Vertebrate Integument, Skeletomuscular Systems, and Locomotion

Vocabulary practice flashcards covering vertebrate integument, skeletal adaptations, muscular organization, and biomechanical modes of aquatic, terrestrial, and aerial locomotion.

Integument

A composite organ consisting of the epidermis, dermis, and basement membrane that accounts for almost 15% of body mass and serves protective, shapes-maintaining, and regulatory functions.

Stratum corneum

The prominent outer cornified layer of the tetrapod epidermis composed of dead, keratinized cells mixed with lipids that resists mechanical abrasion and limits water loss.

Placoid scales

Surface denticles found in Chondrichthyes that lack dermal bone and consist of an enamel/enameloid surface, dentin layer, and an internal pulp cavity anchored into the fibrous dermis.

Fish scale types

Four primary structural types of dermally derived fish scales: placoid scales (cartilaginous fishes), ganoid scales (nonteleost bony fishes), and cycloid and ctenoid scales (teleost fishes).

Chromatophores

Specialized pigment-containing cells found in all vertebrates, classified by pigment type: melanophores (melanin), iridiophores (purines), and xanthophores and erythrophores (carotenoids).

Ecdysis

The process of molting in which the cornified outer epidermal layer is shed all at once, characteristic of snakes and lizards.

Feather types

Specialized keratinous epidermal derivatives categorized into contour feathers (aerodynamic shaping), down feathers (thermal insulation), flight feathers (stabilization and thrust), semiplumes, and filoplumes (display and sensory functions).

Pelage

The thick fur coat of mammals composed of two distinct hair types: coarse outer guard hair and insulating underfur.

Sebaceous glands

Mammalian integumentary glands that secrete an oily substance called sebum directly onto hair follicles to condition and waterproof the fur.

Eccrine glands

Integumentary glands producing thin, watery fluids that open directly onto skin surfaces, function prior to puberty, and are located on friction surfaces like palms, soles, and tails.

Apocrine glands

Integumentary glands associated with hair follicles that produce a viscous, lipid-containing secretion, begin functioning at puberty, and primarily mediate chemical signaling.

Horns vs. Antlers

Horns consist of a permanent, unbranched cornified sheath over a bony core found in both sexes of Bovidae; antlers are branched, vascularized bony structures grown beneath velvet, shed seasonally, and restricted to male deer.

Chondrocranium

The endoskeletal portion of the cranial skeleton that protects the brain and wraps the sensory capsules of the olfactory and inner ear organs.

Splanchnocranium

The visceral portion of the cranial skeleton derived from neural crest cells that ancestrally supported the pharyngeal gill slits and gave rise to vertebrate jaws.

Dermatocranium

The dermal bone component of the skull that arises without a cartilaginous precursor and encases the chondrocranium and splanchnocranium.

Cranial skeleton components

The structural combination forming the vertebrate cranium: the chondrocranium (braincase base and sense capsules), splanchnocranium (visceral gill arches and jaws), and dermatocranium (outer dermal roofing bones).

Serial Theory

The hypothesis proposing that vertebrate jaws arose from a single, unmodified anterior branchial arch without contributions from adjacent arches.

Composite Theory

The hypothesis stating that the mandibular arch formed through the complex incorporation and fusion of elements from multiple adjacent branchial arches.

Hyostylic suspension

A jaw suspension type characteristic of most derived chondrichthyans and bony fishes where the upper and lower jaws attach to the cranium primarily via the hyomandibula.

Craniostylic suspension

The mammalian jaw condition where the upper jaw fuses completely into the braincase and the lower jaw (dentary) articulates directly with the squamosal bone.

Auditory ossicle evolution

The evolutionary transition in which ancestral reptilian jaw hinge elements migrated into the mammalian middle ear: the articular became the malleus, the quadrate became the incus, the columella became the stapes, and the angular formed the ectotympanic.

Cranial kinesis

Significant cranial mobility enabled by hinge joints and sliding contacts across the skull roof and palate, present in most vertebrates except amphibians, turtles, crocodilians, and mammals.

Secondary palate

A horizontal bony partition that isolates the nasal cavity from the oral cavity, enabling continuous respiration while feeding in adults and simultaneous suckling in mammalian infants.

Centra types

The five morphological classifications of vertebral body ends: acoelous (flat-ended), amphicoelous (concave at both ends), procoelous (concave anteriorly), opisthocoelous (concave posteriorly), and heterocoelous (saddle-shaped).

Zygapophyses

Paired interlocking articular processes on adjacent vertebrae that strengthen the vertebral column and resist excessive lateral or vertical torsion.

Gastralia

Dermal ribs situated within the ventral abdominal wall that do not articulate with the vertebral column, found in fishes and some reptiles.

Plastron

The composite structure of flattened, fused bony plates and scutes that constitutes the ventral shell of a turtle.

Caudal fin types

The three morphological classifications of fish tail fins: heterocercal (vertebral column enters enlarged dorsal lobe), diphycercal (symmetrical tail with spine extending straight to tip), and homocercal (externally symmetrical fin with upturned internal urostyle).

Fin-Fold Theory

The evolutionary hypothesis proposing that paired pectoral and pelvic fins arose from continuous lateral paired folds along the ventrolateral body wall.

Tetrapod limb regions

The three homologous proximal-to-distal divisions of the tetrapod limb: stylopodium (humerus/femur), zeugopodium (radius-ulna/tibia-fibula), and autopodium (manus/pes).

Wing structural homologies

Independently evolved aerial appendages: pterosaurs supported wing membranes with an elongated fourth finger, bats use elongated digits 2 through 5, and birds support flight surfaces using flight feathers attached to three reduced fingers.

Alula

A small tuft of feathers anchored to the independent first digit of a bird's wing that generates lift and prevents stalling during low-speed flight.

Syncytium

A single multinucleated cell formed by the fusion of several embryonic myoblasts, characterizing the structure of skeletal muscle fibers.

Excitation-Contraction Coupling

The physiological pathway in which a sarcolemma action potential travels down transverse (T) tubules, prompting $Ca^{2+}$ release from the sarcoplasmic reticulum to trigger sarcomere contraction.

Intercalated disks

Specialized transverse junctions that anchor individual branched cardiac muscle cells end-to-end, facilitating rapid electrical synchronization across the myocardium.

Muscle tissue types

The three microscopic categories of muscle tissue: smooth muscle (nonstriated, spindle-shaped, uninucleated, involuntary), cardiac muscle (striated, branched, uninucleated, involuntary), and skeletal muscle (striated, syncytial, voluntary).

Muscle connective tissue sheaths

The hierarchical fascia wrapping skeletal muscle: endomysium surrounding each muscle fiber, perimysium grouping fibers into fasciculi, and epimysium binding fasciculi into an entire muscle organ.

Motor unit

A somatic motor neuron together with all the individual skeletal muscle fibers that it innervates, contracting together in an all-or-none manner.

Isotonic contraction

A form of muscle contraction in which mechanical tension remains sufficient to cause shortening of the muscle fibers, producing movement.

Isometric contraction

A form of muscle contraction where internal tension develops without any shortening of the muscle length, serving to fix joints and maintain posture.

Extrinsic ocular muscles

The six strap-like axial muscles derived from anterior somites that attach to the sclera to rotate the eyeball: lateral, medial, dorsal, and ventral rectus, alongside dorsal and ventral obliques.

Branchiomeric muscles

Visceral axial muscles located in the pharyngeal wall that develop from paraxial mesoderm and control jaw operation and gill basket movements.

Epaxial and hypaxial musculature

The bilateral division of vertebrate trunk and tail muscles partitioned by a horizontal skeletogenous septum into dorsal (epaxial) and ventral (hypaxial) muscle masses.

Myomeres

Segmented, chevron-shaped muscle blocks in fishes and aquatic vertebrates separated by connective tissue myosepta that contract alternately to produce swimming undulations.

Primary swimmers vs. Secondary swimmers

Primary swimmers are lineage-continuous aquatic craniates that swim as their sole mode of locomotion (e.g., fishes), whereas secondary swimmers are tetrapods that re-entered and adapted secondarily to water (e.g., cetaceans, seals).

Fish swimming modes

Locomotor styles categorized by the degree of lateral wave propagation along the body: anguilliform (full body), subcarangiform (posterior half), carangiform (posterior third), and thunniform (caudal fin and peduncle only).

Transient vs. Periodic swimmers

Transient swimmers are maneuverable, ambush-adapted fishes with deep bodies designed for sudden bursts of acceleration; periodic swimmers are cruising pelagic species with streamlined fusiform shapes built for sustained efficiency.

Serratus ventralis muscular sling

A dominant thoracic muscular support extending from the distal ribs to the dorsal scapular border that suspends the mammalian trunk and absorbs impact shock during walking.

Saltatorial locomotion

Specialized jumping or leaping locomotion distinguished by elongated hind legs, a shortened and stiffened vertebral column, and a center of mass shifted toward the sacrum.

Arboreal vs. Cursorial theories of flight

The arboreal ('top-down') hypothesis states that powered flight evolved from climbing tree-dwellers that jumped and glided between branches; the cursorial ('ground-up') hypothesis posits that feathered bipedal runners generated wing lift while chasing prey.