Nervous Tissue – Saladin Ch. 12

A comprehensive set of vocabulary flashcards covering the structure, function, and physiology of nervous tissue as presented in Saladin Chapter 12.

Central Nervous System (CNS)

Brain and spinal cord; integrative and control centers of the nervous system.

Peripheral Nervous System (PNS)

All nervous tissue outside the CNS; includes cranial and spinal nerves and ganglia.

Nerve

Bundle of axons in the PNS carrying sensory and/or motor signals.

Ganglion

Cluster of neuron cell bodies in the PNS.

Sensory (Afferent) Division

PNS subdivision that conveys impulses from receptors to the CNS.

Somatic Sensory Fibers

Afferent fibers carrying signals from skin, skeletal muscles, and joints to the CNS.

Visceral Sensory Fibers

Afferent fibers conveying signals from organs within the ventral body cavity.

Motor (Efferent) Division

PNS subdivision transmitting impulses from the CNS to effector organs.

Somatic Motor Division

Motor output that controls voluntary contraction of skeletal muscles.

Autonomic Nervous System (ANS)

Visceral motor division controlling cardiac muscle, smooth muscle, and glands.

Sympathetic Division

ANS branch that mobilizes body systems during activity; “fight-or-flight.”

Parasympathetic Division

ANS branch that conserves energy and promotes housekeeping functions; “rest-and-digest.”

Neuron

Excitable, conductive, secretory, long-lived, amitotic cell that transmits electrical signals.

Neuroglia (Glial Cells)

Supportive cells of the nervous system that protect and aid neurons.

Sensory Neuron

Functional class of neuron transmitting impulses toward the CNS.

Interneuron

Neuron confined to CNS that processes, stores, and relays information.

Motor Neuron

Neuron carrying impulses away from the CNS to effectors.

Soma (Cell Body)

Neuronal region containing nucleus, organelles, and chromatophilic substance.

Dendrite

Short, tapering processes forming the receptive (afferent) region of a neuron.

Axon

Single efferent process that generates action potentials and ends in terminals.

Axon Hillock

Cone-shaped area of soma where the axon originates; trigger zone for APs.

Axon Terminal

Knob-like distal ending of an axon containing neurotransmitter-filled vesicles.

Neurofibrils

Actin filaments that compartmentalize rough ER into chromatophilic substance.

Chromatophilic Substance

Stacks of rough ER in soma organized by neurofibrils; site of protein synthesis.

Multipolar Neuron

Neuron with one axon and many dendrites; most common type and major CNS motor neuron.

Bipolar Neuron

Neuron with one dendrite and one axon; found in special senses such as retina and olfactory mucosa.

Unipolar Neuron

Pseudounipolar sensory neuron with a single process that splits into peripheral and central branches.

Schwann Cell

PNS glial cell that forms the myelin sheath around peripheral axons; creates nodes of Ranvier.

Node of Ranvier (Myelin Sheath Gap)

Unmyelinated segment between Schwann cells where voltage-gated channels cluster.

Satellite Cell

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

Oligodendrocyte

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

Astrocyte

CNS glial cell providing structural support, blood-brain barrier maintenance, and ion regulation.

Microglia

Small CNS macrophage-like glial cells that perform immune surveillance and phagocytosis.

Ependymal Cell

Ciliated CNS glial cell that lines ventricles and produces cerebrospinal fluid (CSF).

Myelin Sheath

Lipid-rich, insulating wrapping of axons formed by oligodendrocytes (CNS) or Schwann cells (PNS).

White Matter

CNS regions rich in myelinated axons; appears lighter due to high lipid content.

Gray Matter

CNS regions containing neuron somata and dendrites; less myelin, hence darker appearance.

Conduction Velocity

Speed at which a nerve signal travels, determined by axon diameter and degree of myelination.

Membrane Potential

Electrical charge difference (voltage) across a cell membrane at any moment.

Resting Membrane Potential (RMP)

Stable, polarized voltage (~ –70 mV in neurons) when the cell is not transmitting signals.

Local (Graded) Potential

Short-range, decremental change in membrane voltage occurring mainly on dendrites and soma.

Depolarization

Reduction in membrane potential; inside becomes less negative (e.g., Na⁺ influx).

Hyperpolarization

Increase in membrane potential; inside becomes more negative (e.g., K⁺ efflux or Cl⁻ influx).

Action Potential (AP)

All-or-none, non-decremental wave of depolarization and repolarization along axon and hillock.

Threshold

Critical membrane voltage that opens voltage-gated Na⁺ channels and initiates an AP.

Voltage-Gated Na⁺ Channel

Membrane protein that opens at threshold, allowing rapid Na⁺ influx and depolarization.

Voltage-Gated K⁺ Channel

Channel that opens more slowly; K⁺ efflux repolarizes and hyperpolarizes the membrane.

Absolute Refractory Period

Time during and immediately after an AP when no stimulus can trigger another AP.

Relative Refractory Period

Period following absolute phase when a stronger-than-usual stimulus can initiate an AP.

Propagation (Nerve Signal)

Self-propagating wave of action potentials traveling along an axon from hillock to terminals.

Saltatory Conduction

Rapid AP propagation in myelinated axons where impulses jump from node to node.

Continuous Conduction

Slower AP propagation along unmyelinated axons where the impulse travels every point on the membrane.

Synapse

Point of communication between a presynaptic and postsynaptic neuron or effector cell.

Presynaptic Neuron

Neuron that releases neurotransmitter into a synapse.

Postsynaptic Neuron

Neuron whose membrane receives neurotransmitter and responds with local potentials.

Axodendritic Synapse

Synapse between an axon terminal and a dendrite.

Axosomatic Synapse

Synapse between an axon terminal and a neuron soma.

Axoaxonic Synapse

Synapse between one axon terminal and another axon; often modulatory.

Chemical Synapse

Synapse in which neurotransmitter bridges the synaptic cleft to excite or inhibit the postsynaptic cell.

Neurotransmitter (NT)

Chemical messenger released by neurons to communicate across synapses.

Acetylcholine (ACh)

Neurotransmitter essential at neuromuscular junctions and many CNS/PNS synapses.

GABA (γ-Aminobutyric Acid)

Major inhibitory neurotransmitter in the CNS; opens Cl⁻ channels to hyperpolarize cells.

Catecholamines

Monoamine neurotransmitters derived from tyrosine: epinephrine, norepinephrine, dopamine.

Indolamines

Monoamine neurotransmitters derived from tryptophan or histidine: serotonin and histamine.

Cholinergic (Nicotinic) Receptor

Ionotropic ACh receptor causing Na⁺ influx and excitatory postsynaptic potentials (EPSPs).

GABA-ergic Receptor

Ionotropic receptor that, when bound by GABA, allows Cl⁻ influx producing inhibitory postsynaptic potentials (IPSPs).

EPSP (Excitatory Post-Synaptic Potential)

Depolarizing local potential that moves the postsynaptic neuron closer to threshold.

IPSP (Inhibitory Post-Synaptic Potential)

Hyperpolarizing local potential that drives the postsynaptic membrane farther from threshold.

Acetylcholinesterase (AChE)

Synaptic enzyme that degrades ACh into acetate and choline, terminating the signal.

Monoamine Oxidase (MAO)

Enzyme that degrades monoamine neurotransmitters after reuptake in the presynaptic terminal.

Reuptake

Active transport of neurotransmitter (or its components) back into the presynaptic neuron for recycling.

Neural Integration

Process by which a neuron’s hillock sums all EPSPs and IPSPs to decide whether to fire an AP.