2. Translational motion is detected by the neuroepithelia of the otolith organs

Question

2. Translational motion is detected by the neuroepithelia of the

otolith organs

ampullae within the semicircular canals

3. Rotational motion is detected by the neuroepithelia of the

otolith organs

ampullae within the semicircular canals

4. Recall that the vestibulo-ocular reflex enables the eyes to remain fixed on target and that extrinsic eye muscles are innervated by brainstem -motor neurons. What role does the medial longitudinal fasciculus play in the vestibulo-ocular reflex?

central integration

links the vestibular nuclei with brainstem motor nuclei

5. Descending projections from the vestibular nuclei enable postural adjustments of the head and body. Any stereotypical change in head position that promotes balance is mediated by the vestibulo-cervical reflex. This name stems from the fact that most of the -motor neurons that control the position of the head are located in the motor nuclei of the

brainstem

cervical cord

6. Any stereotypical change in body position that promotes balance is mediated by the vestibulo-spinal reflex. Does this reflex implement the -loop?

yes

no

Explanation / Answer

2. otolith organs.

“Vestibule” is the central part of the inner ear, and it lies between cochlea and semicircular canals. It contains utricle and saccule which are parts of membranous labyrinth. Maculae in the vestibule contains sensory receptors called, hair cells, which are essential to the mechanism of static equilibrium. The hair cells of maculae are embedded in the “otolithic membrane,” which contains small grains of calcium carbonate, called otoliths.

The maculae provide the information regarding the ups and downs of a path and to linear changes in speed, as it responds to the gravitational pull by means of otoliths. According to the gravitational pull (in this case, acceleration of the head), the otoliths cause the hair cells to depolarise or hyperpolarise, and then these hair cells send action potentials to the vestibular part of the eighth cranial nerve (vestibulocochlear nerve).

3. ampullae within the semicircular canals

Each ear has three semicircular canals, filled with endolymph, placed at right angles to each other. They are posterior, superior and lateral semicircular canals. The enlarged end of the semicircular canal is called as ampulla. The ampulla communicates with the axons of vestibular nerve.

Semicircular canals are involved in the maintenance of dynamic equilibrium. Crista ampullaris is a receptor region present in each ampulla, and it contains hair cells with cupula (a gelatinous cap). The activation of hair cells occurs when their cilia are bent by the moment of endolymph.

4. links the vestibular nuclei with brainstem motor nuclei.

Vestibular nerve fibers project to the medial and lateral vestibular nuclei, these nerve fibers originate in the left horizontal semicircular canal. From the medial vestibular nucleus, excitatory fibers pass towards the contralateral abducens nucleus and divides into two outputs. One of the two outputs is a motor pathway is involved in the contraction of the lateral rectus of the right eye. While, the other output is an excitatory projection that after crossing the midline ascends to the left oculomotor nucleus via the medial longitudinal fasciculus thus, activates neurons that cause contraction of the medial rectus of the left eye.  

5. Brain stem

The -motor neurons that control the position of the head and facial movements are located in the motor nuclei of the brainstem, and those that control the body and limb movement are located in the anterior horn of the spinal cord.

6. Yes.

Vestibulo-spinal reflexes are controlled by extensive feedback loops.

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