Micro-Anatomy and Physiology of Neurons

Vocabulary practice flashcards covering neuronal anatomy, cell types, glial functions, electrical signaling, and the ionic basis of action potentials based on the lecture notes.

Soma

Also called the cell body, this region contains the nucleus and is part of the neuronal input zone.

Dendrites

The branching processes of a neuron that receive inputs from other cells and form part of the input zone.

Dendritic Spines

Small protrusions on dendrites that serve as the primary sites of excitatory synapses.

Axon

The conducting zone of the neuron along which electrical signals or action potentials propagate.

Input Zone

The region consisting of the dendrites and soma where the cell receives neurotransmitters from other neurons.

Conducting Zone

The region formed by the axon that allows information to travel over long distances.

Output Zone

The region at the presynaptic terminals where neurotransmitters are released.

White Matter

An area of the nervous system characterized by a concentration of axons and their associated glia, such as oligodendrocytes.

Gray Matter

An area of the nervous system primarily composed of cell bodies and dendrites; it involves both the input and output zones (terminal synapses).

Reticular Theory

A 19th-century theory proposed by Camillo Golgi suggesting the nervous system is one big interconnected network of protoplasmic links.

Neuron Doctrine

The concept championed by Santiago Ramón y Cajal stating that neurons are individual, discrete functional units of the nervous system.

Unipolar Neuron

A neuron with a single process extending from the cell body.

Bipolar Neuron

A neuron with two distinct processes (one dendrite and one axon) coming off the cell body, commonly found in the retina.

Pseudo-unipolar Neuron

A cell found in the somatosensory system with one process that bifurcates into peripheral and central branches.

Multipolar Neuron

A neuron characterized by having one axon and many dendrites, appearing in various morphological complexities.

Amacrine Cell

A specialized type of retinal neuron that lacks an axon and can release neurotransmitter directly from its dendrites.

Purkinje Cell

A type of cerebellar neuron characterized by an extremely large and elaborate dendritic arborization to receive massive numbers of inputs.

Convergence

A circuit motif where a single downstream neuron receives inputs from multiple upstream neurons.

Divergence

A circuit motif where one upstream neuron activates multiple downstream neurons, amplifying the signal.

Afferent Neurons

Sensory neurons that convey information toward the central nervous system (CNS).

Efferent Neurons

Neurons that convey information away from the CNS toward effector organs like skeletal muscles.

Interneurons

Also called association neurons, these are situated within the CNS and are responsible for higher-order cognitive functions.

Oligodendrocytes

Glia in the Central Nervous System (CNS) that form myelin sheaths by spiraling their processes around axons to reduce leak current.

Schwann Cells

Glia in the Peripheral Nervous System (PNS) that perform myelinating functions similar to oligodendrocytes.

Microglia

The resident immune cells of the nervous system that scavenge debris and respond to activation by changing their morphology.

Astrocytes

Glia that buffer potassium ($K^+$), recycle neurotransmitters (like glutamate), influence synapse formation, and contribute to the blood-brain barrier.

Voltage

Used interchangeably with potential, it refers to the charge difference across the plasma membrane.

Current ($I$)

The flow of charged particles, such as $Na^+$, $K^+$, $Cl^-$, and $Ca^{2+}$, typically expressed in nanoamps ($nA$).

Resistance ($R$)

The amount of opposition to the movement of charged particles across an electrical path.

Conductance ($G$)

The inverse of resistance, often used interchangeably with the permeability of the membrane to specific ions.

Ohm's Law

The electrical relationship defined as $V = I \times R$, or $I = G \times V$, where $V$ is voltage, $I$ is current, and $R$ is resistance.

Receptor Potential

A brief increase in voltage caused by mechanical force or other stimuli at a sensory nerve ending.

Synaptic Potential

A brief change in voltage in a postsynaptic neuron following the release of neurotransmitter by a presynaptic cell.

Action Potential

An all-or-nothing electrical spike that occurs when a neuron's voltage surpasses a specific threshold, typically jumping from $-60\,mV$ to roughly $+30\,mV$.

Resting Membrane Potential

The stable charge difference across a neuron's membrane when at rest, typically between $-70\,mV$ and $-60\,mV$.

Passive Response

A voltage change that is proportional to the amount of injected current and does not require unique neuronal properties; it occurs in any cell.

Active Response

A response, such as an action potential, that occurs only in excitable cells due to unique membrane properties and only if threshold is reached.

Threshold

The specific voltage level (often illustrated as a red line on graphs) at which voltage-gated sodium channels open and an action potential is triggered.

Nernst Equation

An equation used to calculate the equilibrium potential for a single ion: $E_x = \frac{58}{z} \times \log_{10}\left(\frac{[X]_{out}}{[X]_{in}}\right)$, assuming room temperature and a 10-fold gradient.

Goldman (GHK) Equation

An equation that calculates the membrane potential by taking into account the relative permeabilities and concentrations of multiple ions ($Na^+$, $K^+$, and $Cl^-$).

Electrochemical Equilibrium

A state where the chemical concentration gradient favoring ion movement is exactly balanced by an opposing electrical gradient, resulting in no net flux.

Potassium Leak Channels

Ion channels that are open at rest and are primarily responsible for establishing the resting membrane potential.

Voltage-Gated Sodium Channels

Channels that open rapidly at threshold to allow an influx of $Na^+$, causing depolarization, and then quickly enter an inactivated state.

Inactivation State

A state where the voltage-gated sodium channel is closed by an inactivation gate and cannot be reopened until the membrane repolarizes to rest.

Voltage-Gated Potassium Channels

Channels that open slowly in response to depolarization, allowing $K^+$ efflux that repolarizes the cell and causes the undershoot.

Saltatory Conduction

The rapid jumping of action potentials from one Node of Ranvier to the next in myelinated axons.

Nodes of Ranvier

Gaps in the myelin sheath enriched in voltage-gated sodium channels where the electrical signal is re-boosted.

Absolute Refractory Period

The timeframe during which a second action potential cannot be initiated because voltage-gated sodium channels are in their inactivated state.

Relative Refractory Period

The timeframe following an action potential where a spike can occur but requires stronger stimulation because the cell is hyperpolarized near $E_K$.

Voltage Clamp Method

A technique used to hold the membrane potential constant at a specified level to measure the underlying ionic currents.

Tetrodotoxin (TTX)

A pharmacological agent that specifically inhibits voltage-gated sodium channels, eliminating the early inward current in voltage clamp experiments.

Tetraethylammonium (TEA)

A pharmacological agent that inhibits voltage-gated potassium channels, eliminating the delayed outward current.

Spatial Summation

The integration of multiple simultaneous synaptic potentials from different locations to reach the firing threshold.

Temporal Summation

The integration of sequential synaptic potentials from a single synapse that occur close enough in time to reach the firing threshold.