Lecture 18, Sensory Physiology 18 (part 3) Flashcards
Special Senses: Hearing and Sound
sound passes through space in waves, caused by the vibration of molecules in the medium
- sound depends on the medium; if there are no molecules in the medium (vacuum), there is no sound
frequency: the number of sounds waves per second (perceived as pitch)
amplitude: the difference between the crest and trough of a sound waves (perceived as loudness)
my notes:
* best visualized as water when ripples are created (vibrations in the air that can be perceived as sound)
* characterize sound by frequency and amplitude
* pitch is changed by frequency
* higher sounds; great amplitude / lower sound; low amplitude
Special Senses: Hearing (2)
sound waves enter the ear via the external auditory canal, to reach the tympanic membrane
* the sound waves reverberate off the auditory canal, creating waves of pressure that push against the tympanic membrane
move in the tympanic membrane is relayed to the internal ear via the auditory ossicles within the middle ear
* tympanic membrane → malleus → incus → stapes → oval window (where we get from middle to inner)
* the ossicles serve to amplify the signal received at the tympanic membrane, and transmit it on the oval window
movement of the stapes at the oval window sends vibration through the cochlea in the inner ear
* the acoustic energy travels up the scala vestibuli (or vestibular duct) to the tip of the spiral
* travels from the tip of the spiral down the scala tympani (or tympanic duct) to the round window, which is sealed by the secondary tympanic membrane
→ external and middle is air filled whereas inner is fluid filled
Structures of the Inner Ear
in between the scala vestibuli and tympani is the cochlear. duct
* the Organ of Corti sits on the basilar membrane of the cochlear duct
* contains the sensory receptors of the ear, known as hair cells
movement of acoustic energy through the scala vestibuli and tympani creates movement within the endolymph of the scala media (cochlear duct)
* stimulates the hair cells in the Organ of Corti
* hair cells are a type of mechanoreceptor, that are activated by movement of the endolymph
Sound Intensity
sound above 80 DB can begin to cause hearing damage (damage to hair cells, membranes of the cochlea, and the tympanic membranes)
* depending on how loud the sound is, hearing damage can be immediate or can develop over time, and may be temporary or permanent
* doctors recommend limiting your headphone volume to <60% of the maximum volume
Structure of the Inner Ear (2)
the inner ear contains structures that contribute to the sensations of both hearing and balance
* the cochlea contributes to hearing
* the vestibular apparatus (semicircular canals, saccule, and utricle) contribute to balance
the semicircular canals are composed of two labyrinths, both containing fluid
* bony labyrinth contains perilymph
* the membranous labyrinth resides within the bony labyrinth, and contains endolymph
Special Senses: Balance
the utricle and saccule are responsible for sensing linear acceleration
* the utricle senses linear acceleration in the horizontal plane
* the saccule senses linear acceleration in the vertical plane
the utricle and saccule contains hair cells, similar to the ones found in the cochlea
* small projections from the hair cells known as stereocilia project into a gelatinous substance called otolith
linear head movement causes the otolith to shift (due to gravity)
* otolith pulls against the stereocilia, activating the hair cell
haircells in the saccule are activated when in a bent-over position, due to the vertical acceleration of gravity
→ movement of stereocilia (hair cells) that enable us to perceive sound
Special Senses: Balance (2)
the semicircular canals are responsible for sensing angular acceleration (rotation) of the head
the head can rotate around 3 axes:
* horizontal axis (nodding “yes” head motion)
* vertical axis (side-to-side “no” head motion)
* anterior-posterior axis (tilting the head (ear-to-shoulder) motion)
the sensory receptors within the circular canal can only senses angular acceleration of the head, not of individual limbs
* limb position and movement is sensed by proprioceptors within the muscle and joints
Special Senses: Balance (ampulla and cupula)
- ampulla: an enlarged region of the semicircular canal
- cupula: a gelatinous mass found within the ampulla that contains hair cells and their stereocilia
- when the head rotates, movement of the fluid within the semicircular canals cause the capula and the stereocilia to bend
◦ the direction of head movement influences the direction that the cupula is bent
Special Senses: Gustation (taste)
the sensory receptors that provide the sensation of taste are found within the taste buds in the mouth and throat
* there are ~10,000 tastebuds, with most present in the mouth and tongue
only five primary tastes can be distinguished by the taste buds:
* sour, sweet, bitter, salty, umami (savoury or meaty)
* all other flavours are a combination of the five primary tastes, as well as olfactory tactile sensations (a mix of all 5 just in different quantities)
each taste bud contains up to 50 gustatory receptor cells, and several supporting cells
* chemoreceptors
different forms of papillae
tastebuds are found in three type of papillae:
* funjiform papillae: found scattered all over the tongue, each containing 5 taste buds
* foliate papillae: located in the trenches and lateral margins of the tongue; initially contain taste buds, but most of which degenerate during childhood
* circumvallate papillae: found in a row at the back of the tongue (n = 12); initially contains 100-300 taste buds
◦ are relatively large
* filiform papillae: papillae found all over the tongue, but do not contain any taste buds
◦ contains tactile receptors
◦ provides friction that helps move objects around in the mouth
Special Senses: Olfaction (Smell)
- olfaction (smell) is the only sensory system that has direct projections to the cortex
◦ signals are not first relayed through the thalamus
-> also contributes to our sensation of taste - sensory receptors involved in olfaction are found within the olfactory epithelium in the superior aspect of the nasal cavity, and are a type of chemoreceptor
◦ these receptors have cilia, which are embedded within a mucus layer
odarant molecules: substances that are able to bind to olfactory receptor cells and initiate a change in the receptor potential
pathway of signal transmission (olfaction)
olfactory receptor cell -> olfactory nerve -> olfactory bulb -> olfactory tract -> primary olfactory cortex and parts of the limbic system
External Ear
external structure of
the ear and auditory canal
* Includes the pinna, ear canal and
tympanic membrane (eardrum)
Middle ear
cavity that contains the
auditory ossicles (small bones within
the middle ear cavity)
Inner ear
the most medial
structure that contains the
cochlea, semicircular canals, and
auditory nerve
* Is the site where sound waves are
transmitted into action
potentials to transmit to the brain
