lukt och smak Fokus på lukt AS VT25

Course Objectives

• Knowledge and Understanding:

  • Types of cells within the nervous system, musculoskeletal system, and sense organs.

  • Macroscopic and microscopic anatomy of the involved organs and organ systems.

  • Senses and sense organs: vision, hearing, balance, smell, taste, and touch.

  • Middle and inner ear anatomy, nasal cavity, sinuses, and oral cavity including teeth and salivary glands.

  • Anatomy of the larynx and trachea.

• Skills and Abilities:

  • Macroscopic, microscopic, and functional anatomy knowledge of the relevant organs and systems based on defined goals.

  • Identify clear anatomical structures in investigations using conventional radiography, CT, or MRI.

Upper Respiratory Tract

• First part of the upper respiratory tract with various functions:

  • Nasal Cavity (Cavum Nasi):

    • Bordered by a septum, side walls, roof, floor, and posterior wall (opening: choana).

    • Contributed by the following bones:

      • Nasal bone (Os nasale)

      • Maxilla (Os maxillae)

      • Palatine bone (Os palatinum)

      • Lacrimal bone (Os lacrimale)

      • Ethmoid bone (Os ethmoidale)

      • Sphenoid bone (Os sphenoidale)

      • Frontal bone (Os frontale)

      • Vomer bone (Os vomer)

  • Regions of the Nasal Cavity:

    1. Vestibulum nasi:

       • Covered with skin containing hair (vibrissae).

    2. Respiratory Region:

       • Lined with respiratory epithelium.

    3. Olfactory Region:

       • Small area located superiorly, lined with olfactory epithelium.

Sinuses (Sinus Paranasales)

• Types of sinuses:

  1. Frontal sinuses (Sinus frontales)

  2. Ethmoid cells (Cellulae ethmoidales)

  3. Sphenoid sinuses (Sinus sphenoidales)

  4. Maxillary sinuses (Sinus maxillares)

• Functions of the Nose and Sinuses:

  • Make the head lighter.

  • Absorb impact/energy.

  • Create resonance and amplify voice.

  • Warm and humidify air.

  • Regulate intranasal pressure.

Nasal Cavity Structure

• Nasal septum (Septum nasi):

  • Divides the nasal cavity into two nasal cavities.

  • Composed of cartilage (anteriorly) and bone (posteriorly):

    • Maxilla (Os maxilla)

    • Palatine (Os palatinum)

    • Vomer (Os vomer)

    • Ethmoid (Lamina perpendicularis)

  • Lamina cribrosa:

    • Roof of the nasal cavity with many perforations (cribriform = perforated) allowing small nerves from the olfactory membrane to pass to the bulb.

Nasal Cavity Walls and Openings

• Turbinates (Conchae):

  • Bony platforms covered with mucosa that protrude into the nasal cavity.

    1. Superior nasal concha

    2. Middle nasal concha

    3. Inferior nasal concha

• Nasal Passages (Meatus nasi):

  • Rosencrantz spheno-etmoidalis: Sinus sphenoidalis.

  • Superior nasal meatus: Posterior ethmoid cells.

  • Middle nasal meatus: Anterior ethmoid cells, frontal sinus, and maxillary sinus.

Histology of the Nasal Mucosa

• Nasal Mucosa:

  • Ciliated columnar epithelium except in the vestibule.

  • Olfactory epithelium: Specialized epithelial tissue, located about 7 cm above and behind the nostrils.

  • Goblet cells produce mucous secretions that form a protective layer.

  • Ciliated epithelium transports secretions backward.

  • Under the basal membrane: blood vessels and nerves.

  • The mucosa is moist and has a rich blood supply.

Blood Supply to Nasal Cavity

• Blood supply: Branches from both internal and external carotid arteries.

• Locus Kiesselbachii: Highly vascularized area in the anterior septum.

  • Alpha-adrenergic receptors trigger vasoconstriction.

  • Beta-adrenergic receptors trigger vasodilation.

Olfactory Nerve (Cranial Nerve I)

• Smell (Action):

  • Connected to the olfactory nerve.

  • Sensory: Trigeminal nerve (V1 and V2).

  • Includes sympathetic and parasympathetic nerve fibers.

Physiology of the Respiratory System

1. Breathing:

   • Normally occurs through the nose.

   • During physical exertion, also occurs through the mouth (increased oxygen intake).

2. Air purification and conditioning:

   • Filtering particulate inhalations via vibrissae and mucus.

   • Air is moistened and warmed or cooled as necessary.

   • Protects lower airways from drying, cooling, and infections.

Smell

• Critical for:

  • Delivering important information about chemical substances in our environment.

  • Food we eat and air we breathe.

  • Discerning safe or nutritious food and deciding whether to swallow or spit out what is in our mouth.

  • Distinguishing between dangerous and unwanted substances.

• Cannot accurately distinguish tastes without the aid of smell; olfactory and tasting senses are functionally linked.

  • Taste experiences rely heavily on the olfactory system; approximately 80-90% of taste is derived from smell.

Olfactory Organ (Olfactory Membrane)

• Description:

  • Specialized epithelial tissue located in the superior part of the nasal cavity.

  • Measures about 5 cm².

  • Comprised of approximately 100 million cells:

    • Support cells

    • Bowman’s glands produce secretions that dissolve odorants.

    • Olfactory cells (receptor cells - bipolar nerve cells).

  • Olfactory dendrites extend 4-25 olfactory cilia that react to odorants.

Stimulation of Olfactory Cells

• Mechanism:

  • Odorants bind to receptor proteins on the cilia membrane.

  • Receptor proteins are long molecules traversing the membrane multiple times.

  • Activation leads to G-protein engagement which activates adenylyl cyclase, converting ATP to cAMP.

  • cAMP activates sodium ion channels, leading to depolarization and generation of an action potential transmitted to the brain via the olfactory nerve.

Brain Pathways for Smell Signals

• Pathway:

  • Tracts of olfactory fibers extend into the brain at the anterior junction between mesencephalon and cerebrum.

  • Signals sent to various brain regions:

    • Anterior olfactory nucleus via the anterior commissure to the contralateral lobe.

    • Entorhinal cortex; information forwarded to hippocampus (learning).

    • Piriform cortex; discrimination of odors.

    • Amygdala and hypothalamus for processing emotional components, including responses to smells.

    • Olfactory tubercle to thalamus and orbitofrontal cortex for conscious odor perception.

Adaptation to Smell

• Process:

  • Strong odors typically become unnoticeable within a minute due to receptor adaptation.

  • Initial exposure leads to a 50% adaptation rate within the first second.

  • Ongoing adaptation occurs in the brain, with feedback from olfactory signals influencing perception.

Conclusion

• Key Takeaways:

  • Study of the anatomy and physiology of the olfactory system is crucial for understanding smell, which significantly influences taste and general sensory processing.