Senses 1
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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 our external or internal environment
• transmit the information to the CNS
• process the information 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 – vision
– hearing
– 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
Distribution of receptors
- receptors of special senses - grouped
- in specific areas of the body (head)
- in complex organs
- general sense receptors – distributed
throughout the body
- skin
- mucosa
- joints
- muscles
- tendons
- viscera http://www.colorado.edu/intphys/Class/IPHY3430-200/image/10-4.jpg
) 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
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 not only 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.
(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 is transduced
by a 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
• usually 3 neurons form a sensory pathway (except smell)
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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
- the difference threshold is the amount of change needed
for us to recognize that a change has occurred
- just noticeable difference
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)
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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 frequency of the waves
• loudness determined by height of the waves
Pitch
• high tone
• deep tone
Loudness
• quiet sound
• loud sound
- decibel
- unit of loudness
- derived as logarithm of acoustic pressure - the acoustic waves exert 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 - 95 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
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
• 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
http://www.neuroreille.com/promenade/english/ear/exear/e_oreille_ext.gif
- cavity in os petrosum, filled with air
- inside: chain of 3 ossicles
malleus - hammer
incus - anvil
stapes – stirrup
- malleus - connected to the eardrum
- stapes - 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
oscillations of the eardrum → transmitted to ossicles → oscillations of the oval window
ossicles
- transduce the sound from outer into the inner ear
- amplify the sound:
- area (eardrum/oval window) - pressure amplification
- high amplitude+low pressure is transduced
to low amplitude/high pressure
- hearing is improved by 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 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
Inner ear - 3 chambers
A/ bony labyrinth - filled with fluid -
perilymph
1. scala vestibuli
2. scala tympani
- communicate through helicotrema in the
apex
B/ membranaceous labyrinth - scala media
(3) - filled with endolymph
http://www.nidcd.nih.gov/staticr
esources/images/electrode_arr
ay.jpg
http://universe-review.ca/I10-85-cochlea2.jpg
Inner ear - 3 chambers
A/ bony labyrinth - filled with fluid - perilymph
1. scala vestibuli
2. scala tympani
- communicate through helicotrema in the apex
B/ membranaceous labyrinth - scala media (3) - filled with endolymph
scala media scala vestibuli
scala tympani
Reissner´s membrane
– separates s.vestibuli and s.media
Basilar membrane
– separates s.tympani from s.media
Inside scala media
• organ of Corti, includes:
• receptor cells = hair cells, their cilia
(kinocilium+ stereocilia) are
embedded in the tectorial membrane
Cross-section through one of the turns of cochlea
https://ccrma.stanford.edu/realsimple/psychoacoustics/img5.png
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
(more stiff) become displaced in different directions
• this causes the stereocilia to displace – this
movement elicits receptor potential
Principle of frequency analysis
- 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
• 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
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
Central auditory pathway
- the pathway may include a series of up to 6 neurons
sensory cells - synapse with cochlear
afferent fibres = vestibulocochlear nerve
(cochlear part)
- the nerve synapses 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 tones
Sound takes longer to reach right ear.
Source of sound
Signals coming from the left reach
the brain first.
Left Right
Top view of head
Sound localization
• 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
• strikes a tuning fork and 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 – then patient)
• 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
sense of spatial orientation, contributes to balance of the body
saccule and utricle (in vestibule) - detect linear movement of the head
3 semicircular canals - detect rotation of the head
http://scientopia.org/blogs/scicurio
us/files/2011/06/vestibular-
system1.gif
• sensory cells – hair cells
• in movement of the head - the hair (cilia) of the hair cells are bent
which generates receptor potential
Head in neutral position
Gravity
Head tilted posteriorly
Gravity
Otolith
Detection of linear acceleration
• areas with sensory cells
– macula utriculi (hairs of the hair cells in vertical position)
– macula sacculi (hairs of the hair cells in horizontal position)
• the hair cells are covered by
gelatinous substance (cupula)
with otolits (earstones) in the
upper layer
• when moving the head – gel with
otolits moves the hair cells to side
– this elicits action potentials
Angular acceleration
• 3 semicircular canals
– horizontal (lateral)
– posterior
– anterior (superior)
• at right angles to each other – cover all 3 planes
• 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
• 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) http://image.absoluteastronomy.com/images/encyclopediai
mages/v/ve/vestibular_pushpull.svg.png
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q8XnnW4JySSBX0RZif93UqMz5of6l-oeOYLDobg
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
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 pendular http://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
