Nervous System – Nervous Tissue (Chapter 12)

Vocabulary flashcards covering major terms and definitions from Chapter 12 on nervous tissue and neurophysiology.

Nervous System

Fast, complex body control system that uses electrical and chemical signals to regulate behavior, memory, and movement.

Endocrine System

Slower homeostatic control system that uses hormones released into the blood to influence target organs.

Sensory (Afferent) Neuron

Neuron that carries information from sensory receptors toward the CNS.

Motor (Efferent) Neuron

Neuron that carries commands from the CNS to effector organs such as muscles or glands.

Central Nervous System (CNS)

Brain and spinal cord; main integration and control center.

Peripheral Nervous System (PNS)

All nervous tissue outside CNS; nerves and ganglia that link body regions to the CNS.

Somatic Nervous System (SNS)

PNS division that carries sensory input from skin/senses and motor output to skeletal muscles; voluntary control.

Autonomic Nervous System (ANS)

PNS division providing involuntary motor output to cardiac muscle, smooth muscle, and glands; includes sympathetic and parasympathetic branches.

Enteric Nervous System (ENS)

Independent network of involuntary sensory and motor neurons that governs the gastrointestinal tract.

Nerve

Bundle of axons in the PNS wrapped in connective tissue layers (endoneurium, perineurium, epineurium).

Ganglion

Cluster of neuron cell bodies in the PNS sharing a common function.

Neuroglia (Glial Cells)

Supportive, protective cells of nervous tissue that maintain environment and aid neurons.

Neuron

Excitable cell that transmits electrical impulses; functional unit of the nervous system.

Soma (Cell Body)

Neuron’s metabolic center containing nucleus, organelles, and Nissl bodies that make neurotransmitters.

Dendrite

Short, branched neuronal process that receives signals and conveys them toward the soma as graded potentials.

Axon

Single long neuronal process that conducts impulses away from the soma to terminals.

Axon Hillock

Cone-shaped region where the axon originates; site of action-potential initiation (trigger zone).

Axon Terminal (Synaptic Knob)

Distal ending of an axon that stores and releases neurotransmitters into a synapse.

Chromatophilic Substance (Nissl Bodies)

Rough ER clusters in neurons responsible for protein synthesis and repair.

Unipolar Neuron

Neuron with one short process that splits into peripheral and central branches; mostly sensory.

Bipolar Neuron

Neuron with one axon and one dendrite; found in retina, olfactory mucosa, and ear.

Multipolar Neuron

Neuron with one axon and many dendrites; most common type, especially motor and interneurons.

Sensory (Afferent) Classification

Functional class of neurons transmitting impulses from receptors toward the CNS; mostly unipolar.

Motor (Efferent) Classification

Functional class of neurons sending impulses from the CNS to effectors; multipolar.

Interneuron (Association Neuron)

Neuron that connects sensory and motor pathways within the CNS; 99 % of all neurons.

Astrocyte

Star-shaped CNS glial cell that forms blood–brain barrier, regulates environment, and guides neuron development.

Oligodendrocyte

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

Microglial Cell

Small CNS phagocyte that removes debris and protects against pathogens.

Ependymal Cell

CNS glial cell lining brain ventricles and spinal canal; produces and circulates cerebrospinal fluid.

Satellite Cell

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

Neurolemmocyte (Schwann Cell)

PNS glial cell that forms myelin around a single axon and aids regeneration.

Myelin

Lipid-protein sheath produced by oligodendrocytes or Schwann cells that insulates axons and accelerates impulse conduction.

Node of Ranvier

Gap between myelin segments where voltage-gated channels cluster, enabling saltatory conduction.

Resting Membrane Potential (RMP)

-70 mV electrical charge difference across a neuron’s membrane due to ion concentration and permeability differences.

Depolarization

Decrease in membrane potential toward zero (inside becomes less negative) typically caused by Na⁺ influx.

Hyperpolarization

Increase in membrane potential (inside becomes more negative than RMP) often via K⁺ efflux or Cl⁻ influx.

Graded Potential

Local, short-distance change in membrane potential whose magnitude varies with stimulus strength; decays with distance.

Action Potential

Rapid, all-or-none electrical impulse that propagates along an axon when threshold is reached.

Threshold Potential

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

Absolute Refractory Period

Time during an action potential when a neuron cannot fire again regardless of stimulus strength.

Relative Refractory Period

Period after absolute phase when only a very strong stimulus can initiate another action potential.

Continuous Conduction

Slow propagation along unmyelinated axons where every membrane segment depolarizes and repolarizes.

Saltatory Conduction

Fast impulse transmission in myelinated axons where action potentials jump from node to node.

A Fibers

Largest, myelinated nerve fibers conducting impulses ~150 m/s; somatic sensory and motor.

B Fibers

Intermediate, lightly myelinated fibers conducting ~15 m/s; autonomic visceral neurons.

C Fibers

Smallest, unmyelinated fibers conducting ~1 m/s; slow pain and some autonomic signals.

Synapse

Junction where a neuron communicates with another neuron or effector cell.

Electrical Synapse

Synapse with gap junctions allowing direct ion flow for rapid, bidirectional signaling without receptors.

Chemical Synapse

Synapse where neurotransmitter crosses a synaptic cleft from presynaptic terminal to postsynaptic receptor; unidirectional.

Neurotransmitter

Chemical messenger released by neurons that binds to receptors and alters postsynaptic cell activity.

Acetylcholine (ACh)

Neurotransmitter active at neuromuscular junctions, many ANS synapses, and some CNS pathways.

Glutamate

Major excitatory amino-acid neurotransmitter in the CNS.

Gamma-Aminobutyric Acid (GABA)

Primary inhibitory neurotransmitter in the brain.

Dopamine

Monoamine neurotransmitter involved in reward, movement, and emotional responses; imbalances linked to Parkinson’s and schizophrenia.

Norepinephrine

Monoamine neurotransmitter and hormone involved in attention, arousal, and the sympathetic “fight-or-flight” response.

Serotonin

Monoamine neurotransmitter affecting mood, appetite, and sleep; imbalance associated with depression.

Endorphins

Peptide neurotransmitters that act as natural painkillers and produce feelings of euphoria.

Excitatory Postsynaptic Potential (EPSP)

Depolarizing graded potential on a postsynaptic membrane that increases likelihood of action potential firing.

Inhibitory Postsynaptic Potential (IPSP)

Hyperpolarizing graded potential that decreases likelihood of action potential generation.

Reuptake

Process whereby presynaptic transporters reclaim neurotransmitter from the synaptic cleft for reuse.

Enzymatic Breakdown

Deactivation of neurotransmitter by specific enzymes, e.g., acetylcholinesterase degrading ACh.

Neuromodulator

Chemical that modifies the effect of neurotransmitters without directly causing postsynaptic potentials.

Agonist

Substance that enhances or mimics the effect of a neurotransmitter at its receptor.

Antagonist

Substance that blocks or reduces the action of a neurotransmitter at its receptor.

Second Messenger

Intracellular molecule (e.g., cAMP) generated by receptor activation that amplifies and prolongs signals.

Cyclic AMP (cAMP)

Common second messenger produced by adenylate cyclase that activates kinases and modulates cell functions.

Neuronal Pool

Functional group of interconnected neurons that process specific types of information.

Converging Circuit

Neuronal pool where multiple inputs synapse onto one postsynaptic neuron, focusing signals.

Diverging Circuit

Circuit where one neuron sends impulses to many others, amplifying the signal.

Reverberating Circuit

Circuit that feeds back on itself to generate repetitive, rhythmic output until inhibited.

Parallel-After-Discharge Circuit

Circuit in which input travels along several paths that reach the postsynaptic neuron at different times, prolonging response.

Multiple Sclerosis (MS)

Autoimmune disorder that destroys CNS myelin, leading to vision changes, muscle weakness, and cognitive problems.

Caffeine

Adenosine receptor antagonist that blocks inhibitory neuromodulator adenosine, producing temporary alertness.

Adenosine

Inhibitory neuromodulator accumulating during wakefulness that promotes drowsiness when binding to its receptors.