Download Senses 1_1011 (Practical)

Senses 1
Introduction to physiology of senses
Sense of hearing
Sense of balance
Practical tasks
Otoscopy
Tests with tuning forks
Audiometry
Examination of nystagmus
http://t2.gstatic.com/images?q=tbn:ANd9GcQLxYEdEk8lRTuToHhhLhGTIA
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 perception
• crucial for survival:
– provide necessary warning to avoid injury,
e.g. feeling heat, seeing danger – external receptors
– to maintain homeostasis – internal receptors
– make it possible for the body to respond to stimuli
• special senses
–
–
–
–
–
vision
hearing
taste
smell
balance
• general (somatic) senses
– touch
– temperature
– pain
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 = stimulus)
• 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 (action potential)
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
• Mechanoreceptors – 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)
• Chemoreceptors – activated by chemical substances (smell, taste)
• Thermoreceptors – activated by heat or cold
• Photoreceptors – activated by light (vision)
• Nociceptors – 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 sensory neuron'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 - brain 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 ear
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
- stapes is connected to oval window
(membrane separating middle/inner ear)
- 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
http://www.ohiohealth.com/mayo/images/image_popup/ans7_inside_ear.jpg
- 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, semicircular canals – sense of balance
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/ bony labyrinth - filled with fluid - perilymph
1. scala vestibuli
2. scala tympani
B/ membranaceous labyrinth - scala media - filled with fluid - endolymph
Reissner´s membrane
– separates scala vestibuli from
scala media
Cross-section through one of the turns of cochlea
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/pons)
2. synapse in superior olive
(med. oblongata/pons)
lemniscus lateralis (ipsi, contra)
to colliculi inferiores (midbrain)
3. corpus geniculatum mediale (thalamus)
=radiatio acustica
cortex – temporal lobe
- primary auditory cortex
- secondary auditory cortex
- tertiary cortex (association)
Otoscopy - examination of external ear
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?
Ear tests with tuning forks
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,
repeat the test in reverse order
http://www.aafp.org/afp/20000501/2749_f4.jpg
• 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
Abnormal result: BC>AC
AC= BC
Rinné positive (R+)
Rinné negative (R-)
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
• repeat the test in reverse order (doctor-patient)
• normally the patient should not hear any sound
patient
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
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)
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→
W lateralization to the
sick side
W lateralization to the
healthy side
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
•
•
•
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
The vestibular system
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
saccule and utricle - detect linear movement of
the head
http://t1.gstatic.com/images?q=tbn:ANd9GcTgpLH6l2qvF
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
planes
http://t1.gstatic.com/images?q=tbn:ANd9GcTgpLH6l2qvFWq8XnnW4JySSBX0RZif93UqMz5of6l-oeOYLDobg
• ampulla – a swelling on the beginning of
each canal
• crista ampullaris - 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
Examination of nystagmus in a human
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 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
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