Department of Human Anatomy KNMU

NEUROLOGY

THE CENTRAL NERVOUS SYSTEM

SPAINAL CORD

Slide-lecture for students of the 6 Faculty of Medicine Lector – associate professor Zharova Nataliya

PLAN:1. NEUROLOGY.2. CLASSIFICATION OF RECEPTORS3. REFLEX ARC4. CLASSIFICATION OF NEURONS5. NS PHYLOGENESIS 6. NS EMBRYOGENESIS 7. DEVELOPMENT OF NEVES SYSTEM.8. THE CENTRAL NERVOUS SYSTEM. SPAINAL CORD.

• Nervous system is a complex of specialized formations which provides perception of irritation to conduct and process the excitation which it causes and form response reactions which adapt to the conditions of existence.

• NS performs its functions very quickly, to the maximum and momentarily as only centiseconds pass from the moment of irritation emersion to its sensation, that is, to the response reaction of the body to it. As a rule, a particular organ or a group of organs react to irritation. When the irritant action ceases, the response reaction immediately stops.

• The role of NS in the body • Coordination and integration of different organs

and organ systems activity.• Adaptation-trophic: provision of adaptation of the

body to the changes of environment.• Intellectual activity and response reflex

accomplishment of intellectual activity processes (particular movements)

• Memory for current and earlier events

• CLASSIFICATIONon topographic anatomical basis

• on function

• NS acts as an mechanism which perceives irritation, interprets received information and provides a response reaction of the body.

CENTRAL PERIFERAL

BRAINSPAINAL CORD

CRANIAL AND SPAINAL NERVES ganglions, plexuses, nerves, peripheral nerve endings

vegetative nervous system(sympatetic and parasympatetic)

somatic (animal) nervous system

innervates the internal organs, the smooth muscles and vessels

controls the striated musculature of the body and primary innervates the organs of animal life, skin, skeleton

• ReceptorsReceptors are the specialized nerve terminations of sensory neurons located

in various tissues, where stimulus transforms into nerve impulse. Depending on location, the following types of receptors are distinguishable:

• exteroceptors, which reside in skin, mucous membranes and specialized tunics of the sensory organs (retina, membranous labyrinth etc.). They receive stimuli from environment. This type of sensitivity is called exteroceptive (pain, temperature, tactile, sight, olfactory and taste);

• proprioceptors are the sensitive nerve terminals in muscles, tendons, fasciae, periosteum and joint capsules). This type of sensitivity is called proprioceptive. Proprioceptive impulses are responsible for spatial orientation and feeling of both active and passive movements;

• interoceptors are located in the viscera (stomach, heart, lungs, liver etc.) and blood vessels. This type of sensitivity is called interoceptive.

Reflexes and reflectory systems form the basis of NS activity.

REFLEX is a response reaction of the body to external or internal irritation unconditioned conditionedinborn (inheritant) reaction acquired on the basis of the body

Reflectory activity of NS: -perception of irritation from external and internal environment -transformation of irritation energy to a nerve impulse -conduction of primary impulses to corresponding nerve centers -interpretation and processing of the incoming information in the nerve center-conduction of a nerve impulse from the nerve center to the working organ-provision of a response reaction

• The simple reflex arch consists of two neurons, one of which connects with a sensory surface (the skin, for instance) and the other, which, with its axon, ends in a muscle or a gland. The distal dendrites of these afferent neurons are the sensory receptors (or are connected to the sensory receptors), which are responsive to internal or external stimulation. When the sensory surface is stimulated, the nervous impulse passes along the neuron connected to the reflex centre where the synapse of both neurons is located. Here the nervous impulse is transferred to the other neuron and directed to the muscle or gland. As a result the muscle contracts or the secretion of the gland changes.

• The basic anatomical element is the nerve cell - THE NEURON. • A long axial process, called the axon or neurite, arises from the body of the

neuron in one direction. Short branched processes called dendrites lead in the other direction. Nervous impulses inside the neuron run from the dendrites to the cell body and from there to the axon. The axons convey the nervous impulses away from the cell body. The body uses a combination of electrical impulses and chemical messengers to react and adjust to stimuli in order to maintain homeostasis.

• Afferent (sensory) neurons of the peripheral nervous system carry information from sensory receptor cells to the central nervous system. Efferent (motor) neurons of the peripheral nervous system convey information away from the central nervous system to the effectors (muscles and glands). A nerve impulse travels along an axon and eventually reaches the branching axon terminals in the transmissive segment of the neuron. The junction between neurons is

called a SYNAPSE.

CLASSIFICATION of nerve cells

According to the form: pyramidal, fusiform, piriform,

multangular, oval, stellate, etc.According to the size:

small (4-19 µm), medium (20-59 µm), large (60-130 µm)

According to the number of processes:

bipolar (two axon), pseudounipolar (false axon),

multipolar (multi axon) unipolar (one axon), According to functional significance:

(three groups of neurons as part of reflex arc)receptor (sensory)neurons perceive irritation from external and internal

environment;effector (efferent) neurons conduct nerve impulse to the working organ;association (interneuron) neurons conduct nerve impulses from receptor neurons to

effector neurons.

There is an association between the structure and function of nerve cells: - pseudounipolar neurons are general sense receptors (pain, heat, touch);- bipolar: special sense neurons (light, smell, hearing, vestibular irritations);- multipolar: small (association), medium and large (pyramidal and motor).Transmission of nerve impulses from a neuron to neuron, from a neuron to working organ is carried

out on certain sites by special formations, called synapses. Synapses are various forms of axon endings which bring impulses to a neuron. Synapse structure conditions the unilateral conductivity of impulses in the direction synapse – neuron – axon.

Local anesthesia and blocking disable the transmission of a nerve impulse along the synapse.

Nerve fibers are nerve cells processes covered by glial membrane which conduct nerve impulses.- myelinated - nonmyelinated Thick fibers are mainly motor ones;Medium fibers are responsible for tactile and heat sensitivity;Thin fibers conduct pain sensitivity. White and grey mattersVisual examination reveals in brain and spinal cord two well distinguishable areas called the white

matter and the grey matter.The grey matter, substantia grisea represent the areas where myelindevoid neurons' bodies

concentrate. The grey matter forms the cortex of brain, cortex cerebri, the cortex of cerebellum, cortex cerebelli, the nuclei of the brain and spinal cord and the columns, columnae of the spinal cord.

The white matter, substantia alba corresponds to the areas that contain myelinated neurons' processes. Whit substance forms the fibers, fibrae and tracts, tractus.

NS PHYLOGENESIS One-celled protozoa (amoeba) do not yet have NS and connection with

external environment is carried out with the help of fluids, located in and out of the organism, this is humoral, prenervous form of regulation.

Later on, with NS development (for the first time in coelenterate as their body consists of two layers, external (ectodermal) and internal (endodermal), it divides into several stages.

Stages of NS development Reticular NS forms a network, interfusing the whole organism,Nodal NS: nerve cells gather into separate accumulations, forming nerve

ganglia and centers, nerve stems and nerves are formed from accumulation of processes,

Tubular NS: lancelets, humans.

• NS EMBRYOGENESIS • NS originates from ectoderm which forms medullary plate, deepens and forms

medullary groove, which edges (ganglionic crests) gradually become higher and fuse with each other, creating neural tube, the posterior end of which forms spinal cord anlage, the anterior one divides into three brain vesicles by shifting which later develop into the brain.

NS DEVELOPMENT IN PRENATAL PERIOD

2,5 weeks – beginning of neural groove development,3,5 weeks – beginning of neural tube development,4 weeks – formation of three brain vesicles, neural ganglia,5 weeks – formation of five brain vesicles,6 weeks – formation of meninges,8 weeks – typical neurons develop in the cortex,10 weeks – development of internal structure of the brain

THE CENTRAL NERVOUS SYSTEMTHE SPINAL CORD

The spinal cord (medulla spina lis) represents a cylinder — shaped stretched cord, slightly flattened in the antero — posterior direction. The length of the male spinal cord is about 41-42 cm. The mass of the spinal cord is about 30 g. Three meninges: dura mater, arachnoid mater and pia mater surround the spinal cord situated in the spinal canal.The spinal cord begins on the level of the foramen magnum occipitale where it transforms into the cerebrum. The lower ending of the spinal cord tapered as a medullary cone (conus medullaris) corresponds to the level of the 2d — lumbar vertebra. Below this level the spinal cord merges into the terminal (thread) surrounded by the radicis of the spinal nerves and the spinal cord meninges that form a closed sack in the inferior part of the spinal canal.

• One filum terminale (filum terminale) consists of internal and external parts. The internal parts extend from the 2d — lumbar vertebra to the 2d sacral vertebra; its length is about 15 cm. The external part of the filum terminale does not contain any nervous tissue and represents a prolongation of the spinal meninges made by the connective tissue. Its length is about 8 cm, and it grows together with the periosteum of the spinal canal on a level of the 2d sacral vertebra.

• The spinal cord has two enlargments (thickenings) a cervical and a lumbo — sacral (intumescentia cervicalis, intumescentia lumbosacralis).

• THE MENINGES • OF THE SPINAL CORD• External, medial and internal tunics

surround the spinal medulla.• The external tunic — spinal dura mater

— is separated from the periosteum of the vertebral canal with the epidural space. Between, the dura mater and the medial tunic — an arachnoid mater — there is the subdural space, it is formed of the fibrous connective tissue and contains the considerable amount of elastic fibers; its external and internal layers are covered with the flat glial cells.

• The arachnoid mater of the spinal medulla (arachnoidea mater spinalis) is presented by a thin translucent lamella of the connective tissue situated under the dura mater.

• The pia (vascular) mater of the spinal cord (pia mater spinalis) tightly adjoins to the surface of the spinal cord. The connective tissue fibers branching off the pia mater accompany the blood vessels and enter together with the vessels into the spinal cord tissue.

From the lateral sides of the pia mater between the anterior and posterior radicis of the spinal nerves a denticulate ligament (ligamentum denticulatum) stretches, it goes right and left in the lateral direction. The ligament grows together with the arachnoid mater and the internal surface of the dura mater, as though it hangs up the spinal cord in the subarachnoid space.

• The epidural space (spatium epidurale) that separates the dura mater from the periosteum is filled with fat and contains the internal vertebral venous plexus. The internal surface of the dura mater is separated from the arachnoid mater with the narrow subdural space (spatium subdural).

• The space between the arachnoid mater and pia mater is called a subarachnoid space (spatium subarachnoideum). It contains 120-140 ml of the cerebrospinal fluid (liquor cerebrospinalis). In its upper parts this space merges into the subarachnoid space of the cerebrum. In its lower parts the subarachnoid space contains only radicis of the spinal nerves. Therefore, by puncturing on a level below the 2d — lumbar vertebra, it is possible to get some cerebrospinal fluid for analysis without the risk of damaging the spinal cord.

INTERNAL STRUCTURE OF SPINAL CORD

• There are white and gray substances (substantia alba, substantia grisea) distinguished in the spinal cord. The gray substance is situated in the central sections of the spinal cord, the white substance — in its periphery. The narrow central canal (canalis centralis) goes downward through the gray matter; this canal represents the remnant of the nervous tube cavity. Its upper end is connected to the fourth ventricle of the cerebrum. Its lower end broadens and forms the closed terminal ventricle (Krause's ventricle, ventriculus terminalis); its unclosed sections still contain the cerebrospinal fluid. The walls of the canal are covered with Ependymocytes.

• The gray matter forms symmetrical right and left gray columns along the spinal cord on the both sides from the cen tral canal. The thin lamella of the gray substance connecting the two gray columns in front of the central canal is called an anterior gray commissure (comissura grisea anterior). There are anterior and posterior parts distinguished in each column (anterior column and posterior column; columna anterior, columna posterior). From the 8th cervical segment to the 2d lumbar segment inclusive on each side the gray matter also forms a lateral bulging — the lateral or intermediate column (columna lateralis, columna intermedia). There are no lateral columns above and below this level. At their place on the cross — sections of the spinal cord the anterior, posteior and lateral horn (cornu anterior, cornu posterior, cornu laterale) of gray substance are distinguished. The anterior cornu is wider than the posterior one. The lateral horn topographically corresponds to the lateral column of the gray substance.

THE GRAY SUBSTANCE• Bodies of neurons, amyelinic and thin myelin fibers and neuroglia form the gray substance

of the spinal cord. • Bodies of the largest neurons of the spinal cord are situated in the anterior horn. They

form five nuclei (clumps). Among these nuclei, there are antero- and postero- lateral nuclei (n. anterolateralis, n.posterolateralis), and a central nucleus (n.centralis). These nuclei are motor centers of the spinal cord.

• Axons of these cells compose main mass of fibres of the spinal nerves anterior radicis. As parts of spinal nerves they go to the periphery and form the motor nerve endings in the skeletal musculature. The anterior- and posterio-medial nuclei, which are well developed throughout the whole spinal cord, innervate muscles of the trunk. The anterior- and posterio-lateral nuclei are better developed on the level of the cervical and lumbo-sacral enlargements. The neuron's of these nuclei innervate extremities.

• The gray matter of the posterior horn is heterogeneous. It consists of a spongious zone, gelatinous (jelly — like) substance (substantia gelatinosa) and proper nuclei (n.proprius). In the basis of the posterior horn of the spinal cord, in its medial part, there is a dorsal thoracic nucleus (Clark's nucleus), (n.thoracicus dorsalis). It consists of large intercalary neurons with well — developed intensively branching dendrites (Schilling's cells).

• On a level of the cervical and superior thoracic segments of the spinal cord between the anterior and the posterior horn in the white substance, a reticular substance (formatio reticularis) is situated.

THE WHITE SUBSTANCE• The white substance of the spinal cord is formed of a totality of the

longitudinally oriented nerve fibers, which go in the ascending or descending directions. Besides the anterior, lateral, and posterior funiculus, an anterior white commissure (comissura alba anterior) is distinguished in the white substance. It is situated behind the anterior median fissure and connects the anterior funiculus of the right and the left sides. The fascicles of the nerve fibers (totality of outgrowth) in the cords of the spinal medulla compose the conducting tracts of the spinal cord.

• There are three systems of fascicles: • short fascicles of associative fibers, • ascending and • descending fascicles.

• Short fascicles of associative fibers connect the segments of the spinal medulla, which are situated on various levels. The ascending (afferent) fascicles go to the centers of cerebellum and cerebrum. The descending (efferent, motor) fascicles go from the cerebrum to the cells of the anterior horn of the spinal medulla. In the white substance of the anterior cords descending conducting tracts follow, in the lateral funiculus — ascending and descending conducting tracts, in the posterior funiculus — the descending conducting tracts.

External structure

of the spinal

cord

• Along the anterior surface of the spinal cord the anterior median fissure (fissura mediana anterior) goes downwards. It juts into, the tissue of the spinal cord deeper than the posterior median sulcus (sulcus mediana posterior), which goes downwards along the dorsal surface of the spinal medulla. On each side of the spinal cord on its anterolateral surface aside from the anterior median fissure there is the anterolateral sulcus (sulcus anterolateralis, sulcus venterolateralis). Through the anterolateral sulcus an anterior radix (radix anterior) goes from each segment; this radix is formed from axons of the motor neurons bedding in the anterior cornu of the gray matter. The afferent posterior radix (radix posterior) is formed of the totality of central processes (axons) of pseudounipolar neurons. The bodies of these neurons form a spinal ganglion (ganglion spinale), which is situated in the spinal canal near a corresponding intervertebral foramen, close to the point of merging of the posterior and anterior radicis into the spinal nerve.

• The section of the spinal cord corresponding to two pairs of spinal nerves radicis (two anterior and two posterior ones) is called the SEGMENT of the spinal cord. Among the segments, there are 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1-3 coccygeal segments (31 segments totally). As to the upper cervical segments, each of them is situated on a level of the body of the corresponding vertebra with the same number. The lower cervical and upper thoracic segments are situated one vertebra higher than the bodies of the corresponding vertebrae. In the middle thoracic section this displacement equals to two vertebrae, in the lower thoracic section — to three vertebrae. The lumbar segments are situated on a level of 10lh and 11th thoracic vertebrae, while sacral and coccygeal segments correspond to the levels of 12th thoracic and 1st lumbal vertebrae.

• THE END

• THANK FOR YOURATTENTION

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