Signal Transduction: Electrical and Synaptic Signaling in Neurons

Comprehensive practice questions covering neuronal structure, resting and action potentials, ion channel mechanics, and synaptic transmission based on the lecture notes.

What are the two main types of cells in the nervous system?

Neurons, which send and receive electrical impulses, and glial cells.

How do sensory neurons differ from motor neurons?

Sensory neurons are specialized for the detection of stimuli, while motor neurons transmit signals from the CNS to muscles and glands.

What is the function of Interneurons?

They process signals and transmit information between different parts of the nervous system.

Which glial cells are responsible for forming the blood-brain barrier?

Astrocytes, which control access of blood-borne components into the extracellular fluid.

What are the roles of Oligodendrites and Schwann cells?

They form the insulating myelin sheath around neurons in the CNS and peripheral nerves, respectively.

What is the function of Microglia?

They fight infections and remove debris within the nervous system.

Distinguish between dendrites and axons.

Dendrites are processes that receive signals, whereas axons are processes that conduct signals away from the cell body.

Define axoplasm.

The cytosol within an axon.

What are the nodes of Ranvier?

Gaps in the discontinuous myelin sheath that insulate segments of the axon.

What is a synapse?

The junction where a synaptic terminal of an axon passes information to a nerve cell, gland, or muscle cell.

What is the difference between ion pumps and ion channels?

Ion pumps use energy ($ATP$) to move ions against concentration gradients, while ion channels allow ions to move along their concentration gradients.

Define membrane potential.

The voltage (difference in electrical charge) across the plasma membrane of a cell.

What is the typical resting potential of a neuron?

Approximately $-60\,mV$.

Describe the ion concentrations in a mammalian neuron at resting potential.

Inside the cell, the concentration of $K^+$ is highest ($140\,mM$), while outside the cell, the concentration of $Na^+$ is highest ($145\,mM$).

What is the stoichiometry of the $Na^+/K^+$ pump?

It continually pumps three $Na^+$ ions out of the cell for every two $K^+$ ions it pumps into the cell.

What produces the major source of membrane potential in a resting neuron?

The buildup of negative charge within the neuron resulting from $K^+$ diffusing out of the cell through leak channels.

What effect does $Na^+$ flowing into the cell have on membrane potential?

It drives the potential in a positive direction, causing depolarization.

How does increased membrane permeability to chloride affect excitability?

It decreases excitability by causing hyperpolarization (making the membrane potential more negative).

What is an action potential?

A rapid set of changes in membrane potential where the potential moves from negative to positive and back again.

Which alpha helix in voltage-gated sodium channels acts as the voltage sensor?

$$S4$$

What is the Hodgkin cycle?

A positive feedback loop where membrane depolarization leads to the opening of $Na^+$ channels, increasing $Na^+$ influx, which further depolarizes the membrane.

Describe the potential changes during the repolarizing phase of an action potential.

The potential falls from a peak of about $+40\,mV$ back toward a negative value due to $Na^+$ channel inactivation and the opening of voltage-gated $K^+$ channels.

What occurs during the hyperpolarizing phase (undershoot)?

The membrane potential temporarily drops to about $-75\,mV$, which is below the resting potential, due to increased $K^+$ permeability.

What is the absolute refractory period?

A brief time after an action potential when it is impossible to trigger a second one because sodium channels are inactivated.

What is saltatory propagation?

The rapid jumping of action potentials from one node of Ranvier to the next in myelinated neurons.

How does an electrical synapse differ from a chemical synapse?

In electrical synapses, neurons are connected by gap junctions for direct ion movement; in chemical synapses, neurons are separated by a synaptic cleft and communicate via neurotransmitters.

Distinguish between ionotropic and metabotropic receptors.

Ionotropic receptors are ligand-gated ion channels, while metabotropic receptors exert effects indirectly via a system of messengers.

Give examples of inhibitory neurotransmitters.

$\gamma$-amino butyric acid (GABA) and glycine.

What is the difference between an agonist and an antagonist in cholinergic systems?

Antagonists compete with acetylcholine to prevent depolarization, while agonists bind the receptor to cause depolarization but cannot be rapidly inactivated.

What ion concentration directly controls neurotransmitter secretion at the synaptic bouton?

Calcium ion ($Ca^{2+}$) concentration.

What is synaptotagmin's role in neurotransmitter release?

It binds $Ca^{2+}$ in the boutons, undergoes a conformational change, and promotes the interaction of t- and v-SNAREs for vesicle docking.

Define kiss-and-run exocytosis.

A transient method of release where a vesicle temporarily fuses with the plasma membrane, releases neurotransmitter, and then reseals.

How does Acetylcholinesterase inactivate a signal?

It hydrolyzes acetylcholine into acetic acid and choline.

Give an example of a drug that acts by blocking neurotransmitter reuptake.

Prozac, which is used as an antidepressant.