Extentor

Why does, in myelinated axons, the conduction of action potential get blocked when the axons lose their myelin

• Unmyelinated axons propagate action potentials continuously along their membrane.

• In myelinated axons, action potentials jump between nodes of Ranvier

  • Sodium channels are concentrated.

• When myelin is lost, current leaks through the exposed membrane,

  • Lack of sodium channels in demyelinated regions prevents action potential propagation leading to conduction block.

What are the functional advantages and disadvantages of electrical synapses?

• Advantages:

  • Fast transmission

  • Works in both directions

  • Non-selective

• Disadvantages

  • Not specific

  • Can get “tired” if over stimulated

Why is the physiological changes of the stress response important to survival in the short term and deleterious when they persist over long periods?

• Short term effects

  • Get ready for a fight or flight.

  • Increased:

    • Heart rate

    • Heart pressure

  • Decreased metabolism

    • Because of epinephrine secretion.

  • Glucocorticoids released (HPA axis) → increased glucose in the blood

    • Easy accessed by the animal

• Chronic term effects

  • Impaired

    • Reproduction

    • Growth

    • Immune system

  • May also result in:

    • Bone atrophy

    • Higher blood pressure

      • In non-fight or flight situations

What causes angiogenesis?

• Exercising muscles

  • The cytokine VEGF, produced and released

    • Stimulates angiogenesis.

• HIF-1 and HIF-2 promote angiogenesis

  • Helps cells facing hypoxia by

    • Increasing blood capillaries

    • Improving oxygen diffusion.

Why does the partial pressure gradient not gradually disappear as more and more oxygen diffuses from the air to the blood?

• Continuously moving through the circulatory system

  • Oxygenated blood is quickly carried away from the lungs

• Deoxygenated blood returns to the lungs

  • Which keeps the PO₂ lower in the blood

• Breathing continuously replenishes the oxygen in the air

  • Keeping the PO₂ in the lungs high

What are the 4 events in skeletal muscle contraction?

1. Latent Period:

   • Brief interval between AP-generation and the onset of muscle contraction

     • Calcium is released from the sarcoplasmic reticulum (SR)

2. Recruitment:

   • Activation of additional motor units

     • Increase muscle force

       • More motor units are recruited → overall contraction strength rises.

3. Summation:

   • Increase in muscle contraction force when successive twitches overlap

     • Occurs when a muscle is stimulated before it has fully relaxed.

4. Tetanic Contraction (Tetanus):

   • Sustained muscle contraction

     • Occurs when stimuli are delivered at high frequency

       • Prevents relaxation between twitches resulting in a strong, continuous contraction.

What could be a good experiment for testing the skeletal muscle contraction?

• Measuring these events in vertebrate skeletal muscle

  1. Preparation: Isolate a skeletal muscle and connect it to a force transducer.

  2. Latent Period: Apply a single electrical stimulus and measure the time from stimulus to contraction onset using high-speed data acquisition.

  3. Recruitment: Gradually increase the stimulus strength and record the corresponding force output to determine the threshold for motor unit activation.

  4. Summation: Deliver successive stimuli at increasing frequencies, measuring the force to observe how overlapping twitches increase contraction strength.

  5. Tetanic Contraction: Apply rapid stimuli at frequencies sufficient to induce tetanus (e.g., above 30 Hz) and measure the sustained contraction force.

What is VO₂max and how can it be measured?

• An animals maximum rate of oxygen consumption per unit of time per kg of body mass.

  • Measured by doing a cardio test while wearing an oxygen mask and simultaneously increasing the resistance in time intervals.

    • Based collected data, VO₂max can be calculated if the oxygen consumption starts to become steady.

    • If the oxygen consumption still increases VO₂max has not been reached.

• What is the Foramen of Panizza?

  • Describe the one situation in which you would be able to measure flow through the Foramen.

• What is the Foramen Ovale?

  • Why is it important for the circulation during fetal development in mammals?

• A small opening connecting the left and right aorta in the hearts of crocodilians

  • Flow is assessed during the transition between aquatic and terrestrial phases.

• A small opening in the fetal heart

  • Permits blood to bypass the pulmonary circuit by flowing directly from the right atrium to the left atrium, essential for fetal circulation because the fetals lungs is not yet active.

Are none thermoregulatory mechanisms in operation, in mammals or birds, within the thermoneutral zone (TNZ)?

• Maintains a constant metabolic rate

  • Despite changes in ambient temperature

    • Adjusting its insulation

• Ambient temperature decreases → temperature difference increases

  • Animal increases its insulation

    • Counterbalance heat loss

• Allows the animal to regulate its heat loss without increasing metabolic heat production

  • Explains why the metabolic rate remains flat in the TNZ

    • Passive thermoregulatory mechanisms are active

      • Insulation adjustments

    • No energy-expensive processes are required

      • Such as shivering or sweating

• Width varies by species

  • Depending on their ability to modulate insulation

1. How does PO₂ in the venous blood and hemoglobin saturation change:

   1. While the animal is diving

   2. When the animal resurfaces?

2. Defend the data considering the diving adaptations displayed by elephant seals

1. PO₂ and hemoglobin saturation in the venous blood

   • During the dive

     • Decreases as the animal consumes its stored oxygen → a drop in hemoglobin saturation.

     • Continue to decline as the dive progresses

       • Especially at deeper depths and longer durations.

   • Resurfacing

     • Rapid re-oxygenation causes PO2 and hemoglobin saturation to rise as it replenishes the oxygen stores.

2. Adapted to tolerate extremely low oxygen levels

   • During dives through:

     • Enhanced oxygen storage

     • Reduced oxygen demand

     • Efficient blood redistribution to vital organs.

   • Adaptations allow survival in hypoxic conditions

     • Fatal to non-diving mammals.

   • Physiology supports function at oxygen pressures

     • Incompatible with life in other species.

1. How and why does PO₂ in the arterial blood and hemoglobin saturation change before, during and after the dive?

2. Defend the data considering the diving adaptations displayed by elephant seals

1. PO₂ change and HB-saturation

   • Before the Dive:

     • How: Increases

     • Why: Deep breaths that maximize O₂-intake and O₂-loading in the blood.

   • During the Dive:

     • How: Decreases → decline

     • Why: Water pressure and metabolic O₂-consumption → O₂ is released to support muscle activity.

   • After the Dive:

     • How: Rapidly increase

     • Why: Inhales fresh air and replenishing O₂ stores

2. Adaptations

   • Adapted to tolerate extremely low oxygen levels

     • During dives through:

       • Enhanced oxygen storage

       • Reduced oxygen demand

       • Efficient blood redistribution to vital organs.

     • Adaptations allow survival in hypoxic conditions

       • Fatal to non-diving mammals.

     • Physiology supports function at oxygen pressures

       • Incompatible with life in other species.

Suppose you stimulate an isolated axon so that you generate an action potential at both ends at the same instant. What happens when they meet?

• Since the AP propagation is unidirectional, it can only travel in one direction.

• If two AP:s are propagated at opposite ends of the axon, they will propagate toward each other and cancel when they meet.

• The axon will be in the refractory period before and after where the two AP:s meet, and therefore they cannot continue along the axon.

What adaptive advantages does centralization and cephalization offer in the evolution of nervous system organization?

• They structure and organize neurons.

  • Centralization allows for the neurons in the brain to be organized and not just spread out randomly.

  • Cephalization is advantageous because it allows for a complex structure at the end of the body, a brain.

Describe the organization of a motor unit in vertebrate skeletal muscle and explain how recruitment of motor units influence the amount of tension produced by whole skeletal muscle.

• A motor unit is a motor neuron and all muscle fiber it innervates.

• In recruitment, more motor units are stimulated and thus more muscle fibers will contract.

  • The more muscle fibers that take part in the contraction, the higher tension.

How can a muscle generate different amounts of tension if fiber muscle contraction is an all-or-none phenomenon?

• Muscles generate varying amounts of tension by recruiting more or fewer motor units.

  • Recruitment follows the “size principle”

    • Activate smaller motor units first and if more force is needed larger motor units with stronger fibers will activate

Explain how the frequency of action potentials in a motor neuron can influence the amount of tension produced by a whole muscle.

• If 1 AP results in 1 contraction in a muscle = single twitch

• If frequency of AP:s increase in the motor neuron, the muscle fibers will not relax completely between stimulations, and contractions will summate into one with a greater force than the single twitch = summation

• If the frequency is increased even more, the muscle fibers will not relax at all between stimulations and it will result in a continuous strong contraction of the muscle = complete tetanic contraction

Describe diffusion and convection, the two ways of transporting O₂ and CO₂ in an air breathing mammal. Also explain where/when, in the animal, O₂ and CO₂ is transported by diffusion and convection, respectively.

• Diffusion

  • O₂ from the alveolus to the blood and from the blood to the cells and tissues

  • CO₂ from the cells and tissues to the blood and from the blood to the alveolus.

• Convection:

  • O₂ from external air to the respiratory organ and from respiratory organ capillaries to systemic circulation

  • CO₂ from systemic circulation to the respiratory organ capillaries and from respiratory organ to the external air

What complementary mechanisms does the animal use to produce ATP during the start up phase, when the oxygen uptake has not yet reached the needed level?

• The animal will use:

  • Anaerobic glycolysis, using glucose and glycogen, to produce ATP + Lactic acid

  • Phosphagens, when their phosphate bonds are broken, to produce ATP

  • Internally stored O₂, bound to myoglobin in muscles, to produce ATP

Explain the reasons why the pressure change is not linear and why there are larger drops in pressure in some parts of the circulation in comparison to other parts.

• Decrease with distance from the heart → pressure change is non-linear

  • Pressure will drop significantly in the arterioles

    • Largest surface area

    • Distributes the pressure to all small capillaries, so the pressure in the capillaries will not be high.

    • Distinction between systolic and diastolic pressure fade.

Explain the mechanism used by tunas that keep their body temperature higher than the waters temperature.

• Tuna's muscles help conserve heat

  • Have specialized tissues (brown adipose tissue)

    • Evolved from skeletal muscle

    • Through nonshivering thermogenesis produce heat.

  • Produced when lipids are oxidized in mitochondria.

    • No work is produced, making it a very efficient mechanism for heat production.

• Conserve this heat using a countercurrent heat exchange system

  • Warm blood from muscles transfers heat to cooler oxygenated blood coming from the gills reducing heat loss to the water.

Why is the increase in 2,3 DPG concentration important for anemic patients?

• Binds to hemoglobin → lowering its affinity for O₂

• In anemic patients the reduced number of red blood cells means less available hemoglobin for oxygen transport.

  • To compensate, hemoglobin must have a lower affinity for O₂, allowing for efficient O₂-delivery to systemic tissues.

• Thus, increase is crucial because reduced affinity ensures that, despite having less hemoglobin, adequate oxygen is released meeting tissue demands.

  • Achieved through the stabilization of hemoglobin's tense state by 2,3-DPG.

• Which different strategies does animals have to produce ATP despite the lack of oxygen? Compare them regarding:

  • Rate of acceleration of ATP production at onset of use

  • Peak rate of ATP production

  • Rate of full return to full potential for ATP production after use

• Anaerobic glycolysis

  • Moderate rate of acceleration (seconds to minutes)

  • Moderate peak ATP production (2 ATP/glucose)

  • Slow recovery time (Hours, due to lactate)

• Use of phosphagen

  • Fast rate of acceleration (seconds)

  • High peak ATP production (Instant ATP)

  • Fast recovery time (minutes)

• Myoglobin oxygen reserve

  • Fast rate of acceleration (seconds to minutes)

  • High peak ATP production (supports aerobic)

  • Moderate recovery time (minutes)

How do animals who do not have the ability to convert lactate to ethanol get rid of the lactate?

Animals must have access to oxygen to get rid of lactate, the lactate is the converted back to pyruvic acid and either enters the Krebs cycle or is used to synthesize glucose.

What are the functional differences between ionotropic and metabotropic receptors?

• An ion channel which opens

  • Directly increases the ion permeability for those ions that can diffuse through the ion channel in the cell

    • When binding of a molecule

• When a metabotropic receptor binds a molecule

  • Metabolic cascade involving second messengers initiates in the cell

    • Can indirectly lead to an increased ion permeability of the cell membrane

• The response of a molecule binding to an metabotropic receptor are usually slower and has a longer effect than the respons of a molecule binding to a ionotropic receptor.

What is “fiber recruitment” in muscle physiology?

An increase in the number of fibers contributing to a muscle contraction.

When and what for is fiber recruitment needed?

When the fibers contributing to the muscle contraction are not sufficient to bear a load and the force needed to contract the muscle needs to increase.

What is the actual mechanism of fiber recruitment and which fiber are recruited?

• Muscle spindle sends signals to the brain about muscle length

• If the muscle hasn’t shortened enough, the brain activates more motor neurons, recruiting additional fibers increasing the contraction force

  • Follows the "size principle"

    • Starting with smaller motor units and progressing to larger ones as needed

      • Ensuring a gradual increase in contraction force

• Describe the ways animals can produce ATP using different pathways and compare them regarding:

  • Speed of ATP production

  • Peak rate of ATP production

  • Length of time during which ATP can be produced

• Anaerobic pathways.

  • Phosphagens and anaerobic glycolysis

    • Metabolisms that do not require oxygen,

    • Fast at producing ATP

    • Can only produce a small amount.

    • Can’t be sustained for a long time.

• Aerobic pathways

  • Krebs cycle, oxidative phosphorylation, coupled with the electron transport chain.

  • Slow and produce much ATP, as long as O2 is available.

Give a concrete example in which one or more of these pathways is used by an animal in facing an environmental challenge.

• Diving mammals when diving

  • Because they cannot take up more O₂ under the surface.

  • Have O₂-stores in muscles, lungs and blood

    • As long as there is O₂, the aerobic pathways can be used to produce ATP.

  • When the O₂-stores are depleted, the anaerobic pathways are used to produce ATP.

    • Only be sustained as long as the there is phosphagens and until the blood becomes acidic due to lactate acid.

Explain how reproductive traits, such as induced ovulation and postpartum estrus, work.

• Induced ovulation: The ovulation (release of an egg) is connected with the act of copulation.

  • Copulation between a male and a female results in a spike in LH in the female 1-2 h after mating, which triggers ovulation.

• Postpartum estrus: A time period directly after giving birth that makes the female ready to mate again

  • Induced ovulation can take place if mating occur in this time period.

    • The fact that rabbits have these reproductive traits make them able to reproduce at a high speed.

• Explain how an experiment would be designed to demonstrate:

  • A) The existence of an endogenous free-running circadian rhythm

  • B) How an external zeitgeber entrains the endogenous rhythm.

• Observe active and awake behaviours during day time with light present according to natural light period during the 24 h time period.

• See inactive sleeping behaviour in dark according to the natural night time during the 24 h time period.

• When an experiment of this animal with 24 h dark time over longer period is done the active and inactive time periods will shift.

• The environmental light/dark times set a circadian rhythm to 24 h but the natural endogenous free-running rhythm is a bit shorter than 24 h.

• With time this rhythm shifts if an external zeitgeber, like the natural light/dark periods, during the 24 h of a day is present to effect the rhythm.

What are facts about skeletal muscle fibers?

• Muscle tension is the force generated by a muscle during contraction

• The amount of tension developed by each contracting fiber in a muscle is determined by the frequency of action potentials from its motor neuron

• The amount of tension developed by each contracting fiber is also determined by the length of the muscle fiber at the time it is stimulated

• The tension generated by a whole muscle is directly related to the number of actively contracting muscle fibers

• The amplitude of the force of contraction, of a whole muscle, depends on the frequency of action potentials (above threshold) that reach the muscle fibers

How can you design a experiment to test the contraction threshold and recruitment of motor units?

• Contraction threshold

  • Stimulate a nerve connected to finger muscles with a low voltage, gradually increasing it until a contraction is observed

    • Shows minimum stimulus required to activate the first motor unit.

• Recruitment

  • Increase the frequency and voltage of the stimuli, showing how more frequent and stronger stimulations results in stronger, sustained contractions by summing the twitches.

Describe the two ways CO₂ is transported in air-breathing mammals and specify which type of transport is used in each part of the transport.

• Diffusion transports CO₂

  • From cells and tissues to the systemic circulation

    • PCO₂ is higher in the cell than in the capillaries.

  • From alveoli capillaries to air

    • PCO₂ is higher in the alveoli capillaries than in the air

• Convection transports CO₂

  • In the blood to the lungs.

  • Out of the respiratory organs to external air

Describe how an animal responds when facing a challenge, for example encountering a predator.

• Sympathetic nervous system triggers the "fight or flight" response.

• Epinephrine secretion increase heart rate and blood pressure

• Blood is directed to vital organs

  • Shifting from digestion to muscles, enabling action

• The nervous system regulates the heart via the SA node

• Respiration increases to supply more oxygen.

• HPA axis releases glucocorticoids enhancing focus and energy availability

  • By raising blood glucose levels.

Why doesn’t, in amphibians heart, the blood mix in the single ventricle. What prevents the mixing from happening?

• The heart's single ventricle has muscular ridges that help compartmentalize blood flow, limiting the mixing of oxygenated with deoxygenated blood.

• Additionally, a spiral valve in the conus arteriosus helps direct blood into separate pathways

• The heart's sequential contraction, where atria contract first and the ventricle follows, ensures the functional separation of blood streams, allowing for relatively efficient oxygen transport

What is the physiological relevance of peripheral vasoconstriction in a seal performing a voluntary dive?

• Decreasing blood flow to less O₂-demanding areas

  • Skin and peripheral tissues

• Helps seals conserve O₂ for vital parts

  • Brain and active muscles

• Redistribution minimizes O₂-consumption in non-essential tissues

  • Increases hemoglobin availability for essential tissues which improves O₂-delivery

• Seals prolong their dive duration

  • Optimizing O₂ use while protecting vital functions during low O₂-periods

How does vasoconstriction take place? Explain the anatomical structures that explain how the central nervous system triggers the constriction of a blood vessel.

• Occurs when smooth muscle fibers which surrounds the blood vessels contract

• CNS sends signals through the SNS which

  • Cause the blood vessels to decrease their diameter causing resistance in the blood flow which decreases the amount of blood and oxygen to those parts.

What is creatine phosphate?

A type of phosphagen used for temporary stores of high-energy phosphate bonds in muscle cells to rapidly regenerate ATP during anaerobic activity

What is the difference between standard metabolic rate (SMR) and basal metabolic rate (BMR)?

• Standard metabolic rate

  • The metabolic rate of a ectothermic animal when it is resting and fasting.

• Basal metabolic rate

  • The metabolic rate of a homeothermic animal when it is in its thermoneutral zone, resting and fasting.

What is aerobic scope for activity?

The difference between an animal’s peak rate of O2 consumption during locomotion and its resting rate of O2 consumption.

What is ductus arteriosus, which animals have it, where in the circulation is it located and what is its function?

• A fetal blood vessel that connects the pulmonary artery to the aorta

  • Allowing blood to bypass the non-functional fetal lungs during embryonic development.

• It is present in mammals, birds and some reptiles where it plays an essential role in fetal circulation.

• In mammals, the ductus arteriosus typically closes shortly after birth, transitioning blood flow to the lungs as they become functional.

How do cardiac output, stroke volume and heart rate change when conducting a VO2max test?

• Cardiac output increases linearly during the test to supply more oxygenated blood to the working muscles.

• Stroke volume increases initially but plateaus at about 40-60% of VO₂max in most individuals. Early in the test, the heart pumps more blood per beat due to enhanced ventricular filling and forceful contractions. However, at higher intensities, stroke volume reaches its maximum as the time for ventricular filling shortens.

• Heart rate increases linearly throughout the test until it reaches the maximum heart rate. To compensate for the plateau in stroke volume, the heart beats faster to maintain the increase in cardiac output. The body has reached its maximal capacity for oxygen uptake and utilization during exercise.

What effect does alcohol have on the body’s ability to osmoregulate, which is the main hormone affected by alcohol and how does this hormone normaly work in nephrons to regulate the filtration and reabsorption of water?

• Alcohol has a diuretic effect on the body

  • Inhibits the secretion of the antidiuretic hormone vassopresin from the pituitary gland

• Vassopresin act to conserve water in the body

  • Preventing the production of a large volume of urine and promoting water reabsorption in the kidneys

    • Specifically in the collecting ducts of the nephrons

• Vassopresin stimulates the incorporation of specific aquaporin molecules into the cell membranes of the epithelial cells that form the wall of the collecting duct

• When Vassopresin is inhibited the wall of the collecting duct is less permeable which causes a higher volume of more diluted urine

What are some facts about the function of skeletal muscles?

• In skeletal muscle, Ca²⁺ controls muscle fiber contraction by binding to troponin, which causes tropomyosin to move and expose actin binding sites, thereby enabling myosin to bind to actin and activate the myosin ATPase.

• In a relaxed skeletal musle contraction does not occur because there is little Ca²⁺ in the cytoplasm

• During an isometric, tetanic contraction, the sarcomeres shorten at the same time as the elastic components lengthen. As a result, the length of the whole muscle does not change

• During skeletal muscle hypertrophy, caused by training, the size of existing muscle fibers increases due to enhanced protein synthesis, the addition of myofibrils, and activation of satellite cells to support growth and repair.

• During peripheral control of rythmic behaviour, a repetitive movement pattern, movment A activates receptor that start movement B and movement B activates receptors that start movement A again. This pattern is repeated

• The term reciprocity refers to the coordination of muscle activity, where one muscle or group of muscles contracts while the antagonistic muscle or group relaxes. Skeletal muscles are arranged in antagonistic pairs, often comprising an extensor and a flexor, to facilitate opposing movements

How would you design an experiment to test the force of contraction of a skeletal muscle during an isotonic single twich that engages all the motor units of the studied muscle?

• Start by connecting a force transducer and stimulate the nerve with a gradually increasing electrical current until the force plateaus

  • Indicating recruitment of all motor units.

• All motor units are engaged when no further increase in force occurs with higher stimulation intensity.

What are some facts about transport of respiratory gases?

• Ventilation of the mammalian lungs is an example of convection of air

• The air pressure gradient is the driving force of the air transport in the mammalian lung

• Oxygen, bound to hemoglobin, is transported in the bloodstream, which is an example of transport by convection

• The blood pressure gradient is the driving force of transportation in the bloodstream

• Oxygen diffuses into metabolizing cells from the blood, while carbon dioxide diffuses out of metabolizing cells into the blood, both driven by their respective partial pressure gradients.

• The driving force of diffusion, when CO2 and O2 are transported to and from the metabolizing cell, is the partial pressure gradient of each gas, not the overall air pressure gradient.

Which factors can affect the diffusion of oxygen across the gas-exchange membrane and for each factor, does the diffusion increase or decrease?

• Incoming deoxygenated blood increases the rate of diffusion

  • Because the difference in pO₂ is high.

• The bohr effect increases O₂- affinity of hemoglobin in the lungs

  • Due to low pCO₂, increasing the rate of diffusion.

• Cooperativity of hemoglobin increases the affinity of the molecule if one O₂ has already bound to it.

  • Helps maximize the saturation of each hemoglobin molecule and increases the rate of diffusion.

• Thickness of the membrane is also a factor

  • Thinner membrane increases the rate of diffusion

  • Thicker membrane decreases the rate of diffusion.

What is adaptation of a sensory receptor, what is the function of adaptation and how do phasic and tonic differ from each other?

• Adaptation of a sensory receptor is a decrease in sensitivity to a repeteated stimuli over time.

• The function of adaptation is to provide new important stimuli to the brain and ignore old unimportant information.

• The difference between a phasic receptor and an tonic one is that the phasic adapt quickly while the tonic receptor adapt slowly, if at all.

Why are the effects of steroid hormones usually seen after a longer delay than the effects of peptide hormones?

• Steriod hormones

  • Pass over membranes and bind to intracellular receptors

  • Modulate gene expression

  • Transported in blood using transport proteins

• Peptide hormones

  • Bind to on-surface receptors

    • Triggers a cascade of 2:nd messengers which amplify the hormonal signal

  • Protein-based and dissolves in the blood