Human Anatomy & Physiology: Nervous System

Comprehensive vocabulary flashcards covering the human nervous system, including anatomical divisions, neuron structure and classification, neuroglia, electrophysiology and action potential phases, brain development, ventricles, cranial nerves, spinal tracts, reflex arcs, and the autonomic nervous system.

Central Nervous System (CNS)

The division of the nervous system consisting of the brain and spinal cord that acts as the key decision maker, receiving and processing sensory information, storing memories, generating thoughts and emotions, and sending information to the body.

Peripheral Nervous System (PNS)

The division of the nervous system consisting of nerves and ganglia outside the brain and spinal cord that detects stimuli and communicates messages between the CNS and the body.

Neuron

The fundamental unit of the nervous system (numbering approximately $100\text{ billion}$ in the human body) that receives and transmits electrical and chemical signals to different parts of the body.

Dendrites

Branching neuron processes that receive signals from other neurons and conduct electrical impulses toward the cell body.

Axon

A single long neuron process originating at the axon hillock that conducts nerve impulses away from the cell body toward axon terminals.

Myelin

A white, fatty material covering axons that insulates, protects nerve fibers, and speeds up nerve impulse transmission.

Schwann Cells

Glial cells of the PNS that wrap around axons in a jelly roll-like fashion to produce the myelin sheath and contain an outer neurilemma.

Nodes of Ranvier

Gaps in the myelin sheath along the axon through which impulse transmission occurs in myelinated nerve fibers.

Oligodendrocytes

Glial cells in the central nervous system that form myelin sheaths around CNS axons and provide a structural framework, lacking a neurilemma.

Multipolar Neuron

A structural classification of neuron featuring many dendrites and a single axon.

Bipolar Neuron

A structural type of neuron characterized by having exactly one dendrite and one axon extending from the cell body.

Pseudo-unipolar Neuron

A type of neuron that appears to have a single axon divided into peripheral and central processes with no dendrites extending directly from the cell body.

Anaxonic Neuron

A neuron characterized by having multiple branching processes but no axon.

Sensory (Afferent) Neurons

Neurons that carry impulses from sensory receptors (such as cutaneous receptors and proprioceptors) toward the central nervous system.

Motor (Efferent) Neurons

Neurons that conduct impulses from the central nervous system outward to effectors such as muscles and glands.

Interneurons (Association Neurons)

Neurons located entirely within the CNS that connect sensory and motor neurons, making up the majority of neurons in the body and playing key roles in learning, memory, and planning.

Astrocytes

Star-shaped CNS neuroglia that maintain the blood-brain barrier, regulate ion and neurotransmitter levels around synapses, and provide metabolic support.

Ependymal Cells

Glial cells lining the central canal of the spinal cord and ventricles of the brain that are involved in producing cerebrospinal fluid (CSF).

Microglia

Immune defense glial cells of the brain that remove pathogens and dead cellular debris through phagocytosis.

Satellite Cells

PNS neuroglia that surround neuron cell bodies within ganglia and regulate neurotransmitter levels.

Sodium-Potassium Pump

An active transport membrane pump that consumes ATP to move $3\,Na^+$ ions out of the cell and $2\,K^+$ ions into the cell, maintaining resting ion gradients.

Leak Ion Channels

Ion channels that are always open, allowing ions to diffuse down their concentration gradients; $K^+$ leak channels are more numerous than $Na^+$ leak channels.

Depolarization

A phase in an action potential where voltage-gated $Na^+$ channels open, allowing inward diffusion of $Na^+$ and making the inside of the cell membrane more positive.

Repolarization

The phase of an action potential where $Na^+$ channels close, $Na^+$ influx stops, and voltage-gated $K^+$ channels open to allow increased $K^+$ efflux, returning membrane potential toward resting levels.

Hyperpolarization

A state in which the membrane potential becomes more negative than the resting potential (moving further from zero), making the neuron less likely to generate an action potential.

Primary Brain Vesicles

The three embryonic brain divisions present in a three- to four-week embryo: Prosencephalon (Forebrain), Mesencephalon (Midbrain), and Rhombencephalon (Hindbrain).

Choroid Plexus

Specialized vascular structures located within brain ventricles that produce cerebrospinal fluid (CSF).

Meninges

The three connective tissue membranes covering the brain and spinal cord, consisting from superficial to deep of the Dura Mater, Arachnoid Mater, and Pia Mater.

Thalamus

The major sensory relay station ('switchboard') of the central nervous system that directs sensory signals to the cerebral cortex.

Hypothalamus

Brain structure that regulates hormonal and autonomic functions, body temperature, hunger, thirst, sleep, and autonomic tone.

Homunculus

A neurological map that portrays the anatomical divisions and somatotopic organization of the primary motor cortex and primary somatosensory cortex.

Cranial Nerve V (Trigeminal Nerve)

A mixed cranial nerve with three branches (ophthalmic $V_1$, maxillary $V_2$, mandibular $V_3$) providing sensory innervation to the face and anterior $2/3$ of the tongue, and motor control to the muscles of mastication.

Cranial Nerve X (Vagus Nerve)

A mixed cranial nerve providing motor innervation to the constrictor muscles of the pharynx and larynx (efferent gag) and extensive parasympathetic innervation to thoracic and abdominal viscera.

Conus Medullaris

The tapered, cone-like inferior tip of the spinal cord extending to the level of the second lumbar vertebra ($L_2$).

Cauda Equina

A collection of lumbosacral spinal nerve roots resembling a horse's tail extending inferiorly from the conus medullaris.

Filum Terminale

A delicate strand of fibrous tissue formed as a prolongation of the pia mater that anchors the conus medullaris inferiorly.

Reflex Arc

The basic neural pathway that mediates an automatic, involuntary response to a stimulus without conscious thought, typically composed of a receptor, sensory neuron, integration center, motor neuron, and effector.

Endoneurium

Delicate connective tissue layer that surrounds each individual axon (nerve fiber) and its associated Schwann cell sheath.

Perineurium

Connective tissue sheath that groups multiple axons together into bundles called nerve fascicles.

Epineurium

The tough outermost connective tissue sheath that binds multiple nerve fascicles and blood vessels together to form a peripheral nerve.

Nociceptors

Specialized sensory receptors that respond to extreme mechanical, chemical, or thermal stimuli and mediate pain.

Proprioceptors

Sensory receptors located within joints, muscles, and tendons that detect body position, tension, and movement.

Spinothalamic Tract

An ascending anterolateral spinal tract transmitting sensations of pain, temperature, light touch, pressure, tickle, and itch from cutaneous receptors to the thalamus and somatosensory cortex.

Fasciculus Gracilis

An ascending pathway in the dorsal column transmitting proprioception, two-point discrimination, pressure, and vibration from the inferior half of the body.

Fasciculus Cuneatus

An ascending pathway in the dorsal column transmitting proprioception, two-point discrimination, pressure, and vibration from the superior half of the body.

Lateral Corticospinal Tract

A direct descending motor tract originating in the cerebral cortex and crossing at the inferior medulla that controls conscious, skilled movements of the neck, trunk, and limbs, especially the fingers.

Rubrospinal Tract

An indirect descending motor tract originating from the red nucleus of the midbrain that coordinates unconscious movements, such as digit and palm positioning when reaching.

Sympathetic Division

The thoracolumbar division of the ANS ($T_1-L_2$ outflow) that drives the 'fight or flight' response, causing pupillary dilation (mydriasis), bronchodilation, tachycardia, and reduced digestive motility.

Parasympathetic Division

The craniosacral division of the ANS (cranial nerves III, VII, IX, X and $S_2-S_4$ outflow) that supports 'rest and digest' activities, conserving energy, stimulating digestion, and decreasing heart rate.

Autonomic Tone

The homeostatic balance between sympathetic and parasympathetic activity across the body, regulated by the hypothalamus.