sensory system - phys.szote.u-szeged.hu · sensory systems i. detection of stimuli ii. transduction...

Sensory SystemPhysiology- Learning Objectives 92-93-94-95.

102.,103.104.,105.

Judit Rosta

2019 19. 04.

SENSORY SYSTEMS

I. Detection of stimuli

II. Transduction into neural signal

III. Neural processing

RECEPTORS

SENSORY AFFERENTS

CNS

Stimulus Receptor activation graded potential action potentialCNS Sensation

Steps of processing:

Sensory Processing?

Roles:

SENSORY SYSTEMS

RECEPTORS

Most special senses- receptor cellsSimple receptors Complex neural receptors

FREE NERVE ENDINGS

skin nociceptors

ENCAPSULATED NERVE ENDINGS

PRIMARY SENSORY

ENDINGS

Olfactoryreceptor cell

glomus cell

taste cell

Olfactorysensoryneuron

mechano-

receptors

hair cell

RECEPTORS

SPECIALIZED SENSORY CELLS

An example: Baroreceptors =

RECEPTORS

And how do receptors become excited?

= free-nerve-ending mechanoreceptors

Muscle spindle

Mechanoreceptor

Glomuscaroticum Chemoreceptor

RECEPTORS

opens ion channels, alters the

permeability of the membrane

Excitation of Receptors

How, say, a glomus cell works

SENSORY TRANSDUCTION

EPSP/IPSP vs. Action potential

Guyton and Hall- Textbook of Medical Phys

Receptor potential is produced in the Pacinian corpuscle

How stimulus be converted to electrical signal ?


4 properties of stimuli is encoded by the nervous system:

• INTENSITY

• DURATION

• LOCALIZATION

• MODALITY

SENSORY PROCESSING

receptor potentials encode the duration and intensity of stimuli

adequate stimulus encodes the nature of the stimulus


labeled line code

how can the CNS tell the difference

between heat and pressure…?

Modality (nature of the stimulus) is encoded by adequate stimulus

Treshold (perceptual threshold)

Adequate stimulus (stimulus intensity)

‚DIFFERENTIAL SENSITIVITY’ OF RECEPTORS

OsmoreceptorsPhotoreceptors…

SENSORY PROCESSING

Intensity is encoded by ‚population and frequency code’

SENSORY PROCESSING

Weber-Fechner Principle: stimulus intensity ~ sensation

Intensity is encoded by ‚population and frequency code’

SENSORY PROCESSING

mechanism of adaptation:

structural readjustment;

inactivation of Na+-channels;

chemical compound decomposition (e.g. photoreceptors)

Duration: receptors adapt to constant stimulus

Rapidly Adapting Receptors Detect Change in Stimulus

“Phasic Receptors

stimulated only

when the stimulus

strength changes

• receptors of the semicircular canals

• Pacinian corpuscle (few millisecs)

• olfactory neurons- (central mechanisms)

SENSORY PROCESSING

Slowly Adapting Receptors Detect Continuous

Stimulus Strength—The “Tonic” Receptors

Duration: receptors adapt to constant stimulus

• Nociceptors

• Baroreceptors- (2 days)

• some chemoreceptors

Tonic receptor Phasic receptor

Stimulus

‚Nonadapting’ receptors

SENSORY PROCESSING

Localization is encoded by a labeled line code

Topographic organization in cortex(somatotopy-refers to cortical representation)

stimulus is preserved once

the stimulus enters the

nervous system

SENSORY PROCESSING

(See later: Lateral inhibition)

Modality is encoded by a labeled line code

SENSORY PROCESSING

= specificity of nerve fibers for transmitting only one modality of sensation

Diameter of a nerve fiber is

correlated with its function

Classification: Lloyd-Hunt (vs. Erlanger-Gasser)

Ia, Ib-(~Aa): muscle spindle primer, Golgi-tendon organ

II-(Ab): muscle spindle sec., touch, mechanosensitive aff.

III (Ad): mechanosensitive and nociceptive aff.

IV-( C): nociceptive aff.

What advantage do myelinated axons provide?

SENSORY PROCESSING

Diameter of a nerve fiber is

correlated with its function

Somatosensory Axis

transmits sensory information from the

receptors of the entire body surface

and from some deep structures

som

atic

po

rtion

of th

e se

nso

ry system

Somatosensory System

The somatic senses:

exteroceptive,

visceral

and deep sensations

RECEPTORS

Golgi tendon

Somatosensory System PRIMARY SENSORY AFFERENTS

Head zones vs. Dermatome (Sherrington)

Thermo-Nociceptors

Mechanoreceptors

Proprioceptors

The somatic senses:

(1)mechanoreceptive somatic senses: tactile

and position sensations- stimulated by

mechanical displacement

(2) thermoreceptive senses - detect heat and

cold

(3)pain sense - activated by factors that

damage the tissues

Somatosensory System SENSES

ANTEROLATERAL

SPINOTHALAMIC ascending

DORSAL COLUMN

- MEDIAL LEMNISCUS ascending


a) nerve fibers

b) spatial orientation

c) transmitted information

b) high degree of spatial orientationb) much less spatial orientation

a) large, myelinateda) smaller myelinated/ unmyelinated

c) discrete types of mechanoreceptive sensationsc) broad spectrum of sensory modalities

PATHWAYS

ANTEROLATERAL

SPINOTHALAMIC ascending Nr.94.

DORSAL COLUMN

- MEDIAL LEMNISCUS ascending Nr.93.


1. pain,

2. warmth, cold,

3. itch,

4. crude tactile sensations,

5. sexual sensations

1. discriminating touch,

2. vibration,

3. proprioception *(kinesthesia= movement sense)

* = unconscious perception of movement and spatial orientation

DORSAL COLUMN ascending Nr.93.

The dorsal column- medial lemniscal pathway. Which of the following statements is FALSE: (E)

a) The pathway transmits ipsilateral tactile and proprioceptive informations

b) Nerve fibers entering the spinal cord synapse in the spinal cord and decussate immediately

to the opposite side

c) The second-order neurons decussate to the opposite side

d) Somatotopic arrangement preserved in the pathway

e) Dorsal pathway called as Goll and Burdach columns, (/gracilis et cuneatus)

f) Primary sensory neuronal axons form the ascending pathway

ANTEROLATERAL

(SPINOTHALAMIC) ascending Nr.94.

DORSAL COLUMN

-MEDIAL LEMNISCUS ascending Nr.93.

Discriminating (Epicritic) Touch, Pressure, and KinesthesiaTemperature, crude touch

Nerve fibers entering the dorsal columns pass uninterrupted up to the dorsal medulla

DORSAL COLUMN ascending Nr.93.

The dorsal column- medial lemniscal pathway. Which of the following statements is FALSE: (S)

a) The pathway transmits ipsilateral tactile and proprioceptive informations

b) Nerve fibers entering the spinal cord synapse in the spinal cord and decussate immediately

to the opposite side

c) The second-order neurons decussate to the opposite side

d) Somatotopic arrangement preserved in the pathway

e) Dorsal pathway called as Goll and Burdach columns, (/gracilis et cuneatus)

f) Primary sensory neuronal axons form the ascending pathway

(Fingers, tounge: 2 millim)

Two-point discrimination

Two separate pathways to the brainWithin the same secondary receptivefield, one signal goes to the brain

fewer convergence

DORSAL COLUMN ascending Nr.93. Discriminating touch

NOTE:

Receptor density vs.

Receptive field

Localization may be enhanced by lateral inhibition

= block lateral spread of the excitatory signal

Simultaneouslyapplied stimuli

NO lateralinhibition

lateralinhibition

DORSAL COLUMN ascending Nr.93. Discriminating touch

slow pain, C, laminae II-III (subst.gel.), SP

ANTEROLATERAL (SPINOTHALAMIC) ascending Nr.94.

fast pain, Ad, lamina-I, glu, localization

Fast vs. Slow pain?

mechanical or acute thermal pain stimuli

Chemical/persisting mechanical stimuli

Neospinothalamic tract

Paleospinothalamic

PAG

tectum

Form.ret.

Thalamus-intralaminar

arousal effect

ANTEROLATERAL (SPINOTHALAMIC) ascending Nr.94.Which of the following explains why individuals in severe pain have difficulty

sleeping without sedative medication?

a) The somatosensory cortical area for pain perception blocks the sleep-generating

circuits

b) Pain fibers entering the dorsal horn and the ascending pain pathways block the

sleep-generating circuits

c) Ascending pain pathways provide excitatory input to brain stem reticular

formation areas that are involved in maintenance of the alert, waking state

d) Neurotransmitters used in the slow pain pathway diffuse into neighboring cell

groups and generally raise the excitability of the brain

e) Neurotransmitters used in the fast pain pathway diffuse into neighboring cell

groups and block the sleep-generating circuits

Which of the following statements is correct? wide dynamic range neurons in the

anterolateral system: (S)

a) WDRs axons convey information from the cortex to spinal cord- (somatosensory

efferent control)

b) WDRs axons form the neospinothalamic tract

c) Transmit Nonspecific signals (multimodal afferents)

d) WDRs are responsible for specific transmission of distinct nociceptive signals


Which of the following statements is correct? wide dynamic range neurons in the

anterolateral system:

a) WDRs axons convey information from the cortex to spinal cord- (somatosensory

efferent control)

b) WDRs axons form the neospinothalamic tract

c) Transmit Nonspecific signals (multimodal afferents)

d) WDRs are responsible for specific transmission of distinct nociceptive signals


PAIN Nr.95.

NOCICEPTORS can not be occured in: (S)

a) bones

b) skin

c) brain parenchima

d) tooth pulp

Polymodal C, A delta fibers

Receptors- e.g. TRPV family

Stimulus: tissue damage

HYPERALGESIA: increased pain from a stimulus that

usually provokes pain

ALLODYNIA: pain due to a stimulus that does not

usually provoke pain

PARESTHESIA= abnormal sensation, no physical cause

ALGOGENIC (pain producing) factors:

•K+ from damaged cells

• Serotonin from activated thrombocytes

• Histamin from mast cells ( ITCH)

• tissue kallikrein

Slow pain is also referred to as burning, aching, or throbbing pain and can be

associated with which of the following?

a) Tissue damage or destruction

b) Inactivation of warmth receptors

c) Type Ad sensory fibers

d) Skin temperatures between 35°C and 45°C

e) Certain encapsulated receptors such as pacinian corpuscles

PAIN Nr.95.

PAIN Nr.95.

Receptor Sensitizationor Central Sensitization

Hyperalgesia, Allodynia

Neuropathic Pain and Inflammatory Pain

AXONREFLEX

Head zone vs. Dermatome ?

Which statement is TRUE?: (S)

a) A dermatome is a skin area innervated by a single peripheral nerve

b) Dermatomes can overlap

c) Head zones refer to cervical dermatomes

PAIN Nr.95.

cortical cell receives input from more than one kind of tissue the cortex may not be able to differentiate between them

PAIN Nr.95.


Referred Pain


Which statement is TRUE?: (S)

a) A dermatome is a skin area innervated by a single peripheral nerve

b) Dermatomes can overlap

c) Head zones refer to cervical dermatomes

PAIN Nr.95.

innervated by one dorsal root

Endogen Opioid System

Opioids: morfium (heroin)

Endorfin, Enkephalin, Dynorfin

m-receptor Antagonist-Naloxone

Opium (morphine): if receptors are

presented endogen ligands do exist?

PAIN Nr.95. Descending Pain Control

ANALGESICS:

opioid-effects (m-receptor agonists)

Serotonin release

feed back loop fromascending pain-sensitive tracts

Guyton and Hall- Textbook ok Medical Phys

PAG and Raphe nucl. stimulation

Block primary and secondary pain-sensitive neuron

Analgesia

Opioid effect in spinal cord

Fonyó –Élettan, Medicina (2011)


NOT CORRECT statement? (S)

a) Periaqueductal grey matter receives afferentation from anterolateral

ascending fibers

b) Stimulation of PAG results in a long-term analgesia

c) beta-endorphin is an endogenous ligand of the opioid-receptors

d) descending pain supression is partly due to the activation of nucl. raphe

magnus serotoninergic fibers

e) naloxon increases the analgesic effect of endogenous opioids


Which part of the gate theory is NOT confirmed experimentally: (S)

a) tactile stimuli (A-beta fibers) can decrease pain sensation even if tactile stimulation

is located more segment far from the site of nociceptive stimulus

b) pain transmission can be supressed by descending systems in the dorsal horn

c) myelinated, non-nociceptive afferents (A-beta) can presynaptically inhibit

nociceptive afferents and transmission of nociceptive signals

d) nociceptive inputs can be modulated in the spinal cord

PAIN Nr.95. GATE CONTROL THEORY

Wall and Melzack, 1965

• No signal: tonically active inhibitory

neurons („gate”) decrease

neurotransmission

• Activation of C-fiber DISINHIBITION (A.)

• Simultaneously activated beta-fiber

depresses nociceptive transmission (B.)

GATE CONTROL THEORY

A. B.

PAIN Nr.95.

Which part of the gate theory is NOT confirmed experimentally: (S)

a) tactile stimuli (A-beta fibers) can decrease pain sensation even if tactile stimulation

is located more segment far from the site of nociceptive stimulus

b) pain transmission can be supressed by descending systems in the dorsal horn

c) myelinated, non-nociceptive afferents (A-beta) can presynaptically inhibit

nociceptive afferents and transmission of nociceptive signals

d) nociceptive inputs can be modulated in the spinal cord

PAIN Nr.95. GATE CONTROL THEORY

BROWN-SEQUARD SYNDROM

TASTE SENSATION Nr.105.

Chandrashekar et al. 2006 Nature Rev.

Concentration-dependent sensitivity(high concentration- no specificity)

Correct statements in terms of taste sensation pathway: (M2)

a) primary afferents terminate in nucleus tractus solitarii

b) some axons exit nucleus tractus solitarii inducing vegetative reflexes

connected to the taste sensation

c) the primary cortical taste-sensing area is located in gyrus precentralis

d) taste pathway do not synapse in thalamus


Which of the following statements is correct? (S)

a) there are over ten well-defined distinct gustatory modalities

b) most, or possibly all taste buds are sensitive to all of the gustatory

modalities

c) the taste receptors are nerve endings of primary sensory neurons

d) the cortical taste area is found in the the postcentral gyrus

OLFACTORY SYSTEM Nr.104.

EPITOP MAP

sensory neurons express one-type receptor form one glomerulus

OLFACTORY SYSTEM Nr.104.

sensory neurons express one-type receptor form one glomerulus

mitral (M) and tufted(T) projecting neurons

Inhibitory interneurons: Periglomerular (PG)Granular (Gr)

Centrum:Prepyriform cortex, amygdala

paleocortex: do not reach thalamus

signal processing first occurs in the olfactory glomeruli

TONOTOPY

HEARING Nr. 104.

Perilympha vs. Endolympha (high K+, scala

media)

Protective reflex: musc.tensor

tympani,stapedius

Tonotopy: nucl.cochlearis, CGM

The contraction of stapedius and tensor tympanic muscles (S)

a) decrease a person's hearing sensitivity to his/her own voice

b) open the Eustachian tube during swallowing

c) move the ossicles of the middle ear, thereby promote transmission of

sound waves

d) protect the cochlea from high-frequency loud sounds

HEARING Nr. 104.

The contraction of stapedius and tensor tympanic muscles (S)

a) decrease a person's hearing sensitivity to his/her own voice

b) open the Eustachian tube during swallowing

c) move the ossicles of the middle ear, thereby promote transmission of

sound waves

d) protect the cochlea from high-frequency loud sounds

After cochlear nucl.- BINAURAL representation

Ggl. spirale

HEARING Nr. 104.

Brainstem Auditory Evoked Potential(BAEP) aka

Brainstem-evoked responseaudiometry (BERA)

Special EEG recordingVery sensitive to brainstempathologies affecting the auditorypathway!

OTOACUSTIC EMISSION

Hair cells efferent innervation(Nucl. Oliv. sup.)

HEARING Nr. 104.

Which one is CORRECT? Localization of a sound source:

A. Involves the evaluation of sound intensity differences between the two ears

B. Is based on the frequency difference between the two ears

HEARING Nr. 104.

sensory system - phys.szote.u-szeged.hu · sensory systems i. detection of stimuli ii. transduction...

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