Nervous System: Cytology, Brain, and Spinal Cord

Comprehensive vocabulary flashcards covering the structural and functional cytology of nervous tissue, the gross anatomy and physiology of the brain, and the organization and reflexes of the spinal cord.

Central Nervous System (CNS)

The structural subdivision of the nervous system comprising the brain and the spinal cord.

Peripheral Nervous System (PNS)

The structural subdivision of the nervous system consisting of the cranial nerves, spinal nerves, and ganglia.

Somatic Sensory Division

The functional sensory component that conscious individuals perceive, transmitting impulses from the five special senses, general skin receptors (touch, pain, pressure, temperature, vibration), and proprioceptors.

Visceral Sensory Division

The functional sensory component transmitting impulses from blood vessels and internal organs (viscera) to the CNS, typically without conscious awareness.

Somatic Motor Division

The voluntary motor component of the nervous system that conducts nerve impulses from the CNS to cause contraction of skeletal muscles.

Autonomic Motor Division

The involuntary motor component (visceral motor) that conducts impulses regulating smooth muscle, cardiac muscle, and glands.

Neuron

The basic structural and functional unit of the nervous system; excitable, conductive, secretory, amitotic, highly metabolic, and extremely long-lived cells that initiate, transmit, and receive electrical nerve impulses.

Chromatophilic Substance

Dense clusters of rough endoplasmic reticulum and free ribosomes found within the neuronal cell body (soma).

Axon Hillock

The specialized triangular cone-shaped region connecting the neuron cell body (soma) to the axon.

Axon Collateral

A side branch extending off the main axon of a neuron.

Synaptic Knob

The expanded bulbous region located at the tip of an axon's terminal arborization where neurotransmitters are stored and released.

Unipolar Neuron

A structural class of neuron with a single, short process emerging from the cell body that branches like a T into peripheral and central axonal processes.

Bipolar Neuron

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

Multipolar Neuron

The most common structural neuron type, possessing multiple dendrites and a single axon extending from the soma.

Interneuron

A functional class of neurons residing entirely within the CNS that retrieves, processes, and stores information while facilitating communication between sensory and motor neurons.

Astrocyte

The most abundant glial cell in the CNS; its perivascular feet envelop brain capillaries to help form the blood–brain barrier and regulate CSF composition.

Ependymal Cell

A ciliated cuboidal epithelial glial cell lining the brain ventricles and spinal central canal that contributes to the production and circulation of cerebrospinal fluid.

Microglial Cell

A small, phagocytic CNS glial cell that engulfs infectious agents, clears cellular debris, and removes damaged nerve tissue.

Oligodendrocyte

A glial cell in the CNS whose cytoplasmic extensions wrap around multiple axons to form their insulating myelin sheaths.

Satellite Cell

An oval PNS glial cell that surrounds and protects neuron cell bodies within ganglia.

Neurolemmocyte

A PNS glial cell (also called a Schwann cell) that wraps around a segment of an axon to form its myelin sheath.

Neurilemma

The delicate outer nucleated cytoplasmic layer of a neurolemmocyte that remains at the periphery of the myelin sheath.

Saltatory Conduction

The rapid mechanism of nerve impulse transmission in myelinated axons, where the electrical signal jumps from one neurofibril node (Node of Ranvier) to the next.

Continuous Conduction

The unmyelinated conduction mechanism where an impulse travels along the entire uninterrupted length of the axon membrane, resulting in slower propagation.

Endoneurium

The delicate areolar connective tissue layer that wraps around an individual axon and its myelin sheath.

Perineurium

The dense irregular connective tissue layer that bundles individual axons into fascicles.

Epineurium

The tough outermost sheath of dense irregular connective tissue that encloses an entire peripheral nerve.

Axodendritic Synapse

A specialized junction where the synaptic knob of an axon contacts a dendrite of a postsynaptic neuron.

Axosomatic Synapse

A synapse formed between the axon synaptic knob of a presynaptic neuron and the cell body (soma) of a postsynaptic neuron.

Axoaxonic Synapse

A specialized junction where a presynaptic axon synaptic knob directly contacts the axon of a postsynaptic neuron.

Gyri

The elevated folds or ridges on the cerebral surface of the brain.

Sulci

The shallow grooves or depressions that separate adjacent gyri on the cerebral surface.

Prosencephalon

The embryonic forebrain vesicle formed by late week 4 that subsequently develops into the cerebrum and diencephalon.

Mesencephalon

The primary embryonic midbrain vesicle that gives rise directly to the adult midbrain.

Rhombencephalon

The embryonic hindbrain vesicle that differentiates into the pons, medulla oblongata, and cerebellum.

Cranial Dural Septa

Double-layered folds of the meningeal layer of dura mater extending into the cranial cavity to stabilize and partition brain regions.

Falx Cerebri

A large vertical sickle-shaped dural fold that projects into the longitudinal fissure, partitioning the left and right cerebral hemispheres.

Tentorium Cerebelli

A horizontal dural fold separating the occipital and temporal lobes of the cerebrum from the cerebellum, featuring the tentorial notch for the brainstem.

Dural Venous Sinuses

Large blood-filled spaces formed where the periosteal and meningeal layers of cranial dura mater separate, draining venous blood from the brain.

Choroid Plexus

A vascular network composed of specialized ependymal cells and permeable capillaries in the pia mater within each brain ventricle that secretes cerebrospinal fluid.

Arachnoid Villi

Knob-like extensions of the arachnoid mater projecting through the dura into the dural venous sinuses, allowing CSF to drain back into venous circulation.

Blood–Brain Barrier (BBB)

A strictly regulated neuroprotective barrier composed of capillary endothelial tight junctions, thick continuous basement membranes, and astrocyte perivascular feet.

Corpus Callosum

The largest commissural white matter tract that bridges and enables communication between the left and right cerebral hemispheres.

Homunculus

A pictorial or sculptural anatomical model whose body proportions reflect the relative amount of primary motor or somatosensory cortex dedicated to innervating those body regions.

Primary Motor Cortex

The somatic motor control center located in the precentral gyrus of the frontal lobe that controls voluntary skeletal muscle contractions.

Primary Somatosensory Cortex

The cortical area located in the postcentral gyrus of the parietal lobe that receives and interprets conscious sensations of touch, pressure, pain, and temperature.

Broca Area

The motor speech area located in the inferolateral left frontal lobe that coordinates the muscular movements needed for vocalization.

Wernicke Area

The multi-association language comprehension area typically situated in the left hemisphere overlapping the parietal and temporal lobes.

Association Tracts

Central white matter axon bundles that connect different cortical areas within the same cerebral hemisphere.

Projection Tracts

Axon bundles connecting the cerebral cortex to inferior regions such as the brainstem and spinal cord.

Thalamus

Paired masses of gray matter situated on either side of the third ventricle that filter and relay all conscious sensory information (except smell) to the cerebral cortex.

Hypothalamus

The anteroinferior diencephalic structure acting as the master regulator of the autonomic nervous system, endocrine system, body temperature, circadian rhythms, and basic drives.

Substantia Nigra

A midbrain nucleus containing dopamine-producing neurons involved in motor control, movement, emotion, and pleasure, whose degeneration causes Parkinson disease.

Arbor Vitae

The branched, tree-like appearance of white matter within the cerebellum as viewed in sagittal section.

Conus Medullaris

The tapering, cone-shaped inferior terminus of the spinal cord proper, situated around the level of the L1 vertebra.

Cauda Equina

The bundle of spinal nerve roots resembling a horse's tail extending inferiorly through the lower vertebral canal from the conus medullaris.

Filum Terminale

A thin, thread-like filament of pia mater that anchors the conus medullaris to the coccyx within the cauda equina.

Posterior Horns

The dorsal gray matter projections in the spinal cord that house interneuron cell bodies receiving somatic and visceral sensory input.

Anterior Horns

The ventral gray matter regions of the spinal cord containing somatic motor neuron cell bodies that innervate skeletal muscles.

Lateral Horns

The gray matter outpocketings located in the T1–L2 spinal segments that house autonomic (visceral) motor neuron cell bodies innervating cardiac/smooth muscle and glands.

Reflex Arc

The specific neural wiring pathway of a reflex, consisting of five components: sensory receptor, sensory neuron, integration center, motor neuron, and effector.

Monosynaptic Reflex

The simplest reflex pathway characterized by direct synapsing of the sensory axon onto a motor neuron without any interneurons (e.g., stretch reflex).

Polysynaptic Reflex

A complex reflex arc involving one or more interneurons that mediate communication between the afferent sensory neuron and the efferent motor neuron (e.g., withdrawal reflex).

Hyporeflexia

An abnormally diminished or completely absent reflex response that serves as a clinical diagnostic indicator of nervous system or muscular damage.