Neurophysiology pages

I. Resting Potential All neural activity begins with a change in the resting membrane potential of a neuron The resting membrane potential is -70mV (the minus indicating the interior is negatively charged) Passive leak channels and the sodium- potassium pump maintain the resting membrane potential (RMP).

The diffusion of potassium K+ and sodium Na+ ions along their electrochemical gradients is responsible for creating the resting membrane potential.

Chemical gated channels: open when they bind to specific chemicals (neurotransmitters). Voltage gated channels: open or close in response to changes in the “trans- membrane” potential. Mechanical gated channels: open in response to physical distortion of membrane surface. Gated channels present on the plasma membrane open or close in response to a specific stimuli. In turn, changing the trans-membrane potential.

II. Graded Potentials Temporary, localized change in the RMP. Opening of gated channels creates a change in the permeability of Na+ or K+ ions. Depolarization: a shift towards a less negative value in the trans-membrane potential. Hyperpolarization: a shift in a more negative trans- membrane potential. The stronger the stimulus the greater the change in the trans-membrane potential. Graded potentials will decrease with distance.

Question 1:A neuron whose polarization has changed from -70 mV to -68 mV a. shows depolarization b. has received excitation from other neurons c. a. and b. are both correct d. neither Question 2:An electrode records the following voltages from inside the dendrites of a neuron. Which of the following polarizations reflects the strongest inhibitor? a. -60 mV b. -72 mV c. -78 mV d. -68 mV

III. Action Potential Propagated (spread out) changes in the trans- membrane potential. Dependent upon voltage-gated channels. Threshold: depolarization of trans-membrane potential where voltage-gated channels open (-55 mV) Occur at the axon hillock of a neuron cell body. “All-or-none-principle”: stimulus either triggers or fails to trigger an action potential.

Question 1: What event(s) happen at the stimulus threshold (-55 mV)? a. voltage-gated sodium (Na+) channels open b. voltage-gated potassium (K+) channels open c. both d. neither Question 2: At -60 mV to +30 mV, which ions cross the membrane and in which direction will they cross? a. Na+ out of neuronc. K+ out of neuron b. Na+ into neurond. K+ into neuron

Question 3: What event(s) happen at +30 mV? a. sodium (Na+) channel inactivation b. voltage-gated potassium (K+) channels open c. both d. neither Question 4: Which statement is true of the refractory period? a. Sodium (Na+) channels remain inactivated b. potassium (K+) channels begin closing c. membrane cannot respond to further stimulation d. all of the above

Propagation of an Action Potential (continuous vs. Saltatory) Continuous: – unmyelinated axons – relatively slow (1 meter/second) Saltatory: – myelinated axons – fast (100 meters/second)

IV. Postsynaptic Potentials Graded potentials that develop on the postsynaptic membrane in response to a neurotransmitter. Two types of postsynaptic potentials: – excitatory (EPSP) depolarization of postsynaptic membrane – inhibitory (IPSP) hyperpolarization of postsynaptic membrane

Summation of Postsynaptic Potentials (summation: cumulative effect) Temporal summation: – single synapse is active repeatedly – “machine gun” Spatial summation: – multiple synapses that are active simultaneously. – “firing squad”

Question 1: A postsynaptic neuron receives temporal EPSPs from four sources. They are as follows: E1= +2 mV; E2= +1 mV; E3= +3 mV; E4= +1 mV. Assuming the resting membrane potential is -70mV, what will the polarization be in response to the four EPSP? a. -77 mV c. -63 mV b. 77 mVd. 63 mV Question 2: Will the above postsynaptic potentials result in an action potential? a. yesb. no

Question 3:Assuming the resting membrane potential is -70 mV, what will the final polarization of a neuron be if the following synapses are active simultaneously? E1= +1 mV; E2= +3 mV; E3= +4 mV; I1= -1 mV; I2= -2 mV a. -74 mV b. 65 mV c. -65 mV d. 60 mV Question 4:What type of summation is described in the above question? a. temporal b. spatial

V. Information Processing Integration of stimuli at the level of the individual neuron is the simplest form of information processing. Factors influencing the response of the postsynaptic neuron – neurotransmitters – extracellular chemicals – regulatory neurons – frequency of action potentials

Pufferfish for dinner? Better have an experienced sushi chef

Fugu is Japanese for pufferfish and the dish prepared from it. Research the neurophysiology behind fugu and answer the questions below. Hand in for an extra credit card. 1.What is the name of the toxin 2.What happens to an individual who consumes the toxin. 3.Neurology: Describe in detail the neurophysiology behind the toxin. Description should include, but not limited to the following terms; sodium gated channels, depolarization, threshold, action potential, propagation, neuromuscular junction, muscle contraction. 4.Is the victim conscious or unconscious when poisoned?