Анатомия домашних животных неврология = Anatomy of domestic animals Neurology. Учебно-методическое пособие

PEOPLES' FRIENDSHIP UNIVERSITY OF RUSSIA

Agricultural-Technological of Institute

Department of Veterinary Medicine

S.B. Seleznev, G.A. Vetoshkina, V.M. Byakhova

ANATOMY

OF DOMESTIC ANIMALS:

NEUROLOGY

For the students of 1-2 courses of Faculty of Agriculture in the specialty «Veterinary Medicine»

Moscow

Peoples’ Friendship University of Russia

2017

Селезнев, С. Б.

С29 Анатомия домашних животных: неврология = Anatomy of domestic animals: Neurology : учебно-методическое посо-

бие / С. Б. Селезнев, Г. А. Ветошкина, В. М. Бяхова. – Москва : РУДН, 2017. – 28 с.

The guidelines include charts and tables, each is accompanied with instructions and explanations, aimed at consolidating the material on myology.

The purpose of the guidelines is to teach students to understand the comparative anatomy of the skeletal muscles and muscle tissue.

For the students of 1–2 courses of Faculty of Agriculture in the specialty «Veterinary Medicine».

Prepared by the Department of Veterinary Medicine of the Peoples' Friendship University of Russia.

INTRODUCTION

Neurology (neurologia) is a branch of anatomy of domestic animals, conceding the structure of nervous system. Nervous tissue, the basis of the system, consists of nervous cell (neurons) and neuroglia. Neurons sense irritation, excite, produce nervous impulse and transmit it. Cells of neuroglia provide supportive, trophic and barrier functions.

Table 1

Neuron

Neurons consist of body, processed and terminations, extending from body.

The neuron body consists of cytoplasm and nucleus. The nucleus is large, rounded, sets in the middle and comprises 1-2 nucleoli. The cytoplasm comprises all organelles, neurofibrils and clots of basophilic substance (polyribosomes, that synthesize protein). The neuron bodies with nearest processes are included in gray matter (substantia grisea) of spinal cord and brain, and also form ganglions (nodes). Ganglions (ganglion) is an accumulation of neuron bodies in peripheral area, meaning outside the spinal cord and brain.

Neuron processes are divided by function:

1.Sensitive processes (dendrites) - they sense irritation and transmit impulse to cell's body. They have branchy shape and thus they are called dendrites.

2.Motional processes (axon, neurite) - transmit nervous impulse from neuron body to target organ (muscle, gland ect.). Neurons always have only one axon.

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Neuron always polarized, meaning it can transmit nervous impulse only in one direction from dendrites to axon. Processes of neurons, covered with glial coats, are called nervous fibers. Nervous fibers are classified according to: length, thickness, presence or absence of myeline coat: myelinated nervous fibers consist of one neuron process, covered by thick myeline coat; nonmyelinated (naked) nervous fibers consist of several nervous processes (3-20) and covered by simple coat of connective tissue. Myelinated fibers have very quick transmission of impulse in contrast with nonmyelinated fibers.

Neuron fibers in central nervous system (CNS) form white matter (substantia alba), in peripheral nervous system (PNS) – nerves. In white matter, nervous fibers are called differently – bundles, funiculus, pathways etc. In peripheral nervous system fibers form nerves and their plexus. Nerve (nervus) is a group of nervous fibers in PNS, united by common connective tissue coat.

Table 2

Nervous processes end with nervous terminations. Sensitive (receptor), motional (effector) nervous

terminations and synapsis, i.e. connection spot between two neurons, are distinguished. Receptors are divided into two main groups: extero-receptors (external) and intero-receptors (internal). Extero-recepors sense irritation from external environment, and intero-receptors – from internal environment.

Intero-receptors are divided into:

a)visceroreceptors – situate in internal organs;

b)proprioreceptors – control locomotor apparatus (muscular-articular segment);

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c)vestibuloreceptors – situate in internal ear (body position).

As a rule, motional nervous terminations (effectors) end in target organs (muscles, glands etc..) and transmit executive orders. Synapsis are the connective points between two adjacent neurons. In synapsis, there is a biologically active substance, that transmits nervous impulse (mediator), it drifts from one termination to another and binds them in one chain.

Classification of neurons by function:

1)Sensitive (afferent, receptive) – sense irritation and transmit it, i.e. transmit nervous impulses from organs and tissues to brain. Bodies of such neurons lie outside CNS in human and animals (lat. Afferens – brining to).

2)Intercalated (transitive, associative, terminative) – transmit excitation from sensitive to motional or secretive neurons. Intercalated neurons lie in CNS.

3)Motionalorsecretiveneurons(efferent,effector)–transmit excitation to target organ (muscle, gland). Bodies lie in CNS or ganglion (lat. Efferens – brining out).

Termination of one motional neuron and striated muscle bundle innervated by it form neuro-muscular complex – myon (motional patch), consisting from one nervous and several muscular fibers. For instance, myon of triceps surae consists of 1 nervous fiber and 227 muscular fibers, and lateral ocular muscle – from 1 nervous and 19 muscular fibers.

The basis of nervous system work is a reflex (lat. Reflexus

– reflection). Reflex is a response of an organism to irritation of receptors (from internal and external environment), conducted with the help of nervous system. Anatomical pathway of reflex is reflex arch.

Reflex arch usually comprises three neurons: 1) afferent neuron (and its receptors); 2) intercalated neuron, confined in CNS; 3) efferent neuron (and its effector). Simple reflexes are

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obtained by “inferior” parts of CNS – spinal cord. Simplest reflex arch consists of two neurons: sensitive and motional. The body of the former (afferent) is situated in spinal ganglion (or in sensitive ganglion of cerebral nerve). The body of the latter (efferent) is situated in gray matter of spinal cord or in brain nuclei. Irritation of one body point can be transmitted not only to corresponding brain segment, but also cover several adjacent segments. Due to it simple reflex develops into response catching several groups of muscles. Complex, coordinated reflective movement occurs.

Currently the theory of reflex is supplemented by term “feedback”,becauseitconcernsnotonlyaboutreflexarch,butalso about reflex circle. Each muscle has receptors, that excite during its contraction. Impulses, informing about contractile grade, are transmitted from this receptors to CNS. Due to feedback CNS evaluatesreflexactandprovidesabsolutecontrolofprocesses,that it can be provided by unidirectional connection.

Classification of nervous system

Nervous system is untied, but nominally it is divide by topography into two parts: central and peripheral. CNS comprises spinal cord and brain, and PNS comprises nerves and nervous ganglions. Central and peripheral nervous systems are inseparably linked by spinal and cerebral roots.

Table 3

Nervous system

Ganglion is an accumulation of neurons’ bodies in periphery. According to location and function ganglions are

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divided into spinal, cerebral and vegetative, and arranged in three levels.

1.First series of ganglions (spinal and cerebral) lies on dorsal spinal and cerebral roots near brain. These ganglions are protective and compensative mechanism, “spare brain”, make decision whether disturb it or not, produce impulse from periphery to brain and vice versa stops it. It is sensitive ganglions.

2.Second series of ganglions lie under vertebral column (sympathetic ganglions). These ganglions provide impulses from centers to blood vessels. It comprises ganglions of sympathetic trunk and two unpaired ganglions and abdominal wall. These ganglions are motional (impulse goes from brain through ganglion to peripheral vessels).

3.Third series of ganglions (parasympathetic ganglions) are situated in wall of internal organs (intramural) or beside them (extramural). It is also motional ganglions (impulse

goes from brain through ganglion to periphery of internal organs wall).

Nerves (nervus) is a group of nervous fibers, united common connective tissue coat. Almost all nerves contain sensitive and motional nervous fibers and thus are mixed. From outside nerves are covered by coats and look like white cord of different thickness. According to origin and development nerves are divided into spinal, that start from spinal cord, cerebral – from brain, vegetative, that are a part of vegetative nervous system.

Nervous system is united, but by functional characteristics, i.e. by zones of innervation, it is divided into somatic and autonomous (vegetative).

Somatic (animate) section is presented by spinal cord and brain with growing away spinal and cerebral nerves, that innervate locomotor apparatus and integument (soma), and also connect an organism with environment by sense organs.

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Autonomous (vegetative) nervous system innervates smooth muscular tissue of internal organs and vessels, and also controls metabolic processes and supports homeostasis of internal organism environment.

Table 4

Autonomous nervous system is divided into sympathetic (pars sympathica) and parasympathetic (pars parasympathica) parts. This division is historical and associated with J.Lengli researches, he was the first to suggest division of autonomous nervoussystemintosympatheticandparasympathetic.Concerning nervous plexus of intestinal walls J. Lengli distinguished them and called "enteral system". Later, academician A.D. Nozdrache continued investigations in this area and suggested to change term "enteral system" to "metasympathetic part". Thus, according to the latest studies, autonomous nervous system is divided into three parts: sympathetic, parasympathetic ad metasympathetic (enteral), all featured by special function ad structures. Sympathetic nervous system innervates smooth muscular tissue of blood vessels, parasympathetic - smooth muscular tissue of glands and internal organs, and metasympathetic provides autonomous work of internal organs (rhythmic contractions of the heart, gastrointestinal motility).

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1. CENTRAL NERVOUS SYSTEM

1.1. Spinal cord

Spinal cord (medulla spinalis) is in the vertebral canal and is presented by longitudinal cylindric cord, squeezed dorsoventrally. It is divided into cervical, thoracic and lumbosacral (sciatica), the later ends with medullary cone (conus medullaris), continuing till 2-3rd lumbar vertebratea. Then it continues with terminal filament (filum terminale), continuing till 6th caudal vertebratea.

Along the entire length of the spinal cord sensitive and motion roots breaches off and connect it with the periphery. Along the whole spinal cord there are dorsal medial sulcus (sulcus medianus dorsalis) and ventral medial fissura (fissura medianus ventralis), which divide the spinal cord into 2 equal symmetrical halves (right and left). Moreover, in ventral medial sulcus lies spinal ventral artery. The segmental section of spinal cord features by cavity (central canal), white and gray matters. The central canal contains cerebrospinal fluid, that acts as mediator between blood and neurons.

Table 5

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Main functions of spinal cord

1)Reflectory: in gray matter of spinal cord there are nervous centers – a group of neurons bodies, that controls particular functions and provides various inborn reflexes. Neurons, forming the nervous center, may set in various parts of CNS. For instance, in cervical area there are centers of diaphragmic nerves, with damage causes respiratory distress. In thoracic area of the spinal cord, there are centers, that innervate musculature of forelimbs and trunk, thus a damage of these centers causes motor disturbance of that body parts, that are innervated by it. In lumbar area, there are centers of musculature of hindlimbs and abdominal wall, and in sacrum area – centers of defecation, urination, erection, uterine activity. All centers of the spinal cord are under control of the brain centers.

2)Conductive: spinal cord is a powerful system of conductive paths. Conductive paths can be main, cerebripetal and cerebrifugal.

a.Main conductive paths (more ancient according to phylogenies) connect sections of the spinal cord and lie near gray matter in all three funiculi.

b.Cerebripetal (afferent, ascending, sensitive) paths connect the periphery of the body with the brain and conduct nervous impulses from integument, skeletal muscles, joint etc. to the brain.

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