Principles of Neural Communication

Comprehensive practice flashcards reviewing the principles of neural communication, including membrane structure, ion gradients, resting and action potentials, synaptic transmission, neurotransmitter classes, and clinical neuromuscular disorders.

What is the primary structural composition of the neuronal plasma membrane?

A lipid bilayer in which proteins, including ion channels, are embedded.

What are the three major types of lipids present in the neuronal membrane?

Phospholipids, cholesterol, and glycolipids.

Which lipid type is the most abundant in the neuronal membrane?

Phospholipids.

How are the hydrophilic and hydrophobic ends of phospholipids arranged in the neuronal lipid bilayer?

Their hydrophobic nonpolar tails face each other internally, while their hydrophilic polar heads are oriented on opposite sides facing aqueous fluid.

What term describes molecules that possess both a hydrophilic (water-soluble) end and a hydrophobic (water-insoluble) end?

Amphiphilic.

In the neuronal membrane, what part of the phospholipid molecule is oriented toward the extracellular and intracellular fluid?

The hydrophilic polar head.

What part of the phospholipid bilayer forms the inner hydrophobic core of the neuronal membrane?

The hydrophobic non-polar tails.

Besides phospholipids, what other lipid component stabilizes the structural integrity of the neuronal cell membrane?

Cholesterol.

What carbohydrate-containing lipid type is found in the neuronal membrane?

Glycolipids.

What major functions do embedded membrane proteins serve in the neuronal lipid bilayer?

They act as ion channels, transport carriers, and receptors.

Why are polar, water-soluble substances generally restricted from freely diffusing across the lipid bilayer core?

Because the interior core consists of nonpolar hydrophobic fatty acid tails.

What is the basic functional unit of the nervous system responsible for integrating and transmitting electrical signals?

The neuron.

Which lipid-soluble (hydrophobic or nonpolar) molecules cross the neuronal membrane by simple diffusion?

Oxygen ($\text{O}_2$) and carbon dioxide ($\text{CO}_2$) molecules.

Which polar (lipid-insoluble or water-soluble) molecules can pass through the neuronal membrane by simple diffusion?

Small and uncharged polar molecules such as urea, ethanol, glycerol, and water molecules.

How does solute concentration affect the rate of simple diffusion across the neuronal membrane?

The rate of simple diffusion is directly proportional to the solute concentration.

Does simple diffusion across the neuronal membrane require metabolic energy?

No, simple diffusion does not require energy.

How does active transport differ from simple diffusion regarding carrier proteins and energy?

Active transport is always mediated by specific carrier proteins and requires metabolic energy (e.g., hydrolysis of $ATP$).

What combined gradient governs the passive movement of ions across a neuronal membrane?

The electrochemical gradient (combination of concentration and electrical potential gradients).

What primary active transport mechanism maintains neuronal ionic gradients by pumping $3\,\text{Na}^+$ out and $2\,\text{K}^+$ in?

The $\text{Na}^+/\text{K}^+$ ATPase pump.

In figure 2, which letter labels represent forms of passive transport (facilitated diffusion)?

Letters B (channel-mediated diffusion) and C (carrier-mediated diffusion).

In figure 2, which letter represents active transport that requires metabolic energy?

Letter D.

What is the primary metabolic energy source for active transport mechanisms in neurons?

Hydrolysis of adenosine triphosphate ($ATP$).

What term describes transport processes that move solutes against their concentration or electrochemical gradient?

Active transport.

What factor determines the direction of passive ion flux through an open channel protein?

The ion's electrochemical gradient.

What structure forms the central water-filled pore of a transmembrane ion channel?

A channel protein spanning the phospholipid bilayer.

What is the approximate extracellular concentration of sodium ($\text{Na}^+$) in neurons?

$150\,mM$.

What is the approximate intracellular concentration of sodium ($\text{Na}^+$) in neurons?

$15\,mM$.

What is the approximate extracellular concentration of potassium ($\text{K}^+$) in neurons?

$5\,mM$.

What is the approximate intracellular concentration of potassium ($\text{K}^+$) in neurons?

$100\,mM$.

What is the approximate extracellular concentration of calcium ($\text{Ca}^{2+}$) in neurons?

$2\,mM$.

What is the approximate intracellular concentration of calcium ($\text{Ca}^{2+}$) in neurons?

$0.0002\,mM$.

What is the approximate extracellular concentration of chloride ($\text{Cl}^-$) in neurons?

$150\,mM$.

What is the approximate intracellular concentration of chloride ($\text{Cl}^-$) in neurons?

$13\,mM$.

What is the approximate intracellular concentration of fixed anions ($\text{A}^-$) such as organic acids and proteins in neurons?

$385\,mM$.

Which major inorganic cation has a significantly higher concentration inside the neuron than outside?

Potassium ($\text{K}^+$).

Which cations have significantly higher concentrations outside the neuron than inside?

Sodium ($\text{Na}^+$) and calcium ($\text{Ca}^{2+}$).

What is the predominant anion in the extracellular fluid of neurons?

Chloride ($\text{Cl}^-$).

Why are fixed anions ($\text{A}^-$) confined entirely to the intracellular compartment?

Because they consist of large organic acids and proteins that cannot cross the cell membrane.

What is the major physiological relevance of the $\text{Na}^+$ concentration gradient in neurons?

Depolarization during an action potential.

What is the major physiological relevance of the $\text{K}^+$ concentration gradient in neurons?

Maintenance of the resting potential and repolarization.

What is the approximate resting membrane potential of a typical neuron?

$-70\,mV$.

What rapid ion movement causes membrane depolarization during the rising phase of an action potential?

Increased influx of $\text{Na}^+$ through voltage-gated $\text{Na}^+$ channels.

As depolarization continues during the rising phase, what ionic potential does the membrane potential approach?

The $\text{Na}^+$ equilibrium potential.

What is the term for the peak portion of the action potential where the inside of the neuron becomes positive relative to the outside?

Overshoot.

What peak voltage is typically reached during the overshoot phase of a neuronal action potential?

Approximately $+35\,mV$ to $+40\,mV$.

What two channel events occur at the end of the rising phase to terminate depolarization?

Voltage-gated $\text{Na}^+$ channels are inactivated and voltage-gated $\text{K}^+$ channels open.

What ion movement drives the falling phase (repolarization) of an action potential?

Efflux of $\text{K}^+$ through open voltage-gated $\text{K}^+$ channels.

What causes the membrane potential to become more negative than the resting potential during after-hyperpolarization (undershoot)?

Increased $\text{K}^+$ permeability caused by the opening of delayed rectifier $\text{K}^+$ channels.

Why is membrane potential closer to the equilibrium potential of $\text{K}^+$ during the undershoot phase?

Because delayed rectifier $\text{K}^+$ channels remain open while there is little $\text{Na}^+$ permeability.

What event allows the membrane potential to return from after-hyperpolarization back to the resting potential?

The closure of delayed rectifier $\text{K}^+$ channels.

What membrane potential threshold must be reached at the trigger zone to initiate an action potential?

Approximately $-55\,mV$ to $-60\,mV$.

What is meant by the 'all-or-none' behavior of an action potential?

Once threshold is reached, an action potential fires at full amplitude regardless of initial stimulus magnitude.

What three crucial principles govern action potential signaling in neurosciences?

All-or-none behavior, refractory periods, and unidirectional propagation.

What happens to the amplitude of an action potential if a stronger suprathreshold stimulus is applied?

The amplitude does not change; it remains constant.

How does the nervous system encode stimulus intensity if individual action potential amplitudes do not change?

Primarily through action-potential frequency and population recruitment.

What major relevance does extracellular $\text{Ca}^{2+}$ play in neuronal function?

Neurotransmitter release and intracellular signaling.

What major relevance does extracellular $\text{Cl}^-$ play in postsynaptic membrane potentials?

It often contributes to neuronal inhibition.

What complete sequence of state transitions occurs during an action potential?

Resting state $\rightarrow$ Threshold $\rightarrow$ Depolarization $\rightarrow$ Repolarization $\rightarrow$ After-hyperpolarization $\rightarrow$ Resting state.

What are the three distinct operational states of the voltage-gated $\text{Na}^+$ channel?

Resting state, Activated state, and Inactivated state.

In the resting state of a voltage-gated $\text{Na}^+$ channel, which gate is closed and which is open?

The activation gate is closed and the inactivation gate is open.

Can $\text{Na}^+$ flow into the neuron when the voltage-gated $\text{Na}^+$ channel is in its resting state?

No, because the channel pore is closed by the activation gate.

In the activated state of a voltage-gated $\text{Na}^+$ channel, what are the positions of the activation and inactivation gates?

Both activation and inactivation gates are open.

During which phase of the action potential do voltage-gated $\text{Na}^+$ channels transition into the activated state?

During the rising phase of the action potential.

In the inactivated state of a voltage-gated $\text{Na}^+$ channel, which gate closes the pore?

The inactivation gate.

Is the activation gate open or closed during the inactivated state of a voltage-gated $\text{Na}^+$ channel?

The activation gate is open.

Can a voltage-gated $\text{Na}^+$ channel in the inactivated state be immediately re-stimulated by depolarization?

No, the neuron cannot be activated until the channel reverts to the resting state.

What period during an action potential occurs when all $\text{Na}^+$ channels are inactivated and no second action potential can be generated?

Absolute refractory period.

What period occurs when some $\text{Na}^+$ channels have reset to resting state, but a stronger-than-normal stimulus is needed to reach threshold?

Relative refractory period.

What structural mechanism ensures that action potentials propagate unidirectionally along an axon?

Inactivation of voltage-gated $\text{Na}^+$ channels in the preceding axonal segment.

What must happen to the membrane potential before an inactivated $\text{Na}^+$ channel can revert back to its resting state?

The membrane potential must repolarize back toward resting potential.

In unmyelinated axons, how does depolarization spread from an active region to an adjacent region?

Passive spread of current generated by the local action potential depolarizes the adjacent region to threshold.

Why does region 1 of an unmyelinated axon repolarize while region 2 generates an action potential?

Because $\text{Na}^+$ channels in region 1 become inactivated and $\text{K}^+$ channels open.

What mode of action potential propagation occurs along myelinated axons?

Saltatory conduction.

Where are voltage-gated $\text{Na}^+$ and $\text{K}^+$ channels concentrated along a myelinated axon?

At the Nodes of Ranvier.

How does passive current spread between Nodes of Ranvier in a myelinated axon?

Passive current spreads rapidly under the myelin sheath from one node to depolarize the next node to threshold.

What effect does myelination have on action potential conduction velocity?

Myelination significantly increases conduction velocity.

Why is saltatory conduction faster than continuous propagation in unmyelinated axons?

Because myelin acts as an insulator, reducing charge leakage and allowing current to jump rapidly between nodes.

What name is given to the periodic unmyelinated gaps along a myelinated axon where action potentials regenerate?

Nodes of Ranvier.

In an unmyelinated axon diagram, what event occurs at time point 2 in region 2?

Depolarization reaches threshold, generating an action potential in region 2.

What prevents an action potential at Node 2 from re-exciting Node 1 in a myelinated axon?

Node 1 is in a refractory period due to $\text{Na}^+$ channel inactivation.

How does axon diameter influence action potential conduction velocity in both myelinated and unmyelinated fibers?

Larger axon diameter decreases internal resistance, increasing conduction velocity.

What charge shift occurs inside the axon relative to the outside during the peak of action potential propagation?

The intracellular charge briefly becomes positive relative to the extracellular fluid.

What basic transformation occurs during neural communication at a chemical synapse?

Electrical signals are transformed into chemical messages and back into electrical or cellular responses.

What complete sequence describes the path of neural information processing from stimulus to network output?

Stimulus $\rightarrow$ Reception $\rightarrow$ Integration $\rightarrow$ Electrical signaling $\rightarrow$ Synaptic transmission $\rightarrow$ Postsynaptic response $\rightarrow$ Network output.

What two most striking properties allow neurons to coordinate complex behaviors?

Their excitability and ability to conduct electrical signals.

What central question drives the study of neural communication mechanisms?

How does a neuron receive, integrate, transmit, and modify information?

How can information travel rapidly through billions of non-touching neurons in chemical synapses?

Through rapid electrical propagation down axons paired with fast neurotransmitter diffusion across narrow synaptic clefts.

What three cellular elements establish the resting excitable state of a neuron?

Ion gradients, selective membrane permeability, and membrane potential.

What site on an efferent neuron acts as the primary integration zone for incoming graded potentials?

The axon hillock.

What happens to network output if synaptic transmission is disrupted or blocked?

Downstream electrical signaling, postsynaptic responses, and coordinated network output are reduced or lost.

What specialized neuronal structures serve as the primary receptive sites for incoming neurotransmitters?

Dendrites and dendritic spines.

What long neuronal process carries action potentials toward presynaptic terminals?

The axon.

What three structural components comprise a chemical synapse?

Pre-synaptic knob, Synaptic Cleft, and Post-synaptic knob.

What three broad functional categories of synapses exist based on target tissue?

Neuro-endocrine (neuro-glandular), Neuro-mucular, and Neuro-neuronal synapses.

What are the three morphological subtypes of neuro-neuronal synapses?

Axosomatic, Axodendritic, and Axoaxonic synapses.

What neuronal structures form an axosomatic synapse?

An axon terminal and a cell body (soma).

What neuronal structures form an axodendritic synapse?

An axon terminal and a dendrite.

What neuronal structures form an axoaxonic synapse?

An axon terminal and another axon terminal.

Which neuro-neuronal synapse type is specifically positioned to regulate neurotransmitter release from another axon terminal?

Axoaxonic synapse.

What fills the microscopic space known as the synaptic cleft between pre- and postsynaptic membranes?

Extracellular fluid.