Chapter 10 - Muscular Tissue Flashcards
Four main functions of muscle tissue
Producing body movements, stabilizing body positions, storing and moving substances within the body, generating heat
Shivering
Involuntary contractions that increase rate of heat production (contraction=heat)
Four properties of muscle tissue that contribute to homeostasis
Electrical excitability (action potentials respond to stimuli)
Contractility
Elasticity
Extensibility (stretch)
Fascia
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.
Fascia allows free movement of muscles; carries nerves, blood vessels, and lymphatic vessels; and fills spaces between muscles.
Epimysium
is the outer layer, encircling the entire muscle. It consists of dense irregular connective tissue.
Perimysium
is 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
Fascicles
The grainy look of meat, bundles of muscle fibers.
Endomysium
penetrates the interior of each fascicle and separates individual muscle fibers from one another. The endomysium is mostly reticular fibers.
Aponeurosis
When the connective tissue elements extend as a broad, flat sheet,
Nerve and blood supply
Generally, an artery and one or two veins accompany each nerve that penetrates a skeletal muscle.
Somatic motor neuron
neurons that stimulate skeletal muscle to contract threadlike axon that extends from the brain or spinal cord to a group of skeletal muscle fibers
Sarcolemma
plasma membrane of a muscle cell
Transverse tubules
Thousands of tiny invaginations of the sarcolemma, tunnel in from the surface toward the center of each muscle fiber.
Sarcoplasm
cytoplasm of a muscle fiber.
Myoglobin
This protein, found only in muscle, binds oxygen molecules that diffuse into muscle fibers from interstitial fluid. and releases when mitochondria need it
Myofibrils
Look like little threads, contractile organelles of skeletal muscle.
Sarcoplasmic reticulum
Fluid-filled system of membranous sacs
Terminal cisterns
Dilated end sacs of the sarcoplasmic reticulum butt against t tubule from both sides.
Triad
A transverse tubule and the two terminal cisterns
Muscular hypertrophy
muscle growth that occurs after birth occurs by enlargement of existing muscle fibers
Fibrosis
the number of new skeletal muscle fibers that can be formed by satellite cells is not enough to compensate for significant skeletal muscle damage or degeneration, the muscular tissue undergoes fibrosis, the replacement of muscle fibers by fibrous scar tissue.
Muscular atrophy
decrease in size of individual muscle fibers as a result of progressive loss of myofibrils.
Thin filament
are 8 nm in diameter and 1–2 m long* and composed mostly of the protein actin,
Thick filament
16 nm in diameter and 1–2 m long and composed mostly of the protein myosin
Sarcomere
basic functional units of a myofibril
Z disc
plate-shaped regions of dense protein material called Z discs separate one sarcomere from the next.
Myosin
motor protein in all three types of muscle tissue. like two twisty golf clubs
Titin
connects a Z disc to the M line of the sarcomere, thereby helping stabilize the position of the thick filament. Accounts for most elasticity and extensibility of myofibrils
Sliding filament mechanism
skeletal muscle shortens during contraction because the thick and thin filaments slide past one another.
Contraction cycle, four steps
ATP hydrolysis, Attachment of myosin to actin to form cross-bridges,
Power stroke,
Detachment of myosin from actin
Excitation contraction coupling
Increase in calcium concentration starts muscle contraction, decrease stops it. When a muscle fiber is relaxed, the concentration of calcium in the sarcoplasm is very low, but there is a large amount of calcium stored inside the SR.
Muscle action potential propagagtes along sarcolemma into T tubles, calcium channels open, flooding, combines/moves tropomyosin away from myosin binding sites on actin. Myosin binds.
Ca2+ release channels
Open in the SR with muscle action potential
Ca2+ active transport pump
Use ATP to move calcium from sarcoplasm into SR.
length tension relationship
Forcefulness of muscle contraction depends on the length of the sarcomeres within a muscle before contraction begins.
Neuromuscular junction
Where muscle action potentials arise, the synapse between a somatic motor neuron and a skeletal muscle fiber
Somatic motor neuron
the neurons that stimulate skeletal muscle fibers to contract. has a threadlike axon that extends from the brain or spinal cord to a group of skeletal muscle fibers.
Synapse
Region where communication occurs between two neurons, or between a neuron and a target cell.
Synaptic cleft
A small gap separating two cells.
Neurotransmitter
a chemical messenger between two cells
Axon terminal
End of the motor neuron
Synaptic end bulb
end divides into a cluster of SEB, the neural part of the NMJ.
Synpatic vesicle
Suspended in the cytosol within each SEB are hundreds of these membrane enclosed sacs.
ACh
Inside each synaptic vesicle are thousands of molecules of acetylcholine, the neurotransmitter
Motor end plate
The region of the sarcolemma opposite the synaptic end bulbs, is the muscle fiber part of the NMJ.
ACh receptor
30-40mil, integral transmembrane proteins to which ACh specifically binds.
Junctional folds
Deep grooves in the motor end plate that provide a large surface area for ACh.
Muscle action potential - steps
1) Release- ACh is released from synaptic vesicle
2) Activation-ACh binds to ACh receptor
3) Production -Muscle action potential is produced
4) Termination-ACh is broken down
AChE
Enzyme which breaks down ACh
Production of ATP in muscle fibers
A large amount of ATP is required to power the contraction cycle, to pump calcium into the sarcoplasmic reticulum, and for other metabolic reactions. However the ATP present inside muscle fibers is only enough for a few seconds. Thus, must make more through 1)creatine phosphate, 2) anaerobic glycolysis or 3) aerobic respiration
Creatine phosphate
When relaxed produce excess ATP. Excess synthesizes creatine phosphate.
The enzyme creatine kinase catalyzes the transfer of 1 phosphate group from ATP to creatine, or from creatine to ADP which generates ATP. (first source, lasts 15seconds)
Anaerobic glycolysis
Glucose is catabolized to generate ATP. Blood to contracting muscle fibers via facilitated diffusion. Also produced through breakdown of glycogen in muscle fibers. Produces 2 molecules of ATP, (w/o oxygen, 2 minutes)
Aerobic respiration
Pyruvic acid formed by glycolysis enters mitochondria (krebs, electron transport chain), producing ATP, CO2, H2O, heat. 30to32 molecules ATP, several minutes to an hour. Relies on oxygen.
Muscle fatigue
The inability of a muscle to maintain force of contraction after prolonged activity.
Central fatigue
Feelings of tiredness before muscle fatigue, caused by changes in central nervous system.
Oxygen debt
Added oxygen, over and above the resting consumption that is taken into the body after exercise. (1) to convert lactic acid back into glycogen stores in the liver, (2) to resynthesize creatine phosphate and ATP in muscle fibers, and (3) to replace the oxygen removed from myoglobin.
Recovery oxygen uptake
metabolic changes that occur during exercise can account for only some of the extra oxygen used after exercise.
elevated temp increases reactions, using more ATP, and tissue repair occurring.
Control of muscle tension
The total force or tension that a single muscle fiber can produce depends mainly on the rate at which nerve impulses arrive at the neuromuscular junction, as well as amount of stretch before contraction, nutrient and oxygen availability. The total tension a whole muscle can produce depends on the number of muscle fibers that are contracting in unison.
Motor unit
consists of a somatic motor neuron plus all of the skeletal muscle fibers it stimulates
Twitch contraction
the brief contraction of all muscle fibers in a motor unit in response to a single action potential in its motor neuron.
Latent period
a brief delay between application of the stimulus and beginning of contraction. 2 msec. the muscle action potential sweeps over the sarcolemma and calcium ions are released from the sarcoplasmic reticulum.
Contraction period
10-100msec. Calcium binds to troponin, myosin-binding sites on actin are exposed and cross-bridges form. Peak tension develops in the muscle fiber.
Relaxation period
10-100msec. Calcium is actively transported back into the sarcoplasmic reticulum, myosin-binding sites are covered by tropomyosin, myosin heads detach from actin, and tension in the muscle fiber decreases.
Refractory period
When a muscle fiber receives enough stimulation to contract, it temporarily loses its excitability and cannot respond for a time. 5msec for skeletal muscle, 300msec for cardiac muscles.
Frequency of stimulation
Number of nerve pulses arriving at neuromuscular junction per second.
Wave summation
stimuli arriving at different times cause larger contractions
Unfused (incomplete) tetanus
sustained but wavering contraction
Fused (complete) tetanus
Sustained contraction, no twitches. When a skeletal muscle fiber is stimulated at a higher rate of 80 to 100 times per second, it does not relax at all.
Motor unit recruitment
number of active motor units increases. Contraction doesn’t occur in unison to delay fatigue. Weakest recruited first.
Muscle tone
small amount of tautness or tension in the muscle due to weak, involuntary contractions of its motor units. established by neurons in the brain and spinal cord that excite the muscle’s motor neurons.
Flaccidity
Limpness, loss of muscle tone due to motor neurons serving a skeletal muscle being damaged or cut.
Isotonic contraction
Tension remains constant while muscle changes length.
Concentric isotonic contraction
tension great enough to overcome resistance, muscle shortens and pulls to produce movement (picking up a book from a table)
Eccentric isotonic contraction
Length of muscle increases during a contraction, muscle lengthens while contracting (placing a book on a table). Causes more damage.
Isometric contraction
Tension generated not enough to exceed resistance, muscle does not change length. (holding something steady, maintaining posture) expends energy without movement.
Slow oxidative fiber
dark red, large amounts of myoglobin and capillaries. many large mitochondria, generate ATP by aerobic respiration. 100to200msec. Resistant to fatigue.
Fast oxidative glycolytic fiber
Largest. Large amount of myoglobin and capillaries, dark red. high intracellular glycogen level generate ATP by anaerobic glycolysis. Fast, less than 100msec but brief.
Fast glycolytic fiber
Low myoglobin, few capillaries, few mitochondria, appear white. large amounts of glycogen generate ATP through glycoysis. strongly and quickly, fatigue quickly.
Distribution and recruitment of different types of fiber
Depends on action of muscle, person’s exercise, and genetics.
SO- postural muscles (neck)
FOG - lower limb muscles
FG - upper limb muscles
Cardiac muscle tissue
principal tissue in the heart wall. sheets of connective tissue that contain blood vessels, nerves, and the conduction system of the heart. has an endomysium and perimysium, but lacks an epimysium.
Intercalated disc
microscopic structures are irregular transverse thickenings of the sarcolemma that connect the ends of cardiac muscle fibers to one another.
Desmosomes
hold the fibers together
Gap junctions
which allow muscle action potentials to spread from one cardiac muscle fiber to another
Smooth muscle tissue
.
Visceral (single unit) smooth muscle tissue
found in the skin and in tubular arrangements that form part of the walls of small arteries and veins and of hollow organs such as the stomach, intestines, uterus, and urinary bladder. Autorhythmic. neighboring fibers, which then contract in unison, as a single unit.
Multiunit smooth muscle tissue
Individuals fibers with their own motor neuron terminals and few gap junctions. Stimulation of one vis- ceral muscle fiber causes contraction of many adjacent fibers, but stimulation of one multiunit fiber causes contraction of that fiber only.
walls of large arteries, airways to the lungs, in the arrector pili muscles that attach to hair follicles, in the muscles of the iris that adjust pupil diameter, and in the ciliary body that adjusts focus of the lens in the eye.
Microscopic anatomy of smooth muscle
A single relaxed smooth muscle fiber is 30–200 um long. It is thickest in the middle and tapers at each end
Caveolae
Small pouch like invaginations for the plasma membrane, contain extracellular calcium used for muscle contraction.
Dense bodies
Attach to thin filaments or bundles of intermediate filaments(similar to z discs), which pull on dense body’s attachment to sarcolemma, causing a length-wise shortening of the muscle fiber.
Calmodulin
A regulatory protein, which binds to calcium in cytosol (regulates contraction/relaxation of smooth muscle cells). After binding to calcium, activates myosin light chain kinase, which uses ATP to add a phosphate group to a portion of the myosin head which then binds to actin so contraction can occur.
Smooth muscle tone
A state of continued partial contraction because calcium ions enter/exit smooth muscle fibers slowly
Stress relaxation response
Can change length but still contract. To action potentials, stretching, hormones, changes in pH, oxygen, co2, temp or ion levels.
When smooth muscle fibers are stretched, they initially contract, developing increased tension. Within a minute or so, the tension decreases.
Hypertrophy
enlargement of existing cells
Hyperplasia
increase in the number of fibers
Myasthenia gravis
an autoimmune disease that causes chronic, progressive damage of the neuromuscular junction. The immune system inappropriately produces antibodies that bind to and block some ACh receptors, thereby decreasing the number of functional ACh receptors at the motor end plates of skeletal muscles
Muscular dystrophy
group of inherited muscle-destroying diseases that cause progressive degeneration of skeletal muscle fibers.
Spasm
sudden involuntary contraction of a single muscle in a large group of muscles
Cramp
painful spasmodic contraction, may be caused by inadequate blood flow, overuse, dehydration, injury, low electrolytes.
Tic
spasmodic twitching made involuntarily by muscles that are ordinarily under voluntary control.
Tremor
rhythmic, involuntary, purposeless contraction that produces a quivering or shaking movement.
Fasciculation
involuntary, brief twitch of an entire motor unit that is visible under the skin; it occurs irregularly and is not associated with movement of the affected muscle.
Fibrillation
spontaneous contraction of a single muscle fiber that is not visible under the skin but can be recorded by electromyography. May signal destruction of motor neurons.
