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Adequate Stimulus

Adequate Stimulus

SensesSenses 11

Introduction to of of Sense of

Practical tasks Otoscopy Tests with tuning forks Audiometry

http://t2.gstatic.com/images?q=tbn:ANd9GcQLxYEdEk8lRTuToHhhLhGTIA Examination of nystagmus OfpOUYUkXwbLaC9dD3FYcpm2XA Senses • gather the stimuli occurring in our external or internal environment, transmit this information to the CNS, process it and allow for sensation an • crucial for survival: – provide necessary warning to avoid injury, e.g. heat, seeing danger – external receptors – to maintain homeostasis – internal receptors – make it possible for the body to respond to stimuli

• special senses • general (somatic) senses – vision – touch – hearing – temperature – – – smell – balance

Each of the principal types of sensation that can be experienced pain, touch, sight, sound, taste, etc. is called a modality of sensation. Sensory receptors • specialized cells or free nerve endings • sensitive to various forms of energy (energy = ) • stimulation elicits receptor potential (change in membrane potential – depolarization or hyperpolarizing) • receptors detect also the intensity of a stimulus • convert the stimulus to nerve impulses ()

Distribution of receptors

- receptors of special senses – grouped in specific areas of the body or in complex organs - general sense receptors – distributed throughout the body – skin, mucosa, joints, muscles, tendons, viscera Classification of receptors

• – activated by mechanical stimuli -deformation, stretching, changing position of the receptor (e.g. touch-skin receptors, hearing, stretch of a muscle, receptors in vessel - blood pressure)

• – activated by chemical substances (smell, taste)

• – activated by heat or cold

• Photoreceptors – activated by light (vision)

• – activated by intense stimuli of any type that result in tissue damage, produced sensation is pain Stimulus  a change in external or internal environment (a form of environmental energy) that stimulates the receptor

 adequate stimulus - type of stimulus (energy) that a receptor is specialised for - receptors are specialised on one type of energy (except nociceptors): light – vision chemical substances – smell, taste, etc.

- even if a receptor can be stimulated also by other type of energy, it is most sensitive to the adequate stimulus, i.e. to a small intensity of stimulus  (minimum) threshold intensity of a stimulus – minimum strength of a stimulus that triggers an action potential in the 's axons (i.e. it is the weakest stimulus that can be reliably detected)

 receptor potential - a change in membrane potential a of a sensory receptor - graded response depending on the strength of the stimulus - is spread with a decrement - if sufficiently strong to reach axon, it is transduced by a nerve as action potential Sensory nerve • conducts nerve impulses to central nerv. system • usually 3 neurons form a sensory pathway

Central nervous system • sensory projection - centres for individual senses • primary cortex (for vision, hearing...) – I can see, hear...something • secondary cortex – I can recognize what I see..hear • tertiary cortex (association) – complex sensation (colour+shape+taste+memories)

Response to a sensory stimulus 1. reflex – quick, stereotype, involuntary response to a stimulus 2. conscious behaviour (voluntary motor activity, memory, etc.) http://t2.gstatic.com/images?q=tbn:ANd9GcQLxYEdEk8lR TuToHhhLhGTIAOfpOUYUkXwbLaC9dD3FYcpm2XA Sense of hearing - The

Sound • vibrations (compression/decompression) of air (water or solids) • audible frequency: 20 – 20 000 Hz (Hertz) • adequate stimulus for sense of hearing • pitch – determined by frequency of the waves • loudness determined by height of the waves

Pitch • high tone • deep tone

Loudness • quiet sound • loud sound - the acoustic waves exert pressure - decibel – unit of loudness (derived as logarithm of acoustic pressure)

0 dB – threshold of hearing - less sensitive people – slightly above 0 dB, - people with very sensitive sense of hearing – can detect even negative dB

60 dB – speech > 100 dB – damage of the ear > 120 dB – pain

• sensitivity of the ear to sound depends on the frequency of sound waves • maximum sensitivity is in the range 1000 - 4000 Hz (frequency of speech) = threshold ~ 0 dB • the ear is less sensitive to lower and higher frequencies than 1000-4000 Hz • the more higher /lower frequency - the louder the sound must be in order to be detectable Function of the external ear

• auricle (pinna) – captures the sound waves and gives them appropriate direction

• ear canal – conducts the sound • tympanic membrane

– separates external ear from middle ear

– sound causes its oscillation http://www.neuroreille.com/promenade/english/ear/exear/e_oreille_ext.gif Function of the middle ear

- cavity in os petrosum, filled with air - chain of 3 ossicles - malleus - hammer - incus - anvil - stapes – stirrup

- malleus is connected to the eardrum http://www.ohiohealth.com/mayo/images/image_popup/ans7_inside_ear.jpg - stapes is connected to oval window (membrane separating middle/)

- ossicles transduce the sound from outer into the inner ear and amplify it: - area (eardrum/oval window) - pressure amplification - hearing is improved by approx 25 dB - m. stapedius, m. tensor tympani - loud sound causes their reflex contraction - dampen movements of the ossicles - protect the ear

- middle ear - communicates with pharynx by Eustachian tube - balance of pressure on both sides of the eardrum (e.g. in airplane)

- risk of infection spreading !!! - from nasopharynx into middle ear - easily in children Function of inner ear Components: • cochlea – sense of hearing • vestibule, –

Cochlea • a spiral shaped organ (2 ¾ turns)

• inside - organ of Corti with sensory receptors - hair cells

http://www.nidcd.nih.gov/staticresources/images/electrode_array.jpg http://www.ohiohealth.com/mayo/images/image_popup/ans7_inside_ear.jpg Inner ear - 3 chambers A/ - filled with fluid - perilymph 1. scala vestibuli 2. scala tympani B/ membranaceous labyrinth - scala media - filled with fluid -

Reissner´s membrane Cross-section through one of the turns of cochlea – separates scala vestibuli from scala media

Basilar membrane – separates scala tympani from scala media

Inside scala media • organ of Corti • receptor cells = hair cells, their cilia are covered by tectorial membrane

https://ccrma.stanford.edu/realsimple/psychoacoustics/img5.png • sound waves cause fluid movement in scala vestibuli • fluid movement is transduced into the fluid of scala media and s.tympani • basilar membrane (soft) and tectorial membrane (rigid) become displaced • this causes cilia to move – this movement elicits receptor potential

https://ccrma.stanford.edu/realsimple/psychoacoustics/img5.png http://www.colorado.edu/intphys/Class/IPHY3730/image/10-21.jpg Cochlea „unfolded“ - tones produce travelling wave on basilar membrane - the farther from oval window – the less stiff the membrane - the wave travels to the point with maximum resonance (then dies out) - the higher the tone the closer the maximum resonance point

• low tones/low frequencies - maximum resonance close to apex

• middle frequencies - middle of the basilar membrane

• high frequencies - max resonance close to the oval window Air conduction of sound - normal sound transmitting in healthy people • external ear • middle ear • internal ear

Bone conduction of the sound • sound causes vibration of bones – os petrosum • vibration of the bones is transmitted directly to inner ear

• significant way of sound transmitting if the air conduction does not work properly (e.g. inflammation of the middle ear) • higher threshold – louder sound necessary in order to hear Central auditory pathway - we can hear the soud when signal (AP) arrives to brain cortex

1. cochlear afferent fibres = n. statoacusticus

- synapses in ventral and dorsal cochlear nuclei (med.oblongata/)

2. synapse in superior olive (med. oblongata/pons) lemniscus lateralis (ipsi, contra) to colliculi inferiores ()

3. corpus geniculatum mediale () =radiatio acustica

cortex – temporal lobe - primary - secondary auditory cortex - tertiary cortex (association) OtoscopyOtoscopy -- examinationexamination ofof externalexternal earear

Principle - examination of ear canal and eardrum using otoscope - otoscope – a device with speculum (ear mirror) and light source that is inserted into ear canal - ear canal and eardrum is visually examined

Procedure: - the patient is sitting sideway – better access to ear - switch the light in otoscope on - pull the auricle – to lateral + cranial + dorsal direction – the ear canal is straightened - insert slowly speculum of the otoscope into the ear - observe the appearance of ear canal and eardrum (light reflex, try to distinguish imprints of malleus - stria mallearis and prominentia mallearis) Results  describe your observation: - skin of ear canal – pink / red, inflamed with rash - presence of cerumen (yellow wax) – normal /excessive quantity - presence of pus, blood - appearance of the eardrum smooth, grey /red-inflamed, perforated

Conclusion:  is the result of examination normal? EarEar teststests withwith tuningtuning forksforks

Examination of • air conduction of sound • bone conduction of sound

Allow to distinguish 1. conduction disorders - external ear - middle ear

2. perception disorders - inner ear - sensory pathway - brain centre for hearing Rinné test • sound a tuning fork with a hammer • place it on the processus mastoideus of the patient (bone conduction) • in the moment as the patient stops to hear the sound, put the fork at patient's pinna (air conduction)

• in case that the patient cannot hear sound, http://www.aafp.org/afp/20000501/2749_f4.jpg repeat the test in reverse order

• record the time – of bone conduction (BC) - how long could the patient hear a sound conducted by bone – of total conduction (TC) how long could the patient hear a sound conducted by bone + air

Normal result: TC:BC = 2:1 Rinné positive (R+) Abnormal result: BC>AC Rinné negative (R-) AC= BC Rinné inconclusive (R±) Schwabach test • sound a tuning fork • place it on the processus mastoideus of the patient • in the moment as the patient stops to hear the sound, put the fork on processus mastoideus of the doctor • normally the doctor should not hear any sound patient • repeat the test in reverse order (doctor-patient) • normally the patient should not hear any sound

Normal result: • Schwabach normal

Abnormal result: doctor • Schwabach shortened – the patient can hear the sound for shorter time then the doctor • Schwabach prolonged – the patient can hear http://www.aafp.org/afp/20000501/2749_f4.jpg the sound for longer time then the doctor Weber´s test • sound a tuning fork • put it in the middle of the patient´s forehead • the patient is asked to say on which side he can hear the sound louder (right, left)

http://www.aafp.org/afp/20000501/2749_f4.jpg

Normal result: • the loudness is the same on both sides (←W→)

Abnormal result: • louder at one side = lateralization • e.g. if louder on the right = lateralization to the right • Conclusion: Resume and evaluate results of all tests together

normal hearing conduction disorder perception disorder

R+ R- R+, R±

Schwabach normal Schwabach prolonged Schwabach shortened

W lateralization to the W lateralization to the ←W→ sick side healthy side AudiometryAudiometry

Principle • sensitivity of the ear to sound depends on the frequency of sound waves

• maximum sensitivity is in the range 1000 - 4000 Hz (frequency of speech) = threshold ~ 0 dB

• the ear is less sensitive to lower and higher frequencies than 1000-4000 Hz

• the more higher /lower frequency - the louder the sound must be in order to be detectable Procedure • each ear is examined separately • air conduction / bone conduction of sound can be examined • patient is not allowed to watch the audiometer (sitting backwards to it) • put earphones on the patient´s (only one is active) • give a switch to the patient´s hand • preset the frequency in audiometer to the lowest value • preset the intensity in audiometer to the lowest value • slowly move the marker for intensity to higher values • when the patient hears the sound, he/she gives a sign by pushing the switch – light flash is seen on audiometer • the value of intensity indicates the threshold for that particular frequency • record the threshold intensity in dB into the sheet (dot)

• repeat the procedure within the predetermined range of intensity • repeat the whole examination for bone conduction

Results • by connecting the dots draw a graph and evaluate it TheThe vestibularvestibular systemsystem

 part of the inner ear  contributes to balance, sense of spatial orientation  provides input about movement

Components  3 semicircular canals - detect rotation of the head  and - detect linear movement of http://t1.gstatic.com/images?q=tbn:ANd9GcTgpLH6l2qvF the head W-q8XnnW4JySSBX0RZif93UqMz5of6l-oeOYLDobg

• semicircular canals, utricle, saccule – filled with liquid - endolymph • sensory cells – hair cells

http://images.suite101.com/2476145_com_innerear4.jpg Linear acceleration • areas with sensory cells – macula utriculi – macula sacculi

• both maculas contain hair cells covered by gelatinous substance (cupula) containing otolits (earstones)

• when moving – gel with otolits moves the hair cells to side – this elicits action potential Angular acceleration

• 3 semicircular canals – horizontal – posterior – superior • at right angles to each other – cover all 3 http://t1.gstatic.com/images?q=tbn:ANd9GcTgpLH6l2qvFW- planes q8XnnW4JySSBX0RZif93UqMz5of6l-oeOYLDobg

• ampulla – a swelling on the beginning of each canal • - contains hair cells • as the body starts to rotate endolymph inside canals starts to move • hair cells are stimulated by the movement of endolymph – action potentialis elicited

http://image.absoluteastronomy.com/images/encyclopediai mages/v/ve/vestibular_pushpull.svg.png ExaminationExamination ofof nystagmusnystagmus inin aa humanhuman

Nystagmus • movement of eyeballs – fast movement to one side – slower movement to the other side

• reaction to stimulation of vestibular apparatus (canales semicirculares) by rotation and by movement of endolymph • signals from the trigger eye (and head) movements to stabilize the visual image on the retina

• it may be caused also by other stimuli

• sign of some neurological disorders http://ivertigo.net/graphics/v4.gif Principle • rotation causes movement of endolymph – in the direction of movement • movement of endolymph is a stimulus for hair cells in vestibular organ • endolymph moves with delay, it reaches the speed of movement of the body only in a few seconds

• at the beginning of rotation – due to delayed movement of endolymph, the hair cells are temporarily bent to the opposite side to movement – within this time perrotation nystagmus occurs • after the rotation stops – endolymph continues to move – hair cells are temporarily bent to the direction of movement – postrotation nystagmus occurs until endolymph stop

• the direction in which the endolymph is moving – is the same as the slow movement of eyeball • the direction of nystagmus is determined according to the fast movement (to the right, to the bottom, etc.) • i.e. after rotation movement nystagmus to the opposite side to direction of movement can be observed Procedure • the examined person is seated into a rotating chair and belted with head in normal position (to stimulate the horizontal canal) • the chair is set into rotation (for approx 20-30 sec, as fast as possible) • the rotation is suddenly interrupted • the nystagmus is observed (lasts just a few seconds)

• the examination is repeated in position with head leaned 1. towards the arm 2. to the front

Result: nystagmus – direction Conclusion: explain your observation

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