Nervous System Anatomy and Physiology Flashcards

Vocabulary practice flashcards covering structural and functional divisions, neuron characteristics, glial cells, nerve structures, axonal transport, electrophysiology, action potentials, and neurotransmitters based on lecture slides.

Somatic sensory system

The functional division of the sensory nervous system that detects stimuli we consciously perceive, such as inputs from the eyes, ears, and skin.

Visceral sensory system

The functional division of the sensory nervous system that detects stimuli we typically do not consciously perceive, such as signals from blood vessels and internal organs like the heart or kidneys.

Somatic motor system

The functional division of the motor nervous system that sends voluntary, consciously controlled motor signals to skeletal muscles.

Autonomic motor system

The functional division of the motor nervous system (also called visceral motor) that sends involuntary motor commands to cardiac muscle, smooth muscle, and glands, divided into sympathetic and parasympathetic divisions.

Excitability

A general trait of neurons defined as responsiveness to a stimulus, which induces a change in the cell's membrane potential.

Conductivity

The ability of a neuron to propagate an electrical signal along its membrane through the sequential opening of voltage-gated channels.

Chromatophilic substance

Structures within the soma of a neuron, also known as Nissl bodies, composed of free and bound ribosomes.

Axon hillock

The triangular region of the neuron cell body (soma) where the axon attaches.

Neurofilaments

Intermediate filaments within the neuronal cytoskeleton that aggregate to form bundles called neurofibrils, providing tensile strength.

Anterograde transport

Movement of material from the neuron cell body toward the synaptic knobs to deliver newly synthesized materials.

Retrograde transport

Movement of used materials from the axon back to the cell body for breakdown and recycling.

Fast axonal transport

Axonal transport occurring at about $400\,mm$ per day along microtubules, powered by ATP-splitting motor proteins in either anterograde or retrograde directions.

Slow axonal transport

Axonal transport occurring at about $0.1\,mm$ to $3\,mm$ per day resulting from the flow of axoplasm, moving substances (enzymes, cytoskeletal components, axoplasm) strictly in an anterograde direction.

Multipolar neurons

Structural neuron classification characterized by multiple processes extending from the soma (typically many dendrites and one axon); the most common type, including all motor neurons and most interneurons.

Bipolar neurons

Uncommon structural neuron classification characterized by two processes extending directly from the soma (one dendrite and one axon), found in special sense organs like the retina of the eye and olfactory epithelium.

Unipolar neurons

Structural neuron classification featuring a single short process extending from the soma that splits like a T into a peripheral process and a central process; includes most sensory neurons.

Anaxonic neurons

Structural neuron classification possessing dendrites but no axon, found as interneurons within the central nervous system.

Interneurons

Also called association neurons, these make up $99\%$ of all neurons, are located entirely within the CNS, integrate information, and communicate between sensory and motor neurons.

Epineurium

A thick outer layer of dense irregular connective tissue that encloses an entire nerve.

Perineurium

A layer of dense irregular connective tissue that wraps a fascicle, which is a small bundle of axons inside a nerve.

Endoneurium

A delicate layer of areolar connective tissue that wraps an individual axon, separating and electrically insulating it.

Mixed nerves

Nerves containing both sensory and motor neurons; most named nerves belong to this category.

Electrical synapse

A fast type of synapse where presynaptic and postsynaptic neurons are bound together directly by gap junctions, allowing passage of electrical signals without synaptic delay.

Synaptic delay

The total duration required for neurotransmitter release from synaptic vesicles, diffusion across the synaptic cleft, binding to postsynaptic receptors, and initiation of a postsynaptic potential.

Astrocytes

Star-shaped CNS glial cells—the most abundant in the CNS—whose perivascular feet help form the blood-brain barrier, regulate tissue fluid composition, assist synapse formation, and provide structural support.

Ependymal cells

Ciliated simple cuboidal or simple columnar epithelial cells lining the internal cavities of the brain and spinal cord that form the choroid plexus to produce and circulate cerebrospinal fluid (CSF).

Microglia

Small, phagocytic immune cells in the CNS that wander through tissue, replicate during infections, engulf infectious agents, and clear cellular debris.

Oligodendrocytes

Large CNS glial cells with slender extensions that wrap around segments of multiple axons to form myelin sheaths, enabling faster action potential propagation.

Satellite cells

PNS glial cells arranged around neuronal cell bodies in a ganglion that electrically insulate them and regulate nutrient and waste exchange.

Neurolemmocytes

Elongated, flat PNS glial cells (also known as Schwann cells) that encircle a $1\,mm$ segment of a single PNS axon to form a myelin sheath and outer neurilemma.

Neurilemma

The delicate outer membrane layer formed by the pushed periphery of a neurolemmocyte's cytoplasm and nucleus during PNS axon myelination.

Neurofibril nodes

Also called nodes of Ranvier, these are unmyelinated gaps along the axon located between adjacent wrapped neurolemmocytes or oligodendrocyte processes.

Wallerian degeneration

The breakdown process occurring distal to an axon cut, where the severed distal axon segment and myelin sheath degenerate while the neurilemma survives.

Regeneration tube

A pathway formed by surviving neurilemma and endoneurium in a severed PNS nerve that guides the regenerating axon back to its original target.

Leak channels

Passive membrane protein pores that remain open continuously to allow specific ions to diffuse down their concentration gradients.

Modality gated channels

Membrane ion channels that open in response to a specific physical stimulus other than chemical binding or voltage change, such as mechanical pressure in skin receptors.

Receptive segment

The functional region of a neuron comprising the dendrites and cell body, containing chemically gated ion channels.

Initial segment

The functional region of a neuron located at the axon hillock that contains voltage-gated $\text{Na}^+$ and $\text{K}^+$ channels where postsynaptic potentials undergo summation.

Conductive segment

The functional region of a neuron consisting of the axon and its branches, containing voltage-gated $\text{Na}^+$ and $\text{K}^+$ channels for propagating action potentials.

Transmissive segment

The functional region at the synaptic knobs of a neuron containing voltage-gated $\text{Ca}^{2+}$ channels and $\text{Ca}^{2+}$ pumps responsible for neurotransmitter release.

Ohm's law

The physical law stating that electrical current is directly proportional to voltage and inversely proportional to resistance, represented as $\text{Current} = \frac{\text{Voltage}}{\text{Resistance}}$.

Resting membrane potential (RMP)

The electrical charge difference across the membrane of an unstimulated neuron, typically measured at $-70\,mV$, established primarily by $\text{K}^+$ leak channels.

Excitatory postsynaptic potential (EPSP)

A temporary local depolarization of the postsynaptic neuron's receptive segment caused by cation entry (such as $\text{Na}^+$) through chemically gated channels, bringing membrane potential closer to threshold.

Inhibitory postsynaptic potential (IPSP)

A temporary local hyperpolarization of the postsynaptic neuron's receptive segment caused by $\text{K}^+$ exit or $\text{Cl}^-$ entry through chemically gated channels, making the inside more negative.

Threshold membrane potential

The minimum membrane potential change (typically about $-55\,mV$) required at the initial segment to trigger the opening of voltage-gated channels and initiate an action potential.

Spatial summation

The integration of postsynaptic potentials generated simultaneously at multiple distinct locations on a postsynaptic neuron's receptive region.

Temporal summation

The integration of postsynaptic potentials generated when a single presynaptic neuron repeatedly releases neurotransmitter in rapid succession within a very short timeframe.

Absolute refractory period

A brief period of approximately $1\,ms$ after an action potential begins during which no stimulus, regardless of strength, can initiate another action potential because $\text{Na}^+$ channels are open or inactivated.

Relative refractory period

The time interval immediately following the absolute refractory period when $\text{Na}^+$ channels have reset, but initiating a new action potential requires a stronger stimulus because the membrane is hyperpolarized due to open $\text{K}^+$ channels.

Saltatory conduction

The rapid mode of action potential propagation along myelinated axons where action potentials occur only at unmyelinated neurofibril nodes.

Group A nerve fibers

Nerve fibers characterized by large diameters and myelination with conduction velocities up to $150\,m/s$, comprising most somatic sensory neurons and all somatic motor neurons.

Acetylcholine (ACh)

A major neurotransmitter synthesized from acetate and choline that stimulates skeletal muscle in the PNS, increases arousal in the CNS, and is degraded in the synaptic cleft by acetylcholinesterase.

Biogenic amines

A class of neurotransmitters synthesized from modified amino acids, including catecholamines (such as dopamine, made from tyrosine) and indolamines (such as serotonin, made from histidine or tryptophan).

Neuropeptides

Neurotransmitters consisting of chains of $2$ to $40$ amino acids, such as endorphins and substance P.

Neuromodulators

Chemical substances released from neurons that alter local neuronal responses by causing either facilitation (enhancing response) or inhibition (suppressing response).

Nitric oxide

A short-lived, nonpolar gas synthesized by postsynaptic neurons that functions as a neurotransmitter or neuromodulator to strengthen memory in the brain and dilate blood vessels in the PNS.