THEME 2: PHYSIOLOGICAL AND PSYCHOLOGICAL FACTORS OF THE VITAL FUNCTIONS SAFETY OF A MODERN MAN

The present stage of sensory physiology associated with the names such scientists as Ivan Mikhailovich Sechenov (1829-1905) and Ivan Petrovich Pavlov (1849-1936). I.P. Pavlov continued, I.M. Sechenov's studies of the brain reflexes, creating a doctrine of the analyzers (энэлайзес) as a combination of neuro-receptor structures.

Analyzers (sensory organs, afferent system, sensory systems) - are a set of interacting structures of the peripheral and central nervous systems, which carry the perception and analysis of phenomena occurring in the environment and within the organism.

All analyzers are similar by their structure (receptor - nerve - brain).

In modern physiology according to the anatomical unity and features there are eight kinds of analyzers:

exteroceptive, which get the information from environment (visual, acoustical, tactile, painful, temperature, gustatory, rhinal (райнел)

and interoceptive, which get the information from inner organs and systems.

Receptors are specialized nerve cells, which have selective sensitivity to the impact of certain factors.

According to the psycho-physiological classification of receptors, they can be divided by their nature of sensations into:

visual,  hearing,  olfactory,   tactile,  pain,  receptors of body position (proprioreceptors and vestibular reсeptors).

Morphologically receptors can be in a form of simple nerve endings (1) or to have the form of cones and rods (2), balls (3), spirals, plates etc.

Depending on the nature of the stimulus receptors are divided into several groups:Mechanoreceptors, which are peripheral parts of the somatic, muscular and vestibular systems.

Thermoreceptors which perceive the temperature inside the body and in the surrounding environment, and they unite skin receptors and internal organs, as well as central heat-sensitive neurons in the cerebral cortex.

vestibular receptors tactile skin receptors

End bulb (колбы Краузе)of mucous and serous membranes

Chemoreceptors  respond to impact of chemicals and include taste and smell receptors, vascular and tissue receptors ( for example, glucoreceptors perceiving  the change in blood sugar levels).

Photoreceptors  perceive light stimuli.

smell receptors

Photoreceptors of the retina  – rods and cones

Adaptation of receptors

Prolonged exposure to the stimulus adapts the receptor and its sensitivity is reduced, however, when the effect of constant stimulus  stopped, the reception sensitivity is growing again.

There is no common law for receptor adaptation and each sensory system can have its own combination of factors determining changes in the excitation process in the analyzer. There are  rapidly adapting (tactile, baroreceptors) and slowly adapting receptors chemoreceptors,  photoreceptors).

Vestibuloreceptory and proprioceptors are not adapted.

Basic characteristics of the analyzers

All analyzers due to its same type of structure have a common physiological characteristics.

The main characteristic of an analyzer is its sensitivity, which provides an ability of a living organism to take action of the stimulus coming from external or internal environment.

There’s a difference between absolute and differential limits of sensation.

The absolute threshold of sensation is the minimal strength of stimulus that can cause a reaction.

The differential threshold of sensation is the minimal amount that has to be changed to cause a change in response.

A period of time from the beginning of the impact of the stimulus until appearing of the sensation is called the latent period.(6)

Life safety in the system of human interaction with the environment deals with the main hazards such as visual, auditory and cutaneous analyzers.

Visual Analyzer

Visual Analyzer provides more than 80-90% of information about the external world.

It has the following features:

1. Visual acuity is an ability to perceive fine details of eye objects at great distances or to differ between the two points that are visible.

2. Field of view is an angular space that is visible by an eye, in conditions of a fixed gaze and fixed head.

The average person has a field of view 55 °-up, 60 °-down 90 ° - outside and 60 ° - inside, which is true only for achromatic vision (due to the fact that there aren't any receptors that can distinguish colours on the edges of the retinal. (20)

coloursizes of field of view

up down outside inside

white 55º 60º 90º 60º

blue 50º 50º 70º 50º

red 40º 40º 50º 40º

green 30º 30º 30º 30º

A man sees with two eyes almost 180 ° in front of him. Different animals have different fields of view.

Some birds have a field of view of almost 360 °.

owlparrot

duck

lateral vision

binocular vision

Factors that cause decrease of the field of view:- Reduction of light- Some diseases (glaucoma)- Defects in blood vessels- Lack of oxygen.Some people have boundaries of the field of view depend on anatomical factors (size and shape of the nose, eyelids, etc).

Field of view:а - at stationary condition; b - while moving.(22)

3. Sensitivity to Luminance contrast it is an important indicator of the visual analyzer.Its threshold is the smallest difference in perceived brightness. It depends on the level of brightness in the visual field and its uniformity.Optimal threshold takes place under natural light.

4. Color perception is an ability to distinguish colors of objects. 

Colour vision may change under the influence of taking certain medications and under the influence of chemicals.

Barbiturates(soporific and sedative drugs)

Cocaine

Caffeine, coffee, coca-cola

Tobacco

Acoustic analyzer

Acoustic analyzer is a set of the structures providing perception of sound information and transforming it into nervous pulses. There are distinguished such sections of an acoustic analyzer:The peripheral section is formed by the acoustical receptors which are situated in a Corti organ of an internal ear; - conducting section (an acoustical nerve); - the central section (an acoustical zone of a cortex of big hemispheres).

The important characteristic of hearing is its acuteness or acoustical sensitivity. It is characterized by the minimal amount of sound stimulus causing acoustical sensation.The human ear is capable to perceive sound fluctuations by frequency from 16 up to 20000 hertz (Hz).The human ear perceives not only different frequency of a sound, but intensity of a sound (dB).

Intensity of a sound (dB)

Leaf rustle 15

Ordinary talk 50-60

Train 95

Intensive moving 100

Helicopter 110

Jet plane takeoff 130 (ear pain)

Rocket takeoff 145 (contusion)

The loudest sound, has been created within the military tests (USA), equaled more then 210 decibels (400 thousand watt).

Skin analyzer

One of the major functions of skin is perceptive. In a skin there is a huge amount of receptors perceiving various external stimulation: - pain, - warm, - cold, - pressure.

On 1 square cm of a skin settles down about200 pain receptors, 20 cold, 5 thermal and 25 perceiving pressure.

Homeostasis and adaptation

A human is compelled to adapt constantly to changing conditions of an environment, keeping the organism from destruction under action of external factors. Protective adaptive reactions have three stages.

I. Normal physiological reaction (homeostasis);Homeostasis is a relative dynamic constancy of structure and properties of the

internal environment and stability of the basic physiological functions of an organism.

II. Normal adaptable changes.

Intervention of external factors in a condition of a homeostasis results in adaptive reorganization of an organism as a result of which one or several functional systems compensate possible abnormalities and restore balance.

III. Pathophysiological adaptable changes.

On a background of decreasing of reserve abilities of an organism, the system of adaptation is enabled to provide necessary boost of functional activity of an organism.

Stress responseScience of stress was introduced by canadian doctor and biologist Hans Selye

(1907-1982). Based on Selye’s studies different forms of stress were defined. Also the

concept of psychological stress was formulated.Stress - non-specific (general) reaction to the effects (physical or

psychological) that impair its homeostasis.In medicine, physiology, psychology distinguish positive and negative forms

of stress.Stress x 2

Acute Stress (Eustress)- alarm reaction- recovery follows quickly- may save your lifeChronic Stress (Distress)- constant/repeated stress- no recovery- impairs immune response/general health.

Stages of Stress Response1. Behavioral

- ascertain stimuli – visual, tactile, olfactory.

Stages cont.2. Autonomic

- EPI release (adrenaline)- increase responses- inhibit unnecessary functions.

3. Endocrine- Aldosterone release

*water retention for increase BP- Cortisol release

*glucose production*protein catabolism*increase vessel sensitivity*reinforce autonomic response*decrease inflammation responcse

4. Exhaustion- Body is at depleted state- Must rest in order to recover- If stress continues without recovery or exhaustion

Illness Perpetuation of illness Death.

Stress Paradox Stress can be the thing that pushes the body into disease Stress resets homeostasis in body and must recover or exhaust to

return to original homeostasis levels Added stress of disease perpetuates the illness by further weakening

the immune system.

So stress is the main instrument of physical and psychic adaptation which provides safety of vital activity.