Lecture 24: Sensory 3 Flashcards
List the main anatomical structures if the external, middle and inner ear that are important for the detection of sound and describe the function of each structure
Refer to slides 5, 6 for pictures and learn them!
Describe the sequence of sound transmission through the 3 bones in the middle ear
- Sound waves strike tympanic membrane, which vibrates
- Vibrations transferred through malleus, incus and stapes which amplify signal
- Vibrations transferred from stapes to oval window, setting up fluid waves within cochlea
- Fluid waves push on flexible membranes of cochlear duct, bending hair cells in organ of corti
- Neurotransmitter released from receptor cells creates AP’s in axons of cochlear division of vestibulocochlear nerve (CN 8)’ which then travels to the CNS
- Energy in the fluid waves transferred to the tympanic duct, and is dissipated back into the middle ear by the flexible round window
Anatomy of the cochlear
Sensory organ for sound is organs of corti, located on basilar membrane Organ of corti contains: -hair cells -supporting cells -tectorial membrane Hair cells -receptor cells -hair like projections called stereocilia -tips imbedded in tectorial membrane
Sound transduction by hair cells
- oscillations of cochlear membranes cause hair cell stereocilia to bend
- stereocilia are different lengths
- bend either towards or away from tallest stereocilium
- signals from hair cells transmitted to brain via cochlear nerve
- hair cells are immersed in fluid (endolymph), which has higher potassium (K+) content than inside of cells
- bending of stereocilia causes increased opening of closing of mechanically-gated K+ channels in hair cells
- bending towards tallest stereocilium opens K+ channel, allowing K+ to enter cell, causing depolarisation, which then opens voltage-gated Ca+ channels, increasing neurotransmitter release, depolarising afferent neuron, generates action potentials
- bending away from tallest stereocilium blocks K+ from entering cell, causing cell membrane to hyper polarise, reducing Ca+ entery into cell, decreasing neurotransmitter release, decreasing action potential ps in afferent neuron
Explain how electrical signals are produced for low and high amplitude sounds
- Sounds of different amplitude (measured in dB) cause stereocilia to bend further in either direction, increasing or decreasing number of action potentials generated
- cochlear is ‘tuned’ to frequency (measured in Hz) cause different regions of basilar membrane to deflect
- cochlear base (close to oval and round windows) “tuned” for high frequencies
- cochlear apex is ‘tuned’ for lower frequencies
Neural pathways for sound
- afferent signals from hair cells travel in vestibulocochlear nerve CN 8 and terminate in cochlear nuclei
- from cochlear nuclei, nerves carry signals to thalamus, from we’re more nerves transmit signals to auditory cortex in brain
- in auditory cortex there is like a frequency “map”
Sound localisation
- brain used differences in timing and level of sound
- sound from side of head reaches one ear before the other (time difference)
- head also deflects sound, leading to lower amplitude at ear facing away from source (level difference)
What is mechanoreception, and how is it detected in invertebrates
It is the detection of motion and position
In invertebrates:
-have simple form of gravity receptor, called statocyst
-in lobsters, statocyst is chamber lined with hairs at base of 2 antennae
-each statocyst contains statolith comprising grains of sand held together by mucus
-gravity moves statoliths within statocyst, giving animal information about its orientation
Lateral line neuromasts in aquatic animals
Aquatic animals such as fish, sharks And frogs have lateral line that runs just below level of skin on either side of body
- lateral lines contain mechanoreceptors called ‘neuromasts’
- detect motion in water
- A lateral line canal lies just below the skin surface
- Structures called cupulae project into the lateral line canal. As the fish moves through the water, fluid in lateral line canal pushes against the cupulae
- Each cupula contains hair cells whose stereocilia are embedd j. Gelatinous material
- Stereocilia on hair cells in the cupula bend
- Creating a signal that causes depolarisation of the dendrites in the lateral line nerve
Motion and position detectors in vertebrates: vestibular system
-mechanoreceptors detect motion and position of head
-contained in set of interconnected chambers in inner ear (vestibular labyrinth)
-information from the vestibular receptors travels to brain
Output from brain plays major role in:
-control of posture and movement
-orientation of head
-stabilisation of gaze
-maintaining sense of spatial orientation of body
Mammalian vestibular apparatus.
What does it comprise of? Refer to slide 23 and learn picture
Comprises: -3 semicircular canals -1utricle -1 saccule Semicircular canals contain endolymph At base of each semicircular canal is ampulla (jug) Within each ampulla is cupula (cap)
Explain the structure of ampullae
- each ampulla has ridge (crista) that extends into lumen of ampulla
- mechanoreceptor hair cells extend out of crista into gelatinous cupula (in lumen)
- capula bridges width if ampulla
- forms mobile barrier through which endolymph cannot circulate
- mechanoreceptor hair cells transmit information to vestibulocochlear nerve CN 8
What are the semicircular canals for?
3 semicircular canals in planes perpendicular to one another enable detection of rotational movements of head in 3 planes
What is the function of capula
When head is rotated (annular acceleration) in plane of canal, inertia of endolymph creates force that moves the capula, causing bending of hair cells (stereocilia)
- movement of stereocilia towards or away from kinocilium causes K+ channels to open or close
- causing depolarisation of hyperpolarisation of hair cells, increasing or decreasing Ca2+ concentration within cells
- end result is increase or decrease in number if action potentials
Anatomy and function of utricle and saccule
Refer to slide 29
Utricle and saccule rectilinear acceleration in Sam way that semicircular canals detect rotational acceleration
-receptor cells are hair cells with stereocilia that extend into gelatinous lay containing small calcium carbonate crystals (otoliths)
Utricle:
-detects backward and forward acceleration
-also plays role in detecting position of head relative to gravity
Saccule:
-functions in same way as utricle but detects up and down linear acceleration (eg riding in elevator)
