Week 5 - Sensory systems Flashcards
What are the three broad functional categories of the sensory system?
- Exteroception - what’s out in the external world?
- Body sense - where is my body? maintaining balance, enable co-ordinated action, adjust for movement.
- Interoception - how is my body?*Keep the body operating optimally – homeostasis, allostasis – tied with motivations and emotions.
E.g. Do I need to change respiration, heart rate etc.
How does the auditory system work? describe in four simple steps.
- Transmit sound to the sensory organ
- Transduce sound energy into a neural signal
- Transmit the neural signal to the brain
- Processing of the neural signal to provide
meaningful (and useful) auditory information
What is the auricle (pinna)?
Part of the outer ear to transmit sound to the mid ear.
Collect sound waves and channel them into the auditory canal
* Important role in localising sounds - folds selectively
reflect sounds of various frequencies around the ear and
into the auditory canal
* As a sound source changes its location relative to the
head, the frequency profile of these reflections changes -
offering a cue to the location of the source
What are the other two parts of the outer ear and what are there functions?
Auditory canal - Channel sound energy to the tympanic membrane
Tympanic Membrane (ear drum)
* Vibrates in response to air pressure changes of the sound waves
* Middle ear ossicles are attached to the TM
What are ossicles and which part of the ear does it belong to?
- Middle ear is for impedance matching – sounds in air
but sensory in fluid - If TM transmitted directly – air to fluid – almost all sound energy would be lost (reflected back)
- Concentrate the vibrations of the tympanic membrane on a very small area on the oval window
How does ossicles mediate sound?
- Think of how pressure is increased by concentrating a
given mass on a small area - In the case of the middle ear, this is a 17 fold increase
- The lever action of the ossicles amplify the vibrations by
approximately 1.3 times - Combined, this accounts for a 22 fold increase in the
strength of vibrations hitting the tympanic membrane - Acoustic reflex – loud sounds and speech
how does the inner ear transmit sound?
- Action of the stapes at
the oval window
produces pressure
changes that propagate
through cochlear - Pressure causes basilar
membrane to vibrate
how does the cochlear and basliar membrane work together to transduce sound?
The hair cells on the cochlear, which are separated by only 100picometers move left to right in tune with the vibration of the basliar membrane. The wiggling of the hair causes the ion channels to separate and allow communication through the membrane.
How does auditory processing allow for pitch perception?
Auditory processing is tonotopic (different tones).
- Basilar membrane - mechanical analyser of frequency
- Structure changes continuously along length
- Much wider at the apex than the base
- Each point along membrane responds preferentially to
a different frequency – high at the base, low at the apex - Preserved throughout early processing
- Also – outer hair cells
What is the auditory pathway in the brain?
Cochlea to the auditory nerve and * No major pathway (cf
retina-geniculate-striate
of vision) – complex
network
* First ipsilateral cochlear
nuclei
* Ultimately medial
geniculate nucleus of
thalamus (MGN) then
primary auditory cortex
(A1)
How does sound localisation work?
The localisation of sound sources are mediated subcortically at the superior olives (SO).
The 2 ears allow for sound impinging on each ear slightly different depending on where the source of the sound is.
Differs in 2 detectable ways:
interaural time difference
Interaural intensity difference
What are the 3 broad classes of hearing loss?
- Conduction deafness - damage to the tympanic membrane and ossicles.
- sensorineural deafness - auditory nerve fibres are not stimulated properly and the deafness is permanent. streptomycin (antibiotics) managed to destroy all the hair cells in the cochlea.
- central deafness - caused by brain lesions in the temporal cortex (e.g. stroke). Typically more complex issues aphasias, agnosias and auditory hallucinations etc.
What is the vestibular system?
The vestibular system is the part of the inner ear that is responsible for balance and spatial orientation. It consists of the vestibular apparatus, which is made up of the vestibular labyrinth and the vestibular nerve, and the vestibular nuclei, which are clusters of neurons in the brainstem that receive and integrate vestibular information.
The vestibular labyrinth is a complex system of fluid-filled channels and sacs that is located in the inner ear. It contains the vestibular organs, which are the semicircular canals and the utricle and saccule. The semicircular canals detect rotational movements of the head, while the utricle and saccule detect linear acceleration and changes in the position of the head.
