PHYSIOLOGY DEPARTMENTPHYSIOLOGY DEPARTMENT

Ass. Prof. VASTYANOV Rooslan

SENSORY SYSTEMS #1SENSORY SYSTEMS #1

GENERAL PROPERTIES OF SENSORY SYSTEMS

PLEASE,

MOBILESSHOULDBE OFF

Reception, perception and transmission of information

Reception, perception and transmission of information

ANALYZER -

it`s specific sensory (receptory) system of neurons that consist of:

•Peripheral part - receptors

•Conductive part – pathways and afferent neurons

•Central part – cerebral cortex

Classification of sensation organs:

• Vision organs• Hearing organs• Eqvilibrium organs• Smell organs• Taste organs• Viscerosensation • Touch organs• Temperature sensation• Pain sensation• Posture sensation

somato- sensory analyzer

GENERAL STRUCTURE OF ANALYZERS

- NEURAL ENDINGS

- RECEPTOR CELLS

- PARTICULARIZED SENSATION ORGANS

PERIFERAL PART

CONDUCTIVE PART

CENTRAL PART

- CONDUCTIVE WAYS

- CEREBRAL STRUCTURES

Main principles of the analyzers composition

• Each analyser has a lot of neurons levels that are related by the pathways

• Each level has a lot of neuronal fibers – pathways

• Each level has a different amount of the cells – they work according principles of convergence and divergens

• Each level has a different function: peripheral part – reception, middle part –conduction, central part – analyse.

MAIN PROPERTIES OF THE ANALYSERS:

• Detection of the stimuli by receptors• Ability to form a receptor (generator)

potential• Perception of the stimulies according to a

definite increasing force of the irritation.• Transmission (spreading) of the stimulies.• Conversion information into a special system

– code• Adaptation to stimulies• Cortical and subcortical information analyse

2. Peripheral part of analyzers

ANALYZER PERIPHERAL PART

•Receptors – specific neural

cells or ending of neural

fibers that are adaptated

to perception of irritation.

Receptor classification #1 1. By localization: - external- - internal: - contact (taste, touch) - visceroreceptors- distance (visual, hearing) - vestibuloreceptors

(equilibrium) - proprioreceptors (muscles) - tissue receptors - vessels receptors2. By nature of irritation: 3. By adaptation:

- baroreceptors (tension) - high adaptation speed- chemoreceptors - low adaptation speed- thermoreceptors - nonadaptive receptors- mechanoreceptors 4. By stimulies

specifity:- photoreceptors - adequate

- inadequate

Receptor classification #2

5. By specificity of irritation perception: - specific receptors - nonspecific receptors 6. By mechanism of excitation generating:

- Primary perceptive receptors (generate GP)- Secondary perceptive receptors (generate RP)7. By ability to percept of irritation types: - Monomodal receptors - Polymodal receptors

MAIN RECEPTOR PROPERTIES

1. EXCITABILITY – ability to excitation generation (RP, GP, AP)

2.   SPECIFICITY – ability to percept only specific irritation

3. Ability to TRANSFORMATE specific irritation in electric impulse (coding)

4. Ability to ADAPTATION – increasing of irritation threshold

MAIN RECEPTOR FUNCTIONS

•Perception of the irritation

•Excitation generating

•Primary analysis of excitation

•Coding information of irritation parameters

MECHANISM OF RECEPTOR EXCITATION

• Irritation impulse + receptor →↑membrane permeability for Na→ depolarization (repolarization is in photoreceptors!) and

- generator potential (GP) develops in primary receptors

- receptor potential (RP) develops in secondary receptors→ RP+RP+RP=GP → GP+GP+GP=AP

Stimulus, sensor and action potential relationships

Graphical representation of the sensory nerve activity in case of stimuli applying of

different intensities and durations

General properties of local potentials (LP)

- it doesn’t spread along the nerve fibers

- it works according to law of gradation

- it has ability to summation- it hasn’t refractory period- short-time duration of LP (but

RP has long-time duration)

PRIMARY ANALYSIS IS PROVIDED for

- Different areas of receptive fields, - Specific perception of irritation by

receptors - Different levels of receptor excitations - Different levels of receptors adaptation, - Different time of excitation development

in receptors, - Mechanisms of feed-back connection

between receptors and neural structures

Coding information

• - it`s a conversion information into a

specific system – code.Transmission of impulses is effected

by a binary code. Presence of an impulse – is 1, its absence equals to 0.

The information about the stimulies is transmitted in the form of individual groups or “volleys” of impulses.

The amplitude and duration of the individual impulses passing identical along the same fiber, but the frequency and number of impulses in volley may be different.

1. By change of number of AP: If the sound has frequency less then 1000 Hz, the cells form equal amount of AP. If the sound has frequency more then 1000 Hz, the cells start to code impulses.

2. By change of impulses speed transmission

Types of information coding

The scheme of stimulus processing and information coding

RECEPTORS ADAPTATION

it’s the increasing of irritation threshold under the specific impulse action, which acts a long period of time

Adaptation mechanisms: - ↓amount of working receptors- ↓ RP amplitude- ↓ frequency of impulse conduction- change of neural centres condition

The scheme of adaptation of slow- and fast-adapting receptors on dependence with their stimulation

3. Conductive part of analyzers

COMPOSITION OF ANALYSERS CONDUCTIVE PART

3 NEURONS:- dendrites of 1-st sensor neurons- axon of 1-st sensor neurons- axon of 2-d sensor neurons (Т-neurons) - axon of 3-d sensor neurons Somato-sensor analyzer: 1-st neuron – spinal ganglies 2-nd neuron – cornu posterior of spinal cord, Goll's and Burdach's nuclei 3-d neuron – thalamus specific nuclei

MAIN FUNCTIONS of ANALYZERS CONDUCTIVE PART

- Excitation conduction

- Secondary analysis of

irritation

- Encoding irritation

information

LAWS OF IMPULSES CONDUCTION in NERVES

- The law of anatomical and physiological continuity of a nerve

- The law of two-way conduction - The law of isolated conduction along a nerve

4. Central part of analyzers

ANALYSER CENTRAL PART Subcortical information

analyse

Cortical information analysis

Motor areas involved with the control of voluntary muscles

Motor speech area (Broca`s area)

Sensory areas involved with cutaneous and other sensesUnderstanding speech, using word Parietal lobe

General interpretative area

Motor and sensory gyrus

Parietal lobe

Sensory area

Central sulcus

Motor and sensory areas

trunkneck

Upper arm

Lower arm

Hand, fingers,and thumbUpper face

Sensory areasMotor areas

FUNCTIONS OF ANALYSERS CENTRAL

PART- tertiary analisis of excitation

- transformation of excitation into sensation

- formation of perceptible image

- memorization of perceptible image

PARAMETERS OF ANALYSIS

• Intensity threshold (force) of irritation – it’s min force of irritation, caused sensation

• Differential threshold of irritation – it’s min force increment of irritation, caused sensation

• Spatial threshold of irritation – it’s min distance between two irritation stimulus, that permits these two stimulus to percept separately The less receptive field the less spatial threshold

• Temporal threshold – it’s min time between two irritation stimulus, that permits these two stimulus to percept separately

Perception of the stimulies according a definite increasing proportion

• 1834 y. – Weber formulated the law that states: S= a log R + b

Receptors in organism percept difference force of the irritation if the index between stimulies increases according a definite proportion

100g – 3g200g – 6g

600g – 18g

4. Proprioceptive sensory system

MechanoreceptorsMechanoreceptors

Mechanical sensationMechanical sensationThe pacinian corpuscle is a

very rapidly adapting receptorwith a large receptive field that is used to encode high-frequency

(100–400 Hz) vibratory sensation.

The receptor is located on the end of a group B myelinated fiber, which is inser-

ted into an onion-like lamellar capsule

The pacinian corpuscle is a very rapidly adapting receptor

with a large receptive field that is used to encode high-frequency

(100–400 Hz) vibratory sensation.

The receptor is located on the end of a group B myelinated fiber, which is inser-

ted into an onion-like lamellar capsule

The spindle-shaped Ruffini's corpuscle is a slowly adapting receptor that encodes pressure. It has a large

receptive field that is used to encode the magnitude of a stimulus.

The receptor is located on the terminal of a group B axon that is covered by a liquid-filled collagen capsule. Collagen

strands within the capsule make contact with the nerve fiber and the overlying skin.

The spindle-shaped Ruffini's corpuscle is a slowly adapting receptor that encodes pressure. It has a large

receptive field that is used to encode the magnitude of a stimulus.

The receptor is located on the terminal of a group B axon that is covered by a liquid-filled collagen capsule. Collagen

strands within the capsule make contact with the nerve fiber and the overlying skin.

Meissner's corpuscle is a rapidly adapting receptor that participates

in the touch sensation and low-frequency (10–100 Hz) vibration.

The receptor is located at the end of a

single group B afferent fiber that is inserted into a small capsule.

Meissner's corpuscle is a rapidly adapting receptor that participates

in the touch sensation and low-frequency (10–100 Hz) vibration.

The receptor is located at the end of a

single group B afferent fiber that is inserted into a small capsule.

Merkel’s disk is a slowly adapting receptor with a small receptive field

that is also used to encode the touch sensation.

The epithelial sensory cells form synaptic

connections with branches of a single group B afferent fiber.

Merkel’s disk is a slowly adapting receptor with a small receptive field

that is also used to encode the touch sensation.

The epithelial sensory cells form synaptic

connections with branches of a single group B afferent fiber.

Skin receptors localizationSkin receptors localization