Organization of the Nervous System, Neural Tissue, and Neurophysiology

Comprehensive vocabulary flashcards covering anatomical and functional divisions of the nervous system, neuroglia, neuron structures, membrane potential mechanics, action potential propagation, and synaptic transmission.

Central Nervous System (CNS)

The anatomical division consisting of the brain and spinal cord that acts as the main processing and control center to receive information, process it, and coordinate responses.

Peripheral Nervous System (PNS)

The anatomical division consisting of peripheral nerves outside the brain and spinal cord that connects the CNS to the rest of the body and carries information to and from the CNS.

Afferent Division

The functional sensory division of the nervous system that receives information from sensory receptors and carries it toward the CNS.

Efferent Division

The functional motor division of the nervous system that carries motor commands away from the CNS to effectors.

Exteroceptors

Receptors that monitor changes in the external environment, including touch, temperature, and other environmental stimuli.

Interoceptors

Receptors that monitor changes and stimuli within the body's internal environment, such as changes inside internal organs.

Proprioceptors

Receptors that monitor body position and movement, specifically the position and movement of muscles and joints.

Effectors

Target structures that receive motor commands from the CNS and produce a response, specifically: skeletal muscle, smooth muscle, cardiac muscle, exocrine glands, and adipose tissue.

Somatic Nervous System (SNS)

The subdivision of the efferent division that controls voluntary motor output specifically to somatic effectors, which are skeletal muscles.

Autonomic Nervous System (ANS)

The subdivision of the efferent division that automatically regulates visceral effectors: smooth muscle, cardiac muscle, exocrine glands, and adipose tissue.

Amitotic

A characteristic of neurons describing their inability to divide, which is associated with their lack of centrioles.

Dendrites

Neuron branching extensions containing chemically gated channels that receive incoming information from other cells.

Soma (Cell Body)

The control center of a neuron containing the nucleus and chemically gated channels that maintains cellular functions.

Axon Hillock

The specialized region of a neuron where the axon begins at the cell body.

Initial Segment

The specific region of a neuron containing voltage-gated channels where action potentials are initiated.

Axon

A long nerve fiber equipped with voltage-gated channels that carries electrical signals away from the cell body toward target cells.

Axon Terminals

The distal endings of an axon equipped with voltage-gated calcium channels that release neurotransmitters to communicate with adjacent cells.

Anterograde Transport

The form of axoplasmic transport that moves materials away from the cell body toward the axon terminal.

Retrograde Transport

The form of axoplasmic transport that moves materials toward the cell body from the axon terminal.

Anaxonic Neurons

Structural class of neurons found in the brain and sense organs that do not have an obvious axon and whose function is not fully understood.

Bipolar Neurons

Sensory neurons having two distinct extensions arising from the cell body, located in the eye, ear, and nasal mucosa.

Unipolar Neurons

Sensory neurons found in the PNS that have a single main extension emerging from the cell body.

Multipolar Neurons

The common structural category of neurons characterized by multiple extensions originating from the cell body, including motor neurons and interneurons.

Interneurons

Association neurons located primarily within the CNS between sensory and motor neurons that process information, mediate reflexes, and participate in cognitive functions.

Ependymal Cells

CNS neuroglia with cilia that line the ventricles of the brain and the central canal of the spinal cord to secrete, monitor, and circulate cerebrospinal fluid (CSF).

Astrocytes

CNS neuroglial cells that maintain the blood-brain barrier, regulate interstitial fluid ions ($\text{Na}^+$, $\text{K}^+$) and gases ($\text{O}_2$, $\text{CO}_2$), provide structural support, and form scar tissue after injury.

Microglia

Phagocytic defense and cleanup neuroglia in the CNS derived from blood stem cells that remove cellular debris, waste, and pathogens.

Oligodendrocytes

Supporting neuroglia in the CNS that produce myelin sheaths around axons and provide structural organization.

Schwann Cells

Supporting neuroglia in the PNS that myelinate most peripheral axons and participate in neural repair.

Satellite Cells

Supporting neuroglial cells located in PNS ganglia that regulate the environment (nutrients, gases, and neurotransmitters) surrounding peripheral neurons.

White Matter

Regions of the CNS composed primarily of myelinated axons, which give the tissue its lighter appearance.

Gray Matter

Regions of the CNS containing neuron cell bodies, dendrites, synapses, and portions of unmyelinated axons responsible for neuronal processing.

Myelination

The wrapping of axons with cell membranes to provide electrical insulation and increase the conduction speed of nerve impulses.

Nodes of Ranvier

The unmyelinated gaps along an axon between adjacent myelin-covered sections.

Internodes

The myelinated sections of an axon located between adjacent nodes of Ranvier.

Resting Membrane Potential (RMP)

The electrical charge difference across the cell membrane at rest, which is approximately $-70\,\text{mV}$ in a typical neuron.

Extracellular Fluid (ECF) Ion Concentrations

The resting ion concentrations outside the neuron: $\text{Na}^+$ at $140\,\text{mM}$ and $\text{K}^+$ at $4\,\text{mM}$.

Intracellular Fluid (ICF) Ion Concentrations

The resting ion concentrations inside the neuron: $\text{Na}^+$ at $10\,\text{mM}$ and $\text{K}^+$ at $140\,\text{mM}$, along with negatively charged proteins.

Leak Channels

Continuously open membrane channels that allow passive ion diffusion, where more $\text{K}^+$ leaves than $\text{Na}^+$ enters due to a higher abundance of potassium channels.

Sodium-Potassium Pump

An active transport carrier protein powered by ATP that maintains resting membrane potential by pumping $3\,\text{Na}^+$ out of the cell and $2\,\text{K}^+$ into the cell per cycle.

Chemically Gated Channels

Membrane ion channels located on dendrites and somas that open or close in response to specific chemical signals, such as neurotransmitters.

Voltage-Gated Channels

Membrane ion channels located on excitable membranes (such as axons) that open or close in response to changes in transmembrane voltage.

Mechanically Gated Channels

Membrane ion channels located in sensory receptors that open in response to physical distortion of the cell membrane.

Depolarization

A shift in transmembrane potential where the inside of the cell becomes less negative (closer to zero), commonly caused by $\text{Na}^+$ entering the neuron.

Hyperpolarization

A shift in transmembrane potential where the inside of the cell becomes more negative (farther from zero), commonly caused by $\text{K}^+$ exiting or $\text{Cl}^-$ entering the neuron.

Graded Potential

A localized change in membrane potential occurring on dendrites and somas that varies in amplitude based on stimulus strength and decreases with distance.

Action Potential

A propagated, all-or-none electrical disturbance across an excitable membrane initiated at the initial segment that travels down the entire axolemma.

All-or-None Principle

The principle stating that an action potential occurs completely if the membrane reaches threshold voltage, or does not occur at all, regardless of stimulus magnitude above threshold.

Threshold Voltage

The minimum membrane voltage depolarization needed to open voltage-gated sodium channels and trigger an action potential.

Repolarization

The stage of an action potential during which voltage-gated $\text{Na}^+$ channels inactivate and voltage-gated $\text{K}^+$ channels open, allowing $\text{K}^+$ to exit and restoring a negative internal potential.

Absolute Refractory Period

The period during depolarization and sodium channel inactivation when another action potential cannot be generated regardless of stimulus strength.

Relative Refractory Period

The recovery period following the absolute refractory period when voltage-gated channels are resetting and an action potential can only be generated by a stronger-than-normal stimulus.

Continuous Conduction

The slower mode of action potential propagation occurring along unmyelinated axons, where the impulse is regenerated step-by-step along the entire membrane.

Saltatory Conduction

The rapid mode of action potential propagation along myelinated axons, where the electrical signal effectively jumps from one node of Ranvier to the next.

Type A Fibers

Large, myelinated axon fibers that propagate signals at $268\,\text{mph}$, carrying somatic motor commands and sensory signals regarding position, balance, and delicate touch.

Type B Fibers

Medium-sized, myelinated axon fibers conducting signals at $40\,\text{mph}$, carrying visceral motor commands and sensations of temperature, pain, and touch.

Type C Fibers

Small, unmyelinated axon fibers conducting signals at $2\,\text{mph}$, carrying visceral motor commands and information regarding temperature, pain, and touch.

Synapse

The specialized site of intercellular communication between a neuron and another cell, such as another neuron, muscle fiber, or gland cell.

Synaptic Cleft

The narrow extracellular space separating the presynaptic membrane from the postsynaptic membrane across which neurotransmitters diffuse.

Electrical Synapse

A rare type of synapse where pre- and postsynaptic membranes are locked together by gap junctions containing connexons, allowing direct ionic and electrical flow.

Chemical Synapse

A synapse that relies on the exocytosis of chemical messengers (neurotransmitters) into the synaptic cleft to bind receptors on the postsynaptic membrane.

Cholinergic Synapse

A chemical synapse that releases acetylcholine (ACh), which opens chemically gated $\text{Na}^+$ channels on the postsynaptic membrane to produce depolarization.

Acetylcholinesterase

The specific enzyme located at cholinergic synapses that hydrolyzes and inactivates acetylcholine to terminate postsynaptic stimulation.

Gamma-Aminobutyric Acid (GABA)

An inhibitory neurotransmitter found at approximately $20\%$ of brain synapses that produces hyperpolarizing effects.

Neuromodulators

Substances (such as opioids or neuropeptides) released by axon terminals that alter synaptic activity, change neurotransmitter release rates, or modify postsynaptic sensitivity.

Excitatory Postsynaptic Potential (EPSP)

A graded depolarization of the postsynaptic membrane caused by $\text{Na}^+$ or $\text{Ca}^{2+}$ influx that moves the transmembrane potential closer to threshold.

Inhibitory Postsynaptic Potential (IPSP)

A graded hyperpolarization of the postsynaptic membrane caused by $\text{K}^+$ efflux or $\text{Cl}^-$ influx that moves the transmembrane potential farther from threshold.

Temporal Summation

The addition of multiple postsynaptic potentials occurring in rapid succession at the same location over time.

Spatial Summation

The cumulative addition of simultaneous postsynaptic potentials generated at multiple different synaptic locations across the cell.

Presynaptic Facilitation

The enhancement of synaptic transmission caused by a regulatory neuron that increases $\text{Ca}^{2+}$ entry into the presynaptic terminal, increasing neurotransmitter release.

Presynaptic Inhibition

The reduction of synaptic transmission caused by a regulatory neuron that decreases $\text{Ca}^{2+}$ entry into the presynaptic terminal, reducing neurotransmitter release.

Action Potential Frequency

The rate at which action potentials are generated along an axon, which serves as the mechanism by which the nervous system communicates the intensity of a stimulus.