Human Physiology Exam 1

What determines the activity of the voltage-gated Na+ channel?

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Discuss differences between neurotransmitters and neuromodulators. (pg 167-168)

1. Neurotransmitters: a chemical released in synapse that can cause either an excitatory response (Depolarization) or inhibitory response (Repolarization). 2. Neuromodulators: Messengers that cause complex responses.

What is the relationship between the presynaptic neuron and the postsynaptic neuron?

1. Presynaptic neurons conduct signals towards a synapse. 2. Postsynaptic neurons conduct signals away from a synapse.

Classify plasma membrane receptors according to the signal transduction pathways they initiate:

1. Receptors that function as an ion channel 2. Receptors that function as an enzyme 3. Receptors that are bound to and activate a cytoplasmic JAK kinase 4. Receptors that activate a G-protein (FIGURE 5-5)

List the components of a reflex arc:

1. Stimulus 2. Receptor 3. Afferent Pathway 4. Integrating Center 5. Efferent Pathway 6. Effector 7. Response

What determines the direction in which net diffusion of a non polar molecule will occur?

1. The concentration gradient (High to Low)

What is the approximate osmolarity of the extracellular fluid?

285-300 mOsm

What is the approximate osmolarity of the intracellular fluid?

285-300 mOsm

Describe the direction of information flow through a neuron in response to input from another neuron.

In the Central Nervous System (CNS) dendrites and the cell body receive most of the inputs from other neurons, with the dendrites (the branched pattern of the dendrites greatly increases the neurons capacity to receive input) generally taking a more important role.

Draw a graded potential and an action potential on a graph of membrane potential versus time. Indicate zero membrane potential, resting membrane potential, and threshold potential; indicate when the membrane is depolarized, repolarizing, and hyperpolarizing:

(FIGURE 6.14)

Draw a simple cell; indicate where the concentrations of Na+, K+, and Cl- are high and low and the electrical potential across the membrane when the cell is at rest:

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Where are afferent neurons, efferent neurons, and interneurons located in the nervous system? Are there places where all three could be found?

1. Afferent Neurons: Convey information from the tissues and organs of the body toward the CNS. Afferent neurons are mainly in the CNS 2. Efferent Neurons: Convey information away from the CNS to effector cells like muscle, gland, or other cell types. Efferent neurons are mainly in the CNS 3. Interneurons: Connect neurons within the CNS. Interneurons are only found in the CNS and consist of 99% of the neurons.

Contrast the postsynaptic mechanism of excitatory and inhibitory synapses.

1. Excitatory Synapses: Excitatory synapses increase the likelihood that a postsynaptic neuron will fire an action potential by depolarizing the membrane, bringing it closer to its threshold. This type of graded potential change is called an excitatory postsynaptic potential (EPSP). 2. Inhibitory Synapses: Inhibitory synapses decrease the likelihood that a postsynaptic neuron will fire an action potential by hyperpolarizing the membrane, driving it farther away from its threshold. This type of graded potential change is called an inhibitory postsynaptic potential (IPSP).

List the general categories of intercellular messengers:

1. Hormones 2. Neurotransmitters 3. Paracrine Agents

List at least 8 ways in which the effectiveness of synapses may be altered. (pg 165-167)

1. Increase leakage of neurotransmitter from vesicle to cytoplasm, exposing it to enzyme breakdown. 2. Increase transmitter release into cleft. 3. Block transmitter release. 4. Inhibit transmitter synthesis. 5. Block transmitter reuptake. 6. Block cleft enzymes that metabolize transmitter. 7. Bind to receptor on postsynaptic membrane to block (antagonist) or mimic (agonist) transmitter action. 8. Inhibit or stimulate second-messenger activity within postsynaptic cell.

In what ways can the net solute flux between two compartments separated by a permeable membrane be increased?

1. Increase the temperature. 2. Decrease the weight or size of the molecule. 3. Increase the surface area of the membrane. 4. Decrease the density of the medium that your molecules are moving through. 5. Decrease the distance to travel.

Name the two fluids that constitute the extracellular fluid:

1. Plasma (in the blood) 2. Interstitial fluid (in the spaces between the cells)

What is the relative proportion of the two fluids making up the extracellular fluid:

1. Plasma makes up 20-25% 2. Interstitial fluid makes up 75-80%

When considering the diffusion of ions across a membrane, what driving force, in addition to the ion concentration gradient must be considered?

1. The electrical charges that exist on the protein channels and this makes these channels very selective as to what ions they will let in. 2. The diameter of the ion channel 3. The membrane potential (This is a measure of the net charge on one side of the membrane compared to the other side).

What determines the magnitude of flux across a membrane in a mediated-transport system?

1. The rate of flux is dependent upon the rate of allosteric change in the protein. 2. the number of transporters in the membrane

Explain how synapses allow neurons to act as integrators; include the concepts of facilitation, temporal and spatial summation, and convergence in your explanation.

A neuron can act as an integrator by processing the synaptic inputs that it receives and converts them into an output signal. 1. Facilitation: 2. Temporal Summation: Two stimulations that are spaced closely together and this creates a greater depolarization than just the one stimulation alone. 3. Spatial Summation: Two stimulations occur at the same time, but they occur at different locations (If spatial summation and temporal summation occur at the same time then you would get an action potential). 4. Convergence: This would occur when the neuron takes multiple synaptic inputs and converts them into one output.

What characteristics distinguish facilitated diffusion from active transport?

Active Transport is different from facilitated diffusion in that it uses cellular energy (ATP) to move material uphill, AGAINST its electrochemical gradient. Facilitated Diffusion on the other hand moves material from high concentration to low concentration.

Describe the role of plasma membrane G proteins:

Adenylyl cyclase is one of the most important effector proteins that is regulated by G-proteins. This regulation can be an activation of the enzyme by a stimulatory G-protein, or it could be an inhibition of the enzyme by an inhibitory G-protein. The corresponding production of more or less second messenger will determine the activity of the target cell. (Maybe????Plasma membrane G-proteins directly and indirectly gate ion channels. An ion channel can be the effector protein for a G-protein).

Describe the propagation of an action potential. Contrast this event in myelinated and unmyelinated axons:

An action potential started at any one point on the membrane excites adjacent portions of the membrane resulting in a propagation of the action potential across the entire cell membrane. At each point it takes < 2 milliseconds for the entire action potential to occur thus the whole cell membrane could be depolarized and repolarized in a few milliseconds depending on the size of the cell. Action Potential in Myelinated Axons: The velocity of action potential transmission can be greatly enhanced by the presence of the myelin sheath. The nodes contain concentrated regions of Na+ channels and the myelin sheath prevents "leakage" of ions across the membrane. (Saltatory Conduction) Action Potential in Unmyelinated Axons: Small unmyelinated axons conduct action potentials at ~0.5m/s while large, myelinated axons conduct action potentials at ~100 m/s!!!!!

How do the two fluids of the extracellular fluid differ in composition?

Both plasma and interstitial fluid have relatively the same amount of oxygen, nutrients, and wastes, but the protein concentration remains much higher in the plasma than in the interstitial fluid.

How can the concentration of water in a solution be decreased?

By adding more solute thus increasing the osmolarity. The decrease in water concentration would be equal to the increase in solute concentration.

Describe the levels of cellular organization and state the 4 types of specialized cells and tissue:

Cells divide and differentiate into four specialized types―muscle, nerve, epithelial, and connective-tissue cells―which associate with each other to form tissues; tissues in combination form organs, many with discreet functional units. Organ systems consist of groups of organs that in combination perform a specific function in the body. An organism is made up of all of its organ systems. Every organ system has one ultimate goal... homeostasis!

Describe how the metabolism of receptors can lead to down-regulation or up-regulation:

Down-regulation: If there is a high concentration of a specific chemical messenger for prolonged periods of time then the receptor for that messenger may decrease in the total number. Up-regulation: If there is a low concentration of the chemical messenger for prolonged periods of time then the total number of receptors for that messenger may increase and also develop a higher sensitivity for the messenger.

What characteristics distinguish simple diffusion from facilitated diffusion?

Facilitated Diffusion may reach its maximum flux at a lower solute concentration than simple diffusion alone. The key difference between the two is that facilitated diffusion requires a transporter to move the solute while simple diffusion does not need a transporter, but both methods still move from high to low concentrations.

Contrast feedforward and negative feedback:

Feedforward regulation happens before homeostasis has been disrupted and helps to minimize fluctuations and speed up the response. Negative feedback occurs only after there has been a change in the environment. Negative feedback mechanisms come into play to restore the variable toward its original set point.

List differences between graded potentials and action potentials:

Graded Potentials: 1. Never reach the threshold. 2. These Changes in membrane potential are confined to a relatively small region of the plasma membrane. 3. They are usually produced when some specific change in the cell's environment acts on a specialized region of the membrane. 4. Are decremental 5. Can be added together 6. Are given various names depending on where they are in the body or what function they are used in. Action Potentials: 1. Will reach the threshold. 2. Are large alterations in the membrane potential. 3. Action potentials are usually very rapid and may repeat at frequencies of several hundred per second. 4. The propagation of action potentials down an axon are what the nervous system uses to communicate over long distances.

Describe several important generalizations about homeostatic control systems:

Homeostatic control systems perform regulatory responses to preserve relatively stable conditions of the internal environment. Important generalizations include: (1) Stability of an internal environmental variable is achieved by the balancing of inputs and outputs. It is not the absolute magnitudes of the inputs and outputs that matter but the balance between them. (2) In negative-feedback systems, a change in the variable being regulated brings about responses that tend to move the variable in the direction opposite the original change—i.e., back toward the initial value or set point. (3) Homeostatic control systems cannot maintain constancy of any given feature of the internal environment in the face of continued change in the external environment, but can only minimize changes. Therefore, any regulated variable will have a more-or-less narrow range of normal values depending upon environmental conditions. (4) The set point of some variables regulated by homeostatic control systems can be reset—i.e., physiologically raised or lowered. (5) It is not possible for everything to be maintained relatively constant by homeostatic control systems. There is a hierarchy of importance, such that the constancy of certain variables may be altered markedly to maintain others at relatively constant levels.

If two solutions with different osmolarities are separated by a water-permeable membrane, why will a change occur in the volumes of the two compartments if the membrane is impermeable to the solutes but no change in volume will occur if the membrane is permeable to solutes?

If the membrane is impermeable to solutes then only the water would be changing sides and this would lead to a change in volume but if both water and solute can change sides then the net volume in each compartment would stay the same.

What is the basic difference between a local homeostatic response and a reflex?

In a reflex, nerves or hormones act as the afferent and efferent pathways. These long-distance communication mechanisms are unnecessary for local responses.

Contrast the two uses of the word receptor:

It can be a protein receiving in an intracellular molecule or it can be a large cellular structure associated with the nervous system.

Describe the mechanism by which a transporter of a mediated transport system moves a solute from one side of a membrane to the other:

Mediated transport involves another type of integral transmembrane protein that moves molecules across the cell membrane (The transporter). These proteins have the ability to change their shape (allosteric). In changing shape they are able to move molecules from one side of the membrane to the other. 1. Facilitated Diffusion 2. Active Transport

Why are membranes more permeable to non polar molecules than to most polar and ionized molecules?

Nonpolar molecules are soluble in the phospholipids of membranes and thus diffuse through the lipid portions of the membranes. Polar molecules and ions require protein channels or carriers to move across membranes due to their low solubility.

Explain why different types of cells might respond differently to the same chemical messenger:

Not all cells may have the specific receptor to respond to the chemical messenger. The chemical messenger would only influence the types of cells that contain that chemical messenger's specific receptor.

Describe the signal transduction pathway that lipid-soluble messengers use:

Once the lipid-soluble messenger (Usually is a hormone) binds to and activates the receptor, it will attach to a specific gene sequence in the DNA and act as a transcription factor. That is, it will either increase or decrease the rate of transcription of the gene, thus controlling the amount of gene product produced. These lipid-soluble messengers penetrate both the cell membrane and the nuclear envelope.

Describe how negative and positive charges interact:

Opposite charges attract while the same charges repel and this property of charges can help move certain ions across cell membranes. The greater the difference in charge, the greater the force. This force is called the potential difference.

What is the first step in the action of a messenger on a cell?

Receptor Activation: This is the first step in the signal transduction pathway and causes a change in the conformation (three-dimension shape) of the receptor.

Contrast receptors that have intrinsic enzyme activity with those associated with cytoplasmic janus kinases:

Receptors with intrinsic enzyme activity: These are all protein kinases with the major one being receptor tyrosine kinase. Specific messengers will bind to these receptors and by doing this the receptor's conformation will be changed so that its enzymatic portion, located on the cytoplasmic side of the plasma membrane, is activated. Receptors associated with cytoplasmic janus kinases: These are cytoplasmic kinases and in these the receptor and messenger act as a unit together.

Describe the direction in which sodium ions and solute transported by secondary active transport move during co-transport and counter-transport:

Secondary active transport uses energy derived from an ion gradient to push other materials uphill against their concentration gradient. Several different ion gradients can be used for this process but the most common one is Na+. The flow of Na+ is always down its concentration gradient, so if the movement of the transported molecule flows the same way as the Na+ then its considered cotransport. If the transported molecule flows the opposite way of Na+ then its considered counter transport.

Ions diffuse across cell membranes by what pathway?

Some integral transmembrane proteins have small micropores that allow for ions to diffuse through.

Why do sodium and chloride ions in the extracellular fluid and potassium ions in the intracellular fluid behave as though they were non penetrating solutes?

The Na+/K+ ATPase pump actively transports Na+ out of the cell immediately after it enters and K+ are immediately removed from the cell through the electrical repulsion generated by the membrane. This makes them both non penetrating since they can't really penetrate the membrane without this kickback.

By what mechanism does the active transport of Na+ lead to the osmotic flow of water across an epithelium?

The active transport of Na+ across the epithelium results in a decrease of Na+ on one side of the epithelial layer and this leads to water flowing by osmosis to the side with all the Na+ because water tends to move from high solute concentration to low solute concentration.

What change in cell volume will occur when a cell is placed in a hypotonic solution

The cell will swell as water will enter through osmosis.

Describe the structure of presynaptic axon terminals, and the mechanism of neurotransmitter release.

The presynaptic axon terminal: 1. Holds the synaptic vesicles that contain the neurotransmitter molecules. 2. Have a synaptic cleft (10-20 mm). 3. Have a dense postsynaptic membrane. Steps in the Mechanism of the Neurotransmitter Release: 1. Action potential reaches the axon terminal 2. Voltage-gated Ca2+ channels open 3. Calcium enters axon terminal 4. Neurotransmitter is released and diffuses into the synaptic cleft 5. Neurotransmitter binds to postsynaptic ligand-sensitive receptors 6. Neurotransmitter is removed from synaptic cleft Depolarization of the axon terminal increases the Ca+ concentration within the terminal, which causes release of the neurotransmitter into the synaptic cleft. The neurotransmitter diffuses across the synaptic cleft and binds to receptors on the postsynaptic cell; the activated receptors usually open ion channels.

What is the result of opening a membrane ion channel?

There is a change in the membrane potential and/or cytosolic Ca2+ concentration.

What is the chemical nature of receptors?

They are proteins or glycoproteins.

Where are the chemical receptors located?

They can be either located inside the cell membrane (Vast majority of them are located here) or inside the cell, either in cytosol or the nucelus.

Describe how ion movement generates the action potential:

This will occur in two steps: 1. Depolarization: Voltage-gated Na+ channels initiate the action potential by letting in enough Na+ to depolarize the membrane. This depolarization of the membrane will lead to it having a positive charge instead of a negative charge. Different ion channels can cause a depolarization of the membrane. 2. Repolarization: Once the peak of depolarization is reached, the Na+ gates will close to stop Na+ flow while the K+ gates will open and K+ is rapidly pushed out of the cell due to the repelling forces of the now positive interior of the cell. (A hyper polarization of the membrane can happen if too much K+ is released and this is often the case).

Explain the conditions that give rise to the resting membrane potential. What effect does membrane permeability have on this potential? What role do Na+/K+ ATPase membrane pumps play in the membrane potential? Is this role direct or indirect?

Three conditions that give rise to the resting membrane potential: 1. The difference in ion concentration across the membrane. 2. The difference in membrane permeability to the Na+ and K+ 3. The Na+/K+ pump begins increasing the Na+ outside the cell and increasing the K+ inside the cell. When the net movement of both Na+ and K+ are zero then the inside of the cell will have a negative charge with respect to the outside (Direct). In resting cells the inside of the cell will be negatively charged with respect to the outside of the cell and this is called the resting membrane potential. (Because of the unequal pumping action of the Na+/K+ pump, and the difference in membrane permeability when the net movement of Na+ and K+ are both equal to zero there is an overall charge of -70 mV on the inside surface of the cell compared to the outside surface of the cell. This is the resting membrane potential. In nerves and muscle cells this potential difference is used to send electrical signals through the body and cause muscular contraction).

Explain threshold and the relative and absolute refractory periods in terms of the ionic basis of the action potential:

Threshold: This is the maximum intensity that must be exceeded for an action potential to take place. Relative Refractory Period: This is an interval following the absolute refractory period in which a second action potential can be produced if the stimulus is quite a bit stronger. Absolute Refractory Period: This is when a second stimulus, no matter how strong it is, will not produce a second action potential. This will occur when the voltage-gated Na+ channels are either already open or have proceeded to the inactivated state during the first action potential.

What change in cell volume will occur when a cell is place in a hypertonic solution?

Water will leave the cell, through osmosis, causing it to shrink.