Sensory systems Taste/gustatory
Sensory systems basic concepts Modality of Sensation Receptor Sensory Tract primary neuron secondary neuron tertiary neuron termination
Receptors of sensory systems - primary sensory neurons The distal ending of the primary afferents is the receptor A special receptor cell conveys to primary afferents
Receptors of sensory systems - primary sensory neurons pseudounipolar bipolar part of PNS (except jaw proprioception) part of CNS
Sensory (afferent) systems General (somatic) sensations somatosensory systems superficial (exteroceptive) skin : pain and temperature vibration, touch and pressure stereognosia deep (proprioceptive) - joints and tendons interoceptive (visceroceptive) - organs and blood vessels Special sensations visual system vestibulocochlear system gustatory system olfactory system
Taste (gustatory) pathway 1 st Modality: Taste Sensation Receptor: Taste Bud Bud Cranial Nerve: VII, VII, IX, IX, X 1 st st Neuron: Geniculate Ganglion (VII) Inferior Ganglion (IX, X) X) 2 nd nd Neuron: Nucleus Tractus Solitarius 2 nd 3 rd (Gustatory Nucleus) solitariothalamic fiber (central tegmental tract) 3 rd rd Neuron: Thalamus (VPMpc) Internal capsule ----- -----Corona radiata Termination: Gustatory Area Brodmann area area 43 43 & parainsular cortex
Tastes are differentially distributed on the tongue
Tongue and lingual papillae 50% of the taste buds 25% of the taste buds 25% of the taste buds Other locations of taste buds - soft palate, oropharynx, and epiglottis
Circumvallate papillae
Taste buds There are about 2000 taste buds in the human tongue. This number decreases progressively with age. Taste buds are lost at a rate of 1% per year with increased rate after 40 years of age.
Sensory transduction in taste cells
Anterior 2/3 of tongue CN VII Posterior 2/3 of tongue CN IX Oropharynx CN X Gustatory pathways
Gustatory part of solitary nucleus integrates taste pathways and visceral sensory information solitarius salivatory ambiguus CN IX There is a close relationship of gustatory and visceral information we should quickly recognize if we are eating something that is likely to make us sick and respond
Gustatory information relays via VPM VPL Thalamic neurons serving taste are grouped separately from neurons concerned with other sensory modalities of the tongue VPM
Gustatory pathways A. nucleus tractus solitarius (gustatory nucleus) B. thalamus (VPMpc) C. Brodmann area 43 D. parainsular cortex E. parabrachial nucleus 1. solitariothalamic fiber (central tegmental tract) 2. corona radiata VII. facial nerve IX. glossopharyngeal nerve X. vagus nerve Axons of solitary nucleus neurons project on reticular nuclei (especially the parabrachial nucleus in the pons) before reaching VPM, giving on their way collateral branches to such nuclei as the nucleus ambiguus and salivatory nuclei for reflex activity
Taste pathways
Processing of gustatory information
Sensory systems Smell/olfactory
Olfactory pathway Modality: Olfaction Receptor: Olfactory receptor cell cell of of olfactory epithelium Cranial Nerve: I I (Olfactory Nerve) 1st Neuron: Olfactory Bulb --- ---Mitral & Tufted Cell Cell olfactory tract olfactory striae Termination: Primary Olfactory Area (Rhinencephalon) piriform lobe lobe (prepiriform cortex, entorhinal cortex) corticomedial amygdala anterior perforated substance (olfactory tubercle)
Olfactory nerve (CN I) CN I
Structure of the olfactory epithelium Olfactory receptor cells - bipolar sensory neurons knoblike expansion extending beyond the epithelial surface (receptors) 100 million receptor cells in the olfactory mucosa Bowman's glands moisten secretions dissolve the gaseous substances Supporting (sustentacular)( cells microvilli Basal cells - progenitors
Odorant receptors & odorant signal transduction Odorant receptors are G-protein coupled receptors (GPCRs) DNA encodes for ~1000 2000 different olfactory GPCRs Each olfactory receptor neuron expresses 1 31 3 of these GPCRs
Olfactory bulb receives signals from olfactory sensory neurons Inhibitory interneurons (granule & periglomerular cells) modulate sensory neuron input
Olfactory bulb & tract
Central olfactory projections
The olfactory system is thus unique among the sensory systems in that it does not include a thalamic relay from primary receptors en route to a cortical region Olfactory nerve & bulb Piriform cortex (paleocortex) Thalamus Neocortex
Olfactory information processing emotive aspects of olfaction pheromones conscious discrimination of odors