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+ BIOL 370 > Midterm Review Slides > Flashcards

Midterm Review Slides Flashcards

1
Q

What are the 4 general types of cellular movement?

A
  • reorganization of the cytoskeletal network – growth of the cytoskeleton in one region of the cell pushes the cell membrane outward (amoeboid movement)
  • motor protons ‘walk’ along relatively fixed elements of the cytoskeleton (can be used for cargo transport throughout the cell)
  • motor proteins attached to the cell membrane (fixed) pull on the skeleton, moving an element of the cytoskeleton
  • motor proteins and cytoskeleton are arranged such that they slide over each other, pulling the cell into a different shape
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2
Q

What are microtubules?

A

long hollow tubes composed of repeating units of tubulin (which is a dimer of alpha-tubulin and beta-tubulin)

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3
Q

How do microtubules grow and shrink?

A
  • grow by adding tubulin dimers on the (+) end
  • shrink by shedding tubulin dimers on the (-) end
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4
Q

What is the main factor that influences the rate of growth and the rate of shrinkage in microtubules?

A

concentration of tubulin (Cc)

  • microtubule grows if the concentration of tubulin is greater than Cc
  • microtubule shrinks if the concentration of tubulin is less than Cc
  • Cc is lower for the (+) end of the microtubule compared to the (-) end
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5
Q

Where is the microtubule-organizing centre (MTOC)?

A

near the nucleus

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6
Q

Where is each end of a microtubule relative to the microtubule-organizing centre (MTOC)?

A
  • (-) end is located at the MTOC
  • (+) end extends out toward the cell membrane
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7
Q

Which motor proteins are associated with microtubules?

A
  • kinesin
  • dynesin
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8
Q

In what direction along the microtubule does kinesin and dynein move in?

A

polarity of the microtubule sets the direction of movement

  • kinesin moves towards the (+) end
  • dynein moves towards the (-) end
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9
Q

What are microfilaments?

A

long strands of the globular protein beta-actin (G-actin)

  • G-actin polymerizes to form F-actin
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10
Q

How does the growth of F-actin (microfilaments) compare to microtubules?

A

similar to microtubules

  • spontaneous growth
  • has polarity
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11
Q

How does actin growth occur?

A
  • capping protein on (-) end of F-actin to prevent shrinking
  • growth at (+) end of F-actin (addition of G-actin monomers)
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12
Q

How does actin treadmilling occur?

A
  • growth at (+) end of F-actin
  • shrinkage at (-) end of F-actin
  • a given G-actin monomer will move from the (+) to (-) end of actin
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13
Q

What is actin polymerization important for?

A
  • amoeboid movement
  • cell movement
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14
Q

What motor protein is associated with microfilaments?

A

myosin (many different types)

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15
Q

How might microfilaments and myosin work together to generate cellular movement?

A
  • microfilaments act as tracks along which myosin moves (important for intracellular transport)
  • myosin can pull on filaments
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16
Q

What is the function of myosin V?

A

recall myosin V moves towards the (+) end of actin filaments – towards the plasma membrane

  • intracellular transport (cargo)
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17
Q

In what direction does myosin move along microfilaments?

A
  • most known types of myosin move towards the (+) end
  • EXCEPTION: myosin VI moves towards the (-) end
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18
Q

What are the functions of myosin VI?

A

recall myosin VI moves towards the (-) end of actin filaments – towards the nucleus

  • intracellular transport (cargo)
  • endocytosis
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19
Q

Sliding Filament Model

What are the stages of the cross-bridge cycle?

A
  1. ATP binds to myosin, causing myosin to detach from actin
  2. releasing actin causes myosin to hydrolyze ATP into ADP and Pi (which remain bound by myosin)
  3. ATP hydrolysis causes myosin to extend and attach to actin (forms a cross-bridge)
  4. release of phosphate promotes the power stroke
  5. ADP is released
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20
Q

Sliding Filament Model

What is unitary displacement?

A

the distance that myosin steps during each cross-bridge cycle

  • this keeps them on track, and avoids interference with other things
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21
Q

Sliding Filament Model

What is the unitary displacement for myosin monomers?

A

variable

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22
Q

Sliding Filament Model

What is the unitary displacement for myosin dimers?

A

dependent on the periodicity of the actin filament

  • ie. myosin V ‘walks’ along a microfilament with ~36 nm steps – 36 nm is the period of the helical actin filament
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23
Q

Sliding Filament Model

What is the duty cycle?

A

proportion of time during each cross-bridge cycle the myosin is attached to actin

  • time spent in cross-bridge divided by time for full cross-bridge cycle
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24
Q

Sliding Filament Model

What is the duty cycle for non-muscle myosin?

A

0.5

  • each myosin has 2 heads
  • duty cycle of 0.5 means that each myosin head is bound to actin for half of the cycle (one myosin is bound for half of the cycle, and the other myosin is bound for the other half of the cycle)
  • at least one myosin head is bound at all times, which will help prevent myosin from falling off the track of the microfilament
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25
Q

Sliding Filament Model

What is the duty cycle for muscle myosin?

A

0.05

  • muscle myosin and non-muscle myosin have different functions
  • myosin heads are sliding by actin filaments
  • want cross-bridges to occur quickly, so that contraction can occur quickly, therefore myosin heads are being bound and detached quickly
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26
Q

Describe the two main ways to categorize muscle.

A
  • striated (skeletal and cardiac) vs. unstriated (smooth)
  • voluntary (skeletal) vs. involuntary (cardiac and smooth)
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27
Q

What are striated muscles composed of?

A
  • thick filaments (myosin)
  • thin filaments (actin)
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28
Q

What are thick filaments?

A

polymers of ~300 myosin II hexamers

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29
Q

What are thin filaments?

A

polymers of alpha-actin

(compare this to microfilaments, which are polymers of beta-actin)

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30
Q

What proteins are associated with thin filaments?

A
  • special proteins that cap the ends of the filament to stabilize structure (filaments are fixed)
  • structural proteins (ie. troponin, tropomyosin)
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31
Q

What filament is tropomyosin and troponin associated with?

A

thin filament

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32
Q

What does tropomyosin and troponin do?

A

regulate the interaction between actin and myosin in striated muscles

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33
Q

What is tropomyosin?

A

long, thin, double-stranded protein that extends over ~7 actin monomers on the thin filament

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34
Q

What is troponin?

A

trimer of (TnC, TnI, and TnT) that binds to every 7th actin on the thin filament

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35
Q

What role does the TnC of troponin play?

A

Ca2+ binds to it, which shifts tropomyosin and allows tropomyosin to interact with myosin

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36
Q

Sarcomere

What is the A-band?

A

the region where thick filaments occur

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37
Q

Sarcomere

What is the I-band?

A

the portion of the thin filaments that does not overlap with the thick filaments

  • spans a Z-disk
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38
Q

Sarcomere

What is a Z-disk?

A

protein plate (composed of actin, titin, and other proteins) at the end of the sarcomere where the (+) end of actin thin filaments are attached

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39
Q

Sarcomere

What is the H-zone?

A

the portion of the thick filaments that does not overlap with the thin filaments

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40
Q

Sarcomere

What is the M-line?

A

the centre of the sarcomere between (-) ends of actin – region where thick filaments do not overlap with thin filaments

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41
Q

What is the sarcomere length-force relationship?

A

recall: cross-bridges can only form when the myosin heads of a thick filament can interact with the actin units of a thin filament

  • the amount of force a sarcomere can produce during contraction increases as the number of myosin heads that can contact a thin filament increases
  • the amount of force a sarcomere can produce decreases as overlap between the thin filaments of adjacent Z-disks increases
  • at the shortest sarcomere length, the thick filaments will collide with the Z-disks and no further contraction is possible
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42
Q

Sarcomere Arrangements

What is a myofibril composed of?

A

many sarcomeres arranged in series

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43
Q

Sarcomere Arrangements

What is a myofibre (striated muscle cell) composed of?

A

many myofibrils arranged in parallel

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44
Q

Sarcomere Arrangements

What occurs when myofibres (striated muscle cells) grow in length?

A

it adds more sarcomeres to the ends of each myofibril

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45
Q

Sarcomere Arrangements

What occurs when myofibres (striated muscle cells) grow in diameter?

A

it increases the number of myofibrils

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46
Q

Sarcomere Arrangements

How long is a myofibril?

A

runs the entire length of a muscle cell

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47
Q

EC Coupling

Give an overview of the events in a typical skeletal muscle.

A

excitation leads to contraction:

  1. AP depolarizes sarcolemma (excitation)
  • AP caused by opening of Ca2+ channels
  1. depolarization linked to Ca2+ release from SR
  • Ca2+ channels in SR are linked to the Ca2+ channels that caused the AP (coupling)
  1. Ca2+ binds to troponin (TnC component specifically), which shifts the configuration of tropomyosin to reveal the myosin binding sites on actin
  2. cross-bridge cycling and sarcomere shortening (contraction

relaxation:

  • sarcolemma repolarizes and cytoplasmic [Ca2+] returns to resting levels
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48
Q

EC Coupling – Excitation

Are most vertebrate skeletal muscles neurogenic or myogenic?

A

neurogenic (neuron causes excitation)

  • they are stimulated by ACh from a motor neuron
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49
Q

EC Coupling – Excitation

Describe the innervation of cells in twitch muscles.

A

each cell is innervated by one neuron

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50
Q

EC Coupling – Excitation

Describe the innervation of cells in tonic muscles. Why does it differ from twitch muscles?

A

each cell is innervated by multiple neurons

  • this is needed because tonic muscles always have some level of contraction
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51
Q

EC Coupling – Excitation

What is the sarcolemma resting membrane potential?

A

around -70 mV

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52
Q

EC Coupling – Excitation

What causes depolarization?

A
  • opening of Na+ channels, allowing influx of Na+
  • then opening of voltage-gated Ca2+ channels, allowing influx of Ca2+
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53
Q

EC Coupling – Excitation

What causes repolarization?

A
  • opening of K+ channels, allowing K+ to leave the cell
  • then opening of Cl- channels (in SKELETAL muscle)
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54
Q

EC Coupling – Excitation

Is the time course of an AP in a muscle cell always the same?

A

no – varies in different types of muscle

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55
Q

EC Coupling – Excitation

Neurogenic twitch muscles are innervated by one (or maybe a couple) motor neurons. How do muscles ensure uniform depolarization of the sarcolemma for contraction?

A
  • multiple innervations (for tonic muscles)
  • invaginations of the sarcolemma called t-tubules, which propagate the AP to multiple places
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56
Q

EC Coupling – Excitation

What are transverse or t-tubules? What do they do? Where are they found?

A

sarcolemmal invaginations that enhance AP penetration

  • more developed in larger, fast-twitching muscles
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57
Q

EC Coupling – Excitation

What does the sarcoplasmic reticulum (SR) do?

A

stores Ca2+

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58
Q

EC Coupling – Excitation

What are terminal cisternae? What do they do?

A

enlargements in the SR that increase Ca2+ storage

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59
Q

EC Coupling – Coupling

Depolarization-induced Ca2+ release. How does this occur?

A
  1. depolarization of the sarcolemma causes DHPR to open
  • DHPR and RyR are physically linked, and the structural change in DHPR opens RyR
  1. Ca2+ exits the SR through RyR, which greatly increases cytoplasmic [Ca2+] and stimulates contraction
  2. Ca2+ ATPase and NaCaX pump Ca2+ out of the cell, and SERCA pumps Ca2+ into the SR, which together decreases cytoplasmic [Ca2+] and allows relaxation
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60
Q

EC Coupling – Coupling

What does troponin and tropomyosin do during relaxation of the muscle?

A
  • during relaxation, cytoplasmic [Ca2+] is low
  • TnC (troponin) regulatory sites cannot bind Ca2+
  • the troponin-tropomyosin complex blocks the myosin bindings sites on the thin filament
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61
Q

EC Coupling – Coupling

What does troponin and tropomyosin do during excitation of the muscle?

A
  • excitation of the muscle increases cytoplasmic [Ca2+]
  • TnC (troponin) regulatory sites bind Ca2+, which causes a structural reorganization of the troponin-tropomyosin complex
  • the troponin-tropomyosin complex rolls into the groove of the thin filament, which exposes the myosin binding sites
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62
Q

What is a single twitch?

A

if a muscle fibre is restimulated after it has completely relaxed, the second twitch is the smae magnitude as the first twitch

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63
Q

What is twitch summation?

A

if a muscle fibre is restimulated before it has completely relaxed, the second twitch is added on to the first twitch

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64
Q

What is tetanus?

A

if a muscle fibre is stimulated so rapidly that it does not have an opportunity to relax at all between stimuli, a maximal sustained contraction known as tetanus occurs

  • eventually, stimulation ceases or fatigue begins
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65
Q

Cardiac Muscle

How are cardiomyocytes arranged?

A

formed into a branching network

  • cells are connected end-to-end by intercalated disks, which contain gap junctions through which APs are propagated to adjacent cells (myogenic)
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66
Q

Describe the difference in the arrangement of contractile units in skeletal vs. cardiac muscle.

A
  • skeletal: linear along the long-axis of the muscle
  • cardiac: branching network
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67
Q

Describe the difference in the type of innervation in skeletal vs. cardiac muscle.

A
  • skeletal: somatic
  • cardiac: autonomic
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68
Q

Describe the difference in the type of excitation in skeletal vs. cardiac muscle.

A
  • skeletal: neurogenic – neural input needed for contraction
  • cardiac: myogenic – cardiomyocytes contract in response to input from other muscle cells
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69
Q

Describe the difference in EC-coupling in skeletal vs. cardiac muscle.

A
  • skeletal: depolarization-induced Ca2+ release
  • cardiac: Ca2+-induced Ca2+ release
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70
Q

Cardiac Muscle

What are pacemaker cells? Where are they located?

A

specialized myocytes that depolarize spontaneously

  • located in specific nodes
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71
Q

Cardiac Muscle

Do pacemaker cells have a stable or unstable membrane potential? Why?

A

unstable RMP, in part due to f-channels which are permeable to both Na+ and K+

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72
Q

Cardiac Muscle

What is the main difference between skeletal muscle and cardiac muscle APs?

A

timing

  • cardiac muscle APs have a plateau phase, caused by the slow influx of Ca2+
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73
Q

EC Coupling – Cardiac Muscle

Ca2+-induced Ca2+ release. How does it occur?

A
  1. depolarization of the sarcolemma causes DHPR to open, which allows extracellular Ca2+ to enter the cell
  2. localized increases in intracellular [Ca2+] triggers the opening of RyR, which greatly increases cytoplasmic [Ca2+] and stimulates contraction
  3. Ca2+ ATPase and NaCaX pumps Ca2+ out of the cell, and SERCA pumps Ca2+ into the SR, which together decreases cytoplasmic [Ca2+] and allows relaxation
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74
Q

EC Coupling

Describe the difference in coupling in skeletal vs. cardiac muscle.

A
  • in skeletal muscle, dihydropyridine receptors (DHPR) and ryanodine receptors (RyR) are physically linked, which allows for depolarization-induced Ca2+ release from the SR
  • in bird and mammal cardiac muscle cells, DHPR and RyR are NOT physically linked
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75
Q

What happens when cardiac muscle is stimulated at a higher frequency? How does this compare to skeletal muscle?

A
  • a point is reached where stimulation occurs while the AP is in the refractory period
  • contractions may or may not occur, and the normal frequency is lost (arrhythmia)
  • in skeletal muscle, twitch summation or tetanus occurs
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76
Q

What shape does smooth muscle have?

A

spindle-shaped

  • no set structure like sarcomeres
  • thick filaments (myosin) and thin filaments (actin) go all around the cell
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77
Q

What aspects of smooth muscle cell shape are affected when contraction occurs? How does this compare with skeletal muscle?

A
  • contraction affects depth, width, and length of the cells
  • in skeletal muscle, only length changes
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78
Q

Why do smooth muscle contract slower than skeletal muscle?

A

they have a longer duty cycle

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79
Q

Smooth Muscle

Regulation of Contraction – Thick Filament

A
  1. Ca2+ enters the cell and is also released from SR, which increases intracellular [Ca2+]
  2. Ca2+ binds to calmodulin
  3. Ca2+-CM activates myosin light chain kinase
  4. activated MLCK phosphorylates the light chains in myosin heads, which increases myosin ATPase activity
  5. active myosin cross-bridges slide along actin, which results in muscle tension
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80
Q

Smooth Muscle

What does myosin light chain phosphatase (MLCP) do?

A

removes phosphorous from myosin head

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81
Q

Smooth Muscle

Does smooth muscle have troponin and tropomyosin?

A

lacks troponin

  • instead, the position of tropomyosin on the actin filament is regulated by caldesmon
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82
Q

Smooth Muscle

Regulation of Contraction – Thin Filament

A
  • in relaxed smooth muscle, both caldesmon and tropomyosin bind to actin, which blocks the myosin binding site

when cytoplasmic [Ca2+] increases:

  • calmodulin binds Ca2+, then binds to caldesmon
  • calmodulin-caldesmon dissociates from actin, and tropomyosin shifts position to expose myosin binding sites, which allows for contraction

when cytoplasmic [Ca2+] decreases:

  • Ca2+ dissociates from calmodulin, then calmodulin dissociates from caldesmon
  • caldesmon binds to actin
  • tropomyosin shifts position to block myosin binding sites, which allows for relaxation
83
Q

Smooth Muscle

What regulates caldesmon activity? How?

A

hormones

  • many of the hormones that affect smooth muscle function act via signaling cascades that lead to phosphorylation or dephosphorylation of caldesmon
  • ie. signaling cascade that leads to phosphorylation of caldesmon by a MAP kinase – phosphorylated caldesmon will not bind to actin, even with low cytoplasmic [Ca2+]
84
Q

Smooth Muscle

What regulates contraction? How?

A

Ca2+ regulates contraction via both thin and thick filaments

  • with increased cytoplasmic [Ca2+], calmodulin binds Ca2+
  • Ca2+-calmodulin binds to caldesmon, which causes it to detach from actin, which exposes myosin binding sites on the thin filaments
  • Ca2+-calmodulin binds to MLCK such that it phosphorylates the myosin light chain, which activates the myosin thick filaments
  • *hormones do not affect the actin part of the pathway – see diagram (slide 46)
85
Q

What is phasic smooth muscle? Where can it be found?

A

muscle that contracts in bursts triggered by APs that cause increased cytosolic Ca2+

ie. gastrointestinal and urogenital systems

86
Q

What is tonic smooth muscle? Where can it be found?

A

muscle that is partially contracted at all times, and varies its contraction according to cytosolic Ca2+ level

ie. large arteries and veins

87
Q

What are two ways in which smooth muscle is organized?

A
  • multi-unit smooth muscle
  • single-unit smooth muscle
88
Q

What are multi-unit smooth muscle?

A

cells must each be separately stimulated by nerves to contract

  • myocytes are NOT electrically coupled with each other
89
Q

Describe the location of multi-unit smooth muscle vs. single-unit smooth muscle.

A
  • multi-unit: surrounding arteries, respiratory airways, and in the eye
  • single-unit: (more common) in walls of most visceral organs
90
Q

Describe the contractile activity of multi-unit smooth muscle vs. single-unit smooth muscle.

A
  • multi-unit: neurogenic and phasic
  • single-unit: myogenic and may be phasic (pacemaker potentials) or tonic (slow-wave potentials)
91
Q

Do multi-unit smooth muscle and single-unit smooth muscle have gap junctions?

A
  • multi-unit: rarely
  • single-unit: yes – electrically link neighbouring cells (functional syncytium)
92
Q

What can multi-unit smooth muscle be initiated to contract by?

A
  • autonomic nervous system
  • hormone signaling
93
Q

What can single-unit smooth muscle be modified by?

A

autonomic nervous system

94
Q

What is the location of skeletal vs. cardiac vs. smooth muscle?

A
  • skeletal: attached to skeleton
  • cardiac: heart
  • smooth: blood vessels and eyes (multi-unit), walls of visceral organs (single-unit)
95
Q

What is the mechanism of contraction of skeletal vs. cardiac vs. smooth muscle?

A
  • skeletal: sliding filament
  • cardiac: sliding filament
  • smooth: sliding filament
96
Q

What type of contraction initiation does skeletal vs. cardiac vs. smooth muscle have?

A
  • skeletal: neurogenic
  • cardiac: myogenic
  • smooth: neurogenic/myogenic
97
Q

Do skeletal vs. cardiac vs. smooth muscle have sarcomeres?

A
  • skeletal: yes
  • cardiac: yes
  • smooth: no
98
Q

Do skeletal vs. cardiac vs. smooth muscle have troponin and tropomyosin?

A
  • skeletal: yes
  • cardiac: yes
  • smooth: tropomyosin only – caldesmon instead of troponin
99
Q

Do skeletal vs. cardiac vs. smooth muscle have t-tubules?

A
  • skeletal: yes
  • cardiac: yes
  • smooth: no
100
Q

Where is the site of Ca2+ regulation in skeletal vs. cardiac vs. smooth muscle?

A
  • skeletal: troponin on thin filament
  • cardiac: troponin on thin filament
  • smooth: myosin thick filament
101
Q

Are there gap junctions in skeletal vs. cardiac vs. smooth muscle?

A
  • skeletal: no
  • cardiac: yes
  • smooth: depends
102
Q

What is a motor unit?

A

group of muscle fibres under the control of one motor neuron

103
Q

How can the strength of contraction in a skeletal muscle be increased?

A

by recruitment of more motor units

104
Q

Describe the diversity in cell innervation in invertebrate tonic muscle cells.

A

in some cells, a single cell is innervated by a single motor neuron at multiple synapses

  • graded contraction – summation of excitatory postsynaptic potentials (EPSPs)

in other cells, a single cell is innervated by multiple motor neurons (each neuron may have multiple synapses with this single muscle cell)

  • some neurons will be excitatory, and some may be inhibitory
  • graded contraction
105
Q

Describe the differences in vertebrate twitch skeletal muscle cell stimulation vs. vertebrate tonic skeletal muscle cell stimulation.

A

twitch skeletal muscle cell:

  • stimulated by a single motor neuron – one motor end plate
  • response to stimulus is always excitatory
  • all-or-none contraction

tonic skeletal muscle cell:

  • innervated by a single motor neuron at multiple motor end plates
  • response to stimulus is always excitatory
  • graded contraction
106
Q

What are the 3 main types of skeletal muscle fibres? Describe the differences in their characteristics.

A

slow oxidative fibres (type I)

  • 60-100 ms to peak tension
  • lower myosin-ATPase activity
  • high resistance to fatigue

fast-oxidative fibres (type IIa)

  • 20-40 ms to peak tension
  • higher myosin-ATPase activity
  • intermediate resistance to fatigue

fast-glycolytic fibres (type IIb, IId, or IIx)

  • similar to fast-oxidative fibres in speed and myosin-ATPase activity
  • low resistance to fatigue
107
Q

Where is obliquely striated muscle found?

A

invertebrates

  • helps with organism’s movement
108
Q

Diversity in Muscle Excitation

How is a weak contraction induced?

A

a single stimulus causes an EPSP, which leads to a relatively small increase of cytoplasmic [Ca2+] and a weak contraction

109
Q

Diversity in Muscle Excitation

How is a strong contraction induced?

A

summation of EPSPs – multiple stimuli within a given time period add together, which causes a larger depolarization, which greatly increases cytoplasmic [Ca2+] for a stronger contraction

110
Q

Diversity in Muscle Excitation

How is an inhibitory postsynaptic potential (IPSP) induced?

A

release of neurotransmitter from an inhibitory neuron causes hyperpolarization of the cell membrane

  • muscle cells relax
111
Q

Where can asynchronous flight muscle be found?

A

in most insects with wing beats > 100 Hz

112
Q

How does asynchronous flight muscle work?

A

AP and contraction do not always align – allows for rapid contraction

  • a single Ca2+ pulse maintains muscle in an activated state for successive cycles
  • contraction is triggered by stretch, and deactivated by shortening in the presence of elevated myoplasmic Ca2+
  • relaxation may occur without [Ca2+] decreasing
  • reduction of Ca2+ cycling reduces ATP demand
113
Q

What are mollusc catch muscles?

A

specialized smooth muscles in bivalves

  • often adductor muscles
114
Q

How do mollusc catch muscles work?

A

capable of maintaining force for long period of time (up to several hours) with a very low ATP turnover – catch state

  • due to the presence of protein twitchin, which allows longer interaction between actin and myosin
  • phosphorylation or dephosphorylation of twitchin allows the protein to be attached or dettached

release of serotonin (monoamine neurotransmitter) ends the catch state and allows for relaxation

115
Q

How do heater organs work?

A

NO MUSCLE CONTRACTION

  • depolarization causes release of Ca2+ from SR by conformational changes in DHPR and RyR
  • RyR isoform in these cells is extremely slow to close, which allows for prolonged release of Ca2+
  • SERCA pumps Ca2+ back into SR
  • futile cycling of Ca2+ (Ca2+ used in substrate interactions to generate heat)
  • oxidative phosphorylation (cells are full of mitochondria) and all energy-transforming reaction generate heat
116
Q

How do electric organs (electrocytes) work?

A
  • excitation: electromotor neurons release ACh, which binds to nicotinic ACh receptors, which generates an endplate potential
  • voltage-gated Na+ channels open, which depolarizes the cell membrane on the innervated (posterior) side of the cell to +65 mV, while the cell membrane on the non-innervated (anterior) side of the cell remains at -85 mV
  • an activated electrocyte has a transcellular potential difference of around 150 mV
  • voltage is generated by the difference in voltage in each side of the cell – all ion channels and nerves are on one side of the cell only
117
Q

What is the total cost of transport (COT_tot)?

A

metabolic rate divided by locomotor velocity

118
Q

What is the net cost of transport (COT_net)?

A

the difference between total metabolic rate and resting metabolic rate

119
Q

What is metabolic rate?

A

amount of energy expended per unit time

  • sum of all energy transformation processes
  • rate of ATP turnover
120
Q

What are the 3 types of metabolic rates?

A
  • standard or basal metabolic rate
  • maximal metabolic rate
  • hypometabolic rate (metabolically suppressed)
121
Q

What are the 3 measurements of metabolic rates?

A
  • O2 consumption rate (VO2 or MO2)
  • CO2 production rate (VCO2 or MCO2)
  • heat dissipation
122
Q

What factors affect the metabolic costs of locomotion? (3)

A
  • metabolic costs increase with speed
  • metabolic costs decrease with body mass
  • metabolic costs differ by mode of locomotion (swimmers < fliers < runners)
123
Q

What are the 2 main factors that influence locomotion?

A
  • gravity
  • fluid mechanics
124
Q

What is gravity?

A

the natural phenomenon by which all things with mass or energy (including planets, stars, galaxies, and even light) are attracted towards each other

125
Q

Do larger bodies of mass have weaker or stronger gravitational forces?

A

stronger

126
Q

Does gravity increase or decrease the locomotive cost of movement?

A

increase – to be in locomotion, you have to contend with gravity

(unless you are falling)

127
Q

What type of animals does gravity exert the greatest effect on?

A

terrestrial animals

128
Q

What type of animals are the effects of gravity reduced in?

A

animals with body densities that approximate the density of their environment (ie. aquatic animals)

129
Q

What is buoyancy?

A

an object will float if it is less dense than water (counteracts gravity)

130
Q

What is fluid mechanics?

A

complex pattern of fluid flow created by objects moving through the fluid (both air and water)

131
Q

What are the two ways that animals move through fluid?

A
  • move the fluids out of their direct path to increase efficiency
  • control the movement of fluid to their advantage (pushing them forward, or lifting them upwards)
132
Q

What are the 3 factors that influence fluid mechanics?

A
  • pattern of flow (laminar or turbulent)
  • fluid viscosity
  • object size, shape, and velocity
133
Q

What is laminar flow?

A

(sheet-like flow) fluid travels smoothly and in regular paths

134
Q

What is turbulent flow?

A

fluid travels in different speeds and directions

  • at points it may intersect or counter the overall direction
135
Q

How is the cost associated with locomotion affected by the pattern of flow (laminar or turbulent)?

A

cost greatly increases in response to the transition from laminar to turbulent flow

136
Q

What factors does the transition from laminar to turbulent flow depend on? (3)

A
  • properties of the fluid (viscosity, density)
  • size and shape of the object
  • velocity and direction of movement
137
Q

What is Reynolds number (Re)?

A

allows for a quantitative assessment of how easily an object will move through a fluid

  • helps predict flow regime (determines if flow is laminar, transitional, or turbulent)
138
Q

What is the equation for Reynolds number (Re)?

A

Re = (VLp) / μ

  • V = velocity
  • L = linear dimension of object that is encountering the fluid – turbulence increases as linear dimension increases
  • p = density of fluid
  • μ = viscosity of fluid
139
Q

How does the linear dimension of an object (L) affect Reynolds number (Re)?

A

as the linear dimension encountering the fluid increases, Re increases, therefore turbulence increases

140
Q

What is density?

A

a measure of the space between two particles in a fluid

141
Q

What is density influenced by?

A

changes in temperature and pressure

142
Q

What is viscosity?

A

the internal friction within a fluid

  • generally fixed in any given environment (although viscosity is influenced by temperature)
143
Q

Do fluids with smaller or larger viscosity resist motion? Why?

A

fluids with larger viscosity resist motion because its molecular makeup gives it a lot of internal friction

144
Q

What happens to flow when an object moves through a solution of low viscosity?

A

each layer of laminar flow moves at the same velocity

145
Q

What happens to flow when an object moves through a solution of high viscosity?

A
  • the layer of laminar flow in contact with the object moves more slowly because of interactions with the object (this is called the boundary layer)
  • the impact of the object is reduced further from the object
146
Q

Do smaller or larger animals have a higher Reynolds number?

A

larger animals have higher Re

147
Q

What is drag?

A

force that oppose forward movement

  • object must overcome drag to move through a liquid
148
Q

What are the two types of drag?

A
  • friction drag
  • pressure drag
149
Q

What is friction drag?

A

drag caused by the friction of a fluid against the surface of an object that is moving through it

150
Q

What factors affect friction drag?

A
  • directly proportional to the area of the surface in contact with the fluid
  • increases with velocity
151
Q

What is pressure drag?

A

the force required to redirect a fluid around a moving object

152
Q

What factors affect pressure drag?

A

the denser the fluid, the greater the drag

153
Q

What factors affect both pressure and friction drag?

A

shape of the object

  • ie. between three objects (flat, circle, teardrop) that have the same L, Re, and velocity through fluid, the teardrop has the lowest overall drag, but the largest friction drag because it is the biggest
154
Q

Locomotion on Land

What is the main challenge facing terrestrial locomotion?

A

gravity

155
Q

Locomotion on Land

Describe the relationship between body mass and skeletal mass.

A
  • most birds and mammals use limbs to lift the body off the ground, requiring thicker and more robust bones and musculature to move it
  • there is a direct relationship between body mass and skeletal mass
156
Q

Locomotion on Land

How do some animals (ie. amphibians) reduce the metabolic costs associated with fighting gravity?

A

by being in direct contact with the ground

157
Q

Locomotion on Land

How does gravity affect the costs of movement?

A

when an animal walks or runs, energy is required to counteract the effects of gravity

  • movement of a leg forward drops the animals centre of gravity, and muscular work is required to slow the descent – this increases the costs of transport
  • forward locomotion adds additional costs
  • relationship between forward velocity and metabolic rate tends to be linear for running animals
158
Q

Locomotion on Land

Describe the relationship between size and muscle contraction.

A
  • animals that display good energy economies tend to have long legs
  • smaller animals have less energy efficient muscle fibres
159
Q

Locomotion on Land

What force is generated when a limb makes contact with the ground?

A

muscular contractions are generated as the vertical component of the ground reaction force

160
Q

Locomotion on Land

How might the efficiency of movement differ due to muscle and bone geometry?

A
  • geometry of muscles and bones determines the relationship between the force generated by the muscle and the type of movement that results
  • where the muscle inserts on the bone can affect level dynamics, speed, and force
161
Q

Locomotion on Land

Describe the different running styles (gaits) of horses and its efficiency.

A
  • walking, trotting, and galloping
  • each style of running has an optimal velocity at which the cost of locomotion is minimal
  • animals typically ‘prefer’ to move at velocities where the cost of locomotion is lower
162
Q

Locomotion on Land

How do kangaroos achieve high rates of locomotion with low costs of transport?

A

energetic efficiencies are thought to be due to storage of elastic energy in tendons and ligaments in rear legs and tail

  • ie. metabolic costs of running decrease with increasing hopping speed, but not running
163
Q

Locomotion on Land

Describe how fleas can jump up to 50x their height at incredible speeds.

A
  • they do not have unique muscles to directly power the jump, but instead muscles are used to deform the exoskeleton which stores mechanical energy in a recoil
  • when stored energy is released, it is transferred to its oversized rear legs, which propels it off the ground
164
Q

Locomotion on Land

Describe the energetic efficiency of penguins.

A
  • penguins use 2x more metabolic energy as other terrestrial animals of a similar mass to walk a given distance – thought to be due to side-to-side waddling requiring excessive work
  • high cost of walking in penguins is due to their short legs, which require them to generate muscular force rapidly
  • waddling allows penguins to recover~80% of their mechanical energy during each stride due to a pendulum-like effects
  • efficiency in walking is as much about technique, as it is about the bones and muscle that power it
165
Q

Locomotion Through Air

What are the main challenges facing animals that fly?

A
  • gravity
  • fluid mechanics
166
Q

Locomotion Through Air

What is the common relationship between velocity and metabolic rate in flying animals?

A

U-shaped curve

  • shape of the curve can vary due to morphological features (wing shape, how streamline, etc.)
167
Q

Locomotion Through Air

What is an airfoil (or hydrofoil)?

A

structure with an upper curved surface and a flattened lower surface

168
Q

Locomotion Through Air

What happens to air as an airfoil moves forward?

A
  • as an airfoil moves forward, air collides with the leading edge, increasing air pressure
  • as air slides upwards, it is compressed
  • as air continues its path along the top of the airfoil as it curves downward, it creates a low pressure area
  • along the bottom of the airfoil, it flows relatively smoothly across the foil
169
Q

Locomotion Through Air

How is lift generated by airfoils?

A

the pressure differential across the vertical axis of the foil equates to a force (lift)

  • some force is lost as drag
  • air must flow over the airfoil in order to generate lift
170
Q

Locomotion Through Air

What does lift force counteract and overcome?

A

counteracts the effects of gravity and overcomes body weight

171
Q

Locomotion Through Air

What influences the amount of lift generated by an airfoil? (2)

A
  • shape
  • angle of attack
172
Q

Locomotion Through Air

What is lift?

A

the force that acts as a right angle to the direction of motion through the fluid, pushing air down and behind, in order to overcome body weight and the effects of gravity

173
Q

Locomotion Through Air

How does shape affect the amount of lift generated by an airfoil?

A

the longer the curved surface, the greater the lift

174
Q

Locomotion Through Air

What is the angle of attack?

A

the angle of the airfoil relative to the horizontal

175
Q

Locomotion Through Air

How does the angle of attack affect the amount of lift generated by an airfoil?

A

AoA influences the pattern of fluid flow, and consequently lift

  • the larger the AoA, the greater the lift
176
Q

Locomotion Through Air

What is thrust?

A

propulsive force – the forward force moving an object in the direction of motion

177
Q

Locomotion Through Air

What does thrust counteract?

A

drag

178
Q

Locomotion Through Air

How can thrust be generated? (3)

A
  • taking advantage of gravity – gliding
  • harnessing naturally occurring air currents – soaring
  • movement of the airfoil (flapping) – flapping
179
Q

Locomotion Through Air

Describe how thrust is generated by gliding.

A
  • airfoil structures are simple in nature compared to true flight
  • airfoil is stationary, and thrust is generated by descent toward ground
  • airfoil relies on a large surface area and provides some lift, but it is not sufficient to remain in air indefinitely
180
Q

Locomotion Through Air

Describe how thrust is generated by soaring.

A
  • soaring involves the act of gliding while maintaining altitude
  • lift is generated by harnessing upward air currents
  • in general, soaring is associated with elongate, narrow wing shapes
  • only birds perform soaring flight
181
Q

Locomotion Through Air

Describe how thrust is generated by flapping in birds.

A
  • during a downstroke, wings typically also twist as it moves, which generates a vortex of air at the leading edge and tips of the wing, which provides thrust
  • diversity in wing structure and flapping patterns
182
Q

Locomotion Through Air

Does the type of flight affect the size of different muscles?

A

yes

183
Q

Locomotion Through Air

Describe how thrust is generated by flapping in insects.

A
  • generation of lift and thrust are through similar mechanisms as with birds
  • muscles arranged for flapping are either direct (attached to wing) or indirect (attached to wall of thorax)
184
Q

Locomotion Through Water

Do swimmers have low or high costs of transport?

A

have some of the lowest costs of transport for a given body mass

185
Q

Locomotion Through Water

How do aquatic animals counteract the effects of gravity?

A

modify body composition to increase buoyancy

186
Q

Locomotion Through Water

Describe the relationship between velocity and metabolic rate. How does this relate to costs associated with swimming?

A
  • upward curve on velocity vs. metabolic rate graph, where metabolic rate increases faster with velocity with higher drag
  • costs associated with swimming typically increase exponentially with velocity, primarily due to increases in drag at high velocity
187
Q

Locomotion Through Water

What are swim bladders (gas bladders)?

A

air-filled bladders in fish that aid in buoyancy

188
Q

Locomotion Through Water

What are the two types of swim bladders?

A
  • physoclist swim bladder
  • physostome swim bladder
189
Q

Locomotion Through Water

What is a physoclist swim bladder?

A
  • no direct connection to outside
  • inflated by a gas gland that causes a localized acidosis in blood, which forces O2 off hemoglobin
  • deflated by O2 diffusion into blood at the oval
190
Q

Locomotion Through Water

What is a physostome swim bladder?

A
  • direct connection to outside
  • inflated by gulping air and transferring it to the swim bladder via a direct connection between the gastrointestinal tract and the swim bladder via the pneumatic duct
191
Q

Locomotion Through Water

Other than swim bladders, how else do some organisms modify buoyancy?

A

by regulating and accumulating the amount of positively buoyant metabolites (ie. fats)

192
Q

Locomotion Through Water

During swimming, how does the manipulation of water flow occur? (2)

A
  • passively, by possessing streamlined body shapes and surface textures which alter flow conditions along the body to reduce drag
  • actively, by using fins and paddles which regulate water movements that are shed into the wake as vortices
193
Q

Locomotion Through Water

What is vorticity? What does it do?

A

tendency of a fluid to spin or rotate

  • vortices and other fluid movements provide the force to propel the animal forward
194
Q

Locomotion Through Water

How do vortices form?

A

vortices of fluid movement are a consequence of the transfer of force from the fin to the environment

  • as the fish moves through the water, the flapping caudal fin leaves a series of interlinked vortices in its wake
  • these fluid movements ultimately provide the force that propels the fish forward
195
Q

Locomotion Through Water

What do hydrofoils generate?

A

lift-based thrust

196
Q

Locomotion Through Water

What are the two types of caudal/tail fins?

A
  • homocercal fins
  • heterocercal fins
197
Q

Locomotion Through Water

What are homocercal fins? Which organisms have them?

A

symmetrical tail fins extending beyond the end of the vertebral column

ie. most bony fishes

198
Q

Locomotion Through Water

What are heterocercal fins? Which organisms have them?

A

tail fins with unequal lobes in which the vertebral column turns upward into the larger lobe

  • ie. sharks
199
Q

Locomotion Through Water

What type of force do homocercal fins produce?

A

produce a horizontal force component (thrust) without a vertical force component (lift)

  • energy is therefore conserved by producing force only in the direction of motion
200
Q

Locomotion Through Water

What type of force do heterocercal fins produce?

A

with each stroke, the large dorsal portion produces a net force to push the tail forward and up

  • this force posterior to the centre of gravity causes torque that pushes the anterior downward
201
Q

Locomotion Through Water

What does the caudal fin shape correspond to?

A

the cruising speed of the fish

202
Q

Locomotion Through Water

How is fish musculature organized?

A
  • muscles are layered and form a W-like pattern along the length of the animal
  • separation of white and red muscle
  • many fish species have ‘pink’ muscle fibres in between white and red muscle
203
Q

Myosin V has a duty cycle of 0.5, while the myosin in the thick filaments of striated muscle has a duty cycle of 0.05. Myosin v has a unitary displacement of 36 nm, while the myosin in the thick filaments of striated muscle has a unitary displacement of 5-15 nm. Why are the duty cycle and the unitary displacement so different for these two types of myosin

A

unitary displacement:

  • myosin V typically transports vesicles throughout the cell by ‘walking’ along a
    microfilament
  • microfilaments are helical in structure, with a period of 36nm
  • with a unitary displacement of 36nm, with each ‘step,’ myosin V reaches the next binding site on the same side of the
    microfilament – this allows it to continue walking along the same side of the microfilament
  • if its unitary displacement were shorter than 36nm, it would need to attach to a binding site on a different side of the
    microfilament, such that it would work its way around and around the microfilament as though it were walking down a spiral staircase
  • if myosin V were transporting cargo, this helical path would make it much more likely to get stuck on other elements of the cytoskeleton within the cell
  • however, in striated muscle, the thick filaments are surrounded by thin filaments, such that any given myosin head on a thick
    filament can easily reach the actin of a thin filament
  • myosin of thick filaments do not ‘walk’ along the thin filaments, but simply need to attach to the closest available binding site, generate a rapid power stroke, and then detach
  • the thin filament will move relative to any given myosin head as the other myosin
    heads pull it, such that if any given myosin head is not able to attach to a binding site at one particular moment, a binding site will soon be available again as the thin filament continues to be pulled along
204
Q

What are single-unit smooth muscle?

A

fibres are self-excitable and contract as a single unit

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