Physiology- Visual, Auditory and Vestibular System Flashcards
Describe the opening and closing of transduction channels in hair cells
Force towards kinocilium opens TRPA1 channels & K+ enters, depolarising cell. Force away shuts channels
Tip links- connect transduction channels (cation channels on hairs)
Describe hair cell transduction
Tectorial membrane vibrates
Hair cells’ cilia bend
Depending on how they bend, hair cells release neurotransmitter
Neurotransmitter is captured in nerve fibres
Neural energy is sent to the brain
What are the two hair cell types of the auditory system?
Inner and outer
Describe inner hair cells
Main source of afferent signal in CNVIII nerve (~10 afferents per hc). Multiple outer HC innervated by single afferent
Describe outer hair cells
Primarily get efferent inputs. Control stiffness, amplify membrane vibration (more outer than inner)
What is the motor protein present in outer hair cells?
Prestin- can change the length of the cell
What direction is the Hair cell K+ current?
Inwards
What is critical for reconstituting K+ in the endolymph?
K channels, transporters and gap junction networks composed of 5 different connexions are critical for reconstituting K+ in the endolymph
What are the two mechanisms for frequency coding?
Place and temporal code
What is place code for?
Pitch
What is temporal code for?
Higher frequencies
What is the central pathway in the auditory system?
Cochlea CNVIII Cochlear nuclei (medulla) Superior olivary nuclei (pons) Nucleus of lateral lemniscus (pons) Inferior colliculus and medial geniculate nucleus (Midbrain) Primary auditory cortex
What are the 3 cochlear nuclei?
Dorsal cochlear nucleus
Posteroventral and anteroventral cochleal nuclei
What does the medial superior olive do?
Computes sound arrival at the two ears…ipsilateral ear earlier than contralateral. This generates an “interaural time difference”…….uses a “delay line”
What movement does the saccule sense?
Vertical/sagittal plane
What movement does the utricle sense?
Horizontal plane
What does the striola of the macula do?
Serves as landmark
Arranges otoconia into narrow trenches dividing each otolith
Orientation of the hair cells change over the course of the macula
Allows otolith organs to have multidirectional sensitivity
What signals exist in the vestibular nerve?
Tonic- deviations from which are proportional to head velocity
What signals exist in the macular (sensory epithelium vestibule) afferents?
Tonic- deviations from which are sensitive to acceleration
What is the vestibulo-ocular reflex?
Keeps eyes still in space when head moves
What is the vestibulo-colic reflex?
Keeps the head still in space, or on a level plane when you walk
What is the vestibulo-spinal reflex?
Adjusts posture for rapid changes in position
What is the organisation of the entire visual field on the primary visual field described as?
Visuotopic
What segregation occurs of the retinal output?
Segregation of cells representing movement and form in the LGN and V1
What are the inputs to the striate cortex?
Magnocellular LGN neurons: Project to layer IVCalpha
Parvocellular LGN neurons: Project to layer IVCbeta
Koniocellular LGN axons: Bypasses layer IV to make synapses in layers II and III (blobs, visible after cytochrome oxidase staining)
Where are the first binocular neurons found?
In striate cortex (most layer III neurons are binocular, but not layer IV)
Describe the cortical receptive fields
Orientation Selectivity/ive neurons
Respond to light/dark bars or edges
Only if in a particular orientation
Peak frequency depends on angle, preferred orientation
All edges representations were equally represented
