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PHYSIOLOGY > Lecture 6+7: Muscle Physiology > Flashcards

Lecture 6+7: Muscle Physiology Flashcards

1
Q

steps in neuromuscular transmission?

A
  1. AP at neuromuscular junction
  2. Ca+ release
  3. myosin and actin interaction
  4. muscle contraction
  5. Ca+ removed
  6. Relaxation
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2
Q

the neuromuscular junction is what type of synapse?

A

Chemical

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2
Q

opening of ACh receptors results in what?

A

end plate potential (EPP)

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2
Q

each vesicle release of ACh causes a miniature _____

A

miniature EPP

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3
Q

what effect does end plate potential cause

A

EPP depolarizes the membrane and initiates APs

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3
Q

the summation of multiple miniature EPPs produces an _____

A

EPP

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4
Q

EPP is a _______ localized to the motor end plate

A

EPP is a GRADED POTENTIAL

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5
Q

what does EPP magnitude depend on

A

the amount of and duration of ACh at the end plate

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6
Q

what factors affect the magnitude of the EPP

A
  • voltage gated Ca+ channel function
  • amount of ACh released
  • rate of ACh breakdown
  • Ach receptor agonists and antagonists
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7
Q

site of Calcium storage inside the muscle

A

Sarcoplasmic reticulum (SR)
- Ca is released for contraction

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8
Q

what does tropomyosin (Tm) do

A

tropomyosin inhibits the binding of myosin to actin

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9
Q

what does Troponin (Tn) do

A

Troponin is a Calcium sensitive molecular switch
— the presence of Ca causes troponin to interact with tropomyosin and make binding sites for the myosin heads available

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10
Q

what is the role of calcium in the regulation of myosin binding to actin

A

Ca binding to troponin complex allows for the repositioning of the tropomyosin filament, this repositioning exposes the mysoin binding sites on actin molecules

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11
Q

The sliding of actin along the myosin filament results in the _____ of the sarcomere

A

shortening (contraction)

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12
Q

what are the steps in neuromuscular transmission?

A
  1. An AP arrives in the presynaptic motorneuron axon terminal
  2. opening of voltage-gated Ca+ channels & entry of Ca into axon terminal
  3. release of ACh from synaptic vesicles into the synaptic cleft
  4. ACh diffuses into sarcolemma
  5. ACh binds to its receptors on the motor end plate within the sarcolemma, increasing the conductance of the motor plate for Na and K, resulting in an EPP
  6. Depolarization of the muscle membrane adjacent to the motor end plate reaches threshold & opens voltage-gated channels that initiate an AP on the sarcolemma
  7. degradation of acetylcholine by acetylcholinesterase (AChE)
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13
Q

what is a myosin molecule (thick filament) composed of

A

two proteins twisted together forming a tail with two heads (cross-bridge)

A single thick filament consists of many myosin molecules

14
Q

what is an actin (thin filament) in a sarcomere composed of

A

3 types of proteins: actin, tropomyosin, troponin

15
Q

the power stroke of myosin results in filament sliding and muscle _____

A

contraction

16
Q

what is the role of Ca in muscle contraction?

A
  1. AP arrives at axon terminal of motorneuron
    - opening of voltage gated Ca channels and entry of Ca into axon terminal
    - release of ACh into synaptic cleft
  2. Upon activation, Ca is released for contraction
    - membrane depolarization opens L-type Ca channels
  3. Mechanical coupling b/w L-type Ca channel and the Ca release channel causes Ca release channels to open
  4. Ca leaves the SR via the Ca releasing channel and activated troponin
    • Ca binding to troponin complex causes the physical repositioning of the tropomyosin filament, which exposes the myosin binding site on actin molecules
17
Q

what removes Ca from the ICF back into the SR and why does this happen

A

the sarcoplasmic reticulum Ca+ ATPase (SERCA pump)

this occurs for the purpose of relaxation / to prepare for the next contraction

18
Q

how is Ca removed from ICF to the ECF

A

by sarcolemmal Ca+ ATPase and a Ca/Na exchanger

19
Q

the Ca/Na exchanger is an example of 2ndary active transport because….

A

it uses the gradient for Na to

20
Q

an action potential travels through the entire sarcolemma and into the ______

A

transverse (T) tubules

21
Q

when Ca is released into muscle fiber, it causes a ______ of the T-tubules

A

depolarization

22
Q

what are cardiac muscle fibers interconnected by

A

intercalated discs and form functional syncytium

23
Q

what are the two kinds of membrane junctions found within intercalated discs

A

Desmosomes
- mechanical junctions
Gap junctions
- electrical junctions which allow the spread of AP

24
Q

where does Ca+ come from in cardiac muscle

A

the SR and the outside (via L-type Ca+ channels)

25
Q

there is a decrease in contractile force when the concentration of ____ decreases

A

calcium

26
Q

what can cytostolic calcium concentrations decrease from

A

the return of Ca into the SR via the SR Ca ATPase (SERCA)

27
Q

where is smooth muscle found?

A

in the walls of organs and tubes

  • arteries and veins
  • trachea and bronchioles
  • GI tract
  • uterus, bladder
28
Q

type of muscle that lacks T tubules and has poorly developed SR

A

smooth muscle

29
Q

what are the types of smooth muscle

A

MULTIUNIT (Neurogenic)
- electrically isolated, can contract independently

SINGLE UNIT (UNITARY/VISCERAL)
- have gap junctions b/w cells (= functional syncytium)

VASCULAR SM
- combination of unitary and multiunit SM

30
Q

where multiunit SM is found

A

eye, skin hair follicles, large blood vessels, small airway, vas deferens

31
Q

where single unit (unitary) SM is found

A

GI tract, bladder, small blood vessels, uterus and ureter

32
Q

what types of filaments are in SM

A

thick myosin filaments are longer in SM than skeletal

Thin actin contains tropomyosin but LACKS troponin

33
Q

What is the purpose of dense bodies

A
  • attachment for actin
  • serve the same role as Z discs do in skeletal muscle
  • some dense bodies are attached to cell membrane

PHYSIOLOGY (25 decks)

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