Physio Exam 1

If an afferent axon is firing with increased frequency how will this likely impact an efferent neuron response?

Increase net signal strength through temporal summation. The first impulse produces a slight EPSP followed by addition EPSP impulses by subsequent impulses summing to threshold.

Describe diffusional transport of Na+, cortisol, insulin (a protein-based hormone) and O2 in respect to the plasma membrane.

There is limited Na+ diffusional transport. Transport is primarily via membrane protein channels.Cortisol is a steroid/lipid based molecule so it freely diffuses across the membrane, down its concentration gradient.Insulin as a protein molecule does not diffuse through the membrane but must bind to cell surface receptors.O2 readily diffuses across the membrane, down its concentration gradient.

Define how the various components of Ficks Law regulate diffusion rate across a porous membrane

he magnitude or steepness of the concentration gradient; increase increases diffusion ratethe permeability of the membrane to the substance; increase increases diffusion ratethe surface area of the membrane across which diffusion is taking place; increase increases diffusion rate the molecular weight of the substance; increase decreases diffusion ratethe distance through which diffusion must take place; increase decreases diffusion rate

Membrane potential

separation of charges across the membrane.

Whichprocessaffects directionality of signal transmission along the axon; why? Which process affects the ability of a cell to respond to varying afferent signal strength despite an "all or none" response of the action potential; why?

Absolute refractory period-because during this phase another action potential is not possible because the membrane potential is not yet begun to be reestablished. Relative refractory period-Strong stimuli cause nerve impulses to be generated more often in a given time interval than do weak stimuli. Thus, stimulus intensity is coded for by the number of impulses generated per second, by frequency of impulse transmission, rather than by increases in the strength of the individual action potentials. This can only occur during relative prior to return to complete membrane potential.

Normally speaking, unlike those of us of slightly more advanced age and eyes that are beginning to wear out, the eye has the ability to focus light rights representing objects both near and far in the field of view. How is this accomplished? What is the process called and explain it. .

Accommodation. Accommodation is the process where the eye controls the relative strength of the lens. When the circulatar shaped ciliary muscles are relaxed the overall diameter of the muscle group increases. This process results in a pulling force on the ligaments attached to the muscle group and to the lens which is suspended in the middle of the muscular circle. The applied force stretches the lens flattening it make it a weak convex shape. This is the default enabling long distance vision. The eye adjusts to short distance vision by inducing contraction of the muscle group relaxing the tension applied to the lens and it returns to its default more thick convex shape increasing its strength. This allows for convergence of divergent light rays entering the lens from the objects a relative short distance away.

CLOSELY examine the graph below. Which of the following transport methods is being utilized to transfer the substance INTO the cell- diffusion down a concentration gradient; facilitated diffusion; active transport; it is impossible to tell with the information provided. WHY?

Active transport. Leveling off of the curve designates saturation of a carrier molecule, so carrier-mediated transport is involved. The graph indicates that active transport is being utilized instead of facilitated diffusion because the concentration of the substance in the intracellular fluid is greater than the concentration in the extracellular fluid is greater than the concentration in the extracellular fluid at all points until transport maximum is reached. Thus, the substance is being moved against a concentration gradient, so active transport must be the method of transport used.

What are the methods of cellular membrane transport related to signal transduction involving a neuron? Furthermore differentiate between them indicating what types of substances are transported by each method, and state whether each is a passive or active means of transport.

All are carrier mediated forms. Passive sodium and potassium gates involved in establishing membrane potential. Sodium and potassium pump involved in maintaining and reestablishing membrane potential requiring energy to pump against respective concentration gradients. This is the only transport that requires energy within this question. Sodium voltage gated channels and potassium gates involved in action potential. Chemical, electrical and mechanical gated channels for sodium involved in creation of graded potential. And one extra, Na chemical gated channels at post synaptic membrane.

Action potential steps

At resting state all gated Na and K channels closed. During depolarization phase (a), Na gates are open but K channels remain closed. During repolarization, Na inactivation gates close (b) the Na channels and K channels open (c). During hyperpolarization (d) both gates of Na channels have closed, but K channels remain open. Return to resting state (e).

Why is the communication flow unidirectional from presynaptic to post-synaptic neuron?

Because only the postsynaptic neuron has cell surface neurotransmitter receptors

In relation to the postsynaptic neuron's resting membrane potential threshold in what direction to does the potential go, and if more that one direction is possible distinguish between them.

Both toward and away from threshold. EPSP is excitatory postsynaptic potentials that occur at excitatory synapses and move a postsynaptic neuron toward its threshold.IPSP is inhibitory postsynaptic potentials that occur at inhibitory synapses and move a postsynaptic neuron away from its threshold

Differentiate between absolute and relative refractory period

During absolute refractory period another action potential is not possible because sufficient membrane potential has not been reestablished. During relative refractory period, enough membrane potential has been reestablished for another action potential to occur.

Define homeostatic control? How is this accomplished (include in your answer the interacting components of a control system)?

Dynamic state of equilibrium, balance or status quo in which internal conditions vary, but always within narrow limits. A change in the controlled variable is sensed by receptors in the control center, which increasing release of positive effecting control aspect to increase controlled variable concentration. The increased concentration is sensed by control center and will decrease subsequent release of positive control aspect.

Differentiate between EPSP and IPSP.

EPSP is excitatory postsynaptic potentials that occur at excitatory synapses and move a postsynaptic neuron toward its threshold.IPSP is inhibitory postsynaptic potentials that occur at inhibitory synapses and move a postsynaptic neuron away from its threshold

When does a cell have to expend energy to transport a substance across its plasma membrane?

Energy is required to concentrate a solute across a membrane against its concentration gradient.

Compare Fick's Law to carrier mediated transport.

Fick's Law is passive and obeys the restrictions as detailed in question 11. Carrier mediated transport is dependent upon a carrier molecule in the plasma membrane which transports the substance across the plasma membrane. Characteristics of carrier mediated transport are specificity, saturation, and competition.

What is the type of potential created at the immediate postsynaptic neuron?

Graded potential.

Define the 3 underlying concepts or ideas for physiology.

Hierarchy of structural organization-the is a defined order progressing from molecular level through cell, tissue, organ, organ system, to organism level Complementarity of structure and function- anatomy and physiology are inseparable because function alwas follows structure, o what a structure can do is dependent on its specific form. Homeostasis- dynamic state of equilibrium or status quo in which internal conditions vary, but always within relatively narrow limits.

Explain the difference between intrinsic and extrinsic control

Intrinsic control is local control mechanisms inherent to an organ or a tissue. Extrinsic control is regulatory mechanisms initiated outside of an organ or a tissue.

What is the physical basis of memory and what are the different forms of memory

Memory is based not on individual cells but on a pathway of cells referred to as memory trace resulting from new synapses or existing synapses being modified to make transmission easier. The three different forms of memory are immediate, short-term and long-term.

Compared to the resting potential, would the membrane potential become more negative or more positive if the membrane were more permeable to Na+ than to K+? Why? Describe a possible situation where this would occur if it occurs.

More positive. Because the electrochemical gradient for Na+ is inward the membrane potential would become more positive as a result of an increased influx of Na+ into the cell if the membrane were more permeable to Na+ than to K+. This is what happens during the rising phase of an action potential once threshold potential is reached.

standard neuron

Neurons are composed of a cell body (soma) where a majority of their cellular organelles are located, and several projections from the cell body that are classified as dendrites and axons. Projecting from the cell body are dendrites that receive synaptic input from axon terminals from other neurons. The dendrites and soma surface receive information (afferent) while the axons transmit information (efferent). At axodendritic synapses (or terminal axon buds within the synaptic cleft), neurotransmitters are released from axon terminals onto the dendrites to generate a change in membrane potential. This allows the integration of numerous synaptic inputs onto the cell body. The action potential travels along the length of the axon in one direction until it reaches the axon terminal, where a synapse is formed for the transfer of signal to the next neuron or effector organ. Graded potentials occur at soma, dendrites and possibly the axon hillock whereas action potentials occur along the length of the axon.

Do the transport processes regulated by Fick's Law require energy input from the cell?

No. Solutes according to Ficks Law will passively transport down their concentration gradient.

Explain the difference in positive feedback and negative feedback control.

Positive feedback- As the controlled variable increases this results in more release of controlled variable Negative feedback- As the controlled variable increases this results in less release of controlled variable

what enables discrimination between signal strength during action potential transmission.

Relative refractory period-Strong stimuli cause nerve impulses to be generated more often in a given time interval than do weak stimuli. Thus, stimulus intensity is coded for by the number of impulses generated per second, by frequency of impulse transmission, rather than by increases in the strength of the individual action potentials. This can only occur during relative prior to return to complete membrane potential.

The rate at which the Na+-K+ pump operates is not constant but is controlled by a combined effect of changes in ICF Na+ concentration and ECF K+ concentration. Do you think a decrease in both ICF Na+ and ECF K+ concentrations would accelerate or slow down the Na+-K+ pump? What would be the benefit of this response?

SLOW DOWN During an action potential, Na+ enters and K+ leaves the cell. Repeated action potentials would eventually "run down" the Na+ and K+ concentration gradients were it not for the Na+-K+ pump returning the Na+ that entered back to the outside and the K+ that left back to the inside. Indeed, the rate of the pump activity is accelerated by the increase in both ICF Na+ and ECF K+ concentrations that occurs as a result of action potential activity, thus hastening the restoration of the concentration gradients. Therefore, as the concentration differences are decreased there is less work to be performed to restore concentration gradients therefore the pump slows down.

Explain the interrelationship between the myelin sheath and the neurilemma. These cell components are associated with what cell? What is the physiological role provided by this cell in regard to communication?

Schwann cells are comprised of multiple wrappings of cell membrane excluding most of cytoplasm and the nucleus. Most of the cytoplasm and the nucleus is exclude into the outer wrapping layer called the neurilemma.Signal transduction rates are controlled by salatory conduction. Schwann cells literally wrap around specific aspects along the axon creating areas of insulation. The nodes of Ravier are the areas along the axon not covered by Schwann cells. Charge polarity changes progressing along the plasma membrane surface of the axon only occur at nodes of Ravier, skipping areas covered by Schwann cells. We can assume for this process that the movement of charges in the ICF between nodes is essentially instantaneous. Therefore, the effective length for transduction is ONLY the combined length of the nodes.

If multiple afferent axons is firing in the same time frame with convergence on the efferent neuron

Spatial summation occurs when the postsyanaptic neuron is stimulated by a large number of terminals form the same or different neurons at the same time which sum to threshold.

Compare the expected changes in membrane potential of a neuron stimulated with a subthreshold stimulus, a threshold stimulus, and a suprathreshold stimulus.

Subthreshold stimulus would transiently depolarize the membrane but not sufficiently to bring the membrane to threshold, so no action potential would occur. For a threshold stimulus, the stimulus will bring the membrane to threshold thus an action potential would occur. For suprathreshold stimulus an action potential of the same magnitude and duration would occur as to a threshold stimulus. Because of the all-or-none law, a stimulus would not produce a larger action potential BUT the magnitude as the stimulus is coded in the frequency of action potentials

Differentiate between temporal and spatial summation.

Temporal summation occurs when one or more presynaptic neurons transmit impulses in rapid-fire order and waves of neurotransmitter release occur in quick succession. The first impulse produces a slight EPSP followed by addition EPSP impulses by subsequent impulses summing to threshold. Spatial summation occurs when the postsyanaptic neuron is stimulated by a large number of terminals form the same or different neurons at the same time which sum to threshold.

what determines the rate of action potential transmission along the axon.

The speed that an action potential can move along the axon is dependent upon the electrical resistance of the axon. The electrical resistance of the axon is determined by the diameter of the axon, with the larger diameter axon having a lower resistance (conduction velocity will be greater) than a smaller diameter axon. In axons that are myelinated, action potentials will occur at discrete points along the axon, known as the nodes of Ranvier, Thus, the action potential jumps from node to node (saltatory conduction). The resistance of the membrane under the insulative myelin sheath is great enough that there is only a small amount of current lost as it moves between nodes. Because the action potential is jumping from node to node, the speed of the action potential along the axon is greatly increased.

why under normal physiological circumstances an action potential is unidirectional.

Unidirectional propagation is a result of the absolute refractory period, the duration time following the initiation of an action potential in which a second action potential can not be generated. Thus, since an action potential initiates at the axon hillock signal propagation proceeds unidirectionally away from the hillock down the axon.

Assume that a membrane permeable to Na+ but not to Cl- separates two solutions. The concentration of sodium chloride on side 1 is much higher than on side 2. Which of the following ionic movements would occur? Why? Na + would move until its concentration gradient is dissipated (i.e. until the concentration of Na+ on side 2 is the same as the concentration of Na+ on side 1). Cl- would move down its concentration gradient from side 1 to side 2. A membrane potential, negative on side 1, would develop. A membrane potential, positive on side 1, would develop. None of the above is correct.

c. Na moves from side 1 to 2 because of its concentration gradient. Cl remains on side 1. This creates unbalanced charges thus a membrane potential with negative on side 1 because Cl does not move across membrane. Na does not continue to move till concentration equilibrium is reached because of opposing electrical gradient.

equilibrium potential

potential that exists when the net outward diffusion of an ion no longer occurs but is in equilibrium due to the balance between its electrical gradient and its concentration gradient.