MCAT Comprehensive Neuro-Endocrine-Respiratory-Cardio-Immune Vocabulary Review

These vocabulary flashcards encapsulate the major terms and definitions spanning neuronal physiology, endocrine signaling, respiratory mechanics, cardiovascular function, and immune defenses, providing a broad review for exam preparation.

Neuron

A highly specialized cell that conducts electrical and chemical impulses throughout the nervous system.

Dendrite

Branch-like projections of a neuron that receive incoming signals from other neurons.

Soma (Cell Body)

Portion of the neuron containing the nucleus and most organelles; integrates incoming signals.

Axon

Long projection that carries action potentials away from the soma toward the nerve terminal.

Axon Hillock

Region where the soma transitions into the axon; site of action-potential initiation after threshold is reached.

Nerve Terminal (Synaptic Bouton)

Enlarged end of an axon that stores and releases neurotransmitters into the synapse.

Synapse

The functional junction consisting of the presynaptic terminal, synaptic cleft, and postsynaptic membrane.

Synaptic Cleft

The microscopic gap between presynaptic and postsynaptic cells across which neurotransmitters diffuse.

Myelin

Fatty insulating substance that wraps axons, preventing signal loss and speeding conduction.

Nodes of Ranvier

Gaps in the myelin sheath where ion exchange occurs, allowing saltatory conduction.

Oligodendrocyte

Glial cell that myelinates axons in the central nervous system (CNS).

Schwann Cell

Glial cell that myelinates axons in the peripheral nervous system (PNS).

Astrocyte

Star-shaped glial cell that nourishes neurons and forms/maintains the blood–brain barrier.

Microglia

Phagocytic glial cells that ingest waste and pathogens in the CNS.

Ependymal Cell

Glial cell lining brain ventricles; produces cerebrospinal fluid (CSF).

Resting Membrane Potential

Baseline charge difference (~-70 mV) across a neuronal membrane, maintained by ion permeability and the Na⁺/K⁺-ATPase.

Na⁺/K⁺-ATPase

Membrane pump that moves 3 Na⁺ out and 2 K⁺ in, maintaining resting potential and ion gradients.

Threshold Voltage

Membrane potential (~-50 mV) that triggers opening of voltage-gated Na⁺ channels and initiates an action potential.

Depolarization

Upward shift in membrane potential toward zero caused mainly by Na⁺ influx.

Repolarization

Return of membrane potential toward resting values due to K⁺ efflux after Na⁺ channel inactivation.

Hyperpolarization

Membrane potential becoming more negative than resting, often due to prolonged K⁺ efflux.

Refractory Period

Time after an action potential when a neuron is unable (absolute) or less likely (relative) to fire again.

Voltage-Gated Calcium Channel

Channel in the nerve terminal that opens on depolarization, allowing Ca²⁺ influx to trigger neurotransmitter release.

Neurotransmitter

Chemical messenger released by neurons that binds receptors on a target cell to alter its activity.

Ligand-Gated Ion Channel

Postsynaptic receptor that opens to allow ion flow when a neurotransmitter binds.

G-Protein-Coupled Receptor (GPCR)

Postsynaptic receptor that activates intracellular signaling cascades when bound by a neurotransmitter.

Temporal Summation

Integration of multiple postsynaptic potentials arriving in rapid succession at the same synapse.

Spatial Summation

Integration of simultaneous inputs at different dendritic locations on the same neuron.

Action Potential

All-or-nothing electrical signal that travels down the axon when threshold is surpassed.

Saltatory Conduction

Jumping of action potentials between nodes of Ranvier in a myelinated axon, accelerating conduction.

Ganglion

Cluster of neuron cell bodies in the peripheral nervous system.

Nucleus (Neuroanatomy)

Cluster of neuron cell bodies within the central nervous system.

Interneuron

Neuron located entirely within the CNS that connects sensory and motor pathways and integrates information.

Sensory (Afferent) Neuron

Neuron that carries information from peripheral receptors toward the CNS.

Motor (Efferent) Neuron

Neuron that carries commands from the CNS to muscles or glands.

Central Nervous System (CNS)

Comprises the brain and spinal cord.

Peripheral Nervous System (PNS)

All neural structures outside the brain and spinal cord, including cranial and spinal nerves.

White Matter

CNS tissue composed primarily of myelinated axons; deep in brain, superficial in spinal cord.

Grey Matter

CNS tissue rich in neuron cell bodies and dendrites; superficial in brain cortex, deep in spinal cord.

Somatic Nervous System

Voluntary division of the PNS controlling skeletal muscle.

Autonomic Nervous System

Involuntary PNS division regulating smooth muscle, cardiac muscle, and glands.

Guillain–Barré Syndrome

Autoimmune demyelinating disorder of peripheral nerves targeting Schwann cells.

Hypothalamus

Brain region that links nervous and endocrine systems; controls pituitary via releasing/inhibiting hormones.

Hypophyseal Portal System

Capillary network that carries hypothalamic hormones directly to the anterior pituitary.

Anterior Pituitary (Adenohypophysis)

Glandular lobe releasing FSH, LH, ACTH, TSH, prolactin, endorphins, and growth hormone.

Posterior Pituitary (Neurohypophysis)

Neural lobe that stores and releases ADH and oxytocin produced in the hypothalamus.

Negative Feedback

Regulatory mechanism in which a pathway’s final hormone inhibits earlier steps to maintain homeostasis.

Gonadotropin-Releasing Hormone (GnRH)

Hypothalamic hormone that stimulates FSH and LH release from the anterior pituitary.

Corticotropin-Releasing Factor (CRF)

Hypothalamic hormone that triggers ACTH secretion.

Thyrotropin-Releasing Hormone (TRH)

Hypothalamic hormone stimulating TSH release.

Growth Hormone-Releasing Hormone (GHRH)

Hypothalamic hormone that promotes growth hormone secretion.

Dopamine (Prolactin-Inhibiting Factor)

Hypothalamic neurotransmitter that decreases prolactin release.

Follicle-Stimulating Hormone (FSH)

Anterior pituitary tropic hormone that stimulates gamete production and estrogen secretion.

Luteinizing Hormone (LH)

Anterior pituitary tropic hormone stimulating ovulation and testosterone synthesis.

Adrenocorticotropic Hormone (ACTH)

Anterior pituitary hormone that triggers glucocorticoid release from the adrenal cortex.

Thyroid-Stimulating Hormone (TSH)

Anterior pituitary hormone that stimulates release of T₃ and T₄ from the thyroid gland.

Prolactin

Direct anterior pituitary hormone that stimulates milk production in mammary glands.

Growth Hormone (GH)

Direct anterior pituitary hormone that promotes bone/muscle growth and raises blood glucose.

Endorphins

Peptide hormones from the anterior pituitary that decrease perception of pain.

Antidiuretic Hormone (ADH / Vasopressin)

Posterior pituitary hormone increasing kidney water reabsorption to raise blood volume and lower osmolarity.

Oxytocin

Posterior pituitary hormone that stimulates uterine contractions and milk ejection; regulated by positive feedback.

Peptide Hormone

Hydrophilic hormone that binds extracellular receptors, uses second messengers, acts quickly but briefly.

Steroid Hormone

Lipid-soluble hormone derived from cholesterol; crosses membranes, binds intracellular receptors, alters gene transcription.

Amino Acid-Derivative Hormone

Hormone derived from one or two amino acids (e.g., epinephrine, T₃); actions resemble peptides or steroids depending on structure.

Triiodothyronine (T₃)

Thyroid hormone that increases basal metabolic rate; more active form of thyroid hormone.

Thyroxine (T₄)

Thyroid hormone that is converted to T₃ in tissues; promotes metabolism.

Calcitonin

Hormone from thyroid parafollicular (C) cells that lowers blood calcium levels.

Parathyroid Hormone (PTH)

Hormone from parathyroid glands that increases blood calcium by bone resorption, renal reabsorption, and vitamin D activation.

Glucocorticoids

Adrenal cortex steroid hormones (cortisol, cortisone) that raise blood glucose and suppress immunity.

Mineralocorticoids

Adrenal cortex steroids (e.g., aldosterone) that regulate sodium/water balance and potassium excretion.

Aldosterone

Mineralocorticoid that increases Na⁺ reabsorption (and thus water) in kidneys while secreting K⁺ and H⁺.

Renin–Angiotensin–Aldosterone System (RAAS)

Hormonal cascade regulating blood pressure and aldosterone secretion.

Cortical Sex Hormones

Androgens and estrogens produced by the adrenal cortex.

Catecholamines

Tyrosine-derived adrenal medulla hormones (epinephrine, norepinephrine) mediating sympathetic fight-or-flight responses.

Insulin

Pancreatic β-cell hormone that lowers blood glucose by promoting cellular uptake and storage.

Glucagon

Pancreatic α-cell hormone that raises blood glucose by stimulating glycogenolysis and gluconeogenesis.

Somatostatin

Pancreatic δ-cell hormone that inhibits insulin and glucagon secretion.

Melatonin

Pineal gland hormone that regulates circadian rhythms and sleep-wake cycles.

Erythropoietin

Kidney hormone that stimulates red blood cell production in bone marrow in response to hypoxia.

Atrial Natriuretic Peptide (ANP)

Heart atrial hormone promoting salt and water excretion to decrease blood volume and pressure.

Thymosin

Thymus hormone essential for T-cell development and differentiation.

Surfactant

Detergent-like substance that decreases alveolar surface tension, preventing lung collapse.

Alveolus

Tiny sac in the lung where gas exchange occurs across a single-cell-thick wall.

Visceral Pleura

Serous membrane covering the lung surface.

Parietal Pleura

Serous membrane lining the chest wall.

Intrapleural Space

Thin fluid-filled cavity between pleurae that lubricates lung movement.

Diaphragm

Primary muscle of inspiration that contracts to expand the thoracic cavity.

External Intercostal Muscles

Muscles between ribs that assist the diaphragm in inhalation.

Internal Intercostal Muscles

Muscles that, with abdominal muscles, actively force exhalation.

Negative-Pressure Breathing

Mechanism where lowered intrapleural pressure draws air into the lungs during inspiration.

Tidal Volume (TV)

Air volume inhaled or exhaled during a normal breath.

Residual Volume (RV)

Air remaining in lungs after maximal exhalation.

Vital Capacity (VC)

Difference between maximum and minimum lung volumes (TLC − RV).

Spirometer

Device that measures lung volumes and capacities except residual volume.

Ventilation Center

Neurons in the medulla oblongata that regulate breathing rate via chemoreceptors.

Hypercarbia (Hypercapnia)

Elevated blood CO₂ that stimulates increased ventilation.

Hypoxemia

Low blood O₂ that triggers increased breathing via peripheral chemoreceptors.

Mucociliary Escalator

Cilia and mucus lining the respiratory tract that trap and transport debris upward.

Lysozyme

Antimicrobial enzyme in saliva, tears, and mucus that breaks down bacterial cell walls.

Alveolar Macrophage

Phagocytic immune cell residing in alveoli, ingesting pathogens and debris.