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Year 1 > Muscles + action potentials > Flashcards

Muscles + action potentials Flashcards

1
Q

What is the peripheral nervous system?

A

all axons + ganglia outside CNS

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2
Q

Subdivisions of the autonomic nervous system?

A

parasympathetic

sympathetic

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3
Q

Subdivisions of the somatic nervous system?

A

efferent motor nerve

afferent sensory nerve

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4
Q

How is resting membrane potential generated + maintained?

A

cell membrane relatively permeable to potassium ions and relatively impermeable to sodium ions
sodium ATPase pump actively transports 2 potassium ions into cell and 3 sodium ions out of cell
maintains concentration gradient of potassium ions and sodium ions
-70mV

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5
Q

How is an action potential initiated and generated?

A
  • resting potential raised slightly by small ionic change (or other changes)
  • threshold voltage for opening of VgNa reached (voltage-gated sodium channels), VgNa channels open
  • sodium ions flow into cell down electrochemical gradient, depolarising cell membrane potential from -70mV –> +30mV
  • VgK channels open + VgNa channels close
  • potassium ions flow out of cell down electrochemical gradient through open VgK channels
  • cell becomes repolarised back near resting membrane potential
  • following AP (action potential), Vg channels become inactive + refractory
  • duration before another AP generated = refractory period
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6
Q

Propagation of an action potential

A
  • unidirectional due to refractory period of VgNa channels
  • propagated signal does not vary in amplitude + is a digital signal (all or none)
  • largely dependent on frequency of firing rates
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7
Q

What does nerve conduction velocity depend on?

A
  • rate at which membrane ahead can reach threshold
  • which depends on longitudinal conductance of cable
  • which depends on cable diameter
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8
Q

What is saltatory conduction?

A

action potential skips from node to node down length of axon

  • insulated axons of large diameter
  • schwann cells produce myelin
  • nodes of ranvier = sodium channels clustered at each node
  • reduces losses, speeds conduction + saves energy
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9
Q

Describe what happens at a neuromuscular junction (synapse)

A
  • arriving AP triggers VgCa channels to open at nerve terminal
  • calcium ions enter cell + triggers a reaction cascade
  • vesicles of acetylcholine integrate with presynaptic membrane
  • contained acetylcholine released
  • acetylcholine neurotransmitter molecules bind to (nicotinic) acetylcholine receptor (AChR) - ligand-gated ion channel on post-synaptic muscle membrane
  • various ions, mainly sodium ions, flow in and depolarise muscle membrane (same way as in axon)
  • muscle action potential propagated over muscle cell membrane (sarcolemma) through T (transverse) tubules to inner aspects of muscle fibre (similar to nerve action potential)
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10
Q

Define muscle

A

bundle of fibrous tissue that can contract to produce movement - voluntary or involuntary

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11
Q

What are the 3 muscle types?

A

striated (skeletal) muscle - locomotion + posture
smooth muscle - peristalsis
cardiac muscle - heart

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12
Q

Define contraction

A

Shortening

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13
Q

Define elasticity

A

Returning to resting state

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14
Q

Define hypertrophy

A

Increase in size

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15
Q

Define hyperplasia

A

Increase in number (of muscle cells)

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16
Q

Describe the structure of skeletal muscle

A
  • muscle attached to bone by tendon
  • epimysium = surrounds muscle
  • epimysium folds inwards to form perimysium which separates muscle chunks into fascicles
  • bundles of muscle fibres within fascicles, fibres separated by endomysium
  • muscle fibres = multinucleated, multicellular structures
  • muscle cells develop from myoblasts (myo = muscle, blast = immature/precursor cell)
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17
Q

Describe a skeletal muscle fibre

A

filled with myofibrils
sarcolemma analogous to plasma membrane
sarcoplasm analogous to cytoplasm
sarcoplasmic reticulum analogous to smooth endoplasmic reticulum
transverse tubular system (TT) = invaginations of sarcolemma

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18
Q

What are transverse tubular systems?

A

invaginations of sarcolemma

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19
Q

What is a triad?

A

2 terminal cisternae of sarcoplasmic reticulum (SR) and transverse tubule (TT) in close proximity

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20
Q

What is a sarcomere?

A

unit of contraction of myofibril

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21
Q

Define Z-line

A

either end of sarcomere

thin filaments insertion

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22
Q

Define M-line

A

origin of thick filaments (middle of sarcomere)

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23
Q

Define A-band

A

overlap of thick and thin filaments

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24
Q

Define I-band

A

only thin filaments

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25
Q

What are sarcomere thick filaments?

A

myosin

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26
Q

What are sarcomere thin filaments?

A

actin

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27
Q

Describe the structure of the thick filaments

A

multiple myosin molecules
head = actin binding site
tail = 2 intertwined heavy chains
2 regulatory light chains = ATPase activity
2 alkali light chains = stabilise myosin head
hinge = movement of myosin head

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28
Q

Describe the structure of thin filaments

A

chain of intertwined actin molecules
tropomyosin = block myosin receptors on actin molecules
troponin = controls tropomyosin position

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29
Q

Describe muscle contraction

A

myosin head attached to actin filaments
greater overlap between thick and thin filaments
Z-lines closer together = shortening of sarcomere - occurs along length of muscle fibre

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30
Q

Describe excitation-contraction coupling

A

plasma membrane invaginates into transverse tubules
sarcoplasmic reticulum = storage organelle for calcium ions
action potential motor nerve end plate propagates along membrane and down T tubules
membrane depolarisation opens L-type Ca2+ channels on T-tubules
[L-type Ca2+ channel (AKA dihydropyridine (DHP) receptor) blocked by antihypertensive drugs]
coupling between DHP receptor and calcium ion release channel opens calcium ion channels
calcium ions released into myofibril - activates troponin C + cross-bridge cycling

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31
Q

Describe initiation of cross-bridge cycling

A

Ca2+ modulates contraction through regulatory proteins rather than direct interaction with actin + myosin
tropomyosin blocks myosin binding site
troponin C = binding of calcium ions to high affinity sites causes conformational change in troponin complex
troponin I = moves away from actin filament
troponin T = pushes tropomyosin away from myosin binding site on actin
myosin head binds to actin

32
Q

What are the 3 types of tropomyosin molecule?

A 
C = binds Ca2+
I = anchors complex to actin
T = binds to tropomyosin
33
Q

What are the 5 stages of cross-bridge cycle in skeletal muscle?

A

1) ATP binding - ATP binds to myosin head, causes dissociation of actin-myosin complex
2) ATP hydrolysis - ATP hydrolysed causes myosin heads to return to resting conformation
3) Cross-bridge formation - cross-bridge forms and myosin head binds to new position on actin
4) Release of Pi from myosin - myosin heads change conformation resulting in power stroke - filaments slide past each other
5) ADP release

34
Q

Describe contraction termination

A

Calcium ions must be removed from cytoplasm for contraction to cease and relaxation to occur
minor = Na-Ca exchanger (NCX) - remove Ca2+ from cell by Ca2+ pump in plasma membrane
major = Ca2+ reuptake into sarcoplasmic reticulum by SERCA-type Ca pump
Calsequestrin = major Ca-binding protein in skeletal muscle (located primarily at triad junction)

35
Q

What does the amount of force generated by a muscle depend on?

A 
number of active muscle fibres
cross-sectional area of muscle
initial resting length of muscle
rate at which muscle shortens
frequency of stimulation
36
Q

What is isometric contraction?

A

muscle length fixed
stimulation of muscle causes increased tension but no shortening
eg. holding weight in hand of outstretched arm
(contraction against resistance where length of muscle remains the same)

37
Q

What is isotonic contraction?

A

muscle length not fixed
stimulation of muscle causes increased shortening provided tension generated is greater than opposing load
eg. holding weight in hand and lifting hand, bending at elbow
(contraction against resistance where length of muscle changes)
concentric or eccentric

38
Q

Describe length-tension relationship

A

muscle can be stretched
passive tension = tension measured before muscle contraction (elasticity)
at any fixed length, if muscle is contracted, active tension develops due to cross-bridge formation

39
Q

Describe force-length relationship

A

muscles elastic due to titin
muscles held at resting length
maximum tension = thick + thin filaments overlapping 80-120%

40
Q

Describe force-velocity relationship

A

speed of change in length
power = force=velocity
velocity increases, force decreases

41
Q

Describe summation in single muscle fibres

A

one action potential = singular skeletal muscle twitch

as muscle twitch longer than AP, a 2nd AP can be initiated before 1st contraction subsided - called summation

42
Q

Describe slow twitch muscle fibres

A 
type 1
fatigue resistant
red (due to myoglobin)
oxidative respiration
lots of mitochondria
low glycogen levels 
prologned endurance
43
Q

Describe fast twitch muscle fibres (2a)

A 
type 2a
fatigue resistant
red (due to myoglobin)
oxidative respiration
higher levels of mitochondria
abundant in glycogen 
endurance or rapid force
44
Q

Describe fast twitch muscle fibres (2b)

A 
type 2b
fatigable 
white (less myoglobin)
glycolytic metabolism
fewer mitochondria
high levels of glycogen
rapid force production
45
Q

What are long skeletal muscle fibres used for?

A

rapid movement

46
Q

What are short skeletal muscle fibres used for?

A

large forces

47
Q

What is concentric muscle contraction?

A

isotonic contraction in direction of contraction

48
Q

What is eccentric muscle contraction?

A

isotonic contraction opposite to direction of contraction

49
Q

Effect of smoking on muscle fibres

A

decreased cross-sectional area of muscle fibres
decreased type 2 fibres
decreased exercise capacity

50
Q

How is creatine phosphate created

A

ATP + creatine combined in resting muscle to produce creatine phosphate + ADP

51
Q

What is the function of creatine phosphate?

A

acts as reservoir within muscles for ATP
exercise initiated - creatine kinase breaks down creatine phosphate - produces creatine + ATP that can be used in muscle contraction

52
Q

Describe glycolysis

A

1st step in respiration
does not require oxygen (anaerobic)
net gain = 2 ATP + 2 pyruvate

53
Q

Describe citric acid cycle (Krebs cycle)

A

pyruvate enters

net gain = 1 ATP, 3 NADH + 1 FADH2 per turn

54
Q

Describe the electron transport chain

A

most energy produced during oxidative process
NADH moved along ETC within mitochondria of muscle cells
NADH reduced - loss of H+ ion - form ADP - converted to ATP by ATP synthase
requires oxygen (oxygen = final electron acceptor - produced water)

55
Q

Describe the function of lactate in respiration

A

pyruvate from glycolysis can enter aerobic or anaerobic systems
pyruvate - lactic acid - liver - ATP
increased lactate build up in athletes
endurance athlete = longer aerobic component

56
Q

What is gluconeogenesis?

A

lactate transported back to liver
converted back to pyruvate - citric acid cycle
then either used for energy production or converted back to glucose (gluconeogenesis)

57
Q

Define oxygen debt

A

amount of oxygen needed after finished exercising to return systems to back where they started

58
Q

What is used for energy in intense short-term exercise?

A

1st 15 seconds = creatine phosphate, ATP

2 minutes = glycogen -> glucose-6-phosphate

59
Q

What is used for energy in longer + less intense exercise?

A

glycogen from circulation
glucose from plasma
increased hepatic glucose production (short term glycogenolysis) (longer term gluconeogenesis - muscle proteolysis, glucagon + insulin, fatty acid release)

60
Q

Define VO2 max

A

oxygen usage under maximal aerobic activity

61
Q

Define EPOC

A

excessive post-exercise oxygen consumption

62
Q

What are the fast and slow components of recovery?

A 
fast = resting levels of ATP + CP restored
slow = lactic acid converted to glucose in liver, lactic acid converted to pyruvic acid
63
Q

How does the respiratory system change to meet oxygen demand during exercise?

A

increase ventilation rate

increase tidal volume

64
Q

Do blood gases change during exercise?

A

arterial oxygen and venous carbon dioxide do not change significantly during exercise
respiratory system can provide adequate aeration

65
Q

How does oxygen consumption change during exercise?

A

increased oxygen consumption

reaches steady state where lactic acid accumulation is minimal

66
Q

Describe changes to VO2 max with age, sex and activity

A

increase in exercise past VO2 max results in increased lactic acid production
VO2 max improves with activity (endurance training increases it)
decreases after age 25
lower in females

67
Q

How does exercise affect alveolar diffusion

A

increased oxygen and carbon dioxide diffusion capacity

related to increased perfusion more than ventilation

68
Q

Cardiac changes with exercise

A

increased cardiac output
increased stroke volume
increased heart rate

69
Q

Define stroke volume

A

volume of blood pumped per contraction

70
Q

Cardiac output formula

A

stroke volume x heart rate

71
Q

What is Starling’s Law?

A

more full heart is, harder it will contract, increased stroke volume
(force of contraction related to how stretched the cardiac muscle is)

72
Q

Benefits of exercise

A

lower BP
increases circulating HDL and lowers triglycerides
changes in arterial wall homeostasis = decreases atherosclerotic disease
increased aortic valve function, decrease in calcification
increased ventricular wall thickness
increased red cells (to a point)
changes in cardiac vasculature to increase oxygen availability
(can also decrease insulin resistance (lower risk of type 2 diabetes))

73
Q

How does exercise affect depression?

A

moderate clinical effect in decreasing depression

no more effective than psychological/pharmacological treatments

74
Q

How does exercise affect RA?

A

increase muscle mass + strength = decrease cachexia
weight-bearing exercise = reduce risk of osteoporosis
resistance training = increase tendon stiffness + strengthen connective tissue
cyclic loading increases cartilage integrity + joint lubrication
mobility exercises = increased ROM

75
Q

Describe epimysium

A

surrounds muscle

76
Q

Describe perimysium

A

inward folds of epimysium

separates muscle chunks into fascicles

77
Q

Describe endomysium

A

separates muscle fibres within fascicles

Year 1 (41 decks)

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