Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

MSK exam 3 AP lower limb > Excitation Contraction Coupling > Flashcards

Excitation Contraction Coupling Flashcards

(83 cards)

Start Studying
1
Q

Somatic motor neurons (what are they and where do their cell bodies sit?)

A

Voluntary or reflex control

Efferent neurons

cell bodies sit in the CNS (ventral horn of spinal cord)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

how many motor neurons is 1 myofiber supplied by?

A

1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

how many muscle cells doe s1 motor neuron axon innervate

A

a few or many individual muscle cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what is a motor unit

A

1 motor neuron and all the muscle fibers it innervates

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

NMJ (neuromuscular junction)

A

specialized synapse between motor neuron and skeletal muscle fiber

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what are the similarities between a synapse and a neuromuscular junction?

A

two excitable cells separated by a narrow cleft that prevents direct electrical activity between them

means of communication is via chemical messengers that are released by the Ca 2+ induced exocytosis of storage vesicles when AP reaches the terminal

via the crossing of a neurotransmitter, and binding of it, induces opening of specific channels in the membrane, permitting ionic movements that result in a graded potential (subthreshold changes in membrane potential)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what are the differences between a synapse vs. neuromuscular junction?

A

synapse is between two neurons and NMJ exist between a motor neuron and a skeletal muscle

whenever you have an AP at a motor neuron you will get an AP of the muscle fiber (one-to-one transmission) WHEREAS one AP is a presynaptic neuron cannot by itself bring about an AP in a postsynaptic neuron ONLY can have AP when summation of EPSP’s brings the membrane to threshold

A NMJ is ALWAYS excitatory VS. synapse which can be both excitatory or inhibitory

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what is an active zone ?

A

dense spots over which synaptic vesicles are clustered (located right over secondary postsynaptic clefts between adjacent postjunctional folds)

waiting to release neurotransmitter

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what are postjunctional folds?

A

extensive invaginations on postsynaptic membrane directly under nerve terminal (high concentration of receptors)

increases surface area of muscle plasma membrane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what is acetylcholinesterase

A

AChE high concentration associated with synaptic basal lamina (basement membrane)

TERMINATES SYNAPTIC TRANSMISSION after AP

hydrolyzes ACh–> choline and acetate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

nicotinic acetylcholine receptors??

A

these are the receptors that are expressed in high density at crests of postjunctional folds

this is the receptor we will be dealing with in skeletal muscles

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

where are NT vesicles produced and how do they get to their destination?

A

motor neuron cell bodies in the spinal cord produce NT vesicles

fast axonal transport translocates vesicles to nerve terminal (microtubule-mediated process)

Vesicles for ACh travel down axon EMPTY but contain presynthesozed peptides/peptide precursors already inside

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what does choline acetyltransferase do?

A

synthesizes ACh from choline and acetyl CoA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what is synaptobrevin?

A

aka V-snare

essential for transmitter release

forms complex with SNAP-25 and syntax in

helps drive vesicle fusion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what are SNAP-25 and syntaxin

A

presynaptic membrane proteins t-SNARES

located on the presynaptic membrane of nerve terminal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what is synaptotagmin

A

Ca2+ receptor of synaptic vesicles

this detects the rise in Ca2+ and triggers exocytosis of docked vesicles

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

what makes calcium come into the nerve terminal?

A

at the nerve terminal there are voltage gated calcium channels that respond to action potentials that have reached the nerve terminal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

steps in vesicle fusion?

A

synaptobrevin coils around free ends of syntax in/snap25 and brings the vesicle closer to the presynaptic membrane

when Ca2+ influx comes in, synaptotagmin detects this

this triggers vesicle fusion and exocytosis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

what do neurotoxins do? and what is their effect

A

interrupt process of ACh release by blocking the fusion of synaptic vesicles (b/c of their effects on t-snares and v-snares)

which leads to no signal being transmitted!

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Tetanus toxin and Botulinum toxins B,D,F and G do what?

A

these are endoproteinases (neurotoxins) that digest synaptobrevin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

what does botulinum toxins A and E do?

A

cleave SNAP-25

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

what does botulinum toxin C1 do?

A

cleaves syntaxin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

what type of receptor is the acetylcholine receptor?

A

Ionotropic, nicotinic AChR channel

nonselective cation channel at motor neuron endplate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

what is the ACh receptor permeable and NOT permeable to?

A

permeable to cations (Na, K, and Ca) (not specific)

(note current of Ca is small under physiological conditions and its contribution can be ignored)

NOT permeable to anions (Cl-)

WEAK ionic selectivity–> function is to raise Vm above threshold

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
what happens when Ach binds to its receptor?
graded potential
26
opening of AChR channel at the muscle end plate does what?
now have increased permeability to Na and K result is increase in the normally low permeability of Na relative to K+ (because Na usually doesn't contribute to the resting membrane potential) Vm shifts to a value between Ek and ENa End-Plate Potential
27
what is End-Plate potential
a type of GRADED POTENTIAL which is a decremental spread of current is is produced by transient opening of AChR it is an EPSP (increased Na+ conductance drives Vm of end-plate region more positive)
28
what are the normal physiological conditions of ACh and EndPlate potentials?
presynaptic motor nerve axon AP--> depolarizing postsynaptic EPP EPP is approximately 40 mV more positive than resting Vm
29
how is the Neurotransmitter action removed?
AChe hydrolyzes ACh to choline and acetate removes ACh from NMJ synaptic cleft
30
Review of events at NMJ
see your drawing
31
what is a myofibril?
contractile element contains thick and thin filaments
32
what is the level of coupling and contraction?
it is at the level of the myofibril and its striations | actin/myosin
33
Sarcomere
Z line to Z line
34
what is the A band
myosin thick filaments overlap with actin
35
what is the h zone
middle of the a band part of myosin where actin does not overlap
36
what is the m line
extends vertically down center of A band
37
what is the I band
part of actin not overlapping myosin (does not project into A band)
38
what is the z line
thin filament attachment
39
what parts of the sarcomere shorten during contraction?
H zone I band Sarcomere is shorter
40
what are the thick filaments?
bipolar assembly of multiple myosin molecules 2 myosin heavy chains (MHC) -each heavy chain has a Rod, Hinge and Head 2 alkali light chains 2 regulatory light chains
41
what are the 2 important binding sites on the head of the myosin heavy chain?
Actin binding site (for cross bridge formation) Myosin ATPase site (for binding and hydrolyzing ATP)
42
each head of myosin heavy chains forms a complex with what?
2 light chains (1 alkali and 1 regulatory)
43
alkali light chain does what?
essential role in stabilizing the myosin head region
44
what does the regulatory light chain do?
regulates myosin ATPase activity
45
F-actin?
backbone of the thin filament it is double stranded polymer of actin molecules associated with Tropomyosin and Troponin
46
what are troponin and myosin
2 important regulatory actin binding proteins
47
what is the important binding site of Actin?
myosin binding site
48
what blocks the myosin binding site on actin at rest?
tropomyosin
49
what does troponin interact with?
1 tropomyosin molecule and actin
50
what does tropomyosin interact with?
7 actin monomers
51
3 components of Troponin
T C I
52
Troponin T function
binds to a single tropomyosin molecule
53
troponin C function
binds to Ca
54
troponin I function
binds to actin and inhibits contraction
55
titin does what?
tethered from M line to Z line contributing to force transmission involved in elastic behavior of muscle by maintaining the resting length of muscle during relaxation (passive stiffness)
56
what is excitation-contraction coupling ?
process by which electrical excitation of the surface membrane triggers an increase of Ca2+
57
what do AP's propagate along?
from sarcolemma to the interior of muscle fibers along the transverse tubule network! Transverse t-tubules
58
what does a depolarization of the sarcolemmal membrane result in?
rise in Ca2+ inside cell
59
what is the location of the T-tubules in relation to the muscle fiber?
extend into the muscle fiber and surround the myofibrils at the junctions of the A and I bands
60
where does intracellular calcium come from?
the sarcoplasmic reticulum
61
what is the triad
T-tubule membrane and its 2 associated cisternae (specialized regions of sarcoplasmic reticulum) propagation of AP into T-tubules depolarizes triad results in Ca release from lateral sacs of the SR
62
what is the function of the Dihydropyridine receptor?
DHP is a voltage gated channel located on the t=tubule membrane it is the L-type Ca 2 channel it induces a conformational change in the Ca release channel (RyR) by mechanical activation
63
what is the RyR receptor
it is the Ca release channel located on the SR membrane that is facing the T-tuble releases stored Ca from the SR
64
what does the release of Ca into the muscle fiber do?
triggers contraction by removing inhibition of cross-bridge cycling NOTE Ca does not directly interact with contractile proteins, but rather it's role in contraction is through binding regulatory proteins
65
in the presence of Ca what does troponin do?
removes tropomyosin from the myosin binding sites on actin
66
what does mATPase do?
hydrolyzes ATP to ADP and Pi | creating potential energy
67
what position are myosin head in at rest?
in the cocked position with stored potential energy
68
what does the interaction between myosin and actin do
pulls the trigger using the stored potential energy allows myosin to pull the actin toward the center of the sarcomere (power stroke) sarcomere shortens Pi is released from the cross bridge to trigger the power stroke
69
when is ADP release
with the power stroke completion
70
what must be present for multiple cross -bridge cycling to occur ?
ATP and Ca
71
what are the steps in the cross bridge cycle?
1= atp binds to myosin head, causing the dissociation of the actin-myosin complex 2= atp is hydrolyzed causing myosin heads to return to their resting conformation 3-= a cross bridge forms and the myosin head binds to a new position on actin 4= pi is released, myosin heads change conformation resulting in the POWER STROKE the filaments slide past eachother 5- ADP is released after power stroke, and the myosin/actin cross bridge remains in the tightened/shortned position again ATp binds to the myosin causing dissociation
72
what is rigor mortis
if their is no fresh ATP available such as after death, then actin and myosin remain bound in rigor complex
73
what does ATP NOT Do
regulate the cross-bridge cycle of actin-myosin interaction | it will generally continue at physiological levles of ATP
74
what is relaxation
requires reuptake of Ca from sarcoplasm AND ATP in order to dissociated myosin and actin from each other it is an ACTIVE process (ca 2+ pumps and ATPase binding site on myosin head)
75
what happens if reuptake is unregulated?
cross bridge cycling would continue until myocyte is depleted of ATP
76
what happens when Ca 2+ levels inside the muscle cell decrease?
troponin and tropomyosin move back into place and cover myosin-binding site on actin
77
what is the minor mechanism for Ca 2 removal from the cytoplasm?
Na-Ca2+ exchanger and Ca2+ pump both extrude Ca+ across sarcolemma
78
what is the major mechanism for Ca2+ removal from the cytoplasm?
sarcoplasmic and endoplasmic reticulum Ca2+-ATPase (SERCA) -type Ca2+ pump
79
what inhibits activity of SERCA?
high Ca2+
80
what is the function of Ca2+ binding proteins
delay inhibition of Ca2+ pump activity they buffer increased Ca2+ during Ca2+ uptake and can increase the Ca2+ capacity of the SR sort of take Ca out of the picture can have up to 50 binding sites per molecule
81
Calsequestrin
principal binding protein in skeletal muscle localized in the SR beneath the triad junction forms a complex with the Ca2+ release channel (RYR) facilitates muscle relaxation by buffering Ca2+ and unloads its Ca2+ in the vicinity of the Ca2+ release channel to facilitate EC coupling
82
Calreticulin
Ca2+ binding protein in smooth muscle
83
look at the summary slides
do it

MSK exam 3 AP lower limb (15 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions