Rat Anatomy: Body Structure

External Anatomy

Head

Snout

The snout represents the anterior projection of the skull and forms the primary portal for food intake and environmental sampling. Its bony framework consists of the paired nasal bones, the premaxilla bearing the incisor sockets, and the maxilla supporting the cheek teeth. The nasofrontal suture defines the junction between the snout and the cranium, while the intermaxillary suture unites the premaxillae.

Sensory structures dominate the snout surface. The olfactory epithelium lines the nasal cavity, providing a high density of receptor neurons for volatile detection. Vibrissae emerge from specialized follicles on the rostral skin, each supplied by the trigeminal nerve, enabling tactile discrimination of objects and textures. A rich vascular plexus supplies oxygenated blood to both olfactory and vibrissal tissues, facilitating rapid metabolic exchange.

Muscular attachments enable complex movements required for feeding and exploration. The levator labii superioris, nasolabialis profundus, and buccinator muscles originate on the snout bones and coordinate lip elevation, snout retraction, and cheek compression. The masseter and temporalis muscles, although primarily attached to the posterior skull, interact with the snout via connective tissues to generate bite forces exceeding 10 N in adult specimens.

Key anatomical elements can be summarized:

• Nasal bones: protect the olfactory chambers.
• Premaxilla: houses the large incisor pair.
• Maxilla: supports premolars and molars.
• Vibrissal follicles: mechanoreceptors linked to the trigeminal system.
• Olfactory epithelium: sensory epithelium for odor detection.
• Vascular plexus: supplies oxygen and nutrients to sensory tissues.
• Associated musculature: controls snout positioning and oral functions.

«The morphology of the rat snout reflects an integration of skeletal rigidity, sensory acuity, and muscular agility, essential for survival in diverse habitats.»

Eyes

The rat visual organ exhibits a compact design optimized for nocturnal activity. External structures include a thin upper eyelid, a lower eyelid lacking a distinct margin, and a nictitating membrane that provides additional protection. Lacrimal glands secrete a tear film that maintains corneal hydration and clears debris.

The globe consists of three concentric layers. The outermost cornea and sclera form a transparent and fibrous shield, respectively. The middle uveal tract comprises the iris, ciliary body, and choroid, which regulate light entry and supply nutrients. The innermost retina houses photoreceptor cells, bipolar neurons, and ganglion cells. Rods dominate the retinal mosaic, granting high sensitivity to low light, while cones, concentrated in a central visual streak, support limited color discrimination.

Ocular motility is driven by six extraocular muscles attached to the scleral surface, enabling precise positioning of the visual axis. The optic nerve emerges from the posterior pole, transmitting visual signals to the lateral geniculate nucleus and visual cortex.

Key vascular elements include the central retinal artery, which penetrates the optic disc, and the posterior ciliary arteries that feed the choroid. Venous drainage follows the retinal veins into the cavernous sinus.

Typical dimensions of the rat eye measure approximately 6 mm in axial length and 4 mm in horizontal diameter, reflecting the species’ small cranial cavity.

• Principal components
  • Eyelids and nictitating membrane
  • Lacrimal gland
  • Cornea and sclera
  • Iris, ciliary body, choroid
  • Retina (rods, cones, interneurons, ganglion cells)
  • Extraocular muscles
  • Optic nerve
  • Central retinal artery and posterior ciliary arteries

These anatomical features collectively support the rat’s reliance on dim‑light vision and rapid visual processing.

Ears

The rat’s auditory system comprises three distinct regions: the outer ear, the middle ear, and the inner ear. The outer ear includes the pinna, a flexible cartilage structure that captures sound waves and directs them into the ear canal. The canal terminates at the tympanic membrane, a thin, tensioned membrane that vibrates in response to acoustic pressure.

The middle ear contains the ossicular chain—malleus, incus, and stapes—connected to the tympanic membrane and the oval window of the inner ear. These bones amplify vibrations and transmit them to the cochlear fluid. The Eustachian tube links the middle ear to the nasopharynx, maintaining pressure equilibrium.

The inner ear houses the cochlea and vestibular apparatus. Key elements include:

• The scala vestibuli and scala tympani, fluid-filled chambers that convey mechanical energy.
• The organ of Corti, where hair cells convert fluid motion into neural impulses.
• The vestibular semicircular canals, which detect angular acceleration.
• The vestibular maculae, responsible for linear acceleration and head position.

Auditory nerve fibers emerge from the spiral ganglion, projecting to the brainstem’s cochlear nuclei. Blood supply is provided by branches of the internal carotid artery, ensuring metabolic support for sensory epithelium. This organization enables precise detection of high-frequency sounds, a characteristic feature of rodent hearing.

Whiskers «Vibrissae»

Whiskers «Vibrissae» are specialized tactile hairs located on the rostral region of the rat, extending from the mystacial pad, supraorbital area, and facial whisker pads. Each vibrissa is anchored in a deep follicle that penetrates the subcutaneous tissue and connects to a rich vascular network and a dense bundle of trigeminal nerve fibers.

The follicle comprises a capsule of collagen, a sinusoidal blood supply, and a mechanoreceptive organ known as the Merkel cell complex. Innervation originates from the infraorbital branch of the trigeminal nerve, providing rapid transmission of mechanical deflection to the somatosensory cortex. Muscular control is achieved through intrinsic muscles (intrinsic musculature of the mystacial pad) that adjust the angle of each vibrissa during exploratory behavior.

Key functional attributes include:

• Detection of airflow changes, allowing identification of obstacles and predators.
• Generation of spatial maps through active whisking cycles at frequencies of 5–12 Hz.
• Integration with motor planning circuits to coordinate head and body movements during navigation.

Density and length of vibrissae vary across body regions; the mystacial macrovibrissae are longest (up to 30 mm) and most numerous, while microvibrissae on the cheeks are shorter and densely packed, enhancing surface texture discrimination. These morphological differences support precise tactile resolution required for foraging and burrow exploration.

Torso

Pelage «Fur»

The pelage of the common rat consists of a dense coat of hair that covers the dorsal and ventral surfaces, providing thermal insulation, tactile feedback, and protection against environmental hazards. Hair shafts are organized into three distinct layers: guard hairs, awn hairs, and under‑coat fibers. Guard hairs are the longest and coarsest, projecting outward to repel debris and moisture. Awn hairs form an intermediate stratum, contributing to the overall density and serving as a transitional barrier. Under‑coat fibers, the finest elements, create a continuous insulating matrix that retains body heat.

Key characteristics of rat pelage include:

• Structure – each hair follicle comprises a bulb, sheath, and associated sebaceous gland; follicles are distributed in a regular pattern, with higher density along the back and tail.
• Growth cycle – anagen (active growth), catagen (regression), and telogen (resting) phases occur continuously, allowing rapid replacement of damaged shafts.
• Coloration – melanin deposition determines pigment; variations range from pale gray to dark brown, reflecting genetic and environmental influences.
• Sensory function – vibrissae, specialized tactile hairs, are integrated within the pelage, providing precise mechanoreceptive input for navigation.

The coat’s composition is primarily keratin, a fibrous protein that confers durability and resistance to abrasion. Sebaceous secretions coat the hair surface, reducing friction and aiding waterproofing. Seasonal changes can trigger alterations in hair length and density, enhancing thermoregulation during colder periods.

Overall, rat pelage represents a multifunctional integumentary system, integrating structural, protective, and sensory roles essential to the animal’s physiology.

Nipples

Rats possess a series of paired mammary papillae extending along the ventral midline. Typically, four pairs are present, positioned from the thoracic region to the inguinal area. The arrangement follows a consistent pattern:

• First pair: thoracic region, near the forelimbs
• Second pair: thoracic‑abdominal junction
• Third pair: abdominal region, close to the umbilicus
• Fourth pair: inguinal region, adjacent to the hindlimbs

Each nipple consists of an external papilla, underlying smooth muscle, and a ductal network converging on a rudimentary mammary gland. In females, the glandular tissue expands during puberty and further during pregnancy, enabling milk secretion. Male rats retain the papillae but lack significant glandular development, rendering them non‑functional for lactation.

Embryologically, mammary ridges appear around day 12 of gestation, giving rise to the nipple primordia. Postnatal growth accelerates at weaning, with full differentiation achieved by sexual maturity. Lactation induces alveolar proliferation and secretory activation, reversible after weaning.

In laboratory settings, nipple count and morphology serve as reliable markers for sex determination, developmental stage assessment, and detection of endocrine disruptions. Pathological changes, such as hyperplasia or neoplasia, are readily observable at the papillae, facilitating early diagnosis.

Limbs

Rats possess a pair of forelimbs and a pair of hindlimbs, each adapted for precise manipulation and rapid locomotion. The forelimbs exhibit a shortened humerus, a robust radius and ulna, and a manus ending in five digits equipped with sharp claws. The hindlimbs feature an elongated femur, a tibia‑fibula complex, and a pes with similarly structured digits, facilitating powerful thrusts during jumping and sprinting.

Key skeletal elements of the limbs include:

• «humerus», «radius», «ulna» (forelimb)
• «femur», «tibia», «fibula» (hindlimb)
• «metacarpals», «metatarsals»
• «phalanges» of each digit

Muscular architecture supports both fine motor control and force generation. The brachial plexus innervates the forelimb muscles such as the biceps brachii and triceps brachii, enabling grasping and digging. The sciatic nerve supplies the hindlimb, driving muscles like the quadriceps femoris and gastrocnemius for propulsion. Tendon attachments to the distal phalanges create a lever system that amplifies grip strength.

The distal extremities are covered with plantar and palmar pads composed of dense keratinized epidermis, providing traction on varied substrates. Sensory receptors within the pads detect pressure and vibration, contributing to the rat’s acute tactile perception. Nail plates at the tips of the digits aid in climbing and object manipulation.

Overall, the limb morphology reflects a balance between dexterity and speed, allowing rats to navigate complex environments, exploit food resources, and evade predators efficiently.

Tail

Function

The rat’s anatomical organization supports a range of physiological processes essential for survival, locomotion, and reproduction. Skeletal elements provide a rigid framework, enabling weight bearing and protection of internal organs. Muscular attachments generate force for movement, posture maintenance, and heat production. Vascular networks deliver oxygen and nutrients while removing metabolic waste, sustaining cellular activity throughout the organism. The digestive tract transforms ingested material into absorbable nutrients, with specialized regions optimizing enzymatic breakdown and microbial fermentation. The nervous system coordinates sensory input and motor output, integrating reflexes and complex behaviors. Endocrine glands regulate metabolism, growth, and stress responses through hormone secretion. Reproductive structures facilitate gamete production, fertilization, and offspring development. Each component functions synergistically, forming an integrated system that maintains homeostasis and adapts to environmental challenges.

Structure

The rat’s body is organized into distinct structural layers that support locomotion, protection, and internal function. The external integumentary covering consists of skin, hair follicles, and a thin subcutaneous layer that houses sensory receptors and vascular networks. Beneath the skin, the musculoskeletal framework provides rigidity and movement.

• Skeletal system: axial skeleton includes the skull, vertebral column, and rib cage; appendicular skeleton comprises the scapulae, pelvis, and limb bones. Bone composition features a cortical outer layer and a trabecular inner matrix, facilitating strength and metabolic exchange.
• Muscular system: skeletal muscles attach to bones via tendons, enabling precise limb motions; smooth muscle lines visceral organs, regulating peristalsis and vascular tone; cardiac muscle forms the heart, delivering circulatory force.
• Organ placement: thoracic cavity houses the heart and lungs, protected by the rib cage; abdominal cavity contains the liver, stomach, intestines, kidneys, and reproductive organs, each encased in connective tissue sheaths.
• Nervous architecture: central nervous system resides within the skull and vertebral canal, while peripheral nerves extend into limbs and sensory fields, coordinating reflexes and voluntary actions.

Connective tissue layers—fascia, tendons, and ligaments—link muscles to bones and organs, distributing mechanical loads and maintaining structural integrity. Vascular networks permeate all layers, delivering oxygen and nutrients while removing metabolic waste. This hierarchical arrangement enables the rat to perform rapid, agile movements and sustain essential physiological processes.

Internal Anatomy

Skeletal System

Skull

The rat skull is a compact, sturdy structure that protects the brain and supports the facial muscles required for mastication and sensory perception. It consists of two major components: the neurocranium, which encloses the cerebral hemispheres, and the splanchnocranium, which forms the jaws and facial region.

The neurocranium comprises the frontal, parietal, occipital, and temporal bones, fused to create a rigid vault. The frontal bone forms the forehead and contributes to the orbital rim. Paired parietal bones meet at the sagittal suture, while the occipital bone closes the posterior skull. Temporal bones house the auditory bulla, a hollow cavity that amplifies sound.

The splanchnocranium includes the maxillae, mandibles, and several smaller elements. The maxillae support the upper dentition, including the incisors, which continuously grow. The mandible, a single fused bone, carries the lower incisors and molars. Additional bones—such as the zygomatic, lacrimal, and nasal bones—contribute to the cheek region, tear ducts, and nasal cavity.

Key morphological features:

• Prominent incisors with enamel restricted to the labial surface, creating a self-sharpening edge.
• Large auditory bulla, relative to body size, enhancing low-frequency hearing.
• Well‑developed infraorbital foramen, allowing passage of the infraorbital nerve and vessels.
• Robust occipital condyles that articulate with the first cervical vertebra, providing head stability.

Vascular and neural pathways traverse the skull through foramina and canals. The carotid arteries enter the cranial cavity via the carotid canal, while the trigeminal nerve branches exit through the infraorbital and mental foramina to innervate facial tissues.

Overall, the rat skull integrates protection, sensory input, and feeding mechanics within a compact architecture adapted to the species’ nocturnal and omnivorous lifestyle.

Vertebral Column

The vertebral column of the laboratory rat forms the central axis of the axial skeleton, extending from the occipital region to the caudal terminus. It consists of a series of articulated osseous units that protect the spinal cord, bear the body’s weight, and serve as attachment sites for musculature.

• Cervical region: 7 vertebrae, each with a relatively large transverse foramen for arterial passage.
• Thoracic region: 13 vertebrae, each bearing a pair of ribs; facets on the vertebral bodies articulate with thoracic ribs.
• Lumbar region: 6 vertebrae, characterized by robust bodies and expansive transverse processes for muscular attachment.
• Sacral region: 4 fused vertebrae forming the sacrum, connecting the pelvis to the spinal column.
• Caudal region: 20–22 vertebrae, progressively diminutive, constituting the tail.

The column’s curvature includes a slight dorsal arch in the cervical and lumbar sections, contributing to balance and locomotor efficiency. Intervertebral discs, composed of a fibrocartilaginous annulus and a gelatinous nucleus pulposus, provide shock absorption and permit limited flexion. Ligamentous structures—interspinous, supraspinous, and ligamentum flavum—stabilize the column while allowing controlled movement. Muscles such as the erector spinae and multifidus attach to the vertebral arches, enabling extension and rotation of the trunk.

Rib Cage

The rib cage of the laboratory rat forms a rigid yet flexible enclosure that safeguards the thoracic organs and provides attachment points for muscles involved in respiration. It consists of twelve pairs of ribs, each articulating with the corresponding thoracic vertebrae at the costovertebral joints. The anterior ends of most ribs connect to the sternum via costal cartilage, creating a semi‑elastic bridge that permits expansion during inhalation while maintaining structural integrity.

Key structural features include:

• True ribs (pairs 1‑7): Directly joined to the sternum by well‑developed costal cartilages.
• False ribs (pairs 8‑10): Connected to the sternum indirectly through the cartilage of the preceding rib.
• Floating ribs (pairs 11‑12): Lack anterior attachment, terminating in the musculature of the abdominal wall.

The sternum comprises three sections—manubrium, body, and xiphoid process—and serves as the central anchor for the costal cartilages. Intercostal muscles occupy the spaces between adjacent ribs, facilitating the elevation and depression of the thoracic wall. The pleural cavities, lined by serous membranes, lie deep to the rib cage and house the lungs, while the heart resides within the mediastinum, protected by the anterior ribs and sternum.

Cartilaginous flexibility allows the rib cage to accommodate the high respiratory rates typical of rodents. The overall geometry—cylindrical in the middle thoracic region and tapering toward the cranial and caudal ends—optimizes space for the heart, lungs, and major blood vessels while preserving a compact body profile essential for the animal’s burrowing behavior.

Limbs «Bones»

The limb skeleton of the laboratory rat consists of a compact arrangement of long, short and irregular bones that support locomotion, manipulation and balance. Each forelimb contains the scapula, humerus, radius, ulna and a series of carpal, metacarpal and phalangeal elements; the hindlimb comprises the pelvis, femur, tibia, fibula and corresponding tarsal, metatarsal and phalangeal bones. All limb bones are enveloped by periosteum, penetrated by nutrient canals, and joined by synovial joints that permit a wide range of motion.

Key characteristics of rat limb bones include:

• High cortical thickness relative to overall size, providing rigidity while maintaining low body mass.
• Presence of a well‑developed medullary cavity that houses marrow and contributes to hematopoiesis.
• Distinct epiphyseal plates in juveniles, which ossify during maturation to form solid ends.
• Robust attachment sites for major muscle groups, such as the deltoid tuberosity on the humerus and the greater trochanter on the femur.

The forelimb and hindlimb share structural similarities but differ in functional emphasis. The forelimb exhibits greater dexterity, reflected in elongated metacarpals and flexible wrist joints, whereas the hindlimb displays enhanced propulsive power, evident in a longer femur and enlarged trochanteric region. Vascularization follows the pattern of nutrient arteries entering the diaphysis, while venous drainage proceeds through periosteal veins and accompanying nerves.

Overall, the limb bone architecture in rats exemplifies an efficient balance between strength, mobility and metabolic support, essential for the species’ agile terrestrial behavior.

Muscular System

Major Muscle Groups

Rats possess a compact musculoskeletal system organized into distinct muscle groups that support locomotion, feeding and postural stability.

The dorsal musculature consists of epaxial muscles, primarily the longissimus and iliocostalis, which extend the vertebral column and maintain spinal rigidity. Below the epaxial layer, hypaxial muscles such as the transversus abdominis and internal oblique compress the abdominal cavity and assist in respiration.

Forelimb muscles are grouped into flexors and extensors. The biceps brachii and brachialis generate elbow flexion, while the triceps brachii provides powerful extension. The deltoid and supraspinatus contribute to shoulder abduction and stabilization of the scapulohumeral joint.

Hindlimb musculature includes the following major groups:

• Gluteal complex (gluteus maximus, medius, minimus) – hip extension and lateral stabilization.
• Quadriceps femoris – knee extension, essential for propulsion.
• Hamstring group (biceps femoris, semitendinosus, semimembranosus) – knee flexion and hip extension.
• Gastrocnemius and plantaris – ankle plantarflexion, critical for jumping and rapid escape.

Masticatory muscles dominate the head region. The masseter and temporalis generate powerful bite forces, while the pterygoid muscles fine‑tune mandibular movements during chewing.

Collectively, these muscle groups enable the rat to perform rapid, agile movements, sustain prolonged foraging activity and maintain a stable posture during complex behaviors.

Function of Muscles

Muscle tissue in rats constitutes the active component of the musculoskeletal system, enabling force generation and movement. Skeletal, smooth, and cardiac muscles differ in structure and control, yet each contributes to the organism’s physiological performance.

Key functions of rat musculature include:

• «Force production» for limb and jaw motion;
• «Postural stabilization» maintaining body orientation during rest and activity;
• «Heat generation» through metabolic activity, supporting thermoregulation;
• «Visceral transport» moving contents through the gastrointestinal, urinary, and reproductive tracts;
• «Cardiac output» propelling blood throughout the circulatory network.

Muscle contraction follows the sliding‑filament model: calcium release triggers troponin‑mediated exposure of actin binding sites, allowing myosin heads to pull filaments past one another. ATP hydrolysis supplies the energy required for cross‑bridge cycling, while neural impulses regulate contraction timing and intensity.

During locomotion, coordinated activation of antagonistic muscle groups produces rhythmic limb cycles, translating neural commands into forward propulsion. Simultaneously, axial muscles generate tonic tension that counters gravity, preserving spinal alignment. Cardiac muscle operates involuntarily, delivering continuous blood flow essential for nutrient distribution and waste removal. Smooth muscle layers in hollow organs contract rhythmically, facilitating peristalsis and sphincter control.

Organ Systems

Digestive System

The rat digestive tract begins with a short, muscular oral cavity equipped with incisors that continuously grow and are self‑sharpening through gnawing. Salivary glands secrete enzymes initiating carbohydrate breakdown, while the tongue aids in bolus formation.

Posterior to the mouth, the esophagus consists of striated and smooth muscle layers that generate peristaltic waves, transporting ingested material to a monogastric stomach. The stomach walls contain glandular regions producing hydrochloric acid and pepsin, creating an acidic environment for protein denaturation and initial hydrolysis.

The small intestine, extending approximately 30 cm, is divided into duodenum, jejunum, and ileum. Villi and microvilli increase absorptive surface, facilitating the uptake of amino acids, glucose, and fatty acids. Enzymes from the pancreas and bile from the liver are released into the duodenum, enhancing lipid emulsification and nutrient digestion.

The large intestine comprises a cecum, colon, and rectum. The cecum hosts microbial fermentation, converting nondigestible fibers into short‑chain fatty acids that serve as an energy source. The colon reabsorbs water and electrolytes, while the rectum stores feces prior to elimination.

Key accessory organs include:

• Liver: synthesizes bile, stores glycogen, detoxifies metabolites.
• Pancreas: secretes digestive enzymes (amylase, lipase, proteases) and bicarbonate.
• Gallbladder: concentrates and releases bile in response to fatty intake.

Overall, the rat digestive system exhibits rapid transit times and a high metabolic rate, reflecting adaptation to a diet rich in seeds, grains, and occasional animal protein. «digestion» proceeds efficiently through coordinated muscular activity, enzymatic secretion, and microbial fermentation, supporting the organism’s growth and energy demands.

Respiratory System

The respiratory apparatus of the laboratory rat occupies the cranial and thoracic regions and comprises a series of hollow, epithelial‑lined passages that culminate in the pulmonary parenchyma. Air enters through the external nares, proceeds into the nasal cavity where olfactory and respiratory epithelia coexist, and then passes to the nasopharynx. The larynx functions as a valve, directing airflow into the trachea, a rigid cartilaginous tube that bifurcates into the primary bronchi.

• Primary bronchi branch into secondary and tertiary bronchi, forming a hierarchical network that distributes air throughout the lung lobes.
• Each lung lobe consists of numerous bronchopulmonary segments, each supplied by a distinct bronchus and accompanying pulmonary artery.
• Alveolar sacs, lined by type I and type II pneumocytes, provide a large surface area for diffusion of oxygen and carbon dioxide.

The rat lung is divided into four lobes on the right and a single lobe on the left, a configuration that maximizes respiratory efficiency while accommodating the compact thoracic cavity. Pulmonary arteries accompany the bronchi, delivering deoxygenated blood for gas exchange; pulmonary veins return oxygen‑rich blood to the left atrium. The diaphragm, a muscular partition separating the thoracic and abdominal cavities, contracts rhythmically to generate negative intrathoracic pressure, thereby drawing air into the alveoli.

Ventilation is regulated by autonomic neural inputs that modulate diaphragm and intercostal muscle activity, ensuring precise control of tidal volume and respiratory rate. The respiratory system, integrated with the circulatory network, maintains arterial oxygen saturation and removes metabolic carbon dioxide, supporting the high metabolic demands of the rodent.

Circulatory System

The rat circulatory system comprises a closed network that transports blood throughout the organism, delivering oxygen and nutrients while removing metabolic waste. Blood is propelled by a four‑chambered heart, which generates sufficient pressure to sustain flow through arteries, arterioles, capillaries, venules, and veins. Systemic and pulmonary circuits operate in parallel, ensuring separation of oxygenated and deoxygenated blood.

Key components include:

• Heart: left and right ventricles and atria, surrounded by a pericardial sac; myocardial thickness varies between chambers to accommodate pressure differences.
• Arteries: elastic and muscular vessels that convey blood away from the heart; the aorta branches into thoracic and abdominal segments supplying major organs.
• Veins: low‑pressure conduits returning blood to the heart; the vena cava aggregates peripheral venous return.
• Capillaries: thin‑walled networks facilitating exchange of gases, nutrients, and waste at the cellular level; high surface area supports efficient diffusion.

Regulatory mechanisms involve autonomic innervation and hormonal signals that adjust cardiac output, vascular resistance, and blood volume. The rat’s relatively high metabolic rate demands rapid circulation, reflected in elevated heart rates and proportionally large cardiac output relative to body mass.

Nervous System

The nervous system of the rat comprises the central and peripheral divisions, coordinating sensory input, motor output, and autonomic regulation. The central component includes the brain and spinal cord. Within the brain, the cerebrum processes cortical functions, the cerebellum refines motor coordination, and the brainstem maintains vital reflexes and autonomic control. The spinal cord transmits signals between the brain and peripheral nerves, integrating reflex arcs.

The peripheral division consists of cranial and spinal nerves. Cranial nerves emerge from the brainstem and serve head and neck structures, while spinal nerves originate from the spinal cord, innervating the trunk and limbs. Each spinal nerve splits into dorsal (sensory) and ventral (motor) roots, forming mixed peripheral pathways.

Key structures of the rat nervous system include:

• «central nervous system» – brain and spinal cord
• «cerebrum» – cortical processing center
• «cerebellum» – motor precision regulator
• «brainstem» – autonomic and reflex hub
• «spinal cord» – conduit for ascending and descending pathways
• «cranial nerves» – sensory and motor fibers for head region
• «spinal nerves» – peripheral connections for body segments
• «dorsal root ganglia» – sensory neuron cell bodies
• «autonomic ganglia» – sympathetic and parasympathetic control centers

Neuronal circuits operate through synaptic transmission, employing excitatory and inhibitory neurotransmitters to modulate activity. Myelination of axons by oligodendrocytes in the central division and Schwann cells in the peripheral division accelerates signal propagation. The rat nervous system thus provides a compact yet comprehensive model for studying mammalian neurophysiology.

Urogenital System

The rat «urogenital system» integrates reproductive and urinary structures within the abdominal and pelvic cavities, sharing vascular and neural connections that support excretory and reproductive functions.

In males, the testes reside in the scrotum, producing sperm and testosterone. The epididymis, positioned along the dorsal surface of each testis, stores and matures sperm. The vas deferens transports sperm to the ejaculatory ducts, which merge with seminal vesicle secretions before entering the urethra. Accessory glands, including the prostate and bulbourethral glands, contribute fluid components that enhance sperm viability.

In females, the ovaries attach to the dorsal abdominal wall, releasing ova and estrogen. The oviducts convey ova to the uterine horns, where implantation occurs. The uterus consists of a single body terminating in two cervical canals that open into the vagina. The vagina leads to an external opening surrounded by the vulvar musculature.

Both sexes possess identical urinary organs. The kidneys filter blood, producing urine that travels through the ureters to the urinary bladder. The bladder stores urine until coordinated contraction empties it via the urethra. In males, the urethra also serves as the conduit for semen; in females, it solely conducts urine.

Endocrine regulation of the «urogenital system» involves hypothalamic releasing factors that stimulate pituitary secretion of gonadotropins, which in turn modulate gonadal activity. Renin‑angiotensin‑aldosterone mechanisms adjust renal sodium handling and blood pressure, influencing overall fluid balance.

Key structures can be summarized:

• Testes, epididymis, vas deferens, seminal vesicles, prostate, bulbourethral glands (male)
• Ovaries, oviducts, uterus, cervix, vagina (female)
• Kidneys, ureters, bladder, urethra (common)