The topic studied actuality. Nervous system diseases place one of the first places as for morbidity and lethality together with heart-vascular disorders and infectional pathology

Nervous system diseases place one of the first places as for morbidity and lethality together with heart-vascular disorders and infectional pathology. Nervous regulation mechanisms dysregulation leads to functions dyscoordination and organism desadaptation. That is why nervous regulation functioning mechanisms and regularities knowledge is so essential for doctor of any speciality. Oral mucosa is often injured at dental diseases. It is expressed on its sensory function.

Knowledge about CNS functions is widely used by doctors of any profile for patients treatment, diseases prevention and diagnostics. CNS state investigation is applied in labor physiology, sport physiology, cosmic physiology and other physiology chapters.

2. Study aims:

To know: reflectory theory main principles; the term “reflex”; reflexes and reflectory arcs types; reflectory arcs main parts; receptors classification, features.

To be able to: draw reflectory arc and designate its main elements; to explain excitement conductance regularities (receptor and generator potentials).

 

3. Pre-auditory self-work materials.

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

Subject	To know	To be able to
Medical biophysics	The explanation of reflex time assessment and irritation threshold determining diagnostic methods physiological basements	Manage the skills of work on electrical and medical devices
Anatomy	Analyze of information about central nervous system structure	Determine the topographical-anatomical interrelations of human organs and systems
Histology	Neurons and receptors membranes structure	Determine total-biological laws action expressions during human ontogenesis; draw membrane structure and analize its functions
Biochemistry	Analyzis of bioorganic chemicals correspondence to physiological functions	Analize enzymatic processes functioning in membranes.

 

Topic content.

Nervous and endocrine system controls all activities of body. Primarily, nervous system is divided into two parts:

1) central nervous system;

2) peripheral nervous system.

CENTRAL NERVOUS SYSTEM

It includes brain and spine. It is formed by neurons and supporting cells called neuroglia. The structures of brain and spinal cord are arranged in two layers namely grey matter and white matter. Grey matter is formed by nerve cell bodies and proximal parts of axons and dendrites. White matter contains nerve fibers.

PERIPHERAL NERVOUS SYSTEM

It is formed by neurons and their processes present in all regions of body. This consists of cranial nerves arising from brain and spinal nerves arising from spinal cord. This is again divided into two subgroups:

a) Somatic nervous system and

b) Autonomic nervous system.

Somatic Nervous System

It includes nerves supplying skeletal muscles. Somatic nervous system controls movements of body by acting on skeletal muscles.

Autonomic Nervous System

It is concerned with regulation of visceral or vegetative functions. So, it is called vegetative or involuntary nervous system with other words. Autonomic nervous system consists of three parts:

a) sympathetic,

b) parasympathetic and

c) metasympathetic.

 

The idea about the fact that organism having nervous system has possibility to react to external stimuli action by type “buttom-answer” was pronounced by French phylosophist Reneh Decart (XVII-th century).

The term “reflex” was introduced by Irgi Prochazka at the end of XVIII-th century.

The theory of reflectory activity was developed by:

I.M.Sechenov (inhibiting phenomenon discovery; to his point of view, all conscious and unconscious reactions are the reflectory ones).

I.P.Pavlov (science about conditioned reflexes).

Reflex action – 1) is a protective phenomenon which occurs in response to a change inside or outside of the body;

2) responce resulting from passage of a nerve impulse through a reflex arc.

Reflex arc:

It is composed of 5 components i.e.:

1) Afferent neuron: from receptor to CNS.

2) Inter Neuron (interneuron) or associative neuron: which lies inside CNS.

3) Synapse: which is the contact between 2 neurons.

4) Efferent Neuron: which comes from CNS upto the effector organ.

5) Efferent Organ: which may be:

– skeletal muscle.

– smooth muscle.

– glands.

Reflex arc types:

1. Simple – without associative link.

Complex – with associative link.

2. Monosynaptic (little amount).

Polysynaptic: tendinous, from skin flexors et al.

3. Somatic (animalous).

Vegetative (autonomic).

Reflex action properties:

1. The law of forward conduction.

2. Localization.

3. Summation:

– Temporal summation.

– Spatial summation.

4. Facilitation phenomenon.

5. Central fatigue phenomenon.

6. Central block phenomenon.

7. Central delay.

8. Fractionation phenomenon.

9. Irradiation phenomenon.

10. Recruitment and after discharge.

11. Reciprocal innervation.

12. Occlusion.

13. Central inhibiton.

14. Rebound phenomenon (feed-back reaction).

 

Reflexes classification:

І.According to reflectory arc formation:

Uncondioned or non-conditioned	Conditioned
Inborn and transmitted by hereditary to all individuals; they are present at birth. Examples: swallowing, breathing, salivation (sialorrhea or ptyalorhea).	They are acquired by organism throughout his life. They are absent at birth.
They are species characteristics.	Individual ones.
They have constant reflectory arcs and are closed at spine and brain stem level.	Reflectory arcs are temporary, they are closed at brain hemispheres level.
They are practically constant, non-changed.	Changeable, may appear and disappear.
They are realized in response to specific (adequate) irritation without any conditions.	They are realized in response to any irritation percepted by organism. They are formed on the base of unconditioned reflexes.
They are realized at level of spine, stem and subcortex nuclei.	They are formed by subcortex but are realized by cortex.
Biological role: they provide organism’s existance at first moments after birth and then they are the base of conditioned reflexes development.	Biological role: they encourage to organism adaptation to environmental conditions.

 

ІІ.According to reflectory arc components:

1. Monosynaptic.

2. Polysynaptic.

ІІІ.According to main arc neurons localization:

1. Spinal.

2. Stem:

– bulbar;

– of pons cerebri.

3. Cerebellar.

4. Mesencephalic.

5. Subcortical.

6. Cortical.

ІV.According to receptors character, the irritation of which causes given reflex:

1. Interoceptive.

2. Proprioceptive.

3. Exteroceptive or:

4. Nociceptive.

5. Visual.

6. Gustatory.

7. Auditory et al.

V.According to receptors localization:

1. Superficial:

A. Skin:

– cremasteric,

– planter,

– abdominal et al.

B. From mucous membranes:

– corneal;

– conjunctival et al.

2. Deep:

A. Muscular.

B. Tendinous:

– biceps jerk;

– triceps jerk;

– knee jerk;

– ankle jerk et al.

C. Periosteal:

– carpo-radial et al.

VI.According to biological significance:

1. Sexual.

2. Defensive.

3. Alimentary et al.

VII.According to principle - what part takes part in reflex realizing:

1. Somatic.

2. Vegetative.

VIII.According to ending result:

1. Alimentary.

2. Respiratory.

3. Cardiac.

4. Vessel.

5. Salivatory et al.

Receptor is a specialized structure at the terminoma (end) of afferent neurons. It responds to minor changes around it, inside or outside the body.

Receptors tasks:

1) giving information about stimulus nature;

2) giving information about stimulus force;

3) giving information about stimulus action time;

4) analysis can not be realized without them.

There are several approaches to the receptors classification (and, thus, several receptors types).

Receptors classification

I. According to the localization:

1. Exteroreceptors:

A. Skin

B. Visual mucosas (particularly of oral cavity)

2. Visceroreceptors:

A. Interoreceptors – in inner organs

B. Proprioreceptors – in motor apparatus and vestibular apparatus.

II. According to the activity character:

1. Exteroreceptors:

A. Contact:

a) tactile (cutaneous):

- tactile corpuscles for touch - Meissner's corpuscles and Merkel's discs;

- Pacinian corpuscles for pressure;

- Rouffinian bodies for vibration

b) temperature:

-free nervous terminals for heat;

-end bulb of Krause for cold;

-receptors of burning sensation

c)nociceptors (pain receptors):

-of skin;

-of mucosas (visual);

d) of taste (4):

 -for bitter;

-for sugar;

-for salty;

-for sour.

B. Distant or telereceptors - give response to stimuli arising away from the body:

a) photoreceptors (to light);

b) phonoreceptors (to sound);

c)olfactory;

d) temperature (if the irritation source is very powerful)

2. Interoreceptors:

A. Presso- (baroreceptors):

-in vessels;

-in sexual organs.

B. Chemo-receptors.

C. Nociceptors.

D. Temperature.

3. Proprioreceptors - give response to change in the position of different parts of the body:

A. Muscular (muscle spindle)

B. Tendinous (Golgi tendon organ)

C. Of ligaments

D. Of joints

E. Receptors in labyrinthine apparatus namely, crista ampullaris in semicircular canals and macula in utricle and saccule.

 

III. By the nature:

1. Mechanoreceptors.

2. Thermoreceptors.

3. Nociceptors.

4. Electromagnetic receptors (which detect light on the retina of an eye)

5. Chemoreceptors – they detect:

– taste in the mouth;

– smell in the nose;

– oxygen level in the artery blood;

– osmolality of the body fluids;

– carbon dioxide.

IV. According to structure:

1. Simple (primary-sensing) – nerve ending:

– olfactory;

– cutaneous.

2. Complex (secondary-sensing) – they have a special receptor cell in front of nerve ending:

– photo-;

– phono-.

Fig.16.Cutaneous receptors.