Bio 125 Lecture- Olfactory and Gustatory

The focus is on the functions of the tongue and the nose as specialized sensory equipment in the body.
- They occupy a small percentage of the body but play crucial roles in special senses.
The special senses include taste, vision, sound, and smell (olfactory).

Olfactory Neurons:
- Enter the nose through openings in the skull.
- Dendrites of olfactory neurons penetrate through the cribriform plate to the nasal mucosa.
- Important to note that these should be identified as dendrites rather than axons as they are sensory nerves.
Synapses:
- Olfactory nerve dendrites synapse with mitral cells, which are postsynaptic neurons located in the olfactory bulb.
- The olfactory bulb is positioned anterior and inferior to the frontal lobes of the brain.
Cranial Nerve Identification:
- The olfactory nerve is designated as cranial nerve number I (1).
Olfactory Cortex:
- Olfactory information is processed in the olfactory cortex, located in the temporal lobe of the brain.

Nasal Conchae:
- The walls of the nasal cavity contain three bumpy structures known as conchae.
- Their function is to facilitate turbulent airflow in the nasal cavity.
Turbulent Flow Mechanism:
- Turbulent flow helps the air stay longer in the nasal cavity, increasing the contact time with the olfactory mucosa.
- Longer contact time improves odor detection due to enhanced interaction with odorant molecules.

Air Conditioning:
- The nose's rich blood supply helps to warm and moisten inhaled air, which is essential for effective olfaction.
- Mucus and hair in the nasal cavity trap particles, filtering the air.
Odor Detection:
- Odorant molecules, the chemicals inducing smell sensations, are detected by olfactory sensory neurons located in the olfactory epithelium at the superior aspect of the nasal cavity.

Cilia in Olfactory Neurons:
- Non-motile cilia at the end of olfactory neurons increase the surface area for odor detection.
Neuronal Regeneration:
- Olfactory neurons have the ability to regenerate, which is uncommon for neurons elsewhere in the body.

Survival Mechanism:
- Olfaction is crucial for detecting dangers; e.g., unpleasant smells often indicate harmful substances.
- Pleasant aromas can enhance digestion, stimulating salivation in anticipation of food intake.

Mucus Role:
- Essential for dissolving odorant molecules, allowing for the detection of various scents.

G-Protein Coupled Receptors:
- Odorant molecules activate G-proteins, leading to the activation of adenylate cyclase.
Calcium's Role:
- Calcium ions contribute to the sensation of smell by providing a temporal stop signal, allowing for adaptation to prolonged odors.
Conscious vs Unconscious Perception:
- Olfactory signals can be processed both consciously and unconsciously.
- Some information arrives at the hypothalamus and limbic system, affecting memory and emotion.

Loss of Smell in COVID Patients:
- About 20% of affected individuals report loss of smell, a condition called anosmia.
- The exact mechanisms remain under investigation, with suggestions that inflammatory processes may disrupt olfactory neurons.
Long-term Consequences:
- Some individuals experience persistent olfactory dysfunction post-infection (long COVID).
- Investigations into related issues like parosmia, where smells become distorted or unpleasant.

Taste and Sensory Detection:
- Taste buds primarily detect touch, vibration, temperature, and texture rather than specific tastes.
- Filiform taste buds function like skin sensors, linked to the trigeminal nerve for sensory processing.

Motor and Sensory Roles:
- The tongue is associated with multiple cranial nerves that manage both sensory detection and motor control, including CN 5 (trigeminal), CN 7 (facial), CN 9 (glossopharyngeal), and CN 10 (vagus).
Conclusion:
- The tongue contains a rich network of neurons crucial for sensory integration, which highlights the intricate connection between sensory experience and physical responses.