Question

Compare and contrast the auditory and gustatory pathways. Start with explaining how stimuli are molecularly detected by the receptor cells and how the membrane potentials are depolarized. Discuss what triggers the action potentials of the sensory neurons and state which cranial nerves relay the action potential to the brainstem. Name the first nuclei in the brainstem (name the region of the brainstem) that form synapses with the central sensory neurons. Trace the rest of the pathways to the primary sensory cortex where the awareness of the special sensory stimuli occurs (name the lobe of the brain).

Answer 1

Auditory pathway.

Bending of the stereocilia of the hair cells of the spiral organ causes the release of neurotransmitter probably glutamate. Which generates nerve impulses in the sensory neurone innevate the hair cells. The cell bodies of the sensory neurone are located in the spiral ganglia. Nerve impulse pass along axxon of these neurones which forms the cochlea branch of the vestibulocochlear nerve. These axon synapse with neurones in the cochlear nucleus in the medula oblongata on the same side. Some of the axons from the cochlear nucleus decussate(cross over) in the medula, ascends in a track called the lateral meniscus on the opposite side, and terminate in the inferior colliculus in the midbrain. Other axons from the cochlear nuclei end in the superior olivary nucleus in the pons on each side. Slight difference in the timing of nerve impulses arriving from the two ear the superior olivary nuclei from the superior olivary nuclei also ascend in the lateral meniscus track on both sides and end in inferior collicli. From each inferior colliculus, nerve impulses are conveyed to the medial geniculate nucleus in the thalamus and finally to primary auditory area of the cerebral cortex in the temporal lobe of cerebrum. Because many auditory axons decussate in the medulla while others remain on the same side, the right and left primary auditory areas receive nerve impulses from both ears.

Gustatory pathway

3 three cranial nerves contain axons of the first order gustatory neurones that innervate the taste buds. The facial nerve serves taste buds in the anterior two third of tongue; the glossopharyngeal nerve serve test buds in the posterior one third of tongue; and vagus nerve serves taste buds in the throat and epiglottis. From the taste buds nerve impulses propagate along these cranial nerves to the nucleus in the medula oblongata. From the medulla,some axons carrying test signals project to the limbic system and the hypothalamus; others project to the thalamus. Test signals that project from the thalamus to the primary gustatory area in the parietal lobe of cerebral cortex give rise to the conscious perception of taste.