Neurophysiology: Introduction, the Neuron, and Glial Cells

Vocabulary practice flashcards covering neurophysiology lecture concepts, including structural and functional classifications of the nervous system, neuronal components, axonal transport, glial cell types, myelination, saltatory conduction, and Wallerian degeneration.

Central Nervous System (CNS)

The major division of the nervous system consisting of the brain and spinal cord, which are protected by the bones of the skull and vertebrae.

Peripheral Nervous System (PNS)

The division of the nervous system composed of receptors, nerves, and ganglia (neuronal bodies outside the CNS) that connects the central nervous system to the limbs and organs.

Sensory (Afferent) Neuron

A functional category of neurons that brings information from sensory receptors in peripheral tissues and organs toward the brain and spinal cord.

Interneuron (Association Neuron)

A functional class of neurons situated within the central nervous system that connects sensory and motor neurons.

Motor (Efferent) Neuron

A functional class of neurons that transmits motor commands and action potentials away from the central nervous system to effector organs, such as muscles and glands.

Somatic Sensory Division

The sensory division of the peripheral nervous system that conveys information regarding position, touch, pressure, pain, and temperature from somatic receptors.

Visceral Sensory Division

The sensory division of the peripheral nervous system that provides information about internal organs via visceral receptors and sensory neurons.

Somatic Motor Division

The motor subdivision of the nervous system that controls skeletal muscle contractions under voluntary control.

Autonomic Nervous System (Visceral Motor Division)

The motor subdivision providing involuntary autonomic regulation of smooth muscle, cardiac muscle, glands, and adipose tissue; further divided into sympathetic and parasympathetic divisions.

Dendrites

Information-receiving extensions of the neuronal cell membrane that integrate incoming signals and determine whether action potentials will be generated.

Dendritic Spines

Small membranous protrusions covering dendrites in certain neurons, each capable of forming synapses with different axons to expand synaptic connections.

Cell Body (Soma or Perikaryon)

The metabolic life-support center of the neuron containing the nucleus and organelles, where axonal proteins are synthesized.

Axon

An information-carrying extension of the neuronal cell membrane that ranges in length from a few micrometers to over $10\,\text{meters}$ and contains the majority of the cell cytoplasm.

Axon Hillock (Trigger Zone)

The conical origin of the axon where action potentials originate.

Presynaptic Terminal

The specialized end of an axon or its terminal branches that transmits information across a synapse by releasing neurotransmitters.

Myelin Sheath

A greatly modified plasma membrane wrapped around an axon in a spiral fashion that acts as an electrical insulator and enhances the speed of signal transfer.

Node of Ranvier

Periodic interruptions or gaps in the insulating myelin sheath along an axon that are critical for the rapid conduction of action potentials.

Anterograde Transport

Axoplasmic transport directed away from the soma toward the axon terminals, carrying synaptic components such as synaptic vesicles and mitochondria.

Retrograde Transport

Axoplasmic transport directed from the axon terminals back toward the cell body, responsible for moving cargo destined for degradation, such as recycled membrane vesicles.

Multipolar Neuron

A structural type of neuron featuring one axon and multiple dendrites; the most common neuronal type, typical of motor (efferent) neurons.

Bipolar Neuron

A structural type of neuron that possesses two processes extending from the cell body: one axon and one dendrite.

Pseudo-unipolar Neuron

A structural type of neuron that features a single stem process bifurcating into two processes (one extending to the PNS and the other to the CNS), characteristic of sensory (afferent) neurons.

Neuroglia (Glial Cells)

Non-neuronal support cells of the nervous system (derived from the Greek for 'glue') that can divide, lack axons and dendrites, and do not directly generate action potentials.

Microglial Cells

The resident immune cells of the CNS making up $10\text{--}20\%$ of all neuroglia; they act as macrophages to phagocytose debris, release nitric oxide ($\text{NO}$) to prevent viral replication, and eliminate unnecessary synapses.

Astrocytes

Star-shaped glial cells constituting approximately $50\%$ of the CNS glial population; they provide structural and metabolic support, form glial limiting membranes, maintain the blood-brain barrier, and regulate extracellular ions ($\text{K}^+$, $\text{Na}^+$, $\text{Ca}^{2+}$, $\text{Cl}^-$, $\text{HCO}_3^-$) and neurotransmitters.

Oligodendrocytes

Glial cells of the central nervous system that possess multiple processes extending to myelinate adjacent axons larger than $1\,\mu\text{m}$ in diameter, forming the brain's white matter.

Ependymal Cells

Glial cells that line the ventricles of the brain and the central canal of the spinal cord, playing a functional role in the production of cerebrospinal fluid (CSF).

Schwann Cells (Neurolemmocytes)

Glial cells arranged side by side in the peripheral nervous system that form myelin sheaths around axons larger than $1\,\mu\text{m}$ and guide peripheral nerve regeneration.

Saltatory Conduction

The mode of impulse propagation in myelinated axons whereby the action potential jumps from node to node (from Latin 'saltare', to jump), resulting in faster depolarization than in unmyelinated fibers.

Wallerian Degeneration

The anterograde disintegration and breakdown of the distal segment of an axon and its myelin sheath following separation from the cell body after a lesion.

Büngner Band

A regenerative tube formed by proliferating Schwann cells following peripheral nerve injury that releases growth factors to guide axonal sprouts advancing at a rate of approximately $1\,\text{mm}$ per day.