Senses 1

http://t2.gstatic.com/images?q=tbn:ANd9GcQLxYEdEk8lRTuToHhhLhGTIA

OfpOUYUkXwbLaC9dD3FYcpm2XA

Introduction to physiology of senses

Sense of hearing

Sense of balance

Practical tasks

Otoscopy

Tests with tuning forks

Audiometry

Examination of nystagmus

Senses• structures in the human body that gather the stimuli

occurring in the external or internal environment

• transmit the information to the CNS

• process the information n the CNS and allow for

sensation an perception

Function of senses

- to interact with the world

- crucial for survival

(to avoid injury, to find food, etc.)

Classification of senses

1. Special senses– hvision

– earing

– taste

– smell

– balance

2. General (somatic) senses– touch

– temperature

– pain

– proprioception

Each of the principal types of sensation that can be experienced

(pain, touch, sight, sound, taste, etc.) is called a modality of sensation.

events in the external and internal worlds must be translated into signals that

the nervous systems can process

Sensory receptors

nerve endings (free or encapsu-

lated) or specialized cells

gather and code signals from the

external and internal environment

sensitive to various forms of

energy (energy = stimulus)

stimulation elicits a change in

transmembrane potential – a

receptor potential

http://www.colorado.edu/intphys/Class/IPHY3430-200/image/10-1.jpg

Classification of receptors I (according to the type of stimulus)

Mechanoreceptors – activated by mechanical stimuli

- deformation, stretching, changing position of the receptor

- (e.g. touch-skin receptors, hearing, stretch of a muscle, but also receptors in vessel

- blood pressure)

Chemoreceptors – activated by chemical substances (smell, taste)

Thermoreceptors – activated by heat or cold

Photoreceptors – activated by light (electromagnetic waves)

Nociceptors – activated by intense stimuli of any type that result in tissue

damage, produced sensation is pain

- the sensory perception is limited to those forms of energy for which the body has receptors

)Classification of sensory receptors II

- Exteroceptors – gather external stimuli (skin sensitivity – touch, temperature, pain)

- Interoceptors (visceroceptors) – detect internal stimuli (e.g.distension of the organs)

- Proprioceptors – detect stimuli about position of the body, muscle tone

http://slideplayer.com/slide/10431288/

Stimulus

a change in external or internal environment (a form of environmental energy)

that acts on a receptor

adequate stimulus

- type of stimulus (energy) that a receptor is sensitive to/specialised for

- receptors are specialised for one type of energy (except nociceptors):

e.g. light – vision

chemical substances – smell, taste, etc.

- the receptor responds to adequate stimuli of low intensity

non-adequate stimulus

- some receptors can respond to adequate stimuli,

but also also to other type of energy

- non-adequate stimulus must be of much higher intensity

in order to elicit action potentials

e.g. if high pressure is produced by a punch

to the eye – a flash of light may be perceived.

receptor

stimulus

(energy)

(minimum) threshold intensity of a stimulus – minimum strength of a stimulus

that triggers an action potential in the sensory neuron's axons (i.e. it is the

weakest stimulus that can be reliably detected)

stimulation elicits receptor potential = a change

in transmembrane potential a of a sensory receptor in

terms of

depolarization

hyperpolarization

- receptor potential = graded response

(the stronger the stimulus, the higher the receptor potential)

- the potential is spread with a decrement

- (the farther from the place of stimulation the lower the

change of transmembrane potential

- if sufficiently strong to reach axon hillock, it

generates action potentials here that are transmitted

by the axon (if axon hillock is not reached no AP is

generated

receptive

membrane

conductive

membrane

mV

stimulus

stimulus

decrement

Sensory pathway

• conducts nerve impulses to CNS

• typically 3 neurons form a sensory pathway

• exception: smell - 2 neurons

http://t2.gstatic.com/images?q=tbn:ANd9GcQLxYEdEk8lRTuToHhhLhGTIAOfpOUYUkXwbLaC9dD3FYcpm2XA

signals from any receptor travel in the same form -

as action potentials

they are decoded depending on to which part of

brain cortex they arrive, e.g.

- visual cortex– signal is inerpreted as visual peception

- auditory cortex – sound, etc.

Difference threshold

- is the amount of change needed to recognize that a

change in intensity has occurred

Sensory projection areas

areas of brain cortex that receive sensory information

• primary cortex (for vision, hearing...)

– I can see, hear...something (sensation)

• secondary cortex (unimodal association areas)

– I can recognize what I see, hear ....(perception)

• tertiary cortex (polymodal association areas)

– complex sensation (e.g. colour+shape+taste+memories)

http://t2.gstatic.com/images?q=tbn:ANd9GcQLxYEdEk8lRTuToHhhLhGTIAOfpOUYUkXwbLaC9dD3FYcpm2XA

Sensation

- sensation is the process of sensory input arriving at the cerebral cortex

- this in turn interprets such impulses as a visual image, a sound, taste, odor,

touch, or pain- I can see, hear, taste.... (something)

Perception

- is the process of interpretation of the sensation

- what I can hear (see, smell,....) - e.g. It´s the sound of my neghbour´s mobile phone, again new malody, but why is it so

loud

Sense of hearing - The ear

Sound• vibrations (compression/decompression) of air (water or solids)

• audible frequency: 20 Hz to 20 000 Hz (Hertz)

• adequate stimulus for sense of hearing

• pitch – determined by the frequency of the waves

• loudness determined by the amplitude of the waves

Pitch

• high tone (frequency)

• low tone (frequency)

Loudness

• quiet sound

• loud sound

Decibel (dB)

- unit of loudness (acoustic pressure)

- derived as logarithm of the acoustic pressure/reference pressure

Threshold of hearing 0 dB

Quiet whisper in library 30 dB

Normal conversation 60 – 70 dB

Telephone dial tone 80 dB

City traffic 85 dB

Train 95 dB

Level at which sustained exposure may result in hearing loss 90 - 100 dB

Pain 125 dB

Jet 140 dB

Even a short time exposure may result in hearing loss (maximum

loudness to be exposed with hearing protection)

140 dB

Death of hearing tissue 180 dB

the threshold for detection of a pure tone varies with its frequency

(sensitivity of the ear to sound depends on the frequency of sound waves)

• maximum sensitivity in range 1000 - 4000 Hz - threshold ~ 0 dB

• frequency of speech 300-3000 Hz

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

• the higher /lower frequency - the louder the sound must be to be detectable

• 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 waves cause its oscillation

Function of the external ear

- cavity in the temporal bone, filled with air

- inside: chain of 3 ossicles

malleus - hammer

incus - anvil

stapes – stirrup

- malleus - connected to the eardrum

- stapes – its footplate connected to the oval

window (membrane separating middle/inner ear)

Function of the middle ear

http://www.ohiohealth.com/mayo/images/image_popup/ans7_inside_ear.jpg

Middle ear

transduction of the sound from outer into the inner ear

- oscillations of the eardrum → ossicles → oscillations of the oval window

amplification of the sound

- area (eardrum/oval window) - pressure amplification

- high amplitude+low pressure is transduced to low amplitude/high pressure

- gain: approx 25 dB

m. stapedius, m. tensor tympani

- loud sound causes their reflex contraction

- weaken vibrations of the membranes and thus

transmission of the sound

- protect against damage caused by very loud sounds

- weaken the perception of the person´s own speech

Eustachian tube – communication between middle ear and pharynx

- allows to balance of pressure on both sides of the eardrum (e.g. in airplane)

- required for normal function of the eardrum + prevention of rupture

- risk of infection spreading - from nasopharynx into middle ear !!!

- easily in children who often suffer from infections of pharynx)

http://i.quizlet.com/i/xDvZDSl59H2K7QQcRb6vXA_m.jpg

m. stapedius

m. tensor

tympani

http://www.merckmanuals.

com/media/home/figures/M

MHE_19_220_01_eps.gif

Function of inner ear

Cochlea

• a spiral shaped organ

(2 ¾ turns)

• inside - organ of Corti

with sensory

receptors - hair cells

Components• cochlea – sense of hearing

• vestibule, semicircular canals – sense of balance

http://www.ohiohealth.com/mayo/images/image_popup/ans7_inside_ear.jpg

Cochlea - 3 chambers

A/ bony labyrinth - filled with fluid – perilymph (high Na+, low K+)

1. scala vestibuli

2. scala tympani

- communicate through helicotrema in the apex

B/ membranaceous labyrinth - scala media

- filled with endolymph (high K+, low Na+)

scala media

scala vestibuli

scala tympani

Inside scala media

• organ of Corti, includes:

• receptor cells = hair cells (inner hair cells, outer hair cells)

• cilia (stereocilia) are embedded in the tectorial membrane

Reissner´s membrane – separates s.vestibuli and s.media

Basilar membrane – separates s.tympani from s.media

Cross-section through one of the turns of cochlea

• 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 (more stiff) become displaced in

different directions

• this causes the stereocilia to displace

• this movement elicits receptor potential

(influx of K+ into the cell)

• release of excitatory neurotransmitter

• action potential at CN VIII

Principle of frequency analysis - how the tone (frequency is detected)

- maximum resonance point on the basilar membrane depends on the frequency of

the tone

- tones produce travelling wave on basilar membrane

- the wave travels to the point with maximum resonance (then dies out)

- the higher the tone (the higher the frequency) the closer the maximum resonance

point (and vice versa)

• deep tones/low frequencies

- maximum resonance close to apex

• middle frequencies

- middle of the basilar membrane

• high frequencies/tones

- max. resonance close to the oval window

Central auditory pathway

- the pathway may include a series of up to 6 neurons

- sensory cells - synapse with cochlear

afferent fibres (cochlear division of the

vestibulocochlear nerve, CN VIII)

- synapse in cochlear nuclei

(m.oblongata/pons)

- ipsilateral

- contralateral

- synapse in superior olive

(med. oblongata/pons)

- lemniscus lateralis (ipsi, contra)

to colliculi inferiores (midbrain)

- corpus geniculatum mediale (thalamus)

radiatio acustica to brain cortex – temporal

lobe (tonotopic organization)

http://www.edoctoronline.com/media/19/photos_5DAD473D-4A69-4D60-B68B-84EC52E3CCA5.jpg

• tonotopic organization of the auditory cortex

http://open.jorum.ac.uk/xmlui/bitstream/handle/123456789/964/Items/SD226_2_013i.jpg

Presbyacusis

• impairment of hearing in elderly

• affects mainly ability to hear high frequencies

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

• most sounds are transmitted by air conduction

• very loud sounds are transmitted also by bone conduction

• bone conduction

– a significant way of sound transmitting if the air conduction is weakene

(e.g. inflammation of the middle ear – otitis media)

– principle of some types of hearing aids

– higher threshold – louder sound necessary in order to hear

Sound takes longerto reach right ear

Sourceof sound

Signals comingfrom the left reachthe brain first.

Left Right

Top view of head

Sound localization

• ability to identify the location or origin of a detected

• binaural hearing

• the brain utilizes subtle differences in intensity and timing cues to allow to

localize sound sources

Task: Otoscopy - examination of external ear

- 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?

Task: Ear tests with tuning forks

Examination of

• air conduction of sound

• bone conduction of sound

The tests allow to distinguish

1. conduction disorders

- external ear

- middle ear

2. perception disorders

- inner ear

- sensory pathway

- brain centre for hearing

Rinné test

• strike a tuning fork

• place it on the patient´s mastoid bone behind one ear

• when the patient can no longer hear the sound, he

signals to the examiner (record the time of bone

conduction BC)

• then move the tuning fork next to patient´s ear canal

• when the patient no longer hears the sound, gives

signal the doctor (record the time of air conduction AC)

• examine both ears

Normal result: AC>BC Rinné positive (R+)

(typically AC = 2x BC)

Abnormal result: BC>AC Rinné negative (R-)

AC= BC Rinné inconclusive (R±)

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

Schwabach test

• sound a tuning fork

• place it on the processus mastoideus of the patient

• when the patient no longer hears the sound, put the fork on your (doctor´s) processus mastoideus

• normally the doctor should not hear any sound

• repeat the test in reverse order (first doctor – thenpatient)

• normally the patient should not hear any sound

• examine both ears

Normal result:

• Schwabach normal

Abnormal result:

• Schwabach shortened – the patient can hear the sound for shorter time then the doctor

• Schwabach prolonged – the patient can hear the sound for longer time then the doctor

patient

doctor

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

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)

• examine both ears

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

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

Conclusion

Resume and evaluate results of all tests together

normal hearing

R+

Schwabach normal

W

conduction disorder

R-

Schwabach prolonged

W lateralization to the

sick side

perception disorder

R+, R±

Schwabach shortened

W lateralization to the

healthy side

Task: Audiometry

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 ears (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

Results:

- by connecting the dots draw a

chart and evaluate it

• 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

Normal audiogram

The vestibular system

part of the inner ear

detects movements/position of the head- provides input about the head movement

adjustments of the posture that maintain balance

trigger head and eye movements to stabilize visual image in the retina

http://scientopia.org/blogs/scicurio

us/files/2011/06/vestibular-

system1.gif

Labyrinths

3 semicircular canals – horizontal, anterior, posterior

detect angular acceleration (rotation) of the head

Otolith organs

saccule and utricle (in vestibule)

detect linear acceleration of the head

Sensory cells

– the hair cells

Detection of linear acceleration

• areas with sensory cells

– macula utriculi - hairs of the hair cells in vertical position - detect

– macula sacculi - hairs of the hair cells in horizontal position - detect

• the hair cells are covered by cupula

(gelatinous substance) with otolits

(earstones) in the upper layer

• when moving the head – gel with

otolits moves the hair cells to side –

this elicits action potentials

Head in neutral position

Gravity

Head tilted posteriorly

Gravity

Otolith

Otolith

• in movement of the head - the

hair (cilia) of the hair cells are

bent which generates receptor

potential

Angular acceleration

• 3 semicircular canals:horizontal, posterior, anterior

• ampulla – a swelling at the beginning of each canal

– crista ampullaris - contains hair cells

• rotation of the head - endolymph starts to move

• hair cells are stimulated by the movement of

endolymph – receptor potential is elicited

http://image.absoluteastronomy.com/images/encyclopediai

mages/v/ve/vestibular_pushpull.svg.png

Equilibrium pathways

Vestibular apparatus

Vestibular branch of

vestibulocochlear

nerve (VIII)

Thalamus

Cerebellum

Cerebral

cortex

Reticular

formation

Vestibular

nuclei of

medulla

Somatic

motor neurons

controlling eye

movements

- action potential is transmitted to

- cerebellum,

- reticular formation

- vestibular nuclei in m. oblongata – connections with the oculomotor centre of the

eye

- stimulation of the hair cells - stimulus for vestibular reflexes (e.g.nystagmus)

Task: Examination of nystagmus in a human

Nystagmus

• movement of eyeballs

– fast movement to one side

– slower movement to the other side

• reflex reaction to stimulation of vestibular apparatus

(canales semicirculares) by rotation and by movement of

endolymph

• signals from the vestibular system 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

• depending on which semicircular canal is stimulated –

nystagmus is horizontal, verital or pendularhttp://ivertigo.net/graphics/v4.gif

Horizontal nystagmus: https://www.youtube.com/watch?v=_zRdrQceb-Y

Rotary nystagmus: https://www.youtube.com/watch?v=5vPCL7MaSDk

• 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

Principle• rotation causes movement of endolymph – in the direction of movement

• movement of endolymph is a stimulus for hair cells in vestibular organ

• inertia of endolymph causes makes it lag behind, 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

– due to inertia endolymph temporarily continues to move

– hair cells are temporarily bent to the direction of movement

– postrotation nystagmus occurs until endolymph stops

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