Nervous System: Organization, Histology, and Membrane Physiology

Comprehensive practice flashcards covering nervous system organization, neuroglia, neuron anatomy, transport mechanisms, and the biophysical principles of resting membrane potential.

Sensory input

The information gathered by sensory receptors about internal and external changes.

Integration

The processing and interpretation of sensory input by the nervous system.

Motor output

The activation of effector organs, including muscles and glands, to produce a response.

Central nervous system (CNS)

The principal division of the nervous system consisting of the brain and spinal cord located in the dorsal body cavity, serving as integrative and control centers.

Peripheral nervous system (PNS)

The portion of the nervous system outside the CNS, consisting chiefly of nerves extending to and from the spinal cord (spinal nerves) and brain (cranial nerves), along with ganglia.

Somatic nervous system

The voluntary division of the motor PNS consisting of somatic motor nerve fibers that conduct impulses from the CNS to skeletal muscles.

Autonomic nervous system (ANS)

The involuntary division of the motor PNS consisting of visceral motor nerve fibers that regulate smooth muscle, cardiac muscle, and glands.

Astrocytes

The most abundant, versatile, and highly branched neuroglia of the CNS that cling to neurons, synaptic endings, and capillaries to support neurons and regulate the chemical environment.

Microglial cells

Small, ovoid CNS neuroglia with thorny processes that monitor neuron health and transform to phagocytize microorganisms and neuronal debris.

Ependymal cells

Ciliated glial cells ranging in shape from squamous to columnar that line the central cavities of the brain and spinal cord to form a permeable barrier between cerebrospinal fluid (CSF) and tissue fluid.

Satellite cells

PNS neuroglia that surround neuron cell bodies within ganglia and perform functions similar to astrocytes of the CNS.

Schwann cells (neurolemmocytes)

PNS neuroglia that surround all peripheral nerve fibers, form myelin sheaths around thicker nerve fibers, and play a vital role in the regeneration of damaged peripheral nerve fibers.

Soma (perikaryon)

The biosynthetic center and receptive region of a neuron containing a spherical nucleus, nucleolus, and major protein-synthesizing organelles.

Chromatophilic substance (Nissl bodies)

The prominent rough endoplasmic reticulum in a neuron cell body responsible for synthesizing proteins and membrane components.

Nuclei

Clusters of neuron cell bodies located specifically within the central nervous system.

Ganglia

Clusters of neuron cell bodies located specifically within the peripheral nervous system.

Tracts

Bundles of neuron processes extending through the central nervous system.

Nerves

Bundles of neuron processes extending through the peripheral nervous system.

Dendrites

Short, tapering, diffusely branched neuron processes that act as receptive regions, conveying incoming signals toward the cell body as graded potentials.

Dendritic spines

Specialized bulbous or spiky appendages on finer dendrites that collect information from other neurons.

Axon hillock

The cone-shaped area of the neuron cell body from which the axon originates.

Axolemma

The plasma membrane of a neuron axon that conducts nerve impulses.

Anterograde transport

Directional axonal movement away from the cell body toward axon terminals, carrying mitochondria, cytoskeletal elements, membrane components, and enzymes.

Retrograde transport

Directional axonal movement toward the cell body, carrying organelles to be degraded, signal molecules, viruses, and bacterial toxins.

Outer collar of perinuclear cytoplasm

The outermost peripheral bulge of a Schwann cell containing its nucleus and cytoplasm, formerly referred to as the neurilemma.

Myelin sheath gaps (nodes of Ranvier)

Gaps between adjacent Schwann cells along a myelinated axon where axon collaterals can emerge.

Oligodendrocytes

Branched CNS glial cells whose processes form insulating myelin sheaths around thicker nerve fibers, wrapping up to $60$ axons at once.

White matter

Regions of the brain and spinal cord containing dense collections of myelinated fibers, primarily organized into fiber tracts.

Gray matter

Regions of the brain and spinal cord composed mostly of neuron cell bodies and nonmyelinated fibers.

Multipolar neurons

The most common structural class of neurons, characterized by three or more processes (one axon and multiple dendrites), comprising the major neuron type in the CNS.

Bipolar neurons

A rare structural class of neurons with two processes extending from the cell body (one fused dendrite and one axon), found in special sensory organs such as the retina and olfactory mucosa.

Unipolar neurons (pseudounipolar)

A structural class of neurons with a single process extending from the cell body that divides T-like into peripheral and central processes, found mainly in PNS sensory ganglia.

Interneurons (association neurons)

Neurons that lie between sensory and motor neurons to shuttle signals through CNS pathways, making up $99\%$ of all neurons in the body.

Voltage

A measure of potential energy generated by separated electrical charge, measured in volts ($V$) or millivolts ($mV$).

Current ($I$)

The flow of electrical charge (ions) between two points, which can be utilized to perform work.

Resistance ($R$)

The hindrance to the flow of electrical charge; substances with high resistance are insulators, whereas substances with low resistance are conductors.

Ohm's law

The physical law stating that electrical current is directly proportional to voltage and inversely proportional to resistance: $I = \frac{V}{R}$ (or $V = IR$).

Leakage (nongated) channels

Membrane ion channels that are perpetually open, allowing uninterrupted passive diffusion of specific ions down their concentration gradients.

Chemically gated (ligand-gated) channels

Membrane ion channels that open and close exclusively upon the binding of a specific chemical ligand, such as a neurotransmitter.

Voltage-gated channels

Membrane ion channels that open and close directly in response to alterations in membrane potential.

Mechanically gated channels

Membrane ion channels that open and close in response to the physical deformation or stretching of receptor membranes.

Electrochemical gradient

The combined effect of electrical and chemical gradients driving ion movement across a membrane toward opposite charges and lower concentrations.

Resting membrane potential (RMP)

The electrical potential difference across the plasma membrane of a resting neuron, typically around $-70\,mV$ (varying from $-40\,mV$ to $-90\,mV$), where the cytoplasmic side is negative relative to the outside.

Potassium permeability ($\text{K}^+$)

The property of the resting plasma membrane being roughly $25$ times more permeable to $\text{K}^+$ than to $\text{Na}^+$ through leakage channels, which establishes the resting membrane potential.

Sodium-potassium pump ($\text{Na}^+/\text{K}^+\text{ ATPase}$)

An active transport pump that stabilizes the resting membrane potential by ejecting three $\text{Na}^+$ ions from the cell while importing two $\text{K}^+$ ions against their concentration gradients.