L(12) : Special senses // Dr Faisal
Done by Dina Alzyoud
Checked by Hyfaa Zreqat
Last lecture , we have started with Auditory sense , and we said that ear is
divided into 3 anatomical regions :
1- External ear :
HE
- Ear pinna
- Auditory canal
- Tympanic membrane
2- Middle ear :
- Auditory ossicles : malleus , incus and stapes
- Stapes lies on the oval window
They work as lever system ( )
- The smallest two muscles of our body are located in middle ear .
- Auditory ( eustachian ) tube
- Passage way of sounds from external to internal ear .
3- Inner ear :
- Oval window , it is first part of cochlea
- Inner ear is connected to pharynx
- Cochlea : structures of hearing are located here .
- Next to cochlea is the Vestibule ( contains semicircular canal ) , and
receptors within the vestibule are sensitive to changes in balance ( i.e.
equilibrium)
- Cochlea and Vestibule innervated by eighth cranial nerve ,
Vestibulocochlear
- If we take a cross section from cochlea :
1
, Upper part : Scala vestibuli ( near the vestibule )
Lower part : Scala tympani ( near to tympanic
membrane )
Middle part : Scala media or Cochlear duct
Each scala is separated from another scala by a membrane , and membrane that
is separating scala media and tympani is Basilar membrane , on the top of the
basilar membrane there the hearing receptors ( Organ of Corti ) .
Basilar membrane :
Triangular in shape , and contains hair like structure (cells)
, one layer of inner hair cell (one row) , and three layers of outer hair cells . It also
contains fibers ( rods ) , fibers near to base are short and thick , and they become
longer and thinner as we move towards helicotrema .
- Above hair cells is a membrane called Tectorial membrane .
- (hair cells are supplied by the cochlear
branch of the 8th nerve )
- Helicotrema is the connection
between cochlea and vestibule .
Now ; hair cells vibrate in response to vibration
of basilar membrane , and because fibers of this
membrane are very thick at the beginning of
cochlea ,
=
unless the frequency is high . If the frequency is moderate , basilar membrane in
the middle way will be vibrated , if the frequency is low , most inner part of this
membrane will be vibrated .
Physiology of hearing :
Audible sound range : 20-20000Hz in children , and 300- 8000 Hz in adults .
Sound > external auditory canal > tympanic membrane(vibration) , its surface
area is 17 times higher than surface area of stapes , so sound is going to be
concentrated .
> stapes > fluid(vibration) > basilar membrane vibration(goes up and
down) >when it goes up the hair cell will vibrate to hit the tectorial membrane
(stimulus) >stretch receptors >open ion channels( depolarization of
membrane) > receptor potential > secretes neurotransmitter > affect
neuron of the cochlea > action potential .
2
Done by Dina Alzyoud
Checked by Hyfaa Zreqat
Last lecture , we have started with Auditory sense , and we said that ear is
divided into 3 anatomical regions :
1- External ear :
HE
- Ear pinna
- Auditory canal
- Tympanic membrane
2- Middle ear :
- Auditory ossicles : malleus , incus and stapes
- Stapes lies on the oval window
They work as lever system ( )
- The smallest two muscles of our body are located in middle ear .
- Auditory ( eustachian ) tube
- Passage way of sounds from external to internal ear .
3- Inner ear :
- Oval window , it is first part of cochlea
- Inner ear is connected to pharynx
- Cochlea : structures of hearing are located here .
- Next to cochlea is the Vestibule ( contains semicircular canal ) , and
receptors within the vestibule are sensitive to changes in balance ( i.e.
equilibrium)
- Cochlea and Vestibule innervated by eighth cranial nerve ,
Vestibulocochlear
- If we take a cross section from cochlea :
1
, Upper part : Scala vestibuli ( near the vestibule )
Lower part : Scala tympani ( near to tympanic
membrane )
Middle part : Scala media or Cochlear duct
Each scala is separated from another scala by a membrane , and membrane that
is separating scala media and tympani is Basilar membrane , on the top of the
basilar membrane there the hearing receptors ( Organ of Corti ) .
Basilar membrane :
Triangular in shape , and contains hair like structure (cells)
, one layer of inner hair cell (one row) , and three layers of outer hair cells . It also
contains fibers ( rods ) , fibers near to base are short and thick , and they become
longer and thinner as we move towards helicotrema .
- Above hair cells is a membrane called Tectorial membrane .
- (hair cells are supplied by the cochlear
branch of the 8th nerve )
- Helicotrema is the connection
between cochlea and vestibule .
Now ; hair cells vibrate in response to vibration
of basilar membrane , and because fibers of this
membrane are very thick at the beginning of
cochlea ,
=
unless the frequency is high . If the frequency is moderate , basilar membrane in
the middle way will be vibrated , if the frequency is low , most inner part of this
membrane will be vibrated .
Physiology of hearing :
Audible sound range : 20-20000Hz in children , and 300- 8000 Hz in adults .
Sound > external auditory canal > tympanic membrane(vibration) , its surface
area is 17 times higher than surface area of stapes , so sound is going to be
concentrated .
> stapes > fluid(vibration) > basilar membrane vibration(goes up and
down) >when it goes up the hair cell will vibrate to hit the tectorial membrane
(stimulus) >stretch receptors >open ion channels( depolarization of
membrane) > receptor potential > secretes neurotransmitter > affect
neuron of the cochlea > action potential .
2
