Week 2

Neurophysiology

What is information processing according to neurophysiology?

Where bioelectrical signals within a neuron (AP) cause a neurotransmitter release (synaptic neurotransmission) that alters the excitability of postsynaptic neurons

Where is the starting point for understanding information processing cells in the nervous system?

Membrane potential

Why is there a difference in voltage potential between intracellular and extracellular spaces?

Typically, there is a surplus of negative charges inside a cell and surplus of positive charges outside a cell

How would you calculate membrane potential?

V(memb) = V(inside) - V(outside)

Membrane potential inside a resting neuron is what?

-70 mV

In regard to membrane potential, what does it mean when a cell is polarized?

It can change to something else

In regard to membrane potential, what does it mean when a cell is depolarized?

The inside of a cell becomes less negative (-70 mV to -50 mV)

In regard to membrane potential, what does it mean when a cell is hyperpolarized?

The inside of a cell becomes more negative than the resting potential (-60 mV to -90 mV)

When will a cell fire?

Depolarized

Since lipid bilayer is impermeable to ions, how do ions cross the membrane?

Ion channels, pumps, and carrier proteins

Where do ions that cross the membrane through an ion channel move?

Down a concentration gradient (fast and energy-free)

How do ion pumps move ions across the membrane?

Against their concentration gradient (slow and requires energy)

Which pump is largely responsible for high intracellular K+ and low intracellular Na+?

Sodium-potassium pump

During each cycle of the sodium-potassium pump, what and how many ions are transported?

3 Na+ ions out and 2 K+ ions in

Sodium-potassium pumps move ions how?

Against their concentration gradients

Does the sodium-potassium pump require energy?

Yes via hydrolysis of ATP

Why does the sodium-potassium pump operate continuously?

To counter diffusion of ions across leak channels down their electrochemical gradient

Cells that are excitable are able to do what?

Generate an action potential

Action potentials will always precede what?

Chemical communication

What is the function for action potentials in neurons?

Bioelectrical signal from cell body to cause transmitter release at axon terminals

Where do the phases of action potentials occur?

Within node of ranvier

In muscle cells, what do action potentials cause?

The release of intracellular stores of Ca++ that forms actin-myosin cross bridges to achieve contraction of muscle cell

What is the most common demyelinating disorder?

Multiple Sclerosis (MS)

Demyelination of axons during MS causes what in regard to action potentials?

It slows or causes a blockade of action potential propagation

Why are deep tendon reflexes impaired or absent in someone with Guillain-Barre Syndrome?

Because GBS knocks out the peripheral nerves that make reflexes work

GBS’s autoimmune response to Schwann cells causes what?

Demyelination of peripheral nerves

When do signs and symptoms often reach their peak in GBS?

Within four weeks

What is the percentage of patients who recover completely with GBS?

70%

What is the percentage of patients who have permanent neurologic deficits after having GBS?

25%

What is the percentage of patients who die with GBS?

5%

What is the site of inter-neuronal communication?

Synapses

What happens when an action potential invades the presynaptic neuron terminal?

Neurotransmitter is released by way of exocytosis

Neurotransmitter release is mediated by what?

Transient increase in cytoplasmic concentration of Ca++ in axon terminal

Synaptic vesicles are recycled

True

How is the action of neurotransmitter on postsynaptic neuron determined?

By the receptor subtype to which it binds

Neurotransmitter has an intrinsic + or - effect

False

Glycine and GABA receptor activation is always what?

Inhibitory

Glutamate and aspartate receptor activation is always what?

Excitatory

What causes postsynaptic potentials (PSPs)?

Ion channels interacting with a neurotransmitter from the presynaptic neuron

Localized to the site of the synapse, excitatory postsynaptic potentials (EPSPs) are what?

Depolarizing - making them more likely to fire an action potential

Localized to the site of the synapse, inhibitory postsynaptic potentials (IPSPs) are what?

Hyperpolarizing - making them less likely to fire an action potential

In neuron excitability, synaptic inputs generate what?

Active currents in the postsynaptic membrane

Where do active currents spread through?

Postsynaptic membrane and extracellular fluid

In regard to neuron excitability, what generates currents that spread down an axon?

Action potential (AP)

What are postsynaptic potentials (PSPs)?

Changes in the postsynaptic neuron’s membrane potential when in the vicinity of the synapse