Sensory modalities

Visual pathway

Photoreceptors, retinal ganglion cells, optic nerve, chiasma, optic tract, lateral geniculate nucleus, optic radiations, calcarine sulcus

Auditory pathway

Hair cells, spiral ganglion cells, cochlear nuclei, lateral lemniscus, inferior colliculi, medial geniculate nucleus, Heschl’s gyrus

Olfactory pathway

Olfactory receptor neuron, mitral cells, olfactory tract, piriform cortex

Gustatory pathway

Taste receptors, cranial nerves, nucleus of the solitary tract, thalamus, insula

Optic radiations pathways

Dorsal = mid temporal lobe = motion perception

Ventral = inferior temporal lobe = object recognition

Signal transduction: vision

Light activates opsins, 11-cis retinal to all-trans retinal, cGMP broken down to GMP, gated Na channels close, hyperpolarisation, less glutamate released

Signal transduction: Sound (up to cochlea)

Airwaves push tympanic membrane, malleus is moved, pulls incus, pushes stapes, moves oval window with force 20x greater to generate waves in cochlea fluid

Signal transduction: sound (actual transduction, cochlea)

Basilar membrane vibrates, hair cells lifted, stereocilia bend against tectorial membrane - potassium channels open and close, hair cells send APs to spiral ganglion cells

Role of outer hair cells

Motor proteins, elongate and contract - shift basilar membrane to amplify signal

Signal transduction: scent

odorants bind to 7TM G protein receptors, activate proteins, signal cascade forms cAMP, opens sodium channels, depolarisation, AP at glomurelus

Signal transduction: taste (salty, sour)

Ligand-gated ion channels are activated, Influx of Na/H causes depolarisation of taste receptor, NTs released

Signal transduction: taste (sweet, bitter, umami)

Amino acids act as ligands for G-coupled receptors: activation of G proteins causes secondary messenger cascade, depolarises cell.

T1R2, T1R3 receptor combo for sweet

T1R1, T1R3 combo for umami

T2R1 for bitter