Fundamentals of Anatomy & Physiology – Chapter 12: Nervous Tissue

Vocabulary flashcards covering key terms and definitions from Chapter 12 (Nervous Tissue) to aid exam preparation.

Nervous System

Organ system that receives sensory input, processes information, and initiates motor outputs via brain, spinal cord, nerves, and receptors.

Central Nervous System (CNS)

Brain and spinal cord; integrates, processes, and coordinates sensory data and motor commands.

Peripheral Nervous System (PNS)

All nervous tissue outside the CNS; delivers sensory information to and carries motor commands from the CNS.

Afferent Division

Functional PNS subdivision that carries sensory information from receptors to the CNS.

Efferent Division

Functional PNS subdivision that carries motor commands from the CNS to effectors.

Somatic Nervous System (SNS)

Efferent division controlling voluntary and reflex skeletal-muscle contractions.

Autonomic Nervous System (ANS)

Efferent division controlling involuntary actions of smooth and cardiac muscle, glands, and adipose tissue.

Sympathetic Division

ANS branch producing "fight-or-flight" responses.

Parasympathetic Division

ANS branch producing "rest-and-digest" responses.

Enteric Nervous System (ENS)

Network of neurons in digestive-tract walls that coordinates local reflexes independently of the CNS.

Neuron

Basic functional cell of nervous tissue specialized for electrical communication.

Neuroglia (Glial Cells)

Supportive cells of nervous tissue that protect, nourish, and insulate neurons.

Cell Body (Soma)

Neuron region containing nucleus and most organelles.

Perikaryon

Cytoplasm of the neuron’s cell body.

Nissl Bodies

Dense clusters of RER and ribosomes in the soma; give gray color and synthesize proteins.

Dendrite

Short, branched neuronal process that receives signals from other neurons.

Dendritic Spine

Fine projection on a dendrite where synapses occur.

Axon

Long cytoplasmic process of a neuron that propagates action potentials.

Axoplasm

Cytoplasm within an axon.

Axolemma

Plasma membrane of an axon.

Initial Segment

First part of the axon adjacent to the axon hillock where action potentials originate.

Axon Hillock

Thickened region linking soma to initial segment; integrates signals.

Collateral

Branch of an axon.

Telodendria

Fine distal branches of an axon or its collaterals.

Axon Terminal (Synaptic Terminal)

Enlarged end of telodendrion that stores and releases neurotransmitters.

Axoplasmic Transport

Movement of materials between soma and axon terminals along neurotubules.

Kinesin

Motor protein driving anterograde axonal transport.

Dynein

Motor protein driving retrograde axonal transport.

Anterograde Transport

Axoplasmic movement from soma toward axon terminals.

Retrograde Transport

Axoplasmic movement from axon terminals toward soma.

Anaxonic Neuron

Small neuron with many dendrites and no obvious axon; found in brain and special senses.

Bipolar Neuron

Neuron with one dendrite and one axon; rare, in special sense organs.

Unipolar (Pseudounipolar) Neuron

Neuron whose dendrites and axon are continuous; most PNS sensory neurons.

Multipolar Neuron

Neuron with one long axon and multiple dendrites; common in CNS and PNS motor pathways.

Sensory (Afferent) Neuron

Neuron carrying information from receptors to the CNS.

Motor (Efferent) Neuron

Neuron carrying commands from CNS to effectors.

Interneuron

Neuron located between sensory and motor neurons; integrates information.

Interoceptor

Sensory receptor monitoring internal organs, stretch, pressure, pain.

Exteroceptor

Sensory receptor monitoring external environment (touch, temperature, special senses).

Proprioceptor

Receptor monitoring position and movement of muscles and joints.

Astrocyte

Star-shaped CNS glial cell that maintains blood-brain barrier, supports neurons, repairs tissue, and regulates interstitial environment.

Oligodendrocyte

CNS glial cell that myelinates axons, forming the myelin sheath.

Ependymal Cell

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

Microglia

Small motile CNS glial cells that remove debris and pathogens by phagocytosis.

Satellite Cell

PNS glial cell surrounding neuron cell bodies in ganglia; regulates interstitial fluid.

Schwann Cell

PNS glial cell that myelinates peripheral axons and aids repair after injury.

Myelin

Lipid-rich insulation around axons that increases action-potential speed.

Internode

Myelinated segment of an axon.

Node of Ranvier

Gap between myelin internodes where axonal membrane is exposed.

Demyelination

Pathological loss of myelin in CNS or PNS leading to impaired conduction.

Wallerian Degeneration

Process in which axon distal to injury disintegrates in the PNS.

Resting Membrane Potential

Electrical potential across a cell membrane of an unstimulated neuron (~ –70 mV).

Electrochemical Gradient

Combined chemical and electrical forces acting on an ion across a membrane.

Sodium–Potassium Exchange Pump

ATP-driven transport moving 3 Na⁺ out and 2 K⁺ in, stabilizing resting potential.

Chemically Gated Ion Channel

Membrane channel that opens when specific ligands (e.g., ACh) bind.

Voltage-Gated Ion Channel

Channel that opens/closes in response to membrane-potential changes.

Mechanically Gated Ion Channel

Channel that opens/closes with physical membrane distortion (touch, pressure).

Graded Potential

Localized, decremental change in membrane potential produced by stimulus-opened channels.

Depolarization

Shift of membrane potential toward 0 mV (less negative).

Hyperpolarization

Shift of membrane potential to more negative values than resting level.

Repolarization

Return of membrane potential to resting level after depolarization.

Action Potential

Large, propagated change in membrane potential that travels along axon.

Threshold

Membrane potential that must be reached to trigger an action potential (about –60 mV to –55 mV).

All-or-None Principle

Once threshold is reached, an action potential is generated fully; if not, none occurs.

Refractory Period

Time during/after an action potential when membrane is less responsive to stimuli.

Absolute Refractory Period

Phase when no stimulus can initiate another action potential because Na⁺ channels are open or inactivated.

Relative Refractory Period

Phase when a stronger-than-normal stimulus can trigger an action potential; membrane is hyperpolarized.

Continuous Propagation

Slow conduction of action potentials along unmyelinated axons where each segment depolarizes sequentially.

Saltatory Propagation

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

Type A Fiber

Large, myelinated axon with fastest conduction; carries motor commands to skeletal muscle and acute sensory info.

Type B Fiber

Medium, myelinated axon conducting at intermediate speeds; visceral sensory & autonomic motor fibers.

Type C Fiber

Small, unmyelinated axon conducting slowly; carries pain, temperature, and autonomic commands.

Synapse

Specialized junction where a neuron communicates with another cell.

Presynaptic Neuron

Neuron that sends a signal across a synapse.

Postsynaptic Neuron

Neuron or effector that receives the synaptic signal.

Electrical Synapse

Synapse where cells are linked by gap junctions allowing direct ion passage and rapid transmission.

Chemical Synapse

More common synapse where neurotransmitters cross a synaptic cleft to affect the postsynaptic cell.

Acetylcholine (ACh)

Common excitatory neurotransmitter at NMJ, many CNS synapses, and parasympathetic junctions.

Cholinergic Synapse

Synapse that releases acetylcholine as its neurotransmitter.

Acetylcholinesterase (AChE)

Enzyme that breaks down ACh in the synaptic cleft, terminating its action.

Synaptic Delay

~0.2–0.5 ms pause between arrival of action potential and postsynaptic response, mainly due to Ca²⁺ influx and transmitter release.

Synaptic Fatigue

Reduced synaptic efficiency due to depleted neurotransmitter after high activity.

Excitatory Neurotransmitter

Chemical that depolarizes postsynaptic membrane, promoting action potentials.

Inhibitory Neurotransmitter

Chemical that hyperpolarizes postsynaptic membrane, suppressing action potentials.

Norepinephrine (NE)

Excitatory biogenic amine released at adrenergic synapses in brain and ANS.

Dopamine

Biogenic amine that may be excitatory or inhibitory; deficiency linked to Parkinson's; reuptake blocked by cocaine.

Serotonin

CNS neurotransmitter affecting mood; low levels linked to depression; increased by SSRIs.

Glutamate

Major excitatory amino-acid neurotransmitter in brain; vital for learning and memory.

Glycine

Inhibitory amino-acid neurotransmitter in spinal cord and brainstem; blocked by strychnine.

Gamma-Aminobutyric Acid (GABA)

Primary inhibitory neurotransmitter in brain; action enhanced by antianxiety drugs.

Substance P

Neuropeptide transmitter involved in pain pathways and gut function.

Opioid

Class of neuromodulatory peptides (enkephalins, endorphins, dynorphins) that reduce pain perception.

Enkephalin

Endogenous opioid peptide that decreases pain signals.

Endorphin

Natural opioid peptide producing analgesia and euphoria.

Dynorphin

Potent opioid peptide modulating pain and emotion.

Nitric Oxide (NO)

Gaseous neurotransmitter/neuromodulator acting via intracellular enzymes; dilates vessels, affects learning.

Carbon Monoxide (CO)

Gaseous neurotransmitter in brain with modulatory functions.

Ionotropic Effect

Direct action of neurotransmitter on chemically gated ion channel altering membrane potential.

Metabotropic Effect

Indirect action of transmitter via G-protein–coupled receptors and second messengers (e.g., cAMP).

Excitatory Postsynaptic Potential (EPSP)

Graded depolarization of postsynaptic membrane making neuron more likely to fire.