Chapter 7: The Nervous System and Neuronal Excitability

Comprehensive vocabulary flashcard set covering Chapter 7: The Nervous System and Neuronal Excitability, including neuroglia, membrane potentials, action potential mechanics, saltatory conduction, synapses, and neurotransmitters.

Integration

Function of the nervous system that processes sensory information, controls body responses and activities, and stores information.

Sensory Input

Function of the nervous system that detects and monitors internal and external stimuli, such as stomach fullness or a bee sting.

Motor Output

Function of the nervous system that causes a response in effectors such as muscles and glands.

Central Nervous System (CNS)

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

Peripheral Nervous System (PNS)

Anatomical division of the nervous system consisting of cranial nerves, spinal nerves, and sensory receptors.

CNS and PNS Anatomic Organization

Structural division separating the brain and spinal cord (CNS) from the cranial/spinal nerves and sensory receptors in skin (PNS).

Sensory Division (Afferent)

Subdivision of the PNS consisting of receptors that detect stimuli and neurons that carry sensory information towards the CNS.

Motor Division (Efferent)

Subdivision of the PNS consisting of neurons that carry motor impulses away from the CNS to effector targets.

Neuron

The excitable functional unit of the nervous system that responds to stimuli, conducts electrical signals, releases neurotransmitters, and is incapable of mitosis once formed.

Neuroglia

Supportive cells of the nervous system, also known as glial cells, that are $10-50\times$ more numerous than neurons and retain the ability to divide.

Neuronal Cell Body

The central part of a neuron containing a single nucleus and cytoplasm surrounding it.

Axon Hillock

The thick region at the base of the neuronal cell body where the axon originates.

Dendrites

Highly branched neuronal processes specialized for contact with other neurons that carry signals towards the cell body.

Dendritic Spines

Small projections on dendrites that increase the surface area and points of contact for synaptic connections.

Axon

A single long process originating at the axon hillock that carries nerve impulses away from the cell body.

Axon Terminals

The distal branches of an axon that contain synaptic vesicles filled with neurotransmitters.

Sensory Neurons

Neurons that transmit sensory information from the PNS to the CNS.

Interneurons

Neurons located entirely within the CNS that interpret sensory information and may elicit a motor response.

Motor Neurons

Neurons that transmit motor commands from the CNS outward to PNS effectors.

Ganglion

A cluster of neuronal cell bodies located in the Peripheral Nervous System (PNS).

Nucleus (in CNS)

A cluster of neuronal cell bodies located within the Central Nervous System (CNS).

Nerve

A bundle of neuronal axons located in the Peripheral Nervous System (PNS).

Tract

A bundle of neuronal axons located within the Central Nervous System (CNS).

Astrocytes

Star-shaped CNS glial cells that form the blood-brain barrier by covering brain capillaries, provide structural support, and direct neuron development.

Oligodendrocytes

CNS glial cells that form myelin sheaths around multiple axon segments within the Central Nervous System.

Microglia

Phagocytic CNS glial cells located near blood vessels that engulf and clear away dead or damaged cells, debris, and pathogens.

Ependymal Cells

CNS glial cells that form an epithelial lining in brain chambers and canals to produce cerebrospinal fluid (CSF).

Blood-Brain Barrier

Protective structural barrier formed by astrocyte processes wrapping around brain capillaries to restrict movement of substances into neural tissue.

Satellite Cells

Flat PNS glial cells that surround neuronal cell bodies in ganglia to provide support and protection.

Schwann Cells

PNS glial cells that wrap around axons in the Peripheral Nervous System to form a myelin sheath.

Myelination

The formation of an insulating myelin sheath around an axon by repeated concentric wrapping of glial cell membranes.

Myelin Sheath

A multilayered lipid and protein covering around axons that acts as an electrical insulator and increases nerve impulse conduction velocity.

Nodes of Ranvier

Unmyelinated gaps along an axon located between adjacent myelin sheath segments that remain in direct contact with extracellular fluid.

Multiple Sclerosis (MS)

An autoimmune disorder characterized by destruction of myelin sheaths surrounding neurons in the Central Nervous System (CNS).

Guillain-Barré Syndrome

An autoimmune disorder characterized by loss of myelin sheaths around neurons in the Peripheral Nervous System (PNS).

Lidocaine

A local anesthetic agent that blocks nerve impulse transmission during procedures by inhibiting voltage-gated $Na^+$ channels.

Carpal Tunnel Syndrome

A compressive neuropathy managed surgically by transecting the transverse carpal ligament to decompress the median nerve.

Excitable Cells

Cells, such as neurons and muscle fibers, capable of changing their membrane potential when adequately stimulated to propagate electrical signals.

Electrochemical Gradient

The combined driving force created by both a chemical concentration gradient and an electrical potential gradient across a membrane.

Chemical Gradient

The concentration difference of a specific solute or ion across a biological membrane.

Electrical Gradient

The difference in electrical charge across a membrane created by unequal distribution of charged particles.

Equilibrium Potential ($E_{ion}$)

The membrane potential at which electrical and chemical forces are balanced for a given ion, resulting in no net movement across the membrane.

Nernst Equation

Mathematical formula used to calculate the equilibrium potential ($E_{ion}$) for a single ion based on its concentrations inside and outside the cell.

Potassium Equilibrium Potential ($E_{K^+}$)

The equilibrium potential for $K^+$, calculated to be approximately $-90\text{ mV}$ given intracellular $[K^+] \text{ of } \thicksim 140\text{ mM}$ and extracellular $[K^+] \text{ of } \thicksim 4\text{ mM}$.

Sodium Equilibrium Potential ($E_{Na^+}$)

The equilibrium potential for $Na^+$, calculated to be approximately $+60\text{ mV}$ given intracellular $[Na^+] \text{ of } \thicksim 10-15\text{ mM}$ and extracellular $[Na^+] \text{ of } \thicksim 145\text{ mM}$.

Membrane Potential

The voltage difference in electrical potential across a cell membrane, measured in millivolts ($\text{mV}$).

Resting Membrane Potential (RMP)

The steady-state voltage across the plasma membrane of an unstimulated cell, typically ranging from $-50\text{ mV}$ to $-100\text{ mV}$.

Neuronal Resting Membrane Potential

The standard baseline electrical potential across a resting neuron membrane, equal to $-70\text{ mV}$.

Voltmeter Measurement of Membrane Potential

Experimental setup placing a recording electrode inside the cell and a reference electrode in a saline bath to measure membrane potential difference ($V_m$).

Intracellular Fluid (Cytosol) Ionic Composition

The internal environment of a neuron characterized by a high concentration of $K^+$ and a low concentration of $Na^+$.

Extracellular Fluid (ECF) Ionic Composition

The external fluid surrounding a neuron characterized by a high concentration of $Na^+$ and a low concentration of $K^+$.

Na+/K+ ATPase Pump

An active transport pump that consumes ATP to move $3\text{ Na}^+$ ions out of the cell and $2\text{ K}^+$ ions into the cell, preserving ion gradients and RMP.

Leak Channels

Non-gated transmembrane protein channels that are permanently open, permitting continuous slow passive movement of ions across the membrane.

Gated Ion Channels

Ion channels that open or close in response to specific chemical, electrical, or mechanical stimuli.

Ligand-Gated Channels

Transmembrane ion channels that open when a specific chemical signal (ligand) binds to its receptor site.

Voltage-Gated Channels

Transmembrane ion channels that open or close in response to shifts in the surrounding membrane potential.

Mechanically-Gated Channels

Transmembrane ion channels that open or close in response to physical deformation, pressure, stretch, touch, or vibration.

Graded Potential

A localized change in membrane potential away from RMP occurring at dendrites or cell bodies, varying in size according to stimulus strength.

Depolarization

A shift in membrane potential making the inside of the cell less negative (more positive) relative to resting membrane potential.

Hyperpolarization

A shift in membrane potential making the inside of the cell more negative relative to resting membrane potential.

Summation

The additive combination of individual graded potentials occurring close in time or space to produce a larger membrane voltage response.

Decremental Spread

The progressive decline in amplitude of a graded potential as it travels further from its point of origin.

Trigger Zone

Specialized area at the axon hillock containing a high density of voltage-gated $Na^+$ channels where an action potential is initiated if threshold is hit.

Threshold Voltage

The critical membrane potential level ($-55\text{ mV}$ in neurons) required at the trigger zone to activate voltage-gated $Na^+$ channels and fire an action potential.

All-or-None Principle

Property of action potentials specifying that if threshold is reached, an impulse fires completely at maximum amplitude; if threshold is not reached, no action potential occurs.

Subthreshold Stimulus

A weak stimulus that depolarizes the membrane slightly but fails to reach the threshold voltage of $-55\text{ mV}$.

Suprathreshold Stimulus

A stimulus stronger than necessary to reach threshold, triggering one or a series of full-amplitude action potentials.

Action Potential

A sequence of rapid electrical events starting at the axon hillock and propagating down the entire length of an axon to trigger neurotransmitter release.

Resting Stage of Action Potential

Initial phase where the neuron membrane is at $-70\text{ mV}$ with voltage-gated $Na^+$ and $K^+$ channels closed.

Depolarizing Phase of Action Potential

Action potential phase where opening of voltage-gated $Na^+$ channels causes rapid influx of $Na^+$, driving membrane potential up toward $+30\text{ mV}$.

Peak Depolarization Voltage

The maximum positive voltage reached during an action potential, approximately $+30\text{ mV}$, which triggers inactivation of voltage-gated $Na^+$ channels.

Repolarizing Phase of Action Potential

Action potential phase where voltage-gated $Na^+$ channels close/inactivate and voltage-gated $K^+$ channels open, allowing $K^+$ efflux to restore negative voltage.

After-Hyperpolarizing Phase of Action Potential

Phase following repolarization where persistent $K^+$ efflux through slowly closing channels temporarily dips membrane potential below $-70\text{ mV}$.

Reversal of Polarization

The portion of an action potential graph between $0\text{ mV}$ and $+30\text{ mV}$ where internal membrane charge temporarily reverses from negative to positive.

Na+ Channel Inactivation Gate

A gating mechanism that automatically closes voltage-gated $Na^+$ channels at $+30\text{ mV}$ to halt sodium influx during an action potential.

Absolute Refractory Period

Time interval from threshold reaching through repolarization when another action potential cannot be initiated, regardless of stimulus intensity.

Relative Refractory Period

Time interval following the absolute refractory period during which a second action potential can be triggered, but only by a suprathreshold stimulus.

Continuous Conduction

Step-by-step propagation of an action potential along every adjacent unmyelinated segment of an axon membrane.

Saltatory Conduction

Rapid impulse propagation in myelinated axons where the action potential leaps from one Node of Ranvier to the next at speeds $10-50\times$ faster.

Action Potential Propagation

The self-propagating electrical conduction mechanism that drives an action potential sequentially down the axon length without loss of signal strength.

Synapse

A specialized contact junction mediating one-directional communication between a neuron and another cell.

Presynaptic Neuron

The neuron that conducts an electrical signal toward a synapse and releases neurotransmitters.

Postsynaptic Cell

The target neuron or effector cell located downstream of a synapse that responds to released neurotransmitters.

Synaptic Cleft

The fluid-filled microscopic space separating the presynaptic membrane from the postsynaptic membrane.

Axodendritic Synapse

A chemical synapse formed between an axon terminal of a presynaptic neuron and a dendrite of a postsynaptic neuron.

Axosomatic Synapse

A chemical synapse formed between an axon terminal of a presynaptic neuron and the cell body (soma) of a postsynaptic neuron.

Axoaxonic Synapse

A chemical synapse formed between an axon terminal of one neuron and the axon terminal of another neuron.

Voltage-Gated Ca2+ Channels

Axon terminal membrane channels that open upon action potential arrival, enabling $Ca^{2+}$ influx to trigger vesicle exocytosis.

Synaptic Vesicles

Membrane-bound spheres inside axon terminals containing concentrated molecules of neurotransmitters.

Exocytosis of Neurotransmitters

Calcium-dependent membrane fusion process that releases synaptic vesicle neurotransmitter contents into the synaptic cleft.

Postsynaptic Potential

A graded local change in postsynaptic membrane potential produced when neurotransmitters bind to ligand-gated ion channels.

Excitatory Postsynaptic Potential (EPSP)

A depolarizing postsynaptic potential that shifts membrane potential closer to threshold, increasing the likelihood of firing an action potential.

Inhibitory Postsynaptic Potential (IPSP)

A hyperpolarizing postsynaptic potential that shifts membrane potential further away from threshold, decreasing the likelihood of firing an action potential.

Acetylcholine (ACh)

A common small-molecule neurotransmitter active at CNS synapses and PNS neuromuscular junctions that can be excitatory or inhibitory.

Acetylcholinesterase (AChE)

Synaptic cleft enzyme that rapidly degrades acetylcholine to end neurotransmitter signaling.

Monoamines (Biogenic Amines)

A class of neurotransmitters mainly in the CNS derived from amino acids, including dopamine, serotonin, histamine, epinephrine, and norepinephrine.

Monoamine Oxidase (MAO)

An enzyme responsible for breakdown and enzymatic inactivation of monoamine neurotransmitters.

Dopamine

A biogenic amine neurotransmitter in the CNS involved in motor control, motivation, behavior, and reward pathways.

Serotonin

A biogenic amine neurotransmitter in the CNS playing key roles in mood, sleep, appetite, and emotional regulation.

Substance P

A neuropeptide neurotransmitter involved in relaying pain sensory input into the Central Nervous System.