Download THE CENTRAL NERVOUS SYSTEM THE SPINAL CORD

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:
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NEUROLOGY.
CLASSIFICATION OF RECEPTORS
REFLEX ARC
CLASSIFICATION OF NEURONS
NS PHYLOGENESIS
NS EMBRYOGENESIS
DEVELOPMENT OF NEVES SYSTEM.
THE CENTRAL NERVOUS SYSTEM. SPAINAL CORD.
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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
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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
• CLASSIFICATION
on topographic anatomical basis
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CENTRAL
PERIFERAL
BRAIN
SPAINAL CORD
CRANIAL AND SPAINAL NERVES
ganglions, plexuses, nerves, peripheral nerve endings
on function
vegetative nervous system
(sympatetic and
parasympatetic)
somatic (animal) nervous system
innervates the internal organs,
controls the striated musculature of the body and
the smooth muscles and vessels primary innervates the organs of animal life, skin,
skeleton
• NS acts as an mechanism which perceives irritation, interprets received
information and provides a response reaction of the body.
• Receptors
Receptors 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
conditioned
inborn (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
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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 matters
Visual 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 SYSTEM
THE SPINAL CORD
The spinal cord (medulla spinalis)
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
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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.
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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
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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.
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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.
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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.
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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
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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.
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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 YOUR
ATTENTION
The end