Chapter 11: Functional Organization of Nervous Tissue

Vocabulary practice flashcards covering the structural and functional organization of nervous tissue, neuroglia, neuron classifications, membrane potentials, and electrophysiological signaling.

Gray Matter

Nervous tissue consisting primarily of neuron cell bodies and dendrites with very little myelin; forms the cortex and nuclei in the CNS, and ganglia in the PNS.

White Matter

Nervous tissue composed of bundles of myelinated axons that propagate action potentials; forms nerve tracts in the CNS and nerves in the PNS.

Nerve Tract

A bundle of myelinated axons located within the central nervous system that propagates action potentials from one region of the CNS to another.

Nerve

A collection of many axons bundled together in the peripheral nervous system; includes 12 pairs of cranial nerves originating from the brain and 31 pairs of spinal nerves originating from the spinal cord.

Ganglia

Clusters of neuron cell bodies located outside the brain and spinal cord within the peripheral nervous system.

Resting Membrane Potential

The charge difference across an unstimulated neuron membrane (typically $-70\,\text{mV}$), established by ion concentration gradients (high $\text{K}^+$ inside, high $\text{Na}^+$ and $\text{Cl}^-$ outside) and selective membrane permeability.

Mechanically Gated Ion Channels

Membrane ion channels that open or close in response to mechanical stimuli other than voltage alterations or chemical ligands, such as sensory receptors for touch, pain, and temperature in the skin.

Depolarization

A shift in membrane potential making the inside of the cell more positive (closer to zero), often triggered by $\text{Na}^+$ or $\text{Ca}^{2+}$ influx, which makes the neuron more likely to fire an action potential.

Hyperpolarization

An increase in membrane potential where the interior of the cell becomes more negative than the resting potential, driven by $\text{K}^+$ efflux or $\text{Cl}^-$ influx, decreasing the likelihood of action potential generation.

Graded Potential

A localized change in membrane potential that varies in magnitude according to stimulus intensity and spreads across the plasma membrane in a decremental fashion.

Summation

The additive combination of individual depolarizing graded potentials at the axon hillock; if the sum reaches the threshold voltage, an action potential is initiated.

Axon Hillock

The specialized, cone-shaped region of the neuron cell body where graded potentials are summated and action potentials originate if the threshold is reached.

Absolute Refractory Period

The initial period of an action potential during which the membrane cannot produce another action potential under any stimulus, ensuring unidirectional signal propagation.

Relative Refractory Period

The interval following the absolute refractory period during which an action potential can only be generated in response to a suprathreshold stimulus.

Continuous Conduction

The mechanism of action potential propagation in unmyelinated axons, wherein every consecutive section of the axolemma generates an action potential.

Saltatory Conduction

The rapid propagation of action potentials along myelinated axons, characterized by the electrical impulse leaping from one node of Ranvier to the next.

Central Nervous System (CNS)

The anatomical division of the nervous system consisting of the brain and spinal cord, responsible for integrating information and coordinating body activities.

Peripheral Nervous System (PNS)

The division of the nervous system comprising all neural structures outside the brain and spinal cord, including nerves, ganglia, and sensory receptors.

Sensory Division (Afferent)

The PNS subdivision that transmits electrical impulses detected by sensory receptors toward the central nervous system.

Motor Division (Efferent)

The PNS subdivision that transmits regulatory commands from the central nervous system outward to effector tissues and organs.

Somatic Nervous System

The voluntary component of the motor division of the PNS that innervates and regulates skeletal muscle effectors.

Autonomic Nervous System

The involuntary component of the PNS motor division that regulates smooth muscle, cardiac muscle, and glands; divided into sympathetic and parasympathetic branches.

Nissl Bodies

Prominent clusters of rough endoplasmic reticulum situated within the neuron cell body that engage in active protein synthesis.

Dendrites

Branching, unmyelinated extensions of the neuron cell body that receive incoming signals from other neurons or sensory receptors and convey them toward the cell body.

Axon

A single elongated projection extending from the neuron cell body that propagates action potentials toward other neurons or target effector cells.

Interneuron

An association neuron situated entirely within the central nervous system that conducts action potentials between neurons to integrate incoming and outgoing signals.

Multipolar Neuron

A neuron with a single axon and multiple dendrites, representing the most prevalent neuron morphology in the CNS and PNS motor pathways.

Bipolar Neuron

A structural type of neuron featuring two processes—one dendrite and one axon—found in specialized sensory organs such as the olfactory epithelium and retina.

Pseudo-unipolar Neuron

A sensory neuron with a single short process branching from the cell body that acts as an axon without true dendrites extending from the soma.

Astrocyte

A star-shaped glial cell of the CNS with perivascular foot processes that encircle brain capillaries and neurons, maintaining the blood-brain barrier and regulating chemical composition.

Ependymal Cells

Ciliated CNS glial cells that line the brain ventricles and the central canal of the spinal cord, forming the choroid plexuses to secrete and circulate cerebrospinal fluid (CSF).

Microglia

Resident macrophage-like immune cells of the CNS that become phagocytic during neuroinflammation to engulf pathogens and cell debris.

Oligodendrocyte

A neuroglial cell of the central nervous system whose cytoplasmic extensions wrap around multiple axons to form myelin sheaths.

Schwann Cell

A peripheral glial cell that wraps around a section of a single axon to produce the myelin sheath in the PNS.

Neurilemma

The outer nucleated cytoplasmic boundary of a Schwann cell encasing a myelinated or unmyelinated peripheral nerve axon.

Satellite Cell

A supporting glial cell in the PNS that surrounds and supplies nutrients to neuron cell bodies in ganglia, safeguarding them by absorbing heavy metal toxins.

Nodes of Ranvier

Non-myelinated gaps along an axon between adjacent Schwann cells or oligodendrocyte processes that contain a high concentration of voltage-gated ion channels.

Multiple Sclerosis

A progressive autoimmune pathology resulting in the destruction of myelin sheaths, impairing or halting action potential propagation and compromising motor control.