Muscular Tissue Flashcards
What are the characteristics of muscles?
- responsiveness (excitability)
- conductivity
- contractility
- extensibility
- elasticity
characteristics of muscles: to chemical signals, stretch, and electrical changes across the plasma membrane
responsiveness (excitability)
characteristics of muscles: local electrical change triggers a wave of excitation that travels along the muscle fiber
conductivity
characteristics of muscles: shortens when stimulated
contractility
characteristics of muscles: capable of being stretched between contractions
extensibility
characteristics of muscles: returns to its original resting length after being stretched
elasticity
plasma membrane of a muscle fiber
sarcolemma
cytoplasm of a muscle fiber
sarcoplasm
long protein bundles that occupy the main portion of the sarcoplasm
myofibrils
stored in abundance to provide energy with heightened exercise
glycogen
red pigment; stores oxygen needed for muscle activity
myoglobin
flattened nuclei pressed against the inside of the sarcolemma
multiple nuclei
stem cells that fuse to form each muscle fiber
myoblasts
unspecialized myoblasts remaining between the muscle fiber and endomysium
-may multiply and produce new muscle fibers to some degree
satellite cells
packed into spaces between myofibrils
mitochondria
smooth ER that forms a network around each myofibril: calcium reservoir
-calcium activates the muscle contraction process
sarcoplasmic reticulum (SR)
dilated end-sacs of SR which cross the muscle fiber from one side to the other
terminal cisternae
tubular infoldings of the sarcolemma which penetrate through the cell and emerge on the other side
T tubules
a T tubule and two terminal cisterns
triad
made of several hundred myosin molecules
-shaped like a golf club
-heads directed outward in a helical array around the bundle
thick filaments
What are thin filaments? (3)
- fibrous (F) actin
- tropomyosin molecules
- troponin molecule
thin filament: two intertwined strands
-string of globular (G) actin subunits each with an active site that can bind to head of myosin molecule
fibrous (F) actin
thin filament: each blocking six or seven active sites on G actin subunits
tropomyosin molecules
thin filament: small, calcium-binding protein on each tropomyosin molecule
troponin molecule
striations: dark; A stands for anisotropic
-part of A band where thick and thin filaments overlap is especially dark
A band
striations: middle of A band; thick filaments only
H band
striations: middle of H band
M line
striations: alternating lighter band; I stands for isotropic
-the way the bands reflect polarized light
I band
striations: provides anchorage for thin filaments and elastic filaments
-bisects I band
Z disc
-when sarcromeres shorten, thick and thin filaments slide past one another
-H zones and I bands get narrower
-Z lines move closer
-explains why skeletal muscles are striated and why muscles contract
sliding filament theory
segment from Z disc to Z disc
-functional contractile unit of muscle fiber
sarcomere
nerve cells whose cell bodies are in the brainstem and spinal cord that serve skeletal muscles
somatic motor neurons
their axons that lead to the skeletal muscle
-each nerve fiber branches out to a number of muscle fibers
-each muscle fiber is supplied by only one motor neuron
somatic motor fibers
one nerve fiber and all the muscle fibers innervated by it
motor unit
dispersed throughout the muscle
-contract in unison
-produce weak contraction over wide area
-provides ability to sustain long-term contraction as motor units take turns contracting (postural control)
-effective contraction usually requires the contraction of several motor units at once
muscle fibers of one motor unit
200 muscle fibers for each motor runit
average motor unit
fine degree of control
-three to six muscle fibers per neuron
-eye and hand muscles
small motor units
more strength than control
-powerful contractions supplied by large motor units (ex: gastrocnemius has 1,000 muscle fibers per neuron)
-many muscle fibers per motor unit
large motor units
point where a nerve fibers meets its target cell
synapse
when target cell is a muscle fiber
Neuromuscular junction (NMJ)
swollen end of nerve fiber
-contains synaptic vesicles filled with acetylcholine (ACh)
synaptic knob
tiny gap between synaptic knob and muscle sarcolemma
synaptic cleft
envelops and isolates all of the NMJ from surrounding tissue fluid
schwann cell
undergo exocytosis releasing ACh into synaptic cleft
synaptic vesicles
quick up-and-down voltage shift from the negative RMP to a positive value, and back to the negative value again
action potential
a state of continual contraction of the muscles; possible suffocation
spastic paralysis
What are the three major phases of contraction and relaxation?
- excitation
- excitation
- contraction
- relaxation
phase of contraction and relaxation: the process in which nerve action potentials lead to muscle action potentials
excitation
phase of contraction and relaxation: contraction coupling
-events that link the action potentials on the sarcolemma to activation of the myofilaments, thereby preparing them to contract
excitation
phase of contraction and relaxation: step in which the muscle fiber develops tension and may shorten
contraction
phase of contraction and relaxation: when its work is done, a muscle fiber relaxes and returns to its resting length
relaxation
hardening of muscles and stiffening of body beginning 3 to 4 hours after death
-deteriorating sarcoplasmic reticulum releases Ca^+2
-deteriorating sarcolemma allows Ca^+2 to enter cytosol
-Ca^+2 activates myosin-actin cross-bridging
-muscle contracts, but cannot relax
rigor mortis
T or F: Rigor mortis peaks about 12 hours after death, then diminishes over the next 48 to 60 hours
true
-muscle is producing internal tension while an external resistance causes it to stay the same length or become longer
-can be a prelude to movement when tension is absorbed by elastic component of muscle
-important in postural muscle function and antagonistic muscle joint stabilization
isometric muscle contraction
all muscle contraction depends on what?
ATP
ATP supply depends on availability of what?
oxygen, organic energy sources such as glucose and fatty acids
what are the two main pathways of ATP synthesis?
- anaerobic fermentation
- aerobic respiration
-enables cells to produce ATP in the absence of oxygen
-yields little ATP and toxic lactic acid, a major factor in muscle fatigue
anaerobic fermentation
-produces far more ATP
-less toxic end products (CO2 and water)
-requires a continual supply for oxygen
aerobic respiration
What are the two enzyme systems that control the phosphate transfers?
- myokinase
- creatine kinase
transfers Pi from one ADP to another, converting the latter to ATP
myokinase
obtains Pi from a phosphate-storage molecule creatine phosphate (CP)
-fast-acting system that helps maintain the ATP level which other ATP-generating mechanisms are being activated
creatine kinase
the pathway from glycogen to lactic acid
Glycogen-lactic acid system
____ produces 36 ATP per glucose
-efficient means of meeting the ATP demands of prolonged exercise
aerobic respiration
abundant mitochondria, myoglobin, capillaries: deep red color
-adapted for aerobic respiration and fatigue resistance
-relative long twitch lasting about 100ms
-soleus of calf and postural muscles of the back
slow oxidative (SO), slow-twitch, red, or type 1 fibers
-fibers are well adapted for quick responses, but not for fatigue resistance
-rich in enzymes of phosphagen and glycogen-lactic acid systems generate lactic acid, causing fatigue
-poor in mitochondria, myoglobin, and blood capillaries which gives pale appearance
fast glycolytic (FG), fast-twitch, white, or type 2 fibers
what are the three classes of muscle fibers?
- slow-twitch fibers (type 1)
- fast-twitch glycolytic fibers (type 2)
- fast-twitch fatigue-resistant fibers (type 2b)
classes of muscles:
-always oxidative
-resistant to fatigue
-red fibers
-most myoglobin
-good blood supply
slow-twitch fibers (type 1)
classes of muscles:
-white fibers (less myoglobin)
-poorer blood supply
-susceptible to fatigue
fast-twitch glycolytic fibers (type 2)
classes of muscles:
-intermediate fibers
-oxidative
-intermediate amount of myoglobin
-pink to red in color
fast-twitch fatigue-resistant fibers (type 2b)
What are the properties of the cardiac muscle? (5)
- Contraction with regular rhythm
- Muscle cells of each chamber must contract in unison
- Contractions must last long enough to expel blood
- Must work in sleep or wakefulness, without fail, and without conscious attention
- Must be highly resistant to fatigue
characteristics of cardiac muscle
striated like skeletal muscle, by myocytes (cardiocytes) are shorter and thicker
smooth muscle compared to skeletal muscle fibers is…
-shorter
-single nucleus
-elongated with tapering ends
-myofilaments randomly organized
-no striations
-lack transverse tubules
-sarcoplasmic reticula not well developed
autoimmune disease in which antibodies attack neuromuscular junctions and bind ACh receptors together in clusters
Myasthenia Gravis
inability to fixate on the same point with both eyes
strabismus
Treatments for Myasthenia Gravis
-cholinesterase inhibitors retard breakdown of ACh allowing it to stimulate the muscle longer
-immunosuppressive agents suppress the production of antibodies that destroy ACh receptors
-Thymus removal (thymectomy) helps to dampen the overactive immune response that causes myasthenia gravis
-Plasmapheresis
technique to remove harmful antibodies from blood plasma
plasmapheresis
The presence of what causes muscle contraction?
Calcium
Contraction where the muscle develops tension but does not shorten
- no movement
Isometric muscle contraction
Contraction where the muscle shortens, tension remains constant
- movement upward
Isotonic concentric contraction
Contraction where the muscle lengthens while maintaining tension
- movement downwards
Isotonic eccentric contraction
