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physiology and anatomy > week 3: 10.4 > Flashcards

week 3: 10.4 Flashcards

1
Q

typical resting membrane potential in unstimulated neurons and skeletal muscle fibers

A

-70mV
-85mV

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2
Q

what is the membrane potential

A

measure of cellular polarisation that compares the cytoplasmic membrane surface charge to the extracellular surface charge

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3
Q

depolarisation

A

influx of sodium ions leads to depolarisation as membrane potential becomes less negative

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4
Q

hyperpolarisation

A

movement of potassium ions out of a cell leads to hyperpolarisation as membrane potential becomes more negative

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5
Q

repolarisation

A

return to resting potential

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6
Q

what do neurons and skeletal muscle fibres have

A

electrically excitable membranes

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7
Q

what do excitable membranes permit

A

rapid communication between different parts of a cell

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8
Q

what does depolarisation and repolarisation cause in neurons and skeletal muscle fibers

A

action potential (electrical impulse)
that is propigated along their plasma membranes

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9
Q

what do excitable membranes contain

A

voltage-gated ion channels

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10
Q

what are voltage gated ion channels activated and inactivated by

A

changes in membrane potential

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11
Q

when do the electrical channels become activated

A

when the membranes of neurons and skeletal muscle fibers first depolarise from resting potential to threshold potential

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12
Q

threshold potential of neurons

A

-60mV

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13
Q

threshold potential of skeletal muscle fibers

A

-55mV

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14
Q

upon reaching threshold potential,

A

voltage-gated sodium ion channels open and there is a rapid influx of positively charged sodium ions into a cell

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15
Q

what causes the closure of the voltage gated sodium ion channels

A

depolarisation peaks at a membrane potential of +30mV

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16
Q

how does repolarisation of membrane begin

A

voltage-gated potassium ion channels open and positively charged potassium ion leave the cell

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17
Q

what causes the membrane potential to become negative again

A

the loss of the more positive charges than entered the cell

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18
Q

what happens during refractory period

A

former conc of sodium and potassium ions across cell are restored through sodium-potassium ion pumps

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19
Q

why does action potential travel in one direction

A

Further depolarisation cannot occur until the refractory period is over
prevents action potential propagating back from where it came from

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20
Q

skeletal muscles fibers cannot begin contracting until,

A

they recieve instructions from motor neurons of the CNS

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21
Q

how do motor neurons carry instructions

A

in the form of action potentials

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22
Q

when does a contraction of a skeletal muscle fiber begin

A

sarcoplasmic reticulum releases stored calcium ions into the cytosol of the muscle fiber

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23
Q

when does a skeletal muscle fiber contraction end

A

as the intracellular calcium ions are reabsorbed

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24
Q

neuromuscular junction

A

synapse of a skeletal muscle fiber and a neuron

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25
what is the NMJ made up of
axon terminal motor end plate synaptic cleft (in between)
26
what is the motor end plate
specialised region of the sacrolemma
27
what is a neurotransmitter
a chemical released by a neuron to change the permeability or other properties if another cell's plasma membrane
28
what does the cytoplasm of the axon terminal contain
vesicles filled with molecules of ACh
29
what does the synaptic cleft and motor end plate contain
molecules of the enzyme AChE which breaks down ACh
30
what is the synaptic cleft
narrow space that separates the axon terminal of the neuron from the opposing motor end plate
31
what is the stimulus for ACh release
arrival of action potential at the axon terminal
32
what happens when AP reaches neurons axon terminal
permeability changes in its membrane, triggers the exocytosis of ACh into synaptic cleft
33
exocytosis occurs as,
vesicles fuse with the neruron's plasma membrane
34
once ACh is released into synaptic cleft,
diffuse across synaptic cleft bind to ACh receptor membrane channels
35
what does ACh binding to ACh receptor channels cause
opens the membrane channel on the surface of the motor end plate
36
sodium ions movement and why
sodium ions rush into the cytosol becuase extracellular fluid contains high conc of sodium ions and sodium ion conc inside cell is vey low
37
what results in the generation of the action potential in the sarcolemma
sudden inrush of sodium ions
38
how is ACh removed from the synaptic cleft
diffuses away from synapse or broken down by AChE
39
what is ACh broken down into by AChE
acetic acid and choline
40
why is the removal of ACh important
leads to the closing of ACh receptor membrane channels
41
excitation contraction coupling
link between the generation of action potnetial in sacrolemma and the start of a muscle contraction
42
where does the excitation contraction coupling occur
at the triads
43
what happens when action potential reaches a triad
triggers the release of Ca2+ from the terminal cisternae of the sarcoplasmic reticulum
44
how long does the change in permeability of the SR to Ca2+ last
0.03 seconds
45
[Ca2+] in and around sarcomere after AP reaches triad
100 times resting level
46
why is the effect of calcium ion release almost instantaneous
because terminal cisternae are loacted at zones of overlpa where thick and thin filaments ineract
47
calcium ions binding to troponin
changes the shape of the troponin molecule weakens the bond between troponin and actin troponin molecule changes position rolling the attached tropomyosin strand away from the active sites contraction cycle begins
48
contraction cycle
series of molecular events that enable muscle contraction
49
after active sights are exposed
myosin heads bind to them forming cross bridges
50
connection between head and tail
functions as a hinge that leads the head pivot pivots using energy released from hydrolysis of ATP head swings towards the M line-power stroke pivoting is the key step in muscle contraction
51
what is the power stroke
when the head swings towards the M line
52
what happens when muscle cells contract
they pull on the attached tendon fibers
53
what type of force is tension
active- energy must be expended to produce it
54
what must applied tension overcome before movement can occur
the objects load (or resistance)
55
what is an objects load/ resistance
a passive force that opposes movement
56
what does the load of an object depend on
weight, shape, friction ect
57
when does the object move
when applied tension exceeds the load
58
what is compression (force)
push applied to the object, tends to force object away from source of compression
59
no movement can occur until applied compression,
exceeds load of object
60
why can muscle cells pull but not push
muscle cells can use energy to shorten and generate tension through interaction between thick and thin filaments, but not to lengthen and generate compression
61
what does each power stroke result in
sarcomere shortened by 0.5 %
62
why does the entire muscle shorten at the same rate
all the sarcomeres contract together
63
what does the speed of the sarcomere shortening depend on
the cycling rate- the number of power stroeks per second
64
relationship between load and cycling rate
the greater the load, the slower the cycling rate
65
duration of contraction depends on
1. period of stimulation at NMJ 2. presence of free calcium ions in cytosol 3. availability of ATP
66
contraction will continue if
additional action potentials arrive at NMJ in rapid sucession
67
what does a series of action potentials arriving at the NMJ causing the continual release of ACh produce
series of action potentials in the sarcolemma that keeps Ca2+ levels elevated in cytosol

physiology and anatomy (31 decks)

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