Comparative Animal Phys Exam 3

Starting at lecture 15 (Muscular Physiology)

what is muscle?

tissue that consists of contractile cells

Do muscles (like nerves) preserve well in the fossil record?

No

What are hypotheses about the evolution of muscle based on?

• based on characteristics of extant animals

• debate about how major clades are related have complicated this, but most studies over the past 10 years suggest, like neurons, muscles either have 2 independent evolutionary origins or have been lost twice

in muscle cells, what are forces of contraction the result of ?

interactions b/w contractile proteins, myosin & actin

Describe striated muscle fibers.

They have bands of myosin & actin organized into repeating units called sarcomeres

Describe striated muscle fibers in arthropods

muscle attached to the exoskeleton, associated w/ the heart & along the digestive tract are striated.

Describe striated muscle fibers in vertebrates

skeletal muscle: striated muscle attached to the bone

cardiac muscle: striated muscle of the heart

Why is smooth muscle (un-striated) different than striated muscle fibers?

these muscle fibers have myosin & actin, but they aren’t arranged into sarcomeres

Where are smooth muscle fibers found in vertebrates?

in tubular organs (digestive tract, uterus, etc.)

what is skeletal muscle composed of?

long cylindrical muscle fibers

why do say “fibers” and “cells” in reference to muscle tissue?

because they develop from the fusion of multiple cells called “myoblasts”

Describe vertebrate skeletal muscle fibers.

• contain many nuclei

• can be as long as a foot (0.3m)

• are composed of hundreds of parallel myofibrils that run the length of the muscle fiber

what 2 types of filaments (polarized protein polymers) compose myofibrils?

thick and thin filaments

Describe thin filaments

high in actin & anchored to Z discs

Describe thick filaments

high in myosin & anchored to M lines

what are “Z” discs

dense areas that line-up across myofibrils within the same fiber, giving striated appearance to skeletal muscle

what is a sarcomere?

portion of the myofibril b/w two Z discs

What is a sarcolemma?

membrane around the skeletal muscle fiber

what is a sarcoplasmic reticulum?

branching tubules that surround all the myofibrils; membranes contain Ca2+, ATPase active transport pumps that keep [Ca2+] inside the SR > [Ca2+] in the cytoplasm

what is a transverse (T) tubule?

runs transversely across myofibrils in an invagination, closely associated w/ the sarcoplasmic reticulum (SR).

what is the sliding filament theory of muscle contraction?

thick (myosin) & thin (actin) filaments within muscle fibers pull past one another during muscle contraction & expansion

For vertebrates, what is each muscle fiber innervated by in regards to vertebrate neuromuscular junction?

innervated by only one motor neuron

What do deep junctional folds on the muscular surface of the synapse contain in regards to vertebrate neuromuscular junction?

• ACh (acetylcholine) receptors at the top

• voltage-gated Na+ channels only at the bottom

Describe what happens during a vertebrate muscle contraction. ( 9 step process)

1. action potential in motor neuron stimulates the release of acetylcholine (ACh) into the neuromuscular synapse

2. ACh binds to ligand-gated Na+ channels in the sarcolemma

3. Action potential travels down into the t-tubule

4. when the action potential reaches DHPRs in the t-tubules, it triggers the release of Ca2+

5. on the thin filaments, Ca2+ molecules bind to troponin, allowing cross bridges to form b/w the thick & thin filaments, pulling the thin filaments in the opp. direction as the thick filaments

6. each cross bridge goes through several cycles (costing 1 ATP each) during one contraction, if Ca2+ is present ( that moves the thin filament about 10 nm/ ATP molecule

7. synaptic ACh is broken down, terminating the action potential

8. DHPR returns to previous state & Ca2+ is pumped back into the SR

9. this ends the contractioin

skeletal muscles have intramuscular connective tissues. what are they composed of?

collagen

what are the 2 main functions of intramuscular connective tissue in skeletal muscles?

• structural organization

• transmit contraction force to the skeletal system

what do intramuscular connective tissues weave themselves into?

tendons, which connect muscles to skeletal elements

what is the only type of force that skeletal muscle can exert ?

pulling force, they can’t lengthen under their own power

How do skeletal muscles function?

often function in antagonistic pairs that, (for vertebrates) pull on opp. sides of skeletal joints. when one muscle shortens, its antagonist partner lengthens & vice versa. this ensures that muscles can be re-lengthened after being contracted.

How are arthropod muscles similar but different in this way? (refer to the card above)

they function same as vertebrates except that they deform the jointed exoskeleton by pulling from the inside

Do contracting muscles always shorten?

No

What is isometric contraction?

cross bridge cycling occurs, but the whole muscle stays the same length as it contracts

What is the purpose of isometric contraction?

• help animals maintain steady postures as they stand still

• Muscles actively spend energy, even though they are not shortening (ex. muscles keeping your head up right now)

what are concentric contractions?

whole muscle shortens as it contracts

what are eccentric contractions?

whole muscle resists lengthening as it contracts

what is a twitch ?

the mechanical response of a muscle to a single action potential

how much force is transmitted to the skeletal structure from a single twitch?

very little force

What is the time duration diff between action potentials & twitches ?

action potentials take 2ms, but twitches are >100 ms in duration

what is a summation?

the fusion of multiple twitches into a single larger contractile force

what is a tetanic contraction (tetanus)?

a strong, sustained muscle contraction that occurs as a result of summation

what is the max force a vertebrate skeletal muscle can produce determined by?

the cross-sectional area

• the forced produced by neighboring myofibrils in a muscle sum together

what are slow oxidative (SO) fibers ?

small cross-sectional areas, with many mitochondria, many capillaries

(specialize in aerobic respiration)

what are fast glycolytic (FG) fibers?

large cross-sectional areas, few mitochondria, few capillaries

(specialize on anaerobic respiration)

what are fast oxidative glycolytic (FOG) fibers?

intermediate diameter, many mitochondria, many capillaries

Are most muscles made of a single type of fibers or a mixture?

a mixture

How did fish exploit modified skeletal muscles to generate electric shocks?

BY:

• electric organs (electrocytes) are used to stun prey

• causes release of ACh into muscular endplates of prey, causing hidden fishh to twitch & reveal their location OR immobilizing their prey

• electric organs have evolved independently at least 5 times

what is a motor unit?

a motor neuron and all the muscle fibers it innervates

describe neural control of vertebrate skeletal muscle

• Each muscle fiber is innervated by 100s – 1000s of motor neuron dendrites

• Each muscle fiber is innervated by 1 motor neuron

• Motor units are distinct

• Muscle fibers are only innervated by excitatory motor neurons

• Excitatory neurotransmitter is ACh

describe neural control of arthropods skeletal muscle.

• Each muscle innervated by 1 – 10 motor neuron dendrites

• Each muscle fiber is innervated by many motor neurons

• Motor units overlap

• Each muscle fiber can be innervated by both excitatory and inhibitory motor neurons, allowing for peripheral inhibition

• Excitatory neurotransmitter is glutamate & inhibitory neurotransmitter is GABA (gamma-aminobutyric acid)

If arthropods don’t have SO & FG muscle fiber types, then what do they have?

short sarcomere vs. long sarcomere fibers

• short sarcomere muscle fibers contract quickly and long sarcomere fibers contract slowly

Most arthropod muscles contain a mix of long & short-sarcomere fibers, with some exceptions. What are the exceptions?

• Flight muscles in Drosophilla are long sarcomere biased

• Muscles in the tails of crawfish are loaded with short sarcomere fibers to allow for sudden & rapid escape

what are examples in vertebrates that consist of smooth (un-striated) muscle? also describe vertebrate smooth muscle.

• Gastrointestinal, respiratory, reproductive, urinary, and cardiovascular systems, iris of the eye, base of hairs & feathers (vertebrates)

• Single nucleus, no transverse tubules

• Contain actin and myosin, not in sarcomeres

• > thin/thick filaments (actin /myosin)

• Thin actin filaments attach to dense bodies in the cytoplasm (not Z plates)

• Filaments in bundles around the cell’s periphery

• Shorter than most skeletal muscles

• Innervated by the autonomic nervous system

• Smooth muscle hydrolyzes ATP more slowly

• Can contract slowly, for longer periods of time

• Smooth muscle of the esophagus remains contracted except in the presence of food

describe single unit smooth muscle.

• Muscle cells are connected (electrically coupled) by gap junctions

• Depolarize and contract together, functioning as a single unit

• Less direct neural control (less innervation from ANS)

• Can be activated by stretch

• Ex: gastrointestinal tract, small blood vessels

describe multi-unit smooth muscle

• Few, if any, gap junctions

• Function more independently from each other

• More direct neural control (more innervation from ANS)

• Not stretch-sensitive

• Ex: hair & feather erectors, eyes, large arteries, respiratory airways

What types of muscle do mammalian uteruses switch between ,when, and what does this allow?

• between single & multi-unit smooth muscle

• only during late stages of pregnancy when estrogen is highest, the uterine smooth muscle cells form gap junctions that couple adjacent cells

• this allows the uterus to produce coordinated contractions that respond well to local stretch cues

describe vertebrate cardiac muscle

• myofibrils are organized into sarcomeres (striated)

• cells are branched, not straight

• each cell has a single nucleus

what is the purpose of intercalated discs in vertebrate cardiac muscle?

• Intercalated discs:

  • gap junction rich

  • allows force of contraction to be transferred across cells

  • ensures that cells beat nearly synchronously

what is vertebrate cardiac muscle controlled by ?

• controlled by autonomic nervous system

• local pacemaker cells generate coordinated muscular rhythm

• action potential of cardiac cells is relatively long (100-500ms)

• ensure a prolonged contraction suitable for pumping blood, rather than a short muscular twitch

Why is it so important that animal cells receive O2 and get rid of CO2?

they are the primary gases that are consumed and produced by aerobic catabolism (aka cellular respiration)

ex: the equation for glucose metabolism. C6H12O6 + 6O2 > 6CO2 + 6H2O + ATP

This is why O2 & CO2 are known as the respiratory gasses.

why is the need for O2 so much more urgent than for any other material animals exchange with the environment?

• the ETC & OXPhos generate the most ATP per molecule of glucose ingested

• O2 plays an especially important role as the final electron receptor in the ETC

• not all cells can perform anaerobic respiration (ex: human neural tissue). Those that can must get rid of lactic acid

what can not voiding enough CO2 lead to?

• acidification of body fluids & other ill effects, but there are ways the body can deal with this, with a little extra energy expenditure

describe the type of transport carries O2 & CO2 across membranes?

• transport of them both is usually passive ( always passive for O2)

• small molecules like these can move by diffusion across membranes

• animals have adaptations that enable this passive transport across barriers throughout the body

By what two mechanisms do respiratory gases move from place to place?

• simple diffusion

• convective transport (bulk flow)

describe simple diffusion

same mechanisms as solutes diffusing through solutions. Has 2 important roles:

1. solutes diffuse from areas of high “concentration” to areas of low “concentration”

2. rate of diffusion is proportional to the difference in concentration

describe convective transport (bulk flow)

gases are moved from place to place due to the flow of a fluid into which they are dissolved (ex: in blood as it flows through vessels)

What are partial pressure gradients?

• a more direct measure of chemical potential to discuss diffusion from one aqueous environment to another

• note partial pressure as P with a subscript of the gas name

describe gas mixtures in regards to partial pressure.

• partial pressure of each gas in a mixture is independent of the other gasses in the mixture

• Dalton’s Law: Pt = Pa + Pb + Pc

How can gases such as O2 exist in aqueous solution?

they can exist in aqueous solution not as bubbles but as molecules interspersed among molecules of water, aka “dissolved” gases

what is the partial pressure of a gas dissolved in an aqueous solution equal to ?

the partial pressure of the same gas in a gas phase at equilibrium

Partial pressure and concentration in aqueous environments are proportioinal, what about the absorption coefficient?

absorption coefficient varies greatly & depends on temp & salinity.

• cold water can “hold”/absorb more dissolved O2 than warm water

• fresh water “holds”/absorbs more dissolved CO2 than salt water

What is one of the first places you see inward diffusion occur?

at the interface b/w the organism’s respiratory surface & the fluid environment

what are the 2 rules for the diffusion of gases?

1. diffuse down partial pressure gradients

2. difference in partial pressure drives diffusion rate

Where does O2 diffuse passively down and where does it not?

diffuses passively down its partial pressure gradient but not necessarily down the concentration gradient

How is bulk flow different than the simple diffusion?

• far faster than diffusion

• more effective for long distance transport

• costs metabolic energy

what are 2 major types of bulk flow in animal bodies?

• breathing (moving gas mixtures around)

• pumping of body fluids (ex: blood flow)

what are the 2 important geometries of bulk flow?

• unidirectional flow

• tidal flow ( bidirectional flow)

what is unidirectional flow?

• occurs through a tube

• ex: flow of blood through a blood vessel

what is tidal flow?

• back and forth flow; occurs in cavities with a single opening for entrance & exit

• ex: flow of air in mammalian lungs

what kinds of animals do/don’t use bulk flow?

• some very small animals don’t require bulk flow

• most animals use an alternating combo of bulk flow & difffusion to transport respiratory gasses to cells throughout their bodies

what is the oxygen cascade?

• the transfer of oxygen from the environment to the mitochondria can be thought of as an oxygen cascade, where potential energy is incrementally lost

• this is like a cascade losing potential energy in the for of height over its length

why does water breathing come at higher metabolic cost than air breathing?

1. water is denser and more viscous than air, so water breathers must expend more energy to move water through their bodies via bulk flow than air-breathers spend to move air via bulk flow

2. O2 is also less soluble in water compared to air, so air can “hold” more molecules of at any given temperature

what is respiration?

exchange of respiratory gasses (O2 & CO2)

• can be internal (moving them around in the body) or external

what is external respiration?

• aka “breathing”; the process by which an animal gains O2 from its environment & voids CO2 into its environment (exchange b/w outer fluid & respiratory exchange membrane)

what is dual breather/bimodal breather?

can breathe both air & water

what is a respiratory exchange (or gas-exchange) membrane ?

1 to 2 layers of epithelial cells that are where external respiration occurs

what is ventilation?

forced flow (convection) of air or water into & out of structures/ surfaces used for external respiration

• not all animals ventilate

how does external respiration work?

• O2 always via diffusion

• CO2 usually via diffusion, but transported actively (as HCO2) in some freshwater animals

• in some animals the whole body surface is a gas exchange membrane

what are 2 types of specialized breathing structures?

• lungs & gills

what are lungs?

• evaginated into the body & contain environmental medium

what are gills?

evaginated into the environment & surrounded by environmental medium

what are external gills?

not in a superficial body cavity

what are internal gills?

in a superficial body cavity

• requires ventilation (costs ATP)

• enables better canalization

what is ventilation

the forced flow (convection) of air or water into & out of structures/surfaces used for external respiration

what is passive ventilation

current is environmental

• doesn’t cost metabolic energy (ATP)

• current is less reliable

what is active ventilation

animal creates the current

• costs metabolic energy (ATP)

• current is more reliable

what are the 3 types of active ventilation?

• nondirectional

• bidirectional

• unidirectional

describe nondirectional active ventilation

fluid flows across the gas-exchange membrane in many directions

describe bidirectional active ventilation

fluid flows to & from the gas exchange membrane via the same passages

• aka tidal gas exchange

describe unidirectional active ventilation

fluid is pumped over the gas exchange membrane in a one way path

what are the 3 types unidirectional active ventilation?

• Co-current gas exchange (aka concurrent gas exchange)

• countercurrent gas exchange - most fish have this

• cross current gas exchange- birds have this