Chapter 7: Nerve Cells and Electrical Signaling

Vocabulary practice flashcards covering nerve cell structure, classifications, transport mechanisms, resting membrane potential, ion channels, graded potentials, and action potential dynamics from Chapter 7: Nerve Cells and Electrical Signaling.

Central nervous system (CNS)

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

Peripheral nervous system (PNS)

The division of the nervous system composed of cranial and spinal nerves that handles afferent input and efferent output.

Afferent neurons

Neurons that transmit sensory and visceral information from peripheral receptors to the CNS; structurally bipolar or pseudo-unipolar.

Efferent neurons

Neurons that transmit motor commands and information from the CNS to effector organs such as muscles and glands; structurally multipolar.

Interneurons

Multipolar neurons located entirely within the CNS that account for $99\%$ of all neurons and perform all CNS functions.

Dendrites

Branching neuronal processes that receive incoming signals and information from other neurons.

Cell body (soma)

The central part of a neuron that houses the nucleus and organelles.

Axon hillock

The specialized region connecting the soma to the axon where action potentials are initiated and generated.

Axon

A long nerve fiber extending from $1\,\text{mm}$ to $1\,\text{m}$ in length that propagates action potentials away from the soma toward the terminal.

Axon terminals

Specialized distal endings of an axon that store and release neurotransmitters across synapses to communicate with postsynaptic cells.

Multipolar neuron

The most common structural classification of neuron, characterized by multiple dendrites and a single axon extending from the cell body.

Bipolar neuron

A structural class of sensory neuron possessing two distinct projections from the cell body: one dendrite and one axon; found in vision and olfaction.

Pseudo-unipolar neuron

A structural class of sensory neuron possessing a single projection from the cell body that divides into a peripheral axon in the periphery and a central axon extending to the CNS.

Ganglion

A cluster of neuronal cell bodies located outside the CNS in the peripheral nervous system.

Kinesins

Motor proteins that walk along microtubules carrying vesicles filled with neurotransmitters and enzymes formed in the soma down the axon.

Anterograde transport

Axonal transport of materials from the cell body (soma) to the axon terminal.

Retrograde transport

Axonal transport of materials from the axon terminal back toward the cell body (soma).

Astrocytes

Glial support cells located in the CNS that link neurons to blood vessels.

Microglia

Glial support cells located in the CNS that interact neuron-to-neuron to maintain cellular health.

Oligodendrocytes

Glial cells in the CNS that form myelin sheaths around axons, with each cell extending processes to myelinate segments of multiple axons.

Schwann cells

The only glial cells located in the PNS, each providing a myelin sheath segment for a single axon.

Nodes of Ranvier

Unmyelinated gaps along an axon between adjacent myelin sheath segments where most ion movement takes place.

Resting membrane potential (RMP)

The baseline electrical potential difference across the plasma membrane when a cell is not actively sending or receiving signals, approximately $-70\,\text{mV}$ in neurons.

Leak channels

Nongated ion channels that are always open; neurons possess approximately $25$ times more $\text{K}^+$ leak channels than $\text{Na}^+$ leak channels, establishing the resting membrane potential.

$$\text{Na}^+/\text{K}^+\text{ pump}$$

An active transporter ($\text{Na}^+/\text{K}^+\text{ ATPase}$) that pumps $3\,\text{Na}^+$ out of the cell and $2\,\text{K}^+$ into the cell against their gradients to counteract leak channels.

Ligand-gated channels

Ion channels that open or close in response to the binding of a specific chemical messenger or ligand.

Mechanically-gated channels

Ion channels that open or close in response to mechanical force, distortion, or pressure applied to the membrane.

Voltage-gated channels

Ion channels that open or close in response to changes in the membrane potential ($V_m$).

Depolarization

A change in membrane potential that makes the inside of the cell more positive, moving away from resting potential toward positive values.

Repolarization

A change in membrane potential where the voltage returns toward the resting membrane potential (becoming more negative back toward $-70\,\text{mV}$).

Hyperpolarization

A change in membrane potential that makes the inside of the cell more negative than the resting membrane potential (moving away from $-70\,\text{mV}$ toward $-85\,\text{mV}$).

Graded potentials

Small, temporary changes in membrane potential that vary in magnitude with stimulus intensity, conduct decrementally, and do not reach the $-55\,\text{mV}$ threshold.

Threshold

The critical membrane potential (typically $-55\,\text{mV}$ in neurons) that must be reached to open voltage-gated $\text{Na}^+$ channels and trigger an action potential.

Temporal summation

The additive effect when a stimulus is applied repeatedly in rapid succession from a single source so that graded potentials summate before dissipating.

Spatial summation

The additive effect when graded potentials from different sources occurring close together in time combine at the axon hillock.

Action potential

A rapid, large depolarization of an excitable membrane (from $-70\,\text{mV}$ to $+30\,\text{mV}$) that functions as an all-or-none communication signal propagated without decrement.

Absolute refractory period

The period spanning depolarization and most of repolarization ($1\text{--}2\,\text{ms}$) during which a second action potential cannot be generated regardless of stimulus strength because voltage-gated $\text{Na}^+$ channels are inactivated.

Relative refractory period

The period following the absolute refractory period when an action potential can be generated only by a stronger-than-normal stimulus because some $\text{Na}^+$ channels are reset while elevated $\text{K}^+$ outflow continues.

Saltatory conduction

The rapid propagation of action potentials along myelinated axons where electrical signals leap from one node of Ranvier to the next, reaching speeds up to $100\,\text{m/s}$.

Frequency coding

The mechanism by which the nervous system communicates stimulus intensity through the frequency of action potentials rather than changes in their magnitude.

Multiple sclerosis

A neurodegenerative disease in which the immune system destroys myelin sheaths surrounding axons, impairing action potential propagation.