Chapter 11: Functional Organization of Nervous Tissue - Vocabulary Flashcards

Vocabulary flashcards covering key structural, functional, cellular, and electrical terminology from Chapter 11 Functional Organization of Nervous Tissue.

Central Nervous System (CNS)

The anatomical division of the nervous system consisting of the brain and spinal cord, housed within the skull and vertebral canal.

Peripheral Nervous System (PNS)

The anatomical division of the nervous system consisting of all nervous tissue outside the CNS, including nerves, ganglia, plexuses, and sensory receptors.

Neuron

An electrically excitable cell of the nervous system that typically consists of a cell body, dendrites, and a single axon.

Glial Cells

Supportive cells of the nervous system that provide structural support, protection, nourishment, and insulation for neurons.

Nerve

A collection of many axons bundled together outside the brain and spinal cord.

Ganglion

A cluster of neuron cell bodies located outside the brain and spinal cord in the peripheral nervous system.

Plexus

A bundle of nerves outside the brain and spinal cord.

Sensory Division

The afferent branch of the PNS that transmits electrical signals from specialized sensory receptors in the body toward the CNS.

Motor Division

The efferent branch of the PNS that transmits electrical signals from the CNS to effector organs, such as muscles and glands.

Somatic Nervous System

The voluntary branch of the PNS motor division that conducts electrical signals from the CNS to control skeletal muscles.

Autonomic Nervous System (ANS)

The involuntary branch of the PNS motor division that regulates activities without conscious control, including contractions of smooth muscle, cardiac muscle, and gland secretions.

Sympathetic Division

A subdivision of the autonomic nervous system that readies the body for physical activity, often called the fight-or-flight division.

Parasympathetic Division

A subdivision of the autonomic nervous system that regulates resting functions such as digesting food or slowing heart rate, often called the rest-and-digest division.

Enteric Nervous System (ENS)

A specialized branch of the nervous system consisting of neuronal networks situated within the wall of the digestive tract.

Neuron Cell Body

The soma of a neuron containing a central nucleus, prominent nucleolus, Nissl bodies, and organelles, functioning as the primary site of protein synthesis.

Nissl Bodies

Abundant, dense areas of rough endoplasmic reticulum (ER) within a neuron cell body that reflect high levels of protein synthesis.

Dendrites

Short, highly branched cytoplasmic extensions of the neuron cell body that receive input from other neurons or the environment and conduct electric currents toward the cell body.

Axon

A single long cytoplasmic process arising from the neuron cell body that propagates action potentials away from the cell body toward an effector or target cell.

Trigger Zone

The combined region of the axon hillock and initial segment of an axon where action potentials are generated.

Synapse

The point of contact where an axon ending communicates with its effector cell or another neuron.

Presynaptic Terminal

The enlarged ending of an axon at a synapse that contains synaptic vesicles filled with neurotransmitters.

Neurotransmitter

A chemical messenger synthesized and stored in synaptic vesicles within presynaptic terminals, released into the synaptic cleft to control target cells.

Multipolar Neuron

A structural class of neuron having many dendrites and a single axon, typical of most CNS neurons and PNS motor neurons.

Bipolar Neuron

A structural class of neuron featuring two processes—one dendrite and one axon—found in specialized sensory organs like the retina and nasal cavity.

Pseudo-unipolar Neuron

A structural class of neuron with a single process extending from the cell body that divides into a peripheral process and a central process, typical of most sensory neurons.

Anaxonic Neuron

A structural class of neuron that lacks an axon and possesses only dendrites, communicating via graded potentials within the brain and retina.

Astrocytes

Star-shaped CNS glial cells with foot processes covering neurons, blood vessels, and the pia mater, providing structural support and contributing to the blood-brain barrier.

Blood-Brain Barrier

A selective barrier formed by capillary endothelial cells with tight junctions promoted by astrocytes, regulating substance entry from blood into CNS tissue.

Ependymal Cells

Glial cells lining the brain ventricles and spinal cord central canal, some of which feature cilia to circulate cerebrospinal fluid or form choroid plexuses to secrete it.

Microglia

Phagocytic immune cells specific to the CNS that become mobile during inflammation to ingest necrotic tissue, microorganisms, and pathogens.

Oligodendrocytes

CNS glial cells with cytoplasmic extensions that form myelin sheaths around segments of multiple axons.

Schwann Cells

PNS glial cells that wrap repeatedly around a segment of a single axon to form its myelin sheath.

Satellite Cells

PNS glial cells surrounding neuron cell bodies within ganglia, providing support, nutrition, and protection against heavy-metal poisons.

Nodes of Ranvier

Unmyelinated gaps in the myelin sheath between adjacent Schwann cells or oligodendrocyte extensions along an axon.

Gray Matter

Nervous tissue consisting primarily of neuron cell bodies, dendrites, and unmyelinated axons, serving as functional integration sites.

White Matter

Nervous tissue consisting of bundles of parallel myelinated axons that propagate action potentials through nerve tracts or nerves.

Resting Membrane Potential

The potential difference across the plasma membrane of an unstimulated cell, typically around $-70\,\text{mV}$ in neurons, established mainly by $\text{K}^+$ diffusion and leak channels.

Depolarization

A shift in membrane potential making the inside of the cell more positive (closer to zero), which increases the likelihood of generating an action potential.

Hyperpolarization

A shift in membrane potential making the inside of the cell more negative (farther from zero), which decreases the likelihood of generating an action potential.

Graded Potential

A small, localized change in membrane potential that varies in magnitude according to stimulus strength and spreads in a decremental fashion.

Action Potential

A large, all-or-none change in membrane potential that propagates without losing magnitude over long distances along the plasma membrane.

Threshold

The specific membrane potential value at which voltage-gated $\text{Na}^+$ channels open to initiate an action potential.

Absolute Refractory Period

The initial phase of the refractory period during which complete insensitivity to further stimulation exists, preventing another action potential regardless of stimulus strength.

Relative Refractory Period

The second phase of the refractory period during which a stronger-than-threshold stimulus can evoke a second action potential.

Continuous Conduction

Action potential propagation along unmyelinated axons where each sequential section of the membrane generates an action potential via local currents.

Saltatory Conduction

Rapid action potential propagation along myelinated axons where the electrical signal effectively jumps from one node of Ranvier to the next.

Electrical Synapse

A type of synapse where cells are connected by gap junctions containing connexons, allowing direct movement of ions and rapid signal transmission.

Chemical Synapse

A junction where neurotransmitters are released from a presynaptic terminal across a synaptic cleft to bind to receptors on the postsynaptic membrane.

Excitatory Postsynaptic Potential (EPSP)

A depolarizing graded potential generated in the postsynaptic membrane that moves the membrane potential closer to threshold.

Inhibitory Postsynaptic Potential (IPSP)

A hyperpolarizing graded potential generated in the postsynaptic membrane that moves the membrane potential farther from threshold.

Spatial Summation

The additive effect produced when action potentials arrive simultaneously at multiple separate presynaptic terminals on a single postsynaptic neuron.

Temporal Summation

The additive effect produced when two or more action potentials arrive in rapid succession at a single presynaptic terminal on a postsynaptic neuron.

Convergent Pathway

A neuronal arrangement where multiple presynaptic neurons converge and form synapses with a smaller number of postsynaptic neurons.

Divergent Pathway

A neuronal arrangement where a smaller number of presynaptic neurons synapse with a larger number of postsynaptic neurons.

Reverberating Circuit

A neuronal pathway involving a chain of neurons with feedback loops to preceding neurons, causing repeated stimulation or after-discharge.

Parallel After-Discharge Circuit

A neuronal circuit in which parallel chains of neurons process input and converge on a single output cell.