Sensory Transduction: Olfactory, Gustatory, and Visual Systems

Posted on Mar 24, 2025 in Biology

Sensory Transduction Mechanisms

Vestibular System

  • Head movements cause stereocilia to move in the opposite direction of head rotation.
  • Neurotransmitter release at the synapse between vestibular hair cells and the afferent neuron involves glutamate.
  • Afferent nerve fibers in the inner ear converge to form the vestibulocochlear nerve.
  • Meniere’s disease can cause dizziness.

Olfactory System

  • The olfactory membrane is located within the nasal conchae.
  • Odorant receptors are G-protein coupled receptors.
  • Olfactory transduction depends on cyclic nucleotide-gated ion channels (cAMP).
  • Adaptation of the olfactory system depends on shutting off the signal transduction cascade via negative feedback in the CNS.
  • Olfactory information is carried to the limbic system.

Gustatory System

  • Gustatory transduction occurs via ion channels and G-protein cascades.

Sensory Receptor Cells

  • Receptor cells in all sensory systems are specialized in both structure and function to capture stimuli.

Visual System

  • Photoreceptor cells in the eye are located in the retina.
  • Specialized cells within the organ of Corti are hair cells.
  • The cochlear and vestibular nerves converge to form cranial nerve VIII.
  • Olfactory sensory neurons and mitral cell bundles form glomeruli.
  • Taste receptor cells are contained within papillae.
  • Cones are responsible for color vision, with photo-pigments capable of absorbing light in blue, red, and green ranges.
  • Linear acceleration of the head is determined by hair cells located in the utricle and saccule.

Olfactory Sensory Neurons

  • Olfactory sensory neurons express the same type of odorant receptors and all converge on the same glomerulus in the olfactory bulb.

Taste Transduction

  • Taste transduction in gustatory cells can be transduced by ion channels and G-protein coupled receptors.

Phototransduction Cascade

  1. Isomerization of 11-cis-retinal.
  2. Activation of G-protein transducin.
  3. Activation of cGMP phosphodiesterase.
  4. Decrease in levels of cGMP inside cells.
  5. Closure of CNG channels.
  6. Cessation of the dark current and cell hyperpolarization.
  7. Decreased release of glutamate.

Olfactory Signal Transduction

  1. Odorant binds to a G-protein coupled receptor on an olfactory neuron.
  2. G-protein gustducin activates adenylate cyclase.
  3. Intracellular levels of cAMP within the olfactory neuron increase.
  4. cAMP-gated channels open, leading to depolarization.
  5. Mitral cells relay information to the olfactory tract.

Sensory Cell Components

  • Photoreceptor cells: Outer segment.
  • Olfactory sensory neuron: Cilia.
  • Olfactory hair cells: Stereocilia.
  • Gustatory cell: Taste hairs.

Physiological Responses

  • Photocells decrease neurotransmitter release in response to a photon, whereas most other sensory cells increase neurotransmitter release in response to their stimulus.
  • Photocells hyperpolarize in response to a photon, whereas most other sensory cells depolarize in response to their stimulus.

Similarities in Signal Transduction

  • Both photoreceptor cells and olfactory sensory neurons involve a G-protein coupled receptor.
  • Both involve nucleotides.
  • Both involve cyclic nucleotide channels.

Common Themes in Sensory Systems

  • Adaptation
  • Change in receptor cell membrane potential
  • Release of neurotransmitter
  • Message carried to the CNS in the form of potential frequency