Human Anatomy and Physiology: Muscular, Nervous, Sensory, Endocrine, Blood, and Immune Systems

Comprehensive vocabulary flashcards covering skeletal muscle physiology, the nervous system, special senses, the endocrine system, hematology, and immunology.

Sarcomere

The smallest contractile unit of skeletal muscle, running from one Z disc to the next.

A band

The dark band representing the full length of the thick filaments in a sarcomere, including regions of overlap with thin filaments; does not change length during contraction.

Sliding filament theory

The model of muscle contraction stating that actin and myosin filaments slide past one another without changing length, causing the I band and H zone to shorten and Z discs to draw closer together.

Tropomyosin

A regulatory protein on the thin filament that covers and blocks myosin-binding sites on actin when muscle is relaxed.

Troponin

A thin filament protein that binds $Ca^{2+}$, undergoing a conformational change that pulls tropomyosin away to expose actin's binding sites.

T-tubules

Invaginations of the sarcolemma that conduct electrical action potentials deep into the muscle fiber to trigger $Ca^{2+}$ release from the sarcoplasmic reticulum.

Power stroke

The step in the cross-bridge cycle where the myosin head pivots and pulls the thin filament toward the center of the sarcomere while ADP and $P_i$ are released.

Rigor mortis

Postmortem muscle stiffness caused by the complete depletion of ATP, preventing myosin heads from detaching from actin filaments.

Orbicularis oculi

A facial muscle that closes the eyelids during blinking and squinting; weakness results in incomplete eye closure.

Buccinator

Known as the "trumpeter's muscle"; compresses the cheek, holds food against the teeth during chewing, and assists in whistling and blowing.

Sternocleidomastoid (SCM)

A neck muscle that unilaterally rotates the head to the opposite side and laterally flexes to the same side; bilaterally flexes the neck.

Supraspinatus

A rotator cuff muscle responsible for initiating arm abduction (the first $\begin{array}{c}\\\sim 15^\circ\\\end{array}$) before the deltoid takes over.

Serratus anterior

A muscle that protracts and holds the scapula against the thoracic wall; damage to its supply (long thoracic nerve) causes a winged scapula.

Triceps brachii

The prime mover of elbow extension, active during pushing movements.

Quadriceps femoris

A four-muscle anterior thigh group (rectus femoris, vastus lateralis, vastus medialis, vastus intermedius) that extends the knee; rectus femoris also crosses and flexes the hip.

Tract

A bundle of nerve axons located within the Central Nervous System (CNS).

Ganglion

A cluster of neuron cell bodies located within the Peripheral Nervous System (PNS).

Astrocytes

The most abundant CNS neuroglia; they support neurons, form the blood-brain barrier, regulate the chemical environment, and take up neurotransmitters.

Microglia

Small, spider-like phagocytic neuroglia in the CNS that engulf cellular debris and microorganisms.

Ependymal cells

Ciliated CNS neuroglial cells that line the brain ventricles and central canal to circulate cerebrospinal fluid (CSF).

Schwann cells

PNS supporting cells that form myelin sheaths around peripheral axons and assist in nerve fiber regeneration.

Glutamate

The principal excitatory neurotransmitter in the CNS, utilized at roughly half of all brain synapses.

Broca's area

A motor speech region located in the frontal lobe of the cerebral cortex.

Postcentral gyrus

The primary somatosensory cortex of the parietal lobe, responsible for processing sensations of touch, pain, temperature, pressure, and proprioception.

Vagus nerve (CN X)

Cranial nerve providing primary parasympathetic innervation to thoracic and abdominal organs, somatic motor supply to the pharynx/larynx, and taste sensation to the throat/epiglottis.

Filiform papillae

The most abundant, thread-like tongue papillae that lack taste buds, serving instead to provide tactile friction for manipulating food.

Vallate (circumvallate) papillae

The largest lingual papillae, arranged in a V-shaped row at the back of the tongue, each housing the highest concentration of taste buds ($\sim 100+$).

Fovea centralis

The central depression of the macula lutea containing exclusively cones, providing the sharpest visual acuity and color reception.

Accommodation

The active process of focusing on near objects wherein the ciliary muscle contracts, suspensory ligaments relax, and the elastic lens thickens/bulges to increase light refraction.

Presbyopia

Age-related loss of lens elasticity and increased rigidity, which impairs near-focusing capabilities and typically requires corrective reading glasses after age $40\text{--}45$.

Organ of Corti

The receptor organ for hearing situated in the cochlea, containing hair cells that convert perilymph fluid vibrations into auditory nerve impulses.

Otosclerosis

A conductive hearing loss disorder caused by abnormal bone growth that immobilizes the stapes footplate against the oval window.

Ménière's disease

An inner-ear pathology characterized by excess or altered endolymph, resulting in episodic vertigo, tinnitus, and progressive hearing loss.

Humoral stimulus

Endocrine gland activation caused directly by changing levels of blood ions or nutrients, such as parathyroid hormone release in response to declining blood $Ca^{2+}$.

Second messenger system

An intracellular signaling cascade utilized by water-soluble hormones that bind cell surface receptors, activating pathways such as G protein $\rightarrow$ adenylyl cyclase $\rightarrow$ cAMP $\rightarrow$ protein kinases.

Hashimoto's thyroiditis

An autoimmune cause of primary hypothyroidism characterized by elevated TSH and low T4 due to loss of negative feedback, presenting with cold intolerance, fatigue, weight gain, and possible goiter.

Parathyroid hormone (PTH)

A peptide hormone secreted during hypocalcemia that increases blood $Ca^{2+}$ by stimulating osteoclasts, enhancing kidney calcium reabsorption, and activating vitamin D (calcitriol).

Zona glomerulosa

The superficial cortical layer of the adrenal gland that secretes mineralocorticoids (aldosterone) to stimulate $Na^+$ retention and $K^+$ excretion.

Addison's disease

Primary adrenal insufficiency where destruction of the adrenal cortex causes deficient cortisol and aldosterone, characterized by low blood pressure, low $Na^+$, elevated $K^+$, and skin darkening.

Hematocrit

The percentage of whole blood volume occupied by erythrocytes, normally averaging between $40\%$ and $45\%$.

Erythropoietin (EPO)

A glycoprotein hormone produced by the kidneys in response to hypoxic conditions that stimulates red blood cell production in red bone marrow.

Hemostasis

The physiological process that stops bleeding, executed across three sequential phases: vascular spasm, platelet plug formation, and blood coagulation.

Hemolytic disease of the fetus and newborn (HDFN)

A condition in which maternal anti-Rh IgG antibodies cross the placenta during a subsequent pregnancy and destroy Rh-positive fetal red blood cells.

Natural killer (NK) cells

Innate defense lymphocytes that recognize and lyse virus-infected cells and tumor cells without prior immunological sensitization.

IgG

The most abundant antibody isotype in blood; capable of crossing the placenta to confer passive immunity to the fetus and dominating the secondary immune response.

IgM

A pentameric antibody class that is the first immunoglobulin produced during a primary immune response, serving as a serological marker of acute infection.

Type I hypersensitivity

An immediate, IgE-mediated allergic response wherein allergen binding to sensitized mast cells triggers rapid degranulation and histamine release within minutes.