Chapter 7: Neurons and Electrical Signaling

Vocabulary and key concepts regarding neuron anatomy, structural/functional classes, membrane potentials, and the mechanics of electrical signaling from Chapter 7.

Central Nervous System (CNS)

The division of the nervous system consisting of the brain and spinal cord.

Peripheral Nervous System (PNS)

All nervous structures located outside the central nervous system.

Soma

The cell body of a neuron, containing the nucleus and most organelles.

Kinesin protein

A motor protein responsible for the axonal transport of vesicles from the soma toward the axon terminals.

Leak channels

Ion channels that are always open and located all over the neuron; there are significantly more of these for $K^+$ than for $Na^+$.

Ligand-gated channels

Ion channels that open or close following the binding of a ligand to a receptor; they are densely located in the dendrites and soma.

Voltage-gated channels

Ion channels that open or close in response to changes in membrane potential; $Na^+$ and $K^+$ types are most dense in the axon and hillock, while $Ca^{++}$ types are densest in the terminal.

Bipolar neuron

A structural class of neuron characterized by having one dendrite and one axon.

Pseudo-unipolar neuron

A structural class of neuron with a peripheral axon and a central axon extending from the cell body.

Multipolar neuron

A structural class of neuron with multiple dendrites and a single axon.

Tract

A group of axons traveling together within the Central Nervous System ($CNS$), constituting white matter.

Nucleus

A group of neuronal soma located within the Central Nervous System ($CNS$), constituting grey matter.

Nerve

A group of axons traveling together in the Peripheral Nervous System ($PNS$); these structures are classified as organs.

Ganglion

A group of neuronal soma found within the Peripheral Nervous System ($PNS$).

Membrane Potential ($V_m$)

The difference in voltage across the plasma membrane, typically around $-70\,mV$ in a resting neuron.

Equilibrium Potential ($E_x$)

The specific electrical force needed to equally oppose the chemical driving force of an ion across the membrane.

$$E_{Na}$$

The equilibrium potential for sodium, which is precisely $+60\,mV$.

Depolarization

A change in the local membrane potential where the inside of the cell becomes less negative (more positive) compared to the resting potential.

Hyperpolarization

A change in the membrane potential where the inside of the cell becomes more negative than the resting potential.

Graded Potentials

Small, decremental changes in $V_m$ that occur when ion channels open or close; the signal magnitude decreases as it moves away from the stimulus site.

EPSP (Excitatory Postsynaptic Potential)

An excitatory graded potential that results in depolarization of the membrane.

IPSP (Inhibitory Postsynaptic Potential)

An inhibitory graded potential that results in hyperpolarization of the membrane.

Temporal Summation

The process where multiple stimuli from the same source occur close enough together in time to sum and reach threshold.

Spatial Summation

The process where stimuli from different sources arrive at the axon hillock simultaneously and are added together.

Action Potential (AP)

A rapid, non-decremental depolarization that reverses the $V_m$ and propagates long distances along the axon.

Threshold

The critical level of depolarization (typically $-55\,mV$) required to trigger an action potential.

Absolute Refractory Period

A phase during and immediately after an action potential where no stimulus, no matter how strong, can generate a second action potential.

Relative Refractory Period

A phase following the absolute refractory period where a stimulus stronger than normal is required to generate a second action potential.

Saltatory Propagation

The rapid conduction of an action potential along a myelinated axon, where the signal jumps between nodes of Ranvier.

Node of Ranvier

The gap in the myelin sheath of an axon where voltage-gated channels are exposed.

A fibers

A class of nerve fibers with large diameters and myelin that provides the fastest propagation speeds.

C fibers

A class of nerve fibers with small diameters and no myelin, resulting in the slowest propagation speeds.

Tetrodotoxin (TTX)

A neurotoxin that specifically blocks voltage-gated $Na^+$ channels.

Peripheral Neuropathy

Irreversible damage to nerves preventing proper signal transmission; approximately $30\%$ of cases are associated with diabetes.