Muscles Flashcards
1
Q
Describe the three types of muscle, including shape and number of nuclei
A
skeletal: striated, cylindrical rods, multiple nuclei per cell
cardiac: striated, cylindrical rods, one nucleus per cell
smooth muscle: no striations, spindle shape, one nucleus
2
Q
What are the roles of skeletal muscle in maintaining homeostasis
A
- Acquisition of nutrients/fuel
- processing food (chewing/swallowing)
- breathing
- escape from harm
- generation of heat for temperature control
- source of amino acids for times of famine
3
Q
Why are skeletal muscles big and expensive?
A
30-40% of total body mass
#1 consumer of nutrients, oxygen, uses lots of ATP
high metabolism produces abundant wastes that tend to disrupt ECF homeostasis
4
Q
What is a muscle cell also known as?
A
muscle fiber, a cylinder
5
Q
What does the sarcoplasm contain
A
organelles
6
Q
Describe the muscle structure, going from largest to smallest?
A
whole skeletal muscle (organ), muscle fiber (one cell), myofibrils, thin and thick filaments, myosin and actin
7
Q
What are myofibrils?
A
organelles, cylinders of intracellular contractile structures arranged in repeating units
8
Q
Are muscles made of one or several tissue types?
A
several
9
Q
What is the H-zone?
A
found in A band, strictly myosin
10
Q
What is the I band?
A
light area, just actin
11
Q
What is the A band?
A
darker area majority myosin
12
Q
What is the M line?
A
myosin attachment, found in the middle of the H zone
13
Q
What is the Z-line?
A
actin attachment
14
Q
What is a sarcomere?
A
one unit of the repeating thin and thick filament pattern within the myofibril
15
Q
What is the functional unit of the muscle?
A
sarcomere
16
Q
What does each myosin molecule containt?
A
a long rod-like segment facing the center of the sarcomere and 2 cross-bridge heads that extend out towards the overlying actin
17
Q
How many bonding sites does each cross-bridge head have? What are they for?
A
two, one for actin and one for ATP, the binding ATP binding site also serves as an enzyme that hydrolyzes ATP
18
Q
Describe the structure of thin filaments
A
globular acting (g-actin) molecules come together to form an actin helix or filament-actin (f-actin), appear as a 2 strand pearl necklace
Tm and Tn join and block the binding site for myosin
19
Q
What do Tropomyosin and Troponin look like?
A
cinnamon stick, mickey mouse head
20
Q
What is the cystolic calcium concentration during muscle relaxation?
A
low, 100nM
21
Q
What is the cystolic calcium concentration during muscle activation?
A
high, 1-10 uM
22
Q
What happens during muscle relaxation?
A
Tn push Tm, Tm blocks binding site
23
Q
What happens during muscle activation?
A
calcium on Tn, Tn stops pushing Tm, Tm gets out of the way
24
Q
Do muscles always lengthen during activation?
A
no
25
What does calcium allow?
the myosin cross-bridge and actin can physically interact to cause the muscle to contract
26
define contraction
activation of myosin cross-bridges to exert force on the thin filaments
27
What is the sarcolemma?
plasma membrane and transverse tubules
28
What is the sarcoplasmic reticulum?
smooth(longitudinal) ER and terminal cisternae (calium storage)
29
Define a motor unit
an alpha motor neuron and the multiple muscle fibers it innervates (stimulates)
30
Describe the relationships between skeletal muscle fibers and alpha-motor neurons
each skeletal muscle fiber is stimulates by one alpha motor neuron, and one alpha motor neuron branches to activate multiple fibers within a motor unit.
31
Where are action potentials propagated on skeletal muscle?
sarcolemma
32
What is excitation -contraction coupling?
complex processes connect the action potentials in a motor neuron to the generation of force by cross-bridges
33
List the events that occur at a neuromuscular junction.
1. motor neuron action potential
2. Ca2+ enters voltage-gated channels
3. acetylcholine degradation
4. acetylcholine binding opens ion channel
5. Na+ entry
6. local current between depolarized end plate and adjacent muscle plasma membrane
7.muscle fiber action potential initiation
8. propagated action potential in muscle plasma membrane
34
What is the graded potential in the neuromuscular junction also known as?
End Plate Potential, EPP
35
Where does the synapse of the neuromuscular junction occur?
motor end plate
36
What are end plate potentials?
HUGE graded potentials, 1 alpha motor neuron per one muscle fiber AP, always excitatory
37
What is binding to what in end plate potentials?
ACh always binding to nicotinic ACh receptors
38
Where does inhibition of skeletal muscle occur?
CNS
39
How does Botulinum toxin affect NMJ?
presynaptic Ach release, cuts of snare proteins, no contraction
40
How does Organophosphates affect NMJ?
block enzymes that break down Ach
41
How does Curare affect NMJ?
AchR antagonist, post-synaptic
42
How does Succinylcholine affect NMJ?
short term AchR antagonist, post-synaptic
43
List the steps that lead to increased calcium concentration in skeletal muscle.
1. Action potential propagated along muscle cell membrane and into T-tubules
2. Ca2+ released from lateral sac
3. Ca2+ binding to troponin removes blocking action of tropomyosin
4. cross-bridges bind and generate force
5. Ca2+ removal from the troponin restores tropomysoin
6. Ca2+ transported back into sarcoplasmic reticulum
44
What type of transport is used to get Ca2+ into the SR?
primary active transport
45
What does the DHP receptor do?
it is a voltage sensor in the sarcolema, and it opens the Ryanodine receptor to release calcium
46
List the steps of the cross bridge cycle
1. cross-bridge binds the actin
2. cross-bridge moves
3. ATP binds to myosin, causing cross-bridge to detach
4. hydrolysis of ATP energizes the cross-bridge
47
What causes Rigor Mortis?
lots of myosin heads bound to actin, no ATP
48
Define a load
the amount of force exerted on a muscle by an object (objects mass or weight)
49
Define tension
the amount of force exerted by a muscle on an object
50
Describe Isometric Contraction
iso=same
metric = length
XB's are formed and cycle
load = force
51
Describe Isotonic Contraction
iso=same
tonic = tone
XB's are formed and cycle
Load is not equal to force
52
What are the two types of Isotonic contraction
eccentric = load greater than force, muscle lengthens
concentric = load less than force, muscle shortens
53
Describe an Isometric Twitch
-Force development from a SINGLE action potential
-Each end of the fiber is fixed (immovable)
54
What explains the latent period?
everything in excitation- contraction coupling prior to XB formation , lack of calcium
55
What HAS to happen for force development to occur?
XB's are formed
56
What does the frequency is isometric frequency refer to?
frequency of stimulation (AKA action potentials from the alpha motor neuron)
57
What are the two types of tetanus?(Isometric)
Fused and Unfused
58
What is summating during tension? (Isometric)
not graded potentials, calcium and cross bridges
59
What type tetanus is most common is daily life? (Isometric)
Unfused tetanus
60
What is happening during unfused tetanus?(Isometric)
increased tension due to increased frequency of action potentials
61
What is happening during fused tetanus? (Isometric)
amount of calcium has become constant, so tension becomes relatively constant
62
What are the two main things to consider about isometric length?
passive force from titin and active force due to the contractile proteins actin and myosin
63
What does L naught represent? (Isometric)
ideal length
64
Describe active force (Isometric)
implies cross bridges are formed and ATP is being consumed
65
Describe passive force (Isometric)
the elastic force from titin
66
Why is the latent period longer in Isotonic twitch compared to isometric?
waiting for tension to be greater than load
67
What are the three sources of ATP in metabolisim?
creatine phosphate, oxidative phosphorylation in mitochondria, glycolysis in cytosol
68
Describe the mode, location, number of ATP per glucose, rate of ATP production, and waste for Aerobic and Anaerobic metabolism
Aerobic:
mode- oxidative phosphorylation
location- mitochondria
#ATP per glucose- 36
Rate of ATP production- slow
waste- CO2 and H2O
Anaerobic:
mode- glycolysis, more dominant with intense muscle activity
location- cytosol
#ATP per glucose- 2
Rate of ATP production- fast
waste- lactic acid
69
What are the functions of ATP in skeletal muscle?
1. Hydrolysis of ATP by the Na+/K+ -ATPase in the plasma membrane maintains Na+ and K+ gradients, which allows the membrane to produce and propagate action potentials
2. Hydrolysis of ATP by the Ca+ -ATPase in the sarcoplasmic reticulum provides the energy for the active transport of calcium ions into the reticulum, lowering cytosolic Ca2+ to prerelease concentrations, ending the contraction, and allowing the muscle fiber to relax
3. Hydrolysis of ATP to myosin-ATPase energies the cross-bridges, providing the energy for force generation
4. Binding of ATP to myosin dissociates cross-bridges bound to actin, allowing the bridges to repeat their cycle of activity (i.e. Allosteric Function)
70
What are the skeletal muscle fiber types categorized by?
1. Rate of myosin ATP hydrolysis (depends of myosin isoform - fast or slow)
2. Metabolic pathway used to form ATP (oxidative phosphorylation)
71
What are the three basic types of skeletal muscle fiber types?
Type 1=slow twitch= slow oxidative (SO)
Type 2A= fast oxidative-glycolytic (FOG)
Type 2X = fast glycolytic (FG)
72
What are type 1 (SO) muscle fibers good for?
posture/antigravity/endurance
73
What are type 2A (FOG) muscle fibers good for?
fast aerobic excersize activities
74
What are type 2X (FG) muscle fibers good for?
high power activities (intense bursts)
75
What drives what type of myosin is expressed?
alpha-motor neuron type
76
Which types of fibers are most resistant to fatigue but require longer rest periods?
slow-oxidative (SO)
77
Which fibers have medium resistance to fatigue?
Fast-oxidative-glycolytic (FOG) fibers
78
Which fibers are least resistant to fatigue but recover rapidly?
Fast-glycolytic fibers (FG)
79
What happens when muscles fatigue?
build up of H+, ADP, and Pi (LACTIC ACID)
the acid buildup impairs enzymes and calcium movements, i.e. protein function
ie RyR, SR Pumps, thin filament Ca sensitivity
80
Describe what happens when muscles fatigue from low-intensity, long-duration excersize
1. All factors listed for high-intensity, short-duration exersize (e.g. build-up of H+, ADP, and Pi)
2. Persistent (Ca2+) elevation from leaky RyRs
-calcium dependent proteases activated and degrade contractile proteins, induces weakness and soreness. SR pumps NOT working normally
3. Decrease in muscle glycogen, low blood glucose, and dehydration
4. Central Command Fatigue
-The CNS(brain) stops sending excitations signals to motor neurons. Muscles may not be fatigued but you stop muscle contractions anyway. Caused by increasing unpleasant, distressful sensations for perceptions or thoughts. Kills your will to go on.
81
How does smooth muscle help maintain homeostasis?
-regulates blood flow (change vessel diameter and radius)
-regulates airway diameter and radius
-helps in expulsion of urine from the body
-helps in delivery of baby during childbirth
-helps move food through the digestive tract
82
Name 4 similarities between smooth and skeletal muscle.
1. Both contain thick, myosin filaments and thin, actin filaments
2. increase in cytosolic Calcium is the key step in the E-C coupling process
3. ATP is directly used to power cross-bridge cycling
4. sliding filament mechanism of concentration applies to both
83
Describe the structure of smooth muscle, including what makes it different from skeletal muscles
spindle-shaped
very small
single nucleus
form sheets
no transverse tubules
no troponin
unstriated (no sarcomeres, no z-lines)
irregularly developed SR
rely on calcium form both inside and outside the cell
contain dense bodies
innervated by the autonomic division of the peripheral nervous system
84
What is the function of dense bodies?
actin attachment in smooth muscle
85
What areas of the nervous system does smooth muscle vs skeletal muscle deal with?
smooth = sympathetic/parasympathetic (autonomic)
skeletal= CNS (peripheral)
86
Which type of muscle has sarcomeres?
skeletal, not smooth
87
What excites or inhibits smooth muscle cells to contract?
neurotransmitters from autonomic axons with varicosities
sympathetic or parasympathetic
88
What does the response of smooth muscle depend on?
type of receptor the cell has
89
What type of hormone goes with sympathetic?
NorEpi
90
What type of hormone goes with parasympathetic
Ach
91
What happens in Alpha-one
smooth muscle contracts
92
What happens in beta-two
smooth muscle relaxes
93
Describe what happens in cells with pacemaker potentials
oscillate to threshold, fire AP
1.Pacemaker Potential spontaneous depolarization to threshold (create AP on their own)
2. action potential upstroke
3. repolarization due to K+ efflux
94
Describe what happens in cells with slow waves
no AP alone
1. spontaneous depolarizations BELOW threshold
2. smaller amount of both depol and repol
3. add excitatory NT/Horm, depolarization to threshold
95
What are the inputs influencing smooth muscle contractile activity?
-spontaneous electrical activity in the plasma membrane of the muscle cell (pacemakers and slow waves)
-neurotransmitters released by autonomic neurons (Ach NE)
-Hormones (Oxytocin, Estrogen, Progesterone)
-Locally induced changes in the chemical composition (paracrine factors, acidity, oxygen, osmolarity, and ion-concentrations) of the extracellular fluid surrounding the cell
-stretch (mechanoreceptors)( Blood pressure and motitlity)
96
What are the different types of gated channels used to take calcium into a smooth muscle cell? Where are they loacated?
1. Voltage-gated
2. Ligand-gated (NT/Horm)
3. Mechano-gated
4. Metabotropic receptors (NT/Horm)
all located in the sarcolemma
97
What type of channel is used to get calcium into the SR of smooth muscle cells?
IP3-ligand-gated Ca2+ channel
98
What is the new function of ATP in muscle contraction that only applies to smooth muscle?
phosphorylation of myosin light chain by MLCKinase; separate ATP molecule
99
Which plateau (smooth or skeletal) spans longer?
smooth
100
Which type of cells can be stretched to up to 3x their length?
smooth muscle due to oblique, irregular arrangement of actin and myosin
101
What type of muscle is thin filament vs thick filament regulation?
smooth is thick filament
skeletal is thin filament
102
What afferent path does the tack example align with?
anterolateral
103
What afferent path does the knee jerk align with?
dorsal column, stretch receptors
