Chapter 8: Nervous System - Cells and Electrical Signals

Vocabulary flashcards covering the anatomical divisions, cellular structures, glial types, membrane properties, and action potential mechanisms of the nervous system.

Central nervous system (CNS)

The division of the nervous system that consists of the brain and spinal cord.

Peripheral nervous system (PNS)

The division of the nervous system that consists of nerves and ganglia located outside the brain and spinal cord.

Autonomic nervous system (ANS)

A motor division of the nervous system that transmits action potentials from the CNS to cardiac muscle, smooth muscle, and glands; divided into sympathetic and parasympathetic divisions.

Enteric nervous system (ENS)

A unique part of the peripheral nervous system with sensory and motor neurons contained wholly within the digestive tract that can function independently of the CNS.

Neurons (nerve cells)

Excitable cells of the nervous system that receive stimuli, conduct action potentials, and transmit signals to other neurons or effector organs.

Neuron cell body

The central part of a neuron containing a single nucleus, extensive rough endoplasmic reticulum, Golgi apparatus, mitochondria, and neurofilaments.

Dendrites

Short, highly branching cytoplasmic extensions tapered from their bases at the neuron cell body to their tips that receive information and transmit it toward the cell body.

Axon

A single long cell process extending from the neuron cell body that conducts action potentials toward the CNS in sensory neurons or away from the CNS in motor neurons.

Axon hillock

The specialized region of the neuron cell body where the axon arises and where threshold depolarization is most often reached.

Collateral axons

Branches that extend from the main axon of a neuron.

Multipolar neurons

Neurons having many dendrites and a single axon; includes most neurons within the CNS and nearly all motor neurons.

Bipolar neurons

Neurons with two processes (one dendrite and one axon) found in specialized sensory organs, such as the retina of the eye and the nasal cavity.

Pseudo-unipolar neurons

Neurons with a single process extending from the cell body that divides into two extensions functioning as a single axon; characteristic of most sensory neurons.

Glial cells (neuroglia)

Supportive, non-conducting cells of the CNS and PNS that enhance neuron function, maintain normal conditions within nervous tissue, and retain the ability to divide.

Astrocytes

Major supporting glial cells of the CNS that regulate neuronal signaling, participate with blood vessel endothelium to form the blood-brain barrier, and form scar tissue in damaged areas.

Blood-brain barrier

A permeability barrier between the blood and the CNS formed by astrocytes participating with the endothelium of blood vessels.

Ependymal cells

Glial cells that line the fluid-filled cavities (ventricles and canals) of the CNS; some produce cerebrospinal fluid (CSF) and others use cilia to circulate it.

Microglia

Small, mobile glial cells that serve as immune cells in the CNS, becoming phagocytic in response to inflammation to clear bacteria and cell debris.

Oligodendrocytes

Glial cells in the CNS with processes that wrap around segments of several axons to form insulating myelin sheaths.

Schwann cells

Glial cells in the PNS that wrap around individual segments of axons to form the myelin sheath or enclose unmyelinated axons.

Satellite cells

Glial cells in the PNS that surround neuron cell bodies, providing support, nutrients, and protection against heavy-metal poisons such as lead and mercury.

Myelin sheath

A specialized insulating layer formed by oligodendrocytes in the CNS and Schwann cells in the PNS that prevents almost all ion movement across the axonal membrane.

Nodes of Ranvier

Gaps in the myelin sheath occurring about every millimeter along an axon where ion movements take place during action potential conduction.

Gray matter

Nervous tissue consisting of groups of neuron cell bodies and their dendrites with very little myelin.

Cortex

The gray matter located on the surface of the brain.

Nuclei

Clusters of gray matter located deep within the brain.

Ganglion

A cluster of neuron cell bodies located in the peripheral nervous system.

White matter

Nervous tissue consisting of bundles of parallel axons with their whitish myelin sheaths.

Nerve tracts

Conduction pathways formed by white matter in the CNS that propagate action potentials from one area of the CNS to another.

Nerves

Bundles of parallel axons and associated connective tissue that constitute white matter in the peripheral nervous system.

Leak channels

Ion channels that remain constantly open, allowing ions to diffuse down their concentration gradients across the cell membrane.

Gated channels

Protein channels that remain closed until opened by specific signals, such as chemical molecules or electrical voltage changes.

Chemically gated channels

Membrane ion channels that open in response to the binding of specific chemical messengers, such as neurotransmitters.

Voltage-gated channels

Membrane ion channels that open or close in response to changes in the electrical potential across the cell membrane.

Resting membrane potential

The voltage difference measured across the cell membrane of an unstimulated cell, established primarily by ion concentration gradients and membrane permeability to $K^+$ and $Na^+$.

Sodium-potassium pump

An active transporter that pumps $Na^+$ out of the cell and $K^+$ into the cell, consuming about $25\%$ of a typical cell's ATP and $70\%$ of a neuron's ATP.

Depolarization

A decrease in membrane polarity where $Na^+$ enters the cell through open channels, causing the inside of the cell membrane to become positive relative to the outside.

Threshold

The critical membrane potential level that triggers the opening of voltage-gated $Na^+$ channels, producing a massive $600\text{-fold}$ increase in $Na^+$ permeability.

Repolarization

The phase during an action potential when voltage-gated $Na^+$ channels close and voltage-gated $K^+$ channels open, allowing $K^+$ to leave the cell and return the membrane toward its resting potential.

Hyperpolarization

A brief phase at the end of repolarization where the membrane potential becomes more negative than the resting level due to prolonged opening of voltage-gated $K^+$ channels.

Continuous conduction

The slower mode of action potential conduction along unmyelinated axons in which local currents stimulate adjacent membrane regions along the entire length of the axon.

Saltatory conduction

The rapid mode of action potential conduction in myelinated axons where action potentials leap from one node of Ranvier to the next.

Synapse

The functional junction where an axon terminal of one neuron communicates with another neuron or an effector cell, such as a muscle or gland cell.

Central Nervous System (CNS)

The division of the nervous system that consists of the brain and spinal cord.

Peripheral Nervous System (PNS)

The division of the nervous system consisting of nerves and ganglia that connects the CNS to the rest of the body.

Autonomic Nervous System (ANS)

The motor subdivision of the PNS that transmits action potentials from the CNS to cardiac muscle, smooth muscle, and glands; subdivided into sympathetic and parasympathetic divisions.

Enteric Nervous System (ENS)

A unique part of the peripheral nervous system with sensory and motor neurons contained wholly within the digestive tract, capable of functioning without input from the CNS or PNS.

Neuron

An excitable nerve cell that receives stimuli, conducts action potentials, and transmits signals to other neurons or effector organs.

Neuron Cell Body

The central region of a neuron containing a single nucleus, extensive rough endoplasmic reticulum, Golgi apparatus, mitochondria, neurofilaments, and microtubules.

Dendrites

Short, highly branching cytoplasmic extensions tapered from their bases at the neuron cell body to their tips that receive information and transmit it toward the cell body.

Axon

A single long cell process of uniform diameter that extends from the neuron cell body and conducts action potentials.

Axon Hillock

The specific area of the neuron cell body where the axon originates and where action potential threshold is most often reached.

Collateral Axons

Branches that diverge from the main axon process of a neuron.

Multipolar Neurons

Neurons structurally characterized by having many dendrites and a single axon; includes most neurons within the CNS and nearly all motor neurons.

Bipolar Neurons

Neurons possessing two processes: one dendrite and one axon; found in sensory organs such as the retina of the eye and the nasal cavity.

Pseudo-unipolar Neurons

Neurons with a single process extending from the cell body that divides into two extensions functioning together as a single axon; characteristic of most sensory neurons.

Glial Cells

Non-conducting supportive cells of the CNS and PNS that retain the ability to divide, outnumber neurons, and maintain normal conditions in nervous tissue.

Astrocytes

The major supporting glial cells in the CNS that regulate signaling, contribute to neural tissue repair (forming scars that block axon regeneration), and help form the blood-brain barrier.

Blood-Brain Barrier

A permeability barrier formed by astrocytes participating with blood vessel endothelium to regulate substance exchange between the blood and the CNS.

Ependymal Cells

Glial cells lining the ventricles and canals of the CNS; some produce cerebrospinal fluid (CSF) while others possess cilia that circulate CSF.

Microglia

Specialized immune glial cells of the CNS that become phagocytic in response to inflammation to remove bacteria and cellular debris.

Oligodendrocytes

CNS glial cells whose cytoplasmic processes repeatedly wrap around segments of multiple axons to form myelin sheaths.

Schwann Cells

PNS glial cells that repeatedly wrap around axons to form myelin sheaths or enclose unmyelinated axons.

Satellite Cells

Glial cells that surround neuron cell bodies in PNS ganglia to provide support, nutrients, and protection from heavy-metal poisons like lead and mercury.

Myelin Sheath

A specialized insulating layer of tightly wrapped cell membranes formed by oligodendrocytes or Schwann cells that prevents almost all ion movement across the axonal membrane.

Nodes of Ranvier

Gaps occurring approximately every millimeter between adjacent segments of myelin sheath where ion movement across the axon membrane can occur.

Unmyelinated Axons

Axons lacking myelin sheaths that rest within indentations of oligodendrocytes or Schwann cells; they outnumber myelinated axons in a typical small nerve.

Gray Matter

Nervous tissue consisting of groups of neuron cell bodies and their dendrites with very little myelin.

Cortex

The superficial layer of gray matter located on the surface of the brain.

Nuclei

Distinct clusters of gray matter located deeper within the brain.

Ganglion

A cluster of neuron cell bodies located within the peripheral nervous system (plural: ganglia).

White Matter

Whitish nervous tissue consisting of bundles of parallel myelinated axons.

Nerve Tracts

Bundles of parallel myelinated axons forming conduction pathways in the CNS that propagate action potentials between areas.

Nerves

Bundles of parallel axons and associated connective tissue located in the peripheral nervous system.

Leak Channels

Ion channels that remain constantly open, permitting ions to leak down their concentration gradients across the cell membrane.

Gated Channels

Protein channels in the cell membrane that remain closed until opened by specific chemical or electrical signals.

Chemically Gated Channels

Membrane ion channels that open in response to the binding of specific chemical molecules, such as neurotransmitters.

Voltage-Gated Channels

Membrane ion channels that open or close in response to changes in the electrical properties across the cell membrane.

Polarized Membrane

A state of unequal charge distribution across a membrane where the intracellular surface is negatively charged relative to the positively charged extracellular surface.

Resting Membrane Potential

The electrical potential difference across the cell membrane of an unstimulated cell, established by ion concentration gradients and differential leak channel permeability.

Sodium-Potassium Pump

An active transport protein that pumps $K^+$ into the cell and $Na^+$ out; it consumes approximately $25\%$ of ATP in a typical cell and $70\%$ of ATP in a neuron.

Depolarization

A decrease in membrane polarity occurring when $Na^+$ diffuses inward through open channels, turning the intracellular side of the membrane positive relative to the outside.

Local Potential

A localized change in membrane potential resulting from initial inward $Na^+$ current that can disappear if threshold is not attained.

Threshold

The level of depolarization required to open voltage-gated $Na^+$ channels, triggering a $600\text{-fold}$ increase in $Na^+$ membrane permeability and producing an action potential.

Repolarization

The return of the membrane potential toward resting levels caused by the closure of voltage-gated $Na^+$ channels and outward movement of $K^+$ via opening voltage-gated $K^+$ channels.

Hyperpolarization

A brief period at the conclusion of repolarization where the membrane potential becomes more negative than the resting membrane potential because voltage-gated $K^+$ channels remain open slightly longer.

All-or-None Principle

The principle stating that an action potential occurs at full, uniform magnitude if threshold is reached, or does not occur at all if threshold is missed.

Continuous Conduction

Action potential propagation along unmyelinated axons where local currents stimulate action potentials in adjacent membrane regions sequentially along the entire length.

Saltatory Conduction

Rapid action potential propagation along myelinated axons where action potentials leap from one node of Ranvier to the next via local currents.

Synapse

A specialized junction where the axon of one neuron communicates with another neuron or an effector cell, such as a muscle or gland.