Chapter 12 – Nervous System: Nervous Tissue (Vocabulary)

A comprehensive set of vocabulary flashcards covering key terms and concepts from Chapter 12 on Nervous Tissue, including neural organization, cell types, physiology, signaling, and integration.

Central Nervous System (CNS)

Composed of the brain and spinal cord; serves as the control and integration center of the nervous system.

Peripheral Nervous System (PNS)

All nervous tissue outside the CNS that connects it to sensory receptors, muscles, and glands.

Afferent (Sensory) Nervous System

Functional division that carries sensory information from receptors to the CNS.

Somatic Sensory System

Part of the sensory division that detects stimuli we consciously perceive (e.g., touch, vision).

Visceral Sensory System

Sensory subdivision that monitors internal organs; typically not consciously perceived.

Efferent (Motor) Nervous System

Division that transmits motor commands from the CNS to effectors.

Somatic Motor System

Sends voluntary motor signals to skeletal muscles.

Autonomic Motor System

Sends involuntary commands to cardiac muscle, smooth muscle, and glands; includes sympathetic and parasympathetic divisions.

Enteric Nervous System (ENS)

Intrinsic nervous network of the GI tract regulating digestive functions.

Neuron

Excitable cell of the nervous system specialized for communication via electrical and chemical signals.

Glial Cell (Neuroglia)

Non-excitable supporting cell that protects, nourishes, and organizes neurons; capable of mitosis.

Excitability

Neuron property of responding to a stimulus by altering membrane potential.

Conductivity

Ability of a neuron to propagate an electrical signal along its membrane.

Secretion

Release of neurotransmitter from a neuron in response to an electrical signal.

Cell Body (Soma)

Neuronal region containing the nucleus and most organelles; integrates inputs.

Dendrite

Short, unmyelinated neuronal process that receives incoming signals and conveys them toward the soma.

Axon

Long neuronal process that propagates action potentials and ends in synaptic knobs.

Axon Hillock

Cone-shaped region of the soma where the axon originates; site of action-potential initiation.

Axoplasm

Cytoplasm within the axon.

Axolemma

Plasma membrane of the axon.

Axon Collateral

Branch of an axon that enables communication with multiple targets.

Neuronal Cytoskeleton

Framework of microtubules, actin filaments, and neurofilaments that maintains neuron shape and supports axonal transport.

Anterograde Transport

Movement of materials from the soma toward the synaptic knobs.

Retrograde Transport

Movement of substances from the axon terminal back to the soma for recycling or signaling.

Fast Axonal Transport

Rapid, ATP-dependent movement of vesicles and organelles along microtubules (both directions).

Slow Axonal Transport

Gradual movement of enzymes and cytoskeletal elements from soma to axon only.

Anaxonic Neuron

Neuron with many processes but no distinguishable axon; primarily interneurons.

Bipolar Neuron

Neuron with one dendrite and one axon; found in special senses (e.g., retina, olfactory epithelium).

Pseudounipolar (Unipolar) Neuron

Sensory neuron with single process that splits into peripheral and central branches.

Multipolar Neuron

Most common neuron type; one axon and many dendrites.

Sensory (Afferent) Neuron

Neuron that conducts input from receptors to the CNS.

Motor (Efferent) Neuron

Neuron that carries commands from the CNS to effectors.

Interneuron

Neuron located entirely within the CNS that processes information; 99 % of all neurons.

Nerve

Bundle of parallel axons in the PNS enclosed by connective tissue layers.

Epineurium

Dense irregular connective tissue that surrounds an entire nerve.

Perineurium

Dense irregular connective tissue wrapping a fascicle within a nerve.

Endoneurium

Delicate areolar connective tissue insulating individual axons.

Cranial Nerve

Nerve that emerges directly from the brain.

Spinal Nerve

Nerve arising from the spinal cord.

Mixed Nerve

Nerve containing both sensory and motor axons.

Astrocyte

Star-shaped CNS glial cell that forms the blood–brain barrier, regulates interstitial fluid, and supports neurons.

Ependymal Cell

Ciliated CNS glial cell lining ventricles and central canal; produces and circulates cerebrospinal fluid.

Microglia

Small CNS phagocytic glial cell that removes debris and pathogens.

Oligodendrocyte

CNS glial cell that myelinates and insulates multiple axons, increasing conduction speed.

Satellite Cell

PNS glial cell that surrounds neuron cell bodies in ganglia and regulates their environment.

Schwann Cell (Neurolemmocyte)

PNS glial cell that myelinates a single axon segment and forms the neurilemma.

Glioma

Primary CNS tumor arising from glial cells; may be benign or malignant.

Myelination

Process by which glial cells wrap axons with lipid-rich layers to insulate and speed signal conduction.

Neurilemma

Outer cytoplasmic layer and nucleus of a Schwann cell surrounding a myelinated axon in the PNS.

Node of Ranvier (Neurofibril Node)

Gap between myelin sheaths where voltage-gated channels are concentrated.

White Matter

Region of the CNS containing myelinated axons.

Gray Matter

CNS region containing neuron cell bodies, unmyelinated axons, and glia.

Guillain–Barré Syndrome

Autoimmune disorder causing demyelination of PNS nerves, leading to weakness and paralysis.

Regeneration Tube

Structure formed by neurilemma and endoneurium guiding PNS axon regrowth.

Ohm’s Law (Neurophysiology)

Current = Voltage ÷ Resistance; describes ionic current flow across neuronal membranes.

Resting Membrane Potential (RMP)

Baseline electrical charge difference across the neuronal membrane, typically –70 mV.

Leak Channel

Always-open ion channel that contributes to the RMP.

Chemically Gated Channel

Ion channel that opens in response to neurotransmitter binding.

Voltage-Gated Channel

Channel that opens or closes when membrane potential changes.

Excitatory Postsynaptic Potential (EPSP)

Depolarizing graded potential in a postsynaptic neuron.

Inhibitory Postsynaptic Potential (IPSP)

Hyperpolarizing graded potential in a postsynaptic neuron.

Spatial Summation

Addition of simultaneous postsynaptic potentials at different locations on the neuron.

Temporal Summation

Addition of postsynaptic potentials from rapid, repeated input at one synapse.

Threshold Potential

Membrane voltage (≈ –55 mV) that must be reached to trigger an action potential.

All-or-None Law

Principle that action potentials occur with uniform amplitude once threshold is reached.

Depolarization

Phase of action potential where Na⁺ influx makes the inside of the neuron positive.

Repolarization

Return toward negative potential due to K⁺ efflux following depolarization.

Hyperpolarization

Membrane potential becomes more negative than the resting level, often at action-potential end.

Absolute Refractory Period

Time during which a second action potential cannot be initiated, regardless of stimulus strength.

Relative Refractory Period

Interval when a stronger-than-normal stimulus can trigger another action potential.

Continuous Conduction

Action-potential propagation along unmyelinated axons involving sequential opening of channels.

Saltatory Conduction

Rapid impulse propagation in myelinated axons where action potentials leap from node to node.

Neurotransmitter

Chemical messenger released by neurons to stimulate or inhibit other cells.

Acetylcholine (ACh)

Most common neurotransmitter; excites skeletal muscle and influences CNS arousal.

Biogenic Amine

Neurotransmitter derived from modified amino acids, e.g., dopamine, serotonin.

Catecholamine

Subclass of biogenic amines synthesized from tyrosine, e.g., dopamine, norepinephrine.

Indolamine

Biogenic amine derived from tryptophan or histidine, e.g., serotonin.

Amino Acid Neurotransmitter

Simple amino acids functioning as transmitters, including glutamate, GABA, and glycine.

Neuropeptide

Chain of 2–40 amino acids acting as neurotransmitter or neuromodulator, e.g., endorphins.

Neuromodulation

Process by which chemicals alter the responsiveness of neurons to neurotransmitters.

Facilitation (Neuromodulation)

Modulatory effect that enhances postsynaptic response by increasing neurotransmitter or receptors.

Inhibition (Neuromodulation)

Modulatory effect that diminishes postsynaptic response by decreasing neurotransmitter or receptors.

Nitric Oxide (NO)

Short-lived gaseous neuromodulator involved in memory and vasodilation.

Endocannabinoid

Lipid-based neuromodulator that binds cannabinoid receptors influencing memory and appetite.

Converging Circuit

Neuronal pool where inputs from several neurons converge onto a single postsynaptic neuron.

Diverging Circuit

Neuronal circuit that spreads information from one neuron to many targets.

Reverberating Circuit

Neuronal pathway with feedback loops producing repetitive, cyclical activity.

Parallel-After-Discharge Circuit

Circuit where inputs travel along parallel paths arriving at different times, prolonging the response.