Human Anatomy: Nervous System, Special Senses, Blood, and Endocrine System

Comprehensive vocabulary flashcards covering the human nervous system, special senses, blood composition, and endocrine glands from BIO 250 lecture materials.

Receptive Field

The distribution area of the endings of a sensory neuron; smaller receptive fields allow for more precise localization of a stimulus.

Free Nerve Endings

Terminal ends of unencapsulated sensory neuron dendrites that reside close to the skin surface and in mucous membranes; mainly detect pain and temperature, but also light touch and pressure.

Root Hair Plexus

Unencapsulated tactile receptors that wrap around hair follicles in the deeper layer of the dermis to detect hair displacement.

Tactile Discs

Flattened dendritic endings of sensory neurons that contact specialized epithelial cells (Merkel cells) in the basal layer of the epidermis to respond to light touch.

End Bulbs (Krause Bulbs)

Encapsulated dendritic endings ensheathed in connective tissue that detect pressure and low-frequency vibration.

Lamellated Corpuscles (Pacinian Corpuscles)

Encapsulated tactile receptors composed of dendritic endings wrapped in neurolemmocytes and concentric connective tissue layers, located deep in the dermis and hypodermis to detect deep pressure, coarse touch, and high-frequency vibration.

Bulbous Corpuscles (Ruffini Corpuscles)

Encapsulated receptors wrapped in connective tissue within the dermis and subcutaneous layer that detect deep pressure and skin distortion.

Tactile Corpuscles (Meissner Corpuscles)

Intertwined dendritic endings enclosed by modified neurolemmocytes and connective tissue in dermal papillae that provide discriminative light touch for recognizing texture and shape.

Muscle Spindles

Proprioceptors composed of intrafusal muscle fibers surrounded by a connective tissue capsule that detect changes in stretch within skeletal muscle.

Tendon Organs (Golgi Tendon Organs)

Proprioceptors consisting of sensory nerve endings located within tendons or near muscle-tendon junctions that detect changes in tension caused by muscle contraction.

Joint Kinesthetic Receptors

Proprioceptors located within the articular capsule of synovial joints that detect stretch relative to joint position and movement.

Referred Pain

The inaccurate localization of sensory signals where visceral pain is perceived as originating from somatic regions (skin or muscle) because both sensory pathways converge on the same ascending spinal cord tracts.

Vallate (Circumvallate) Papillae

The largest and least numerous tongue papillae, arranged in an inverted V-shape of $10\text{ to }12$ along the posterior dorsal surface of the tongue, housing the majority of taste buds.

Lacrimal Apparatus

The accessory eye structure consisting of the lacrimal gland, puncta, canaliculi, lacrimal sac, and nasolacrimal duct, responsible for producing, circulating, and draining lacrimal fluid across the ocular surface into the nasal cavity.

Fovea Centralis

A central depression within the macula lutea containing the highest concentration of cones and almost no rods, serving as the area of sharpest vision.

Spiral Organ (Organ of Corti)

The sensory receptor organ for hearing situated within the cochlear duct on the basilar membrane, consisting of inner and outer hair cells whose stereocilia and kinocilia project into the tectorial membrane.

Buffy Coat

The thin middle layer of centrifuged whole blood, comprising less than $1\%$ of total blood volume, composed of leukocytes and platelets.

Hematocrit

The percentage of the volume of all formed elements in whole blood, clinically defined as the percentage of red blood cells (erythrocytes).

Albumins

The smallest and most abundant plasma proteins ($58\%$ of total plasma protein), which exert the greatest colloid osmotic pressure and act as transport carriers for lipids, ions, and hormones.

Hemoglobin

A red-pigmented protein found in erythrocytes consisting of four globin subunits (two alpha and two beta chains), each containing a heme group with an iron ion ($\text{Fe}^{2+}$) that reversibly binds oxygen.

Diapedesis

The process by which motile leukocytes squeeze through the endothelial wall of blood vessels to enter infected or injured interstitial tissues.

Neutrophils

The most numerous granulocytes in blood ($50\text{--}70\%$ of leukocytes), characterized by a multilobed nucleus and pale granules; specialized for phagocytizing bacterial pathogens.

Eosinophils

Granulocytes ($1\text{--}4\%$ of leukocytes) with a bilobed nucleus and reddish-staining granules that phagocytize antigen-antibody complexes or allergens and destroy parasitic worms.

Basophils

The rarest granulocytes ($0.5\text{--}1\%$ of leukocytes) featuring blue-violet cytoplasmic granules that secrete histamine to promote vasodilation and heparin to inhibit blood clotting.

Monocytes

Agranulocytes ($2\text{--}8\%$ of leukocytes) with a large, kidney-shaped or C-shaped nucleus that exit blood vessels to differentiate into phagocytic tissue macrophages.

Cranial Dural Septa

Inward folds of the meningeal layer of the dura mater (including the falx cerebri, tentorium cerebelli, falx cerebelli, and diaphragma sellae) that partition and support major brain compartments.

Choroid Plexus

A specialized vascular structure composed of ependymal cells and permeable capillaries located within brain ventricles that produces cerebrospinal fluid (CSF) by filtering blood plasma.

Blood-Brain Barrier (BBB)

A strictly regulated neuroprotective barrier consisting of continuous capillary endothelial cells joined by tight junctions, a thickened basement membrane, and the perivascular feet of astrocytes.

Corpus Callosum

The largest commissural white matter tract connecting the left and right cerebral hemispheres, providing a communication bridge between them.

Primary Motor Cortex

The somatic motor control region located within the precentral gyrus of the frontal lobe that controls contralateral voluntary skeletal muscle contractions, organized topographically as a motor homunculus.

Primary Somatosensory Cortex

The cortical region located in the postcentral gyrus of the parietal lobe that receives and interprets conscious somatic sensory input from proprioceptors, touch, pressure, pain, and temperature receptors.

Caudate Nucleus

A paired cerebral nucleus with an enlarged head and slender tail paralleling the lateral ventricle that helps produce the subconscious pattern and rhythm of walking movements.

Substantia Nigra

A midbrain nucleus containing dopamine-producing neurons involved in voluntary movement and emotional regulation, whose degeneration causes Parkinson disease.

Decussation of the Pyramids

The crossover point of corticospinal motor tracts located on the anterior inferior surface of the medulla oblongata, resulting in contralateral motor control of skeletal muscles.

Conus Medullaris

The tapering, cone-shaped inferior end of the official spinal cord proper, typically ending at the level of the L1 vertebra in adults.

Cauda Equina

The collection of lumbar, sacral, and coccygeal spinal nerve roots extending inferiorly through the vertebral canal from the conus medullaris, resembling a horse's tail.

Spinal Nerve (Mixed Nerve)

A peripheral nerve formed by the union of an anterior (motor) root and a posterior (sensory) root, carrying both afferent and efferent axons.

Denticulate Ligaments

Paired lateral, tooth-like triangular extensions of the spinal pia mater that suspend and anchor the spinal cord within the dura mater.

Posterior Horns

The posterior gray matter projections of the spinal cord that contain the cell bodies of interneurons and axons of somatic and visceral sensory neurons.

Anterolateral Pathway

An ascending sensory pathway consisting of anterior and lateral spinothalamic tracts that relays signals for crude touch, pressure, pain, and temperature to the primary somatosensory cortex via a three-neuron chain.

Dermatome

A specific segment of skin innervated by cutaneous sensory fibers originating from a single pair of spinal nerves.

Phrenic Nerve

A major motor and sensory branch arising from cervical plexus rami C3–C5 that travels through the thoracic cavity to innervate the diaphragm.

Sciatic Nerve

The largest and longest nerve in the human body, arising from the sacral plexus (L4–S3) and composed of two major divisions: the tibial division and common fibular division.

Chromatophilic Substance (Nissl Bodies)

Dense clusters of free ribosomes and rough endoplasmic reticulum found in a neuron's perikaryon that stain darkly with basic dyes and carry out protein synthesis.

Fast Axonal Transport

Microtubule-dependent movement powered by ATP-splitting motor proteins (kinesin and dynein) that transports vesicles, organelles, and materials toward or away from the synaptic knob at approximately $400\,\text{mm/day}$.

Astrocytes

The most abundant star-shaped glial cells in the CNS; they form perivascular feet contributing to the blood-brain barrier, regulate interstitial fluid composition, provide structural support, and assist neuronal development.

Microglia

Small wandering phagocytic neuroglial cells of immune origin in the CNS that replicate during infection to engulf pathogens, cellular debris, and unneeded synapses.

Oligodendrocytes

Large neuroglial cells of the CNS with slender cytoplasmic processes that wrap around segments of multiple axons to synthesize and form the myelin sheath.

Neurolemmocytes (Schwann Cells)

Elongated, flattened glial cells of the PNS that wrap around a $1\text{-mm}$ portion of an axon to form the myelin sheath and peripheral neurilemma, accelerating action potential propagation.

Neurilemma

The outermost nucleated cytoplasmic layer of a neurolemmocyte that is pushed to the periphery around an axon during myelination in the PNS.

Wallerian Degeneration

The breakdown and disintegration of the axon and myelin sheath distal to a site of transection following peripheral nerve trauma, during which the surrounding neurilemma and endoneurium remain intact to create a regeneration tube.

Hypothalamo-Hypophyseal Tract

A neural tract running through the infundibulum composed of unmyelinated axons arising from soma in the supraoptic and paraventricular nuclei of the hypothalamus that transport oxytocin and ADH to synaptic terminals in the posterior pituitary.

Hypothalamo-Hypophyseal Portal System

A vascular network consisting of a primary plexus in the hypothalamus, hypophyseal portal veins, and a secondary plexus in the anterior pituitary, through which hypothalamic regulatory hormones directly access anterior pituitary target cells.

Thyroid Follicles

Microscopic spherical units of the thyroid gland composed of cuboidal follicular cells encircling a central lumen filled with protein-rich colloid containing thyroglobulin.

Parafollicular Cells (C Cells)

Endocrine cells located in the connective tissue spaces between thyroid follicles that synthesize and secrete calcitonin in response to elevated blood calcium levels.

Zona Glomerulosa

The thin, outermost layer of the adrenal cortex that synthesizes mineralocorticoids (primarily aldosterone) to regulate sodium and potassium electrolyte balance.

Zona Fasciculata

The thick middle cortical layer of the adrenal gland composed of parallel cords of lipid-rich cells that produce glucocorticoids (primarily cortisol) to regulate glucose metabolism.

Zona Reticularis

The innermost layer of the adrenal cortex directly bordering the adrenal medulla that synthesizes gonadocorticoids, primarily adrenal androgens.

Pancreatic Islets (Islets of Langerhans)

Small endocrine cell clusters scattered among the exocrine acini of the pancreas, containing alpha cells (secrete glucagon) and beta cells (secrete insulin).

Chief (Principal) Cells

The predominant endocrine cells of the parathyroid glands that produce and secrete parathyroid hormone (PTH) to raise circulating blood calcium concentrations.