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Biology 102 > Lecture 9 - Motor Systems and Respiration > Flashcards

Lecture 9 - Motor Systems and Respiration Flashcards

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1
Q

Motor System Overview

A
  • Sarcomere contains actin and myosin filaments and is shortened in muscle contraction
  • Acetylcholine depolarizes muscle cell membrane and releases calcium from intracellular stores
  • Calcium allows myosin to bind to actin
  • Myosin: binds actin –> conformation change –> ATP binding –> actin releases –> ATP hydrolysis
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2
Q

Respiratory system Overview

A

Efficient Gas Exchange

  • increase surface area - alveoli of lungs
  • ventilation and perfusion (inhalation and exhalation)
  • Hemoglobin as a carrier molecule to deliver oxygen to tissues
  • cooperativity - rapid loading in lungs and unloading in tissues
  • delivered preferentially to tissues that need it most
  • CO2 transport: mpves through blood as HCO3
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3
Q

Muscles (3 types)

A

Skeletal

Cardiac

smooth

  • all three relay on sliding of actin and myosin
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4
Q

Skeletal muscle

A
  • voluntary movements
  • movement of bones
  • some involuntary movements - facial expressions, shivering, breathing
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5
Q

Cardiac Muscle

A
  • involuntary

- beating of heart and pumping of blood

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6
Q

Smooth muscle

A
  • involuntary

- lines inner organs such as gut, bladder, blood vessels

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7
Q

Muscle composition

A
  • made up of hundreds of muscle fibers
  • 1 fiber = 1 cell
  • many myofibrils within 1 cell
  • myofibril = hihgly ordered assembly of actin and myosin filaments
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8
Q

Sarcomeres

A

Repeating units of myofibrils

  • as the muscles contract they shorten
  • organized pattern appears striated

Overlapping units of actin and myosin

  • actin - cytoskeletal proteins found along the two sides of the sarcomere, anchored to the z-line
  • myosin - motor proteins found in the middle
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9
Q

Myosin

A
  • motor protein
  • globular head with long tail
  • myosin filament is made up of several hundred myosin molecules arranged in opposite directions
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10
Q

Actin

A
  • long thin cytoskeletal filaments
  • tryptomyosin - protein that wraps around the actin filaments
  • troponin - protein attahced to tropomyosin at regular intervals
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11
Q

How actin and myosin work together

A
  • Myosin walks along actin to shorten the sarcomere
  • length of actual actin and myosin filaments do not change, just their orientation/amount of overlap
  1. myosin head binds specific site on actin
  2. myosin walks along actin towards the z-line
  3. rapid synchronized shortening of thousands of sarcomeres lying end to end allows muscles to contract quickly
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12
Q

What signals muscles to contract?

A

*acetylcholine/neurotransmitter

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13
Q

Process of Signal for muscles to contract

A
  1. motor neuron releases acetylcholine/neurotransmitter
  2. binds to receptor on muscle fibers
  3. opens ion channels (mostly Na+)
  4. depolarization spreads across membrane
  5. calcium released from internal reserve (sarcoplasmic reticulum)
  6. Ca++ causes the contraction of the muscle fibers
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14
Q

Myasthenia Gravis

A

Disorder where body produces antibodies against acetylcholine receptors

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15
Q

Where is the calcium reserve stored?

A
  • internal reserve

- sarcoplasmic reticulum

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16
Q

Role of calcium in contraction

A
  • allows myosin to bind to actin
  • at rest, TROPOMYOSIN wraps around actin with TROPONIN bound at regular intervals
  • tropomyosin blocks myosin binding sites on actin
  • Ca++ binds to troponin
  • causes troponin to change conformation
  • twists tropomyosin to expose myosin binding sites on actin
  • myosin can then bind/grip the actin
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17
Q

tropomyosin

A

protein molecule that blocks myosin binding sites on actin

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18
Q

Myosin walks along actin:

Stage I

A
  1. myosin binds to ATP
  2. at rest, myosin is not bound to actin - can hydrolyze the bound ATP to ADP + Pi
    - Pi not released, stays associated
  3. Calcium causes troponin and tropomyosin to change their conformation - myosin can now bind to actin
    - myosin has ADP + Pi bound
  4. myosin binds to actin, myosin kicks out the Pi
  5. release of Pi changes the conformation of the myosin head, bending it and cause”power stroke”
    - actin moves relative to myosin
    - ADP is kicked out during power stroke
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19
Q

Myosin walks along actin:

Stage II

A
  1. ADP bound to myosin was kicked out in power stroke
  2. NEW molecule of ATP can bind to myosin in open binding site
  3. Binding ATP causes myosin to release from actin
  4. myosin hydrolyzes ATP to ADP +Pi
    - causes myosin head to return to an extended, relaxed conformation
  5. Myosin is now able to bind to actin once again
    - so long as Ca++ is still around and the myosin binding sites on actin are still revealed

*multiple cycles of binding and release cause myosin to walk along/down actin

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20
Q

Fast twitch vs slow twitch

A
  • how rapidly the atp can be hydrolyzed determines how fast a muscle can recycle their actin-myosin associations
  • different types of muscle fibers have myosin with different rates of ATPase activity
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21
Q

Slow twitch fibers

A
  • slower ATPase activity
  • develop tension more slowly but can maintain it for longer
  • can maintain steady, prolonged production of ATP (so that it can be hydrolyzed) to replenish the cycle of binding and release
  • long distance, aerobic workouts
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22
Q

Fast Twitch fibers

A
  • higher ATPase activity
  • develop maximum tension more rapidly
  • fatigue rapidly
  • ATP is put to work quickly, but fibers cannot replenish ATP as fast as they are using it
  • short term work that requires maximum strength (ex: sprinting, weight lifting)
23
Q

Ca++ and muscle contraction

A
  1. at rest: troponin blocks interaction of actin and myosin
  2. Ca++ binds to troponin, causing it to shift and revealing myosin binding site
  3. myosin head binds actin and bends, causing filaments to slide
  4. ATP allows the heads to unbind, and unbend, ready to repeat
    * as long as there is still Ca++ and ATP around
24
Q

Goals of respiration

A
  • Need to supply cells with O2 (so that they can produce APT by cellular respiration)
  • Need to remove CO2
  • no active transport mechanism to move respiratory gasses across biological membranes
  • must cross by diffusion
25
Q

Specialized Systems if Gas Exchange

Limitation

A
  • needed to deliver O2 close to target tissues
  • rely of diffusion for uptake - cells can never be more than a few mm away from good source of O2
  • invertebrates without specialized internal systems for delivering O2 (size and shape constraints to maximize external surface area)
  • for species with larger, more complex bodies:
  • specialized respiratory systems
  • large surface areas for gas exchange - gills, lungs
  • efficient oxygen delivery (use circulatory system, hemoglobin)
26
Q

Strategies to maximize gas exchange in complex organisms

A
  • increase surface area
  • decrease length of path across which molecules must diffuse
  • ventilation and perfusion
  • efficient transport of oxygen
27
Q

Increased Surface Area

A

Gills
- highly branched and folded extensions of the body surface

Lungs

  • highly branched and divided
  • elastic - can be inflated with air and deflated
28
Q

Path to lungs

A
  • air enters through nose and mouth, cavities join to form pharynx
  • pharynx splits to form:

esophagus: food to stomach
trachea: air to lungs

Larynx: voice box, at beginning of trachea

29
Q

Lungs (parts)

A

Bronchi

Bronchioles

Alveoli

30
Q

Bronchi

A

Trachea branches into 2 bronchi

  • one leads to each lung
  • bronchi branch repeatedly
31
Q

Bronchioles

A
  • after 4 branchings of bronchi they lose their cartilage support and become bronchioles
32
Q

Alveoli

A
  • after many more branchings, bronchioles are less than 1 mm in diameter, alveoili appear
  • tiny, thin walled air sacs
  • surrounded by networks of capillaries
  • sites of gas exchange
  • branchings of the airway occur that lead to clusters of alveoli
  • human lungs have ~ 300 million alveoli - combines surface area of 70 meters squared
33
Q

Alveoli and emphysema

A
  • inflammatory damage to lungs leads to breakdown of walls that divide the alveoli
  • fewer but larger alveoli
  • decrease surface area for gas exchange
  • air sacs unable to hold structural shape upon exhalation
  • collapse and trap air in lungs
34
Q

Diffusion distance of O2 from alveoli to blood

A
  • each alveolus is made of very thin cells
  • walls of capillaries surrounding the alveoli are also made up of very thin cells
  • where capillary meets alveolus, very little tissue separates the two spaces
  • diffusion path is less than 2 micro meters
  • O2 easily diffuses from lungs into blood, where it can be picked up by hemoglobin for transport
35
Q

Ventilation and Perfusion

A

Maximizes gas exchange by keeping concentration gradients high

Ventilation

  • actively moving the external medium over the gas exchange surfaces
  • regularly exposes suface to fresh air containing maximum O2
  • ex: breathing

Perfusion

  • actively moving the internal medium over the internal side of the gas exchange surfaces
  • transports O2 away from the surface, maximizing the concentration gradient
  • transports CO2 to the surface
    ex: blood flow
36
Q

Ventilation: inhalation and exhalation

A
  • lungs are contained within the thoracic cavity
  • closed compartment bounded on bottom by a sheet of muscle called the diaphragm
  • outside of lung is stuck to wall of thoracic cavity
  • inhalation and exhalation involve changes in the volume of the thoracic cavity
  • causes lungs to expand or contract and air to rush in or out
37
Q

Inhalation

A
  • contraction of diaphragm
  • pulls down
  • expands thoracic cavity and pulls down on lungs
  • air rushes in through trachea from outside
  • lungs expand as they are filled with air
  • active process
38
Q

Exhalation

A
  • diaphragm relaxes and is recoiled upwards
  • diaphragm being pulled up pushes air out through the airways
  • passive process
39
Q

How is oxygen effectively delivered from lungs to other tissues?

A
  • oxygen is non polar and thus not very soluble in blood
  • need carrier molecules that reversibly bind oxygen to transport it through blood
    (pick up O2 where O2 concentration is high, release O2 wehre O2 concentration is low)
  • carrier = hemoglobin (protein found in high concentrations in red blood cells)
40
Q

Problem of oxygen transport

A

Need mechanism for oxygen to be:

  1. efficiently picked up from the lungs
  2. transported by the blood without any oxygen being “lost” along the way (released in arteries during transport)
  3. delivered specifically to tissues that need oxygen
41
Q

Requirements for Effective Transport of Oxygen

A
  • Need a molecule that can transition from a high-affinity to a low affinity state
  • -> high affinity in lungs: O2 pickup
  • -> low affinity in tissues: O2 drop off
  • linear affinity would release too much O2 along the way before it reaches target tissue
  • S shaped (sigmoidal curve) provides a distinct “switch”
  • hemoglobin can switch between high and low affinity states using the principles of cooperativity
42
Q

Hemoglobin Cooperativity

A
  • hemoglobin has 4 subunits - each of which can bind to a molecule of oxygen
  • the 4 subunits load and unload oxygen in sync
43
Q

Loading of hemoglobin

A
  • with no oxygen bound, hemoglobin does not have a very high affinity for O2
  • in lungs, very high concentration of 02 allows a molecule of O2 to bind to one of the four open sites on the hemoglobin
  • when one molecule of oxygen binds, it greatly increases the affinity of the other 3 subunits for oxygen

*rapidly pick up 4 O2 molecules in high concentration areas

44
Q

Unloading of hemoglobin

A
  • in tissues, very low )2 concentration promotes dissociation of a molecule of O2 from hemoglobin
  • when one molecule of oxygen dissociates, decreases the affinity of the other 3 subunits for oxygen
  • rapid unloading in low oxygen areas
  • oxygen not “dropped off” randomly in blood stream (mid-transport) - only at desired destination
  • more metabolically active a particular tissue is, the lower its O2 concentration, and the more likely hemoglobin is to unload
45
Q

Key of hemoglobin

A
  • oxygen is picked up efficiently in the oxygen-rich lungs and then delivered to tissues precisely where and when it is needed most
46
Q

Bohr shift

A
  • the dissociation of oxygen from hemoglobin is also influenced by blood pH
  • more acidic pH decreases affinity for O2, promoting dissociation
  • metabolically active tissue produces acidic metabolites from Co2, which lower blood pH
  • dissociation curve of hemoglobin shifts to the right
  • hemoglobin will release more oxygen in active tissues
  • hyperventilation = not enough C02
47
Q

How CO2 is transported…

A

As bicarbonate ions (HCO3-)

  • CO2 diffuses out of tissues and into blood
  • in presence of CO2, red blood cells convert CO2 to bicarboate (HCO3-) for transport
  • -> enzyme carbonic anhydrase
  • HCO3- now leaves the red blood cells and enters blood plasma, where it travels through bloodstream through lungs
48
Q

Promotion of CO2 uptake in the blood

A
  • conversion of CO2 to HCO3- reduces the concentration of CO2 in the blood
  • therefore, CO2 continues to diffuse into blood from tissues down its concentration gradient
  • HCO3- cannot diffuse out of blood (ideal for transport)
49
Q

How CO2 exits blood stream

A
  • in lungs, ventilation keeps CO2 levels in alveoli very low
  • once blood levels of CO2 are very low, it favors the conversion of HCO3- back to CO2 (reverse reaction)
  • one CO3- is converted back to CO2, the CO2 immediately diffuses down the concentration gradient and out into the lungs
50
Q

Regulation of breathing

A
  • firing of neurons in medulla (middle for brainstem) normally generate the rhythmic patterns
  • CO2 levels are the main feedback indicator to regulate breathing rate
  • receptors in medulla recognize increased CO2 levels and change breathing pattern accordingly
  • -> in reality, detecting more acidic pH
51
Q

How is CO2 removed from the tissues?

A
  • moves through blood in the form of HCO3-
  1. CO2 diffuses out of tissue into the blood
  2. in presence of CO2 red blood cells convert CO2 to HCO3- for transport
    - Carbonic anhydrase in the enzyme
  3. HCO3- nowl eaves the red blood cells and enters plasma where it travels through blood stream to lungs
52
Q

Promotion of uptake of CO2

A

conversion to bicarbonate reduces the concentration of CO2 in the blood

  • CO2 continues to diffuse down its gradient from tissues into blood stream
  • HCO3- cannot diffuse out of the blood
53
Q

How CO2 exits the bloodstream

A
  • int he lungs
  • ventilation keeps the CO2 levels in the alveoli very low
  • since blood levels of CO2 are very low, it favors the conversion of HCO3- back to CO2 (reverse reaction)
  • Once HCO3- is converted back to CO2, the CO2 immediately diffuses down the concentration gradient and out into the lungs
54
Q

How is breathing regulated?

A
  • firing of neurons in the medulla (middle of brainstem)
  • CO2 levels are main feedback indicator
  • receptors in medulla recognize increased CO2 levels and change breathing pattern accordingly

Biology 102 (15 decks)

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