Chapter 9 Muscle Tissue Flashcards
1
Q
Types of muscle tissue
A
differ by structure, location, function, means of activation
- skeletal
- cardiac
- smooth
2
Q
Contraction uses protein
A
protein myofilaments
- actin (thin)
- myosin (thick)
3
Q
sarcolemma
A
muscle cell plasma membrane
- multiple glycosomes
- myoglobin (oxygen binding protein)
4
Q
sarcoplasm
A
cytoplasm of muscle cell
5
Q
prefixes for muscle
A
myo, mys, sarco
6
Q
contraction
A
excitability
- muscle cells respond to signals with changing sarcolemma electrical potential: VOLTAGE
- causing force generation: CONTRACTION
7
Q
Contractibility
A
active shortening of muscle cell and generation of tension
force
8
Q
extensibility
A
passive stretching of muscle cells
9
Q
elasticity
A
return of muscle cells to original resting length after being stretched
10
Q
relaxation
A
absence of excitatory input
11
Q
skeletal muscle tissue
A
- striated muscle (obvious stripes)
- solely voluntary or reflex
- contracts rapidly
- tires easily
12
Q
cardiac muscle tissue
A
- heart
- striated
- NOT voluntary
- neural control allows heart to respond to changes with oxygen and fuel delivery: autonomic nervous system changes rate of contraction, force
- contracts at a rate set by heart’s pacemaker
- branched myocytes
- myocytes joined at intercalated discs (mechanical syncytium)
- gap junctions for electrical signaling (electrical syncytium)
- requires Ca2+ to enter
- Very long action potentials
13
Q
smooth muscle tissues
A
- primarily in hollow visceral organs (stomach, intenstines, bladder, uterus, blood vessels, respiratory passages)
- forces food/substances through internal body cavities
- not striated
- involuntary
14
Q
skeletal muscle as an organ
A
muscle cells, blood vessels, nerve fibers, connective tissue
served by one nerve, one artery, and one or more veins
15
Q
three connective tissue sheaths
A
- endomysium
- perimysium
- epimysium
16
Q
Endomysium
A
1 of 3 connective tissue sheaths
- fine sheath
- reticular fibers surrounding each muscle fiber
17
Q
Perimysium
A
1 of 3 connective tissue sheaths
- fibrous connective tissue
- surrounds groups of muscle fibers called fascicles
18
Q
Epimysium
A
1 of 3 connective tissue sheaths
- outer layer of dense regular connective tissue
- surrounds entire muscle
19
Q
veins vs arteries in skeletal muscles
A
Blood in arteries: provides constant oxygen and nutrients for contraction/relaxation
Blood in veins: removes wastes
20
Q
bone involvement in contraction
A
when muscles contract moveable bone (INSERTION) moves toward immoveable bone (ORIGIN)
21
Q
Indirect muscle attachment to bone
A
more common
tendons
aponeurosis
examples: abdominal muscles, letting you puff out your cheeks
22
Q
myocyte/muscle fiber
A
- single muscle cell
- size: 10-100um in diameter, tens of cm long
- long, cylindrical cell with multiple nuclei
- fusion of multiple precursor cells: MYOBLASTS
- include myofibrils, sarcoplasmic reticulum, and t tubules
23
Q
myofibrils in skeletal muscle
A
- densely packed rodlike contractile elements
- arrangement of myofibrils in a fiber = perfectly aligned, repeating series of dark A bands and light I bands
24
Q
sarcomere
A
smallest contractile unit of muscle
region of myofibril between two successive Z discs
thick and thin myofilaments (each made of contractile proteins)
25
thick filament myofilaments in skeletal muscle
myosin
extend entire length of A band
rodlike tail, two globular heads
bundle with heads protruding out in spiral pattern
26
thin myofilaments in skeletal muscle
- actin
- extend across I band and partway into A band
- primary contractile protein=F-actin
- G-actin subunit contains ACTIVE SITE where myosin head attaches during contraction
- troponin
27
Z disc of myofilament
coin shaped sheet of connectin proteins that anchor thin filaments and connect myofibrils to one another
28
elastic filaments
stretch from Z disc through thick myofilament to the M line
| made of titin
29
troponin
regulatory protein complex bound to f-actin in thin myofilaments
binds calcium ions
30
sarcoplasmic reticulum (SR)
- Elaborate, smooth ER
- surrounds each myofibril
- longitudinal
- regulates intracellular calcium levels
- T-tubules=elongated tubes of sarcolemma
- paired terminal cisternae form perpendicular cross channels
31
triad junctions
paired terminal cisternae and t tubules in sarcoplasmic reticulum
32
role of Ca2+ in muscle contraction
- t tubles=electrical impulses conduction
- signal release of Ca 2+ from adjacent terminal cisternae into sarcoplasm
- Ca2+ binds to troponin, moves tropomyosin, myosin binding sites of F-actin exposed
- muscle contraction
33
sliding filament model of contraction
-relaxed state: thin and thick filaments overlap but are not bound (myosin sites covered)
-after stimulus:
1. thin filaments slide past thick so overlap increases
2. power stroke: myosin head binds and detaches to f-actin several times, generating tension to pull thin filaments toward center of sarcomere
with many, generates force and shortens
34
To contract a myocyte
1. be stimulated by nerve ending
2. action potential along sarcolemma
3. rise in sarcoplasmic Ca++, triggers contraction
35
excitation-contraction coupling
linkage of sarcoplasmic electrical signal to contraction
36
motor neurons
stimulate skeletal muscle
if not, paralysis
cell bodies in brainstem or spinal cord
each axonal branch forms neuromuscular junction with a myocyte
37
motor unit
motor neuron and all the myocytes it innervates is motor unit
38
spatial summation
when subset of motor units are activated for sub maximal amount of force
total force of contraction is summation of all active motor units
39
neuromuscular junction
```
axon terminal (with synaptic vesicles that contain neurotransmitter ACh)
motor endplate=part of sarcolemma that contains ACh receptors
motor endplates separated by synaptic cleft
```
40
neuromuscular toxins/paralysis
- pesticides contain inhibitors of acesylcholinesterase, binds to active site so it cannot degradeAch --> rigid paralysis of skeletal muscles, suffocation
- tetanus (lockjaw): spastic rigid paralysis from Clostridium bacteria; blocks release of inhibitory neurotransmitter in spinal cord, overstimulation of muscles
- Curare: poisonous frogs blocks action of ACh, prevents from binding to sarcolemma receptor, flaccid paralysis while conscious
41
action potential
transient plasma membrane electrical depolarization event
- polarity reversal
- propagation of wave along membrane
42
repolarization
voltage gated Na channels close
voltage gated K channels open
K flows out down concentration gradient
same direction as depolarization
occurs before muscle can be stimulated again: Refractory period
Na+ -K+ ATPase pump restores ionic concentrations of resting state
43
Cross bridge cycling
1. cross bridge formation: myosin heads attach to actin filaments
2. working (power) stroke: myosin head pivots, pulls actin filament toward M line
3. Cross bridge detachment: ATP binds to mosin head, cross bridge detaches
4. Cocking of myosin head: energy from hydrolysis of ATP cocks myosin head back into high energy state
When inactive, contraction ends
44
shortening contraction
- CONCENTRIC CONTRACTION
- tension generated by cross bridge exceeds load
- muscle decreases in length
45
eccentric contration
load greater than muscle force generation
| muscle lengthens during contraction
46
Isometric contraction
increasing muscle TENSION (muscle does not shorten)
47
Isotonic contraction
decreasing muscle LENGTH (muscle shortens during contraction)
48
Muscle twitch
1. latent period (excitation contraction coupling)
2. period of contraction: cross bridges cycle, muscle shortens or develops tension
3. period of relaxation: Ca2+ resequestered into SR, muscle tension goes to zero
single stimulus results in single contractile response
49
graded muscle responses
```
variations in amount of force
proper control of skeletal movement
graded in response to changing
-frequency of stimulation
-strength of stimulation
```
50
incomplete tetanus
higher stimulus frequency
51
complete tetanus
stimulus frequency high enough
52
wave summation
low stimulus frequency increases contractile force because muscle doesn't have time to completely relax
53
multiple motor unit summation
- controls force of contraction
| - recruitment brings more and more muscles into action
54
muscle tone
- constant, low level stimulation of muscles
- no active movements
- keeps muscles firm, healthy, ready to respond
- spinal reflexes
55
ATP
Only source used directly for contraction
Also for for relaxation
-as soon as ATP hydrolyzed, regenerated by
-CP to ADP
-anaerobic glycolysis
-Aerobic respiration
56
Muscle fatigue
- muscle physiologically unable to contract
- intense exercise=rapid fatigue with rapid recovery
- low intensity exercise=slow developing fatigue with slow recovery
57
EPOC (Excess Post-Exercise Oxygen Consumption
extra amount of oxygen needed to restore muscle to resting state (lactic acid back to pyruvic acid, glycogen stores, ATP and CP restored, oxygen replaced)
58
Efficiency of energy use
- only 40% energy released in muscle for work
- remaining 60% is heat
- prevent overheating by radiation of heat and evaporative cooling (sweating)
59
Rigor mortis
-stiffening of muscles
-after 3-4 hours after death
-peaks at 12 hours, decreases after 48
-due to lack of ATP after death
caused by
-Ca2+ leaks out of SR (static cross bridges)
-Actin myosin cross bridges form (but no power strokes because no ATP)
-Static cross bridges remain until proteases start degrading the myofilament proteins
60
Oxidative fibers
skeletal muscle fibers that use aerobic pathways
61
Glycolytic fibers
skeletal muscle fibers that use anaerobic pathways
62
Slow oxidative fivers
contract slowly
slow acting myosin ATPase
fatigue resistent
63
Fast oxidative fibers
contract quickly
fast myosin ATPase
moderate resistant to fatigue
64
Fast glycolytic fibers
contract quickly
fast myosin ATPase
easily fatigued
65
Muscular dystrophies
- inherited muscle-destroying diseases
- muscles enlarge due to fat and connective tissue deposits
- muscle fibers atrophy and degenerate
- most are progressive
66
Duchenne muscular dystrophy (DMD)
- Sex linked: carried in females, expressed in males
- 1 / 3,500
- diagnosed 2-10yo
- become clumsy and fall frequently as muscles weaken
- progresses from distal extremities inward
- usually die from respiratory failure or cardiac complications in 20s
- lack of cytoskeletal protein: Dystrophin
- no cure, therapies
67
Smooth muscle
- spindle shaped fibers
- 2-10um diameter, a couple hundred um long (much smaller than skeletal)
- no coarse connective tissue sheaths
- endomysium
- two layers (longitudinal and circular) fibers
- walls of hollow organs except heart
- same contractile proteins as skeletal muscle: actin and myosin
- no T tubules
- caveoli
- no sarcomeres
- also thin (actin) and thick (myosin) filaments
68
Peristalsis
alternating waves of contraction and relaxation of smooth muscle layers that mix and squeeze substances through the lumen of hollow organs
69
Myofilament in smooth muscle, difference
- no troponin complex
- thick and thin filaments arranged diagonally
- contracts in corkscrew manner
- ratio of thick to thin muscles lower
- thick filaments have heads along entire length
70
what makes smooth muscle tissue unique
- tone (constant, but with dimmer switch); state of partial contraction always active
- slow, prolonged
- low energy req
- some = stress-relaxation process
71
stress-relaxation response
property of some smooth muscle tissue
responds to stretch only briefly, then adapts to new length
new length retains ability to contract
enables temporary expansion to store (uterus, urinary bladder, stomach)
72
innervation of smooth muscle tissue
- indirect neural input (no true neuromuscular junction)
- involuntary
- varicosities: bulbous swellings in innervating nerves; specks of neurotransmitter release
- varicosities release neurotransmitters into wide synaptic clefts DIFFUSE JUNCTIONS
- gap junctions: action potentials directly from cell to cell
- cells contract in unison
- whole sheets of smooth muscle exhibit slow, synchronized contraction
- some cells=pacemaker for sheet
73
Hyperplasia
in smooth muscle, diff than the combo in skeletal: by size, not fused
- 1 nucleus
- mitosis
- doesnt go through cross bridges as fast, so less ATP consumption
74
Single unit smooth muscle aka
| Visceral muscle
- more common
- contract rhythmically as unit
- electrically coupled with gap junctions
- exhibit spontaneous action potentials
- arranged in opposing sheets
- digestive tract, blood vessels, uterus, urinary bladder
75
Multi unit smooth muscle
- electrically and structurally independent muscle fibers (like skeletal)
- infreq spontaneous depolarizations
- rich nerve supply, motor units
- graded responses
- large airways to lungs, large arteries, arrector pili muscles (hair follicles), internal eye muscles
76
development of muscle tissue
- Develops froom myoblasts: embryonic cells
- skeletal: multinucleated because fusion of many myoblasts
- cardiac and smooth do not fuse: gap junctions
77
regeneration
- cardiac and skeletal are amitotic in adulthood, but can lengthen in thicken
- skeletal muscle, only in childhood
- cardiac lacks satellite cells
- smooth has better regenerative ability
78
gender differences
women skeletal muscle is 36% of body mass
| men skeletal muscle is 42-45% body mass
79
sarcopenia
by age 80, 50% of muscle mass lost
regular exercise minimizes
connective tissue increases and muscle fibers decrease with age
80
artherosclerosis
aging
affects distal arteries
intermittent claudication (blockage)
severe pain in leg muscles, heart attacks, strokes
81
arteriosclerosis
- "hardening of arteries"
- less elastic and more rigid
- smooth muscle is replaced by connective tissue
