Tongue sensory organ
- Taste is detected by taste receptor cells, which are located on specialised papillae of the taste buds and are stimulated by taste chemicals.
- The cellular mechanism for transduction of taste stimuli depends upon the stimulus.
- Receptors for molecules associated with sweet and bitter tastes utilise second messengers,
- Receptors for sour and salty-tasting molecules act directly upon the ion channels.
- Taste buds on the anterior two thirds of the tongue have fungiform papillae and primarily detect sweet and salty tastes.
- They send signals centrally through the lingual nerve to the chorda tympani and finally into CN VII (facial).
- Taste buds on the posterior one third of the tongue have circumvallate papillae and foliate papillae, which detect bitter and sour tastes.
- Most of them send signals centrally through CN IX (glossopharyngeal);
- However, some located in the back of the throat and epiglottis send signals centrally through CN X (vagus).
Tracts
- Afferent
- CN7/9/10 → Nucleus solitarius → Solitariothalamic fibres (taste) → VPM thalamus → sensory cortex
- Efferent
- Solitary cells project to the
- Salivatory nucleus
- Hypoglossal
- Dorsal motor vagal nuclei
- Nucleus ambiguus
- Nucleus ambiguus are largely bilateral and are the intermediate neurons in the pathway for the gag reflex.
- Solitariospinal fibres → phrenic nerve → vomiting/Gag reflex
- 1st order neurons
- CN VII, IX, and X synapse with the tractus solitarius (solitary nucleus).
- 2nd order neurons
- Solitary nucleus (Solitary tract) → ipsilaterally ventral posterior medial nucleus of the thalamus.
- 3rd order neurons
- Thalamus → taste cortex located in the primary somatosensory cortex.
- Taste discrimination and perception occur as a result of the comparison of the activation pattern of different groups of taste fibers.
Primary gustatory cortex
- Aka gustatory cortex
- Function responsible for the perception of taste and flavour.
- Location
- Anterior insula cortex
- Frontal opercular gyrus
- Afferent inputs
- Ipsilateral Nucleus solitarius
Q&A:
- Where on the tongue is salty taste detected?
- The tip of the tongue
- Where is the first-order neuron of the olfactory pathway located?
- The first-order neurons are the olfactory cells located in the olfactory epithelium. These bipolar cells send axons through the cribriform plate to the olfactory bulb.
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