Human Anatomy - H. I. Koliadenko 2009

Nervous system
Central nervous system
Brain (encephalon)

The human Brain occupies the entire cranial cavity, the bones of which protect the brain tissue from external mechanical damage. As it grows and develops, the brain takes on the shape of the Skull. Externally, the brain resembles a yellowish, jelly-like mass, which led early anatomists to believe it was a substance intended to cool the Blood; consequently, it was discarded during the embalming of corpses.

The average brain mass is 1,375 g in men and 1,275 g in women. In men, it accounts for 2% of total body mass, compared to 2.5% in women. For a long time, the prevailing view was that a person's intellectual abilities depended directly on brain mass: the larger the brain, the more gifted the individual. However, subsequent findings disproved this notion. For instance, Ivan Turgenev's brain weighed 2,012 g, whereas Anatole France's weighed 1,017 g. The heaviest recorded brain, weighing 2,900 g, was found in an individual who lived for only 3 years, yet suffered from severe functional impairment. Consequently, no direct correlation has yet been established between brain mass and human intelligence. Nevertheless, a lower threshold of brain mass (900 g) has been identified, below which the brain is considered functionally deficient.

The degree of brain development depends on The ratio of Spinal Cord mass to brain mass. For example, this ratio is 1:1 in cats, 1:3 in dogs, 1:16 in monkeys, and 1:50 in humans.

The volume of the human brain accounts for 91–95% of the cranial capacity and comprises three main divisions: the Brainstem, the subcortical region, and the Cerebral Cortex.

The brainstem is formed by the Medulla Oblongata, the Pons, the Cerebellum, the cerebral peduncles, and the corpora quadrigemina.

The subcortical region comprises the Diencephalon and the subcortical nuclei of the cerebral hemispheres.

The cerebral cortex covers the two cerebral hemispheres: the right and the left.

According to another Classification, the brain is divided into 5 parts: the medulla oblongata; the Hindbrain, which includes the pons and cerebellum; the Midbrain; the diencephalon; and the Telencephalon.

Meninges of the brain. Like the spinal cord, the brain is enveloped by three membranes: the pia mater, the arachnoid mater, and the dura mater.

The pia mater, or vascular membrane of the brain (pia mater encephali), adheres directly to the brain tissue, extending into all sulci and covering all gyri. It consists of loose Connective Tissue containing numerous Blood Vessels that nourish the brain. Tiny connective tissue processes extend from the vascular membrane deep into the brain mass.

The arachnoid mater of the brain (arachnoid encephali) is a thin, translucent membrane devoid of blood vessels. It closely adheres to the cerebral gyri but does not extend into the sulci. Consequently, subarachnoid cisterns filled with CEREBROSPINAL FLUID are formed between the vascular and arachnoid membranes, which serve to nourish the arachnoid mater. The largest of these, the cerebellomedullary cistern, is located posterior to the Fourth ventricle and receives the median aperture of the fourth ventricle; the cistern of the lateral fossa lies within the lateral sulcus of the cerebrum; the interpeduncular cistern is situated between the cerebral peduncles; and the chiasmatic cistern is located in the region of the optic chiasm.

The dura mater of the brain (dura mater encephali) serves as the periosteum for the inner cranial surface of the skull bones.

The dura mater is constructed of Cytology/practical/45.html">Dense connective tissue lined on its inner surface by flattened, moistened Cells, and it fuses tightly with the Cranial bones in the region of the internal skull base. Between the dura mater and the arachnoid mater lies the subdural space, filled with serous fluid.

Several folds or extensions project from the dura mater. The largest of these are the falx cerebri, the tentorium cerebelli, and the diaphragma sellae (Fig. 157). The falx cerebri is situated between the cerebral hemispheres. The posterior end of this process fuses with the tentorium cerebelli and attaches to the crista galli of the Ethmoid bone. The falx cerebri reduces the pressure of one hemisphere upon the other when the HEAD is tilted laterally. The small falx extends from the internal occipital protuberance to the foramen magnum, passing between the cerebellar hemispheres in its posterior section, and performs a protective function. The tentorium cerebelli lies between the occipital lobes of the cerebral hemispheres and the superior surface of the cerebellum. The cerebellum is housed within the cavity thus formed.

Class="center">

Fig. 157. The dura mater of the brain and its Dural Venous Sinuses:

1 — falx cerebri; 2 — superior sagittal sinus; 3 — inferior sagittal sinus; 4 — infundibulum; 5 — Internal Carotid Artery; 6 — Optic nerve; 7 — crista galli; 8 — diaphragma sellae; 9 — sella turcica ( dorsum sellae ); 10 — cavernous sinus; 11 — sigmoid sinus; 12 — tentorium cerebelli; 13 — transverse sinus; 14 — confluence of sinuses; 15 — straight sinus; 16 — tentorial notch; 17 — great cerebral vein; 18 — superior cerebral Veins

The diaphragma sellae is a fold of the dura mater that extends from the dorsum sellae of the sella turcica and the Base of the lesser wings of the Sphenoid bone. In the center of the diaphragma sellae is an aperture through which passes the infundibulum of the tuber cinereum, to which the Pituitary Gland is attached. Additionally, the dura mater forms sheaths along the course of the Cranial Nerves as they exit the cranial cavity.

In certain areas, the dura mater splits to form narrow, triangular cavities known as dural venous sinuses. The most important dural sinuses are the superior and inferior sagittal sinuses, the straight sinus, the transverse sinus, the sigmoid sinus, and the cavernous sinus (see Fig. 157).

The superior sagittal sinus runs along the upper margin of the falx cerebri. The inferior sagittal sinus is narrow and courses along the lower margin of the falx cerebri. The straight sinus is short but wide, extending along the junction of the falx cerebri and the tentorium cerebelli. The transverse sinus follows the transverse sulcus of the Occipital bone. The sigmoid sinus originates from the transverse sinus and terminates near the jugular foramen. The cavernous sinus is located in the region of the sella turcica.

The inner surface of the dural venous sinuses is lined with endothelium. The sinuses act as auxiliary channels for the outflow of venous blood from the brain, auditory Organs, and visual organs. The walls of the sinuses are taut and do not collapse when cut. Blood flows from the sinuses into the internal jugular veins, and via emissary foramina of the skull into the external VEINS OF THE head. The sinuses are filled with venous blood.

The medulla oblongata develops from the fifth (accessory) brain vesicle. It is a continuation of the spinal cord with a disrupted segmental Structure. The Gray matter of the medulla oblongata consists of isolated cranial nerve nuclei. The White matter comprises ascending and descending tracts connecting the spinal cord and brain, extending upward into the brainstem and vice versa (Fig. 158).

As the neural tube expands, it forms the cavity of the fourth ventricle. The walls of the tube grow unevenly; the posterior wall remains thin, while the anterior and lateral walls thicken significantly.

On the anterior surface of the medulla oblongata lies the anterior median fissure, flanked on both sides by thickened white bundles known as the pyramids. The pyramids taper inferiorly because a portion of their fibers crosses over to the opposite side, forming the pyramidal decussation, which gives rise to the lateral corticospinal (pyramidal) tract. Uncrossed white fibers form the anterior corticospinal (pyramidal) tract. The Hypoglossal nerve (XII pair) emerges laterally to the pyramids. Lateral to the pyramids lie the lateral funiculi, the upper part of which forms oval elevations called the olives, while the dorsal part forms the inferior cerebellar peduncles. On a cross-section, the olives feature Nerve Cells arranged in a folded pouch-like structure. The nuclei of the olives are functionally connected to the cerebellum and contribute to body posture and equilibrium, helping to maintain an upright position.

Fig. 158. Brainstem (anterior view):

1 — optic chiasm; 2 — optic nerve; 3 — optic tract; 4 — cerebral peduncle; 5 — pons; 6 — olive of the medulla oblongata; 7 — decussation of pyramids; 8 — pyramid of the medulla oblongata; 9 — mammillary body; 10 — tuber cinereum; 11 — anterior perforated substance; 12 — olfactory trigone; 13 — olfactory tract

The inferior cerebellar peduncles, or restiform bodies, are massive structures that diverge at an angle, laterally bounding the inferior angle of the Rhomboid fossa of the fourth ventricle. Dorsal to the olives emerge the rootlets of the IX, X, and XI cranial nerve pairs, namely the glossopharyngeal, vagus, and accessory nerves (Fig. 159). On the dorsal surface of the medulla oblongata runs the posterior median sulcus, flanked on both sides by the gracile fasciculi carrying ascending pathways from the spinal cord.

Fig. 159. Brainstem.

Sites of emergence of the cranial nerves (anterior view):

1 — olfactory tract; 2 — optic nerve; 3 — Oculomotor nerve; 4 — Trochlear nerve; 5 — Trigeminal nerve; 6 — Abducens nerve; 7 — Facial Nerve; 8 — vestibulocochlear (auditory) nerve; 9 — Glossopharyngeal nerve; 10 — Vagus nerve; 11 — Accessory nerve; 12 — hypoglossal nerve

Each gracile fasciculus terminates in a tubercle (clava). Lying lateral to the gracile fasciculi are the cuneate fasciculi, topped superiorly by the cuneate tubercles. The fibers of the clava and cuneate tubercle form the external and internal arcuate fibers. The external fibers pass into the inferior cerebellar peduncles, whereas the internal fibers decussate anterior to the central canal to form the medial lemniscus, which ascends superiorly. Lateral to the medial lemniscus lies the reticular formation. This region is referred to as the tegmentum of the medulla oblongata. The reticular substance contains intercalated and effector cells that interconnect various Neurons of the medulla oblongata as well as vital centers, including the cardiovascular, respiratory, and digestive centers.

The rhomboid fossa (Fig. 160), which forms the floor of the fourth ventricle, is located on the posterior surface of the medulla oblongata and pons. A median sulcus divides it into two halves, each featuring an elevation known as the facial colliculus. Within the depth of the facial colliculus lie the nuclei of the VI (abducens) and VII (facial) cranial nerve pairs. The inferior part of the rhomboid fossa presents two elevations: the trigones of the hypoglossal and vagus nerves. The lateral margins of the fossa form recesses bounded by the cerebellar peduncles. The lateral Regions of the rhomboid fossa house the nuclei of the VIII cranial nerve pair (vestibulocochlear). Transverse medullary fibers extend from the auditory nuclei to the median sulcus, lying at the border between the medulla oblongata and the pons; these fibers represent the Projection Pathways of the Vestibulocochlear nerve.

Fig. 160. Brainstem (posterior view):

1 — optic thalamus, thalamus; 2 — Third ventricle; 3 — Pineal Gland; 4, 10 — superior colliculi of the midbrain tectum; 5, 9 — inferior colliculi of the midbrain tectum; 6 — facial colliculi of the rhomboid fossa; 7 — cuneate tubercle; 8 — gracile fasciculi

The depth of the rhomboid fossa contains the nuclei of 8 cranial nerve pairs, specifically: cranial nerve V (trigeminal), VI (abducens), VII (facial), VIII (vestibulocochlear), IX (glossopharyngeal), X (vagus), XI (accessory), and XII (hypoglossal). Closer to the center, surrounding the median sulcus, are the motor nuclei of these nerves, while the autonomic nuclei are situated laterally, though still in proximity to the center. The superficial or lateral nuclei of the rhomboid fossa are the afferent nuclei.

The trigeminal nerve possesses four nuclei: one motor and three sensory. The abducens nerve has a single motor Nucleus; the facial nerve contains a motor, an autonomic, and a sensory nucleus; the vestibulocochlear nerve features two auditory and four vestibular nuclei. The glossopharyngeal nerve has three nuclei (motor, autonomic, and sensory); the vagus nerve similarly features three nuclei (motor, sensory, and parasympathetic); whereas the accessory and hypoglossal nerves each possess a single motor nucleus.

The roof of the fourth ventricle is formed by two medullary vela: the cranial (superior) medullary velum, stretched between the superior cerebellar peduncles, and the caudal (inferior) medullary velum, located between the inferior cerebellar peduncles as a rudimentary wall of the brain vesicle. The choroid plexus of the fourth ventricle attaches to the caudal (posterior) medullary velum. Three small openings, or apertures, are located in the posterior velum, through which the ventricular cavity communicates with the subarachnoid space, allowing cerebrospinal fluid to pass from the fourth ventricle into the subarachnoid space.

The pons lies superior to the medulla oblongata as a thickened prominence with transversely oriented fibers. Running along its center is the basilar sulcus, which lodges the Basilar artery of the brain. Prominent elevations are situated on both sides of this sulcus, formed by the Pyramidal Tracts. The pons consists of a vast number of transverse fibers that constitute its white matter (nerve fibers). Interspersed among these fibers are numerous clusters of gray matter forming the pontine nuclei. Extending toward the cerebellum, these nerve fibers form its middle peduncles (see Fig. 158).

The pons is composed of a ventral (basilar) part and a dorsal part (tegmentum), which lies within its concavity as a continuation of the tegmentum of the medulla oblongata. The tegmentum of the pons contains the reticular formation, which houses the nuclei of four cranial nerve pairs: the trigeminal (V), abducens (VI), facial (VII), and vestibulocochlear (VIII). The dorsal surface of the tegmentum forms part of the floor of the rhomboid fossa (see Fig. 160). Ascending and, partially, descending pathways pass through the tegmentum, alongside the medial lemniscus and the medial longitudinal fasciculus, which helps maintain bodily balance. The trigeminal lemniscus originates here from the corresponding nerve, conducting sensory impulses from the facial Skin. At the border between the ventral and dorsal surfaces of the pons lies the trapezoid body, formed by the nuclei and transverse fibers of the Auditory pathway.

The cerebellum is situated on the posterior surface of the pons and medulla oblongata within the posterior cranial fossa (Fig. 161). It comprises two hemispheres and the vermis, which connects them. The mass of the cerebellum ranges from 120 to 150 g.

Fig. 161. Cerebellum and brainstem:

1 — corpus striatum; 2 — pineal gland; 3 — superior (anterior) colliculus; 4 — inferior (posterior) colliculus; 5 — cerebellorubral tract; 6 — fastigial nucleus; 7 — cerebellar vermis; 8 — dentate Nucleus of the cerebellum; 9 — superior (anterior) cerebellar peduncles; 10 — superior (anterior) medullary velum; 11 — frenulum of the superior (anterior) medullary velum; 12 — thalamus; 13 — third ventricle

The cerebellum is separated from the cerebrum by a horizontal fissure in which the dura mater forms the tentorium cerebelli, stretched over the posterior cranial fossa. Each cerebellar hemisphere consists of gray and white matter.

The gray matter of the cerebellum lies superficial to the white matter, forming the cortex. Nerve nuclei are embedded deep within the cerebellar hemispheres, the bulk of which consists of white matter. The cortical surface forms parallel sulci separated by convolutions of identical shape. These sulci divide each cerebellar hemisphere into several lobes. One particular lobe, the flocculus, which lies adjacent to the middle cerebellar peduncles, is more prominent than the others; it is phylogenetically ancient. The flocculus and the nodulus of the vermis appear as early as in lower vertebrates and are functionally linked with the vestibular apparatus.

The cerebellar cortex is composed of two layers of nerve cells: an outer molecular layer and an internal granular layer. The thickness of the cortex ranges from 1 to 2.5 mm.

The gray matter of the cerebellum branches within the white matter (a mid-sagittal section of the cerebellum resembles the fronds of an evergreen arborvitae), which is why it is poetically referred to as the arbor vitae (tree of life) of the cerebellum.

In addition, four pairs of nuclei are located within the WHITE MATTER OF the cerebellum: the largest of these is the dentate nucleus, which regulates equilibrium; medial to it lies the cuneate nucleus (emboliform nucleus), closer to the center is the globose nucleus, and in the very center is the fastigial nucleus.

The cerebellum is connected to the brainstem by three pairs of peduncles, which are formed by bundles of nerve fibers. The inferior (caudal) cerebellar peduncles extend to the medulla oblongata and are also referred to as the restiform bodies; they incorporate the posterior spinocerebellar tract. The middle (pontine) cerebellar peduncles connect with the pons, transmitting transverse fibers to the neurons of the cerebral cortex via the corticopontine tract, through which the cerebral cortex exerts its influence on the cerebellum. The superior cerebellar peduncles consist of white fiber bundles directed toward the midbrain, where they course alongside and closely adhere to the cerebral peduncles. Composed primarily of fibers originating from the cerebellar nuclei, the superior (cranial) cerebellar peduncles serve as the principal pathways conveying impulses to the thalamus, subthalamic region, and red nuclei.

The primary function of the cerebellum is the reflex coordination of movement and the distribution of Muscle tone. Furthermore, it houses the higher centers of the autonomic (sympathetic) Nervous system. The phylogenetically older STRUCTURE OF THE cerebellum is the vermis, which is associated with the Movements of the axial body structures—the trunk, neck, and head—whereas the phylogenetically younger structures, the cerebellar hemispheres, coordinate the movements of the upper and lower limbs.

In a newborn infant, the cerebellum is not yet fully developed, but During the first year of life, it grows at a rate exceeding that of other brain structures. Particularly rapid growth of the cerebellum is observed between the fifth and eleventh months of life, coinciding with the acquisition of sitting and standing postures. By the age of 6, the cerebellum reaches a mass of 120–150 g, thereby nearly attaining the weight of an adult cerebellum.

The midbrain (mesencephalon) develops from the middle cerebral vesicle and consists of the tegmentum and the cerebral peduncles. The peduncles are situated anteriorly, while the tegmentum lies posteriorly. The cerebral aqueduct (Sylvian aqueduct) runs between the tegmentum and the peduncles, connecting the fourth ventricle to the third ventricle (Fig. 162).

Via the peduncles, the brainstem connects superiorly with the cerebral hemispheres and inferiorly with the superior cerebellar peduncles. A cross-section of the midbrain reveals that the peduncles consist of a base (crus cerebri) and a tegmentum. The boundary between the base and the tegmentum is marked by a dark cluster of nerve cells known as the substantia nigra. The dark coloration of these nerve cells is attributed to the presence of the pigment melanin.

Fig. 162. Midbrain:

1 — cerebral aqueduct; 2 — central gray matter; 3 — midbrain tegmentum; 4 — red nucleus; 5 — substantia nigra; 6 — oculomotor nerve; 7 — crus cerebri (base of the cerebral peduncle); 8 — tectum of the midbrain (corpora quadrigemina)

The base of the peduncles is composed of motor nerve fibers that continue into the pyramids of the medulla oblongata. The tegmentum consists of phylogenetically ancient structures that form the floor of the aqueduct, surrounding the reticular formation, which is a continuation of the reticular Formation of the medulla oblongata and pons. Passing beneath the gray matter (reticular formation) is the medial longitudinal fasciculus—a phylogenetically ancient pathway originating from the vestibular nuclei that transmits impulses to the nuclei of the III, IV, V, and XI pairs of cranial nerves. Lateral to the aqueduct extends The Nucleus of the mesencephalic tract of the trigeminal nerve. Situated within the tegmentum is the paired red nucleus (nucleus ruber), which gives rise to the rubrospinal tract, a descending motor pathway and one of the important subcortical motor centers. Additionally, the midbrain tegmentum houses the nuclei of the III and IV cranial nerve pairs (oculomotor and trochlear).

The tectum of the midbrain lies dorsal to the tegmentum, overlying the cerebral aqueduct. It features the tectal plate (corpora quadrigemina). The two superior colliculi are associated with the visual analyzer and serve as centers for orienting Reflexes in response to visual stimuli, hence they are termed visual colliculi. The two inferior colliculi are auditory centers associated with orienting reflexes to sound stimuli. The superior colliculi connect with the lateral geniculate bodies of the diencephalon via the superior brachia, while the inferior colliculi connect via the inferior brachia with the medial geniculate bodies. The tectospinal tract originates from the tectal plate, connecting the brain to the spinal cord and transmitting efferent impulses in response to visual and auditory stimuli.

Forebrain (telencephalon). The forebrain comprises the diencephalon and the cerebral hemispheres.

The diencephalon consists of four regions: the thalamus, Hypothalamus, metathalamus, and epithalamus. The cavity of the diencephalon is the third ventricle.

The thalamus (thalamus opticus) is a paired, egg-shaped gray matter structure with an anteriorly pointed pole. Its posterior part is thickened and termed the pulvinar. Its lateral surface is fused with the cerebral hemispheres, and the third ventricle lies between its medial surfaces. The thalamus (see Fig. 165) Functions as a primitive "sensory" organ, with its primary role being the conduction of afferent impulses from the receptors of all Sense Organs (except Olfaction) to the cerebral cortex.

Based on their functional characteristics, thalamic nuclei can be divided into three groups: 1. Nuclei with subcortical connections, which include the ventral nucleus—where the spinothalamic tract, medial lemniscus, trigeminal lemniscus, and superior cerebellar peduncles terminate. 2. Cortico-Relay nuclei, through which ascending pathways from all receptors pass. 3. Associative nuclei of the pulvinar and the lateral nucleus, which connect the thalami with the associative areas of the cerebral hemispheres.

The thalamus also houses the reticular formation, represented by nonspecific nuclei located between the lateral and ventral nuclei. The reticular formation regulates the tone of all Divisions of the Central Nervous System and exerts an active influence on the cerebral cortex. Motor activity, Respiration, and Blood Circulation are closely linked to the reticular formation, which also serves as The Site of Action for pharmacological agents administered during illness.

Processes originating from the nerve Cells of the thalamus project toward the cerebral cortex as well as to subcortical nuclei, forming the corona radiata that links the cortex with subcortical structures, thereby integrating the thalami into the extrapyramidal system.

The hypothalamus consists of the tuber cinereum, which terminates in the infundibulum to which the pituitary gland (hypophysis) is attached. Anterior to the tuber cinereum lies the optic chiasm. The tuber cinereum contains nuclei that function as higher subcortical autonomic centers, regulating metabolic processes in The Human Body (carbohydrate, lipid, Water, and electrolyte METABOLISM) as well as thermoregulation. Posterior to the tuber cinereum are the mamillary bodies, which belong to the subcortical olfactory centers and serve as the termination site for the columns of the fornix.

The hypophysis is closely connected to the infundibulum of the tuber cinereum, rests within the sella turcica of the sphenoid bone at the base of the skull, and functions as a ductless (endocrine) gland.

The metathalamus consists of two geniculate bodies—lateral and medial—which are connected via their respective brachia to the tectal plate of the midbrain. The lateral geniculate bodies serve as the subcortical center for the visual pathway, whereas the medial geniculate bodies connect via the brachia of the superior colliculi and act as the subcortical pathway for the Auditory Analyzer.

The epithalamus consists of the striae medullares, which broaden toward the midbrain into the trigemone of the habenula, extending into the habenulae from which the pineal gland (epiphysis cerebri) is suspended.

The third ventricle is the cavity of the diencephalon, presenting as a narrow vertical cleft. Its lateral walls are formed by the medial surfaces of the thalami. The roof of the third ventricle is formed by the choroid plexus, covered by Epithelial Tissue. The anterior wall contains the columns of the anterior pillars of the fornix, constructed of white matter. Anterior to these columns lies the anterior commissure of the brain, inferior to which is the thin terminal lamina. The floor of the crus cerebri, the posterior perforated substance located between the cerebral peduncles, the mamillary bodies, and the tuber cinereum. The posterior wall contains the posterior commissure and the opening of the cerebral aqueduct, through which the third ventricle communicates with the aqueduct of the midbrain. Anteriorly, the third ventricle communicates with the Lateral ventricles of the cerebral hemispheres via the interventricular foramina. The cavity of the third ventricle, like that of the fourth, is filled with cerebrospinal fluid.

Fig. I. Human blood smear:

1 — basophilic granulocyte; 2 — small lymphocyte; 3 — erythrocyte; 4 — neutrophilic granulocyte; 5 — monocyte; 6 — medium lymphocyte; 7 — thrombocyte (platelet); 8 — eosinophilic granulocyte; 9 — large lymphocyte

Fig. II. Heart and its blood vessels:

a — anterior view:

1 — ascending aorta; 2 — right pulmonary artery; 3 — brachiocephalic trunk; 4 — left common carotid artery; 5 — left Subclavian Artery; 6 — aortic arch; 7 — arterial ligament; 8 — left pulmonary artery; 9 — pulmonary trunk; 10 — left auricle; 11 — left coronary artery; 12 — great cardiac vein; 13 — anterior interventricular sulcus of The Heart; 14 — left ventricle; 15 — apex of the heart; 16 — right ventricle; 17 — conus arteriosus; 18 — coronary sulcus; 19 — right coronary artery; 20 — right auricle; 21 — SUPERIOR VENA CAVA;

b — posterior view:

1 — aortic arch; 2 — left subclavian artery; 3 — left common carotid artery; 4 — brachiocephalic trunk; 5 — superior vena cava; 6 — right pulmonary artery; 7 — right Pulmonary veins; 8 — right atrium; 9 — INFERIOR VENA CAVA; 10 — right coronary artery; 11 — coronary sinus with valve; 12 — right ventricle; 13 — middle cardiac vein; 14 — apex of the heart; 15 — left ventricle; 16 — circumflex branch of the left coronary artery; 17 — great cardiac vein; 18 — left pulmonary veins; 19 — left atrium; 20 — left pulmonary artery; 21 — arterial ligament

Fig. III. Respiratory organs:

1 — Larynx; 2 — Trachea; 3 — Lungs; 4 — aortic arch; 5 — pulmonary vein; 6 — pulmonary artery; 7 — Diaphragm; 8 — aorta; 9 — inferior vena cava; 10 — bronchial tree; 11 — alveoli (internal surface); 12 — pulmonary acinus

Fig. IV. SYSTEMIC AND PULMONARY circulations:

1 — aorta and its branches; 2 — capillary network of the lungs; 3 — pulmonary veins; 4 — left atrium; 5 — left ventricle; 6, 7, 8, 18 — Arteries of the abdominal visceral organs; 9 — capillary network of the unpaired abdominal organs, giving rise to the portal Venous system; 10 — systemic capillary network; 11 — portal vein; 12 — hepatic veins; 13 — right ventricle; 14 — inferior vena cava; 15 — right atrium; 16 — pulmonary trunk; 17 — superior vena cava

Cerebral hemispheres (hemispherium cerebralis; Fig. 163). These include the hemisphere lobes, the cerebral cortex (Pallium), Basal Ganglia, olfactory brain, and lateral ventricles. The cerebral hemispheres are separated by the longitudinal cerebral fissure, at the bottom of which lies the corpus callosum connecting them. Each hemisphere presents the following surfaces: 1) superolateral surface, convex and facing the inner surface of the cranial vault; 2) inferior surface, located on the inner surface of the cranial base; 3) medial surface, through which the hemispheres connect with each other. Each hemisphere features prominent poles and regions: anteriorly — the frontal pole, posteriorly — the occipital pole, and laterally — the temporal pole. Furthermore, each cerebral hemisphere is divided into four major lobes: frontal, parietal, occipital, and temporal. Deep within the lateral sulcus of the brain lies a small lobe — the insula. The hemisphere is subdivided into lobes by sulci. The deepest of these is the lateral sulcus, also known as the Sylvian fissure. The lateral sulcus separates the temporal lobe from the frontal and parietal lobes. Descending from the upper border of the hemispheres is the central sulcus, or Rolandic fissure. It separates the frontal lobe of the brain from the parietal lobe. The occipital lobe is separated from the parietal lobe only on the Medial surface of the hemispheres by the parieto-occipital sulcus.

In addition to the aforementioned sulci, each lobe has shallower sulci (grooves) that define the cerebral gyri. Thus, on the frontal lobe, anterior to the central sulcus, lies the precentral sulcus; between it and the central sulcus is the precentral gyrus. Perpendicular to the precentral sulcus are two frontal sulci: the superior and inferior, which bound the superior, middle, and inferior frontal gyri. On the inferior orbital gyrus, third-order sulci form the opercular, triangular, and orbital gyri. Adjacent to the orbital gyrus lies the olfactory sulcus, containing the olfactory bulbs, from which the olfactory tract originates and continues into the olfactory trigone. On the parietal lobe, parallel to the central sulcus, lies the postcentral sulcus, which bounds the postcentral gyrus. Perpendicular to the postcentral sulcus runs the intraparietal sulcus, dividing the parietal lobe into superior and inferior parietal lobules. Below these lobules lies the supramarginal gyrus anteriorly, and posteriorly — the angular gyrus, which caps the posterior end of the superior temporal sulcus.

On the occipital lobe, the sulci and gyri are variable and often asymmetrical in both hemispheres. The largest sulcus of this lobe is considered to be the transverse occipital sulcus, which is sometimes a continuation of the intraparietal sulcus.

The temporal lobe has the most distinct boundaries and sulci. The lateral sulcus demarcates the temporal lobe from the frontal lobe, while the rhinal (hippocampal) sulcus separates it from the brainstem. The temporal lobe features three sulci: the superior, middle, and inferior temporal sulci, as well as the collateral sulcus. Between these sulci lie the gyri: the superior, middle, and inferior temporal gyri, the fusiform gyrus, and the parahippocampal gyrus. At the anterior end of this gyrus is a small lobule called the uncus.

Fig. 163. Sulci and gyri of the lateral surface of the cerebral hemisphere:

1, 2, 4 — inferior frontal gyrus; 3 — inferior frontal sulcus; 5 — middle frontal gyrus; 6 — superior frontal sulcus; 7 — superior frontal gyrus; 8 — precentral sulcus; 9 — precentral gyrus; 10 — postcentral gyrus; 11 — central sulcus (fissure of Rolando); 12 — postcentral sulcus; 13 — superior parietal lobule; 14 — inferior parietal lobule; 15 — intraparietal sulcus; 16 — angular gyrus; 17, 21 — superior temporal gyrus; 18 — inferior temporal sulcus; 19 — middle temporal sulcus; 20 — superior temporal sulcus; 22 — lateral sulcus (Sylvian fissure)

The sulci and gyri of the insula do not have specific dedicated names.

On the medial surface of the hemispheres, running parallel to the corpus callosum, is the cingulate gyrus, which transitions posteriorly into the parahippocampal gyrus (Fig. 164). Together, they form the limbic lobe (or gyrus of the fornix).

Superior to the cingulate sulcus, flanking the central sulcus, lies the paracentral lobule, posterior to it is the precuneus, and adjacent to that is the cuneus. Inferior to the calcarine sulcus is the lingual gyrus, and inferior to that is the medial occipitotemporal gyrus.

Fig. 164. Sulci and gyri of the medial surface of the cerebral hemisphere:

1 — superior frontal gyrus; 2 — septum pellucidum; 3 — fornix; 4 — cingulate gyrus; 5 — sulcus of corpus callosum; 6 — corpus callosum; 7 — cingulate sulcus; 8 — marginal ramus of cingulate sulcus; 9, 10 — paracentral lobule; 11, 12 — precuneus; 13 — cuneus; 14 — calcarine sulcus; 15 — lingual gyrus; 16 — vermis; 17 — right cerebellar hemisphere; 18 — pons; 19 — superior colliculus (tectal plate); 20 — pineal gland; 21 — oculomotor nerve; 22 — mamillary body; 23 — infundibulum; 24 — optic chiasm

The rhinencephalon, or limbic system, comprises the olfactory bulb, olfactory tract, olfactory trigone, anterior perforated substance, cingulate gyrus, and parahippocampal gyrus.

The section of the medial surface of the cerebral hemispheres, bounded superiorly by the cingulate gyrus and inferiorly by the collateral sulcus, is called the limbic, or marginal, lobe.

Structure of the cerebral cortex (pallium). The cerebral hemispheres are externally covered by gray matter, which forms the cerebral cortex, or pallium. The cortex contains approximately 15 billion cells; considering that each of them forms between 7 and 1,000 connections with neighboring cells, one can infer the remarkable flexibility, resilience, and reliability of cortical functions. The surface area of the cortex is significantly increased through sulci and gyri. Phylogenetically, the cortex is the newest brain structure, with a surface area of about 220,000 square millimeters.

The neocortex constitutes 95% of the hemispheric surface area and consists of six or seven layers of nerve cells ranging in thickness from 1.3 to 5 mm. The first layer of the cortex is the molecular layer. It contains relatively few cells but a high density of pyramidal neuron dendrites, as well as tangential fibers running parallel to the surface that originate from deeper-lying cells.

Fig. 165. Sulci of the medial and inferior surfaces of the cerebral hemisphere:

1 — thalamus; 2 — fornix; 3 — parieto-occipital sulcus; 4 — calcarine sulcus; 5 — hippocampal sulcus; 6 — inferior temporal sulcus; 7 — collateral sulcus; 8 — mammillary body; 9 — corpus striatum; 10 — interventricular foramen; 11 — sulcus of the corpus callosum

The second layer is the external granular layer, composed of small granular neurons and a small number of cells of other shapes.

The third layer is the external pyramidal layer, consisting of pyramidal neurons whose size gradually increases from top to bottom.

The fourth layer is the internal granular layer, composed of small granular and stellate neurons. In certain areas of the cortex, this layer is absent.

The fifth layer is the ganglionic layer, consisting of giant pyramidal neurons (Betz cells). Their axons form the pyramidal system. This layer is particularly well developed in the precentral gyrus of the cerebral cortex.

The sixth layer is the multiform layer, which includes multiform, triangular, and fusiform neurons.

The seventh layer has a cellular composition similar to that of the sixth layer, but with a sparse Cell population and a higher proportion of fibers; therefore, like the first layer, it is also referred to as the molecular layer. This is a transitional layer that directly contacts the white matter of the cerebral hemispheres.

Localization of functions in the cerebral cortex. The cytoarchitectonics of various cortical regions exhibit significant differences related to their Structural and functional characteristics. Recently, the cerebral cortex has been subdivided into 200 fields, each possessing a unique cytoarchitectonic structure and performing a specific function.

According to I.P. Pavlov, the cerebral cortex functionally consists of the cortical ends of analyzers and serves as the highest integrative center of The Nervous System. The cortex processes complex analytic and synthetic transformations of afferent impulses arriving from the periphery, as well as complex reflex activity. Each analyzer has its own representation in the cortex. That subset of cortical nerve cells performing a specific function is termed the cortical center. The most important among these are the centers of general sensation, motor function, Hearing, Vision, and others.

The cortical center for general sensation (pain, Temperature, tactile) is located in the postcentral gyrus. The centers representing the lower extremities and lower trunk lie within the longitudinal cerebral fissure. Lower down, within the lateral sulcus, lie the receptive fields for the upper extremities, upper trunk, and head.

The cortical center of the motor analyzer lies in the precentral gyrus. This region receives various stimuli (proprioceptive, kinesthetic) originating from the skin, muscle tendons, joints, skeletal Muscles, and other structures. The upper fields of the precentral gyrus harbor the centers for the lower trunk and lower extremities, whereas its lower part contains the centers regulating the Muscles of the head. The size of a central regulatory zone depends on the Functional Significance of the corresponding organ. For instance, the regulatory area for the hand is larger than that for the shoulder and forearm combined.

The cortical center of the auditory analyzer is located in the middle part of the superior temporal gyrus, close to the insular lobe.

The cortical center of the visual analyzer is localized on the medial surface of the occipital lobe along the margins of the calcarine sulcus. The core of the visual analyzer in the right hemisphere is connected via projection pathways with the temporal half of the right retina and the nasal half of the left retina, whereas the core of the left hemisphere is connected with the temporal half of the left retina and the nasal half of the right retina.

The cortical center of the olfactory analyzer is situated in the region of the uncus of the parahippocampal gyrus and the anterior perforated substance. It is connected with the allocortex (paleocortex and archicortex).

The cortical center for complex coordinated movements in right-handed individuals is located in the left inferior parietal lobule, whereas in left-handed individuals it is found in the corresponding region of the right hemisphere.

The cortical motor center for articulate speech is located in the posterior part of the inferior frontal gyrus, whereas the cortical motor center for writing lies in the posterior part of the middle frontal gyrus.

The bulk of the ascending fibers of an analyzer terminate within its corresponding nuclear zone, but individual afferent fibers extend beyond the nuclear zone and branch into adjacent cortical areas. Thus, the localization of functions in the cerebral cortex is not restricted to a single field but is also distributed to other cortical areas; consequently, in the event of a loss of function in the nuclear zone of an analyzer, its role is assumed by peripheral cells located relative to the nuclear center.

The aforementioned cortical ends of analyzers perform the analysis and synthesis of signals originating from the external and internal environments, constituting the first signaling system of reality (according to I.P. Pavlov). The second signaling system of reality is unique to humans, with its functions intrinsically linked to articulate speech. Human speech and thinking are associated with The activity of the entire cortex. The motor center for spoken and written speech is located in the frontal lobes. The analyzers for the perception of visual and auditory speech are concentrated in their respective cortical centers. It should be noted that the language analyzer centers are located in the left hemisphere in right-handed individuals and in the right hemisphere in left-handed individuals.

The basal ganglia (nuclei) of the cerebral hemispheres are clusters of gray matter forming subcortical nodes that appeared phylogenetically much earlier than the cortex itself. These include the corpus striatum, claustrum, and amygdala.

The corpus striatum consists of the caudate and lentiform nuclei (Fig. 166). The caudate nucleus (nucleus caudatus) is visible on a horizontal brain section; its medial, anterior, thickened part—the head—lies anterior to the thalamus, while its body extends in a sagittal direction and gradually transitions into the tail. The caudate nucleus arches anteriorly, superiorly, and laterally around the thalamus. The lentiform nucleus (nucleus lentiformis) is located lateral to the caudate nucleus, shaped like a three-sided pyramid, and is composed of the darker putamen situated lateral to the globus pallidus, which consists of two segments and lies medially, adjacent to the thalami. The caudate nucleus and putamen are connected via fibers to the CEREBRAL CORTEX AND thalamus.

Fig. 166. Corpus striatum:

1 — corpus callosum; 2 — head of caudate nucleus; 3 — internal capsule; 4 — anterior horn of lateral ventricle; 5 — claustrum; 6 — septum pellucidum; 7 — fornix; 8 — lentiform nucleus; 9 — thalamus

The globus pallidus transmits impulses via descending pathways to such brain structures as the red nucleus and the substantia nigra of the midbrain. The caudate and lentiform nuclei are separated by the internal capsule (corona radiata). The internal capsule is formed by white fibers that represent a continuation of the white matter of the cerebral hemispheres. These capsular fibers group together in the cerebral peduncles and, forming Neural Pathways, connect the cortex with the brainstem and spinal cord. The corpus striatum is also referred to as the striopallidal system and is classified as part of the efferent extrapyramidal system. It includes the thalamus of the diencephalon and the red nuclei of the midbrain. Unconditioned reflex arcs are closed within the nuclei of the corpus striatum. The corpus striatum participates in complex locomotion (walking, running, climbing) associated with autonomic functions that regulate thermal and Carbohydrate Metabolism.

Lateral to the putamen of the lentiform nucleus lies a thin sheet of gray matter—the claustrum—which is separated from the lentiform nucleus by the external capsule.

The amygdaloid body (corpus amygdaloideum) is a cluster of nerve cells located in the white matter of the temporal lobe. The anterior commissure connects the corresponding bodies of both cerebral hemispheres. The amygdaloid body is involved in emotional responses and is functionally linked to the olfactory analyzer.

The lateral ventricles (Fig. 167) are slit-like cavities within the cerebral hemispheres, situated within the white matter beneath the corpus callosum. Each ventricle consists of a central part and three horns.

The central part is located in the parietal lobe above the thalamus, resembling a narrow slit, and contains a choroid plexus. The anterior horn extends from the central part into the frontal lobe and is also known as Ammon's horn. It is separated from the anterior horn of the opposite hemisphere by the septum pellucidum. Lateral to the central part extends the inferior horn, which lies within the substance of the temporal lobe. Its medial wall extends deep into the hippocampal sulcus, forming the hippocampus—a part of the allocortex (old cortex). The hippocampus regulates overall body movements and also shapes human emotional states. The posterior horn of the lateral ventricles extends into the occipital lobe of the hemisphere; its inner wall features an elevation known as the calcar avis, resulting from the indentation of the calcarine sulcus into the posterior horn.

The interventricular foramina open from the lateral wall of the third ventricle into the lateral ventricles between the central part and the anterior horn. These foramina connect the choroid plexuses of the third and lateral ventricles and allow the mixing of their cerebrospinal fluid.

The white matter of the cerebral hemispheres lies directly beneath the cortex and essentially constitutes the Neural Pathways of the nervous system, consisting of nerve fibers that connect individual divisions of the central nervous system, as well as clusters of gray matter, namely nuclei. The white matter is formed by capsules surrounding the subcortical ganglia. The largest of these is the internal capsule, which is a continuation of the basis pedunculi. The white matter includes association, commissural, and projection fibers.

Fig. 167. Lateral ventricles of the brain:

1 — corpus callosum; 2 — anterior horn of lateral ventricle; 3 — caudate body; 4 — choroid plexus of lateral ventricle; 5 — splenium of corpus callosum; 6 — calcar avis; 7 — crus of fornix; 8 — posterior horn of lateral ventricle; 9 — thalamus; 10 — inferior horn of lateral ventricle; 11 — body of fornix; 12 — lamina of septum pellucidum; 13 — cavity of septum pellucidum

Association fibers are subdivided into short and long. Short fibers connect neurocytes with adjacent individual gyri within a single lobe, whereas long fibers connect the cortical neurocytes of different lobes of the hemisphere. An example of long association fibers is the arcuate fasciculus, which connects the frontal, occipital, and temporal lobes.

Commissural fibers connect corresponding lobes of both hemispheres. The largest commissural pathway is the corpus callosum; it is 5–7 cm long and 1.5 cm wide. Its posterior part is thickened, while its anterior part—the genu of the corpus callosum—terminates in the rostrum. The rostrum continues as a thin lamina of the optic chiasm. Due to its transversely arranged fibers, the corpus callosum forms the radiation of the corpus callosum. The Inferior surface of the corpus callosum is connected to the fornix by the septum pellucidum. The fibers of the fornix connect the diencephalon with the temporal lobe.

Projection fibers form the pathways that connect the cerebral cortex with lower divisions of the nervous system. Short projection fibers connect the cerebral cortex with subcortical nuclei, the diencephalon, midbrain, cerebellum, and medulla oblongata, as well as with sensory analyzers.

Between the internal capsule and the cortex, projection fibers form the corona radiata. Long projection tracts connect the cerebral cortex with the spinal cord and all Organs of the body.