2.1 Membrane Potential

Write out the functions of neuronal dendrites, cell body, axon hillock, axon, axon terminal, myelin sheath, dynein, and kinesin.

Dendrite: Branches of neurons that receive information and transmit toward the cell body. Cell body: Central region of neuron containing the nucleus. Axon hillock: Initial region of axon, where action potentials are often initiated. Axon: Branch of neuron carrying information away from the cell body. Myelin sheath: Layers of plasma membrane wrapping around axon, produced by glial cells, which speed up information transmission. Dynein: Motor protein that moves materials along the cytoskeleton of the axon toward the cell body. Kinesin: Motor protein that moves materials along the cytoskeleton of the axon away from the cell body.

Use the Nernst equation to calculate the equilibrium potential for K+ if the concentration of K+ inside the cell was 150 mmolar and the concentration of K+ outside of the cell was 15 mmolar.

Equilibrium potential = 61 mvolts * z * log (concentration out/in)Z = 1 for K+, so this reduces to 61 mvolts * log(15/150 = 61 * log(1/10) = 61 * -1 = -61 mvolts

Explain in your own words why the resting membrane is close to the potassium equilibrium potential. Why is the resting potential not the same as the potassium equilibrium potential?

For most cells, at rest, the permeability of the membrane to potassium is much greater than the permeability of the membrane to sodium (or other ions such as calcium). For a resting neuron (or other type of cell) potassium leak channels tend to be open and most other channels are closed. Therefore, potassium leaks out of the cell down its concentration gradient, producing a negative membrane potential. If potassium was the only ion leaking, then the membrane potential would be identical to the potassium equilibrium potential. However, some positive ions do leak (e.g. small sodium leak in), causing the membrane potential to be less negative than the potassium equilibrium potential.

Predict the effect of raising the extracellular K+ to a value exactly equal to the intracellular K+ on membrane potential.

If potassium levels were equal inside and outside of the cell, there would be no potassium movement across the membrane, and the membrane potential would be near zero (assuming no other changes ion channels-in reality, this might trigger an opening of voltage-gated sodium channels-but that is for a later section).

Write out the normal concentration of Na+ and K+ in mammalian cells. What causes these concentration differences?

Na+ levels are high outside of the cell (145 mmolar) relative to inside of the cell (15 mmolar). K+ levels are high inside the cell ( 150 mmolar) relative to outside of the cell (5 mmolar). This ionic difference is caused by the Na+/K+ pumps in the plasma membrane.

Write out and explain Ohm's law. How will an increase in resistance affect current flow, assuming the voltage across the resistor is constant? How will an increase in resistance affect voltage across the resistor, assuming that the current is constant?

Ohm's law: V = IR or I = V/R, where V is voltage, I is current, and R is resistance.If R increases, and V is constant, then current flow will decrease. If R increases and I is constant, then V will increase.

List the types of glial cells and their functions.

Oligondendrocytes (CNS)/Schwann (PNS) help form the myelin sheath of the axons. Astrocytes help regulate ionic and nutritional composition of the cerebrospinal fluid bathing the brain, stimulate the capillaries of the brain to form the blood-brain barrier by forming tight junctions between the capillary epithelial cells, provide nutrients and remove wastes for neurons, guide growing neurons to proper destination, participate in information signaling. Microglia cells act like macrophage cells that preform immune functions in the CNS and may contribute to synapse remodeling and plasticity. Ependymal cells help regulate the production of cerebral spinal fluid.

Which classes of neurons are most likely to repair themselves after damage?

Peripheral neurons (afferent and efferent) are more likely to repair themselves than interneurons in the central nervous system.

How are neurons plastic in their structure and how does it change with age?

The structure of neurons can change dramatically, with many neurons being destroyed with age, and other developing from stem cells. Most importantly, which neurons are connected by synapses, and the strength of those neuronal connections can vary. These structural changes are associated with changes in experience. The capacity of the brain to change in structure declines with age.

Why would a cell with these ion concentrations, and only K+ channels open, have a membrane potential of -90 mvolts?

With only K+ channels open, K+ diffuses out of the cell down its concentration gradient. As this occurs, the membrane potential becomes more negative inside (positives are leaving). As can be calculated by the Nernst equation, when the membrane potential reaches -90 mvolts, the electrical attraction pulling K+ in exactly equals the concentration force pushing K+ out.

Suppose that the concentration of K+ inside the cell was 10, and the concentration of K+ outside of the cell was 100 mmol/l. Assuming 37C, the K+ equilibrium potential is ________. a. -70 mV b. +61 mV c. -61 mV d. -90 mV

b. +61 mV

Blocking the voltage-gated sodium channels will have what effect on the action potential? a. The membrane potential will be more positive than normal (greater depolarization) b. The membrane will not depolarize (no action potential) c. The membrane will depolarize but not repolarize d. The membrane will hyperpolarize

b. The membrane will not depolarize (no action potential)

Assuming normal concentrations of all ions inside and outside of the cell, and that K+ and Cl- channels are blocked but Na+ channels are open, the membrane potential will be ________. a. 70 mV b. -60 mV c. + 60 mV d. +30 mV

c. + 60 mV

A drug that blocked the Na+/K+ ATPase would have what effect on ion concentrations and the membrane potential? a. The ion concentrations across the membrane would immediately equalize and the membrane potential would go to zero. b. Ion concentrations would slowly equalize, and over time, the membrane potential would become more negative. c. Ion concentrations would slowly equalize, and over time, the membrane potential would go toward zero. d. Ion concentrations would not change, but the membrane potential would go to zero.

c. Ion concentrations would slowly equalize, and over time, the membrane potential would go toward zero.

Which classes of neurons are most likely to repair themselves after damage? a. Afferent neurons b. Efferent neurons c. Interneurons d. A and B e. A, B and C

d. A and B