Content module 4: “cns role in motor functions regulation”

First of all, we would like to tell few words about new investigative methods used in neurology and neurophysiology for nervous system functions assessment.

Method of surgical extirpations. It includes different brain structures removal, their mechanical destruction or coagulation with constant current anode. Brain structures functional switching off is achieved by their cooling or anodic polarization. This method disadvantage is expressed in haemorrhagias in the injury zone and further irritation with forming scared tissue. This method separate type is brain tissue local extirpation through injected canules.

Method of different brain structures electrical and chemical irritation. It includes naked brain structures irritation. German investigators G.Frich and E.Gitzig were the first who have performed brain cortex direct irritation. This method is also non-exact and rough. It is accompanied by cerebral sheathes section, intracerebral pressure disorders and others.

Stereotaxic method of irritating electrodes introducing got wide distribution. It is performed in brain definite points through trepanative foramens in skull.

Animal head under narcosis is fixated in stereotaxic device with fixators injected in auricular meatuses, for orbitae inferior limbs or maxillae. Stereotaxic atlases for definite animals are used for electrodes orientation in brain. Brain serial cuttings in frontal, horizontal and sagittal planes are represented in them. The counting is performed from zero planes. In cats, for example, frontal zero plane passes through external acoustic meatuses. Horizontal zero plane – 10 mm higher than external acoustic meatuses. Zero sagittal plane coincides to sagittal suture. Frontal plane is chosen for electrodes putting because necessary structure is the most distinctly visual here (for example, numerals for hypothalamus are equal to: F=12 mm, L=2 mm, H=12 mm).

Introduced electrode is fixated in electrode holder. First of all, holder should be located so that electrode end was located above frontal plane. Than electrode holder must be putted 12 mm forward and 2 mm laterally. Foramen must be drilled in the point in skull bone. Electrode is putted in 12 mm in depth. X-ray-scopy controls additionally electrodes ends location in brain.

Stereotaxises for human being with special atlases are performed for clinical aims.

Brain structures irritation can be made (except ends) with isolated bipolar electrodes (distance between their ends are 0,5 mm and less) or unipolarly when indifferent electrode is located above nasal sinus or in muscle.

Canules-chemotrodes are used for brain structures chemical stimulation. Brain irritation can be performed by contact or by telestimulation.

Method of functional degeneration. One can see degeneration of synapses and neurons of brain parts located below at axons cutting for example of brain cortex pyramidal neurons.

Method of horseradish peroxidase. Horseradish peroxidase injection in brain definite parts causes reaction in neighboring brain locuses.

Strichnin neuronography. Strichnin application to definite brain locuses leads to spike activity not only in application point but also in brain structures connected with them.

Chemicals application, microionophoresis. Synaptic transmission blockators or activator application can be performed directly to brain cortex or by way of their giving through electrodes (chemotrodes) to different deep brain structures. Substances can be applicated to the separate brain neurons through microcanules by charges electrical pushing away – microionophoresis.

Microdialysis. It is performed by liquids microdoses taking from brain definite structures at experimental animals definite states with special micropumps.

Method of caused potentials. Caused potentials are registrated in different subcortical structures at singular irritations applying to the peripheral receptors or afferent nervous fibers in cortex projectional zones.

Caused potentials in cortex projectional zones have following phases:

1) primary positive potential – it occurs due to axo-somatic synapses excitement on neurons of the 3^rd-4^th cortex layer;

2) primary negative potential - it occurs due to axo-somatic synapses excitement on neurons of the 3^rd-4^th cortex layer inhibiting;

3) secondary potentials – are determined by axo-dendrite synapses excitement.

Different distribution maps are observed at different narcosis types for instance of somato-sensor caused potentials through brain cortex which indicates to different drugs selective action to brain synaptic structures.

Microelectrode investigations. Metallic or glass electrodes filled with sodium chloride are used for separate neurons electrical activity investigation. Microelectrodes ends diameter is fluctuated from 1 to 0,5 mcm. Methods of extracellular and intracellular biopotentials leading are applied in microelectrode investigations.

Magneto-resonance tomography. Brain liquids (for example, water molecules) dipoles acquire the direction of irradiating field at brain irradiation with electrical-magnetic field. Dipoles are returned to their initial position at external magnetic field switching off. Magnetic signal are appeared at this which is percepted by special devices and are registrated as graphic in computer. As external magnetic field can be made plane, than brain can be “cutted” layer by layer. This method allows tumors and brain circulation zones detection in brain.

Positrone-emission tomography. This investigation is based on positrons-irradiating short-lived isotopes injection to brain circulation. Data about radioactivity distribution in brain are calculated for definite time periods in computer and then are reconstructed in three-dimensioned image. This method gives an opportunity to see excitement focuses in different brain parts at investigated people mental activity.

Brain functions modeling with computer. It became widely-spread during the latest years. Nervous nets models were built performing separate brain functions. “Intellect detector” has been made giving an opportunity to determine individual features of human psychical activity systemic organization different stages.

Brain electrical activity registration. Biopotentials registration from head surface or skull is known as electroencephalogram. It reflects spontaneous activity of such brain structures as: neurons, synapses, glia and intercellular substance. You will get acquainted with this method while chapter “Highest nervous activity and brain functions” study.

 

 

LESSON 11
Spinal cord physiology. Spinal cord role investigation in motor organism functions regulation

1.Topic studied actuality:

Spine represents main canal for afferent (cutaneous, temperature, proprioceptive and noceoceptive or pain) signalization from peripheral receptors to CNS highest parts. At afferent impulses conductance disorders through spine (at syphilitic spine injury i.e. tabes dorsalis) human being can not perform movements at closed eyes (ataxy). For example, mother can not take his baby on her arms. Spine is main canal of opposite afferentation about motor acts results. Also spine is a leading tract of excitement passage from CNS to motoneurons and associative neurons of lateral corns which form motor and vegetative reactions. One can tell that spine provides relatively primitive, simple, stereotypic activity. Spinal neurons excitability is low: exciting influence from brain is essential for their activity. Spine is responsible for most reflexes realization. Spinal reflexes are specifically changed or even disappeared at spine injury.

Spinal shock is observed after spine cutting. All spine functions disappear rapidly at this. Spinal reflector reactions are restored quickly in lower animals (in frogs – in 10-15 min), moreover, the lower alive organism is, the restoration time less is because they have developed subcortex comparatively to cortex. Cutted spine is practically not restored in human being. There are some theories of spinal shock. F.Goltz considered spinal shock as an irritation result. But Ch. Sherrington, G.Trendelenburgh also studied spinal shock at spine cooling blockade. Repeated cutting of spine lower than first cutting also does not cause spinal shock. All this indicates to the fact that spinal shock occurs due to spine separation from brain parts located above.

Microelectrode investigations demonstrated that motoneurons do not suffer at spinal shock. Associative neurons are injured due to which reactions to afferent stimuli are absent.

 

Paralyses belong to one of the most widely-spread motor disorders.

Main distinguishing features of central and peripheral paralyses are given in a table.

 

Paralysis type	Central or spastic	Peripheral, sluggish or atrophic
Injuries location	Cortex motor projectional area or pyramidal fascicles	Spine anterior corn, peripheral nerves anterior fascicles and anterior fibers
Paralysis distribution	More often diffused	More often limited
Muscles tone	Hypertony, spasticity	Hypotony, atrophy
Reflexes	Deep reflexes are increased, abdominal and plantar are decreased or lost	Deep and skin reflexes are decreased or lost
Pathological reflexes	Some of them are present	Absent
Conjugating movement	Present	Absent
Degeneration reaction	Absent	Present

 

Motor ways different floors injuries are accompanied by varies symptoms complexes:

1. Peripheral nerve injury causes peripheral paralysis in the area of muscles innervated by given nerve. Also sensitivity disorders are observed because biggest amount of nerves are mixed (with motor and sensor fibers).

2. Plexuses injuries lead to peripheral paralyses, pain and sensitivity disorders.

3. Spine anterior corns and anterior radixes (also cranial nerves motor nuclei) pathology causes only peripheral paralyses without pain and sensitivity disorders.

4. Spine lateral corn (with lateral cortico-spinal tract passing in it) injury causes diffused (central paralysis below from the injury locus); leg paralysis if thoracical part is injured; arm and leg central paralysis is observed if pyramidal fascicle is injured upper than cervical plexus. Also lateral corn injury is accompanied by noceoceptive and temperature sensitivity loosing on opposite side.

5. Spine transversal cutting gives lower extremities central paraplegia (pyramidal fascicles two-sided injury) – at location in thoracical part, or tetraplegia (all 4 extremities injury) – at upper (superior cervical injuries).

6. Brown-Sequard’ syndrome (spine half injury) – spastic paralysis and deep sensitivity disorders on the injury side and superficial sensitivity loosing on an opposite side.

7. Pyramidal fascicle injury in brain stem (pons cerebri, medulla oblongata, peduculi cerebri) gives central hemiplegia on opposite side because pyramidal ways are crossed below, on the boarder with spine. Usually cranial nerves are involved on the focus side. It creates the picture of so-called alternating (crossing) paralysis: cranial nerves injury on injury focus side, central hemiplegia – on opposite side.

8. Pyramidal fibers injury in internal capsule causes central hemiplegia (leg and arm on one side), facial musculature inferior part central paralysis on opposite side because cortico-nuclearis tract is also injured at the same time.

9. Motor projectional zone irritation causes epileptic fits (local or generalized).

 

2. Study aims:

To know: spine structure, reflectory function, role in motor and vegetative functions regulation, activity principles, pyramidal and extrapyramidal ways; muscular tone spinal regulation mechanisms; spinal reflexes study role for spine disorders topic diagnostics; spinal shock and its developmental mechanisms.

To be able to: assess tendineal reflexes existence and muscular tone in the investigated person.

 

3. Pre-auditory self-work materials.

3.1.Basic knowledge, skills, experiences, necessary for study the topic:

Subject	To know	To be able to
Histology	Spine histological structure	Recognize spinal cord preparation
Anatomy	Spine anatomical structure and conductive ways	Draw spine ascending and descending conductive ways
Biochemistry	Nervous tissue metabolism peculiarities
Neurology	Spine external and internal structure, superficial and deep reflexes; disorders of motor activity delt with spine.	Draw spine ascending and descending conductive ways; reproduce spine reflexes on the patient.

Topic content.

Spinal cord lies loosely in the vertebral canal. It extends from foramen magnum where it is continuous with medulla oblongata, above and up to the lower border of first lumbar vertebra below. The coverings of the spinal cord are membranous in nature and are called the meninges. The meninges are dura mater, pia mater and arachnoid mater. These meninges are responsible for protection and nourishment of the nervous tissues. The length of the spinal cord is about 45 cm in males and about 43 cm in females.

Spinal cord is cylindrical in shape with two spindle shaped swellings—the cervical and lumbar enlargements. These two portions of spinal cord innervate upper and lower extremities respectively. Below the lumbar enlargement, the spinal cord rapidly narrows to a cone shaped termination called conus medullaris. A slender non-nervous filament called filum terminale extends from conus medullaris downward to the fundus of the dural sac at the level of second sacral vertebra. Spinal cord is made up of 31 segments.

Cervical segments   = 8

Thoracic segments  = 12

Lumbar segments    = 5

Sacral segments         = 5

Coccygeal segment      =     1

In fact, the spinal cord is a continuous structure. The appearance of the segment is given by the 31 pairs of nerves arising from the spinal cord. Thus, the segments of spinal cord correspond to the 31 pairs of spinal nerves in a symmetrical manner.

Cervical nerves= 8

Thoracic nerves= 12

Lumbar nerves=   5

Sacral nerves=      5

Coccygeal nerve= 1

Each spinal nerve is formed by an anterior (ventral) root and a posterior (dorsal) root. Both the roots on either side leave the spinal cord and pass through the corresponding intervertebral foramina. The first cervical spinal nerves pass through the foramen between occipital bone and the first vertebra called atlas. The cervical and thoracic roots are shorter whereas, the lumbar and sacral roots are longer. The long nerves descend in dural sac to reach their respective intervertebral foramina. This bundle of descending roots surrounding the filum terminale resembles the tail of horse. Hence, it is called cauda equina.

On the anterior surface of spinal cord, there is a deep furrow known as anterior median fissure. The depth of this is about 3 mm. Lateral to the anterior median fissure on either side, there is a slight depression called the anterolateral sulcus. This denotes the exit of anterior nerve root. On the posterior aspect, there is a depression called posterior median sulcus. The posterior median sulcus is continuous with a thin glial partition called the posterior median septum. It extends inside the spinal cord for about 5 mm and reaches the gray matter. On either side, lateral to the posterior median sulcus, there is posterior intermediate sulcus. It is continuous with posterior intermediate septum, which extends for about 3 mm into the spinal cord. Lateral to the posterior intermediate sulcus, is the posterolateral sulcus. This denotes the entry of posterior nerve root.

 

INTERNAL STRUCTURES OF SPINAL CORD

Substance of spinal cord is divided into inner gray matter and outer white matter. Gray matter is the collection of nerve cell bodies, dendrites and parts of axons. It is placed centrally in the form of wings of the butterfly and it resembles the letter H. Exactly in the center of gray matter, there is a canal called the spinal canal. White matter is the collection of myelinated and non-myelinated nerve fibers (Fig. 18).

GRAY MATTER OF SPINAL CORD

Ventral and the dorsal portions of each lateral half of gray matter are called ventral (anterior) and dorsal (posterior) gray horns respectively. Lateral horns of gray matter are present in the thoracic segments and first two lumbar segments only. The part of the gray matter anterior to central canal is called the anterior gray commissure and the part of gray matter posterior to the central canal is called the posterior gray commissure.

Nerve cells present in the gray matter are multipolar type. Golgi I type cells with long axons are usually found in anterior horns and Golgi II type cells with short axons are found mostly in posterior horns. Axons of Golgi I type cells form the tracts of spinal cord and short axons from type II cells pass towards the anterior horn of same side or opposite side.

Neurons in Gray Matter of Spinal Cord

In the gray matter of spinal cord, the neurons are arranged in different groups. Following are the important neurons in the gray matter (Fig.19).