SENSORY RECEPTORS

RECEPTORS

GATEWAY TO THE PERCEPTION

AND SENSATION

Registering of inputs, coding, integration

and adequate response

CLASSIFICATION OF THE RECEPTORS

According the type of the stimulus: According to function:

MECHANORECEPTORS Telereceptors

CHEMORECEPTORS Exteroreceptors

THERMORECEPTORS Proprioreceptors

PHOTORECEPTORS interoreceptors

NOCICEPTORS

Reception

Receptor – modified nerve or epithelial cell responsive to changes in external

or internal environment with the ability to code these changes as electrical potentials

Adequate stimulus – stimulus to which the receptor has lowest threshold – maximum

sensitivity

Transduction – transformation of the stimulus to membrane potential – to generator

potential– to action potential

Transmission – stimulus energies are transported to CNS in the form of action

potentials

Integration – sensory information is transported to CNS as frequency code (quantity

of the stimulus, quantity of environmental changes)

CLASSIFICATION OF

RECEPTORS

PHASIC– RAPIDLY ADAPTING

TONIC – SLOWLY ADAPTING

- NONADAPTING – PAIN

CONSTANT FIRING BY

CONSTANT STIMULUS

ACCOMODATION –

CHARACTERISTIC OF PHASIC

RECEPTORS

TYPES OF RECEPTORS

Sensory organs Sensory receptors – they convert the energy from outer

environment to action potentials (electicity) to be sent to the central nervous system and brain cortex for perception, sensation and integration.

QUALITY OF THE STIMULUS (modality) depends on the receptor localisation and the fibers that connect the receptor with the projection centres (cortex)

Adequate stimulus1) produces receptor (generator, local) potential

– does not propagate, is only local 2) After reaching threshold level of depolarisation the action

potential arises – propagate to the brain centres (projection areas)

Example: Once we see the light, means, that the threshold was rerached, the action potential was created and propagated to the brain representation areas

QUANTITY OF THE STIMULUS (MODALITY) depends on the frequency of action potentials that arrive in defined time duration to the projection areas in the brain cortex

SENSORY RECEPTORS

RECEPTORS

GATEWAY TO THE PERCEPTION

AND SENSATION

THE EYE

The light must pass through

various layers of nerve cells and

vessels before reaching

the photoreceptors on the back of

retina.

CORNEA, ANTERIOR AND

POSTERIOR

CHAMBERS, IRIS, PUPIL, LENS,

VITREOUS BODY, RETINA

THE PHOTORECEPTORS ARE

PLACED ON RETINA

COMPUTER

PERIMETRY

SKOTOMA

PERIMETRY – VISUAL FIELD IN GLAUCOMA

LEFT EYE

PERIMETERY

GLAUCOMAA CONDITION OF INCREASED

INTRAOCULAR PRESSURE

Auqeous humor maintains the

Intraoccular pressure within the

Anterior and posterior chambres.

The liquid is secreted is secreted

into the posterior chamber, flows

through the pupil and drains to the

canal of Schlemm.

ACCOMODATION

ACCOMODATION TRIAS

1. LENS ACCOMODATION

Contraction of cilliary muscle

decreases its diameter and loosens

Zonular fibers that makes the lens

thicker

2. MIOSIS

Constriction of the pupil enables the

light to concentrate to fovea centralis –

The site of the sharpest vision

3. CONVERGENCY OF THE BULBS

The eyes converge so as the image is

cast upon the fovea centralis

in both eyes

EMETROPY -

AMETROPY

AMETROPY1) AXIAL = THE LENGTH OF THE BULB IS INADEQUATE TO THE REFRACTION

2) REFRACTION = REFRACTION OF THE LENS IS INADEQUATE TO THE LENGTH

OF THE BULB

CATARACT

AFAKIA – the eye without the lens

NEARSIGHTEDNESS

Light rays focus in front

of the retina

FARSIGHTEDNESS

Light rays focus behind

the retina

Concave lens

Convex lens

IRIS - MIOSIS, MYDRIASIS

Iris – is made of muscles that enable dilation

or constriction of the pupil – opening in the iris

Pigments of iris give colour to the eyes

In dim light radially arranged smooth muscle fibers

are stimulated to contract by activation of

sympaticus – the consequence is DILATION

In bright light the circularly arranged muscle fibers

Are stimulated to contract by parasympaticus –

the consequence is CONSTRICTION

THE HUMAN EYE IS SENSITIVE TO ELECTROMAGNETIC

LIGHT OF CERTAIN WAVELENGTH 400 – 700 nm

= VISIBLE LIGHT SPECTRUM

ULTRAVIOLET LIGHT (X-RAYS, GAMMA RAYS)

INFRARED LIGHT (MICROWAVES, RADIO WAVES)

= NONVISIBLE LIGHT SPECTRUM

RODS – scotopic vision CONES – photopic vision

VISIONRETINAL RECEPTORS ARE SENSITIVE TO ELECTROMAGNETIC WAVES –

ADEQUATE STIMULI

Štruktúry oka

CONES – receptors for colour

vision – PHOTOPIC VISIONTRICHROMATIC THEORY

(YOUNG)

PRIMARY COLOURS – RED - 560 nm

- GREEN - 530 nm

- BLUE - 430 nm

COMPLEMENTARY (OPONENT)

COLOURSRED-GREEN,

BLUE YELLOW,

WHITE-BLACK

RODS – receptors for black and

white vision- SCOTOPIC VISION

HORIZONTAL CELLS

AMACRINE CELLS

PHOTORECEPTORS

BIPOLAR CELLS

GANGLION CELLS

EXAMINATION OF COLOUR PERCEPTION

Ishihara pseudoisochromatic charts – for detection red-green deficiency

Protanopia – red deficiency

Deuteranopia – green deficiency

Daltonism – red-green deficiency

Tritanopia – blue deficiency

This colours can be distiguishes also by

colour blind people

This colours cannnot be distinguished

by people with the impairment

of red - green colour perception

DISTRIBUTION OF RODS AND

CONES IN THE RETINA

Colour vision

Binocular disparity – the pictures are focused in both eyes on disparate sites of the retina

(not exactly on the same place in each eye) that causes shift. The consequence is 3D

vision

Larger difference causes DIPLOPIA no difference causes 2D vision

Monocular keys

Perspective

Moving paralax

STEREOSCOPIC

VISION

ADAPTATION TO DARK

RHODS

CONES

PHOTOPIC VISION

SCOTOPIC VISION

In dim light less intensity is needed

for light perception,

the adapatation to dark vision lasts

up to 20 minutes

Rods are responsible for dark vision

Red colour is almost not seen in dark

perceived as dark

Blue colour is better seen in dark

perceived as less dark

Dark vision is black and white vision

Ophtalmoscopic view of the retina(eye background)

Visual pathway. From nasal halves of the retina through

crossing (chiasma opticum), from temporal halves of the

retina uncrossed to the thalamus and through optic

radiation to primary visual cortex in the occipital lobe (BA 17)

RETINA – rods and cones

are the receptors enabling

vision (dark, light)

through bipolar and

ganglion cells - transmit the

potentials to optic nerve

SENSORY RECEPTORS

RECEPTORS

GATEWAY TO THE PERCEPTION

AND SENSATION

THE EAR

THE EAROUTER - AIR

MIDDLE - LIQUID

INNER - LIQUID

AUDITORY PATHWAY

From the receptors (hair cells) in the

organ of Corti through vestibulocochlear

nerve (VIII.) to thalamus and to primary

auditory cortex in temporal lobes

HEARING - SOUND RECEPTORY

MECHANORECEPTORS IN COCHLEA (INNER EAR)Scala vestibuli

Scala media – hair cells - mechanoreceptors

Scala tympani

PERCEPTION OF SOUND FREQUENCIES

ORGAN OF CORTI IN THE INNER EAR

Normal audiogram Perception hypoacusis

AUDIOMETRY

HEARING IMPAIRMENTS –

PERCEPTION DEAFNESS

due to impairments of

receptors, nerves or brain

centres – cochlear implates

AUDIOMETRYHEARING IMPAIRMENTS

CONDUCTION DEAFNESSDue to impairments of outer or middle ear

-otosclerosis

Blue line – hearing conducted by bone through mastoid process

Red line – hearing conducted by air through outer and inner,

this line normally lies more or less above the blue line

SENSORY RECEPTORS

RECEPTORS

GATEWAY TO THE PERCEPTION

AND SENSATION

THE PAIN

PAIN RECEPTORS AND TRANSMISSION OF PAIN STIMULI

Pain receptors are free nerve endings in the superficial lAyers of the skin and internal tissues

Excitation of receptors by mechanical thermal and chemical stimuli

Pain receptors are nonadapting for being apprised of damaging stimulus

– the increase of sensitivity – HYPERALGESIA

- the decrease of sensitivity – HYPOALGESIA

Dual transmission of pain signals – two separate pathways for transmitting pain signals

correspond to the two types of pain

FAST (SHARP) PAIN – mechanical or thermal stimulation

Transmission by fast A delta fibers (6-30 m/s)

Makes the person to know where is the pain and to react immediately to remove the particular

part of the body from the stimulus

THALAMUS and spreading of the singnals throughout the brain cortex

SLOW (CHRONIC) PAIN – chemical stimulation or chronic mechanical and thermal s.

Transmission by slow C fibers (0,5 – 2 m/s)

Becomes more and more painful over a period of time, intolerable suffering

Spinothalamic tract, thalamocortical tract to somatic sensory areas

PERCEPTION AND SENSATION OF PAIN

CLASIFICATION OF PAIN:

SURFACE (FROM SKIN RECEPTORS)

a) FAST (pricking)

Sharp pain, short duration, precise localization

via A delta fibersCauses: techykardia, BP increase, increase of blood sugar, sweating,

Decrease of GIT motility

b) SLOW (burns)

Less precise localization, persisting

via C fibers

DEEP

a) VISCERAL

(spasms a distension of smooth m.,tumors, inflamations)

Not precise but constant localization

– „referred pain“

Via C fibersCauses: bradykardia, hypotension (fainting), vomiting, sweating

b) SOMATIC (muscle and joint destruction)

Not precise localization

Via A delta and C fibers, release of substance P

QUANTIFICATION OF PAIN SENSATION AND PERCEPTION

Sensation of pain is uniform

Proof: dolorimeter developed by HARDY

(system of lenses, heat from the condensed light

centered on the black-coloured skin)

Unit – 1 JND (just noticeable difference)

0 JND – subthreshold pain

1 JND – threshold pain

21 JND – maximal (intolerable) pain

HYPOALGESIA– LOWER PERCEPTION OF PAIN

(acupuncture, acupressure, wounds in war)

ANALGESIA – NO PAIN PERCEPTION

(local, regional)

HYPERALGESIA – HIGHER PERCEPTION OF PAIN

(thalamic syndrom in postero-inferior infarction of the

thalamus – facilitation of pain transmission

REFERRED PAIN

CONVERGENCE THEORY

Less number of second order neurons

than afferent fibers from receptors –

convergence of stimuli from particular sites

of the skin and visceral organs on spinal

neurons (the heart and skin of the left arm)

- symptoms of myocardial infarction

FACILITATION THEORY

AP from visceral organ facilitate –

predepolarises the second order neuron,

weak stimulus from somatic structure

excite afferent neuron, on which both of them

converge, but the sensation comes from

somatic structure

REFERRED PAIN

PHANTOM PAINCNS identifies quality and location of pain via

receptors and ascending tracts, that transmit AP

CNS cannot distinguish AP from receptors

and those which were elicited on ascending fibers

MECHANISMS OF HYPOALGESIA

CENTRIFUGAL INHIBITION OF PAIN

Influence of second order neuron

via interneurons from reticular formation

descending collaterals inhibit

pain afferentations by decrease

of neurotransmitter on ascending neuron

– lower frequency of AP transmission to

thalamus

MECHANISM OF PRESYNAPTIC

INHIBITION - PAIN GATING

MECHANISMS OF HYPOALGESIA

Non-painful sensations e.g. from pressure

receptors in the skin overlay painful sensation

from the same skin locality, because the

nerve fibers of both converge

on the same afferent neuron

Mechanism:

- Collaterals of non-painful fibers form

axo-axonal synapse with “pain” fibers

and predepolarize them

- AP on pain fibre loses its previous

amplitude

- less neurotransmiter is released on

target neuron

- Transmission of AP to second order neuron

is less probable