Study Guide - Ch 12, 13, 14 - Spring 2026: Nervous System Structure, Function, and Signaling

Vocabulary flashcards covering the anatomical organization, cell types, conduction mechanics, action potentials, and synaptic neurotransmission outlined across Chapters 12, 13, and 14.

Central Nervous System (CNS)

A primary structural division of the nervous system composed of the brain and spinal cord, contrasted with the peripheral nervous system (PNS) in terms of included structures and primary functions.

Peripheral Nervous System (PNS)

The structural division of the nervous system outside the CNS, consisting of afferent and efferent divisions that route sensory input and motor output.

Afferent Division

The sensory division of the peripheral nervous system (PNS) in which nerve impulses travel toward the central nervous system.

Efferent Division

The motor division of the peripheral nervous system (PNS) in which nerve impulses travel away from the central nervous system toward effectors.

Somatic Nervous System

A division of the efferent nervous system under voluntary control that regulates somatic effectors, specifically skeletal muscle.

Autonomic Nervous System

A division of the efferent nervous system under involuntary control that regulates visceral effectors such as smooth muscle, cardiac muscle, and glands.

Dendrites

Receptive neuronal processes that receive incoming electrical signals and stimuli, directing them toward the soma (cell body).

Soma (Cell Body)

The biosynthetic center of a neuron containing the nucleus and major organelles, responsible for integrating incoming signals.

Axon

A long cylindrical process of a neuron that conducts nerve impulses away from the cell body toward target cells.

Axon Terminals

The distal, branching ends of an axon that form synaptic junctions and release neurotransmitters into the synaptic cleft.

Unipolar Neurons

Neurons possessing a single short process extending from the cell body that branches into central and peripheral processes, typically located in sensory ganglia.

Bipolar Neurons

Neurons possessing two distinct processes (one axon and one dendrite) extending from opposite sides of the cell body, typically found in special sensory organs such as the retina and olfactory mucosa.

Multipolar Neurons

Neurons featuring three or more processes (one axon and multiple dendrites), representing the most common structural class and serving predominantly as motor neurons and interneurons.

Interneurons

The most abundant functional category of neurons in the central nervous system (CNS), responsible for complex information processing, integration, and higher-order signaling beyond simple reflexes.

Neuroglia (Glial Cells)

Non-excitable supporting cells that do not transmit action potentials but are vital for structural support, insulation, metabolic maintenance, and protection of neurons.

Astrocytes

Star-shaped CNS glial cells responsible for regulating extracellular ion concentrations, maintaining the blood-brain barrier, and providing metabolic and structural support.

Oligodendrocytes

Central nervous system (CNS) glial cells that form myelin sheaths around multiple axon segments simultaneously.

Microglia

Small, specialized CNS glial cells that function as resident phagocytes, removing cellular debris, pathogens, and damaged nervous tissue.

Ependymal Cells

Ciliated epithelial-like CNS glial cells lining the brain ventricles and central canal of the spinal cord, involved in producing and circulating cerebrospinal fluid.

Schwann Cells

Peripheral nervous system (PNS) glial cells that wrap around and myelinate a single axon segment, playing a key role in peripheral nerve regeneration.

Myelin

A lipid-rich insulating substance wrapping axons that significantly increases the conduction velocity of nerve impulse transmission.

White Matter

Nervous tissue composed primarily of myelinated axons, located internally in the brain and externally in the spinal cord.

Gray Matter

Nervous tissue composed predominantly of neuronal cell bodies (soma), dendrites, unmyelinated axons, and neuroglia, forming the outer cortex of the brain and central core of the spinal cord.

Saltatory Conduction

A rapid mode of electrical impulse propagation in myelinated axons where action potentials leap from one node of Ranvier to the next, conserving cellular energy.

Continuous Conduction

A slower mode of impulse propagation occurring along unmyelinated axons that requires sequential opening of voltage-gated channels along the entire length of the axolemma, consuming more energy.

Resting Membrane Potential

The baseline electrical charge difference across the resting neuronal plasma membrane, established by unequal ion distribution and leak channel permeability.

Depolarization

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

Repolarization

The restoration of the resting membrane potential following depolarization, driven predominantly by the outflow of potassium ions.

Hyperpolarization

An increase in membrane potential magnitude making the interior of the neuron more negative than its normal resting level.

All-or-None Principle

The physiological principle dictating that an action potential is triggered at full amplitude if the membrane reaches threshold, or does not fire at all if threshold is not reached.

Action Potential

A rapid, self-propagating electrical reversal across the neuronal membrane that progresses from threshold depolarization through repolarization and hyperpolarization back to resting potential.

Absolute Refractory Period

The interval during an action potential when voltage-gated sodium channels are open or inactivated, preventing any subsequent action potential from firing and ensuring unidirectional signal flow.

Relative Refractory Period

The period following the absolute refractory period during which voltage-gated sodium channels have reset but potassium channels remain open, requiring a suprathreshold stimulus to generate a new action potential.

Chemical Synapse

A junction between two excitable cells where electrical signals are converted into chemical signals via neurotransmitter release across the synaptic cleft.

Calcium ($\text{Ca}^{2+}$)

The divalent cation that enters the axon terminal through voltage-gated channels upon depolarization to trigger synaptic vesicle exocytosis and neurotransmitter release.

Excitatory Neurotransmitters

Chemical messengers that induce postsynaptic depolarization, shifting the membrane potential closer to threshold.

Inhibitory Neurotransmitters

Chemical messengers that induce postsynaptic hyperpolarization, shifting the membrane potential farther away from threshold.

Receptor Type

The specific postsynaptic receptor protein that dictates whether the physiological response to a neurotransmitter is excitatory or inhibitory.

Acetylcholine

A common neurotransmitter active in both the central and peripheral nervous systems, known for initiating skeletal muscle contraction at neuromuscular junctions.

Dopamine

A biogenic amine neurotransmitter involved in motor control, motivation, reward pathways, and emotional regulation.

Serotonin

A monoamine neurotransmitter that influences mood, sleep-wake cycles, appetite, and emotional states.

GABA

Gamma-aminobutyric acid, the primary inhibitory neurotransmitter in the central nervous system that reduces neuronal excitability.

Voltage-Gated Sodium Channels

Membrane proteins responsible for the rapid influx of sodium during depolarization; blocking them halts action potential generation and propagation.