Hearing and Balance Pathways Flashcards
What does the primary auditory pathway begin with?
The inner hair cells in the cochlea
Where do the afferent neurons terminate?
The cochlear nuclei in the pons
How many cochlear nuclei are there?
4- 2 dorsal and 2 ventral
Where are the dorsal cochlear nuclei located?
One either side of the midline
What are the dorsal cochlear nuclei mainly concerned with?
Tone
Where do most of the dorsal cochlear nuclei output neurons project to?
The contralateral inferior colliculus
What are the Ventral cochlear nuclei mainly concerned with?
Intensity
Which nerve fibres input into the anterior VCN?
fast Type 1 nerve fibres
What are the subtypes of bushy cells?
2- Spherical BC and Globular BC
Where do most of the anterior VCN project to?
The superior olivary nucleus through the trapezoid body
What does the superior olivary complex comprise of?
Three primary nuclei- medial superior olivary, lateral superior olivary and medial nucleus of trapezoid body
What is the MSO sensitive to?
time difference in arrival of sounds from different ears
What is the LSO sensitive to?
the difference in sound intensity between the ears
What are the lateral lemnisci formed from?
From fibres arising from dorsal and ventral cochlear nuclei and from the superior olivary nuclei
Where does the lateral lemniscus terminate?
The central nucleus of the inferior colliculus
Where does the lateral lemniscus send contralaterals to?
Cranial Nerves CNV (trigeminal) and CNVII (facial nerve)
Where are the inferior colliculi located?
Either side of the midline in the lower brain
What connects the inferior colliculi to the mediate geniculate body of the thalamus?
The inferior brachium
What is the medial geniculate body?
The specific thalamic nucleus . for hearing
Where do fibres of the Medial Geniculate Nucleus travel to?
The primary auditory cortex in temporal lobe
What does the primary auditory cortex respond to?
Auditory stimuli within the contralateral sound field
Why does lateral lemniscus send fibres to nuclei of trigeminal and facial nerves?
These nerves supply tensor tympani and stapedius- muscles exert dampening action on ossicles of middle ear to dampen loud noise
What is the startle response mediated by?
Outputs from reticular formation to spinal cord and to motor nucleus of facial nerve- sudden loud noises causes subject to flinch e.g. alarm clock
What do fibres entering the medial longitudinal fasciculus mediate?
Head turning reflex
Where does the balance pathway begin?
1st order neurons in semicircular canals
Where is the vestibular nuclei located?
In the pons
What is the function of the lateral vestibulospinal tract?
Keeps centre of gravity between feet
Which muscle reacts when a person vocalises normally to reduce sound intensity?
Stapedius
Unexpectedly loud noises cause reflex stimulation of nuclear groups controlling which muscles?
Stapedius and tensor tympani
What is the tectospinal tract involved in?
Coordination of head and eye movements
Where is primary auditory cortex located?
Anterior two transverse gyri of temporal lobe (gyri of Heschl)
How many vestibular nuclei are there in the lower medulla and pons?
4- superior, inferior, medial and lateral
What is function of medial vestibular nucleus?
Contributes fibres to ipsilateral medial longitudinal fasiculus- integrates movements directed by gaze-centre and generates some head-turning reflexes
What is the vestibulo-ocular reflex?
Reflex eye movement that stabilises images on retina during head movement by producing eye movement in opposite direction to head movement
