Bio 2, Unit 4

what is the longest human axon?

Longest human axon is the sciatic nerve, 1.3 m(Sciatic pain) 

Describe the end of the axon.

At the terminal end of an axon often branched, are synaptic terminals, where the signal is conveyed to the receiving cell(or cells), typically by the release of chemical or neurotransmitters 

What makes vertebrate axons different from invertebrates?

In vertebrates, neurons are surrounded by glia, or glial cells, with a variety of functions, including maintaining osmotic gradients, physical protection/structure, and facilitating signal transduction, and the glue that holds neurons in place

What does the nerve resting potential result from?

• Resting potential results from an unequal distribution of ions between the outside and inside of a nerve cell (across a cell membrane)(ionic imbalance)

  • results in a nerve cell being negatively charged relative to its external fluid medium

  • More negative inside/more positive outside

what is membrane potential?l

The charge difference, measured as voltage, is the membrane potential

Nat-K+ pumps?

 For every 3 Nat pumped out of the cell, 2 K+ pumped in; ATP-dependent; generates only a few mV potential - 70% of nerve cell energy is used up by this! THIS IS HAPPENING ALL THE TIME

Sodium potassium pumps? where and what they pump

• There are sodium potassium pumps embedded in the membrane 

• They pump sodium out of the cell and potassium into the cell, against their concentration gradients 

• It needs ATP to do this

What happens if there are open or leak channels?

K+ leave cell, Nat enter cell

are there more Nat leak channels or K+? and what is the greater effect? more + or - charge then we are gaining or losing

Far fewer leak Nat channels than leak K+ channels

More potassium leak channels, we lose more positive charge then we are gaining 

why would sodium leak into the cell?

sodium leaks into the cell ebcause it is higher on the outside, they go down their concentration gradient

why would potassium leak out of the cell?

it is higher outside, they go down their concentration gradient

what happens when Na+ gated ion chennels open?

cause flux of Na+ into cell

what happens when K+ gated ion channels open? down or up?

Cause a flux of K+ out of the cell, it falls down its concentration gradient

are gated ion channels involved in the maintenance of the resting membrane potential?

NO

Suppose resting potential is -70 mV and a stimulus causes gated Na⁺ channels to open so that Na⁺ diffuses into the cell(sodium goes into the cell) 

What happens to the membrane potential? 

Gets more positive:  say -60 mV - depolarization

Suppose resting potential is -70 mV and a stimulus causes gated K⁺ channels to open so that K⁺ diffuses out of cell – 

What happens to the membrane potential?

Gets more negative:  say -80 mV - hyperpolarization

When you open the sodium-gated ion potential, you become…

more positive, DEPOLARIZATION

When you open the potassium-gated ion channels..

it goes out, you get more negative, HYPERPOLIZATION

what are graded potentials

Small excursions of membrane potential

What are action potentials?

The transmission of nervous impulses along axons, results from the activity of voltage-gated ion channels

what happens when depolarization reaches a threshold, generally about  55 mV for mammalian neurons…

 voltage-gated Na⁺ channels  open – the resulting influx of Na⁺ into the cell causes further depolarization, ALL NO NONE RESPONSE

What does “positive feedback mean in terms of action potentials?

There is a positive feedback – because these Na⁺ voltage-gated ion channels open as a result of depolarization, as  depolarization continues, more Na⁺ voltage-gated ion channels open leading to further depolarization, When they get to 35+

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the full development of an action potential

Once initiated (threshold is passed) the magnitude of the action potential is …

independent of the strength of the stimulus – an all-or-none response

As the action potential develops, what happens to the Na+ and K+ voltage-gated ion channels?

As the action potential develops, the Na⁺ voltage-gated ion channels close and the K⁺ voltage-gated ion channels open, allowing K⁺ to diffuse out of  the cell, lowering the membrane potential

Talk about the speed and length of the Na+ and K+ voltage-gated ion channels during action potential.

The K⁺ voltage-gated ion channels open more slowly than the Na⁺voltage-gated ion channels, and remain open longer (~1.5 msec for K⁺voltage-gated ion  channels vs. ~1.5 msec for Na+ voltage-gated ion   channels

What creates an undershoot?

K⁺ voltage-gated ion channels open more slowly and longer, the membrane potienal is less than -70

what cannot happen during the undershoot?

a new action potential cannot be generated

For invertebrates, why is speed not the same for every nerve cell?

• Skinny-slow

• Fat-fast

why are smaller diameter axons slower?

Smaller diameter axons conduct action potentials much more slowly that larger diameter axons – resistance to ionic current flow decreases as axon diameter increases.

why are vertebrate axons so fast?

Vertebrate axons are insulated by the myelin sheath, comprised of glial cells (oligodendrocytes in the CNS and Schwann cells in the PNS), allowing for saltatory conduction)

Why does the action potential only move down the axon?

Undershoot-refractory period 

what allows for saltatory conduction?

But there is gap when there is no glial cells(inbetween each schwann cell), this allows for saltatory conduction(or jumping conduction)

What is saltatory conduction?

• Extracellular fluid is in contact with the nerve cell membrane only at the nodes of Ranvier (Nodes of Ranvier is where the axon is naked)

  • Voltage-gated Na⁺ channels and voltage-gated K⁺ channels are restricted to the nodes of Ranvier

  • Action potentials are not generated between the nodes – depolarization propagated as current moves down the axon between nodes of Ranvier –

what needs to happen for depolization?

sodium must come in

why is saltatory conduction so fast?

Saltatory conduction is really really fast bc it only happens in the nodes of ranvier(action potential only in the nodes of ranvier)

(nodes of Ranvier, they pass along sodium)

describe chemical synapses and their travel

involving the release of a chemical, a neurotransmitter, packaged in synaptic vesicles, by the presynaptic cell at  the synaptic terminals

for chemical synapses, what happens at the end of the axon, after it releases a neurotransmitter?

At the end of axon, the increase in membrane potential causes voltage gated calcium channels,  allow calcium to move into the cell(down concentration gradient

where are the voltage-gated calcium channels 

only at the end of the axon

For chemical synapses, what happens when there is an influx of calcium?

• Influx of calcium causes synaptic vesicles(containing neurotransmitters) 

• synaptic vesicles fuse with plasma membrane, releasing the neurotransmitter into the synaptic cleft(small,l fluid filled area between the pre and post synaptic cell), diffusion across the cleft  

what happens due to the Depolarization of the plasma membrane?

Depolarization of the plasma membrane opens  voltage-gated Ca²⁺ channels

what happens due to Ca²⁺ infusion?

Ca²⁺ infusion causes synaptic vesicles to fuse with the plasma membrane, releasing the  neurotransmitter into the synaptic cleft

—-Neurotransmitter rapidly diffuses across the synaptic cleft – distance of less than 50 nm (human hair- 50-100 μm)

what does Postsynaptic cell have near the synaptic terminal

ligand-gated ion channels clustered near the synaptic terminal

What is an excitatory post-synaptic potential (EPSP)? What opens it?

Binding of the ligand (neurotransmitter) may open channels allowing Na⁺ to diffuse  across the plasma membrane, causing a small depolarization, a postsynaptic potential, a graded potential

 inhibitory post-synaptic potential (IPSP) what opens it?

Binding of the ligand (neurotransmitter) may  open channels allowing K ⁺ to diffuse  across the plasma membrane, causing a small hyperpolarization, a postsynaptic  potential, a graded potential

what happens to molecules that did not bind?

• Neurotransmitter enzymatically broken down with products taken back into the  presynaptic cell or diffuses out of cleft

  • The molecules that did not bind get broke down in the cleft for energy, or they can be taken back up in the presynaptic cell 

  • Very efficient

What is summation?

process of adding together multiple excitatory and inhibitory postsynaptic potentials to determine if a neuron reaches threshold to fire an action potential.

what is thought to be the cause of depression?

Depression is thought to be related to decreased activity of synapses that release biogenic amines (such as serotonin) in areas of the brain involved in emotion

how do drugs fix depression?

Drugs like Celexa, Prozac, Zoloft, Paxil, Lexapro are in the class of selective serotonin reuptake inhibitors, allowing serotonin to accumulate in the synaptic cleft, counteracting the decreased activity of these synapses

—The drugs slow down reuptake 

what is Multiple sclerosis?

Multiple sclerosis is an autoimmune disease in which a person’s own immune system attacks the myelin sheath of axons in the CNS, affecting function in cognitive, emotional, motor, sensory, or visual areas

—-Results in plaques or lesions (sclera)

MS descriptions?

• Several types of MS, each with a different set of symptoms and progression. Symptoms may vary considerably from person to person

  • Ultimate cause is unknown

  • No definitive diagnostic tests; MS is a diagnosis of exclusion

  • Drug treatments, but no known cure

• Most common in young adults and females, 1.8 million people  

Amyotrophic Lateral Sclerosis; ALS; Lou Gehrig’s Disease

• Lou Gehrig’s Disease is when motor neurons in the brain and spinal cord degenerate and die

  • As a result, muscles lose function and progressively weaken ultimately leading to paralysis

  • Motor neurons are weakened or damaged, worse over time

  • Cause unknown

In 2021, researchers came up with potential remedy, worked with mice(dancing molecules)

• Could you replace spinal cords? Not really

• The team took tissues from fat cells in their belly(mice with SPC), reprogram the fat to become embryonic stem cells(develop into almost anything)

• embryonic stem cells grow in personalized hydrogel(

• Grow the cells in a medium that mimics the central nerve cord, the cells grow into the spinal cord  

What did gas exchange systems in aniamls consist of?

-Body surfaces that are specialized to accommodate gas exchange

-Ventilation(breathing) mechanisms to move air or water across these specialized body surfaces

-Perfusion mechanisms that circulate extracellular fluids(blood) to these specialized body surfaces for gas exchange

What are the ways animals can exchange gases?

• Diffusion is the only mechanism by which gases are exchanged between the organism and its external environment

  • There is no active (ATP-dependent) transport of gases in any animal

How do lungless salamanders exchange gas? this vs humans

• Lungless salamander, all of their gas exchange happens through the skins

  • Vertebrates that have no lungs 

• Humans-a tiny portion of our gas exchange happens through our skin

  • Paper cut but you don’t bleed! 

Eastern Newt

-Tetrodotoxin-nerve toxin, hurt predators who eat them 

-It blocks sodium voltage gated ion channels(responsible for the rise in membrane potential at beginning of action potential) 

What is air made up of?

• 78% N

• 21% O2

• <1% CO2

partial pressure is higher when…

The concentration is higher

atmospheric pressure and elevation

Atmospheric  pressure decreases with elevation because gravitational forces decrease and there are fewer gas molecules/volume

Atmospheric  pressure is the sum of the pressures exerted by each gas, in exact proportion to their amounts

what is the partial pressure of O2?

P_O2 is 21 % of atmospheric pressure, regardless of elevation

what is the driving force for diffusion?

P_O2 (partial pressure of O2) in the environment is the driving force for diffusion from air or water across the respiratory surface into blood    

relationship bewteen partial pressure of O2 and CO2 and blood

• The partial pressure of O2 is higher than in blood, so that drive diffusion of O2 in blood

• The partial pressure of CO2 in blood is higher than in air, so it goes out 

is gas soluble in water?

• Most gases are not very soluble in water

  • O₂ diffuses through air 8000x faster than through water(not easily in water)

How does O₂ solubility change?

O₂ solubility decreases with warm water temperature and decreases with increasing salinity of  water

O2 avalibitly in water and temp

Organisms living in cold fresh water have more O₂ available to them than those living in warmer, saltier water

Animals have evolved a diversity of strategies to maximize the efficiency of gas exchange, like…

-Increasing the total surface area for gas exchange 

-Maximize the partial pressure gradient driving diffusion 

-Minimize the diffusion path length

-Maximize D, the diffusion coefficient or diffusivity 

How do insects do gas exchange?

Insects do gas exchange through air tubes, spiracles are the opening of the air tubes to the external environment

tracheoles and cell distance?

Spiracles branch into trachea, and they branch into tracheoles

*So that no cell is more than one or two cells away from a tracheoles *

what are teacheoles?

Tracheoles are air filled tubes and are always open because of spiracles 

—Inside the tip of the tracheole, the Partial pressure of O2 is low so O2 diffusions into each nearby cell  

how can spiracles be opened/closed? and what does this cause?

• Spiracles can be opened/closed by means of valves to control water loss

  • But when you do this, you shut down gas exchange 

how do O2 and Co2 move in tracheal system?

• No cell far from a tracheole – circulatory system and hemolymph not involved in gas exchange; 

  • movement of O₂ and CO₂ is solely by diffusion through tracheal system

what happens when some trachea branches end up in air sacs?

• Some branches end up in air sacks, they are like balloons

  • Once the grasshopper begins to move, the muscular contradictions control the sacks

  • It ventilates the body→Greater access to air

what do chitinous rings do?

Trachea and tracheoles reinforced with chitinous rings

what are tracheloles?

Highly branched system of air tubes – spiracle (1-10 pairs) – trachea – tracheoles(air filled tubes that do not collapse bc they are reinforced with chitinous rings) – cell bodies and air sacs (in larger insects – body movement like flight results in rhythmic contractions of the air sacs, increasing ventilation)

They extend from the larger tracheae to deliver oxygen directly to tissues and cells, serving as the primary site for gas exchange, and are often filled with fluid that is reduced during high metabolic activity to increase efficiency

describe gill arches in fish!

• In the gill arch there are blood vessels, some are O2 rich and some are O2 poor   

  • They pick up O2 and take it into the body 

  • On the inside of the V, is where the deoxygenated blood flows, it travels through lamella(capillary bed) to the oxygenated said 

  • The wall of the blood vessel is only one cell thick, make it easy for the gas to exchange

  • The water moves through the gill filaments, towards the inside of the V(both sides) 

  • Blood and water flow opposite directions 

  • Counter current exchange

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• The 100 degree water gets colder and the 20 degree water gets hotter

• Heat is transferred

  • Heat is a thing, cold is not!

• At the end, they both end at 60 degrees, concurrent exchange 

describe countercurrent exchange?

• Now the tubes are going opposite directions

• This time, the hot water gets colder, and the cold water gets hotter 

• Maintains a 10 degree difference between warmer and cooler water 

  • 80 degree of heat transferred 

• More heat got transferred!

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counterucrrent

do fish use countercurrent or concurrent? and what does it allow for them to do(features)

Fish have countercurrent exchange 

• With countercurrent

  • Exchange is more complete

  • 65% of O2 in water transferred to blood 

  • A gradient of O2 saturation exists over the full length of exchange surfaces

What would happen if fish had concurrent exchange?

• But if they have concurrent, they would reach an equilibrium

  • No more gas exchange 

  • 50% of O2 in water transferred to blood 

what do Anchovies, sharks, tuna do to ventilate gils?

constantly swim

Nornean flat-headed frogs, respiratory system

• Bornean flat-headed frog does not have lungs so it relies on diffusion through skin

  • They do but they actually are just very very small

positive or negative pressure for frogs and humans

Frogs always use positive pressure

Humans with negative

what are the only terrestrial vertebrates without lungs?

 lungless salamanders and the Bornean flat-headed frog

A 30-g mouse lung has 50 times more surface area for gas exchange per cm³ than a 30-g frog lung – Why is this the case?

The mouse is warm blooded, it must maintain its body temp, and it needs O2 to do this 

size of amphibian lungs?

Amphibian lungs, when present, are relatively small with low surface area

explain how frogs breathe

• When the frog is simply sitting there: The flap of skin under its oral cavity goes up in down in time with the nostrils

• When the frog need air in lungs, open nostrils, expand oral cavity, when you drop that tissue down(bigger cavity), it pulls air into mouth, then you close nostrils and close oral cavity, pushes air into lung and ventilates lung using positive pressure 

how do birds get enough O2 to fly?

-When a bird inhales, it brings air into posterior air sacks

-It takes 2 cycles for a breathe of air to move through the system of the bird

-The bird is always getting fresh O2

talk about the antomy of the bird that allows max O2

• Parabronchi, no alveoli; air sacs act as bellows, not for gas exchange

  • Constant flow of oxygenated air, posterior to anterior, across parabronchi(humans do not have constant flow)

  • Blood flows crosscurrent to air flow

  • Takes two inhalation/exhalation cycles to move air through bird

  • 60-80 % efficiency of O₂ removal from air to blood

are is human Respiratory System con or countercurrent?

NEITHER

Give an overview of Respiratory Systems-Lungs(US-humans)

-Our lungs branch into structures, and end in balloon-like structures called alveoli, surrounded by capillaries

-This is where gas exchange happens 

-Each capillary is continues with the external air 

-Cilia and mucus line the epithelium of the major branches of the respiratory system

describe surfactant in human respiratory system

• Human lung contains millions of alveoli, with a surface area of 100 m²

• Film of liquid with protein/phospholipid surfactant covering alveolar surface prevents then from collapse

surfactant and early development

Surfactant in humans usually develops at 33 weeks (38 weeks is normal full term)

Failure to develop surfactant related to respiratory distress syndrome – common in premature infants

how do mammals breath?

The thoracic cavity expands, leads to negative pressure breathing  

• Contraction of diaphragm and ribcage muscles expands volume of thoracic cavity

Is human O2 uptake good?

• Human O2 uptake efficiency 24%(this is worse than fish, we suck)

  • Why is our % of removal of O2 so low?

  • Because do not fully exchange all the air in our lungs when we breathe

  • Only 10% of lung air is exhaled at rest

describe the double membrane of our lungs and what it does

Double membrane surrounds lungs – inner membrane adheres to outside of lungs; outer membrane adheres to thoracic cavity wall – fluid between membranes holds them together by surface tension – confers fluidity while holding membranes together

when we inhale….

• our diaphragm muscles contract , pulling downwards 

  • Muscles in between ribs contract 

  • Both of these things increase thoracic volume

  • This creates negative pressure breathing 

Is O2 soluble in blood? and describe O2 requirement of the heart

• O₂ is not very soluble in blood (4.5 mL O₂  per L of blood in humans)

  • When at the gym, O₂ requirement can be as high as 2 L O₂ /min (2000 mL O₂/min)

  • Would require the heart to deliver 444 L of blood/minute(cannot rely on O2 alone! So you need hemoglobin)

  • Normal resting cardiac output of 5.25 L/min; up to 12.5 L/min during exercise

what are respiratory pigments?

proteins with metal ions that covalently and reversibly bind O₂(Usually packaged in blood cells (but not in octopi)