brief contraction of all the muscle fibers in a motor unit of a muscle in response to a single action potential in its motor neuron
tendon
a cord of dense regular connective tissue that attaches muscle to the periosteum of bone
synapse
a region where communication occurs between two neurons, or between a neuron and a target cell—in this case, between a somatic motor neuron and a muscle fiber
endomysium
a sheath of areolar connective tissue that wraps around individual skeletal muscle fibers
Electromyography
a test that measures the electrical activity (muscle action potentials) in resting and contracting muscles
endon (synovial) sheath
a two‐layer tube of fibrous connective tissue enclosing certain tendons
Perimysium
also a layer of dense, irregular connective tissue, but it surrounds groups of 10 to 100 or more muscle fibers, separating them into bundles called fascicles
recovery oxygen uptake
amount of oxygen needed to restore the body's metabolic conditions back to resting levels after exercise
I band
area in the sarcomere where only thin filaments are present but thick filaments are not
H Zone
area of only thick filaments
subcutaneous layer
areolar and adipose connective tissue that separates muscle from skin
2
axon terminal
fascicles
bundles of muscle fibers
Fibromyalgia
chronic, painful, nonarticular rheumatic disorder that affects the fibrous connective tissue components of muscles, tendons, and ligaments
M line
composed of supporting proteins holding thick filaments together at the H zone
aponeurosis
connective tissue elements extended as a broad, flat layer
sarcomere
contracting unit of a skeletal muscle fiber
eccentric isotonic contraction
contraction in which a muscle lengthens
isometric contraction
contraction in which muscle tension is generated without shortening of the muscle
concentric isotonic contraction
contraction in which the muscle shortens
Sarcoplasm
cytoplasm of a muscle fiber
fascia
dense irregular connective tissue that lines the body wall and limbs and holds functional muscle units together
Perimysium
dense irregular connective tissue that separates a muscle into groups of individual muscle fibers
Muscle fatigue
inability of a muscle to maintain its strength of contraction or tension during prolonged activity
muscular hyperplasia
increase in the number of fibers
transverse tubules
invaginations of the sarcolemma from the surface toward the center of the muscle fiber
wave summation
larger contractions resulting from stimuli arriving at different times
A Band
middle area in the sarcomere where thick and thin filaments are found
Muscle fiber
muscle cell
Satellite Cells
myoblasts that persist in mature skeletal muscle
4
neuromuscular junction (NMJ)
myoglobin
oxygen‐binding protein found only in muscle fibers
sarcolemma
plasma membrane of a muscle fiber
motor unit recruitment
process of increasing the number of activated motor units
Muscle Tone
produced by the continual involuntary activation of a small number of skeletal muscle motor units; results in firmness in skeletal muscle
5
sarcolemma
9
sarcolemma
Z Disc
separates the sarcomeres from each other
Motor unit
somatic motor neuron plus all the skeletal muscle fibers it stimulates
fused (complete) tetanus
sustained contraction of a muscle, with no relaxation between stimuli
unfused (incomplete) tetanus
sustained, but wavering contraction with partial relaxation between stimuli
neuromuscular junction
synapse between a motor neuron and a muscle fiber
3
synaptic end bulb
5
synaptic vesicle containing acetylcholine (ACh)
twitch contraction
the brief contraction of all the muscle fibers in a motor unit in response to a single action potential in its motor neuron
somatic motor neurons
the neurons that stimulate skeletal muscle fibers to contract
epimysium
the outermost connective tissue layer that encircles an entire skeletal muscle
sarcolemma
the plasma membrane of a muscle cell
stress-relaxation response
the smooth muscle action that allows the fibers to maintain their contractile function even when stretched
neuromuscular junction (NMJ)
the synapse between a somatic motor neuron and a skeletal muscle fiber
transverse (T) tubules
tunnel in from the surface toward the center of each muscle fiber
Concentric and eccentric
two types of isotonic contractions
