Nervous System, Spinal Cord, and Brain Flashcards

Comprehensive vocabulary flashcards covering the Nervous System (Chapter 12), Spinal Cord & Spinal Nerves (Chapter 14), and Brain & Cranial Nerves (Chapter 13).

Effectors

Muscles and glands that execute a response dictated by the central nervous system, such as muscle contraction or alteration of gland secretion.

Central Nervous System (CNS)

Structural division of the nervous system consisting of the brain and spinal cord, responsible for processing and evaluating sensory information.

Peripheral Nervous System (PNS)

Structural division of the nervous system consisting of nerves (bundles of axons) and ganglia (clusters of neuron cell bodies) outside the CNS.

Somatic Sensory System

Functional subdivision of the sensory nervous system that detects consciously perceived stimuli from receptors in the eyes, nose, tongue, ears, skin, and proprioceptors.

Visceral Sensory System

Functional subdivision of the sensory nervous system that detects stimuli from internal organs and blood vessels that are not consciously perceived.

Somatic Motor System

Functional subdivision of the motor nervous system that conducts motor output from the CNS to voluntarily controlled skeletal muscles.

Autonomic Motor System

Functional subdivision of the motor nervous system that innervates and involuntarily regulates cardiac muscle, smooth muscle, and glands.

Neurons

The basic structural and functional units of the nervous system, characterized by excitability, conductivity, secretion, extreme longevity, and an amitotic nature.

Dendrites

Short, branching cellular processes extending from the neuron cell body that receive sensory input and conduct signals toward the soma (afferent).

Axon

Single long nerve fiber extending from the neuron cell body specialized to conduct nerve impulses away from the cell body (efferent).

Axon Hillock

The triangular, cone-shaped region of the neuron cell body where the axon originates.

Fast Axonal Transport

ATP-dependent movement along microtubules occurring at $400\,mm/day$; carries vesicles, organelles, and glycoproteins anterograde, and recycled vesicles or harmful agents retrograde.

Slow Axonal Transport

Anterograde-only movement occurring at $0.1$ to $3\,mm/day$ driven by axoplasmic flow, conveying enzymes, cytoskeletal components, and axoplasm for regenerating axons.

Structural Classification of Neurons

Categorization of neurons based on process count: Multipolar (many dendrites, one axon), Bipolar (one dendrite, one axon), Unipolar (single fused process branching T-like), and Anaxonic (only dendrites, no axon).

Interneurons (Association Neurons)

Neurons located entirely within the CNS that connect other neurons, direct impulses, and process/interpret incoming sensory information.

Epineurium

Thick outer layer of dense irregular connective tissue surrounding an entire nerve, providing support and protection.

Perineurium

Layer of dense irregular connective tissue wrapping individual nerve fascicles and supporting blood vessels.

Endoneurium

Delicate layer of areolar connective tissue surrounding and insulating each individual axon within a nerve.

Astrocytes

Star-shaped CNS glial cells whose perivascular feet help form the blood-brain barrier (BBB), regulate interstitial fluid composition, offer structural support, and participate in brain repair.

Ependymal Cells

Ciliated simple cuboidal or columnar epithelial cells lining brain ventricles and the spinal cord central canal that produce and circulate cerebrospinal fluid (CSF).

Microglia

Small phagocytic CNS glial cells that act as macrophages to defend against infectious agents and remove debris from dead or dying neurons.

Oligodendrocytes

Large CNS glial cells with bulbous bodies and slender processes that wrap around multiple axons to form myelin sheaths.

Satellite Cells

Flattened PNS glial cells surrounding neuron cell bodies in ganglia that provide electrical insulation and regulate nutrient and waste exchange.

Neurolemmocytes (Schwann Cells)

PNS glial cells that wrap around peripheral axons to form myelin sheaths, facilitating faster nerve signal conduction and guiding axon regeneration.

Nodes of Ranvier (Neurofibril Nodes)

Unmyelinated gaps between adjacent myelin sheath segments along an axon where action potentials occur during saltatory conduction.

Wallerian Degeneration

Process in which the distal portion of a severed axon and its myelin sheath disintegrate, while the surviving neurolemma and endoneurium form a regeneration tube.

Resting Membrane Potential (RMP)

Electrical charge difference across the plasma membrane of an unstimulated neuron, typically $-70\,mV$, established mainly by leak of $\text{K}^+$ ions.

Depolarization

Shift in membrane potential toward a more positive value relative to RMP, caused by the influx of positively charged $\text{Na}^+$ ions into the cell.

Hyperpolarization

Change in membrane potential making the inside of the cell more negative than RMP, driven by $\text{K}^+$ outflow or $\text{Cl}^-$ influx.

Absolute Refractory Period

Time interval from action potential initiation until repolarization is one-third complete, during which no stimulus, regardless of strength, can trigger another action potential.

Relative Refractory Period

Time interval during repolarization (from one-third to two-thirds complete) when an action potential can be elicited only by a stimulus greater than threshold.

Continuous Conduction

Sequential opening of voltage-gated channels along the entire length of an unmyelinated axon, propagating signals slowly at $2\,m/s$.

Saltatory Conduction

Rapid signal propagation ($120\,m/s$) along myelinated axons, where action potentials jump from one neurofibril node to the next.

Converging Circuit

Neuronal pool pattern where inputs from multiple presynaptic neurons converge onto a single postsynaptic neuron, such as multiple sensory inputs inducing salivation.

Diverging Circuit

Neuronal pool pattern that spreads information from one presynaptic neuron to multiple postsynaptic neurons, such as brain motor signals controlling walking posture.

Reverberating Circuit

Neuronal circuit utilizing feedback to produce repeated, cyclical output until interrupted by an inhibitory signal or synaptic fatigue, controlling continuous rhythms like breathing during sleep.

Parallel-After-Discharge Circuit

Neuronal circuit that transmits input simultaneously along paths of varying synapse numbers to arrive at a postsynaptic cell at different times, involved in higher-order thinking.

Conus Medullaris

The tapered, cone-shaped inferior end of the spinal cord located between the L1 and L2 vertebrae.

Filum Terminale

A thin strand of pia mater extending from the conus medullaris that anchors the spinal cord to the coccyx.

Cauda Equina

Bundle of nerve roots and the filum terminale extending inferiorly from the conus medullaris within the vertebral canal.

Posterior Root Ganglion

Nodular swelling on the posterior root of a spinal nerve housing the cell bodies of sensory neurons.

Subarachnoid Space

Space deep to the arachnoid mater and superficial to the pia mater containing cerebrospinal fluid (CSF) and arachnoid trabeculae.

Lumbar Puncture

Clinical procedure involving needle insertion into the subarachnoid space below L1 (typically between L3-L4) to safely sample CSF.

Decussation

The crossing of nerve axons from one side of the CNS to the contralateral side along a nerve pathway.

Posterior Funiculus-Medial Lemniscal Pathway

Sensory pathway processing discriminative touch, precise pressure, vibration, and conscious proprioception via a 3-neuron chain to the somatosensory cortex.

Anterolateral Pathway

Ascending pathway (spinothalamic tracts) conducting signals for crude touch, pressure, pain, and temperature through a 3-neuron chain to the primary somatosensory cortex.

Spinocerebellar Pathway

Ascending sensory pathway transmitting unconscious proprioceptive input via a 2-neuron chain directly to the cerebellum.

Lateral Corticospinal Tracts

Direct motor tracts whose upper motor neuron axons decussate in the medullary pyramids and control skilled voluntary movements of the limbs.

Anterior Corticospinal Tracts

Direct motor tracts whose axons descend uncrossed in the anterior funiculus and decussate at the target spinal cord segment to innervate axial muscles.

Dermatome

Specific area of skin innervated by cutaneous sensory fibers of a single spinal nerve (with the exception of C1).

Shingles

Reactivation of latent varicella-zoster virus in a posterior root ganglion causing painful skin blisters along the corresponding dermatome.

Phrenic Nerve

Important nerve originating from the cervical plexus ($C3$, $C4$, $C5$) that innervates the diaphragm to drive breathing.

Brachial Plexus

Nerve network formed by anterior rami of $C5$–$T1$ that supplies the pectoral girdle and upper limb via five major terminal branches: axillary, median, musculocutaneous, radial, and ulnar nerves.

Sciatic Nerve

Largest and longest nerve in the human body, arising from the sacral plexus ($L4$–$S4$) and dividing into tibial and common fibular nerves.

Reflex Arc

The neural pathway generating a rapid, pre-programmed, involuntary reaction to a stimulus, consisting of receptor, sensory neuron, integration center, motor neuron, and effector.

Stretch Reflex

Monosynaptic, ipsilateral spinal reflex causing muscle contraction in response to passive stretching detected by muscle spindle proprioceptors.

Golgi Tendon Reflex

Polysynaptic spinal reflex that prevents muscle tear by inducing muscle relaxation when Golgi tendon organs detect excessive tendon tension.

Withdrawal Reflex

Polysynaptic spinal reflex that causes contraction of flexor muscles to pull a limb away from a painful stimulus.

Crossed-Extensor Reflex

Polysynaptic reflex accompanying a withdrawal reflex, in which interneurons cross the spinal cord to stimulate contralateral extensor muscles for body support.

Quadriplegia

Paralysis affecting all four limbs and lower body caused by cervical spinal cord injury.

Paraplegia

Paralysis affecting the lower body and legs caused by spinal cord injury below the cervical region.

Primary Brain Vesicles

The three embryonic brain swellings formed by the late 4th week: Prosencephalon (forebrain), Mesencephalon (midbrain), and Rhombencephalon (hindbrain).

Secondary Brain Vesicles

Five embryonic brain swellings formed by the 5th week: Telencephalon, Diencephalon, Mesencephalon, Metencephalon, and Myelencephalon.

Cranial Dural Septa

Double-layered sheets of meningeal dura mater extending into the cranial cavity to partition brain regions: Falx cerebri, Tentorium cerebelli, Falx cerebelli, and Diaphragma sellae.

Meningitis

Inflammation of the meninges surrounding the brain and spinal cord, typically caused by bacterial or viral infection, marked by fever, headache, and neck stiffness.

Brain Ventricles

Ependymal cell-lined cavities filled with cerebrospinal fluid within the brain: two Lateral ventricles, Third ventricle, and Fourth ventricle.

Blood-Brain Barrier (BBB)

Protective structural system of tight endothelial junctions, basement membranes, and perivascular astrocyte feet strictly regulating substance passage into brain interstitial fluid.

Corpus Callosum

The main thick tract of white matter commissural fibers connecting and allowing communication between the left and right cerebral hemispheres.

Primary Motor Cortex

Functional area located in the precentral gyrus of the frontal lobe that controls voluntary skeletal muscle movement on the contralateral side of the body.

Broca Area (Motor Speech Area)

Functional cortical region in the inferolateral left frontal lobe regulating muscle movements required for vocalization.

Primary Somatosensory Cortex

Cortical area located in the postcentral gyrus of the parietal lobe that receives general somatic sensory information for touch, pressure, pain, temperature, and proprioception.

Wernicke Area

Functional brain region typically located in the left cerebral hemisphere involved in recognizing, understanding, and comprehending spoken and written language.

Cerebral Lateralization

Specialization of the two cerebral hemispheres; the categorical hemisphere (left) specializes in language and analysis, while the representational hemisphere (right) handles visuospatial relationships and creativity.

Cerebral Nuclei (Basal Ganglia)

Deep masses of gray matter within central white matter (caudate nucleus, putamen, globus pallidus) that help regulate motor output and inhibit unwanted movements.

Huntington Disease

An autosomal dominant hereditary disorder causing progressive degeneration of cerebral nuclei, leading to involuntary jerky movements (chorea), personality changes, and memory loss.

Thalamus

Paired oval diencephalic gray matter masses serving as the final relay and filtering center for all conscious sensory information (except olfaction) ascending to the cerebral cortex.

Hypothalamus

Anteroinferior diencephalic region that serves as the master controller of the autonomic nervous system, endocrine system, body temperature, food/water intake, and emotional behavior.

Substantia Nigra

Midbrain nucleus containing dopamine-producing neurons that project to cerebral nuclei to help control voluntary motor activity.

Superior and Inferior Colliculi

Midbrain tectal nuclei acting as reflex centers; superior colliculi control visual reflexes, while inferior colliculi control auditory reflexes.

Arbor Vitae

Tree-like branching pattern of internal white matter within the cerebellum.

Limbic System

Functional brain structure ring ('emotional brain') consisting of cingulate gyrus, hippocampus, amygdala, and mammillary bodies that processes and experiences emotions.

Hippocampus

Essential limbic system structure in the temporal lobe required for memory consolidation and long-term memory formation.

Alzheimer Disease

Progressive neurodegenerative disease marked by severe brain atrophy, formation of amyloid plaques and neurofibrillary tangles, and memory loss.