HISTOLOGY LE2 COVERAGE

Sarcolemma

What specialized term describes the plasma membrane of a skeletal muscle fiber together with its external and reticular lamina?

Sarcoplasmic reticulum

In a skeletal muscle fiber, what specialized smooth ER forms the intracellular Ca²⁺ storage network responsible for excitation-contraction coupling?

Myofibril

What longitudinal bundle of myofilaments extends throughout a muscle fiber and contains repeating sarcomeres?

Sarcomere

What is the smallest contractile unit of striated muscle, extending from one Z line to the next?

Multinucleated syncytium

What cellular organization results when multiple skeletal myoblasts fuse, producing a single muscle fiber containing many peripheral nuclei?

Endomysium

What delicate connective-tissue layer composed largely of reticular fibers surrounds an individual skeletal muscle fiber?

Perimysium

What connective-tissue sheath surrounds a skeletal muscle fascicle and carries larger vessels and nerves?

Epimysium

What dense connective-tissue layer encloses the entire skeletal muscle and is continuous with deeper connective tissues?

Type I

Which skeletal muscle fiber is small, oxidative, slow-twitch, rich in mitochondria and myoglobin, and highly resistant to fatigue?

Type IIa

Which skeletal muscle fiber is fast-twitch but retains substantial oxidative capacity, making it relatively fatigue-resistant?

Type IIb

Which skeletal muscle fiber is large, fast-twitch, predominantly glycolytic, and rapidly fatigued?

Succinic dehydrogenase / NADH-TR histochemistry

Which histochemical techniques can be used to distinguish skeletal muscle fiber types according to their oxidative activity?

Myoglobin

During extensive muscle injury such as rhabdomyolysis, which oxygen-binding muscle protein can be released into blood and contribute to acute renal injury?

A band

Which sarcomere band corresponds to the full length of thick filaments and therefore remains essentially unchanged in length during contraction?

I band

Which sarcomere region contains thin filaments without overlapping thick filaments and becomes shorter during contraction?

H band

Which lighter central portion of the A band contains thick filaments without thin-filament overlap and narrows during contraction?

M line

Which dense structure in the center of the H band organizes and links the thick filaments?

Z line

Which dense zig-zag structure defines sarcomere boundaries and anchors the thin filaments?

A band

Which sarcomere region is anisotropic and therefore appears birefringent under polarized light microscopy?

A stays constant

I shortens

Tropomyosin

At rest, which actin-associated protein physically covers the myosin-binding sites and prevents cross-bridge formation?

Troponin C

Which troponin subunit directly binds Ca²⁺ during skeletal and cardiac muscle contraction?

Troponin T

Which troponin subunit binds the troponin complex to tropomyosin?

Troponin I

Which troponin subunit inhibits actin-myosin interaction when intracellular Ca²⁺ is low?

Nebulin

Which thin-filament protein functions as a molecular ruler and helps determine the length and organization of actin filaments?

α-Actinin

Which Z-line protein cross-links thin filaments and anchors them at the Z line?

Titin

Which enormous elastic protein extends from the Z line toward the M line, centers thick filaments, and resists excessive sarcomere stretch?

Desmin

Which muscle-specific intermediate filament connects myofibrils at the level of the Z lines and helps maintain their alignment?

Dystrophin

Which large cytoskeletal protein links the intracellular actin cytoskeleton to the extracellular matrix through the sarcolemma-associated protein complex?

Duchenne muscular dystrophy

What X-linked muscular dystrophy results from severe dystrophin deficiency and causes progressive skeletal-muscle degeneration?

Cross-bridge cycle

What sequence describes ATP-dependent attachment of myosin to actin, power stroke, ATP-mediated detachment, and re-cocking of the myosin head?

Power stroke

During contraction, what event occurs when release of Pi from the myosin head produces movement of the actin filament?

Rigor state

What condition occurs when ATP is unavailable and myosin heads remain tightly attached to actin?

Recovery stroke

After ATP binds and causes myosin to detach from actin, what ATP-dependent step repositions the myosin head into its energized conformation?

Triad

What skeletal-muscle structure consists of one transverse tubule flanked by two terminal cisternae of the sarcoplasmic reticulum?

RyR1

Which ryanodine receptor located in the terminal cisternae releases Ca²⁺ into the sarcoplasm during skeletal-muscle excitation?

SERCA

Which sarcoplasmic-reticulum Ca²⁺-ATPase uses ATP to actively return Ca²⁺ into the SR during muscle relaxation?

Motor unit

What functional unit consists of one somatic motor neuron and all of the skeletal muscle fibers it innervates?

Nicotinic acetylcholine receptor

Which ligand-gated ion channel on the motor end plate opens when acetylcholine is released from the somatic motor neuron?

Myasthenia gravis

What autoimmune neuromuscular disorder causes weakness through antibodies directed primarily against postsynaptic acetylcholine receptors?

Botulinum toxin

Which toxin causes flaccid paralysis by interfering with acetylcholine release from presynaptic motor nerve terminals?

Curare

Which neuromuscular-blocking agent produces paralysis by competitively blocking nicotinic acetylcholine receptors at the motor end plate?

Succinylcholine

Which depolarizing neuromuscular blocker initially activates nicotinic receptors but produces prolonged depolarization and paralysis?

Intercalated disc

What specialized junctional complex connects adjacent cardiac muscle cells and contains fascia adherens, desmosomes, and gap junctions?

Diad

What cardiac muscle structure consists of one T tubule associated with one terminal cisterna of the sarcoplasmic reticulum?

Calcium-induced calcium release

What mechanism describes extracellular Ca²⁺ entry through L-type Ca²⁺ channels triggering additional Ca²⁺ release from the cardiac SR?

Purkinje fiber

Which specialized cardiac muscle cell conducts impulses rapidly through the ventricles and contains abundant glycogen with relatively peripheral myofibrils?

Atrial granules

Which membrane-bound granules in atrial cardiomyocytes contain atrial natriuretic peptide?

Troponin I

Which cardiac muscle biomarker is released after myocardial injury and is highly useful for detecting myocardial infarction?

Smooth muscle

Which muscle type lacks sarcomeres, T tubules, and troponin but contracts through Ca²⁺-calmodulin activation of MLCK?

Dense bodies

What structures in smooth muscle serve as functional analogues of Z lines by anchoring actin filaments?

Calmodulin

Which intracellular Ca²⁺-binding protein activates myosin light-chain kinase in smooth muscle?

Myosin light-chain kinase

Which enzyme is activated by Ca²⁺-calmodulin and phosphorylates the regulatory myosin light chain in smooth muscle?

Latch state

What smooth-muscle state permits prolonged force maintenance with relatively low ATP consumption?

Satellite cell

Which quiescent skeletal-muscle stem cell lies between the sarcolemma and external lamina and participates in muscle regeneration?

Pax7

Which transcription factor is characteristically associated with skeletal-muscle satellite cells and their maintenance?

Motor neuron

In the spinal cord, which large neuron in the ventral horn has abundant Nissl substance and directly supplies skeletal muscle?

Nissl substance

Which basophilic neuronal cytoplasmic material reflects abundant rough ER and ribosomes involved in protein synthesis?

Node of Ranvier

What interruption between adjacent myelin segments permits saltatory conduction along a myelinated axon?

Schmidt-Lanterman cleft

What cytoplasmic channel within a Schwann-cell myelin sheath allows communication between the Schwann-cell cytoplasm and the periphery of the myelinated fiber?

Schwann cell

Which PNS glial cell forms myelin around individual axonal segments and also supports regeneration after peripheral nerve injury?

Oligodendrocyte

Which CNS glial cell forms myelin and can myelinate segments of multiple axons?

Astrocyte

Which CNS glial cell extends perivascular end feet and contributes to maintenance of the blood-brain barrier and extracellular environment?

GFAP

Which intermediate filament protein is characteristically expressed by astrocytes and is useful as a marker for astrocytic tumors?

Microglia

Which CNS cell of mesodermal origin acts as the principal resident phagocytic cell of nervous tissue?

Ependyma

Which simple epithelial-like cell layer lines the ventricles and central canal and contributes to the lining associated with CSF circulation?

Satellite cell

Which PNS glial cell forms a sheath around neuronal cell bodies within peripheral ganglia?

Enteric glia

Which PNS-supporting glial cells resemble astrocytes functionally and are associated with neurons of the enteric nervous system?

Blood-brain barrier

What selective barrier depends primarily on endothelial tight junctions, basal lamina, and astrocytic end feet rather than ependymal tight junctions?

Aquaporin-4

Which water channel concentrated in astrocytic end feet is particularly important in CNS water movement and edema?

Circumventricular organs

In which CNS regions is the blood-brain barrier physiologically absent or modified to permit sampling or secretion into the circulation?

Endoneurium

Which connective-tissue layer surrounds an individual peripheral nerve fiber?

Perineurium

Which connective-tissue sheath surrounds a peripheral nerve fascicle and contributes to the blood-nerve barrier?

Epineurium

Which outer connective-tissue layer surrounds an entire peripheral nerve and contains larger vessels and adipose tissue?

Pseudounipolar neuron

What neuronal morphology is characteristic of sensory neurons in dorsal-root and many cranial sensory ganglia?

Sensory ganglion

Which PNS ganglion contains large pseudounipolar neurons surrounded by satellite cells and generally lacks synaptic connections within the ganglion?

Autonomic ganglion

Which peripheral ganglion contains multipolar neurons that receive synaptic input from preganglionic autonomic neurons?

Myenteric plexus

Which enteric plexus, also called Auerbach plexus, is located between the muscular layers of the gastrointestinal tract?

Submucosal plexus

Which enteric plexus, also called Meissner plexus, primarily regulates mucosal secretion and blood flow?

Adrenal medulla

What endocrine tissue represents a modified sympathetic ganglion in which chromaffin cells function as modified postganglionic neurons?

Guillain-Barré syndrome

Which autoimmune disorder causes demyelination of peripheral nerves and can produce ascending weakness?

Multiple sclerosis

Which demyelinating disease primarily affects the CNS rather than peripheral nerves?

Parkinson disease

Which neurologic disorder is associated with degeneration of dopaminergic neurons and reduced dopamine signaling?

Osteoprogenitor cell

Which mesenchymal-derived bone precursor expresses RUNX2/CBFA1 and can differentiate into osteoblasts?

Osteoblast

Which mononuclear, basophilic bone-forming cell synthesizes osteoid and initiates matrix mineralization?

Osteocyte

What former osteoblast becomes embedded within bone matrix, occupies a lacuna, extends processes through canaliculi, and helps maintain bone homeostasis?

Bone-lining cell

Which flattened, quiescent cell represents an inactive osteoblast covering a resting bone surface?

Osteoclast

Which multinucleated, TRAP-positive cell forms a ruffled border and sealing zone within a Howship lacuna to resorb bone?

Howship lacuna

What shallow depression on the bone surface contains an actively resorbing osteoclast?

Ruffled border

Which highly folded osteoclast membrane concentrates proton pumps and lysosomal enzymes at the bone-resorbing surface?

TRAP

Which histochemical marker is characteristically expressed by osteoclasts and is useful for identifying these bone-resorbing cells?

Cathepsin K

Which osteoclast protease is particularly important for degradation of the collagenous organic component of bone matrix?

RANKL

Which osteoblast-lineage/osteocyte-associated ligand promotes osteoclast differentiation by activating RANK on osteoclast precursors?

Osteoprotegerin

Which osteoblast-lineage-derived decoy receptor inhibits osteoclastogenesis by binding RANKL and preventing RANK activation?

Calcitonin

Which hormone directly inhibits osteoclast activity and therefore tends to lower circulating Ca²⁺?

PTH

Which hormone raises blood Ca²⁺ largely by acting indirectly on osteoclasts through osteoblast-lineage cells rather than by binding osteoclasts directly?

Woven bone

Which immature bone has randomly arranged collagen, relatively high cellularity, and is characteristic of fetal development and early fracture repair?

Lamellar bone

Which mature bone has highly organized collagen arranged in parallel or concentric lamellae and provides greater mechanical strength?

Osteon

What structural unit of compact bone consists of concentric lamellae surrounding a central Haversian canal?

Interstitial lamellae

What irregular lamellae between osteons represent remnants of older osteons partially removed during bone remodeling?