General and Sports Anatomy - L.V. Kapilevich, K.V. Davletyarova 2008

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Nervous System

Regulatory function: integrates all PARTS OF THE Organism into a single, cohesive entity.

Classification:

1. central, peripheral;

2. somatic, autonomic (vegetative).

The basic unit of The Nervous system is the nerve Cell (neuron), which consists of a cell body and processes. Processes that conduct impulses toward The Cell body (there may be several of these) are called dendrites, while the single process that conducts impulses away from the cell body is called the axon. Neurons form chains through which excitation is transmitted, communicating with one another via synapses. Synapses are categorized into Electrical and Chemical.

Central Nervous System: Brain

Located within the cranium and spherical in shape. Its mass ranges from 1000 to 2200 g (averaging 1375 g) (Figure 31).

Medulla Oblongata.

It continues from the Spinal Cord, with bundles of nerve fibers on its surface forming the pyramids. Lateral to the pyramid lies an elevation known as the olive.

It houses the nuclei of the Cranial Nerves IX–XII, as well as the vasomotor and respiratory centers.

Hindbrain. Comprises the Pons and Cerebellum.

Pons. Consists primarily of fibers (White matter) and contains cranial nerve nuclei (Gray matter).

Cerebellum. Composed of two hemispheres and a central region called the vermis. It consists of a cortex and white matter (in cross-section, it resembles a tree, known as the arbor vitae).

Its primary function is the reflex coordination of Muscle movement and the maintenance of balance.

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Figure 31. Brain anatomy.

The Fourth ventricle is located between them.

Midbrain.

Upper section: the tectum (corpora quadrigemina), containing visual and auditory Neural Pathways.

Lower section: the cerebral peduncles, containing the red Nucleus, a crucial motor center.

Diencephalon.

Located between the hemispheres (Figure 32).

Thalamus (optic thalamus). It forms the wall of the Third ventricle and contains nuclei of gray matter. Adjacent structures include: the metathalamus posteriorly (two geniculate bodies), the epithalamus (Pineal Gland), and the Hypothalamus (mammillary bodies, optic chiasm, and Pituitary Gland).

Cerebral Cortex (Pallium).

Frontal, occipital, and temporal poles.

Superolateral, medial, and inferior surfaces.

Between the hemispheres lies the longitudinal fissure.

The hemispheres consist of gray matter—the cerebral cortex (externally)—and white matter (internally).

The cortex forms sulci and gyri.

The largest are the central and lateral sulci, with four lobes: frontal, parietal, temporal, and occipital.

Deep within lie the First and Second ventricles.

The cortex is 3 mm thick and comprises six layers:

1. molecular layer - fibers, Glia;

2. external granular layer - Cells 4-10 µm in diameter;

3. external pyramidal layer - cells 10-20 µm in diameter;

4. internal granular layer - not present everywhere;

5. internal pyramidal layer - 14-40 µm, with projections extending to the spinal cord;

6. multiform layer - 10-30 µm of various shapes.

Functionally, the entire cortex consists of the cortical ends of analyzers (motor, auditory, olfactory, visual, etc.).

The white matter contains neural pathways: association fibers (within a single hemisphere), commissural fibers (between the hemispheres), and projection fibers (to the spinal cord and Organs), which are subdivided into sensory and motor fibers, namely corticospinal tracts.

Figure 32. Diencephalon.

Meninges of the brain.

Dura mater - Connective Tissue that attaches to the bones.

Arachnoid mater - also connective tissue, does not extend into the sulci. Pia mater - extends into the sulci and gyri; between it and the brain lies the clear CEREBROSPINAL FLUID, which fills the ventricles.

Spinal cord

Located within the vertebral canal, extending inferiorly to the 1st or 2nd lumbar vertebrae. This is followed by the conus medullaris and the cauda equina. The spinal cord consists of an inner core of gray matter surrounded by white matter. On the lateral surfaces of the spinal cord, the posterior (sensory) roots enter and the anterior (motor) roots exit symmetrically (Figure 33).

Figure 33. Cross-section of the spinal cord.

The region of the spinal cord corresponding to each pair of roots is called a segment.

31 segments: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal.

Each segment is associated on each side with: two roots, a spinal ganglion containing sensory neurons, and a spinal nerve formed by the fusion of the anterior and posterior roots.

Branches:

✵ anterior (motor + sensory; in Thoracic nerves, it continues as intercostal nerves, while in others, it forms plexuses: brachial, femoral, lumbar, coccygeal);

✵ posterior (supplying the Muscles and Skin of the back);

✵ communicating (leading to autonomic ganglia);

✵ meningeal (innervating the meninges of the spinal cord).

It features two enlargements: the cervical and lumbosacral enlargements.

It is symmetrical, with the anterior median fissure on the ventral side and the posterior median sulcus on the dorsal side.

In the center lies the central canal.

Gray matter forms three columns: anterior, posterior, and lateral.

White matter forms three funiculi (columns): anterior, posterior, and lateral.

It is enveloped by three meninges: the dura mater, arachnoid mater, and pia mater.

Peripheral Nervous System

Nerves act as pathways and consist of fibers covered with a myelin sheath.

Cranial nerves.

1. Olfactory — sensory.

2. Optic — sensory.

3. Oculomotor — motor.

4. Trochlear — motor, also related to the eye.

5. Trigeminal (mixed — skin and facial expression muscles): ophthalmic — sensory, skin and lacrimal gland; maxillary — sensory, facial skin; mandibular — mixed, Tongue and masticatory muscles.

6. Abducens nerve — motor, innervates the eyeballs.

7. Facial — mixed, innervates all Muscles of facial expression.

8. Vestibulocochlear — sensory.

9. Glossopharyngeal — mixed.

10. Vagus - motor - Larynx; autonomic parasympathetic - thoracic and abdominal cavities.

11. Accessory - mixed, formed from cranial and cervical components, primarily motor - sternocleidomastoid muscle.

12. Hypoglossal - motor - tongue and neck.

Spinal Nerves.

Plexuses: cervical, brachial, lumbar, sacral, coccygeal.

Cervical plexus.

C1–C4 vertebrae, giving rise to branches. They primarily innervate the skin and Muscles of the neck.

Brachial Plexus.

C5–T1 (5th–8th cervical and 1st thoracic) vertebrae. Short branches supply the scapula and axilla. Long branches include: the median nerve (muscles of the anterior forearm, digits 1–3, and the lateral half of digit 4; note: reference to Facial Nerve here appears to be a source text anomaly, supplying the triceps brachii, superficial and deep forearm nerves), the ulnar nerve (runs along the humerus, prone to entrapment; supplies the ulnar side of the forearm and deep palmar muscles), and the musculocutaneous nerve (forearm flexors and skin).

Lumbar plexus.

L1–L5 segments. Short nerves supply the lower back region. Long branches include: the iliohypogastric nerve (skin and muscles of the abdominal wall), the genitofemoral nerve (to the genitalia), the femoral nerve (skin and muscles of the anterior thigh), and the obturator nerve (skin and muscles of the medial thigh).

Sacral Plexus.

Lower 1.5 lumbar and upper 3.5 sacral segments. Gluteal nerves (superior and inferior); the sciatic nerve divides into the tibial nerve (which continues as the plantar nerve) and the fibular (peroneal) nerve (which continues as the sural and dorsal cutaneous nerves).

Coccygeal plexus.

Co1 (5th sacral and coccygeal) segments. Skin and Muscles surrounding the coccyx.

Autonomic nervous system

It innervates the entire body and is regulated by the CNS (Figure 34). The central component comprises structures of the brain (nuclei of the midbrain and medulla oblongata) and the spinal cord.

The peripheral component consists of the parasympathetic and sympathetic

divisions, which exert antagonistic effects.

Figure 34. The autonomic nervous system.

The parasympathetic division comprises pathways originating from the brain and the sacral region of the spinal cord. Accordingly, it is subdivided into the craniosacral division—specifically the midbrain outflow (Vagus nerve, along with parts of the glossopharyngeal and facial nerves)—and the pelvic division (supplying the intestines and reproductive organs).

The sympathetic division is represented by the thoracic and lumbar segments of the spinal cord, the lateral horns of which form the Sympathetic trunk. The trunk innervates thoracic organs, while its secondary pathways form the celiac (solar) plexus, extending into the mesenteric ganglia.